{"id": "10.1007#s11082-008-9184-y.html_0", "title": "10.1007#s11082-008-9184-y.html", "context": "In this paper a model and simulation results of integrated semiconductor passively modelocked ring lasers are presented. The model includes nonlinear effects such as two-photon absorption and a non-linear refractive index, a logarithmic gain-carrier relation, and concentration dependent radiative and non-radiative carrier recombination rates. The optical bandwidth of the system is controlled by a digital filter. The model has been used to simulate two geometries of ring modelocked lasers. The first is a symmetric design, where the two counter propagating pulses in the cavity experience the same amplification and absorption. The second is an asymmetric design where the differences for the two directions of pulse propagation are maximised. Simulation results show that a symmetrical cavity shows a several times wider window for its operating parameters for stable modelocking.", "question": "What topic is studies in this paper?", "answers": {"text": "a model and simulation results of integrated semiconductor passively modelocked ring lasers", "answer_start": [14]}}
{"id": "10.1007#s11082-008-9184-y.html_1", "title": "10.1007#s11082-008-9184-y.html", "context": "In this paper a model and simulation results of integrated semiconductor passively modelocked ring lasers are presented. The model includes nonlinear effects such as two-photon absorption and a non-linear refractive index, a logarithmic gain-carrier relation, and concentration dependent radiative and non-radiative carrier recombination rates. The optical bandwidth of the system is controlled by a digital filter. The model has been used to simulate two geometries of ring modelocked lasers. The first is a symmetric design, where the two counter propagating pulses in the cavity experience the same amplification and absorption. The second is an asymmetric design where the differences for the two directions of pulse propagation are maximised. Simulation results show that a symmetrical cavity shows a several times wider window for its operating parameters for stable modelocking.", "question": "What is the first nonlinear effect that is included in the model?", "answers": {"text": "two-photon absorption", "answer_start": [166]}}
{"id": "10.1007#s11082-008-9184-y.html_3", "title": "10.1007#s11082-008-9184-y.html", "context": "In this paper a model and simulation results of integrated semiconductor passively modelocked ring lasers are presented. The model includes nonlinear effects such as two-photon absorption and a non-linear refractive index, a logarithmic gain-carrier relation, and concentration dependent radiative and non-radiative carrier recombination rates. The optical bandwidth of the system is controlled by a digital filter. The model has been used to simulate two geometries of ring modelocked lasers. The first is a symmetric design, where the two counter propagating pulses in the cavity experience the same amplification and absorption. The second is an asymmetric design where the differences for the two directions of pulse propagation are maximised. Simulation results show that a symmetrical cavity shows a several times wider window for its operating parameters for stable modelocking.", "question": " 'What has the model been used to do?", "answers": {"text": "simulate two geometries of ring modelocked lasers", "answer_start": [443]}}
{"id": "10.1007#s11082-008-9184-y.html_4", "title": "10.1007#s11082-008-9184-y.html", "context": "In this paper a model and simulation results of integrated semiconductor passively modelocked ring lasers are presented. The model includes nonlinear effects such as two-photon absorption and a non-linear refractive index, a logarithmic gain-carrier relation, and concentration dependent radiative and non-radiative carrier recombination rates. The optical bandwidth of the system is controlled by a digital filter. The model has been used to simulate two geometries of ring modelocked lasers. The first is a symmetric design, where the two counter propagating pulses in the cavity experience the same amplification and absorption. The second is an asymmetric design where the differences for the two directions of pulse propagation are maximised. Simulation results show that a symmetrical cavity shows a several times wider window for its operating parameters for stable modelocking.", "question": "What is the first geometry simulated by the model?", "answers": {"text": "a symmetric design, where the two counter propagating pulses in the cavity experience the same amplification and absorption", "answer_start": [507]}}
{"id": "10.1007#s11082-008-9184-y.html_5", "title": "10.1007#s11082-008-9184-y.html", "context": "In this paper a model and simulation results of integrated semiconductor passively modelocked ring lasers are presented. The model includes nonlinear effects such as two-photon absorption and a non-linear refractive index, a logarithmic gain-carrier relation, and concentration dependent radiative and non-radiative carrier recombination rates. The optical bandwidth of the system is controlled by a digital filter. The model has been used to simulate two geometries of ring modelocked lasers. The first is a symmetric design, where the two counter propagating pulses in the cavity experience the same amplification and absorption. The second is an asymmetric design where the differences for the two directions of pulse propagation are maximised. Simulation results show that a symmetrical cavity shows a several times wider window for its operating parameters for stable modelocking.", "question": "What is maximised in the second design?", "answers": {"text": "differences for the two directions of pulse propagation", "answer_start": [677]}}
{"id": "10.1007#s11082-009-9294-1.html_0", "title": "10.1007#s11082-009-9294-1.html", "context": "Owing to advanced manufacturing techniques, it is possible to produce cylindrical single-mode fibres with nearly arbitrary refractive index profiles. For the design of optical fibres automated optimisation schemes have yet to be exploited. We have employed deterministic local, and stochastic global optimisation schemes for the minimisation of a cost function based on dispersion, dispersion slope, macro-bending losses and mode-field diameter, on the space of continuous piecewise linear dopant concentration profiles. For the local schemes (modified and quasi Newton), it appears possible to select a few initial profiles, such that the optimisation results are close to the \u201cglobal optima\u201d (within 8%), found using global schemes (simulated annealing and differential evolution), while reducing computation times significantly (minutes instead of days). For the local schemes, the cost function gradient is required. Fr\u00e9chet derivatives are more efficient than finite-difference approximations. A sensitivity analysis provides useful information for manufacturers regarding the required profile accuracy. A comparison of our optimised fibre designs with commercially available optical fibres demonstrates that existing fibres can be improved.", "question": "What can be produced owing to advanced manufacturing techniques?", "answers": {"text": "cylindrical single-mode fibres with nearly arbitrary refractive index profiles", "answer_start": [70]}}
{"id": "10.1007#s11082-009-9294-1.html_1", "title": "10.1007#s11082-009-9294-1.html", "context": "Owing to advanced manufacturing techniques, it is possible to produce cylindrical single-mode fibres with nearly arbitrary refractive index profiles. For the design of optical fibres automated optimisation schemes have yet to be exploited. We have employed deterministic local, and stochastic global optimisation schemes for the minimisation of a cost function based on dispersion, dispersion slope, macro-bending losses and mode-field diameter, on the space of continuous piecewise linear dopant concentration profiles. For the local schemes (modified and quasi Newton), it appears possible to select a few initial profiles, such that the optimisation results are close to the \u201cglobal optima\u201d (within 8%), found using global schemes (simulated annealing and differential evolution), while reducing computation times significantly (minutes instead of days). For the local schemes, the cost function gradient is required. Fr\u00e9chet derivatives are more efficient than finite-difference approximations. A sensitivity analysis provides useful information for manufacturers regarding the required profile accuracy. A comparison of our optimised fibre designs with commercially available optical fibres demonstrates that existing fibres can be improved.", "question": "What is less efficient than Fr\u00e9chet derivatives?", "answers": {"text": "finite-difference approximations", "answer_start": [965]}}
{"id": "10.1007#s11082-009-9349-3.html_0", "title": "10.1007#s11082-009-9349-3.html", "context": "The optical properties of slab-like photonic crystals are often discussed on the basis of effective index (EI) approximations, where a 2-D effective refractive index profile replaces the actual 3-D structure. Our aim is to assess this approximation by analogous steps that reduce finite 2-D waveguide Bragg-gratings (to be seen as sections through 3-D PC slabs and membranes) to 1-D problems, which are tractable by common transfer matrix methods. Application of the EI method is disputable in particular in cases where locally no guided modes are supported, as in the holes of a PC membrane. A variational procedure permits to derive suitable effective permittivities even in these cases. Depending on the structural properties, these values can well turn out to be lower than one, or even be negative. Both the \u201cstandard\u201d and the variational procedures are compared with reference data, generated by a rigorous 2-D Helmholtz solver, for a series of example structures.", "question": "What approximation is often used when discussing the optical properties of slab-like photonic crystals?", "answers": {"text": "effective index (EI) approximations", "answer_start": [90]}}
{"id": "10.1007#s11082-009-9349-3.html_1", "title": "10.1007#s11082-009-9349-3.html", "context": "The optical properties of slab-like photonic crystals are often discussed on the basis of effective index (EI) approximations, where a 2-D effective refractive index profile replaces the actual 3-D structure. Our aim is to assess this approximation by analogous steps that reduce finite 2-D waveguide Bragg-gratings (to be seen as sections through 3-D PC slabs and membranes) to 1-D problems, which are tractable by common transfer matrix methods. Application of the EI method is disputable in particular in cases where locally no guided modes are supported, as in the holes of a PC membrane. A variational procedure permits to derive suitable effective permittivities even in these cases. Depending on the structural properties, these values can well turn out to be lower than one, or even be negative. Both the \u201cstandard\u201d and the variational procedures are compared with reference data, generated by a rigorous 2-D Helmholtz solver, for a series of example structures.", "question": "In which case is the application of the EI method being disputable?", "answers": {"text": "locally no guided modes are supported", "answer_start": [520]}}
{"id": "10.1007#s11082-009-9349-3.html_2", "title": "10.1007#s11082-009-9349-3.html", "context": "The optical properties of slab-like photonic crystals are often discussed on the basis of effective index (EI) approximations, where a 2-D effective refractive index profile replaces the actual 3-D structure. Our aim is to assess this approximation by analogous steps that reduce finite 2-D waveguide Bragg-gratings (to be seen as sections through 3-D PC slabs and membranes) to 1-D problems, which are tractable by common transfer matrix methods. Application of the EI method is disputable in particular in cases where locally no guided modes are supported, as in the holes of a PC membrane. A variational procedure permits to derive suitable effective permittivities even in these cases. Depending on the structural properties, these values can well turn out to be lower than one, or even be negative. Both the \u201cstandard\u201d and the variational procedures are compared with reference data, generated by a rigorous 2-D Helmholtz solver, for a series of example structures.", "question": "What does a variational procedure permit to derive?", "answers": {"text": "suitable effective permittivities", "answer_start": [635]}}
{"id": "10.1007#s11082-012-9629-1.html_0", "title": "10.1007#s11082-012-9629-1.html", "context": "A Mach-Zehnder interferometer (MZI) electro-optic (EO) modulator based on micro-strip line (MSL) electrode and guest-host EO polymer DR1/SU-8 is experimentally demonstrated. For achieving high response speed, electrode structure is especially optimized and fabrication technology is seriously controlled. The final characteristic impedance of electrode is about 49.4\u00a0\u03a9, and the difference between microwave index (1.5616) and lightwave index (1.6006) is also minimized. At 1,550\u00a0nm, the insertion loss and extinction ratio are 12 and 16\u00a0dB, respectively, and under switching operation, the rise time and fall time are 16.3 and 16.7\u00a0ns, respectively. A long-term monitoring over 2000 hours at room temperature (25\u00a0\u00b0C) is performed on switching response, and a novel mathematical modeling on response time variation is established using logistic function. The rise time and fall time are observed to change from the initial value of ~16\u00a0ns to the stable value of ~28\u00a0ns within 300 and 2000 hours, respectively. The device exhibits nanosecond response time by virtue of impedance-matched electrode, small index mismatch and serious control on fabrication process.", "question": "What is experimentally demonstrated in this paper?", "answers": {"text": "A Mach-Zehnder interferometer (MZI) electro-optic (EO) modulator", "answer_start": [0]}}
{"id": "10.1007#s11082-012-9629-1.html_1", "title": "10.1007#s11082-012-9629-1.html", "context": "A Mach-Zehnder interferometer (MZI) electro-optic (EO) modulator based on micro-strip line (MSL) electrode and guest-host EO polymer DR1/SU-8 is experimentally demonstrated. For achieving high response speed, electrode structure is especially optimized and fabrication technology is seriously controlled. The final characteristic impedance of electrode is about 49.4\u00a0\u03a9, and the difference between microwave index (1.5616) and lightwave index (1.6006) is also minimized. At 1,550\u00a0nm, the insertion loss and extinction ratio are 12 and 16\u00a0dB, respectively, and under switching operation, the rise time and fall time are 16.3 and 16.7\u00a0ns, respectively. A long-term monitoring over 2000 hours at room temperature (25\u00a0\u00b0C) is performed on switching response, and a novel mathematical modeling on response time variation is established using logistic function. The rise time and fall time are observed to change from the initial value of ~16\u00a0ns to the stable value of ~28\u00a0ns within 300 and 2000 hours, respectively. The device exhibits nanosecond response time by virtue of impedance-matched electrode, small index mismatch and serious control on fabrication process.", "question": "What is the microwave index?", "answers": {"text": "1.5616", "answer_start": [414]}}
{"id": "10.1007#s11082-012-9629-1.html_2", "title": "10.1007#s11082-012-9629-1.html", "context": "A Mach-Zehnder interferometer (MZI) electro-optic (EO) modulator based on micro-strip line (MSL) electrode and guest-host EO polymer DR1/SU-8 is experimentally demonstrated. For achieving high response speed, electrode structure is especially optimized and fabrication technology is seriously controlled. The final characteristic impedance of electrode is about 49.4\u00a0\u03a9, and the difference between microwave index (1.5616) and lightwave index (1.6006) is also minimized. At 1,550\u00a0nm, the insertion loss and extinction ratio are 12 and 16\u00a0dB, respectively, and under switching operation, the rise time and fall time are 16.3 and 16.7\u00a0ns, respectively. A long-term monitoring over 2000 hours at room temperature (25\u00a0\u00b0C) is performed on switching response, and a novel mathematical modeling on response time variation is established using logistic function. The rise time and fall time are observed to change from the initial value of ~16\u00a0ns to the stable value of ~28\u00a0ns within 300 and 2000 hours, respectively. The device exhibits nanosecond response time by virtue of impedance-matched electrode, small index mismatch and serious control on fabrication process.", "question": "What is the lightwave index?", "answers": {"text": "1.6006", "answer_start": [443]}}
{"id": "10.1007#s11082-013-9667-3.html_0", "title": "10.1007#s11082-013-9667-3.html", "context": "In this paper, the exact solution of Schr\u00f6dinger equation for multi-layered quantum dot (MLQD) within the effective mass approximation and dielectric continuum model is obtained with finite and infinite confining potential (CP). The MLQD is a nano-structured semiconductor system that consists of a spherical core (GaAs) and a coated spherical shell (Ga\\(_{1-x}\\)Al\\(_{x}\\)As) as the whole dot is embedded inside a bulk material (Ga\\(_{1-y}\\)Al\\(_{y}\\)As). Using the obtained energies, wave functions and taking advantage of numeric calculations, the oscillator strength, refractive index and absorbtion coefficient change associated with intersubband electronic transition from the ground state to the first allowed excited state are investigated for different CPs (both finite and infinite) and shell thicknesses. The results show that all values of ground state energy for large core dot radius approach the same value (the energy of bulk material) independent of CPs and shell thicknesses. Also it is shown that the optical properties are strongly affected by the changes in CPs and shell thicknesses.", "question": "What are the optical properties affected by?", "answers": {"text": "the changes in CPs and shell thicknesses", "answer_start": [1064]}}
{"id": "10.1007#s11082-013-9668-2.html_0", "title": "10.1007#s11082-013-9668-2.html", "context": "Now, new metamaterials are intensively studied and applied in various waveguide systems. Such materials are also called left-handed materials (LHMs) or media with negative refractive index. Their dielectric permittivity and magnetic permeability are simultaneously negative (Smith et al. 2000; Zhao et al. 2007). As a rule, the metamaterials are artificial magneto-dielectrics (composites). They have unique electromagnetic properties (negative refraction of waves, reversed Cherenkov radiation, etc.). Presently the new LHMs with changing parameters are designed; their parameters can be governed by external actions (for example, external static fields). Note that applications of the metamaterials (with peculiar properties) can radically change the base principles of optical systems engineering.", "question": "What is studied and applied in waveguide systems?", "answers": {"text": "new metamaterials", "answer_start": [5]}}
{"id": "10.1007#s11082-013-9668-2.html_1", "title": "10.1007#s11082-013-9668-2.html", "context": "Now, new metamaterials are intensively studied and applied in various waveguide systems. Such materials are also called left-handed materials (LHMs) or media with negative refractive index. Their dielectric permittivity and magnetic permeability are simultaneously negative (Smith et al. 2000; Zhao et al. 2007). As a rule, the metamaterials are artificial magneto-dielectrics (composites). They have unique electromagnetic properties (negative refraction of waves, reversed Cherenkov radiation, etc.). Presently the new LHMs with changing parameters are designed; their parameters can be governed by external actions (for example, external static fields). Note that applications of the metamaterials (with peculiar properties) can radically change the base principles of optical systems engineering.", "question": "What other names are used to describe metamaterials?", "answers": {"text": "left-handed materials (LHMs) or media with negative refractive index", "answer_start": [120]}}
{"id": "10.1007#s11082-013-9668-2.html_2", "title": "10.1007#s11082-013-9668-2.html", "context": "Now, new metamaterials are intensively studied and applied in various waveguide systems. Such materials are also called left-handed materials (LHMs) or media with negative refractive index. Their dielectric permittivity and magnetic permeability are simultaneously negative (Smith et al. 2000; Zhao et al. 2007). As a rule, the metamaterials are artificial magneto-dielectrics (composites). They have unique electromagnetic properties (negative refraction of waves, reversed Cherenkov radiation, etc.). Presently the new LHMs with changing parameters are designed; their parameters can be governed by external actions (for example, external static fields). Note that applications of the metamaterials (with peculiar properties) can radically change the base principles of optical systems engineering.", "question": "What external action can govern the parameters of the new LHMs?", "answers": {"text": "external static fields", "answer_start": [632]}}
{"id": "10.1007#s11082-013-9668-2.html_3", "title": "10.1007#s11082-013-9668-2.html", "context": "Now, new metamaterials are intensively studied and applied in various waveguide systems. Such materials are also called left-handed materials (LHMs) or media with negative refractive index. Their dielectric permittivity and magnetic permeability are simultaneously negative (Smith et al. 2000; Zhao et al. 2007). As a rule, the metamaterials are artificial magneto-dielectrics (composites). They have unique electromagnetic properties (negative refraction of waves, reversed Cherenkov radiation, etc.). Presently the new LHMs with changing parameters are designed; their parameters can be governed by external actions (for example, external static fields). Note that applications of the metamaterials (with peculiar properties) can radically change the base principles of optical systems engineering.", "question": "What may the application of the metamaterials change?", "answers": {"text": "base principles of optical systems engineering", "answer_start": [753]}}
{"id": "10.1007#s11082-013-9668-2.html_4", "title": "10.1007#s11082-013-9668-2.html", "context": "To date, the guided modes of regular LHM waveguides were studied in sufficient detail (Shadrivov et al. 2003; Wu et al. 2003; He et al. 2005). At the same time, the scattering problems for such structures are poorly understood. In this paper we examine the problem of guided mode reflection from the abruptly terminated planar LHM waveguide (Fig.\u00a01). We study the LHM structures with surface and oscillating modes. The problem in question is solved by a variational method (Morse and Feshbach 1953; Lewin 1975; Manenkov 1982). For comparison we also present the results obtained for the problem of mode reflection from the end of the RHM waveguide.\n", "question": "What is poorly understood for such structures?", "answers": {"text": "the scattering problems", "answer_start": [161]}}
{"id": "10.1007#s11082-013-9668-2.html_5", "title": "10.1007#s11082-013-9668-2.html", "context": "To date, the guided modes of regular LHM waveguides were studied in sufficient detail (Shadrivov et al. 2003; Wu et al. 2003; He et al. 2005). At the same time, the scattering problems for such structures are poorly understood. In this paper we examine the problem of guided mode reflection from the abruptly terminated planar LHM waveguide (Fig.\u00a01). We study the LHM structures with surface and oscillating modes. The problem in question is solved by a variational method (Morse and Feshbach 1953; Lewin 1975; Manenkov 1982). For comparison we also present the results obtained for the problem of mode reflection from the end of the RHM waveguide.\n", "question": "What are the LHM structures studies with?", "answers": {"text": "surface and oscillating modes", "answer_start": [384]}}
{"id": "10.1007#s11082-013-9668-2.html_6", "title": "10.1007#s11082-013-9668-2.html", "context": "To date, the guided modes of regular LHM waveguides were studied in sufficient detail (Shadrivov et al. 2003; Wu et al. 2003; He et al. 2005). At the same time, the scattering problems for such structures are poorly understood. In this paper we examine the problem of guided mode reflection from the abruptly terminated planar LHM waveguide (Fig.\u00a01). We study the LHM structures with surface and oscillating modes. The problem in question is solved by a variational method (Morse and Feshbach 1953; Lewin 1975; Manenkov 1982). For comparison we also present the results obtained for the problem of mode reflection from the end of the RHM waveguide.\n", "question": "When did Lewin solve the scattering problem?", "answers": {"text": "1975", "answer_start": [505]}}
{"id": "10.1007#s11082-013-9668-2.html_7", "title": "10.1007#s11082-013-9668-2.html", "context": "To date, the guided modes of regular LHM waveguides were studied in sufficient detail (Shadrivov et al. 2003; Wu et al. 2003; He et al. 2005). At the same time, the scattering problems for such structures are poorly understood. In this paper we examine the problem of guided mode reflection from the abruptly terminated planar LHM waveguide (Fig.\u00a01). We study the LHM structures with surface and oscillating modes. The problem in question is solved by a variational method (Morse and Feshbach 1953; Lewin 1975; Manenkov 1982). For comparison we also present the results obtained for the problem of mode reflection from the end of the RHM waveguide.\n", "question": "When did Manenkov solve the scattering problem?", "answers": {"text": "1982", "answer_start": [520]}}
{"id": "10.1007#s11082-013-9668-2.html_8", "title": "10.1007#s11082-013-9668-2.html", "context": "The variational approach is based on the integral equation for the component \\(E_x\\) of the electric field in the terminal plane \\(z = 0\\) of the waveguide end (Lewin 1975; Manenkov 1982). In turn, the integral equation kernel is expressed in terms of the fields of eigenmodes (Tigelis and Manenkov 1999). The set of the eigenmodes of open waveguide includes the discrete spectrum modes (for example, the guided modes) and continuous spectrum modes (the radiation modes). Below, we shortly describe their characteristics that we use to derive the variational equations. A detailed analysis of guided modes properties can be found elsewhere (Shadrivov et al. 2003; Wu et al. 2003).", "question": "What is an example of the discrete spectrum modes?", "answers": {"text": "the guided modes", "answer_start": [401]}}
{"id": "10.1007#s11082-013-9668-2.html_9", "title": "10.1007#s11082-013-9668-2.html", "context": "The variational approach is based on the integral equation for the component \\(E_x\\) of the electric field in the terminal plane \\(z = 0\\) of the waveguide end (Lewin 1975; Manenkov 1982). In turn, the integral equation kernel is expressed in terms of the fields of eigenmodes (Tigelis and Manenkov 1999). The set of the eigenmodes of open waveguide includes the discrete spectrum modes (for example, the guided modes) and continuous spectrum modes (the radiation modes). Below, we shortly describe their characteristics that we use to derive the variational equations. A detailed analysis of guided modes properties can be found elsewhere (Shadrivov et al. 2003; Wu et al. 2003).", "question": "What is an example of the continuous spectrum modes?", "answers": {"text": "the radiation modes", "answer_start": [450]}}
{"id": "10.1007#s11082-013-9668-2.html_10", "title": "10.1007#s11082-013-9668-2.html", "context": "The variational approach is based on the integral equation for the component \\(E_x\\) of the electric field in the terminal plane \\(z = 0\\) of the waveguide end (Lewin 1975; Manenkov 1982). In turn, the integral equation kernel is expressed in terms of the fields of eigenmodes (Tigelis and Manenkov 1999). The set of the eigenmodes of open waveguide includes the discrete spectrum modes (for example, the guided modes) and continuous spectrum modes (the radiation modes). Below, we shortly describe their characteristics that we use to derive the variational equations. A detailed analysis of guided modes properties can be found elsewhere (Shadrivov et al. 2003; Wu et al. 2003).", "question": "Where can a detailed analysis of guided modes properties be found?", "answers": {"text": "(Shadrivov et al. 2003", "answer_start": [640]}}
{"id": "10.1007#s11082-013-9668-2.html_11", "title": "10.1007#s11082-013-9668-2.html", "context": "The variational method can be also used to calculate the far-zone radiation pattern. However, this way leads to complicated expressions, therefore we use simple way that is based on the physical optics approximation (Huygens\u2019 principle). Using this principle we represent the terminal field as the sum of the fields of the incident and reflected guided modes. In this case we neglect the fields of the edge waves that are excited by the edge points (their coordinates are \\(z = 0\\) and \\(y = \\pm d\\)). This approximation of the terminal field allows us to compute the pattern only for the forward direction (i.e., the radiation into the right-hand half-space \\(z>0\\)). Using Eq.\u00a013 we get the far-zone electric field is equal to\n", "question": "What can be used to calculate the far-zone radiation pattern?", "answers": {"text": "The variational method", "answer_start": [0]}}
{"id": "10.1007#s11082-013-9668-2.html_12", "title": "10.1007#s11082-013-9668-2.html", "context": "The properties of the oscillating modes (dispersion characteristics and field distributions) are described in detail in several publications (Shadrivov et al. 2003; He et al. 2005; Manenkov et al. 2010). Recall that these modes exist if the parameters of the LHM waveguide satisfy the following inequality: \\(\\varDelta _{21} > 0\\); the ratio \\(|\\mu _2 / \\mu _1|\\) can be arbitrary. There are three main features of the oscillating modes that distinguish them from the surface modes. (i) The oscillating modes have cut-offs. (ii) Inside the central slab the fields of the oscillating modes are described by trigonometric functions. (iii) There are two branches of these modes: forward and backward. The forward branch exists in a small parameter region and, as a rule, is not of practical interest; therefore we treat only the backward modes. The dominant oscillating mode is denoted as \\(\\text{ TE}_2\\).", "question": "What is the first main feature that distinguishs the oscillating modes from the surface modes?", "answers": {"text": "The oscillating modes have cut-offs", "answer_start": [487]}}
{"id": "10.1007#s11082-013-9668-2.html_13", "title": "10.1007#s11082-013-9668-2.html", "context": "The properties of the oscillating modes (dispersion characteristics and field distributions) are described in detail in several publications (Shadrivov et al. 2003; He et al. 2005; Manenkov et al. 2010). Recall that these modes exist if the parameters of the LHM waveguide satisfy the following inequality: \\(\\varDelta _{21} > 0\\); the ratio \\(|\\mu _2 / \\mu _1|\\) can be arbitrary. There are three main features of the oscillating modes that distinguish them from the surface modes. (i) The oscillating modes have cut-offs. (ii) Inside the central slab the fields of the oscillating modes are described by trigonometric functions. (iii) There are two branches of these modes: forward and backward. The forward branch exists in a small parameter region and, as a rule, is not of practical interest; therefore we treat only the backward modes. The dominant oscillating mode is denoted as \\(\\text{ TE}_2\\).", "question": "What are the two branches of the oscillating modes?", "answers": {"text": "forward and backward", "answer_start": [676]}}
{"id": "10.1007#s11082-013-9668-2.html_14", "title": "10.1007#s11082-013-9668-2.html", "context": "Now consider the abruptly ended RHM waveguide (i.e., we examine the mode reflection from the end of the waveguide with usual dielectric media). The problem was treated in many publications. Various techniques, including the integral equation methods, FSRM method, FDTD approach, and others were applied to treat this problem (Rozzi et al. 1980; Vassallo 1988; Kendall et al. 1993; Tigelis and Manenkov 2000; Manenkov et al. 2001; Brovko et al. 2003). Under the weak guidance condition all the methods mentioned give very close data (Kendall et al. 1993; Tigelis and Manenkov 2000). Here, for uniformity, we calculate the reflectivity using the variational technique.", "question": "What technique is used to calculated the reflectivity?", "answers": {"text": "the variational technique", "answer_start": [640]}}
{"id": "10.1007#s11082-013-9668-2.html_15", "title": "10.1007#s11082-013-9668-2.html", "context": "The method described here is approximate, since we utilize approximate terminal field distributions. There are many other versions of the variational technique, which are more accurate. For example, we can represent the terminal field in the form of a linear combination of some basic functions (with unknown coefficients) and then search for a stationary point of the functional (Rozzi et al. 1980). However, for the problem in question the implementation of this scheme is connected with various great difficulties, including the known problem of stability for first kind integral equations, strong field singularities at the edge points, etc. Some of these difficulties were discussed elsewhere (Vassallo 1988).", "question": "What is the first difficulty that the implementation of this scheme is connected with?", "answers": {"text": "stability for first kind integral equations", "answer_start": [549]}}
{"id": "10.1007#s11082-013-9708-y.html_0", "title": "10.1007#s11082-013-9708-y.html", "context": "The II-VI compound semiconductors are known for their wide direct band gaps, and for their optical and electrical properties. This make them an important class of materials and competing candidates for silicon and other materials in photovoltaic conversion and optoelectronic applications (Aqili et al. 2000). ZnTe is one such II-VI semiconductor, having a direct band gap of 2.26\u00a0eV at room temperature (Ibrahim et al. 2004). This band gap energy corresponds to a wavelength of about 550 nm which falls in the green region of the electromagnetic spectra. Hence ZnTe is a potential candidate for the fabrication of green light emitting diodes (Shan et al. 2002). Besides ZnTe is also a promising material for the fabrication of various devices such as THz emitters and detectors and photodetectors. One of the main potential applications of ZnTe is the photo detection in visible region. At present, silicon is widely used for photodetectors in the visible region although its band gap is not optimal and its quantum efficiency is very low. However, ZnTe has optimum band gap energy and high quantum efficiency for photodetection in visible region. Studies on photo detection properties of ZnTe are therefore very useful for the fabrication of photodetectors (Rao et al. 2010).", "question": "What is a potential candidate for the fabrication of green light emitting diodes?", "answers": {"text": "ZnTe", "answer_start": [310]}}
{"id": "10.1007#s11082-013-9708-y.html_1", "title": "10.1007#s11082-013-9708-y.html", "context": "The II-VI compound semiconductors are known for their wide direct band gaps, and for their optical and electrical properties. This make them an important class of materials and competing candidates for silicon and other materials in photovoltaic conversion and optoelectronic applications (Aqili et al. 2000). ZnTe is one such II-VI semiconductor, having a direct band gap of 2.26\u00a0eV at room temperature (Ibrahim et al. 2004). This band gap energy corresponds to a wavelength of about 550 nm which falls in the green region of the electromagnetic spectra. Hence ZnTe is a potential candidate for the fabrication of green light emitting diodes (Shan et al. 2002). Besides ZnTe is also a promising material for the fabrication of various devices such as THz emitters and detectors and photodetectors. One of the main potential applications of ZnTe is the photo detection in visible region. At present, silicon is widely used for photodetectors in the visible region although its band gap is not optimal and its quantum efficiency is very low. However, ZnTe has optimum band gap energy and high quantum efficiency for photodetection in visible region. Studies on photo detection properties of ZnTe are therefore very useful for the fabrication of photodetectors (Rao et al. 2010).", "question": "What is currently widely used for photodetectors in the visible region?", "answers": {"text": "silicon", "answer_start": [202]}}
{"id": "10.1007#s11082-013-9708-y.html_2", "title": "10.1007#s11082-013-9708-y.html", "context": "The II-VI compound semiconductors are known for their wide direct band gaps, and for their optical and electrical properties. This make them an important class of materials and competing candidates for silicon and other materials in photovoltaic conversion and optoelectronic applications (Aqili et al. 2000). ZnTe is one such II-VI semiconductor, having a direct band gap of 2.26\u00a0eV at room temperature (Ibrahim et al. 2004). This band gap energy corresponds to a wavelength of about 550 nm which falls in the green region of the electromagnetic spectra. Hence ZnTe is a potential candidate for the fabrication of green light emitting diodes (Shan et al. 2002). Besides ZnTe is also a promising material for the fabrication of various devices such as THz emitters and detectors and photodetectors. One of the main potential applications of ZnTe is the photo detection in visible region. At present, silicon is widely used for photodetectors in the visible region although its band gap is not optimal and its quantum efficiency is very low. However, ZnTe has optimum band gap energy and high quantum efficiency for photodetection in visible region. Studies on photo detection properties of ZnTe are therefore very useful for the fabrication of photodetectors (Rao et al. 2010).", "question": "What are the advantages of ZnTe for photodetection in visible region?", "answers": {"text": "optimum band gap energy and high quantum efficiency", "answer_start": [1059]}}
{"id": "10.1007#s11082-013-9708-y.html_3", "title": "10.1007#s11082-013-9708-y.html", "context": "The optical absorption is the most direct method for determining the absorption coefficient of a material. In the absorption process, a photon is absorbed by the semiconductor. If the energy of the photon is above a certain threshold, it excites an electron from the valence band and passes to an excited and not initially occupied level. This process usually involves a transition from band to band, as an electron moves from the valence band (VB) in the conduction band (CB). We noted that at very low temperature (\\(<\\)20\u00a0K), vacant hole in the valence band and the excited electron to the next level tend to form a pair, named exciton. We know that the binding energy of the electron-hole is small. The exciton tends to recombine and emit light (luminescence).", "question": "What is the most direct method for determining the absorption coefficient of a material?", "answers": {"text": "The optical absorption", "answer_start": [0]}}
{"id": "10.1007#s11082-014-0052-7.html_0", "title": "10.1007#s11082-014-0052-7.html", "context": "Optical properties of ZnO doped with Silicon and Aluminum were studied by first principle calculations using the density functional theory. The optical absorption, transmittance and optical constants are investigated using the full potential-linearized augmented plane wave method with the generalized gradient approximation and mBJ approximation, implemented in Wien2k package. With the mBJ approximation the direct optical gap of a pure ZnO is about 3.34 eV, which is in good agreement with experimental results. The behavior of the transmittance and the absorption of the Al-doped ZnO are higher and better than those of the Si-doped ZnO. The transmittance of Al-doped ZnO is stable and high in the visible light range and can reach 96 % at 400 nm. This confirms the physical characteristics that can present Al to be used as suitable transparent material electrodes in solar cells.", "question": "What is the direct optical gap of a pure ZnO with the mBJ approximatioon?", "answers": {"text": "3.34 eV", "answer_start": [452]}}
{"id": "10.1007#s11082-014-0052-7.html_1", "title": "10.1007#s11082-014-0052-7.html", "context": "The zinc oxide is a transparent semiconductor of type II-VI with a normal type n conductivity. Among the significant properties of ZnO are the direct wide band gap (3.4 eV) at ambient temperature, the high energy binding of exciton (60 meV), which is higher than some materials usually used such as ZnSe (20 meV) and GaN (25 meV) (Mihailovic et al. 2009; Peng et al. 2012). The no toxicity and the abundance on the ground make ZnO an ideal candidate for transparent electrical contact for the solar cells in thin layers. This material is of great importance in the field of optoelectronics and of photovoltaics. It can be used in several applications in various scientific and industrial fields such as the piezoelectric transducers (\u00d6zg\u00fcr et al. 2005), wave guides, gas detectors (Kim et al. 2010), and conducting transparent electrodes (Lucas et al. 2007).", "question": "What is the high energy binding of exciton of ZnO?", "answers": {"text": "60 meV", "answer_start": [233]}}
{"id": "10.1007#s11082-014-0052-7.html_2", "title": "10.1007#s11082-014-0052-7.html", "context": "The zinc oxide is a transparent semiconductor of type II-VI with a normal type n conductivity. Among the significant properties of ZnO are the direct wide band gap (3.4 eV) at ambient temperature, the high energy binding of exciton (60 meV), which is higher than some materials usually used such as ZnSe (20 meV) and GaN (25 meV) (Mihailovic et al. 2009; Peng et al. 2012). The no toxicity and the abundance on the ground make ZnO an ideal candidate for transparent electrical contact for the solar cells in thin layers. This material is of great importance in the field of optoelectronics and of photovoltaics. It can be used in several applications in various scientific and industrial fields such as the piezoelectric transducers (\u00d6zg\u00fcr et al. 2005), wave guides, gas detectors (Kim et al. 2010), and conducting transparent electrodes (Lucas et al. 2007).", "question": "What is the energy binding of exciton of ZnSe?", "answers": {"text": "20 meV", "answer_start": [305]}}
{"id": "10.1007#s11082-014-0052-7.html_3", "title": "10.1007#s11082-014-0052-7.html", "context": "The zinc oxide is a transparent semiconductor of type II-VI with a normal type n conductivity. Among the significant properties of ZnO are the direct wide band gap (3.4 eV) at ambient temperature, the high energy binding of exciton (60 meV), which is higher than some materials usually used such as ZnSe (20 meV) and GaN (25 meV) (Mihailovic et al. 2009; Peng et al. 2012). The no toxicity and the abundance on the ground make ZnO an ideal candidate for transparent electrical contact for the solar cells in thin layers. This material is of great importance in the field of optoelectronics and of photovoltaics. It can be used in several applications in various scientific and industrial fields such as the piezoelectric transducers (\u00d6zg\u00fcr et al. 2005), wave guides, gas detectors (Kim et al. 2010), and conducting transparent electrodes (Lucas et al. 2007).", "question": "What is the energy binding of exciton of GaN?", "answers": {"text": "25 meV", "answer_start": [322]}}
{"id": "10.1007#s11082-014-0052-7.html_4", "title": "10.1007#s11082-014-0052-7.html", "context": "Figure 1a-d shows the calculated band structure and total electronic density of states (TDOS) of pure ZnO. We can see that the bottom of the conduction band and the top of the valence band are at the same point (sigma \\(\\varGamma \\)). It represents a characteristic of direct gap semiconductor. The calculating of the energy gap in the first principles based on the local density functional theory is lower than that in the experiment. A study realized with CASTEP code found that the energy gap is 0.73 eV (Hsuan-Chung et al. 2012) using GGA approximation. In the present work the calculation of the band structure shows that it is 1 eV with GGA approximation, which is lower than the experimental value (3.3 eV). In some studies this gap can be placed in the range 3.1-3.37 eV (Thomas 1960; Hengehold et al. 1970; Liang and Yoffe 1968; Gupta 1990; Landolt-Bornstein 1982; Freeouf 1972; Pankove 1971; Liu et al. 1992; Kossanyi et al. 1990; Srikant and Clarke 1997; Natsume et al. 1995; Roth et al. 1981; Srikant and Clarke 1997).\n", "question": "What is the range of the band gap of ZnO in some studies?", "answers": {"text": "3.1-3.37 eV", "answer_start": [767]}}
{"id": "10.1007#s11082-014-0052-7.html_5", "title": "10.1007#s11082-014-0052-7.html", "context": "Figure 1a-d shows the calculated band structure and total electronic density of states (TDOS) of pure ZnO. We can see that the bottom of the conduction band and the top of the valence band are at the same point (sigma \\(\\varGamma \\)). It represents a characteristic of direct gap semiconductor. The calculating of the energy gap in the first principles based on the local density functional theory is lower than that in the experiment. A study realized with CASTEP code found that the energy gap is 0.73 eV (Hsuan-Chung et al. 2012) using GGA approximation. In the present work the calculation of the band structure shows that it is 1 eV with GGA approximation, which is lower than the experimental value (3.3 eV). In some studies this gap can be placed in the range 3.1-3.37 eV (Thomas 1960; Hengehold et al. 1970; Liang and Yoffe 1968; Gupta 1990; Landolt-Bornstein 1982; Freeouf 1972; Pankove 1971; Liu et al. 1992; Kossanyi et al. 1990; Srikant and Clarke 1997; Natsume et al. 1995; Roth et al. 1981; Srikant and Clarke 1997).\n", "question": "What is the experimental value of the band gap of ZnO?", "answers": {"text": "3.3 eV", "answer_start": [706]}}
{"id": "10.1007#s11082-014-0052-7.html_6", "title": "10.1007#s11082-014-0052-7.html", "context": "In our studies we deduced the results in Figs. 7 and 8. According to Fig. 7, the behaviors of absorption are shown for Aluminum substituted in oxygen site, Zinc site, and for pure ZnO versus wavelength. Using the GGA and mBJ approximation, good results were found for mBJ. The absorption displays excellent physical behavior in the range of visible light (400-800 nm) for the Aluminum substitute in Zinc sites in the \\(2\\times 2\\times 1\\) structure. This substitution is more crucial than a pure ZnO from the 300 nm wavelength because the absorption becomes very low. In this range the material does not absorb, however the substitution of Al at the site of oxygen shows a high absorption which will influence the transparency of ZnO. The introduction of Al atoms in the oxygen site is not vital for the optical properties.\n", "question": "In what range does the absorption display excellent physical behavior for the Aluminum substitute in Zinc sites?", "answers": {"text": "visible light (400-800 nm)", "answer_start": [341]}}
{"id": "10.1007#s11082-014-0052-7.html_7", "title": "10.1007#s11082-014-0052-7.html", "context": "According to the Figs. 9 and 10, the substitution of Al in Zinc sites in the \\(2\\times 2\\times 1\\) model is more important than that of oxygen sites and that of doping Silicon. It shows that the transmittance is high and stable in the visible light. Therefore the Al in Zinc sites can be used to improve this property and can be used in several PV applications. According to the curves in Fig. 11, small doping concentrations (6.25 %) present a relatively stable transmission in the range of visible light. This stability is clearly seen in the case of Silicon, with the absence of the attenuation observed for 25 and 12.5 % above 500 nm.\n", "question": "What doping concentrations present a relatively stable transmission in the range of visible light?", "answers": {"text": "(6.25 %)", "answer_start": [426]}}
{"id": "10.1007#s11082-014-0052-7.html_8", "title": "10.1007#s11082-014-0052-7.html", "context": "For ZnO doped Si, Al substitute in Oxygen site and Al substitute in Zinc site, the static refractive index value is respectively 2.72, 4.18, 1.78. According to Fig. 12, the refractive index of ZnO doped Si varies according to energy. \\(\\mathrm{n}=3.80\\) is the maximum value corresponding to energy 1.24 eV. This value shows a weak transparence and a considerable absorbance. For the substitution of Aluminum in the oxygen site in the range 300-500 nm, the refractive index reached respectively these two peaks 2.92 and 2.55. They correspond to a very weak transmittance of 65 %. The substitution of Al in the site of oxygen does not produce transparency. This result is consistent with Fig. 7 where the absorption is important in the same range.\n", "question": "What is the static refractive index value of ZnO doped Si?", "answers": {"text": "2.72", "answer_start": [129]}}
{"id": "10.1007#s11082-014-0052-7.html_9", "title": "10.1007#s11082-014-0052-7.html", "context": "For ZnO doped Si, Al substitute in Oxygen site and Al substitute in Zinc site, the static refractive index value is respectively 2.72, 4.18, 1.78. According to Fig. 12, the refractive index of ZnO doped Si varies according to energy. \\(\\mathrm{n}=3.80\\) is the maximum value corresponding to energy 1.24 eV. This value shows a weak transparence and a considerable absorbance. For the substitution of Aluminum in the oxygen site in the range 300-500 nm, the refractive index reached respectively these two peaks 2.92 and 2.55. They correspond to a very weak transmittance of 65 %. The substitution of Al in the site of oxygen does not produce transparency. This result is consistent with Fig. 7 where the absorption is important in the same range.\n", "question": "What is the static refractive index value of Al sustitute in Oxygen site?", "answers": {"text": "4.18", "answer_start": [135]}}
{"id": "10.1007#s11082-014-0052-7.html_10", "title": "10.1007#s11082-014-0052-7.html", "context": "For ZnO doped Si, Al substitute in Oxygen site and Al substitute in Zinc site, the static refractive index value is respectively 2.72, 4.18, 1.78. According to Fig. 12, the refractive index of ZnO doped Si varies according to energy. \\(\\mathrm{n}=3.80\\) is the maximum value corresponding to energy 1.24 eV. This value shows a weak transparence and a considerable absorbance. For the substitution of Aluminum in the oxygen site in the range 300-500 nm, the refractive index reached respectively these two peaks 2.92 and 2.55. They correspond to a very weak transmittance of 65 %. The substitution of Al in the site of oxygen does not produce transparency. This result is consistent with Fig. 7 where the absorption is important in the same range.\n", "question": "What is the static refractive index value of Al substitute in Zinc site?", "answers": {"text": "1.78", "answer_start": [141]}}
{"id": "10.1007#s11082-014-0052-7.html_11", "title": "10.1007#s11082-014-0052-7.html", "context": "The decrease of absorption coefficient, a stable and high transmittance in the visible light range were gained with the incorporation of Al in ZnO. We showed effective results between calculations and the existing experimental data. These studies based on first-principles calculations investigate that the substitution of Al in the sites of oxygen is not optimal for optical properties of ZnO. However, substituting it in the Zinc sites produced agreeable results. Therefore when comparing Si with Al in the \\(2\\times 2\\times 1\\) structure, Silicon does not present a stability of transmittance to the length of visible light. This confirms the performance that can present Al to be used as suitable transparent material electrodes in solar cells.", "question": "What benefic will be gained with the incorporation of Al in ZnO?", "answers": {"text": "The decrease of absorption coefficient, a stable and high transmittance in the visible light range", "answer_start": [0]}}
{"id": "10.1007#s11082-014-0052-7.html_12", "title": "10.1007#s11082-014-0052-7.html", "context": "The decrease of absorption coefficient, a stable and high transmittance in the visible light range were gained with the incorporation of Al in ZnO. We showed effective results between calculations and the existing experimental data. These studies based on first-principles calculations investigate that the substitution of Al in the sites of oxygen is not optimal for optical properties of ZnO. However, substituting it in the Zinc sites produced agreeable results. Therefore when comparing Si with Al in the \\(2\\times 2\\times 1\\) structure, Silicon does not present a stability of transmittance to the length of visible light. This confirms the performance that can present Al to be used as suitable transparent material electrodes in solar cells.", "question": "The substitution of Al in the sites of oxygen is not optimal for what of ZnO?", "answers": {"text": "optical properties", "answer_start": [368]}}
{"id": "10.1007#s11082-014-0052-7.html_13", "title": "10.1007#s11082-014-0052-7.html", "context": "The decrease of absorption coefficient, a stable and high transmittance in the visible light range were gained with the incorporation of Al in ZnO. We showed effective results between calculations and the existing experimental data. These studies based on first-principles calculations investigate that the substitution of Al in the sites of oxygen is not optimal for optical properties of ZnO. However, substituting it in the Zinc sites produced agreeable results. Therefore when comparing Si with Al in the \\(2\\times 2\\times 1\\) structure, Silicon does not present a stability of transmittance to the length of visible light. This confirms the performance that can present Al to be used as suitable transparent material electrodes in solar cells.", "question": "What does not the silicon present to the length of visible light?", "answers": {"text": "a stability of transmittance", "answer_start": [567]}}
{"id": "10.1007#s11082-014-9901-7.html_0", "title": "10.1007#s11082-014-9901-7.html", "context": "The external electroabsorption (EA) modulators are photonic semiconductor devices which are widely used in optical fiber communication networks. The theoretical results of optical absorption near the band gap were first developed by Franz (1958) and Keldysh (1958) (F-K effect) in the presence of electric field. Although these results have been further studied by Callaway (1963) and Tharmalingam (1963) using known properties of Airy function, there were no reports about the excitonic electroabsorption in bulk material at RT. These calculations have been observed experimentally by Moss (1961). The excitonic electroabsorption had been realized only in quantum well (QW) structure at RT due to its good carrier confinement. Casey et al. (1975) reported that the exciton absorption peak can be observed for high purity \\((5\\times 10^{16}\\,\\hbox {cm}^{-3})\\) bulk GaAs even at RT. The theory by Dow and Redfield (1970) predicted that the discrete exciton states should respond even more sensitively with applied electric field than the bound states. Efficient modulation can be obtained when the F-K effect is dominated by the excitonic effects which enhance the absorption features below the bandgap.", "question": "What are photonic semiconductor devices which are widely used in optical fiber communication networks?", "answers": {"text": "The external electroabsorption (EA) modulators", "answer_start": [0]}}
{"id": "10.1007#s11082-014-9901-7.html_1", "title": "10.1007#s11082-014-9901-7.html", "context": "The external electroabsorption (EA) modulators are photonic semiconductor devices which are widely used in optical fiber communication networks. The theoretical results of optical absorption near the band gap were first developed by Franz (1958) and Keldysh (1958) (F-K effect) in the presence of electric field. Although these results have been further studied by Callaway (1963) and Tharmalingam (1963) using known properties of Airy function, there were no reports about the excitonic electroabsorption in bulk material at RT. These calculations have been observed experimentally by Moss (1961). The excitonic electroabsorption had been realized only in quantum well (QW) structure at RT due to its good carrier confinement. Casey et al. (1975) reported that the exciton absorption peak can be observed for high purity \\((5\\times 10^{16}\\,\\hbox {cm}^{-3})\\) bulk GaAs even at RT. The theory by Dow and Redfield (1970) predicted that the discrete exciton states should respond even more sensitively with applied electric field than the bound states. Efficient modulation can be obtained when the F-K effect is dominated by the excitonic effects which enhance the absorption features below the bandgap.", "question": "Who developed the theoretical results of optical absorption near the band gap in 1958?", "answers": {"text": "Franz", "answer_start": [233]}}
{"id": "10.1007#s11082-014-9901-7.html_2", "title": "10.1007#s11082-014-9901-7.html", "context": "The external electroabsorption (EA) modulators are photonic semiconductor devices which are widely used in optical fiber communication networks. The theoretical results of optical absorption near the band gap were first developed by Franz (1958) and Keldysh (1958) (F-K effect) in the presence of electric field. Although these results have been further studied by Callaway (1963) and Tharmalingam (1963) using known properties of Airy function, there were no reports about the excitonic electroabsorption in bulk material at RT. These calculations have been observed experimentally by Moss (1961). The excitonic electroabsorption had been realized only in quantum well (QW) structure at RT due to its good carrier confinement. Casey et al. (1975) reported that the exciton absorption peak can be observed for high purity \\((5\\times 10^{16}\\,\\hbox {cm}^{-3})\\) bulk GaAs even at RT. The theory by Dow and Redfield (1970) predicted that the discrete exciton states should respond even more sensitively with applied electric field than the bound states. Efficient modulation can be obtained when the F-K effect is dominated by the excitonic effects which enhance the absorption features below the bandgap.", "question": "Who predicted that the discrete exciton states should respond even more sensitively with applied electric field than the bound states?", "answers": {"text": "Dow and Redfield", "answer_start": [897]}}
{"id": "10.1007#s11082-014-9901-7.html_3", "title": "10.1007#s11082-014-9901-7.html", "context": "The external electroabsorption (EA) modulators are photonic semiconductor devices which are widely used in optical fiber communication networks. The theoretical results of optical absorption near the band gap were first developed by Franz (1958) and Keldysh (1958) (F-K effect) in the presence of electric field. Although these results have been further studied by Callaway (1963) and Tharmalingam (1963) using known properties of Airy function, there were no reports about the excitonic electroabsorption in bulk material at RT. These calculations have been observed experimentally by Moss (1961). The excitonic electroabsorption had been realized only in quantum well (QW) structure at RT due to its good carrier confinement. Casey et al. (1975) reported that the exciton absorption peak can be observed for high purity \\((5\\times 10^{16}\\,\\hbox {cm}^{-3})\\) bulk GaAs even at RT. The theory by Dow and Redfield (1970) predicted that the discrete exciton states should respond even more sensitively with applied electric field than the bound states. Efficient modulation can be obtained when the F-K effect is dominated by the excitonic effects which enhance the absorption features below the bandgap.", "question": "What is the F-K effect dominated by?", "answers": {"text": "excitonic effects which enhance the absorption features below the bandgap", "answer_start": [1129]}}
{"id": "10.1007#s11082-014-9901-7.html_4", "title": "10.1007#s11082-014-9901-7.html", "context": "\nKayastha et al. (2009) have succeeded in fabricating of ultra-high-purity GaAs epilayers with background impurity less than \\(1\\times 10^{13}\\) cm\\(^{-3}\\) and Hall mobility of 312,000 \\(\\hbox {cm}^{2}\\,\\hbox {V}^{-1}\\,\\hbox {s}^{-1}\\) at 77 K by using a liquid phase epitaxy (LPE). These high purity epilayers exhibit a clear exciton absorption peak at RT. This has made it possible to fabricate a spatial light modulator (SLM) operating at surface normal configuration and two-dimensional array due to large depletion layer over 30 \\(\\upmu \\hbox {m}\\). This SLM has an extinction ratio of 20 dB at operating voltage of 33 V at RT (Kayastha et al. 2010). This operating voltage for SLM device is much smaller when compared with Bitou and Minemoto (1998) where 2.4 kV was needed to obtain 20 dB. Sapkota et al. (2012) had studied theoretically and experimentally about the excitonic electroabsorption in bulk material at RT, where continuum band transition broadening had been used as the same with the Bottka and Hutcheson (1975) and Somerfield factor was also not considered.", "question": "What is the extinction ratio of SLM at operating voltage of 33V?", "answers": {"text": "20 dB", "answer_start": [592]}}
{"id": "10.1007#s11082-014-9901-7.html_5", "title": "10.1007#s11082-014-9901-7.html", "context": "\nKayastha et al. (2009) have succeeded in fabricating of ultra-high-purity GaAs epilayers with background impurity less than \\(1\\times 10^{13}\\) cm\\(^{-3}\\) and Hall mobility of 312,000 \\(\\hbox {cm}^{2}\\,\\hbox {V}^{-1}\\,\\hbox {s}^{-1}\\) at 77 K by using a liquid phase epitaxy (LPE). These high purity epilayers exhibit a clear exciton absorption peak at RT. This has made it possible to fabricate a spatial light modulator (SLM) operating at surface normal configuration and two-dimensional array due to large depletion layer over 30 \\(\\upmu \\hbox {m}\\). This SLM has an extinction ratio of 20 dB at operating voltage of 33 V at RT (Kayastha et al. 2010). This operating voltage for SLM device is much smaller when compared with Bitou and Minemoto (1998) where 2.4 kV was needed to obtain 20 dB. Sapkota et al. (2012) had studied theoretically and experimentally about the excitonic electroabsorption in bulk material at RT, where continuum band transition broadening had been used as the same with the Bottka and Hutcheson (1975) and Somerfield factor was also not considered.", "question": "At what voltage does this SLM have an extinction ratio of 20 dB?", "answers": {"text": "33 V", "answer_start": [622]}}
{"id": "10.1007#s11082-014-9901-7.html_6", "title": "10.1007#s11082-014-9901-7.html", "context": "\nKayastha et al. (2009) have succeeded in fabricating of ultra-high-purity GaAs epilayers with background impurity less than \\(1\\times 10^{13}\\) cm\\(^{-3}\\) and Hall mobility of 312,000 \\(\\hbox {cm}^{2}\\,\\hbox {V}^{-1}\\,\\hbox {s}^{-1}\\) at 77 K by using a liquid phase epitaxy (LPE). These high purity epilayers exhibit a clear exciton absorption peak at RT. This has made it possible to fabricate a spatial light modulator (SLM) operating at surface normal configuration and two-dimensional array due to large depletion layer over 30 \\(\\upmu \\hbox {m}\\). This SLM has an extinction ratio of 20 dB at operating voltage of 33 V at RT (Kayastha et al. 2010). This operating voltage for SLM device is much smaller when compared with Bitou and Minemoto (1998) where 2.4 kV was needed to obtain 20 dB. Sapkota et al. (2012) had studied theoretically and experimentally about the excitonic electroabsorption in bulk material at RT, where continuum band transition broadening had been used as the same with the Bottka and Hutcheson (1975) and Somerfield factor was also not considered.", "question": "What voltage is needed to obtain 20 dB according to the study by Bitou and Minemoto?", "answers": {"text": "2.4 kV", "answer_start": [762]}}
{"id": "10.1007#s11082-014-9901-7.html_7", "title": "10.1007#s11082-014-9901-7.html", "context": "The loss at zero external voltage is estimated to be about 0.09 dB at photon energy of 1.404 eV. In Fig.  1, the transmission spectra with zero external applied voltage are slightly higher in experimental result than that of the theoretical result for photon energy less than 1.419 eV. This may be due to the reflection loss, coupling loss and substrate free-carrier loss. The tail of transmission spectra at zero external applied voltage of theoretical result lie below the experimental result; on the other hand, it nearly coincides at external applied voltage. This is due to the fact that the contribution of the F-K effect increases and Coulomb interaction exhibits negligible at high electric field. The excitonic peak remains stable toward the lower energy having large red-shift even at normalized electric field of 1 indicating that the electric field is uniform inside the active layer, which implies the very high-purity in the active region. It is surprising that excitonic peak shifts toward large energy over 20 meV, which reasonably showed good agreement with the experimental results.", "question": "Why is the transmission spectra with zero external applied voltage higher in experimental result than that of the theoretical result?", "answers": {"text": "reflection loss, coupling loss and substrate free-carrier loss", "answer_start": [309]}}
{"id": "10.1007#s11082-014-9901-7.html_8", "title": "10.1007#s11082-014-9901-7.html", "context": "The loss at zero external voltage is estimated to be about 0.09 dB at photon energy of 1.404 eV. In Fig.  1, the transmission spectra with zero external applied voltage are slightly higher in experimental result than that of the theoretical result for photon energy less than 1.419 eV. This may be due to the reflection loss, coupling loss and substrate free-carrier loss. The tail of transmission spectra at zero external applied voltage of theoretical result lie below the experimental result; on the other hand, it nearly coincides at external applied voltage. This is due to the fact that the contribution of the F-K effect increases and Coulomb interaction exhibits negligible at high electric field. The excitonic peak remains stable toward the lower energy having large red-shift even at normalized electric field of 1 indicating that the electric field is uniform inside the active layer, which implies the very high-purity in the active region. It is surprising that excitonic peak shifts toward large energy over 20 meV, which reasonably showed good agreement with the experimental results.", "question": "Why does the tail of transmission spectra at zero external applied voltage of theoretical result lie below the experimental result?", "answers": {"text": "the contribution of the F-K effect increases and Coulomb interaction exhibits negligible at high electric field", "answer_start": [593]}}
{"id": "10.1007#s11082-014-9901-7.html_9", "title": "10.1007#s11082-014-9901-7.html", "context": "The loss at zero external voltage is estimated to be about 0.09 dB at photon energy of 1.404 eV. In Fig.  1, the transmission spectra with zero external applied voltage are slightly higher in experimental result than that of the theoretical result for photon energy less than 1.419 eV. This may be due to the reflection loss, coupling loss and substrate free-carrier loss. The tail of transmission spectra at zero external applied voltage of theoretical result lie below the experimental result; on the other hand, it nearly coincides at external applied voltage. This is due to the fact that the contribution of the F-K effect increases and Coulomb interaction exhibits negligible at high electric field. The excitonic peak remains stable toward the lower energy having large red-shift even at normalized electric field of 1 indicating that the electric field is uniform inside the active layer, which implies the very high-purity in the active region. It is surprising that excitonic peak shifts toward large energy over 20 meV, which reasonably showed good agreement with the experimental results.", "question": "What does the excitonic peak show suprisly?", "answers": {"text": "peak shifts toward large energy over 20 meV", "answer_start": [986]}}
{"id": "10.1007#s11082-014-9901-7.html_10", "title": "10.1007#s11082-014-9901-7.html", "context": "The loss at zero external voltage is estimated to be about 0.09 dB at photon energy of 1.404 eV. In Fig.  1, the transmission spectra with zero external applied voltage are slightly higher in experimental result than that of the theoretical result for photon energy less than 1.419 eV. This may be due to the reflection loss, coupling loss and substrate free-carrier loss. The tail of transmission spectra at zero external applied voltage of theoretical result lie below the experimental result; on the other hand, it nearly coincides at external applied voltage. This is due to the fact that the contribution of the F-K effect increases and Coulomb interaction exhibits negligible at high electric field. The excitonic peak remains stable toward the lower energy having large red-shift even at normalized electric field of 1 indicating that the electric field is uniform inside the active layer, which implies the very high-purity in the active region. It is surprising that excitonic peak shifts toward large energy over 20 meV, which reasonably showed good agreement with the experimental results.", "question": "What is the estimated loss at zero external voltage at photon energy of 1.404 eV?", "answers": {"text": "0.09 dB", "answer_start": [59]}}
{"id": "10.1007#s11082-014-9901-7.html_11", "title": "10.1007#s11082-014-9901-7.html", "context": "The loss at zero external voltage is estimated to be about 0.09 dB at photon energy of 1.404 eV. In Fig.  1, the transmission spectra with zero external applied voltage are slightly higher in experimental result than that of the theoretical result for photon energy less than 1.419 eV. This may be due to the reflection loss, coupling loss and substrate free-carrier loss. The tail of transmission spectra at zero external applied voltage of theoretical result lie below the experimental result; on the other hand, it nearly coincides at external applied voltage. This is due to the fact that the contribution of the F-K effect increases and Coulomb interaction exhibits negligible at high electric field. The excitonic peak remains stable toward the lower energy having large red-shift even at normalized electric field of 1 indicating that the electric field is uniform inside the active layer, which implies the very high-purity in the active region. It is surprising that excitonic peak shifts toward large energy over 20 meV, which reasonably showed good agreement with the experimental results.", "question": "At what photo energy is the loss at zero external voltage estimated to be 0.09 dB?", "answers": {"text": "1.404 eV", "answer_start": [87]}}
{"id": "10.1007#s11082-014-9901-7.html_12", "title": "10.1007#s11082-014-9901-7.html", "context": "The exciton linewidth broadening with normalized electric field has been plotted based on the relation (Schultheis et al. 1987) in Fig. 3. In the case of low purity three-dimensional excitons, it is well known that the application of an external applied voltage significantly reduces the exciton lifetime because of a finite probability of exciton tunnelling through the field modified band gap. However, excitons in high-purity case are much stronger with respect to the electric field. As a result, high purity three-dimensional excitons demonstrate an appreciable field induced shift, while the exciton linewidth does not change very much as shown in Fig. 3. The exciton linewidth broadening below the normalized electric field of 0.36 increases very slowly and then it abruptly increases after 0.36 upto a value of 4 meV at \\(\\hbox {f}=1\\) and the exciton peak after the normalized electric field of 1 may be completely destroyed. Theoretical result shows good agreement with the experimental result.\n", "question": "Why does the application of an external applied voltage reduce the lifetime of the exciton?", "answers": {"text": "a finite probability of exciton tunnelling through the field modified band gap", "answer_start": [316]}}
{"id": "10.1007#s11082-014-9901-7.html_13", "title": "10.1007#s11082-014-9901-7.html", "context": "The height of transmission spectra associated with exciton as a function normalized electric field at RT is shown in Fig. 4. The variation of height of transmission spectra is slightly and sharply reduced with increasing electric field before and after the normalized electric field of 0.36, respectively, and follows roughly as \\(F^\\mathrm{S}\\) law after 0.36, where \\(S = 0.1\\). This is expected as two reasons: first, it is the fact that the exciton is slowly broadened with uniform electric field when the depletion width is smaller, whereas, it is broadened faster with higher field because the exciton has been ionized almost completely, second, the F-K effect is dominated by exciton effect at low field and starts to increase faster at high field. Owing this advantage of initially slow variation of height of transmission spectra associated with exciton, we obtained the large change in transmission spectra. As results, the extinction ratio is estimated to be 14 dB for high speed device at f = 1; however the applied voltage is comparatively high due to relatively large background impurity.\n", "question": "What will the F-K effect behave at high field?", "answers": {"text": "starts to increase faster", "answer_start": [715]}}
{"id": "10.1007#s11082-014-9901-7.html_14", "title": "10.1007#s11082-014-9901-7.html", "context": "The extinction ratio has been calculated as difference in transmission spectra (\\(T_{2}-T_{1})\\) as a function of normalized electric field at detuning energy of 25 meV. In Fig. 5, the separation of curve between the extinction ratio with and without exciton is very small at low electric field. The separation increases with the increasing of electric field. The extinction ratio is estimated to be about 7 times higher in the case of exciton absorption than that of without exciton at normalized electric field of 1. This is due to the advantage of enhancement of absorption with exciton by which we obtained the large change in absorption coefficient in high-purity GaAs material. The extinction ratio with exciton has been compared with experimental result as shown in Fig. 5.\n", "question": "How many times is the extinction ratio estimated to be in the case of exciton absorption than that of without exciton at normalized electric field of 1?", "answers": {"text": "7", "answer_start": [406]}}
{"id": "10.1007#s11082-014-9901-7.html_15", "title": "10.1007#s11082-014-9901-7.html", "context": "The electric field effect on the shape transmission spectra with exciton in high purity GaAs has been theoretically studied. The theoretical results showed the good agreement with the experimental results. The large Stark red-shift about 3 times higher than the exciton binding energy has been estimated without excessive exciton linewidth broadening. This is excellent result in bulk structure. We appeal that the height of exciton peak varies slowly at low electric field due to the uniform distribution of electric field in high-purity GaAs material. The extinction ratio of 13.9 dB is determined at normalized electric field of 1 as a performance characteristic, which shows close agreement with experimental result.", "question": "Why does the height of exciton peak vary slowly at low electric field?", "answers": {"text": "due to the uniform distribution of electric field in high-purity GaAs material", "answer_start": [474]}}
{"id": "10.1007#s11082-014-9924-0.html_0", "title": "10.1007#s11082-014-9924-0.html", "context": "The wafer design of a widely tunable InGaAs/GaAs quantum wells vertical-external-cavity surface-emitting laser (VECSEL) at 1,064 nm was presented. A GaAs/AlAs based double-band mirror (DBM) was employed to yield sufficient reflectivity (\\(>\\)0.999) over 118 nm wavelength coverage, which is 54 nm wider than that of a usually used distributed Bragg reflector. In the active region, an antiresonant subcavity, formed by the DBM and the air-semiconductor interface, was introduced to produce extended longitudinal confinement factor, and two kinds of InGaAs quantum wells with different In composition were used to expand the material gain. As a result, a broadband gain spectrum of the semiconductor wafer with 85 nm FWHM bandwidth was obtained, and this was valuable for broadband performance of a tunable VECSEL.", "question": "What is presented in this study?", "answers": {"text": "The wafer design of a widely tunable InGaAs/GaAs quantum wells vertical-external-cavity surface-emitting laser", "answer_start": [0]}}
{"id": "10.1007#s11082-014-9924-0.html_1", "title": "10.1007#s11082-014-9924-0.html", "context": "To obtain broadband tunability, F. Li et al used two gain chips to provide higher modal gain and broader bandwidth of the gain, and 33 nm tuning range centre at 975 nm VECSEL was demonstrated (Li et al. 2007). In the work reported by C. Borgentun et al, an antireflection (AR) structure between the active region and the air-semiconductor interface was used, broadband performance was then obtained by deliberately making the subcavity formed between the air-semiconductor interface and the distributed Bragg reflector (DBR) antiresonant at the center wavelength, and 43 nm tuning range of a 996 nm VECSEL is achieved (Borgentun et al. 2010). Using the broad gain bandwidth of quantum dot (QD) materials, wavelength tunability up to 60 nm around 1,040 nm, 69 nm around 1,180 nm, and 25 nm around 1,260 nm was demonstrated by Butkus et al. 2011. By the use of a modified gain structure comprising three different kinds of quantum wells (QWs) with different well width, J. Paajaste et al had achieved a spectral tuning range of about 156 nm in a 1,970 nm VECSEL (Paajaste et al. 2009).", "question": "What materials did Butkus use to show a wavelength tunability up to 60 nm around 1,040 nm?", "answers": {"text": "the broad gain bandwidth of quantum dot (QD) materials", "answer_start": [649]}}
{"id": "10.1007#s11082-014-9924-0.html_2", "title": "10.1007#s11082-014-9924-0.html", "context": "In the semiconductor wafer of a VECSEL, the so-called subcavity (or named as microcavity), formed between the end reflector (DBR or DBM) and the air-semiconductor interface, must be designed carefully because the finally lasing modes of the VECSEL are determined by the overlaps of the subcavity modes and the external-cavity modes. Two typical kinds of subcavity are used in a VECSEL: resonant subcavity and antiresonant subcavity, which are specified by the maximum amplitude and the zero amplitude of the optical field at the air-semiconductor interface, respectively. Resonant subcavity can provide higher gain and is generally used in a high output power VECSEL (Tropper and Hoogland 2006) , while antiresonant subcavity can yield wider gain bandwidth and is more often used for broadband spectroscopy application (Garnache et al. 2000) or mode locking operation (H\u00e4ring et al. 2002).", "question": "What is the first typical kind of subcavity that is used in a VECSEL?", "answers": {"text": "resonant subcavity", "answer_start": [386]}}
{"id": "10.1007#s11082-014-9924-0.html_3", "title": "10.1007#s11082-014-9924-0.html", "context": "In the semiconductor wafer of a VECSEL, the so-called subcavity (or named as microcavity), formed between the end reflector (DBR or DBM) and the air-semiconductor interface, must be designed carefully because the finally lasing modes of the VECSEL are determined by the overlaps of the subcavity modes and the external-cavity modes. Two typical kinds of subcavity are used in a VECSEL: resonant subcavity and antiresonant subcavity, which are specified by the maximum amplitude and the zero amplitude of the optical field at the air-semiconductor interface, respectively. Resonant subcavity can provide higher gain and is generally used in a high output power VECSEL (Tropper and Hoogland 2006) , while antiresonant subcavity can yield wider gain bandwidth and is more often used for broadband spectroscopy application (Garnache et al. 2000) or mode locking operation (H\u00e4ring et al. 2002).", "question": "What is the second typical kind of subcavity that is used in a VECSEL?", "answers": {"text": "antiresonant subcavity", "answer_start": [409]}}
{"id": "10.1007#s11082-014-9924-0.html_4", "title": "10.1007#s11082-014-9924-0.html", "context": "In the semiconductor wafer of a VECSEL, the so-called subcavity (or named as microcavity), formed between the end reflector (DBR or DBM) and the air-semiconductor interface, must be designed carefully because the finally lasing modes of the VECSEL are determined by the overlaps of the subcavity modes and the external-cavity modes. Two typical kinds of subcavity are used in a VECSEL: resonant subcavity and antiresonant subcavity, which are specified by the maximum amplitude and the zero amplitude of the optical field at the air-semiconductor interface, respectively. Resonant subcavity can provide higher gain and is generally used in a high output power VECSEL (Tropper and Hoogland 2006) , while antiresonant subcavity can yield wider gain bandwidth and is more often used for broadband spectroscopy application (Garnache et al. 2000) or mode locking operation (H\u00e4ring et al. 2002).", "question": "What are the two typical kinds of subcavity that are used in a VECSEL?", "answers": {"text": "resonant subcavity and antiresonant subcavity", "answer_start": [386]}}
{"id": "10.1007#s11082-014-9924-0.html_5", "title": "10.1007#s11082-014-9924-0.html", "context": "The calculated longitudinal confinement factors of the designed wafer with antiresonant and resonant subcavity are given in Fig. 3, the total lengths of the antiresonant and resonant subcavity are 21 and 22 times of quaterwave, respectively, and the detailed methods for computation can be found in the article (Tropper and Hoogland 2006) . The FWHM width of the longitudinal confinement factor of the wafer with antiresonant subcavity is about 82 nm, which is approximately 6 times of that with resonant subcavity. It means that through appropriate design of material gain of QWs (which will be demonstrated below), along with the above modulation of the broadband longitudinal confinement factor, a wideband gain spectrum over 82 nm FWHM width of the semiconductor wafer can be expected.\n", "question": "What is the FWHM width of the longitudinal confinement factor of the wafer with antiresonant subcavity?", "answers": {"text": "82 nm", "answer_start": [445]}}
{"id": "10.1007#s11082-014-9927-x.html_0", "title": "10.1007#s11082-014-9927-x.html", "context": "Although hybrid III-V/Si MDLs are promising light sources for silicon optical interconnects, their thermal performance is quite poor due to inefficient heat dissipation. To improve the thermal performance, we propose an optimal design with a heat sink structure. It thermally connects the active region with the highly thermal-conductive Si substrate, so that the heat generated can be efficiently dissipated through the Si substrate. The isolation material is also optimized by using those with high thermal conductivity. This could further improve the thermal performance of the MDLs. Through calculation, the optimal design reduces the thermal resistance by 64 % and enhances the maximal CW output power by several times. It is shown that the thermal performance as well as the CW lasing performance of the hybrid MDL is greatly improved with the present optimal design.", "question": "Why is the thermal performance of hybrid III-V/Si MDLs quite poor?", "answers": {"text": "inefficient heat dissipation", "answer_start": [140]}}
{"id": "10.1007#s11082-014-9927-x.html_1", "title": "10.1007#s11082-014-9927-x.html", "context": "Although hybrid III-V/Si MDLs are promising light sources for silicon optical interconnects, their thermal performance is quite poor due to inefficient heat dissipation. To improve the thermal performance, we propose an optimal design with a heat sink structure. It thermally connects the active region with the highly thermal-conductive Si substrate, so that the heat generated can be efficiently dissipated through the Si substrate. The isolation material is also optimized by using those with high thermal conductivity. This could further improve the thermal performance of the MDLs. Through calculation, the optimal design reduces the thermal resistance by 64 % and enhances the maximal CW output power by several times. It is shown that the thermal performance as well as the CW lasing performance of the hybrid MDL is greatly improved with the present optimal design.", "question": "To what extent can the thermal resistance be reduced by the optical design?", "answers": {"text": "64 %", "answer_start": [661]}}
{"id": "10.1007#s11082-014-9954-7.html_0", "title": "10.1007#s11082-014-9954-7.html", "context": "The sol-gel technique is a very flexible, relatively simple, and low-cost method to fabricate many different innovative photonic structures characterized by specific functionalities. During synthesis, starting from the molecular level, compounds or composites with well controlled composition can be obtained as thin films, powders or monoliths. These materials can be used to prepare such structures as waveguides, photonic crystals, coatings, and bulk glasses including spheres, rings and other geometries exploited in optical resonators fabrication. This article presents some results obtained by the authors in the field of the sol-gel-derived photonic structures. To emphasise the scientific and technological interest in this kind of systems and the versatility of the sol-gel route, the glass-based nano and micrometer scale range systems are discussed. Particularly, the following systems are described: silica-hafnia glass and glass-ceramic planar waveguides, nanosized tetraphosphates, and silica colloidal crystals. The attention is focused on the spectroscopic properties of \\(\\hbox {Er}^{3+}\\)-activated materials that due to the light emission can be used in the integrated optics area covering application in sensing, biomedical diagnostic, energy conversion, telecommunication, lighting, and photon management.", "question": "What field is this paper focusing on?", "answers": {"text": "the sol-gel-derived photonic structures", "answer_start": [628]}}
{"id": "10.1007#s11082-014-9954-7.html_1", "title": "10.1007#s11082-014-9954-7.html", "context": "The sol-gel processing due to the advantages in terms of design, form, composition, structure, and optical properties are successfully applied for fabrication of photonic structures. Silica-based glasses have already had a wide range of application (Iraj Najafi 1998; Stein and Schroden 2001; Gan and Xu 2006). However, not only amorphous systems can be synthesized by the sol-gel route. Recently, of specific interest are glass-ceramic materials that combine properties of glasses and crystals (Berneschi et al. 2011). The sol-gel-based modified Pechini method (Pechini 1967) enables synthesis of crystalline nanopowders useful for preparation of colloidal solution, nanoceramic, or composites. Finally, rare earth (RE) doped glasses, glass-ceramics or nanocrystals can be used as active building blocks of integrated optics components.", "question": "Why is the sol-gel processing popular for fabrication of photonic structures?", "answers": {"text": "due to the advantages in terms of design, form, composition, structure, and optical properties", "answer_start": [23]}}
{"id": "10.1007#s11082-014-9979-y.html_0", "title": "10.1007#s11082-014-9979-y.html", "context": "All-solid photonic crystal fibers (ASPCFs) are an alternative approach to the more popular air-glass solid core PCFs. In this case, air holes are replaced with glass inclusions of a different refractive index to that of the background glass. The advantage of APCFs, as compared to the air hole-based PCFs, is the possibility of dispersion control with an additional parameter, which in this case is material dispersion of the second type of glass used for lattice design. Moreover, control of the fiber parameters during the drawing process is simpler and obtaining fiber parameters similar to the designed ones is straightforward (Buczynski et al. 2012a, b). The development of ASPCFs has been reported by several groups (Feng et al. 2003; Luan et al. 2004; Buczynski et al. 2012a, b) and successfully reported for supercontinuum generation (Kibler et al. 2009; Wang et al. 2012; Stepniewski et al. 2014). Introduction of subwavelength inclusions in the core enables an additional degree of freedom in shaping of dispersion profile, while maintaining a constant value of effective mode area (Buczynski et al. 2011).", "question": "What is the advantage of APCFs compared to the air hole-based PCFs?", "answers": {"text": "the possibility of dispersion control with an additional parameter", "answer_start": [309]}}
{"id": "10.1007#s11082-014-9979-y.html_5", "title": "10.1007#s11082-014-9979-y.html", "context": "Widely used techniques for dispersion characterization, like the time-of-flight method or the modulation phase shift method (Cohen 1985), require use of long sections of optical fiber. Apart from high cost, mentioned techniques are inapplicable for optical fibers made of highly nonlinear glasses due to their high attenuation. Another approach is to use an interferometer combined with a broadband light source (Diddams and Diels 1995). A modified Mach\u2013Zehnder interferometer technique enables measurement of dispersion characteristic in short lengths of optical fiber (Hlubina et al. 2007). We used this relatively cheap and easily applicable method for dispersion measurements of all-solid microstuctured fiber with nano-inclusion in the core.", "question": "What technique is widely used for dispersion characterization?", "answers": {"text": "time-of-flight method", "answer_start": [64]}}
{"id": "10.1007#s11082-014-9979-y.html_1", "title": "10.1007#s11082-014-9979-y.html", "context": "Widely used techniques for dispersion characterization, like the time-of-flight method or the modulation phase shift method (Cohen 1985), require use of long sections of optical fiber. Apart from high cost, mentioned techniques are inapplicable for optical fibers made of highly nonlinear glasses due to their high attenuation. Another approach is to use an interferometer combined with a broadband light source (Diddams and Diels 1995). A modified Mach\u2013Zehnder interferometer technique enables measurement of dispersion characteristic in short lengths of optical fiber (Hlubina et al. 2007). We used this relatively cheap and easily applicable method for dispersion measurements of all-solid microstuctured fiber with nano-inclusion in the core.", "question": "What does the time-of-flight method require for dispersion characterization?", "answers": {"text": "long sections of optical fiber", "answer_start": [152]}}
{"id": "10.1007#s11082-014-9979-y.html_2", "title": "10.1007#s11082-014-9979-y.html", "context": "New type of microstructured fiber with flat dispersion was designed and fabricated. A modified method of spectral interferometry for the chromatic dispersion measurements was used to verify its properties. The dispersion of an all-solid nano-inclusion microstructured fiber was measured in a wide spectral range between 600 and 1,800 nm. Taking into account the approximation curve of the measured dispersion, the zero dispersion wavelength was located in this fiber at 1,680 nm. The discrepancy between experimental and numerical results is assigned to the uncertainty of dimensions of the fabricated structure, taken from its SEM images for the calculations, which was related to the diffusion effect between the glasses.", "question": "What is designed in this study?", "answers": {"text": "New type of microstructured fiber with flat dispersion", "answer_start": [0]}}
{"id": "10.1007#s11082-014-9979-y.html_3", "title": "10.1007#s11082-014-9979-y.html", "context": "New type of microstructured fiber with flat dispersion was designed and fabricated. A modified method of spectral interferometry for the chromatic dispersion measurements was used to verify its properties. The dispersion of an all-solid nano-inclusion microstructured fiber was measured in a wide spectral range between 600 and 1,800 nm. Taking into account the approximation curve of the measured dispersion, the zero dispersion wavelength was located in this fiber at 1,680 nm. The discrepancy between experimental and numerical results is assigned to the uncertainty of dimensions of the fabricated structure, taken from its SEM images for the calculations, which was related to the diffusion effect between the glasses.", "question": "In what spectral range did the dispersion of an all-solid nano-inclusion microstructured fiber measured?", "answers": {"text": "between 600 and 1,800 nm", "answer_start": [312]}}
{"id": "10.1007#s11082-014-9979-y.html_4", "title": "10.1007#s11082-014-9979-y.html", "context": "New type of microstructured fiber with flat dispersion was designed and fabricated. A modified method of spectral interferometry for the chromatic dispersion measurements was used to verify its properties. The dispersion of an all-solid nano-inclusion microstructured fiber was measured in a wide spectral range between 600 and 1,800 nm. Taking into account the approximation curve of the measured dispersion, the zero dispersion wavelength was located in this fiber at 1,680 nm. The discrepancy between experimental and numerical results is assigned to the uncertainty of dimensions of the fabricated structure, taken from its SEM images for the calculations, which was related to the diffusion effect between the glasses.", "question": "What is the zero dispersion wavelength of the reported fiber?", "answers": {"text": "1,680 nm", "answer_start": [470]}}
{"id": "10.1007#s11082-014-9983-2.html_0", "title": "10.1007#s11082-014-9983-2.html", "context": "We show that application of the double clad hollow core fiber (DCHCF) significantly affects efficiency of collecting a two photon fluorescence signal. In our approach we propose a new construction of the hollow core double clad fiber which can be used to send simultaneously an ultrafast signal through the single-mode air core and collect the florescence signal through a multimodal clad. The presented fiber has a dispersion equal to 5.13 ps/nm km and losses 0.5 dB/m in the range of 800 nm. In the wavelengths range between 770 to 850 nm the fiber is endlessly single mode with higher order modes HOM\u2019s losses above 17 dB/m. The use of such a fiber allows elimination of prevalent precompensation dispersion systems and considerably simplifies the two photon fluorescence endoscopy setup.", "question": "What is the effect of the application of the double clad hollow core fiber?", "answers": {"text": "efficiency of collecting a two photo fluorescence signal", "answer_start": [-1]}}
{"id": "10.1007#s11082-014-9983-2.html_1", "title": "10.1007#s11082-014-9983-2.html", "context": "We show that application of the double clad hollow core fiber (DCHCF) significantly affects efficiency of collecting a two photon fluorescence signal. In our approach we propose a new construction of the hollow core double clad fiber which can be used to send simultaneously an ultrafast signal through the single-mode air core and collect the florescence signal through a multimodal clad. The presented fiber has a dispersion equal to 5.13 ps/nm km and losses 0.5 dB/m in the range of 800 nm. In the wavelengths range between 770 to 850 nm the fiber is endlessly single mode with higher order modes HOM\u2019s losses above 17 dB/m. The use of such a fiber allows elimination of prevalent precompensation dispersion systems and considerably simplifies the two photon fluorescence endoscopy setup.", "question": "What is the dispersion of the presented fiber in the range of 800 nm?", "answers": {"text": "5.13 ps/nm", "answer_start": [436]}}
{"id": "10.1007#s11082-014-9983-2.html_2", "title": "10.1007#s11082-014-9983-2.html", "context": "We show that application of the double clad hollow core fiber (DCHCF) significantly affects efficiency of collecting a two photon fluorescence signal. In our approach we propose a new construction of the hollow core double clad fiber which can be used to send simultaneously an ultrafast signal through the single-mode air core and collect the florescence signal through a multimodal clad. The presented fiber has a dispersion equal to 5.13 ps/nm km and losses 0.5 dB/m in the range of 800 nm. In the wavelengths range between 770 to 850 nm the fiber is endlessly single mode with higher order modes HOM\u2019s losses above 17 dB/m. The use of such a fiber allows elimination of prevalent precompensation dispersion systems and considerably simplifies the two photon fluorescence endoscopy setup.", "question": "What is the loss of the presented fiber in the range of 800 nm?", "answers": {"text": "0.5 dB/m", "answer_start": [461]}}
{"id": "10.1007#s11082-014-9983-2.html_3", "title": "10.1007#s11082-014-9983-2.html", "context": "Two photon fluorescence is a phenomenon which provides a new quality for noninvasive imaging of biological tissue. It allows to obtain higher resolution in comparison to one photon fluorescence and it has a better ability to penetrate the tissue due to the fact that in two photon fluorescence infrared light is applied (Elahi and Wang 2011; Yicong, Xingde 2010). Moreover, the risk of tissue\u2019s damage caused by the light is lower. The most commonly used endoscopic setup design involves the use of a double clad fiber. In this case, the core of the fiber is used for transmission of the excitation signal, whereby the inner clad is used for receiving fluorescent signal. But delivery of ultra-short pulses with a flexible optical fiber is very difficult to achieve due to the fact that femtosecond pulses suffer from temporal and spectral broadening especially operating near 800 nm wavelength, where normal dispersion is large (Clark et al. 2001; Kalashyan et al. 2012). Therefore, in order to design an efficient setup for two-photon endoscopy it is necessary to compensate dispersion.", "question": "Why is the delivery of ultra-short pulses with a flexible optical fiber very difficult to achieve?", "answers": {"text": "due to the fact that femtosecond pulses suffer from temporal and spectral broadening", "answer_start": [766]}}
{"id": "10.1007#s11082-014-9983-2.html_4", "title": "10.1007#s11082-014-9983-2.html", "context": "Two photon fluorescence is a phenomenon which provides a new quality for noninvasive imaging of biological tissue. It allows to obtain higher resolution in comparison to one photon fluorescence and it has a better ability to penetrate the tissue due to the fact that in two photon fluorescence infrared light is applied (Elahi and Wang 2011; Yicong, Xingde 2010). Moreover, the risk of tissue\u2019s damage caused by the light is lower. The most commonly used endoscopic setup design involves the use of a double clad fiber. In this case, the core of the fiber is used for transmission of the excitation signal, whereby the inner clad is used for receiving fluorescent signal. But delivery of ultra-short pulses with a flexible optical fiber is very difficult to achieve due to the fact that femtosecond pulses suffer from temporal and spectral broadening especially operating near 800 nm wavelength, where normal dispersion is large (Clark et al. 2001; Kalashyan et al. 2012). Therefore, in order to design an efficient setup for two-photon endoscopy it is necessary to compensate dispersion.", "question": "How can be design an efficient setup for two-photo endoscopy?", "answers": {"text": "to compensate dispersion", "answer_start": [1066]}}
{"id": "10.1007#s11082-014-9984-1.html_0", "title": "10.1007#s11082-014-9984-1.html", "context": "Broadbandly flat birefringence in optical fibers is required in interferometric sensor systems, where broadband sources are used. It allows to keep similar sensitivity of measurement in all measurement range (Frazao et al. 2007). In this paper, for the first time to our best knowledge, we consider introduction of a nanodefect in the lamellar core and we study its influence on birefringence characteristics. Use of a nanostructure in the fiber core was successfully verified in case of development of nonlinear all-solid MOFs with flat dispersion (Buczynski et al. 2011). The study is undertaken with the aid of a finite difference time domain (FDTD) method (Taflove and Hagness 2005), implemented in the QuickWave software package (QuickWave-3D 1997).", "question": "What method is used in this study?", "answers": {"text": "finite difference time domain (FDTD) method", "answer_start": [616]}}
{"id": "10.1007#s11082-014-9984-1.html_1", "title": "10.1007#s11082-014-9984-1.html", "context": "Broadbandly flat birefringence in optical fibers is required in interferometric sensor systems, where broadband sources are used. It allows to keep similar sensitivity of measurement in all measurement range (Frazao et al. 2007). In this paper, for the first time to our best knowledge, we consider introduction of a nanodefect in the lamellar core and we study its influence on birefringence characteristics. Use of a nanostructure in the fiber core was successfully verified in case of development of nonlinear all-solid MOFs with flat dispersion (Buczynski et al. 2011). The study is undertaken with the aid of a finite difference time domain (FDTD) method (Taflove and Hagness 2005), implemented in the QuickWave software package (QuickWave-3D 1997).", "question": "Which software package is the finite difference time domain (FDTD) method implemented?", "answers": {"text": "QuickWave", "answer_start": [707]}}
{"id": "10.1007#s11082-014-9986-z.html_0", "title": "10.1007#s11082-014-9986-z.html", "context": "Electromagnetic absorbers have a much longer history than any kind of numerical modeling. Their possible applications range from modification of radar echo, through applications related to electromagnetic compatibility, up to photovoltaics. Early real-world absorbers were based on resistive sheets separated from a ground plate by quarter wave distances. With several sheets and multiple resonances it was possible to achieve broadband operation. The idea evolved into the theory of frequency selective surfaces (Munk 2000). Furthermore, it is possible to obtain a tailored impedance at a surface transition region using homogenized periodic one-dimensional or two-dimensional corrugated surfaces (Kristensson 2005). A static periodic magnetization obtained with ferromagnetic or ferrimagnetic materials is another route to obtaining broadband absorbers (Ramprecht and Norgren 2008). A recent overview paper (Watts et al. 2012) can serve as a tutorial on absorbers with the focus on novel metamaterial absorbers based on split-ring and electric-ring resonators.", "question": "What are the possible applications of the electromagnetic absorbers?", "answers": {"text": "modification of radar echo, through applications related to electromagnetic compatibility", "answer_start": [129]}}
{"id": "10.1007#s11082-014-9986-z.html_1", "title": "10.1007#s11082-014-9986-z.html", "context": "Electromagnetic absorbers have a much longer history than any kind of numerical modeling. Their possible applications range from modification of radar echo, through applications related to electromagnetic compatibility, up to photovoltaics. Early real-world absorbers were based on resistive sheets separated from a ground plate by quarter wave distances. With several sheets and multiple resonances it was possible to achieve broadband operation. The idea evolved into the theory of frequency selective surfaces (Munk 2000). Furthermore, it is possible to obtain a tailored impedance at a surface transition region using homogenized periodic one-dimensional or two-dimensional corrugated surfaces (Kristensson 2005). A static periodic magnetization obtained with ferromagnetic or ferrimagnetic materials is another route to obtaining broadband absorbers (Ramprecht and Norgren 2008). A recent overview paper (Watts et al. 2012) can serve as a tutorial on absorbers with the focus on novel metamaterial absorbers based on split-ring and electric-ring resonators.", "question": "What does Watts' study focus on?", "answers": {"text": "novel metamaterial absorbers", "answer_start": [984]}}
{"id": "10.1007#s11082-014-9987-y.html_0", "title": "10.1007#s11082-014-9987-y.html", "context": "Photonic crystal fibers (PCFs) are a new class of fibers applicable in areas such as nonlinear optics (Knight and Skryabin 2007), generation of supercontinuum (Dudley et al. 2006), biomedical measurements or sensors (Konorov et al. 2005). Several numerical methods, dedicated to the electromagnetic (EM) analysis of PCFs, have been developed (Szpulak et al. 2006). The most commonly used are the finite element method (Rahman et al. 2007), plane wave expansion method, (Ho et al. 1990), the polar Fourier decomposition method, (Issa and Poladian 2003), finite-difference time-domain (FDTD) method, (Taflove and Hagness 2005), and finite-difference frequency-domain (FDFD) method, (Zhu and Brown 2002). Since dispersive properties of PCFs, critical for nonlinear phenomena, are very sensitive to geometrical properties of a structure, it is essential to have access to a highly reliable EM simulation method in order to reduce costly hardware prototyping to the necessary minimum.", "question": "What is the first most commonly used method dedicated to the electromagnetic (EM) analysis of PCFs?", "answers": {"text": "finite element method", "answer_start": [396]}}
{"id": "10.1007#s11082-014-9987-y.html_1", "title": "10.1007#s11082-014-9987-y.html", "context": "Photonic crystal fibers (PCFs) are a new class of fibers applicable in areas such as nonlinear optics (Knight and Skryabin 2007), generation of supercontinuum (Dudley et al. 2006), biomedical measurements or sensors (Konorov et al. 2005). Several numerical methods, dedicated to the electromagnetic (EM) analysis of PCFs, have been developed (Szpulak et al. 2006). The most commonly used are the finite element method (Rahman et al. 2007), plane wave expansion method, (Ho et al. 1990), the polar Fourier decomposition method, (Issa and Poladian 2003), finite-difference time-domain (FDTD) method, (Taflove and Hagness 2005), and finite-difference frequency-domain (FDFD) method, (Zhu and Brown 2002). Since dispersive properties of PCFs, critical for nonlinear phenomena, are very sensitive to geometrical properties of a structure, it is essential to have access to a highly reliable EM simulation method in order to reduce costly hardware prototyping to the necessary minimum.", "question": "What property of PCFs is sensitive to geometrical property of a structure?", "answers": {"text": "dispersive properties", "answer_start": [708]}}
{"id": "10.1007#s11082-014-9987-y.html_2", "title": "10.1007#s11082-014-9987-y.html", "context": "Consequently, computational effort of the EM analysis can be substantially reduced. In addition, since the analysis is restricted to the fundamental mode with a priori known symmetries, the FDTD model can be reduced to a quarter of the fiber\u2019s cross-section with electric and magnetic symmetry conditions imposed, as indicated in Fig. 1. The model is truncated with a perfectly matched layer (PML) surrounding the fiber (Berenger 1996). Before the analysis is started, material properties need to be determined and properly represented with the models available in FDTD. The fibers investigated in this paper are made of Schott glasses, the refractive index of which can be represented by the Sellmeier equation:\n", "question": "What are the fibers investigated in this paper made of?", "answers": {"text": "Schott glasses", "answer_start": [621]}}
{"id": "10.1007#s11082-014-9987-y.html_3", "title": "10.1007#s11082-014-9987-y.html", "context": "Consequently, computational effort of the EM analysis can be substantially reduced. In addition, since the analysis is restricted to the fundamental mode with a priori known symmetries, the FDTD model can be reduced to a quarter of the fiber\u2019s cross-section with electric and magnetic symmetry conditions imposed, as indicated in Fig. 1. The model is truncated with a perfectly matched layer (PML) surrounding the fiber (Berenger 1996). Before the analysis is started, material properties need to be determined and properly represented with the models available in FDTD. The fibers investigated in this paper are made of Schott glasses, the refractive index of which can be represented by the Sellmeier equation:\n", "question": "What can the refractive index of the fibers investigated in this paper be represented by?", "answers": {"text": "the Sellmeier equation", "answer_start": [689]}}
{"id": "10.1007#s11082-014-9987-y.html_4", "title": "10.1007#s11082-014-9987-y.html", "context": "As it can be seen in Fig. 5c, the measured and calculated dispersion characteristics are in decent agreement, indicating that both numerical methods give reasonable results. However, if the zero dispersion wavelength (ZDW) has to be determined, the FDTD method gives a result much closer to the experimental data. In this case, ZDW is 1,356 and 1,492 nm according to results of the FDTD and FDFD method, respectively, while the measurements indicate that ZDW = 1,382 nm. It means that discrepancy is at the level of about 1.9 and 8.0 % for FDTD and FDFD solutions, respectively. Since determination of ZDW is critical for supercontinuum generation in nonlinear PCFs (Buczynski et al. 2011), the use of the FDFD method can bring a meaningful inaccuracy. Discrepancy between experimental and modeled result is mostly related to credibility of SEM image of the fiber. Since fiber is covers with layer of gold/palladium before the SEM image is taken, diameters of air holes might be slightly different on SEM image and in real fiber. Although the difference is very small it can noticeably influence the dispersion curvature, since dispersion is proportional to the second derivative of effective refractive index (see Eq. 2).", "question": "What is critical for supercontinuum generation in nonlinear PCFs?", "answers": {"text": "determination of ZDW", "answer_start": [585]}}
{"id": "10.1007#s11082-015-0117-2.html_0", "title": "10.1007#s11082-015-0117-2.html", "context": "The calculation of phonon-assisted Auger recombination rate also requires the phonon band structure. To study the lattice dynamic it was used Kane\u2019s valence-force model which has originally been introduced for diamond and zinc-blende crystals (Kane 1985). Siegle et al. (1997) modified this model to calculate the phonon dispersion curves of hexagonal GaN. The short-range valence-force elastic potential consisted of bond stretching, bond bending interactions (including two different bond bending configurations) and bond bending interaction between three adjacent lattice bonds (so-called MSBN interaction). Two set of the valence-force constants were used to take into account the anisotropy of hexagonal GaN. The long-range Coulomb interaction was described by the rigid ion model using the only one fitting parameter, i.e., ionic charge. The values for eight valence-force constants and ionic charge for GaN were taken from Siegle et al. (1997). The calculations of the Auger recombination rate in the ternary alloys were performed using the phonon band structure of GaN.", "question": "Who invented the Kane's valence-force model?", "answers": {"text": "Kane", "answer_start": [142]}}
{"id": "10.1007#s11082-015-0117-2.html_1", "title": "10.1007#s11082-015-0117-2.html", "context": "The calculation of phonon-assisted Auger recombination rate also requires the phonon band structure. To study the lattice dynamic it was used Kane\u2019s valence-force model which has originally been introduced for diamond and zinc-blende crystals (Kane 1985). Siegle et al. (1997) modified this model to calculate the phonon dispersion curves of hexagonal GaN. The short-range valence-force elastic potential consisted of bond stretching, bond bending interactions (including two different bond bending configurations) and bond bending interaction between three adjacent lattice bonds (so-called MSBN interaction). Two set of the valence-force constants were used to take into account the anisotropy of hexagonal GaN. The long-range Coulomb interaction was described by the rigid ion model using the only one fitting parameter, i.e., ionic charge. The values for eight valence-force constants and ionic charge for GaN were taken from Siegle et al. (1997). The calculations of the Auger recombination rate in the ternary alloys were performed using the phonon band structure of GaN.", "question": "When did Kane invent the Kane's valence-force model?", "answers": {"text": "1985", "answer_start": [249]}}
{"id": "10.1007#s11082-015-0117-2.html_2", "title": "10.1007#s11082-015-0117-2.html", "context": "The calculation of phonon-assisted Auger recombination rate also requires the phonon band structure. To study the lattice dynamic it was used Kane\u2019s valence-force model which has originally been introduced for diamond and zinc-blende crystals (Kane 1985). Siegle et al. (1997) modified this model to calculate the phonon dispersion curves of hexagonal GaN. The short-range valence-force elastic potential consisted of bond stretching, bond bending interactions (including two different bond bending configurations) and bond bending interaction between three adjacent lattice bonds (so-called MSBN interaction). Two set of the valence-force constants were used to take into account the anisotropy of hexagonal GaN. The long-range Coulomb interaction was described by the rigid ion model using the only one fitting parameter, i.e., ionic charge. The values for eight valence-force constants and ionic charge for GaN were taken from Siegle et al. (1997). The calculations of the Auger recombination rate in the ternary alloys were performed using the phonon band structure of GaN.", "question": "What fitting parameter was used by the rigid ion model to describe the long-range Coulomb interaction?", "answers": {"text": "ionic charge", "answer_start": [830]}}
{"id": "10.1007#s11082-015-0117-2.html_3", "title": "10.1007#s11082-015-0117-2.html", "context": "The calculation of phonon-assisted Auger recombination rate also requires the phonon band structure. To study the lattice dynamic it was used Kane\u2019s valence-force model which has originally been introduced for diamond and zinc-blende crystals (Kane 1985). Siegle et al. (1997) modified this model to calculate the phonon dispersion curves of hexagonal GaN. The short-range valence-force elastic potential consisted of bond stretching, bond bending interactions (including two different bond bending configurations) and bond bending interaction between three adjacent lattice bonds (so-called MSBN interaction). Two set of the valence-force constants were used to take into account the anisotropy of hexagonal GaN. The long-range Coulomb interaction was described by the rigid ion model using the only one fitting parameter, i.e., ionic charge. The values for eight valence-force constants and ionic charge for GaN were taken from Siegle et al. (1997). The calculations of the Auger recombination rate in the ternary alloys were performed using the phonon band structure of GaN.", "question": "What was the photon band structure of GaN used for?", "answers": {"text": "calculations of the Auger recombination rate", "answer_start": [956]}}
{"id": "10.1007#s11082-015-0147-9.html_0", "title": "10.1007#s11082-015-0147-9.html", "context": "We proposed a novel design of photonic crystal fiber with the characteristics of high birefringence and zero dispersion. The structure of the photonic crystal fiber is composed of the rectangular lattice with double-cladding and there is an elliptical air hole in the core of the photonic crystal fiber which has the same size with the holes of inner ring. Simulation results show that the elliptical air hole in the core can enhance the performance of mode birefringence and control the properties of chromatic dispersion at the same time. We obtain the high birefringence B = 2.1 \u00d7 10\u22123 and B = 2.9 \u00d7 10\u22123 at the wavelength of 1.31 and 1.55 \u03bcm respectively and the zero dispersion point at the wavelength of 1.31 \u03bcm. The proposed photonic crystal fiber with high birefringence and zero dispersion will be important in the applications of polarization maintaining transmission systems.", "question": "What is purposed by this study?", "answers": {"text": "a novel design of photonic crystal fiber", "answer_start": [12]}}
{"id": "10.1007#s11082-015-0147-9.html_1", "title": "10.1007#s11082-015-0147-9.html", "context": "We proposed a novel design of photonic crystal fiber with the characteristics of high birefringence and zero dispersion. The structure of the photonic crystal fiber is composed of the rectangular lattice with double-cladding and there is an elliptical air hole in the core of the photonic crystal fiber which has the same size with the holes of inner ring. Simulation results show that the elliptical air hole in the core can enhance the performance of mode birefringence and control the properties of chromatic dispersion at the same time. We obtain the high birefringence B = 2.1 \u00d7 10\u22123 and B = 2.9 \u00d7 10\u22123 at the wavelength of 1.31 and 1.55 \u03bcm respectively and the zero dispersion point at the wavelength of 1.31 \u03bcm. The proposed photonic crystal fiber with high birefringence and zero dispersion will be important in the applications of polarization maintaining transmission systems.", "question": "What is the structure of the photonic crystal fiber composed of?", "answers": {"text": "rectangular lattice with double-cladding", "answer_start": [184]}}
{"id": "10.1007#s11082-015-0147-9.html_2", "title": "10.1007#s11082-015-0147-9.html", "context": "Photonic crystal fibers (PCFs) present a wavelength-scale periodic microstructure running along their length. It has been intensively studied due to their unique properties which could be difficult to realize in conventional optical fibers because of the flexibility for the cross section design (Russell 2007; Birks and Kinght 2001; Knight 2003; Russell 2003; Philip 2009). Taking into consideration the propagation mechanism behind light guidance in PCFs, there are basically two types of PCFs: index-guiding PCFs which is based on modified total internal reflection and photonic bandgap PCFs which is based on the effect (Hansen et al. 2001; Saitoh and Koshiba 2002; Knight et al. 1998).", "question": "What is the first type of PCFs?", "answers": {"text": "index-guiding PCFs", "answer_start": [497]}}
{"id": "10.1007#s11082-015-0147-9.html_3", "title": "10.1007#s11082-015-0147-9.html", "context": "Photonic crystal fibers (PCFs) present a wavelength-scale periodic microstructure running along their length. It has been intensively studied due to their unique properties which could be difficult to realize in conventional optical fibers because of the flexibility for the cross section design (Russell 2007; Birks and Kinght 2001; Knight 2003; Russell 2003; Philip 2009). Taking into consideration the propagation mechanism behind light guidance in PCFs, there are basically two types of PCFs: index-guiding PCFs which is based on modified total internal reflection and photonic bandgap PCFs which is based on the effect (Hansen et al. 2001; Saitoh and Koshiba 2002; Knight et al. 1998).", "question": "What is the second type of PCFs?", "answers": {"text": "photonic bandgap PCFs", "answer_start": [573]}}
{"id": "10.1007#s11082-015-0147-9.html_4", "title": "10.1007#s11082-015-0147-9.html", "context": "Photonic crystal fibers (PCFs) present a wavelength-scale periodic microstructure running along their length. It has been intensively studied due to their unique properties which could be difficult to realize in conventional optical fibers because of the flexibility for the cross section design (Russell 2007; Birks and Kinght 2001; Knight 2003; Russell 2003; Philip 2009). Taking into consideration the propagation mechanism behind light guidance in PCFs, there are basically two types of PCFs: index-guiding PCFs which is based on modified total internal reflection and photonic bandgap PCFs which is based on the effect (Hansen et al. 2001; Saitoh and Koshiba 2002; Knight et al. 1998).", "question": "What is the index-guiding PCFs based on?", "answers": {"text": "modified total internal reflection", "answer_start": [534]}}
{"id": "10.1007#s11082-015-0159-5.html_0", "title": "10.1007#s11082-015-0159-5.html", "context": "With development of the novel nanofabrication technology such as chemical lithography, molecular beam epitaxy (MBE), etching method and Stranski\u2013Krastanov, more physicists worldwide are paying considerable attention to the researches and applications of quantum dots due to their unique optoelectronic and transport properties (Hersee and Duchemim 1982; Datta and Ghosh 2011; Cappelluti and Pietronero 2005). Because the quantum dot is a semiconductor nanostructure, some optical and transport properties are quite different from those of the bulk structures. Using aforementioned methods, it is possible to fabricate semiconductor quantum dots with various geometrical shapes and sizes like spherical, pyramidal, ellipsoidal, lens-shaped, cone-like (Ledentsov et al. 1998; Lu et al. 2002; Schmidbauer et al. 2006; Lozovski and Piatnytsia 2011). These structures open a new field in fundamental physics and also offer a wide range of applications for semiconductor optoelectronics devices.", "question": "Why do more physicists pay considerable attention to the researches and applications of quantum dots?", "answers": {"text": "unique optoelectronic and transport properties", "answer_start": [280]}}
{"id": "10.1007#s11082-015-0159-5.html_1", "title": "10.1007#s11082-015-0159-5.html", "context": "With development of the novel nanofabrication technology such as chemical lithography, molecular beam epitaxy (MBE), etching method and Stranski\u2013Krastanov, more physicists worldwide are paying considerable attention to the researches and applications of quantum dots due to their unique optoelectronic and transport properties (Hersee and Duchemim 1982; Datta and Ghosh 2011; Cappelluti and Pietronero 2005). Because the quantum dot is a semiconductor nanostructure, some optical and transport properties are quite different from those of the bulk structures. Using aforementioned methods, it is possible to fabricate semiconductor quantum dots with various geometrical shapes and sizes like spherical, pyramidal, ellipsoidal, lens-shaped, cone-like (Ledentsov et al. 1998; Lu et al. 2002; Schmidbauer et al. 2006; Lozovski and Piatnytsia 2011). These structures open a new field in fundamental physics and also offer a wide range of applications for semiconductor optoelectronics devices.", "question": "What are possible geometrical shapes and sizes of semiconductor quantum dots?", "answers": {"text": "spherical, pyramidal, ellipsoidal, lens-shaped, cone-like", "answer_start": [692]}}
{"id": "10.1007#s11082-015-0159-5.html_2", "title": "10.1007#s11082-015-0159-5.html", "context": "In recent years, the electronic and optical properties of quantum dots have been widely studied (Bimberg 2005; Khordad 2014; Bahramiyan and Khordad 2014). It is fully known that the various confinement potential models are usually applied in the study of physical properties of quantum dots. Examples of these models are rectangular potential well (Bednarek et al. 1999; Szafran et al. 1999), parabolic potential (Johnson 1995), disk-like (cylindrical) model (Tchoffo et al. 2009) and the spherical model. Adamowski et al. (2000, 2005) and Xie (2008a, b) considered a new confinement potential in quantum dots which is called the spherical Gaussian potential. Also, Ciurla et al. (2002) proposed a new class of the confinement potentials, called the power-exponential potentials. Recently, we have proposed a new confinement potential in quantum dots which is called the modified Gaussian potential (Gharaati and Khordad 2010).", "question": "What model is usually applied in the study of physical properties of quantum dots?", "answers": {"text": "confinement potential models", "answer_start": [190]}}
{"id": "10.1007#s11082-015-0159-5.html_3", "title": "10.1007#s11082-015-0159-5.html", "context": "In recent years, the electronic and optical properties of quantum dots have been widely studied (Bimberg 2005; Khordad 2014; Bahramiyan and Khordad 2014). It is fully known that the various confinement potential models are usually applied in the study of physical properties of quantum dots. Examples of these models are rectangular potential well (Bednarek et al. 1999; Szafran et al. 1999), parabolic potential (Johnson 1995), disk-like (cylindrical) model (Tchoffo et al. 2009) and the spherical model. Adamowski et al. (2000, 2005) and Xie (2008a, b) considered a new confinement potential in quantum dots which is called the spherical Gaussian potential. Also, Ciurla et al. (2002) proposed a new class of the confinement potentials, called the power-exponential potentials. Recently, we have proposed a new confinement potential in quantum dots which is called the modified Gaussian potential (Gharaati and Khordad 2010).", "question": "What model did Ciurla propose in 2002?", "answers": {"text": "power-exponential potentials", "answer_start": [750]}}
{"id": "10.1007#s11082-015-0159-5.html_4", "title": "10.1007#s11082-015-0159-5.html", "context": "In recent years, the electronic and optical properties of quantum dots have been widely studied (Bimberg 2005; Khordad 2014; Bahramiyan and Khordad 2014). It is fully known that the various confinement potential models are usually applied in the study of physical properties of quantum dots. Examples of these models are rectangular potential well (Bednarek et al. 1999; Szafran et al. 1999), parabolic potential (Johnson 1995), disk-like (cylindrical) model (Tchoffo et al. 2009) and the spherical model. Adamowski et al. (2000, 2005) and Xie (2008a, b) considered a new confinement potential in quantum dots which is called the spherical Gaussian potential. Also, Ciurla et al. (2002) proposed a new class of the confinement potentials, called the power-exponential potentials. Recently, we have proposed a new confinement potential in quantum dots which is called the modified Gaussian potential (Gharaati and Khordad 2010).", "question": "What confinement potential is developed in this study?", "answers": {"text": "modified Gaussian potential", "answer_start": [871]}}
{"id": "10.1007#s11082-015-0159-5.html_5", "title": "10.1007#s11082-015-0159-5.html", "context": "During the last few years, there has been growing interest in the topic regarding the effect of various conditions such as electron\u2013phonon interaction, magnetic field, electric field, and impurity on optical properties of quantum dots. For example, Liu et al. (2005) studied the third order nonlinear optical susceptibility for InxGa1\u2212xN/GaN cylinder quantum dots. Harutyunyan and Kazaryan (2007) investigated interband absorption coefficient in cylindrical layer quantum dot under the influence of both magnetic and electric fields. The optical absorption and refractive index changes in a cylindrical quantum dot were studied by Liu and Xu (2008). Recently, we have studied the second and third harmonic generations in a pyramid quantum dot (Bahramiyan and Khordad 2014).", "question": "What property did Liu study for InxGa1\u2212xN/GaN cylinder quantum dots?", "answers": {"text": "third order nonlinear optical susceptibility", "answer_start": [279]}}
{"id": "10.1007#s11082-015-0159-5.html_6", "title": "10.1007#s11082-015-0159-5.html", "context": "Among the aforementioned conditions, great attention has been devoted to the study of electron\u2013phonon interaction and its effect on optical properties of nanostructures. It is fully known that research on electron\u2013phonon interaction has become a main subject in the condensed matter physics. Hitherto, several authors have studied the influence of the electron\u2013phonon interaction on physical properties on nanostructures. For first time, Lucas et al. (1970) studied the electron\u2013phonon interaction in a dielectric confined system. Wendler developed the framework of the theory of optical phonon and electron\u2013phonon interaction for the spatially confined systems (Wendler 1985). Li and Chen (1997) studied electron\u2013phonon interaction in a cylindrical quantum dot and they found that there exist two types of SO phonon modes. Xie and Chen (1998) have investigated the phonon contribution to the binding energy of the on center and off center impurities in a spherical quantum dot. Li et al. (2008) investigated the ground-state lifetime of bound polaron in a parabolic quantum dot. Recently, we have studied the effect of electron\u2013phonon interaction on optical properties of a triangular quantum wire (Bahramiyan and Khordad 2013). To more information, the reader can refer to (Cai et al. 2013; Li and Xiao 2011; Khordad and Bahramiyan 2014).", "question": "Who studied the electron\u2013phonon interaction in a dielectric confined system for the first time?", "answers": {"text": "Lucas et al.", "answer_start": [438]}}
{"id": "10.1007#s11082-015-0159-5.html_7", "title": "10.1007#s11082-015-0159-5.html", "context": "The e\u2013p interaction and optical phonon modes play an important role in many physical properties of quantum nanostructures such as the binding energy, linear and nonlinear optical properties. There are several theoretical models for studying the optical phonon modes and e\u2013p interaction in low-dimensional semiconductor structures. Examples of these models are dielectric continuum (DC) model (Lucas et al. 1970; Wendler 1985; Fuchs and Kliewer 1965; Licari and Evrard 1977; Huang and Zhu 1988), hydrodynamic model (Ridley 1989), and microscopic calculation model (R\u00fcker et al. 1991; Bhatt et al. 1993). It is to be noted that the DC model has been widely used due to its simplicity and efficiency. In this work, we have applied the DC model to investigate linear and nonlinear optical properties of a modified Gaussian quantum dot under e\u2013p interaction. We also present the hydrodynamic model, briefly, in Appendix 2.", "question": "Why has the DC model been widely used?", "answers": {"text": "simplicity and efficiency", "answer_start": [671]}}
{"id": "10.1007#s11082-015-0159-5.html_8", "title": "10.1007#s11082-015-0159-5.html", "context": "The e\u2013p interaction and optical phonon modes play an important role in many physical properties of quantum nanostructures such as the binding energy, linear and nonlinear optical properties. There are several theoretical models for studying the optical phonon modes and e\u2013p interaction in low-dimensional semiconductor structures. Examples of these models are dielectric continuum (DC) model (Lucas et al. 1970; Wendler 1985; Fuchs and Kliewer 1965; Licari and Evrard 1977; Huang and Zhu 1988), hydrodynamic model (Ridley 1989), and microscopic calculation model (R\u00fcker et al. 1991; Bhatt et al. 1993). It is to be noted that the DC model has been widely used due to its simplicity and efficiency. In this work, we have applied the DC model to investigate linear and nonlinear optical properties of a modified Gaussian quantum dot under e\u2013p interaction. We also present the hydrodynamic model, briefly, in Appendix 2.", "question": "What is studied in this work by applying the DC model?", "answers": {"text": "linear and nonlinear optical properties of a modified Gaussian quantum dot", "answer_start": [756]}}
{"id": "10.1007#s11082-015-0166-6.html_0", "title": "10.1007#s11082-015-0166-6.html", "context": "Because the plasmon phenomenon in optical and telecommunication frequencies typically originates from the collective oscillations of free charges in a material due to an applied electromagnetic (EM) field, plasmonic devices generally require metallic components, which have an abundance of free electrons. These free electrons provide the negative real permittivity that is an essential property of any plasmonic material. However, metals are plagued by large losses, arising in part from interband electronic transitions. These losses are detrimental to the performance of plasmonic devices, seriously limiting the feasibility of many plasmonic applications. As alternatives to conventional metals, new plasmonic materials, e.g., transparent conducting oxides (TCOs), offer many advantages in the rapidly growing fields of plasmonics and metamaterials (Naik and Boltasseva 2010; Naik et al. 2011).These advantages include low intrinsic loss, semiconductor-based design, compatibility with standard nano fabrication processes, tunable, and others.", "question": "What property is essential of any plasmonic material?", "answers": {"text": "negative real permittivity", "answer_start": [339]}}
{"id": "10.1007#s11082-015-0166-6.html_1", "title": "10.1007#s11082-015-0166-6.html", "context": "Because the plasmon phenomenon in optical and telecommunication frequencies typically originates from the collective oscillations of free charges in a material due to an applied electromagnetic (EM) field, plasmonic devices generally require metallic components, which have an abundance of free electrons. These free electrons provide the negative real permittivity that is an essential property of any plasmonic material. However, metals are plagued by large losses, arising in part from interband electronic transitions. These losses are detrimental to the performance of plasmonic devices, seriously limiting the feasibility of many plasmonic applications. As alternatives to conventional metals, new plasmonic materials, e.g., transparent conducting oxides (TCOs), offer many advantages in the rapidly growing fields of plasmonics and metamaterials (Naik and Boltasseva 2010; Naik et al. 2011).These advantages include low intrinsic loss, semiconductor-based design, compatibility with standard nano fabrication processes, tunable, and others.", "question": "What are the advantages of transparent conducting oxides (TCOs) in the fields of plasmonics and metamaterials?", "answers": {"text": "low intrinsic loss, semiconductor-based design, compatibility with standard nano fabrication processes, tunable", "answer_start": [923]}}
{"id": "10.1007#s11082-015-0166-6.html_2", "title": "10.1007#s11082-015-0166-6.html", "context": "The optical response of composite mixtures change drastically with the structural geometry of individual particles and the aggregate topology. The geometric and aggregation complexity in such systems makes the precise modeling somewhat formidable. Instead, these systems can be treated as an optically quasi-homogeneous effective-medium material, with a proper macroscopic dielectric function that describes the linear response to the external EM field. Effective medium theories define an effective dielectric function for a composite material in terms of the dielectric function of its components and their geometrical arrangement (Shalaev 2000; Bosch et al. 2000). The applicability of effective medium theories is restricted by the size of the structures composing the mixture: sufficiently large to preserve locally their own EM behavior and small enough for the composite to appear homogeneous compared to the wavelength of the interacting radiation. Over the last century numerous effective medium theories have been proposed, being the Maxwell\u2013Garnett (MG) (1904) and the Bruggeman (1935) expressions the most successful to explain the effective behavior of a large number of composites.", "question": "What restricts the applicability of effective medium theories?", "answers": {"text": "size of the structures composing the mixture", "answer_start": [736]}}
{"id": "10.1007#s11082-015-0166-6.html_3", "title": "10.1007#s11082-015-0166-6.html", "context": "The LMS method is ideally suited for the calculation of the transmission, reflection, and absorption coefficients of an EM wave incident on a composite slab consisting of a number of layers that can be either planes of non-overlapping particles with the same 2D periodicity or homogeneous plates. For each plane of particles, the method calculates the full multipole expansion of the total multiply scattered wave field and deduces the corresponding transmission and reflection matrices in the plane-wave basis. The transmission and reflection matrices of the composite slab are evaluated from those of the constituent layers. By imposing periodic boundary conditions one can also obtain the (complex) frequency band structure of an infinite periodic crystal. The method applies equally well to non-absorbing systems and to absorbing ones. Its chief advantage over the other existing numerical methods lies in its efficient and reliable treatment of systems containing strongly dispersive materials such as Drude-like and polaritonic materials (Stefanou et al. 1992, 1998, 2000).", "question": "What method is suited for the calculation of the transmission?", "answers": {"text": "LMS method", "answer_start": [4]}}
{"id": "10.1007#s11082-015-0166-6.html_4", "title": "10.1007#s11082-015-0166-6.html", "context": "The LMS method is ideally suited for the calculation of the transmission, reflection, and absorption coefficients of an EM wave incident on a composite slab consisting of a number of layers that can be either planes of non-overlapping particles with the same 2D periodicity or homogeneous plates. For each plane of particles, the method calculates the full multipole expansion of the total multiply scattered wave field and deduces the corresponding transmission and reflection matrices in the plane-wave basis. The transmission and reflection matrices of the composite slab are evaluated from those of the constituent layers. By imposing periodic boundary conditions one can also obtain the (complex) frequency band structure of an infinite periodic crystal. The method applies equally well to non-absorbing systems and to absorbing ones. Its chief advantage over the other existing numerical methods lies in its efficient and reliable treatment of systems containing strongly dispersive materials such as Drude-like and polaritonic materials (Stefanou et al. 1992, 1998, 2000).", "question": "What can be obtained by imposing periodic boundary conditions?", "answers": {"text": "the (complex) frequency band structure", "answer_start": [688]}}
{"id": "10.1007#s11082-015-0166-6.html_5", "title": "10.1007#s11082-015-0166-6.html", "context": "Silicon carbide (SiC) is an indirect wide band gap semiconductor. Owing to its wide band gap (E  g  ~ 3 eV) and strong covalent bonds, it has an extreme thermal stability and high breakdown fields, and may therefore outclass silicon in high-power, high-voltage switching applications, high-temperature electronics (including sensors), high power microwave applications, high radiation environment or UV optoelectronic devices (Lazanu et al. 2002). Since many of ionic materials, like SiC, exhibit phonon-polariton excitations within near infrared regime, they would be very good choices for these nano structures. We take Silicon Carbide (\u03b2-SiC) with a zinc blende crystal structure as an ionic material whose permittivity is given by (12) having \u03c9  T  = 23.8 \u00d7 1012 Hz, \u03c9  L  = 29.06 \u00d7 1012 Hz, and \u03b5  \u221e  = 6.51. The radius of the spheres is R = 320 nm and the volume filling fraction occupied by them is f = 0.37.", "question": "What is the band gap of the silicon carbide?", "answers": {"text": "3 eV", "answer_start": [102]}}
{"id": "10.1007#s11082-015-0166-6.html_6", "title": "10.1007#s11082-015-0166-6.html", "context": "Metals are the most familiar candidate for the plasmonic materials because metals tend to have large plasma frequencies and high electrical conductivity; they have traditionally been the materials of choice for plasmonics. One of important disadvantage of conventional metals is high loss. Conventional metals have very high carrier concentrations, which in turn makes their plasma frequencies very large. A large plasma frequency produces a large imaginary permittivity, which translates to large loss. Alternative plasmonic materials have lower carrier concentrations and, hence, smaller losses. Recently, we present a new set of nano structured composites which can exhibit a phenomenon known as surface plasmon resonance in a broad frequency range from the deep infrared to the terahertz region (Sadeghi et al. 2014; Zolanvar et al. 2014; Sadeghi et al. 2015). We have proposed a doped semiconductor (n-type Ge) as a plasmonic material and the effective permittivity and refractive index of zinc sulfide/Ge and zinc oxide/Ge composites have been calculated over terahertz frequencies (Sadeghi et al. 2014). Moreover, TCOs such as Al:ZnO, Ga:ZnO and indium-tin-oxide (ITO) exhibit losses nearly five times smaller than that of the best metal (Ag) in the near-IR (Naik et al. 2011).", "question": "What is the tranditional material of choice for plasmonics?", "answers": {"text": "Metals", "answer_start": [0]}}
{"id": "10.1007#s11082-015-0178-2.html_1", "title": "10.1007#s11082-015-0178-2.html", "context": "\nElectronic, optical properties and spontaneous polarization of cubic perovskite BaHfO3 have been investigated using the Full Potential Linear Augmented Plane Wave method, implemented in the Wien2k code, in connection with the Generalized Gradient Approximation (GGA) and the Tran\u2013Blaha modified Becke\u2013Johnson exchange potential approximation (TB-mBJ). The calculation of band structure and density of state using TB-mBJ approach shows that the gap of BaHfO3 is direct and equal to 5.9 eV which is in good agreement with the experiment data (6.0 eV), compared with GGA which gives 3.9 eV. The absorption coefficient \u03b1 (\u03c9) and the complex dielectric function \u03b5 (\u03c9) are also investigated and predict that this compound can be effectively used in UV based optoelectronic devices. Furthermore, Using the PI approach, we can calculate the spontaneous polarization which is equal to 0.40 C/m2 and predict that is in the same order as the Ps of other perovskite.", "question": "What is the calculated gap of BaHfO3 using TB-mBJ approach?", "answers": {"text": "5.9 eV", "answer_start": [482]}}
{"id": "10.1007#s11082-015-0178-2.html_2", "title": "10.1007#s11082-015-0178-2.html", "context": "\nElectronic, optical properties and spontaneous polarization of cubic perovskite BaHfO3 have been investigated using the Full Potential Linear Augmented Plane Wave method, implemented in the Wien2k code, in connection with the Generalized Gradient Approximation (GGA) and the Tran\u2013Blaha modified Becke\u2013Johnson exchange potential approximation (TB-mBJ). The calculation of band structure and density of state using TB-mBJ approach shows that the gap of BaHfO3 is direct and equal to 5.9 eV which is in good agreement with the experiment data (6.0 eV), compared with GGA which gives 3.9 eV. The absorption coefficient \u03b1 (\u03c9) and the complex dielectric function \u03b5 (\u03c9) are also investigated and predict that this compound can be effectively used in UV based optoelectronic devices. Furthermore, Using the PI approach, we can calculate the spontaneous polarization which is equal to 0.40 C/m2 and predict that is in the same order as the Ps of other perovskite.", "question": "What is the experiment data of the gap of BaHfO3?", "answers": {"text": "6.0 eV", "answer_start": [542]}}
{"id": "10.1007#s11082-015-0178-2.html_3", "title": "10.1007#s11082-015-0178-2.html", "context": "\nElectronic, optical properties and spontaneous polarization of cubic perovskite BaHfO3 have been investigated using the Full Potential Linear Augmented Plane Wave method, implemented in the Wien2k code, in connection with the Generalized Gradient Approximation (GGA) and the Tran\u2013Blaha modified Becke\u2013Johnson exchange potential approximation (TB-mBJ). The calculation of band structure and density of state using TB-mBJ approach shows that the gap of BaHfO3 is direct and equal to 5.9 eV which is in good agreement with the experiment data (6.0 eV), compared with GGA which gives 3.9 eV. The absorption coefficient \u03b1 (\u03c9) and the complex dielectric function \u03b5 (\u03c9) are also investigated and predict that this compound can be effectively used in UV based optoelectronic devices. Furthermore, Using the PI approach, we can calculate the spontaneous polarization which is equal to 0.40 C/m2 and predict that is in the same order as the Ps of other perovskite.", "question": "What is the calculated spontaneous polarization using the PI approach?", "answers": {"text": "0.40 C/m2", "answer_start": [877]}}
{"id": "10.1007#s11082-015-0178-2.html_4", "title": "10.1007#s11082-015-0178-2.html", "context": "The Fermi level EF is set at 0 eV, it coincides with the top of the valence band. Using GGA calculations, the maximum of the valence band (VBM) and the minimum of the conduction band (CBM) are at the same point \u0393 and the gap is equal to 3.9 eV, which means that this compound has a direct band gap (\u0393\u2013\u0393), as shown the Fig. 2, the result is consistent with other calculations (Bouhemadou et al. 2008; Liu et al. 2010). The occupied Hf d-states and p-states of Oxygen are positioned mainly between \u22124 and \u22121 eV, at the very top of the valence band. On the other hand, the full Hf d-states and d-states of Ba in the conduction band are within a narrow band centered at approximately 4 eV, making the band gap of 3.9 eV which is in strong disagreement with the experimental measurements Eg = 6 eV (Vali 2008).", "question": "What is the gap between maximum of the valence band (VBM) and the minimum of the conduction band?", "answers": {"text": "3.9 eV", "answer_start": [237]}}
{"id": "10.1007#s11082-015-0183-5.html_0", "title": "10.1007#s11082-015-0183-5.html", "context": "In recent decades, after the invention of artificial experimental techniques such as molecular beam epitaxy, liquid phase epitaxy and chemical vapour deposition (Watanabe et al. 2000; Junichi 1995; Kunrugsa 2014), researchers have shown great interest to study the optical properties of low-dimensional semiconductor materials. The most studied semiconductor nanostructures are QD and QAD (Sadeghi 2009; Naimi and Jafari 2012; Karimi and Rezaei 2012; Jafari and Naimi 2013; Davatolhagh et al. 2012; Holovatsky et al. 2009; Peter 2005; \u00c7akir et al. 2015; \u00d6zmen et al. 2013; \u00c7akir et al. 2012. The behavior of low-dimensional systems is governed by quantum mechanical laws and for investigating the optical properties of such systems, the main problem is to find the eigenvalues and eigenstates of Hamiltonian of system. Many theoretical works (Naimi 2013; Naimi and Jafari 2013; Raigoza et al. 2005; Dane et al. 2011; Baser et al. 2010; Rezaei and Shojaeian Kish 2013; Raigoza et al. 2005; Xie 2012; Perez-Merchancano et al. 2008; Liang et al. 2011; Liang and Xie 2011; Safarpour et al. 2012; Rezaei et al. 2012; Sivakami and Gayathri 2013; Kasapoglu 2008; Farkoush et al. 2013; Karimi et al. 2014; Khordad 2013, 2012, 2010; Khordad et al. 2012) have shown that, when the Hamiltonian of system perturbs with external factors, such as magnetic and electric fields, temperature and hydrostatic pressure, then the electronic states and consequently the optical properties of system will substantially change.", "question": "What are the most studies semiconductor nanostructures?", "answers": {"text": "QD and QAD", "answer_start": [378]}}
{"id": "10.1007#s11082-015-0183-5.html_1", "title": "10.1007#s11082-015-0183-5.html", "context": "In recent decades, after the invention of artificial experimental techniques such as molecular beam epitaxy, liquid phase epitaxy and chemical vapour deposition (Watanabe et al. 2000; Junichi 1995; Kunrugsa 2014), researchers have shown great interest to study the optical properties of low-dimensional semiconductor materials. The most studied semiconductor nanostructures are QD and QAD (Sadeghi 2009; Naimi and Jafari 2012; Karimi and Rezaei 2012; Jafari and Naimi 2013; Davatolhagh et al. 2012; Holovatsky et al. 2009; Peter 2005; \u00c7akir et al. 2015; \u00d6zmen et al. 2013; \u00c7akir et al. 2012. The behavior of low-dimensional systems is governed by quantum mechanical laws and for investigating the optical properties of such systems, the main problem is to find the eigenvalues and eigenstates of Hamiltonian of system. Many theoretical works (Naimi 2013; Naimi and Jafari 2013; Raigoza et al. 2005; Dane et al. 2011; Baser et al. 2010; Rezaei and Shojaeian Kish 2013; Raigoza et al. 2005; Xie 2012; Perez-Merchancano et al. 2008; Liang et al. 2011; Liang and Xie 2011; Safarpour et al. 2012; Rezaei et al. 2012; Sivakami and Gayathri 2013; Kasapoglu 2008; Farkoush et al. 2013; Karimi et al. 2014; Khordad 2013, 2012, 2010; Khordad et al. 2012) have shown that, when the Hamiltonian of system perturbs with external factors, such as magnetic and electric fields, temperature and hydrostatic pressure, then the electronic states and consequently the optical properties of system will substantially change.", "question": "What is the main problem for investigating the optical properties of low-dimensional systems?", "answers": {"text": "find the eigenvalues and eigenstates of Hamiltonian", "answer_start": [756]}}
{"id": "10.1007#s11082-015-0183-5.html_2", "title": "10.1007#s11082-015-0183-5.html", "context": "Another interest is the study of these systems when they are doped with hydrogenic impurities (Janssens et al. 2001; Lien and Trinh 2001; Brasken et al. 2000; Nithiananthi and Jayakumar 2003; Yuen 1993). The results of these studies confirm the essential role of impurity in the quantum electronic and optical properties of nanostructures. The majority of studies have used of the effective mass theory to solve the corresponding Schr\u00f6dinger equation. But, since the confined regions may vary from a few Angstrom to several hundred Angstrom units, the validity of effective mass approximations requires examination. Peter et al. (2008) calculated and compared the binding energy of donor impurities in a QD with a constant effective mass (CEM) and position dependent effective mass (PDEM). Also, Rajashabala et al. (2008) investigated the effects of PDEM on donor ionization energies and donor diamagnetic susceptibility on a quantum well. Some other works in the case of PDEM are Rajashabala and Navaneethakrishnan (2007), Li et al. (2000), Qi et al. (1998).", "question": "What theory did the majority of studies use to solve the corresponding Schr\u00f6dinger equation?", "answers": {"text": "effective mass theory", "answer_start": [381]}}
{"id": "10.1007#s11082-015-0183-5.html_3", "title": "10.1007#s11082-015-0183-5.html", "context": "Another interest is the study of these systems when they are doped with hydrogenic impurities (Janssens et al. 2001; Lien and Trinh 2001; Brasken et al. 2000; Nithiananthi and Jayakumar 2003; Yuen 1993). The results of these studies confirm the essential role of impurity in the quantum electronic and optical properties of nanostructures. The majority of studies have used of the effective mass theory to solve the corresponding Schr\u00f6dinger equation. But, since the confined regions may vary from a few Angstrom to several hundred Angstrom units, the validity of effective mass approximations requires examination. Peter et al. (2008) calculated and compared the binding energy of donor impurities in a QD with a constant effective mass (CEM) and position dependent effective mass (PDEM). Also, Rajashabala et al. (2008) investigated the effects of PDEM on donor ionization energies and donor diamagnetic susceptibility on a quantum well. Some other works in the case of PDEM are Rajashabala and Navaneethakrishnan (2007), Li et al. (2000), Qi et al. (1998).", "question": "Who investigated the effects of PDEM on donor ionization energies and donor diamagnetic susceptibility on a quantum well?", "answers": {"text": "Rajashabala et al.", "answer_start": [796]}}
{"id": "10.1007#s11082-015-0190-6.html_0", "title": "10.1007#s11082-015-0190-6.html", "context": "The photonic band gap through acousto-optic interaction in a face-centred cubic silicon crystal is theoretically studied. The dispersion relation for acoustic wave is obtained using method of potentials with boundary conditions involving the bulk and surface stress of considered materials. The dispersion relation for optical wave is derived by transfer matrix method and boundary conditions based on electromagnetic theory. Observation shows that the central frequency of photonic band gap in silicon crystal can be chosen in any desired infrared optical frequency range by adjusting the frequency of acoustic wave. Also, the size of these band gaps in chosen optical frequency range can be further tuned through incident angle of light wave. This study may provide an efficient method to obtain tuneable photonic crystal.", "question": "What is studies in this paper?", "answers": {"text": "photonic band gap through acousto-optic interaction", "answer_start": [4]}}
{"id": "10.1007#s11082-015-0190-6.html_1", "title": "10.1007#s11082-015-0190-6.html", "context": "The photonic band gap through acousto-optic interaction in a face-centred cubic silicon crystal is theoretically studied. The dispersion relation for acoustic wave is obtained using method of potentials with boundary conditions involving the bulk and surface stress of considered materials. The dispersion relation for optical wave is derived by transfer matrix method and boundary conditions based on electromagnetic theory. Observation shows that the central frequency of photonic band gap in silicon crystal can be chosen in any desired infrared optical frequency range by adjusting the frequency of acoustic wave. Also, the size of these band gaps in chosen optical frequency range can be further tuned through incident angle of light wave. This study may provide an efficient method to obtain tuneable photonic crystal.", "question": "How can the size of the photonic band gap in chosen optical frequency range be tuned?", "answers": {"text": "incident angle of light wave", "answer_start": [715]}}
{"id": "10.1007#s11082-015-0190-6.html_2", "title": "10.1007#s11082-015-0190-6.html", "context": "The theory of Lamb wave was developed by Horace Lamb in 1916 to describe the characteristics of wave propagating in plates and referred as plate waves (Lin et al. 2013). Lamb waves are elastic perturbations propagating in solid plate with free boundaries; there is infinite number of modes for both symmetric and anti-symmetric displacements within the layer. These waves arise from coupling of shear and longitudinal waves reflected at the top and bottom surfaces of the plate, leading to an infinite number of dispersive modes. The average displacement over the thickness of the plate or layer in the longitudinal direction is called symmetric modes or longitudinal modes. The anti-symmetric modes are observed to exhibit average displacement in the transverse direction and called flexural modes. The acoustic wave propagation problem can be analysed using the classical elastodynamic wave equation (Campbell et al. 2000).\n", "question": "When was the theory of Lamb developed?", "answers": {"text": "1916", "answer_start": [56]}}
{"id": "10.1007#s11082-015-0190-6.html_3", "title": "10.1007#s11082-015-0190-6.html", "context": "The theory of Lamb wave was developed by Horace Lamb in 1916 to describe the characteristics of wave propagating in plates and referred as plate waves (Lin et al. 2013). Lamb waves are elastic perturbations propagating in solid plate with free boundaries; there is infinite number of modes for both symmetric and anti-symmetric displacements within the layer. These waves arise from coupling of shear and longitudinal waves reflected at the top and bottom surfaces of the plate, leading to an infinite number of dispersive modes. The average displacement over the thickness of the plate or layer in the longitudinal direction is called symmetric modes or longitudinal modes. The anti-symmetric modes are observed to exhibit average displacement in the transverse direction and called flexural modes. The acoustic wave propagation problem can be analysed using the classical elastodynamic wave equation (Campbell et al. 2000).\n", "question": "What is the average displacement over the thickness of the plate or layer in the longitudinal direction called?", "answers": {"text": "symmetric modes", "answer_start": [636]}}
{"id": "10.1007#s11082-015-0190-6.html_4", "title": "10.1007#s11082-015-0190-6.html", "context": "The theory of Lamb wave was developed by Horace Lamb in 1916 to describe the characteristics of wave propagating in plates and referred as plate waves (Lin et al. 2013). Lamb waves are elastic perturbations propagating in solid plate with free boundaries; there is infinite number of modes for both symmetric and anti-symmetric displacements within the layer. These waves arise from coupling of shear and longitudinal waves reflected at the top and bottom surfaces of the plate, leading to an infinite number of dispersive modes. The average displacement over the thickness of the plate or layer in the longitudinal direction is called symmetric modes or longitudinal modes. The anti-symmetric modes are observed to exhibit average displacement in the transverse direction and called flexural modes. The acoustic wave propagation problem can be analysed using the classical elastodynamic wave equation (Campbell et al. 2000).\n", "question": "What can be analysed using the classical elastodynamic wave equation?", "answers": {"text": "acoustic wave propagation problem", "answer_start": [804]}}
{"id": "10.1007#s11082-015-0190-6.html_5", "title": "10.1007#s11082-015-0190-6.html", "context": "As the acoustic excitation is switched on for the desired Lamb mode it produces displacement and strain in structure. Corresponds to an incident acoustic signal with a maximum displacement amplitude 10\u22123\u039b/3, and a strain level in the structure does not exceed 7 \u00d7 10\u22123, which is below the material limit. The index n  y  and n  z  varies above and below, which corresponds to effective average modulation of the guided optical waves via AO interaction. Refractive indices vary alternatively about the unperturbed refractive index value of Si (n = 3.42). The special distribution of the refractive index variation in the Si slab depends on the pattern of the displacement fields; hence there may be different effects in AO interaction using symmetric and antisymmetric Lamb modes. Taking their symmetric perturbation patterns and variation ranges into account these refractive index variations exhibit from 3.351 to 3.489 in z direction as shown in Fig. 3 and causes one dimensional photonic crystal.\n", "question": "What is the unperturbed refractive index of Si?", "answers": {"text": "3.42", "answer_start": [547]}}
{"id": "10.1007#s11082-015-0199-x.html_0", "title": "10.1007#s11082-015-0199-x.html", "context": "We studied the spectral properties of a one-dimensional photonic crystal structure with a nanoplasmonic layer consisting of silver nanoparticles suspended in a transparent medium. The optical spectra of the photonic crystal structure was shown to be controlled by changing the size and volume fraction of nanoparticles. Variation in particle size has an effect on the number of defect modes in the optical spectra. For relatively large nanoparticles, the influence of the size correction of the dielectric permittivity is negligible and the splitting of the defect mode in the transmission and reflection spectra takes place. The magnitude of splitting of the defect mode is very sensitive to nanoparticle concentration. For relatively small nanoparticles, splitting is not observed. This size and concentration dependence can be used to design photonic structures with given parameters of the energy spectrum.\n", "question": "What property of a one-dimensional photonic crystal structure is studied in this paper?", "answers": {"text": "spectral", "answer_start": [15]}}
{"id": "10.1007#s11082-015-0199-x.html_1", "title": "10.1007#s11082-015-0199-x.html", "context": "We studied the spectral properties of a one-dimensional photonic crystal structure with a nanoplasmonic layer consisting of silver nanoparticles suspended in a transparent medium. The optical spectra of the photonic crystal structure was shown to be controlled by changing the size and volume fraction of nanoparticles. Variation in particle size has an effect on the number of defect modes in the optical spectra. For relatively large nanoparticles, the influence of the size correction of the dielectric permittivity is negligible and the splitting of the defect mode in the transmission and reflection spectra takes place. The magnitude of splitting of the defect mode is very sensitive to nanoparticle concentration. For relatively small nanoparticles, splitting is not observed. This size and concentration dependence can be used to design photonic structures with given parameters of the energy spectrum.\n", "question": "What is very sensitive to nanoparticle concentration?", "answers": {"text": "The magnitude of splitting of the defect mode", "answer_start": [626]}}
{"id": "10.1007#s11082-015-0208-0.html_0", "title": "10.1007#s11082-015-0208-0.html", "context": "We present theoretical results of a left-handed metamaterial engineered by a combination of coated and solid nano-spheres. The structure is a binary composite of CdS\u2013TiO 2 core\u2013shell and Au solid nano-spheres which simultaneously dispersed in the air matrix. The effective medium parameters derived by extended Maxwell-Garnett (EMG) effective medium theory. It is shown the possibility of fine-tuning the metamaterial in order to observe left-handed behavior. The results are supplemented with transmittance curves, calculated by layer-multiple-scattering (LMS) method. The predictions of the EMG theory are in good agreement with those of LMS method; thus the (CdS\u2013TiO 2)/Au nano-composite is an appropriate choice as a three-dimensional left-handed metamaterial.", "question": "What is possible to be observed of fine-tuning the metamaterial?", "answers": {"text": "left-handed behavior", "answer_start": [438]}}
{"id": "10.1007#s11082-015-0208-0.html_1", "title": "10.1007#s11082-015-0208-0.html", "context": "We present theoretical results of a left-handed metamaterial engineered by a combination of coated and solid nano-spheres. The structure is a binary composite of CdS\u2013TiO 2 core\u2013shell and Au solid nano-spheres which simultaneously dispersed in the air matrix. The effective medium parameters derived by extended Maxwell-Garnett (EMG) effective medium theory. It is shown the possibility of fine-tuning the metamaterial in order to observe left-handed behavior. The results are supplemented with transmittance curves, calculated by layer-multiple-scattering (LMS) method. The predictions of the EMG theory are in good agreement with those of LMS method; thus the (CdS\u2013TiO 2)/Au nano-composite is an appropriate choice as a three-dimensional left-handed metamaterial.", "question": "What is an appropriate choice as a three-dimensional left-handed metamaterial?", "answers": {"text": "(CdS\u2013TiO 2)/Au nano-composite", "answer_start": [661]}}
{"id": "10.1007#s11082-015-0208-0.html_2", "title": "10.1007#s11082-015-0208-0.html", "context": "In this paper, we report on the design of a NRI metamaterial in the form of a binary composite which consists of both coated and solid nano-spheres in the air matrix. The respective binary composite is a 3D array of CdS\u2013TiO 2 core\u2013shell nano-spheres and Au solid nano-spheres which simultaneously embedded in the air matrix. To study this nano-composite theoretically, the extended Maxwell-Garnett (EMG) effective medium theory is used. Left-handed behavior is observed within a small frequency region. The results of the effective medium theory are supplemented with transmittance curves of light incident on a finite slab of a photonic crystal [the crystal consists of alternating planes of Au and (CdS\u2013TiO 2) nano-spheres], calculated by layer-multiple-scattering (LMS) method.", "question": "What theory is used to study this nano-composite?", "answers": {"text": "extended Maxwell-Garnett (EMG) effective medium theory", "answer_start": [373]}}
{"id": "10.1007#s11082-015-0208-0.html_3", "title": "10.1007#s11082-015-0208-0.html", "context": "The above mentioned effective medium theory can be used to study all the optical properties of the multiphase composites. In our previous works (Sadeghi et al. 2014a, b; Zolanvar et al. 2014), we have studied the optical properties of binary composites that consist of two different types of solid nano-spheres, one made from a dielectric material and the other from a plasmonic material, which are embedded in a host medium. Their electromagnetic responses have been studied using the extended Maxwell-Garnett effective medium theory. Such composites can show responses to an electric (magnetic) field at infrared frequencies which absolute values can be adjusted by controlling the filling fraction and size parameters. The magnetic dipole response is usually weak. This can be driven into resonance, however, by using materials with a large permittivity, such as ferroelectrics. However, their extreme permittivity drops off before infrared frequencies. Instead, the polaritonic resonances of crystals (reststrahlen region) can serve this purpose in the infrared (Huang et al. 2004). The large dielectric permittivity of the spheres also aids in scaling the resonances into the long-wavelength limit. The dielectric function in such materials is provided by the Drude\u2013Lorentz model (Ibach and Luth 2003)\n", "question": "What will aid the sphere in scaling the resonances into the long-wavelength limit?", "answers": {"text": "large dielectric permittivity", "answer_start": [1091]}}
{"id": "10.1007#s11082-015-0208-0.html_4", "title": "10.1007#s11082-015-0208-0.html", "context": "The above mentioned effective medium theory can be used to study all the optical properties of the multiphase composites. In our previous works (Sadeghi et al. 2014a, b; Zolanvar et al. 2014), we have studied the optical properties of binary composites that consist of two different types of solid nano-spheres, one made from a dielectric material and the other from a plasmonic material, which are embedded in a host medium. Their electromagnetic responses have been studied using the extended Maxwell-Garnett effective medium theory. Such composites can show responses to an electric (magnetic) field at infrared frequencies which absolute values can be adjusted by controlling the filling fraction and size parameters. The magnetic dipole response is usually weak. This can be driven into resonance, however, by using materials with a large permittivity, such as ferroelectrics. However, their extreme permittivity drops off before infrared frequencies. Instead, the polaritonic resonances of crystals (reststrahlen region) can serve this purpose in the infrared (Huang et al. 2004). The large dielectric permittivity of the spheres also aids in scaling the resonances into the long-wavelength limit. The dielectric function in such materials is provided by the Drude\u2013Lorentz model (Ibach and Luth 2003)\n", "question": "What properties of binary composites were studied in their previous works?", "answers": {"text": "optical properties", "answer_start": [73]}}
{"id": "10.1007#s11082-015-0208-0.html_5", "title": "10.1007#s11082-015-0208-0.html", "context": "The above mentioned effective medium theory can be used to study all the optical properties of the multiphase composites. In our previous works (Sadeghi et al. 2014a, b; Zolanvar et al. 2014), we have studied the optical properties of binary composites that consist of two different types of solid nano-spheres, one made from a dielectric material and the other from a plasmonic material, which are embedded in a host medium. Their electromagnetic responses have been studied using the extended Maxwell-Garnett effective medium theory. Such composites can show responses to an electric (magnetic) field at infrared frequencies which absolute values can be adjusted by controlling the filling fraction and size parameters. The magnetic dipole response is usually weak. This can be driven into resonance, however, by using materials with a large permittivity, such as ferroelectrics. However, their extreme permittivity drops off before infrared frequencies. Instead, the polaritonic resonances of crystals (reststrahlen region) can serve this purpose in the infrared (Huang et al. 2004). The large dielectric permittivity of the spheres also aids in scaling the resonances into the long-wavelength limit. The dielectric function in such materials is provided by the Drude\u2013Lorentz model (Ibach and Luth 2003)\n", "question": "What theory was used to study the electromagnetic responses of binary composites in their previous works?", "answers": {"text": "extended Maxwell-Garnett effective medium theory", "answer_start": [486]}}
{"id": "10.1007#s11082-015-0208-0.html_6", "title": "10.1007#s11082-015-0208-0.html", "context": "A negative refraction index (NRI) requires both a negative permeability and permittivity at the same frequency. Unfortunately, both cannot be made negative in the same frequency range. Nevertheless, the same concepts can be applied to more complex structures. We solve this problem by now considering coated spheres. We are ready to confront with a case of binary composite materials consisting of both coated and solid nano-spheres. The respective binary composite is a 3D array of CdS\u2013TiO 2 core\u2013shell nano-spheres and Au solid nano-spheres which simultaneously embedded in the air matrix. The resulting structure can also be visualized as two interpenetrating simple cubic lattices of the respective CdS\u2013TiO 2 core\u2013shell and Au nano-spheres. Therefore, this binary composite comprises two different kinds of non-overlapping nano-spheres with lattice constant a = 1 \u03bcm. Figure 2 shows a schematic of the (CdS\u2013TiO 2)/Au binary composite.\n", "question": "What does a negative refraction index require?", "answers": {"text": "both a negative permeability and permittivity", "answer_start": [50]}}
{"id": "10.1007#s11082-015-0231-1.html_0", "title": "10.1007#s11082-015-0231-1.html", "context": "The theory of plasmonic oscillations proposed in this work is characterized by the minimalism of axiomatics since the principal assumption underlying it has been actually the only one postulating the form of the dependence of the density function upon its internal arguments. In what follows just two less favored assumptions have been formulated: one for providing interconnection of the density with its derivatives [see (11)], and the other having a geometrical sense about leveraging of the initial state configuration in power series expansion (12). All the rest of the phases of the theory demonstrate absolutely consistent technical character and rely on utilizing of the least action principle and charge conservation. Universality of the variational technique of derivation of basic equations enables further buildup of their structure by introducing into a system lagrangian additional exchange-correlation and/or kinetic energy correction terms. Their concrete form could be borrowed from the adjacent theories: Hartree\u2013Fock, Thomas\u2013Fermi and density functional as well. In view of these considerations the applicability of the theory could be expanded. For instance, it seems to be possible to construct its modification for predicting of the ground state and also for accounting temperature effects in the explicit form (Nikiforov et al. 2000).", "question": "What theory is proposed in this work?", "answers": {"text": "theory of plasmonic oscillations", "answer_start": [4]}}
{"id": "10.1007#s11082-015-0244-9.html_0", "title": "10.1007#s11082-015-0244-9.html", "context": "In this work, both the effect of electron\u2013phonon (e\u2013p) interaction and pressure on the optical properties of GaN triangular quantum wires has been studied. In this regard, the electronic transition energy and dipole matrix elements are calculated, by taking the effects of the electron\u2013LO\u2013phonon interaction and the hydrostatic pressure into account. Then, the refractive index (RI) changes and absorption coefficients (ACs) are computed within the framework of the compact density matrix approach and iterative method. It is found that the transition energy and dipole matrix elements decrease under the e\u2013p interaction and the hydrostatic pressure. Obviously, it is shown that the hydrostatic pressure increase the effect of e\u2013p interaction on the transition energy. The ACs and RI changes shift toward lower energies under the e\u2013LO\u2013p interaction and the pressure. RI changes and ACs are increased in the influence of e\u2013p interaction but they are decreased under the hydrostatic pressure. The influence of e\u2013LO\u2013p interaction under the hydrostatic pressure on the RI changes and ACs cannot be neglected for a GaN triangular quantum wire.", "question": "What properties are computed within the framework of the compact density matrix approach and iterative method?", "answers": {"text": "the refractive index (RI) changes and absorption coefficients (ACs)", "answer_start": [357]}}
{"id": "10.1007#s11082-015-0244-9.html_1", "title": "10.1007#s11082-015-0244-9.html", "context": "Electronic properties of quantum nanostructures have been intensively studied due to the high potential applications and fundamental physics. Among these nanostructures, quantum dots (QDs) are three dimensional wells that can trap electrons and holes resulting in quantized energy levels. We know that optical properties of nanostructures can be changed under various factors like electric and magnetic fields, temperature, pressure, and e\u2013p interaction. It is worth mentioning that the e\u2013p interaction in nanostructures plays an important role in many physical properties such as the binding energy and optical properties. Hitherto, the effect of the e\u2013p interaction on optical properties of several nanostructures has been theoretically investigated. For example Guo and Chen (1995) presented the polaron effects on second-harmonic generation in quantum well within an electric field. Cui-Hong et al. (2002) discussed polaron effects on the third-order nonlinear optical susceptibility in quantum disk. Also, the effect of e\u2013p interaction on the third harmonic generation in a square quantum well investigated in Liu et al. (2005).", "question": "What plays an important role in many physical properties such as the binding energy and optical properties?", "answers": {"text": "e\u2013p interaction", "answer_start": [438]}}
{"id": "10.1007#s11082-015-0244-9.html_2", "title": "10.1007#s11082-015-0244-9.html", "context": "Electronic properties of quantum nanostructures have been intensively studied due to the high potential applications and fundamental physics. Among these nanostructures, quantum dots (QDs) are three dimensional wells that can trap electrons and holes resulting in quantized energy levels. We know that optical properties of nanostructures can be changed under various factors like electric and magnetic fields, temperature, pressure, and e\u2013p interaction. It is worth mentioning that the e\u2013p interaction in nanostructures plays an important role in many physical properties such as the binding energy and optical properties. Hitherto, the effect of the e\u2013p interaction on optical properties of several nanostructures has been theoretically investigated. For example Guo and Chen (1995) presented the polaron effects on second-harmonic generation in quantum well within an electric field. Cui-Hong et al. (2002) discussed polaron effects on the third-order nonlinear optical susceptibility in quantum disk. Also, the effect of e\u2013p interaction on the third harmonic generation in a square quantum well investigated in Liu et al. (2005).", "question": "What effects did Cui-Hong discuss in 2002 on the third-order nonlinear optical susceptibility in quantum disk?", "answers": {"text": "polaron effects", "answer_start": [799]}}
{"id": "10.1007#s11082-015-0244-9.html_3", "title": "10.1007#s11082-015-0244-9.html", "context": "Electronic properties of quantum nanostructures have been intensively studied due to the high potential applications and fundamental physics. Among these nanostructures, quantum dots (QDs) are three dimensional wells that can trap electrons and holes resulting in quantized energy levels. We know that optical properties of nanostructures can be changed under various factors like electric and magnetic fields, temperature, pressure, and e\u2013p interaction. It is worth mentioning that the e\u2013p interaction in nanostructures plays an important role in many physical properties such as the binding energy and optical properties. Hitherto, the effect of the e\u2013p interaction on optical properties of several nanostructures has been theoretically investigated. For example Guo and Chen (1995) presented the polaron effects on second-harmonic generation in quantum well within an electric field. Cui-Hong et al. (2002) discussed polaron effects on the third-order nonlinear optical susceptibility in quantum disk. Also, the effect of e\u2013p interaction on the third harmonic generation in a square quantum well investigated in Liu et al. (2005).", "question": "When did Liu et al. investigate the effect of e\u2013p interaction on the third harmonic generation in a square quantum well?", "answers": {"text": "2005", "answer_start": [1127]}}
{"id": "10.1007#s11082-015-0244-9.html_4", "title": "10.1007#s11082-015-0244-9.html", "context": "We have presented our results concerning the optical properties of a GaN triangular quantum wire under applied pressure and the e\u2013p interaction. In this regard, we have calculated energy levels, refractive index changes and absorption coefficients with and without impurity under the pressure. According to the results, it is found that the absorption coefficients and refractive index changes increase and shift toward the lower energies in the presence of e\u2013LO\u2013p interaction. In addition, the refractive index changes and absorption coefficients decrease and shift toward the lower energies when the pressure is increasing. The dipole matrix elements with the e\u2013p interaction are larger than that in the without e\u2013p interaction under the pressure. According to the results, it is deduced that the pressure increases the effect of e\u2013p interaction on the transition energy. The pressure and the e\u2013p interaction have key roles on the optical properties of a GaN triangular quantum wire.", "question": "What plays a key role on the optical properties of a GaN triangular quantum wire?", "answers": {"text": "pressure and the e\u2013p interaction", "answer_start": [111]}}
{"id": "10.1007#s11082-015-0269-0.html_0", "title": "10.1007#s11082-015-0269-0.html", "context": "In recent years one observes a revival of interest in multimode fibers. There are several key domains in which they are an interesting alternative to their single mode counterparts. These are short-range applications like: optical data interconnects (Hoffmann et al. 2011; Bigot et al. 2015), local area networks (Guillory et al. 2013) and specific radio-over-fiber designs (Maksymiuk et al. 2014). Furthermore, the fiber manufacture process has become so precise nowadays that it is technically possible to design a fiber exhibiting equal mode delays of all propagating modes. However, due to the so called profile dispersion, this is possible only in a very narrow wavelength range. In addition, several studies indicate (Qiu et al. 2013; Molin et al. 2011) that in fibers of the latest generation (like OM4) it is the chromatic dispersion that becomes the dominating source of intersymbol interference, as opposed to modal dispersion, which was regarded as the dominating distortion source for many years.", "question": "Why is the design of a fiber exhibiting equal mode delays of all propagating modes only possible in a very narrow wavelength range?", "answers": {"text": "profile dispersion", "answer_start": [608]}}
{"id": "10.1007#s11082-015-0308-x.html_0", "title": "10.1007#s11082-015-0308-x.html", "context": "In this paper, we propose and numerically investigate a graphene monolayer equilateral triangle nanocavity with a cut corner at one of the vertices which connected to a directional output waveguide. This integrated plasmonic device is surrounded by an infinite area of graphene with another chemical potential. The size of the equilateral triangle nanocavity is from 20 to 30 nm, while the width of the output waveguide is in sub-10 nm scale. Such a nano scale device could be fabricated by self-assemble material growth method, or it could be promising with the future development of nano material engineering. The mode Q factor and the output efficiency are systematically investigated by using the commercial software COMSOL Multiphysics Version 4.3b, RF Module, eigenfrequency solver. It is necessary to reveal the optimal parameters setting for a trade-off between the output efficiency and the Q factor through the systematic study. The directional output nanocavity resonator with relatively high output efficiency and relatively high Q factor could be a key component of the future plasmonic integrated circuits techniques.", "question": "How can the nano scale device mentioned in this study be fabricated?", "answers": {"text": "self-assemble material growth method", "answer_start": [491]}}
{"id": "10.1007#s11082-015-0308-x.html_1", "title": "10.1007#s11082-015-0308-x.html", "context": "It is clearly shown in Fig. 4 that when the relaxation time of the graphene increases from the 0.5 to 1.5 ps, the Q factor rises from 29.6 to 35.2, while the output coupling coefficient almost remains at the constant of 24.4 %. Here, the key parameters of the nanocavity and the graphene are set as R 1 = 30 nm, w = 5 nm, \u03bc  c1 = 0.9 eV and \u03bc  c2 = 0.5 eV. We know that the carrier scattering rate \u0393 (Gosciniak and Tan 2013) is inversely proportional to the relaxation time of graphene. Hence, the increasing of the relaxation time leads to the decreasing of absorption loss which can be a reasonable explanation for the increasing of the Q factor. On the other hand, the variation of the relaxation time does not modify the ratio between the energy flux in the waveguide section and the counterpart in the total integrated device. Thus, the coupling coefficient keeps constant at 24.4 % when the relaxation time increases from 0.5 to 1.5 ps.\n", "question": "What is the relaxation time of the graphene when the Q factor is 35.2?", "answers": {"text": "1.5 ps", "answer_start": [102]}}
{"id": "10.1007#s11082-015-0308-x.html_2", "title": "10.1007#s11082-015-0308-x.html", "context": "It is clearly shown in Fig. 4 that when the relaxation time of the graphene increases from the 0.5 to 1.5 ps, the Q factor rises from 29.6 to 35.2, while the output coupling coefficient almost remains at the constant of 24.4 %. Here, the key parameters of the nanocavity and the graphene are set as R 1 = 30 nm, w = 5 nm, \u03bc  c1 = 0.9 eV and \u03bc  c2 = 0.5 eV. We know that the carrier scattering rate \u0393 (Gosciniak and Tan 2013) is inversely proportional to the relaxation time of graphene. Hence, the increasing of the relaxation time leads to the decreasing of absorption loss which can be a reasonable explanation for the increasing of the Q factor. On the other hand, the variation of the relaxation time does not modify the ratio between the energy flux in the waveguide section and the counterpart in the total integrated device. Thus, the coupling coefficient keeps constant at 24.4 % when the relaxation time increases from 0.5 to 1.5 ps.\n", "question": "What is the output coupling coefficient when the Q factor rises from 29.6 to 35.2?", "answers": {"text": "24.4 %", "answer_start": [220]}}
{"id": "10.1007#s11082-015-0308-x.html_3", "title": "10.1007#s11082-015-0308-x.html", "context": "In conclusion, we propose and analyze the graphene equilateral triangle nanocavity with a cut corner at one vertex of triangle which is connected to an output waveguide in this article. The Q factor and the output coupling coefficient have been numerically investigated as function of the parameters of the cavity and graphene material. The integrated nanocavity with relatively high directional output efficiency offers a wide range applications in the field of nanophotonic devices, such as ultra-low threshold plasomic emitter and single photonic source. It might be one of the key components of high density plasmonic integrate circuits or transformation plasmonics in the future.", "question": "What might be one of the key components of high density plasmonic integrate circuits or transformation plasmonics in the future?", "answers": {"text": "integrated nanocavity", "answer_start": [341]}}
{"id": "10.1007#s11082-016-0404-6.html_0", "title": "10.1007#s11082-016-0404-6.html", "context": "Applications Energy harvesting have increased for powering wireless sensors and low power devices during the past few decades. Smart materials used as generators have received considerable attention lately and several prototypes were built to demonstrate the process. At present, the investigation of using electrostrictive polymers for energy harvesting (a conversion of mechanical to electrical energy) is beginning to show their potential. The focus of this paper is to show how the electrostrictive polymers can be used as generator, and to propose a solution for artificially increasing the coupling factor of electrostrictive materials. Based on a new technique SSHI-Max, with a transverse strain of 0.5 % and a bias field of 10 V/\u03bcm, such a process rendered it possible to increase the converted power by 500 % with a low-frequency mechanical excitation. This study contributes to provide a framework for developing an innovative energy harvesting technology that collects vibrations from the environment and converts them into electricity to power a variety of sensors.", "question": "What is energy harvesting?", "answers": {"text": "conversion of mechanical to electrical energy", "answer_start": [358]}}
{"id": "10.1007#s11082-016-0428-y.html_0", "title": "10.1007#s11082-016-0428-y.html", "context": "It is shown in this paper that a finite-difference time-domain method can be successfully applied to rigorous electromagnetic analysis of supercontinuum generation in photonic crystal fibers. Large computational requirements of the method are alleviated by the use of a hybrid procedure where, at first, vector two-dimensional simulation is applied in order to determine mode properties of the fiber. Subsequently, one-dimensional simulation of a pulse propagating in a transmission line filled with effective material is performed. The parameters of the line take into account nonlinear characteristics of the filling material as well as the previously computed mode dispersion. It is depicted that the proposed novel hybrid approach opens the way for rigorous, yet, computationally-efficient modeling of third order nonlinear processes in optically long fibers. The example investigated in this paper shows very promising results as compared with experiments and approximate numerical simulations of a nonlinear Schrodinger equation performed with the aid of the split-step Fourier method.", "question": "What model is proposed in this paper?", "answers": {"text": "a finite-difference time-domain method", "answer_start": [31]}}
{"id": "10.1007#s11082-016-0428-y.html_1", "title": "10.1007#s11082-016-0428-y.html", "context": "The alternative is to apply a rigorous full-wave approach in order to solve such a nonlinear problem. One of prospective candidates is the finite-difference time-domain (FDTD) method as a versatile numerical tool naturally adapted to broadband EM analysis (Taflove and Hagness 2005). Although several valuable papers focused on FDTD modelling of third-order nonlinear effects, that stay behind SC generation, have been published (Fujii et al. 2004; Lubin et al. 2011), large computational effort and memory requirements involved in the full-wave EM analysis of centimeter-long PCFs make the method inapplicable (Hu et al. 2008). For that reason, a novel approach that takes the advantage of the accuracy of the FDTD method, while substantially alleviating its prohibitive computational requirements, is proposed in this paper.", "question": "What makes the full-wave EM analysis of centimeter-long PCFs inapplicable?", "answers": {"text": "large computational effort and memory requirements", "answer_start": [469]}}
{"id": "10.1007#s11082-016-0428-y.html_2", "title": "10.1007#s11082-016-0428-y.html", "context": "\nConsider as an example a PCF fabricated from lead\u2013bismuth\u2013gallium-oxide glass (PBG-08) proposed in (Sobon et al. 2014), which is well-suited for SC generation (see Fig. 1). Solid lines in Figs. 2a and 3 show the characteristics of the corresponding effective refractive index n  eff  and dispersion D, respectively, computed in (Sobon et al. 2014) in the range from 500 nm to 4000 nm. In the first attempt, a triple-pole Lorentz model will be fitted to the aforementioned curves using the Levenberg\u2013Marquardt algorithm executed with no bounds imposed on the Lorentz parameters. According to (Sobon et al. 2014), SC evolves in the considered PCF in the 500\u20132400 nm range (see Fig. 5 therein), so the fitting has been limited to that range. The obtained Lorentz model (see the 2nd column in Table 1) provides the effective refractive index (dispersion) with a normalized root-mean-square deviation (NRMSD) of 0.047 % (0.777 %) in that spectrum. Due to negligibly small discrepancy, these curves are not plotted in Figs. 2 and 3.\n", "question": "What glass did Sobon proposed in 2014?", "answers": {"text": "lead\u2013bismuth\u2013gallium-oxide glass", "answer_start": [46]}}
{"id": "10.1007#s11082-016-0428-y.html_3", "title": "10.1007#s11082-016-0428-y.html", "context": "The whole FDTD simulation executed on Intel Core i7-3930 K CPU took 10 h with the speed of 182 iterations per second, which is about 2 times faster than rigorous computation without a hybrid approach proposed in (Salski et al. 2015). What needs to be stressed out, the model elaborated without the use of PBCs would extend the S1D-FDTD analysis to about 15 days. There is still a lot of room for additional acceleration with such techniques as GPU computing or multi-threading (Rudnicki and Sypniewski 2012), but that subject goes beyond the main scope of this paper. In comparison, similar simulation undertaken with SSFM takes about 4 min. Nevertheless, it can be clearly seen that rigorous FDTD modeling of the whole supercontinuum evolution in microstructured optical fibers performed in reasonable time limits on a personal computer is well within reach.", "question": "What device did the whole FDTD simulation execute on in this study?", "answers": {"text": "Intel Core i7-3930 K CPU", "answer_start": [38]}}
{"id": "10.1007#s11082-016-0428-y.html_4", "title": "10.1007#s11082-016-0428-y.html", "context": "The whole FDTD simulation executed on Intel Core i7-3930 K CPU took 10 h with the speed of 182 iterations per second, which is about 2 times faster than rigorous computation without a hybrid approach proposed in (Salski et al. 2015). What needs to be stressed out, the model elaborated without the use of PBCs would extend the S1D-FDTD analysis to about 15 days. There is still a lot of room for additional acceleration with such techniques as GPU computing or multi-threading (Rudnicki and Sypniewski 2012), but that subject goes beyond the main scope of this paper. In comparison, similar simulation undertaken with SSFM takes about 4 min. Nevertheless, it can be clearly seen that rigorous FDTD modeling of the whole supercontinuum evolution in microstructured optical fibers performed in reasonable time limits on a personal computer is well within reach.", "question": "How long does it take for a simulation with SSFM?", "answers": {"text": "4 min", "answer_start": [635]}}
{"id": "10.1007#s11082-016-0434-0.html_0", "title": "10.1007#s11082-016-0434-0.html", "context": "A series of new oxyfluoro aluminum-borate glasses can be used as upconversion host glass is prepared by the conventional melt-quenching technique. The effect of replacement lithium partner elements on the optoelectronic properties of the prepared glasses is studied. With increasing the ratio of LiF/LiF+Li2O the ionic character of the glass increases leading to a decrease in both of the average oscillator strength and the average interband oscillator. Fluctuation in Urbach energy is recorded which is attributed to a fluctuated structural disorder-induced broadening. The increase in LiF/LiF+Li2O molar ratio shortened the estimated radiative lifetime for luminescent dopant ions. The radiative life time decreased with decreasing the average glass molecular weight associated with an increase in the glass ion packing ratio.", "question": "What technique was used to prepare a series of new oxyfluoro aluminum-borate glasses in this study?", "answers": {"text": "conventional melt-quenching technique", "answer_start": [108]}}
{"id": "10.1007#s11082-016-0434-0.html_1", "title": "10.1007#s11082-016-0434-0.html", "context": "The decrease in molecular vibrations and the increase in the energy of electronic excitation increase the width of spectral range of glass transparency. Materials having small ions with strong bonding, such as alkali halides, are expected to comprise a wide UV transparency (Rittner 1951). Addition of Li ions increases humidity resistance and also the capacity to concentrate transition metal ions increases as well. Furthermore, addition of Al2O3 increases the chemical durability of glass (Reddy et al. 2007). LiF is a good host for dopant ions. It permits the formation of intrinsic color centers, especially when the glass is exposed to an ionizing radiation (Baldacchini 2002). Optical borate glasses containing Li+ ions and LiF have been investigated for stable UV-transparent systems (Chowdari and Zhou 1995; Naresh and Buddhudu 2012). Existence of Al2O3 may lead to a considerable increase in the free Li+ ion concentration (Abrahams and Hadzifejzovic 2000).", "question": "What is materials having small ions with strong bonding expected to comprise?", "answers": {"text": "wide UV transparency", "answer_start": [253]}}
{"id": "10.1007#s11082-016-0434-0.html_2", "title": "10.1007#s11082-016-0434-0.html", "context": "The decrease in molecular vibrations and the increase in the energy of electronic excitation increase the width of spectral range of glass transparency. Materials having small ions with strong bonding, such as alkali halides, are expected to comprise a wide UV transparency (Rittner 1951). Addition of Li ions increases humidity resistance and also the capacity to concentrate transition metal ions increases as well. Furthermore, addition of Al2O3 increases the chemical durability of glass (Reddy et al. 2007). LiF is a good host for dopant ions. It permits the formation of intrinsic color centers, especially when the glass is exposed to an ionizing radiation (Baldacchini 2002). Optical borate glasses containing Li+ ions and LiF have been investigated for stable UV-transparent systems (Chowdari and Zhou 1995; Naresh and Buddhudu 2012). Existence of Al2O3 may lead to a considerable increase in the free Li+ ion concentration (Abrahams and Hadzifejzovic 2000).", "question": "What will be increased if Al2O3 is added to the glass?", "answers": {"text": "chemical durability", "answer_start": [463]}}
{"id": "10.1007#s11082-016-0434-0.html_3", "title": "10.1007#s11082-016-0434-0.html", "context": "The decrease in molecular vibrations and the increase in the energy of electronic excitation increase the width of spectral range of glass transparency. Materials having small ions with strong bonding, such as alkali halides, are expected to comprise a wide UV transparency (Rittner 1951). Addition of Li ions increases humidity resistance and also the capacity to concentrate transition metal ions increases as well. Furthermore, addition of Al2O3 increases the chemical durability of glass (Reddy et al. 2007). LiF is a good host for dopant ions. It permits the formation of intrinsic color centers, especially when the glass is exposed to an ionizing radiation (Baldacchini 2002). Optical borate glasses containing Li+ ions and LiF have been investigated for stable UV-transparent systems (Chowdari and Zhou 1995; Naresh and Buddhudu 2012). Existence of Al2O3 may lead to a considerable increase in the free Li+ ion concentration (Abrahams and Hadzifejzovic 2000).", "question": "How to increase the humidity resistance and the capacity to concentrate transition metal ions of the glass?", "answers": {"text": "Addition of Li ions", "answer_start": [290]}}
{"id": "10.1007#s11082-016-0434-0.html_4", "title": "10.1007#s11082-016-0434-0.html", "context": "Fluoride glass fibers have a different applications in optical fiber communications, mid-infrared spectroscopy, fiber-optic sensors, thermometry, imaging, high-capacity data storage and medical purposes in ophthalmology and dentistry. Fluoroaluminate fibers doped with rare earth ions were used in fiber lasers and amplifiers (Abdel-Baki and El-Diasty 2013). In the field of white light emitting diodes, rare earth-codoped oxyfluoride aluminoborate glasses have been applied (Babu and Kumar 2014). Among oxide glasses oxyfluoride borate glasses have relative high mechanical strength and low phonon energy of fluoride glasses (Chen et al. 2008). Major changes in the luminescence are achieved with the addition of transition metal ions and alkali/alkaline metal ions into the host glass matrix (Azeem et al. 2009; Venkatramu et al. 2006; Marimuthu et al. 2009; Karunakaran et al. 2009; Marimuthu et al. 2009). Therefore, present work is committed to study the effect of replacement lithium partner elements on the electronic interband transition properties. The effect of the characteristics of the host oxyfluoro aluminum-borate glasses on the estimated radiative lifetime of doped ions is investigated.", "question": "Which kind of glasses have been applied in the field of white light emitting diodes?", "answers": {"text": "oxyfluoride aluminoborate glasses", "answer_start": [404]}}
{"id": "10.1007#s11082-016-0434-0.html_5", "title": "10.1007#s11082-016-0434-0.html", "context": "Fluoride glass fibers have a different applications in optical fiber communications, mid-infrared spectroscopy, fiber-optic sensors, thermometry, imaging, high-capacity data storage and medical purposes in ophthalmology and dentistry. Fluoroaluminate fibers doped with rare earth ions were used in fiber lasers and amplifiers (Abdel-Baki and El-Diasty 2013). In the field of white light emitting diodes, rare earth-codoped oxyfluoride aluminoborate glasses have been applied (Babu and Kumar 2014). Among oxide glasses oxyfluoride borate glasses have relative high mechanical strength and low phonon energy of fluoride glasses (Chen et al. 2008). Major changes in the luminescence are achieved with the addition of transition metal ions and alkali/alkaline metal ions into the host glass matrix (Azeem et al. 2009; Venkatramu et al. 2006; Marimuthu et al. 2009; Karunakaran et al. 2009; Marimuthu et al. 2009). Therefore, present work is committed to study the effect of replacement lithium partner elements on the electronic interband transition properties. The effect of the characteristics of the host oxyfluoro aluminum-borate glasses on the estimated radiative lifetime of doped ions is investigated.", "question": "How to achieve a major change in the luminescence of the host glass matrix?", "answers": {"text": "addition of transition metal ions and alkali/alkaline metal ions", "answer_start": [702]}}
{"id": "10.1007#s11082-016-0434-0.html_6", "title": "10.1007#s11082-016-0434-0.html", "context": "Glass system of composition (20-x)Li2O\u2013xLiF\u201375B2O3\u20135Al2O3, where 0 \u2264 x \u2264 15 mol%, was prepared using the normal melt-quenching technique. The raw materials were analytical grade chemicals of Li2CO3, LiF, H3BO3 and Al2O3. Appropriate amounts of these chemicals were mixed well in a Porcelain crucible and melted at 1000 \u00b0C for 1 h. The amount of the glass in each batch was 50 g/melts. During the synthesis process the mixture was shaken frequently to ensure the homogeneity of the prepared samples. The melts were then poured rapidly into a stainless steel mould. Disk-shaped samples were cut in the form of slaps and polished well to be suitable for optical measurements. The prepared samples were annealed at temperature 400 \u00b0C to relieve any internal mechanical stresses. The density, \u03c1, of each sample was measured by Archimedes\u2019s method with an error of \u00b110\u22124. Figure 1 contains the measured values of density and calculated molar volumes, V  m , for the present glass samples.\n", "question": "How was the glass system of composition (20-x)Li2O\u2013xLiF\u201375B2O3\u20135Al2O3 prepared in this study?", "answers": {"text": "melt-quenching technique", "answer_start": [112]}}
{"id": "10.1007#s11082-016-0434-0.html_7", "title": "10.1007#s11082-016-0434-0.html", "context": "Glass system of composition (20-x)Li2O\u2013xLiF\u201375B2O3\u20135Al2O3, where 0 \u2264 x \u2264 15 mol%, was prepared using the normal melt-quenching technique. The raw materials were analytical grade chemicals of Li2CO3, LiF, H3BO3 and Al2O3. Appropriate amounts of these chemicals were mixed well in a Porcelain crucible and melted at 1000 \u00b0C for 1 h. The amount of the glass in each batch was 50 g/melts. During the synthesis process the mixture was shaken frequently to ensure the homogeneity of the prepared samples. The melts were then poured rapidly into a stainless steel mould. Disk-shaped samples were cut in the form of slaps and polished well to be suitable for optical measurements. The prepared samples were annealed at temperature 400 \u00b0C to relieve any internal mechanical stresses. The density, \u03c1, of each sample was measured by Archimedes\u2019s method with an error of \u00b110\u22124. Figure 1 contains the measured values of density and calculated molar volumes, V  m , for the present glass samples.\n", "question": "At what temperature were the prepared samples annealed?", "answers": {"text": "400 \u00b0C", "answer_start": [723]}}
{"id": "10.1007#s11082-016-0434-0.html_8", "title": "10.1007#s11082-016-0434-0.html", "context": "The blue shifts in the cutoff wavelengths \u03bb cutoff are determined. The cutoff wavelength of the first glass sample is demonstrated as an example in Fig. 2. The cutoff wavelength of sample 2 is shifted to 401.5 nm with respect to the first sample with \u03bb cutoff = 409.3 nm. The third sample and fourth one have \u03bb cutoff equal to 386.4 and 374.6 nm, respectively. The decrease in the values of ultraviolet \u03bb cutoff as LiF incooperated into the glass matrix instead of Li2O means that the position of the fundamental absorption edge shifts to shorter wavelengths with the decrease in average molecular weight of the glass (Ratnakaram and Reddy 2000).", "question": "What is the cutoff wavelength of the first sample?", "answers": {"text": "409.3 nm", "answer_start": [262]}}
{"id": "10.1007#s11082-016-0434-0.html_9", "title": "10.1007#s11082-016-0434-0.html", "context": "Through applying Drude\u2013Voigt dispersion theory (Wood 1936), it has been found that, glasses containing monovalent alkali metal ions, divalent alkali earthed metal ions and trivalent rare earthed ions such as Y3+ and La3+ are characterized by small \u03bb 0 and large S 0 values (Hirota and Izumitani 1978). This behavior is correlated with the absorption of the nonbridging oxygen ion (NBO). In the same time, both of \u03bb 0 and S 0 values increase with decreasing the ion field strength Z/a 2, where Z is the atomic number of Li and a is the ionic radius of the oxide. Since the ionic radius of Li2O and LiF are 0.6 and 0. \u00c5, respectively, so it is expected that the field strength increases and hence both values of \u03bb 0 and S 0 values decrease with introduction of LiF in glass network on the expense of Li2O. This is attributed to a decrease in the ionic refraction of NBO ions associated with a gain in electronic shell of oxygen ion. It is also ascribed to the increase in the cation polarization associated with the decrease in the ionic radius of the oxide (Hirota and Izumitani 1978).", "question": "Who proposed the Drude\u2013Voigt dispersion theory?", "answers": {"text": "Wood", "answer_start": [48]}}
{"id": "10.1007#s11082-016-0434-0.html_10", "title": "10.1007#s11082-016-0434-0.html", "context": "Through applying Drude\u2013Voigt dispersion theory (Wood 1936), it has been found that, glasses containing monovalent alkali metal ions, divalent alkali earthed metal ions and trivalent rare earthed ions such as Y3+ and La3+ are characterized by small \u03bb 0 and large S 0 values (Hirota and Izumitani 1978). This behavior is correlated with the absorption of the nonbridging oxygen ion (NBO). In the same time, both of \u03bb 0 and S 0 values increase with decreasing the ion field strength Z/a 2, where Z is the atomic number of Li and a is the ionic radius of the oxide. Since the ionic radius of Li2O and LiF are 0.6 and 0. \u00c5, respectively, so it is expected that the field strength increases and hence both values of \u03bb 0 and S 0 values decrease with introduction of LiF in glass network on the expense of Li2O. This is attributed to a decrease in the ionic refraction of NBO ions associated with a gain in electronic shell of oxygen ion. It is also ascribed to the increase in the cation polarization associated with the decrease in the ionic radius of the oxide (Hirota and Izumitani 1978).", "question": "When did Wood propose the Drude\u2013Voigt dispersion theory?", "answers": {"text": "1936", "answer_start": [53]}}
{"id": "10.1007#s11082-016-0434-0.html_11", "title": "10.1007#s11082-016-0434-0.html", "context": "Figure 5 illustrates that the estimated radiative lifetime decreases with increasing the LiF/LiF+Li2O molar ratio. For example, the radiative lifetime is shortened by ~0.19 % from sample 1 to sample 4. Figure 6 shows that the calculated radiative lifetime increases with increasing the glass molecular weight, M, taking into consideration that the molecular weight of LiF = 25.94 g/mol and that of Li2O is 29.88 g/mol. However, for our proposed host glass the radiative lifetime can be controlled by the adjusting the LiF/LiF+Li2O molar ratio, or in another word adjusting the glass molar ratio. Such trend confirms that, the spectroscopic properties of doped rare earth ions will be strongly affected by the structure of host glass and hence the environment for ions sites (Weber 1990; Reisfeld 1973, 1975).\n", "question": "What is the molecular weight of LiF?", "answers": {"text": "25.94 g/mol", "answer_start": [374]}}
{"id": "10.1007#s11082-016-0434-0.html_12", "title": "10.1007#s11082-016-0434-0.html", "context": "Figure 5 illustrates that the estimated radiative lifetime decreases with increasing the LiF/LiF+Li2O molar ratio. For example, the radiative lifetime is shortened by ~0.19 % from sample 1 to sample 4. Figure 6 shows that the calculated radiative lifetime increases with increasing the glass molecular weight, M, taking into consideration that the molecular weight of LiF = 25.94 g/mol and that of Li2O is 29.88 g/mol. However, for our proposed host glass the radiative lifetime can be controlled by the adjusting the LiF/LiF+Li2O molar ratio, or in another word adjusting the glass molar ratio. Such trend confirms that, the spectroscopic properties of doped rare earth ions will be strongly affected by the structure of host glass and hence the environment for ions sites (Weber 1990; Reisfeld 1973, 1975).\n", "question": "What is the molecular weight of Li2O?", "answers": {"text": "29.88 g/mol", "answer_start": [406]}}
{"id": "10.1007#s11082-016-0484-3.html_0", "title": "10.1007#s11082-016-0484-3.html", "context": "Following from the absolute T and R values, we have calculated the optical constants n and k of As-deposited and illuminated FeTPPCl thin films. Figure 3a and b shows the spectral dependences of the real part of the refractive index, n, and the absorption coefficient, \u03b1, respectively; considering the experimental errors estimated above. The real part of the refractive index exhibits anomalous dispersion in the wavelength region 400\u20131200 nm, a multi-oscillator model (Stendal et al. 1996) can be used in this region of spectra. A normal dispersion is observed in the region 1200\u20132500 nm, a single oscillator model (Wemple and DiDomenico 1971; Wemple 1973) can be used in this region of spectra. It is also found that the illumination leads to film with lower refractive indices which correlated with a decrease of mass density as reported by other workers (Andreas et al. 2005). Also, the decrease in n(\u03bb) is related to decreasing in molecular polarizability (Ksianzou et al. 2006; Zha et al. 2007).\n", "question": "Within what wavelength range is a normal dispersion observed?", "answers": {"text": "1200\u20132500 nm", "answer_start": [577]}}
{"id": "10.1007#s11082-016-0498-x.html_0", "title": "10.1007#s11082-016-0498-x.html", "context": "Influence of electric field on the direct absorption spectra is also studied in this work. In presence of different values of applied electric field, Eigen state solutions are obtained for \u0393-CB, HH and LH band. Energy bands in the QW tilted downwards as shown in Fig. 4a\u2013d. It is observed from these figures that \u0393-CB Eigen wavefunction and HH band Eigen wavefunction shift in opposite direction with increasing electric field. This is due to the opposite charges of carriers in CB and HH band. So, overlap of wave functions in CB and HH band will also change with electric field and it results in changing in absorption coefficient. This can be clearly understood from the plot of absorption coefficient.\n", "question": "Influence of electric field on what is studied in this work?", "answers": {"text": "direct absorption spectra", "answer_start": [35]}}
{"id": "10.1007#s11082-016-0498-x.html_1", "title": "10.1007#s11082-016-0498-x.html", "context": "Influence of electric field on the direct absorption spectra is also studied in this work. In presence of different values of applied electric field, Eigen state solutions are obtained for \u0393-CB, HH and LH band. Energy bands in the QW tilted downwards as shown in Fig. 4a\u2013d. It is observed from these figures that \u0393-CB Eigen wavefunction and HH band Eigen wavefunction shift in opposite direction with increasing electric field. This is due to the opposite charges of carriers in CB and HH band. So, overlap of wave functions in CB and HH band will also change with electric field and it results in changing in absorption coefficient. This can be clearly understood from the plot of absorption coefficient.\n", "question": "Why \u0393-CB Eigen wavefunction and HH band Eigen wavefunction shift in opposite direction with increasing electric field?", "answers": {"text": "opposite charges of carriers in CB and HH band", "answer_start": [447]}}
{"id": "10.1007#s11082-016-0498-x.html_2", "title": "10.1007#s11082-016-0498-x.html", "context": "The electric field dependent absorption coefficient for HH to \u0393-CB transition is also plotted as a function of wavelength and is shown in Fig. 5b. The absorption increases up to 1.2 \u00d7 104 cm\u22121 due to higher oscillator strength of excitonic transition. The peak wavelength of absorption for HH-CB\u0393 transition is redshifted on increasing electric field due to tilting of energy bands as shown in Fig. 4 earlier. Moreover, absorption coefficient reduces due to shifting of \u0393-CB and HH Eigen wave functions in opposite directions which reduces the overlap integral, I (shown in the inset of Fig. 5b). This reduction of absorption with electric field, and shifting of peak absorption wavelength demonstrates quantum confined Stark effect in the well which can enable the design of GeSn based electro absorption modulator for infrared range applications.", "question": "Why does the absorption increase?", "answers": {"text": "higher oscillator strength", "answer_start": [200]}}
{"id": "10.1007#s11082-016-0498-x.html_3", "title": "10.1007#s11082-016-0498-x.html", "context": "In this work, we proposed device structure of a strain balanced SiGeSn/GeSn QWIP and analyzed the absorption spectra in the active layer of the device. Absorption spectra are determined by using Eigen energy states for \u0393-CB, HH band and LH bands and corresponding wave functions. Effect of charge density in the well is considered while obtaining bound states by solving Poisson equation and Schr\u00f6dinger equation self-consistently. Due to compressive strain in the well, HH Eigen energy state is up-shifted and thus HH-\u0393CB transition i.e. TE mode transition dominates. Significant direct interband absorption for HH-\u0393CB transition in Gr-IV material based photodetector is observed in infrared region of wavelengths. Effect of electric field on the energy states, wave functions and hence, on absorption coefficient is also studied by considering the excitonic effect. Peak absorption wavelength shifts towards longer wavelengths with increasing electric field. So, this structure is suitable for low cost, high performance monolithic integrated infrared photodetector. Besides photodetection applications, the proposed model is also viable for electric field dependent modulator.", "question": "Which direction will the peak absorption wavelength shift with increasing electric field?", "answers": {"text": "longer wavelengths", "answer_start": [910]}}
{"id": "10.1007#s11082-016-0499-9.html_0", "title": "10.1007#s11082-016-0499-9.html", "context": "An integrated ormocomp nanowire coated with gold metal layer is proposed and its optical characteristics with the effect of surface plasmon resonance (SPR) are studied. The integrated rib-like nanowire has a trapezoidal shape with sidewall angles of 75\u00b0. It is coated with 50 nm gold layer to introduce the SPR and enhance the evanescent field in the sensing region located at the dielectric/metal interface. The possible field modes, the normalized power confinement, and the SPR peak position of the nanowire are studied over the wavelength and the metal thickness by using the full-vectorial H-field FEM in quasi-TM mode. The attenuation coefficient of the nanowire, the SPR peak wavelength, and the wavelength shift is experimentally extracted for three different cladding materials. The redshift of the supermode coupling between the dielectric mode and the anti-symmetric supermode is observed with the higher cladding-index and larger metal thickness. The improvement of the power confinement in the sensing region with the SPR effect is ten times (10\u00d7) better than a previous similar study.", "question": "What is the sidewall angle of the integrated rib-like nanowire?", "answers": {"text": "75\u00b0", "answer_start": [250]}}
{"id": "10.1007#s11082-016-0499-9.html_1", "title": "10.1007#s11082-016-0499-9.html", "context": "An integrated ormocomp nanowire coated with gold metal layer is proposed and its optical characteristics with the effect of surface plasmon resonance (SPR) are studied. The integrated rib-like nanowire has a trapezoidal shape with sidewall angles of 75\u00b0. It is coated with 50 nm gold layer to introduce the SPR and enhance the evanescent field in the sensing region located at the dielectric/metal interface. The possible field modes, the normalized power confinement, and the SPR peak position of the nanowire are studied over the wavelength and the metal thickness by using the full-vectorial H-field FEM in quasi-TM mode. The attenuation coefficient of the nanowire, the SPR peak wavelength, and the wavelength shift is experimentally extracted for three different cladding materials. The redshift of the supermode coupling between the dielectric mode and the anti-symmetric supermode is observed with the higher cladding-index and larger metal thickness. The improvement of the power confinement in the sensing region with the SPR effect is ten times (10\u00d7) better than a previous similar study.", "question": "What is observed with the higher cladding-index and larger metal thickness?", "answers": {"text": "redshift of the supermode coupling", "answer_start": [792]}}
{"id": "10.1007#s11082-016-0499-9.html_2", "title": "10.1007#s11082-016-0499-9.html", "context": "The design of gold coated polymer nanowires, the characterization of their guided modes using finite element method (FEM) and the experimental measurements of their optical characteristics obtained are presented in the this work. The polymer nanowires examined are considered to be trapezoidal, as shown in Fig. 1a, with their height to be about 0.5 \u03bcm and the top and bottom widths, 1.0 and 1.5 \u03bcm, respectively, with the dimensions of their guided area, being much smaller than the core diameter of single mode fibers (SMF). Therefore, the polymer nanowires with the integrated optics structure are designed in order to minimize the power losses occurred when launching the light from the source into the nanowires. Also, the integrated optics structure allows the nanowires to be easily used with other optical devices for sensing applications. In this paper, the polymer nanowires coated with a thin metal layer are intended to be used as optical transducers to detect the change of effective index when the cladding-index is varied.\n", "question": "What is the height of the polymer nanowires?", "answers": {"text": "0.5 \u03bcm", "answer_start": [346]}}
{"id": "10.1007#s11082-016-0499-9.html_3", "title": "10.1007#s11082-016-0499-9.html", "context": "The design of gold coated polymer nanowires, the characterization of their guided modes using finite element method (FEM) and the experimental measurements of their optical characteristics obtained are presented in the this work. The polymer nanowires examined are considered to be trapezoidal, as shown in Fig. 1a, with their height to be about 0.5 \u03bcm and the top and bottom widths, 1.0 and 1.5 \u03bcm, respectively, with the dimensions of their guided area, being much smaller than the core diameter of single mode fibers (SMF). Therefore, the polymer nanowires with the integrated optics structure are designed in order to minimize the power losses occurred when launching the light from the source into the nanowires. Also, the integrated optics structure allows the nanowires to be easily used with other optical devices for sensing applications. In this paper, the polymer nanowires coated with a thin metal layer are intended to be used as optical transducers to detect the change of effective index when the cladding-index is varied.\n", "question": "What is the top width of the polymer nanowires?", "answers": {"text": "1.0", "answer_start": [384]}}
{"id": "10.1007#s11082-016-0499-9.html_4", "title": "10.1007#s11082-016-0499-9.html", "context": "The design of gold coated polymer nanowires, the characterization of their guided modes using finite element method (FEM) and the experimental measurements of their optical characteristics obtained are presented in the this work. The polymer nanowires examined are considered to be trapezoidal, as shown in Fig. 1a, with their height to be about 0.5 \u03bcm and the top and bottom widths, 1.0 and 1.5 \u03bcm, respectively, with the dimensions of their guided area, being much smaller than the core diameter of single mode fibers (SMF). Therefore, the polymer nanowires with the integrated optics structure are designed in order to minimize the power losses occurred when launching the light from the source into the nanowires. Also, the integrated optics structure allows the nanowires to be easily used with other optical devices for sensing applications. In this paper, the polymer nanowires coated with a thin metal layer are intended to be used as optical transducers to detect the change of effective index when the cladding-index is varied.\n", "question": "What is the bottom width of the polymer nanowires?", "answers": {"text": "1.5 \u03bcm", "answer_start": [392]}}
{"id": "10.1007#s11082-016-0499-9.html_5", "title": "10.1007#s11082-016-0499-9.html", "context": "The design of gold coated polymer nanowires, the characterization of their guided modes using finite element method (FEM) and the experimental measurements of their optical characteristics obtained are presented in the this work. The polymer nanowires examined are considered to be trapezoidal, as shown in Fig. 1a, with their height to be about 0.5 \u03bcm and the top and bottom widths, 1.0 and 1.5 \u03bcm, respectively, with the dimensions of their guided area, being much smaller than the core diameter of single mode fibers (SMF). Therefore, the polymer nanowires with the integrated optics structure are designed in order to minimize the power losses occurred when launching the light from the source into the nanowires. Also, the integrated optics structure allows the nanowires to be easily used with other optical devices for sensing applications. In this paper, the polymer nanowires coated with a thin metal layer are intended to be used as optical transducers to detect the change of effective index when the cladding-index is varied.\n", "question": "What is the polymer nanowires with the integrated optics structure designed for?", "answers": {"text": "minimize the power losses", "answer_start": [622]}}
{"id": "10.1007#s11082-016-0499-9.html_6", "title": "10.1007#s11082-016-0499-9.html", "context": "The ormocomp polymer nanowires were fabricated using the nano-imprint method (Viphavakit et al. 2014a). A silicon nanowire is used as a master mold in the nano-imprint process. The master mold silicon nanowire results in slanted sidewalls from the anisotropic wet etching along the crystal plane. Consequently, the non-vertical sidewalls ormocomp nanowires are considered and their optical imaging and optical properties including the attenuation coefficient are studied. The surface roughness, as a result of the fabrication process, enhances the sensitivity of the non-vertical sidewalls ormocomp nanowires (Viphavakit et al. 2014a). The effect of the surface roughness is not strong enough to maximize the sensitivity of the nanowires. However, the sensitivity can be improved by introducing surface plasmon resonance at the top surface of the nanowires where the evanescent field exists.", "question": "How to improve the sensitivity of the nanowires?", "answers": {"text": "introducing surface plasmon resonance", "answer_start": [783]}}
{"id": "10.1007#s11082-016-0499-9.html_7", "title": "10.1007#s11082-016-0499-9.html", "context": "In this paper, we present the effect of surface plasmon resonance (SPR) to the non-vertical sidewalls ormocomp nanowires. A thin gold layer with the thickness of 50 nm is coated on the nanowires using the sputtering technique. Due to the slanted structure, the gold layer covers both the top surface and the sidewalls. A cross-section of the non-vertical sidewalls nanowire coated with gold layer is presented in Fig. 1a. The ormocomp nanowire structure has height 0.5 \u03bcm. The top and bottom widths of the trapezoidal core are 1.0 and 1.5 \u03bcm, respectively. The ormocomp nanowires have rib-shaped structure due to the leftover ormocomp layer from the stamping process in the nano-imprint (Viphavakit et al. 2014a). The sidewall angle (\u03b8) is measured to be around 75\u00b0. The gold layer at the top surface has a uniform thickness of 50 nm. The nanowires are designed to be easily used with other optical devices, such as optical couplers, by having feed waveguides and tapered waveguides attached to their ends as shown in Fig. 1b.", "question": "What is the thickness of the gold layer that is coated on the nanowires?", "answers": {"text": "50 nm", "answer_start": [162]}}
{"id": "10.1007#s11082-016-0499-9.html_8", "title": "10.1007#s11082-016-0499-9.html", "context": "In this paper, we present the effect of surface plasmon resonance (SPR) to the non-vertical sidewalls ormocomp nanowires. A thin gold layer with the thickness of 50 nm is coated on the nanowires using the sputtering technique. Due to the slanted structure, the gold layer covers both the top surface and the sidewalls. A cross-section of the non-vertical sidewalls nanowire coated with gold layer is presented in Fig. 1a. The ormocomp nanowire structure has height 0.5 \u03bcm. The top and bottom widths of the trapezoidal core are 1.0 and 1.5 \u03bcm, respectively. The ormocomp nanowires have rib-shaped structure due to the leftover ormocomp layer from the stamping process in the nano-imprint (Viphavakit et al. 2014a). The sidewall angle (\u03b8) is measured to be around 75\u00b0. The gold layer at the top surface has a uniform thickness of 50 nm. The nanowires are designed to be easily used with other optical devices, such as optical couplers, by having feed waveguides and tapered waveguides attached to their ends as shown in Fig. 1b.", "question": "How is the gold layer coated on the nanowires?", "answers": {"text": "sputtering technique", "answer_start": [205]}}
{"id": "10.1007#s11082-016-0499-9.html_9", "title": "10.1007#s11082-016-0499-9.html", "context": "where\nH is the full vectorial magnetic field, * represents the complex conjugate and transpose, \u03c9 is the angular frequency of the wave, \u03c9 2 is the eigenvalue, and \u03b5 and \u03bc are the permittivity and permeability, respectively. In this work, 125,000 first order triangles are used to represent the one half of the nanowire structure by exploiting the existing one-fold symmetry. The main advantage of the FEM over the other numerical methods is that it can incorporate triangles of different shapes and sizes to achieve numerical efficiency. In our case, vertical resolution of 0.8 nm or better is achieved for the 50 nm thick metal layer.", "question": "How many first order triangles are used to represent the one half of the nanowire structure?", "answers": {"text": "125,000", "answer_start": [238]}}
{"id": "10.1007#s11082-016-0499-9.html_10", "title": "10.1007#s11082-016-0499-9.html", "context": "where\nH is the full vectorial magnetic field, * represents the complex conjugate and transpose, \u03c9 is the angular frequency of the wave, \u03c9 2 is the eigenvalue, and \u03b5 and \u03bc are the permittivity and permeability, respectively. In this work, 125,000 first order triangles are used to represent the one half of the nanowire structure by exploiting the existing one-fold symmetry. The main advantage of the FEM over the other numerical methods is that it can incorporate triangles of different shapes and sizes to achieve numerical efficiency. In our case, vertical resolution of 0.8 nm or better is achieved for the 50 nm thick metal layer.", "question": "What resolution is ahieved for the 50 nm thick metal layer?", "answers": {"text": "0.8 nm", "answer_start": [574]}}
{"id": "10.1007#s11082-016-0499-9.html_11", "title": "10.1007#s11082-016-0499-9.html", "context": "The two possible optical modes in the nanowire structures are the dielectric mode inside ormocomp region and the plasmonic mode at the dielectric/metal interface. These two modes can be clearly separated or coupled with each other to create a supermode depending on the parameters of the nanowire structure, especially the height of the nanowire. In the case of nanowires with height 0.5 \u03bcm, the coupled dielectric-plasmonic mode is shown in Fig. 3, where the supermode coupling between the dielectric mode and the odd-like plasmonic supermode can be clearly seen from the Hx profile along the y-direction. The inset shows the Hx-field contour plot of the coupled mode with water cladding.\n", "question": "What are the two possible optical modes in the nanowire structures?", "answers": {"text": "dielectric mode inside ormocomp region and the plasmonic mode", "answer_start": [66]}}
{"id": "10.1007#s11082-016-0499-9.html_12", "title": "10.1007#s11082-016-0499-9.html", "context": "Variations of the effective indices of the fundamental Hx modes in three different cladding mediums with respect to the operating wavelength are shown in Fig. 4. The effective indices of the optical mode decrease when the wavelength is increased regardless of the cladding-index because the wavelength becomes larger compared to the dimension of the nanowire. However, from the characteristics of the effective indices, particularly the peak at some specific wavelengths, it can be used to identify the SPR wavelengths. Effective index of the plasmonic mode is normally higher than that of the fundamental dielectric mode. Hence, the effective index of the coupled dielectric-plasmonic mode occurring at a certain wavelength is slightly higher than that of the dielectric mode alone.\n", "question": "What can the characteristics of the effective indices be used to identify?", "answers": {"text": "SPR wavelengths", "answer_start": [503]}}
{"id": "10.1007#s11082-016-0499-9.html_13", "title": "10.1007#s11082-016-0499-9.html", "context": "The experimental results presented below include the extraction of the attenuation coefficient of the ormocomp nanowires (\u03b1  nw ) and the analysis of the SPR peak and its shift with the use of different cladding materials. The actual nanowires used in the experiment were fabricated using the nano-imprint method (Viphavakit et al.). The gold layer is coated on the ormocomp nanowires using the sputtering technique. The cladding materials are water (n = 1.333) and two iso-propanol solutions. The iso-propanol solution is a mixture of water and iso-propanol. For this paper, iso-propanol solutions with two different volume ratios, 1:1 and 1:3, are used, yielding refractive indices of 1.365 and 1.351, respectively. The light source used in this experiment is a broadband light source where the operating wavelength is in visible wavelength (\u03bb = 400\u2013700 nm).", "question": "What is the refractive index of water?", "answers": {"text": "1.333", "answer_start": [455]}}
{"id": "10.1007#s11082-016-0499-9.html_14", "title": "10.1007#s11082-016-0499-9.html", "context": "The experimental results presented below include the extraction of the attenuation coefficient of the ormocomp nanowires (\u03b1  nw ) and the analysis of the SPR peak and its shift with the use of different cladding materials. The actual nanowires used in the experiment were fabricated using the nano-imprint method (Viphavakit et al.). The gold layer is coated on the ormocomp nanowires using the sputtering technique. The cladding materials are water (n = 1.333) and two iso-propanol solutions. The iso-propanol solution is a mixture of water and iso-propanol. For this paper, iso-propanol solutions with two different volume ratios, 1:1 and 1:3, are used, yielding refractive indices of 1.365 and 1.351, respectively. The light source used in this experiment is a broadband light source where the operating wavelength is in visible wavelength (\u03bb = 400\u2013700 nm).", "question": "What is the visible wavelength?", "answers": {"text": "400\u2013700 nm", "answer_start": [848]}}
{"id": "10.1007#s11082-016-0499-9.html_15", "title": "10.1007#s11082-016-0499-9.html", "context": "The average attenuation coefficient of the nanowires (dashed line) and the feed waveguides (solid line) is presented in Fig. 9. The absorption peak for both the feed waveguide and the nanowires are found to occur at \u03bb = 590 nm. The feed waveguide has absorption coefficient of \u03b1  wg  = 1.03 \u00d7 10\u22124 \u03bcm\u22121, which is lower than the absorption coefficient of the nanowires \u03b1  nw  = 1.93 \u00d7 10\u22124 \u03bcm\u22121, since the feed waveguides are multimode and the nanowires are single mode waveguides. In the multimode waveguide the power is distributed in many modes, causing a reduction of optical power in each mode. In addition, each mode has different SPR momentum. Therefore, the absorption peak of the SPR in each mode is located at different wavelength, causing the broadening of the absorption peak in the feed waveguide.", "question": "What is the absorption peak for the feed waveguide?", "answers": {"text": "590 nm", "answer_start": [220]}}
{"id": "10.1007#s11082-016-0499-9.html_16", "title": "10.1007#s11082-016-0499-9.html", "context": "The average attenuation coefficient of the nanowires (dashed line) and the feed waveguides (solid line) is presented in Fig. 9. The absorption peak for both the feed waveguide and the nanowires are found to occur at \u03bb = 590 nm. The feed waveguide has absorption coefficient of \u03b1  wg  = 1.03 \u00d7 10\u22124 \u03bcm\u22121, which is lower than the absorption coefficient of the nanowires \u03b1  nw  = 1.93 \u00d7 10\u22124 \u03bcm\u22121, since the feed waveguides are multimode and the nanowires are single mode waveguides. In the multimode waveguide the power is distributed in many modes, causing a reduction of optical power in each mode. In addition, each mode has different SPR momentum. Therefore, the absorption peak of the SPR in each mode is located at different wavelength, causing the broadening of the absorption peak in the feed waveguide.", "question": "What is the absorption peak for the nanowires?", "answers": {"text": "590 nm", "answer_start": [220]}}
{"id": "10.1007#s11082-016-0499-9.html_17", "title": "10.1007#s11082-016-0499-9.html", "context": "As described earlier in the previous section, the optical modes examined in the nanowires are the coupled supermode between the dielectric mode and the plasmonic mode. In addition, the plasmonic mode itself is also a supermode due to coupling between two surface plasmon modes at the ormocomp/gold and cladding/gold interfaces. It is sensitive to the change of the cladding index which can be studied by investigating the wavelength shift with different refractive indices of cladding materials. The cladding materials used in this study are water (n = 1.333), and the iso-propanol solutions. The solutions are prepared with different volume ratio of iso-propanol to water. With 1:1 volume ratio, the solution has refractive index of 1.365 and the index of 1.351 is measured for the ratio of 1:3. The transmittance is measured again for different cladding materials. Then, the attenuation coefficient of a nanowire showing the SPR peak wavelength for three cladding materials is illustrated in Fig. 10.\n", "question": "Why is the plasmonic mode itself also a supermode?", "answers": {"text": "coupling between two surface plasmon modes", "answer_start": [234]}}
{"id": "10.1007#s11082-016-0499-9.html_18", "title": "10.1007#s11082-016-0499-9.html", "context": "As described earlier in the previous section, the optical modes examined in the nanowires are the coupled supermode between the dielectric mode and the plasmonic mode. In addition, the plasmonic mode itself is also a supermode due to coupling between two surface plasmon modes at the ormocomp/gold and cladding/gold interfaces. It is sensitive to the change of the cladding index which can be studied by investigating the wavelength shift with different refractive indices of cladding materials. The cladding materials used in this study are water (n = 1.333), and the iso-propanol solutions. The solutions are prepared with different volume ratio of iso-propanol to water. With 1:1 volume ratio, the solution has refractive index of 1.365 and the index of 1.351 is measured for the ratio of 1:3. The transmittance is measured again for different cladding materials. Then, the attenuation coefficient of a nanowire showing the SPR peak wavelength for three cladding materials is illustrated in Fig. 10.\n", "question": "What is the refractive index of water?", "answers": {"text": "1.333", "answer_start": [553]}}
{"id": "10.1007#s11082-016-0499-9.html_19", "title": "10.1007#s11082-016-0499-9.html", "context": "The average SPR peak wavelength for those three cladding materials is shown in Fig. 11. The comparison of the peak position between the simulation and experimental results is also presented in Fig. 11. From the experimental work, the SPR peak wavelength for the water cladding (n = 1.333) was found to be about \u03bb = 578 \u00b1 0.5 nm. For iso-propanol solution cladding with refractive index of 1.351 the peak position is at \u03bb = 590 \u00b1 0.9 nm. For the largest cladding-index in this work (n = 1.365), the SPR is observed at the wavelength of \u03bb = 595 \u00b1 1.7 nm. The SPR peak from the experiment is compared with the 55 nm gold-coated nanowire in the simulation. The comparison shows the same trend of the peak redshift with the cladding index. However, the effect from the large surface roughness due to the fabrication process has to be taken into account for the experimental works. The surface roughness of the nanowire is about 0.1\u20130.2 \u03bcm as shown in the inset of Fig. 11.\n", "question": "What is the surface roughness of the nanowire?", "answers": {"text": "0.1\u20130.2 \u03bcm", "answer_start": [923]}}
{"id": "10.1007#s11082-016-0499-9.html_20", "title": "10.1007#s11082-016-0499-9.html", "context": "The average SPR peak wavelength for those three cladding materials is shown in Fig. 11. The comparison of the peak position between the simulation and experimental results is also presented in Fig. 11. From the experimental work, the SPR peak wavelength for the water cladding (n = 1.333) was found to be about \u03bb = 578 \u00b1 0.5 nm. For iso-propanol solution cladding with refractive index of 1.351 the peak position is at \u03bb = 590 \u00b1 0.9 nm. For the largest cladding-index in this work (n = 1.365), the SPR is observed at the wavelength of \u03bb = 595 \u00b1 1.7 nm. The SPR peak from the experiment is compared with the 55 nm gold-coated nanowire in the simulation. The comparison shows the same trend of the peak redshift with the cladding index. However, the effect from the large surface roughness due to the fabrication process has to be taken into account for the experimental works. The surface roughness of the nanowire is about 0.1\u20130.2 \u03bcm as shown in the inset of Fig. 11.\n", "question": "What is the refractive index of iso-propanol?", "answers": {"text": "1.351", "answer_start": [389]}}
{"id": "10.1007#s11082-016-0499-9.html_21", "title": "10.1007#s11082-016-0499-9.html", "context": "The average SPR peak wavelength for those three cladding materials is shown in Fig. 11. The comparison of the peak position between the simulation and experimental results is also presented in Fig. 11. From the experimental work, the SPR peak wavelength for the water cladding (n = 1.333) was found to be about \u03bb = 578 \u00b1 0.5 nm. For iso-propanol solution cladding with refractive index of 1.351 the peak position is at \u03bb = 590 \u00b1 0.9 nm. For the largest cladding-index in this work (n = 1.365), the SPR is observed at the wavelength of \u03bb = 595 \u00b1 1.7 nm. The SPR peak from the experiment is compared with the 55 nm gold-coated nanowire in the simulation. The comparison shows the same trend of the peak redshift with the cladding index. However, the effect from the large surface roughness due to the fabrication process has to be taken into account for the experimental works. The surface roughness of the nanowire is about 0.1\u20130.2 \u03bcm as shown in the inset of Fig. 11.\n", "question": "At which wavelength is the SPR observed for the largest cladding-index in this work?", "answers": {"text": "595 \u00b1 1.7 nm", "answer_start": [539]}}
{"id": "10.1007#s11082-016-0507-0.html_0", "title": "10.1007#s11082-016-0507-0.html", "context": "Even though very similar to graphite in the lattice structure and parameters, hexagonal boron nitride materials possess quite different properties and have been attracted extensive studies (Du et al. 2009; Topsakal et al. 2009; Beiranvanda and Valedbagiba 2015, 2016; Wang et al. 2011; Wu et al. 2014). Based on the density functional theory (DFT) Beiranvand et al. investigated the electronic and optical properties of hexagonal BN (h-BN), h-AlN and h-GaN nanosheets in parallel and perpendicular electric field polarizations and found that the hexagonal XN (X=B, Al and Ga) are semiconductors with wide band gap of about 4.96, 2.73 and 1.95 eV, respectively. Moreover, the optical spectra are isotropic along these two polarizations and the optical conductivities in two directions start with different gaps (Beiranvanda and Valedbagiba 2015, 2016). Using the first-principles calculations Wang et al. studied the electronic and optical properties of quasi-one-dimensiona BN nanomaterials, that is BN nanoribbons (BNNRs), and show that the reduced dimensionality as well as the wide band gaps of the BNNRs significantly enhances the exciton binding energies up to several eV. Moreover, the absorption spectra of zigzag BNNRs (ZBNNRs) distinctly differ from those of armchair BNNRs (ABNNRs) (Wang et al. 2011).", "question": "What is the band gap of BN?", "answers": {"text": "4.96", "answer_start": [623]}}
{"id": "10.1007#s11082-016-0507-0.html_1", "title": "10.1007#s11082-016-0507-0.html", "context": "Even though very similar to graphite in the lattice structure and parameters, hexagonal boron nitride materials possess quite different properties and have been attracted extensive studies (Du et al. 2009; Topsakal et al. 2009; Beiranvanda and Valedbagiba 2015, 2016; Wang et al. 2011; Wu et al. 2014). Based on the density functional theory (DFT) Beiranvand et al. investigated the electronic and optical properties of hexagonal BN (h-BN), h-AlN and h-GaN nanosheets in parallel and perpendicular electric field polarizations and found that the hexagonal XN (X=B, Al and Ga) are semiconductors with wide band gap of about 4.96, 2.73 and 1.95 eV, respectively. Moreover, the optical spectra are isotropic along these two polarizations and the optical conductivities in two directions start with different gaps (Beiranvanda and Valedbagiba 2015, 2016). Using the first-principles calculations Wang et al. studied the electronic and optical properties of quasi-one-dimensiona BN nanomaterials, that is BN nanoribbons (BNNRs), and show that the reduced dimensionality as well as the wide band gaps of the BNNRs significantly enhances the exciton binding energies up to several eV. Moreover, the absorption spectra of zigzag BNNRs (ZBNNRs) distinctly differ from those of armchair BNNRs (ABNNRs) (Wang et al. 2011).", "question": "What is the band gap of h-AlN?", "answers": {"text": "2.73", "answer_start": [629]}}
{"id": "10.1007#s11082-016-0507-0.html_2", "title": "10.1007#s11082-016-0507-0.html", "context": "Even though very similar to graphite in the lattice structure and parameters, hexagonal boron nitride materials possess quite different properties and have been attracted extensive studies (Du et al. 2009; Topsakal et al. 2009; Beiranvanda and Valedbagiba 2015, 2016; Wang et al. 2011; Wu et al. 2014). Based on the density functional theory (DFT) Beiranvand et al. investigated the electronic and optical properties of hexagonal BN (h-BN), h-AlN and h-GaN nanosheets in parallel and perpendicular electric field polarizations and found that the hexagonal XN (X=B, Al and Ga) are semiconductors with wide band gap of about 4.96, 2.73 and 1.95 eV, respectively. Moreover, the optical spectra are isotropic along these two polarizations and the optical conductivities in two directions start with different gaps (Beiranvanda and Valedbagiba 2015, 2016). Using the first-principles calculations Wang et al. studied the electronic and optical properties of quasi-one-dimensiona BN nanomaterials, that is BN nanoribbons (BNNRs), and show that the reduced dimensionality as well as the wide band gaps of the BNNRs significantly enhances the exciton binding energies up to several eV. Moreover, the absorption spectra of zigzag BNNRs (ZBNNRs) distinctly differ from those of armchair BNNRs (ABNNRs) (Wang et al. 2011).", "question": "What is the band gap of h-GaN?", "answers": {"text": "1.95 eV", "answer_start": [638]}}
{"id": "10.1007#s11082-016-0507-0.html_3", "title": "10.1007#s11082-016-0507-0.html", "context": "Unlike the zero band gap semiconducting graphene, boron nitride single atomic layer sheet is a broadband gap (about 6 eV) semiconductor material. What is more, like graphene nanoribbons (GNRs), ZBNNRs and ABNNRs present a strong quantum confined effect due to electronic and magnetic properties anisotropy arising from the edge effect. Usually bare (also named dangling bonds) BNNRs are unstable in thermodynamics and more prone to refactoring. Zheng et al. (2011) investigated the electronic and magnetic properties of BNNRs with dangling bond and found that the dangling bond give rise to crucial changes in the electronic distribution and thus modifies the electronic structure as well as the electronic properties. Moreover, the edge nitrogen atoms tend to ferromagnetic coupling mode and the edge boron atoms tend to anti ferromagnetic coupling mode when two edges of the BNNR are bare (Wu et al. 2009). Zeng et al. (2010) produced few- and single-layered ZBNNRs under unwrapping multiwalled BN nanotubes through plasma etching and using the ab initio simulations they found that BNNRs become semiconducting due to doping-like conducting edge states and vacancy defects.", "question": "Why do ZBNNRs and ABNNRs present a strong quantum confined effect?", "answers": {"text": "electronic and magnetic properties anisotropy", "answer_start": [260]}}
{"id": "10.1007#s11082-016-0507-0.html_4", "title": "10.1007#s11082-016-0507-0.html", "context": "Fluorine (F) atom has the strongest electronegativity and thus bonding easily with B or N. Our theoretical studies show that the band gap of F-passivated BNNRs (BNNRs-F) is lower than that of the H-passivated one with the same ribbon width because of the mixing effects from the non-bonding 2p electrons of F and N atoms. That is the electronic properties of the BNNRs can be modulated by the passivated F atom (Lu et al. 2012). However, to the best of our knowledge, the effects of the passivated F atom on the optical properties of BNNRs have rarely been theoretically explored. Therefore, in this work we focus on the optical properties of the ZBNNRs-F and ABNNRs-F. It is important to explore the optical properties of the BNNRs for the potential applications of optoelectronic nanodevices.", "question": "What can modulate the electronic properties of the BNNRs?", "answers": {"text": "passivated F atom", "answer_start": [393]}}
{"id": "10.1007#s11082-016-0507-0.html_5", "title": "10.1007#s11082-016-0507-0.html", "context": "We ask the most popular material simulation and computational software VASP to achieve the computation. The electron-ionic core interaction is represented by the projector augmented wave (PAW) potentials (Kresse and Joubert 1999). The Perdew\u2013Burke\u2013Ernzerhof (PBE) (Perdew et al. 1996) formulation of the GGA was chosen to treat electron exchange and correlation. A generalized gradient approximation (GGA) is used to relax the ions into their ground states, and the energies are converged within 1.0 \u00d7 10\u22124 eV/atom. The cutoff energy for the plane-waves is chosen to be 450 eV. In order to simulate infinite long isolated single-layer BNNRs, we use a supercell geometry where each plane is separated from its replica by 20 \u00c5 in both edge-to-edge and layer-to-layer directions. The periodicity of the BNNRs was set to along the ribbon axis. The sampled k points 1 \u00d7 11 \u00d7 1 in the Brillouin zone is carried out by the Monkhorst\u2013Pack scheme during geometry optimization with 0.02 eV/\u00c5, together with a Gaussian smearing broadening of 0.2 eV, and 1 \u00d7 20 \u00d7 1 are used to obtain the electronic properties.", "question": "What is used to relax the ions into their ground states?", "answers": {"text": "generalized gradient approximation (GGA)", "answer_start": [365]}}
{"id": "10.1007#s11082-016-0507-0.html_6", "title": "10.1007#s11082-016-0507-0.html", "context": "We ask the most popular material simulation and computational software VASP to achieve the computation. The electron-ionic core interaction is represented by the projector augmented wave (PAW) potentials (Kresse and Joubert 1999). The Perdew\u2013Burke\u2013Ernzerhof (PBE) (Perdew et al. 1996) formulation of the GGA was chosen to treat electron exchange and correlation. A generalized gradient approximation (GGA) is used to relax the ions into their ground states, and the energies are converged within 1.0 \u00d7 10\u22124 eV/atom. The cutoff energy for the plane-waves is chosen to be 450 eV. In order to simulate infinite long isolated single-layer BNNRs, we use a supercell geometry where each plane is separated from its replica by 20 \u00c5 in both edge-to-edge and layer-to-layer directions. The periodicity of the BNNRs was set to along the ribbon axis. The sampled k points 1 \u00d7 11 \u00d7 1 in the Brillouin zone is carried out by the Monkhorst\u2013Pack scheme during geometry optimization with 0.02 eV/\u00c5, together with a Gaussian smearing broadening of 0.2 eV, and 1 \u00d7 20 \u00d7 1 are used to obtain the electronic properties.", "question": "How do we treat electron exchange and correlation in our simulation?", "answers": {"text": "Perdew\u2013Burke\u2013Ernzerhof (PBE)", "answer_start": [235]}}
{"id": "10.1007#s11082-016-0507-0.html_7", "title": "10.1007#s11082-016-0507-0.html", "context": "We ask the most popular material simulation and computational software VASP to achieve the computation. The electron-ionic core interaction is represented by the projector augmented wave (PAW) potentials (Kresse and Joubert 1999). The Perdew\u2013Burke\u2013Ernzerhof (PBE) (Perdew et al. 1996) formulation of the GGA was chosen to treat electron exchange and correlation. A generalized gradient approximation (GGA) is used to relax the ions into their ground states, and the energies are converged within 1.0 \u00d7 10\u22124 eV/atom. The cutoff energy for the plane-waves is chosen to be 450 eV. In order to simulate infinite long isolated single-layer BNNRs, we use a supercell geometry where each plane is separated from its replica by 20 \u00c5 in both edge-to-edge and layer-to-layer directions. The periodicity of the BNNRs was set to along the ribbon axis. The sampled k points 1 \u00d7 11 \u00d7 1 in the Brillouin zone is carried out by the Monkhorst\u2013Pack scheme during geometry optimization with 0.02 eV/\u00c5, together with a Gaussian smearing broadening of 0.2 eV, and 1 \u00d7 20 \u00d7 1 are used to obtain the electronic properties.", "question": "What is the cutoff energy for the plane-waves?", "answers": {"text": "450 eV", "answer_start": [570]}}
{"id": "10.1007#s11082-016-0507-0.html_8", "title": "10.1007#s11082-016-0507-0.html", "context": "We ask the most popular material simulation and computational software VASP to achieve the computation. The electron-ionic core interaction is represented by the projector augmented wave (PAW) potentials (Kresse and Joubert 1999). The Perdew\u2013Burke\u2013Ernzerhof (PBE) (Perdew et al. 1996) formulation of the GGA was chosen to treat electron exchange and correlation. A generalized gradient approximation (GGA) is used to relax the ions into their ground states, and the energies are converged within 1.0 \u00d7 10\u22124 eV/atom. The cutoff energy for the plane-waves is chosen to be 450 eV. In order to simulate infinite long isolated single-layer BNNRs, we use a supercell geometry where each plane is separated from its replica by 20 \u00c5 in both edge-to-edge and layer-to-layer directions. The periodicity of the BNNRs was set to along the ribbon axis. The sampled k points 1 \u00d7 11 \u00d7 1 in the Brillouin zone is carried out by the Monkhorst\u2013Pack scheme during geometry optimization with 0.02 eV/\u00c5, together with a Gaussian smearing broadening of 0.2 eV, and 1 \u00d7 20 \u00d7 1 are used to obtain the electronic properties.", "question": "How far is each plane seperated from its replica in the supercell geometry?", "answers": {"text": "20 \u00c5", "answer_start": [720]}}
{"id": "10.1007#s11082-016-0518-x.html_0", "title": "10.1007#s11082-016-0518-x.html", "context": "Piezoelectric composites of PU/PZT with 0\u20133 connectivity were prepared in the film form. Homogeneous dispersion of the ceramic PZT in polyurethane matrix has been obtained and has been verified by SEM analysis. Dielectric properties reveal that under an electrical field of 1000 V the remnant polarization increased from 1.9 to 4 \u03bcC/cm\u22122 when the volume fraction of PZT increased from 50 to 80 %. Modeling and vibratory energy harvesting tests has been realized. At very low frequency and deformation, and without application of any static electric field, 1.15 \u03bcW of power has been obtained. The results obtained in this work contribute to demonstrate the ability of the incorporation of PZT particles in the polymer matrix to improve the conversion efficiency of the vibratory energy into electrical energy for the development of \u03bc-generators.", "question": "How much power has been obtained at very low frequency and deformation?", "answers": {"text": "1.15 \u03bcW", "answer_start": [556]}}
{"id": "10.1007#s11082-016-0518-x.html_1", "title": "10.1007#s11082-016-0518-x.html", "context": "Recent advance in Micro Electro Mechanical Systems and other fields of technology have led to the fabrication of low cost and low power consumption sensors (Kim et al. 2007). Today, many sensing systems can operate efficiently without significant power requirements (Baerta et al. 2006). Unfortunately, effective usage of these sensors is currently being limited by their power sources, usually batteries that have fixed storage capacity and low energy density. To overcome this problem, many research studies are currently being directed toward harvesting energy from the ambient environment. The vibratory energy harvesting is one of the methods developed to transform mechanical motions directly into electricity. This realized by exploiting the ability of some active materials to generate an electric potential in response to external vibrations (Sodano et al. 2004; Stephen 2006).", "question": "What limites the effective usage of the low cost and low power consumption sensors?", "answers": {"text": "power sources", "answer_start": [372]}}
{"id": "10.1007#s11082-016-0518-x.html_2", "title": "10.1007#s11082-016-0518-x.html", "context": "The PU/PZT composites were prepared by solution casting. Polyurethane was dissolved in tetrahydrofurane (THF) and the PZT was added in the second step. Ultrasonic agitation was used to disperse the powder in the matrix. The composite films were fabricated by tape casting method which is a ceramic forming technique, and dried in the open air during 12 h. Composites with volume fraction ranging from 50 vol% PZT to 80 vol% PZT were fabricated with a thickness around 40\u201380 \u03bcm. Gold electrodes were sputtered onto both sides of the specimens. The distribution of PZT powder inside the polymer matrix was investigated by the Scanning Electron Microscope (SEM, HITACHI S3000-N). The samples were electroded with chromium\u2013gold by evaporation for subsequent measurements. Thermal properties of the composites were analyzed by using Differential Scanning Calorimetry (131evo, Setaram).", "question": "What instrument was used to investigate the distribution of PZT powder inside the polymer matrix?", "answers": {"text": "Scanning Electron Microscope", "answer_start": [624]}}
{"id": "10.1007#s11082-016-0518-x.html_3", "title": "10.1007#s11082-016-0518-x.html", "context": "The PU/PZT composites were prepared by solution casting. Polyurethane was dissolved in tetrahydrofurane (THF) and the PZT was added in the second step. Ultrasonic agitation was used to disperse the powder in the matrix. The composite films were fabricated by tape casting method which is a ceramic forming technique, and dried in the open air during 12 h. Composites with volume fraction ranging from 50 vol% PZT to 80 vol% PZT were fabricated with a thickness around 40\u201380 \u03bcm. Gold electrodes were sputtered onto both sides of the specimens. The distribution of PZT powder inside the polymer matrix was investigated by the Scanning Electron Microscope (SEM, HITACHI S3000-N). The samples were electroded with chromium\u2013gold by evaporation for subsequent measurements. Thermal properties of the composites were analyzed by using Differential Scanning Calorimetry (131evo, Setaram).", "question": "What were the samples electroded?", "answers": {"text": "chromium\u2013gold", "answer_start": [710]}}
{"id": "10.1007#s11082-016-0518-x.html_4", "title": "10.1007#s11082-016-0518-x.html", "context": "The PU/PZT composites were prepared by solution casting. Polyurethane was dissolved in tetrahydrofurane (THF) and the PZT was added in the second step. Ultrasonic agitation was used to disperse the powder in the matrix. The composite films were fabricated by tape casting method which is a ceramic forming technique, and dried in the open air during 12 h. Composites with volume fraction ranging from 50 vol% PZT to 80 vol% PZT were fabricated with a thickness around 40\u201380 \u03bcm. Gold electrodes were sputtered onto both sides of the specimens. The distribution of PZT powder inside the polymer matrix was investigated by the Scanning Electron Microscope (SEM, HITACHI S3000-N). The samples were electroded with chromium\u2013gold by evaporation for subsequent measurements. Thermal properties of the composites were analyzed by using Differential Scanning Calorimetry (131evo, Setaram).", "question": "How were the samples electroded with chromium\u2013gold?", "answers": {"text": "by evaporation", "answer_start": [727]}}
{"id": "10.1007#s11082-016-0518-x.html_5", "title": "10.1007#s11082-016-0518-x.html", "context": "The PU/PZT composites were prepared by solution casting. Polyurethane was dissolved in tetrahydrofurane (THF) and the PZT was added in the second step. Ultrasonic agitation was used to disperse the powder in the matrix. The composite films were fabricated by tape casting method which is a ceramic forming technique, and dried in the open air during 12 h. Composites with volume fraction ranging from 50 vol% PZT to 80 vol% PZT were fabricated with a thickness around 40\u201380 \u03bcm. Gold electrodes were sputtered onto both sides of the specimens. The distribution of PZT powder inside the polymer matrix was investigated by the Scanning Electron Microscope (SEM, HITACHI S3000-N). The samples were electroded with chromium\u2013gold by evaporation for subsequent measurements. Thermal properties of the composites were analyzed by using Differential Scanning Calorimetry (131evo, Setaram).", "question": "How were the thermal properties of the composites analyzed?", "answers": {"text": "Differential Scanning Calorimetry", "answer_start": [828]}}
{"id": "10.1007#s11082-016-0518-x.html_6", "title": "10.1007#s11082-016-0518-x.html", "context": "The PU/PZT composites were prepared by solution casting. Polyurethane was dissolved in tetrahydrofurane (THF) and the PZT was added in the second step. Ultrasonic agitation was used to disperse the powder in the matrix. The composite films were fabricated by tape casting method which is a ceramic forming technique, and dried in the open air during 12 h. Composites with volume fraction ranging from 50 vol% PZT to 80 vol% PZT were fabricated with a thickness around 40\u201380 \u03bcm. Gold electrodes were sputtered onto both sides of the specimens. The distribution of PZT powder inside the polymer matrix was investigated by the Scanning Electron Microscope (SEM, HITACHI S3000-N). The samples were electroded with chromium\u2013gold by evaporation for subsequent measurements. Thermal properties of the composites were analyzed by using Differential Scanning Calorimetry (131evo, Setaram).", "question": "What was the polyurethane dissolved?", "answers": {"text": "tetrahydrofurane", "answer_start": [87]}}
{"id": "10.1007#s11082-016-0518-x.html_7", "title": "10.1007#s11082-016-0518-x.html", "context": "In the second part of this work, energy harvesting tests were realized. Figure 1 provides a schematic representation of the setup used (Belhora et al. 2012) in order to characterize the power harvested by the PU/PZT composites. This structure was mounted on a test rig comprising an immobile part and a second part that could be moved in the 1-direction with the help of an XM550 ironless linear motor (Newport Cop., Irvine, CA). As a consequence, the film was driven with a given strain profile and assumed to be strained along the 1-direction. The generated stress was measured with the help of a force sensor (ELPF-T2M-250N, Measurement Specialities, Paris). In order to simplify the study, the measurements were performed under harmonic excitation. The pseudo-piezoelectric responses, which corresponded to the current generated when a strain was applied, were measured by a current amplifier (SR 570, Stanford Research Systems Inc, Sunnyvale, CA, USA).\n", "question": "What instrument was the generated stress measured by?", "answers": {"text": "force sensor", "answer_start": [599]}}
{"id": "10.1007#s11082-016-0518-x.html_8", "title": "10.1007#s11082-016-0518-x.html", "context": "Thermal properties of pure polyurethane, PU/PZT 60 vol% and PU/PZT 80 vol% are shown in (Fig. 3). It can be seen that the values of glass transition (Tg) move toward lower values. The value of \u221245.1 \u00b0C is obtained for polyurethane and \u221266.2 \u00b0C is obtained for the composite with 80 % vol. Melting temperature (TII\u2013TIII) illustrated in (Table 1) shows a disappearance of the two picks at 144 and 158 \u00b0C initially obtained for pure polyurethane. The disappearance of these picks is due to the disappearance of the two crystallized segments of PU. Melting temperature of PU/PZT 60 vol% was 150 \u00b0C. 145 \u00b0C was observed for PU/PZT 80 vol% composite. Concerning PU/PZT 70 vol% composite a new phenomenon was observed. It is a cold re-crystallization. It was obtained at 145 \u00b0C. This phenomenon indicates that the composite PU/PZT prepared, was amorphous and it was due to the reorganization of the molecules of PU under temperature effect. Finally, it can be observed on cooling an exothermic peak close to 55\u2013155 \u00b0C due to the re-crystallization phenomenon. The allure of this peak indicates the strong diminution of the crystalline phase of these composites.\n", "question": "Why was the composite PU/PZT amorphous?", "answers": {"text": "reorganization of the molecules of PU", "answer_start": [870]}}
{"id": "10.1007#s11082-016-0518-x.html_9", "title": "10.1007#s11082-016-0518-x.html", "context": "Thermal properties of pure polyurethane, PU/PZT 60 vol% and PU/PZT 80 vol% are shown in (Fig. 3). It can be seen that the values of glass transition (Tg) move toward lower values. The value of \u221245.1 \u00b0C is obtained for polyurethane and \u221266.2 \u00b0C is obtained for the composite with 80 % vol. Melting temperature (TII\u2013TIII) illustrated in (Table 1) shows a disappearance of the two picks at 144 and 158 \u00b0C initially obtained for pure polyurethane. The disappearance of these picks is due to the disappearance of the two crystallized segments of PU. Melting temperature of PU/PZT 60 vol% was 150 \u00b0C. 145 \u00b0C was observed for PU/PZT 80 vol% composite. Concerning PU/PZT 70 vol% composite a new phenomenon was observed. It is a cold re-crystallization. It was obtained at 145 \u00b0C. This phenomenon indicates that the composite PU/PZT prepared, was amorphous and it was due to the reorganization of the molecules of PU under temperature effect. Finally, it can be observed on cooling an exothermic peak close to 55\u2013155 \u00b0C due to the re-crystallization phenomenon. The allure of this peak indicates the strong diminution of the crystalline phase of these composites.\n", "question": "At what temperature can an exothermic peak be observed on cooling?", "answers": {"text": "55\u2013155 \u00b0C", "answer_start": [1001]}}
{"id": "10.1007#s11082-016-0518-x.html_10", "title": "10.1007#s11082-016-0518-x.html", "context": "Thermal properties of pure polyurethane, PU/PZT 60 vol% and PU/PZT 80 vol% are shown in (Fig. 3). It can be seen that the values of glass transition (Tg) move toward lower values. The value of \u221245.1 \u00b0C is obtained for polyurethane and \u221266.2 \u00b0C is obtained for the composite with 80 % vol. Melting temperature (TII\u2013TIII) illustrated in (Table 1) shows a disappearance of the two picks at 144 and 158 \u00b0C initially obtained for pure polyurethane. The disappearance of these picks is due to the disappearance of the two crystallized segments of PU. Melting temperature of PU/PZT 60 vol% was 150 \u00b0C. 145 \u00b0C was observed for PU/PZT 80 vol% composite. Concerning PU/PZT 70 vol% composite a new phenomenon was observed. It is a cold re-crystallization. It was obtained at 145 \u00b0C. This phenomenon indicates that the composite PU/PZT prepared, was amorphous and it was due to the reorganization of the molecules of PU under temperature effect. Finally, it can be observed on cooling an exothermic peak close to 55\u2013155 \u00b0C due to the re-crystallization phenomenon. The allure of this peak indicates the strong diminution of the crystalline phase of these composites.\n", "question": "Why an exothermic peak close to 55\u2013155 \u00b0C on cooling can be observed?", "answers": {"text": "re-crystallization phenomenon", "answer_start": [1022]}}
{"id": "10.1007#s11082-016-0518-x.html_11", "title": "10.1007#s11082-016-0518-x.html", "context": "The hysteresis loops of the PU/PZT composites with different volume fraction are shown in (Fig. 4). For comparison, the hysteresis loop of the pure polymer was also shown. The results obtained show that under a low electric field the PU has no hysteresis loop. PU/PZT 50 vol%, PU/PZT 60 vol% and PU/PZT 80 % have the polarization saturation higher than the pure PU. Indeed, under an electrical field of 1000 V the remnant polarization increases from 1.9 to 4 \u03bcC/cm\u22122 when the volume fraction increases from 50 vol% PZT to 80 vol% PZT (Fig. 5). These results can be attributed to the contribution of the PZT particles which have piezoelectric properties. Consequently, composites prepared in this work, combine the advantages of the polymer matrix (good mechanical properties, low density and flexibility) with those of the ceramic phase which provides high piezoelectric properties. Composites with 0\u20133 connectivity have several advantages (Tiwari and Srivastava 2015). They are easy to produce, the volume fraction of the ceramic phase can be varied in a wide range, and it is possible to process film composites with well established techniques adapted to its applications. In this work, composites of PU/PZT in the film form have been prepared in the order to use them for vibratory energy harvesting tests.\n", "question": "What are the advantages of the polymer matrix mentioned in this paragraph?", "answers": {"text": "good mechanical properties, low density and flexibility", "answer_start": [748]}}
{"id": "10.1007#s11082-016-0518-x.html_12", "title": "10.1007#s11082-016-0518-x.html", "context": "PU/PZT composites developed in this work are designed essentially for the creation of generators of \u03bc-energy harvested from mechanical vibrations. The application of a low deformation should be able to generate an electric field which can supply an electrical device autonomously (without battery). Polyurethane has the advantage to be flexible and able to deform in the desired geometry. This polymer was used by Lebrun et al. (2009) and they have showed the possibility to use this polymer for vibratory energy harvesting. However, it was subject to a static electric field (Cottinet et al. 2011). This presents the main drawback of this polymer because it is necessary to provide energy to recover another. This inconvenience is caused by the electrostriction properties of polyurethane.", "question": "Who revealed the possibility of using polyurethane for vibratory energy harvesting?", "answers": {"text": "Lebrun et al.", "answer_start": [414]}}
{"id": "10.1007#s11082-016-0518-x.html_13", "title": "10.1007#s11082-016-0518-x.html", "context": "PU/PZT composites developed in this work are designed essentially for the creation of generators of \u03bc-energy harvested from mechanical vibrations. The application of a low deformation should be able to generate an electric field which can supply an electrical device autonomously (without battery). Polyurethane has the advantage to be flexible and able to deform in the desired geometry. This polymer was used by Lebrun et al. (2009) and they have showed the possibility to use this polymer for vibratory energy harvesting. However, it was subject to a static electric field (Cottinet et al. 2011). This presents the main drawback of this polymer because it is necessary to provide energy to recover another. This inconvenience is caused by the electrostriction properties of polyurethane.", "question": "When did Lebrun et al. showed the possibility to use polyurethane for vibratory energy harvesting?", "answers": {"text": "2009", "answer_start": [429]}}
{"id": "10.1007#s11082-016-0518-x.html_14", "title": "10.1007#s11082-016-0518-x.html", "context": "PU/PZT composites developed in this work are designed essentially for the creation of generators of \u03bc-energy harvested from mechanical vibrations. The application of a low deformation should be able to generate an electric field which can supply an electrical device autonomously (without battery). Polyurethane has the advantage to be flexible and able to deform in the desired geometry. This polymer was used by Lebrun et al. (2009) and they have showed the possibility to use this polymer for vibratory energy harvesting. However, it was subject to a static electric field (Cottinet et al. 2011). This presents the main drawback of this polymer because it is necessary to provide energy to recover another. This inconvenience is caused by the electrostriction properties of polyurethane.", "question": "What causes the main drawback of polyurethane?", "answers": {"text": "electrostriction properties", "answer_start": [746]}}
{"id": "10.1007#s11082-016-0520-3.html_0", "title": "10.1007#s11082-016-0520-3.html", "context": "In recent years, a great number of experimental and theoretical works have been done on the electronic and optical properties of QDs due to their unique optoelectronic and transport properties (Lu et al. 2011; Chen 2011; Bahramiyan and Khordad 2014). It is noteworthy that the various confinement potential models are usually employed for studying of physical properties of quantum dots. Examples of these models are rectangular potential well, parabolic potential (PP), spherical Gaussian potential, and power-exponential potentials (Bednarek et al. 1999; Szafran et al. 1999; Johnson 1995; Adamowski et al. 2005, 2000; Xie 2008a, b; Khordad et al. 2011). Recently, we have proposed a new confinement potential in quantum dots which is called the modified Gaussian potential (MGP) (Gharaati and Khordad 2010).", "question": "What model is widely employed for studying the physical properties of quantum dots?", "answers": {"text": "confinement potential models", "answer_start": [285]}}
{"id": "10.1007#s11082-016-0520-3.html_1", "title": "10.1007#s11082-016-0520-3.html", "context": "In recent years, a great number of experimental and theoretical works have been done on the electronic and optical properties of QDs due to their unique optoelectronic and transport properties (Lu et al. 2011; Chen 2011; Bahramiyan and Khordad 2014). It is noteworthy that the various confinement potential models are usually employed for studying of physical properties of quantum dots. Examples of these models are rectangular potential well, parabolic potential (PP), spherical Gaussian potential, and power-exponential potentials (Bednarek et al. 1999; Szafran et al. 1999; Johnson 1995; Adamowski et al. 2005, 2000; Xie 2008a, b; Khordad et al. 2011). Recently, we have proposed a new confinement potential in quantum dots which is called the modified Gaussian potential (MGP) (Gharaati and Khordad 2010).", "question": "What is the name of the model that is proposed by the author in 2010?", "answers": {"text": "modified Gaussian potential", "answer_start": [748]}}
{"id": "10.1007#s11082-016-0520-3.html_2", "title": "10.1007#s11082-016-0520-3.html", "context": "Hitherto, the problem of impurity states and e\u2013p interaction in QDs has investigated by several authors. For example, some experimental and theoretical studies show that electrons confined in QDs are strongly coupled to the longitudinal optical (LO) vibrations of the underlying semiconductor lattice (Hameau et al. 1999, 2002). Lucas et al. (1970) studied the electron\u2013phonon interaction in a dielectric confined system. Wendler developed the framework of the theory of optical phonon and electron\u2013phonon interaction for the spatially confined systems (Wendler 1985). Chen et al. (1998) have reported the two- and three-dimensional polarons in a symmetric QD with arbitrary e\u2013p coupling strength. Magna and Deretzis (2008) presented a polaron model of the electronic transport in a nanotube QD. The optical properties of impurity-bound polaron in a parabolic QD have been studied by Peeters et al. (1986). To obtain more information, the reader can refer to Khordad (2015a, b), Li and Xiao (2012), Xiao and Xiao (2013).", "question": "Who presented a polaron model of the electronic transport in a nanotube QD?", "answers": {"text": "Magna and Deretzis", "answer_start": [698]}}
{"id": "10.1007#s11082-016-0520-3.html_3", "title": "10.1007#s11082-016-0520-3.html", "context": "It is fully known that nonlinear optical properties such as optical absorption have great potential for optoelectronic devices. Some of these applications include semiconductor lasers, single-electron transistors, quantum computing, optical memories, cellular automata and infrared photodetectors. In practice, the electron\u2013phonon interaction is essential to understand the optical absorption spectra in semiconductors. Research on the polaron effect has become a main subject in the physics of low-dimensional quantum systems. Especially in a quantum dot system, electron\u2013phonon interactions are enhanced by the geometric confinement. Previous theoretical studies show that electrons confined in quantum dots are strongly coupled to optical LO vibrations of the underlying semiconductor lattice (Li and Chen 1997; Xie and Chen 1998; Chen 2014).", "question": "What factor is essential to understand the optical absorption spectra in semiconductors?", "answers": {"text": "electron\u2013phonon interaction", "answer_start": [315]}}
{"id": "10.1007#s11082-016-0520-3.html_4", "title": "10.1007#s11082-016-0520-3.html", "context": "In Fig. 6, we have presented the total absorption coefficient as a function of the photon energy for two different quantum dot sizes as 3 and 4 nm with V 0 = 0.4 meV and I = 10 MW/m2. From the figure, without taking into account the LO phonon interaction, we observe the total absorption coefficient is sensitive to the quantum dot size R. Here, we find from the figure that the electron\u2013LO-phonon interaction has a great influence on the total absorption coefficient. The peak values have a remarkable increasing with considering LO phonon. It is observed from the figure that the resonant peaks will move to the left of the curve when the dot size R increases, and the narrower the size of quantum dot is, the smaller the value of total absorption coefficient will be. This is due to the fact that the quantum confinement effect results in the separation of energy levels, the larger the size, the smaller the energy distance.\n", "question": "Why will the resonant peaks move to the left of the curve when the dot size R increases?", "answers": {"text": "quantum confinement effect", "answer_start": [804]}}
{"id": "10.1007#s11082-016-0520-3.html_5", "title": "10.1007#s11082-016-0520-3.html", "context": "In this work, we have studied the effects of polaron and the Coulomb impurity on the linear, third-order nonlinear, and total optical absorptions of a GaAs modified Gaussian quantum dot. In this regard, we have applied the LLPH variational procedure and the compact density-matrix approach. According to the results obtained from the present work reveal that the optical absorption coefficients are strongly affected by the LO phonon interaction and the Coulomb potential. With considering the e\u2013p interaction and the Coulomb potential, the resonance peaks of absorption coefficients shift toward higher energies. Therefore, it can be said that the Coulomb impurity effect has a marked influence on the optical properties of ionic crystals. It is expected that an optimum system will be achieved by choosing appropriate values of the dot size R and confinement potential V 0 to obtain a stronger optical absorption coefficient. Thus, the theoretical study presented in this paper may make some contributions to experimental studies, may have profound consequences with regard to improvements of practical devices such as ultrafast optical switches and may open up new opportunities for practical exploitation of quantum-size effect in devices.\n", "question": "How to obtain a stronger optical absorption coefficient?", "answers": {"text": "choosing appropriate values of the dot size R and confinement potential", "answer_start": [799]}}
{"id": "10.1007#s11082-016-0528-8.html_0", "title": "10.1007#s11082-016-0528-8.html", "context": "Photonic crystal fibre (PCF)\u2013fibre bragg grating (FBG) integration opens up new possibilities in multi-parameter fibre-optic sensing, owing to their active control over light characteristics and mode confinements. Their integration results in a mismatch in their mode field diameters (MFDs), which in turn causes various types of losses such as confinement loss, scattering loss, etc. This paper primarily investigates the effect of geometrical parameters on fibre parameters such as confinement loss and MFD, which plays a significant role in long distance fibre-optic remote sensing. Liquid crystal PCFs (LCPCFs) are utilized in the sensor configuration, exploiting their optical properties for photonic bandgap based tighter mode confinements and wavelength tunability. Furthermore, the LCPCF\u2013FBG combo enables multi-parameter fibre-optic sensing which can be effectively utilized in oil and gas sensing applications. Theoretical study conducted on the fibre sensor revealed that confinement loss and MFD can be reduced by properly optimizing their structural parameters.", "question": "Why does Photonic crystal fibre (PCF)\u2013fibre bragg grating (FBG) integration open up new possibilities in multi-parameter fibre-optic sensing?", "answers": {"text": "active control over light characteristics and mode confinements", "answer_start": [149]}}
{"id": "10.1007#s11082-016-0528-8.html_1", "title": "10.1007#s11082-016-0528-8.html", "context": "Photonic crystal fibre (PCF)\u2013fibre bragg grating (FBG) integration opens up new possibilities in multi-parameter fibre-optic sensing, owing to their active control over light characteristics and mode confinements. Their integration results in a mismatch in their mode field diameters (MFDs), which in turn causes various types of losses such as confinement loss, scattering loss, etc. This paper primarily investigates the effect of geometrical parameters on fibre parameters such as confinement loss and MFD, which plays a significant role in long distance fibre-optic remote sensing. Liquid crystal PCFs (LCPCFs) are utilized in the sensor configuration, exploiting their optical properties for photonic bandgap based tighter mode confinements and wavelength tunability. Furthermore, the LCPCF\u2013FBG combo enables multi-parameter fibre-optic sensing which can be effectively utilized in oil and gas sensing applications. Theoretical study conducted on the fibre sensor revealed that confinement loss and MFD can be reduced by properly optimizing their structural parameters.", "question": "What are the possible applications of the LCPCF\u2013FBG combo?", "answers": {"text": "oil and gas sensing", "answer_start": [887]}}
{"id": "10.1007#s11082-016-0528-8.html_2", "title": "10.1007#s11082-016-0528-8.html", "context": "Photonic crystal fibre (PCF)\u2013fibre bragg grating (FBG) integration opens up new possibilities in multi-parameter fibre-optic sensing, owing to their active control over light characteristics and mode confinements. Their integration results in a mismatch in their mode field diameters (MFDs), which in turn causes various types of losses such as confinement loss, scattering loss, etc. This paper primarily investigates the effect of geometrical parameters on fibre parameters such as confinement loss and MFD, which plays a significant role in long distance fibre-optic remote sensing. Liquid crystal PCFs (LCPCFs) are utilized in the sensor configuration, exploiting their optical properties for photonic bandgap based tighter mode confinements and wavelength tunability. Furthermore, the LCPCF\u2013FBG combo enables multi-parameter fibre-optic sensing which can be effectively utilized in oil and gas sensing applications. Theoretical study conducted on the fibre sensor revealed that confinement loss and MFD can be reduced by properly optimizing their structural parameters.", "question": "How would the confinement loss and MFD be possibly reduced?", "answers": {"text": "optimizing their structural parameters", "answer_start": [1035]}}
{"id": "10.1007#s11082-016-0528-8.html_3", "title": "10.1007#s11082-016-0528-8.html", "context": "Sensing is always a challenging, but indispensable task in the oil and gas sector. In recent years, oil and gas exploration and production has been moving into deeper and deeper zones in order to meet the growing demand. This results in harsh operating conditions, which is reflected by critical parameters like temperature, pressure, strain, etc. Therefore, reliable sensors which are able to continuously and accurately report current down-hole conditions has become very important in managing oil and gas reservoirs and wells (Algeroy et al. 2010). To support this need, multi-point distributed and multimodal simultaneous measurements will be required for drilling and oil and gas production monitoring. Hence, more sensors are required, with longer sensing range, for effective remote monitoring of down-hole. However, this results in higher signal attenuation, crosstalks and losses. In order to alleviate this situation, there is a need to enhance the sensing signals and reduce the fibre losses.", "question": "Why do we need to enhance the sensing signals and reduce the fibre losses?", "answers": {"text": "higher signal attenuation, crosstalks and losses", "answer_start": [840]}}
{"id": "10.1007#s11082-016-0528-8.html_4", "title": "10.1007#s11082-016-0528-8.html", "context": "Combination of LCPCF and FBG technologies enables effective control over the mode confinements and light characteristics. This is because, the liquid crystal infused in the cladding holes creates a PBG (Photonic Bandgap) effect, restricting the modes within the core region rather than leaking. However, LCPCF\u2013FBG integration is quite challenging, mainly due to their difference in core sizes and mode field diameters (MFDs). Furthermore, this results in different forms of losses, which are dominated by confinement loss. Therefore, it is important to develop approaches to reduce losses occurring within the fibre core, so that signal power is enhanced and thereby transmission and sensing range of the fibre can also be increased. By optimizing geometrical parameters such as hole distribution, hole sizes, etc. of the PCF, confinement losses can be minimized. Furthermore, analyzing effective area and MFD gives a better insight of leakage loss, macro-bending loss and numerical aperture of the fibre sensor.", "question": "Why is the LCPCF\u2013FBG integration challenging?", "answers": {"text": "difference in core sizes and mode field diameters", "answer_start": [368]}}
{"id": "10.1007#s11082-016-0528-8.html_5", "title": "10.1007#s11082-016-0528-8.html", "context": "Combination of LCPCF and FBG technologies enables effective control over the mode confinements and light characteristics. This is because, the liquid crystal infused in the cladding holes creates a PBG (Photonic Bandgap) effect, restricting the modes within the core region rather than leaking. However, LCPCF\u2013FBG integration is quite challenging, mainly due to their difference in core sizes and mode field diameters (MFDs). Furthermore, this results in different forms of losses, which are dominated by confinement loss. Therefore, it is important to develop approaches to reduce losses occurring within the fibre core, so that signal power is enhanced and thereby transmission and sensing range of the fibre can also be increased. By optimizing geometrical parameters such as hole distribution, hole sizes, etc. of the PCF, confinement losses can be minimized. Furthermore, analyzing effective area and MFD gives a better insight of leakage loss, macro-bending loss and numerical aperture of the fibre sensor.", "question": "How can the confinement lossess be minimized?", "answers": {"text": "optimizing geometrical parameters", "answer_start": [737]}}
{"id": "10.1007#s11082-016-0528-8.html_6", "title": "10.1007#s11082-016-0528-8.html", "context": "There are several sources of losses in fibres, such as structural imperfections, fibre bending, intrinsic material absorption, Rayleigh scattering, etc. Losses induced at the time of fabrication can be reduced by careful optimization and monitoring of the fabrication process. Confinement loss is another major type of loss that occurs mainly in fibres fabricated from raw material (Saitoh and Koshiba 2005). Confinement loss which is also known as leakage loss is the leakage of power from the core into the cladding and it occurs mainly in single mode fibres. The guided modes of PCFs are inherently leaky, as the refractive index of core is the same as that of outer cladding without air-holes (Pourmahyabadi and Nejad 2009). Theoretically, PCF with infinite number of air-holes in the cladding is expected to achieve lossless propagation. However, practically fabricated fibre experiences leaky modes due to finite number of air-holes in the photonic crystal cladding.", "question": "Why does the fabricated fibre experience leaky modes?", "answers": {"text": "finite number of air-holes", "answer_start": [755]}}
{"id": "10.1007#s11082-016-0528-8.html_7", "title": "10.1007#s11082-016-0528-8.html", "context": "COMSOL MULTIPHYSICS software which is a finite element analysis software package, was used for the modelling and simulation of LCPCF. Figure 2 shows the 2D and 3D views respectively of a perfect Gaussian electric field pattern obtained in a four ring LCPCF. A Perfectly Matched Layer (PML) is introduced around the photonic crystal cladding, which acts as an additional domain to absorb incident radiations without producing back reflections. The PML is made of an artificial absorbing material which has anisotropic permeability and permittivity that matches with the physical medium outside. With the addition of liquid crystals, the fibre exhibits the common properties of photonic bandgap fibre (PBG) i.e. only certain frequencies of light propagate through the core and all other wavelengths tends to pass through the cladding which has a higher refractive index (Knight et al. 1998).\n", "question": "What software was used for the modelling and simulation of LCPCF?", "answers": {"text": "COMSOL MULTIPHYSICS", "answer_start": [0]}}
{"id": "10.1007#s11082-016-0528-8.html_8", "title": "10.1007#s11082-016-0528-8.html", "context": "From the current theoretical investigation, it was identified that, structural parameters have significant effects on fibre parameters such as confinement loss, effective mode area and MFD. It was found that confinement loss is a strong function of air-filling fraction (d/\u039b) and the number of rings employed in the LCPCF cladding. Investigations carried out by varying the hole size and hole\u2013hole distance also resulted in reduction of leakage losses and MFD. Low confinement loss automatically results in improved signal power, which in turn improves the accuracy and spatial range of the sensor. Besides this, the tunability of the photonic bandgap of the LCPCF by changing the liquid crystal material adds to its sensing capabilities. The present results shows promising future in the direction of PCF\u2013FBG based long distance remote sensing system for oil and gas applications. Based on our investigation, the synergy of PCF and FBG develops an advanced fibre-optic sensing system with longer sensing range and enhanced accuracy for condition monitoring of oil and gas fields in deeper zones. Further analysis will be carried out on LCPCF\u2013FBG based temperature sensing and simultaneous measurement of multiple parameters.\n", "question": "What is identified to have significant effects on fibre parameters?", "answers": {"text": "structural parameters", "answer_start": [68]}}
{"id": "10.1007#s11082-016-0528-8.html_9", "title": "10.1007#s11082-016-0528-8.html", "context": "From the current theoretical investigation, it was identified that, structural parameters have significant effects on fibre parameters such as confinement loss, effective mode area and MFD. It was found that confinement loss is a strong function of air-filling fraction (d/\u039b) and the number of rings employed in the LCPCF cladding. Investigations carried out by varying the hole size and hole\u2013hole distance also resulted in reduction of leakage losses and MFD. Low confinement loss automatically results in improved signal power, which in turn improves the accuracy and spatial range of the sensor. Besides this, the tunability of the photonic bandgap of the LCPCF by changing the liquid crystal material adds to its sensing capabilities. The present results shows promising future in the direction of PCF\u2013FBG based long distance remote sensing system for oil and gas applications. Based on our investigation, the synergy of PCF and FBG develops an advanced fibre-optic sensing system with longer sensing range and enhanced accuracy for condition monitoring of oil and gas fields in deeper zones. Further analysis will be carried out on LCPCF\u2013FBG based temperature sensing and simultaneous measurement of multiple parameters.\n", "question": "What will a low confinement loss bring to the sensor?", "answers": {"text": "improved signal power", "answer_start": [507]}}
{"id": "10.1007#s11082-016-0536-8.html_0", "title": "10.1007#s11082-016-0536-8.html", "context": "Time distribution of ablated species inside the plasma plume is very important for understanding the PLD processes and the thin films deposition. The experimental apparatus for laser ablation process is shown in Fig. 1. A pulsed XeCl excimer laser beam (\u03bb = 308 nm, pulse duration = 10 ns, repetition rate = 10 Hz) was incident on the rotating target at an angle of 45\u00b0 with a spot diameter around 0.1 mm. A step motor was used for rotation of the target and the frequency was equal to 10 turns per minute. The distance between the target and substrate was around 4 cm. Quartz substrates were thoroughly cleaned to remove the surface native pollutions before loading into the chamber. The MgO ion\u2013atomic plume was produced by irradiation of the MgO target by the excimer laser beam (Zawadzka et al. 2015a; Rumianowski and P\u0142\u00f3ciennik 2006; Zieli\u0144ski et al. 2000). A constant field for time-of-flight (TOF) mass spectrometer was used to investigate the expansion dynamics of the ionic species ejected during ablation process (Zawadzka et al. 2015a; Rumianowski and P\u0142\u00f3ciennik 2006). Pressure within the vacuum chamber was kept at 5 \u00d7 10\u22126 mbar and ablation process lasted 30 min. In order to study the structural as well as linear and nonlinear properties, the films were deposited in the substrate temperature range of room temperature (RT)\u2014600 \u00b0C.\n", "question": "What is the pulse duration of the XeCl excimer laser beam?", "answers": {"text": "10 ns", "answer_start": [283]}}
{"id": "10.1007#s11082-016-0536-8.html_1", "title": "10.1007#s11082-016-0536-8.html", "context": "Time distribution of ablated species inside the plasma plume is very important for understanding the PLD processes and the thin films deposition. The experimental apparatus for laser ablation process is shown in Fig. 1. A pulsed XeCl excimer laser beam (\u03bb = 308 nm, pulse duration = 10 ns, repetition rate = 10 Hz) was incident on the rotating target at an angle of 45\u00b0 with a spot diameter around 0.1 mm. A step motor was used for rotation of the target and the frequency was equal to 10 turns per minute. The distance between the target and substrate was around 4 cm. Quartz substrates were thoroughly cleaned to remove the surface native pollutions before loading into the chamber. The MgO ion\u2013atomic plume was produced by irradiation of the MgO target by the excimer laser beam (Zawadzka et al. 2015a; Rumianowski and P\u0142\u00f3ciennik 2006; Zieli\u0144ski et al. 2000). A constant field for time-of-flight (TOF) mass spectrometer was used to investigate the expansion dynamics of the ionic species ejected during ablation process (Zawadzka et al. 2015a; Rumianowski and P\u0142\u00f3ciennik 2006). Pressure within the vacuum chamber was kept at 5 \u00d7 10\u22126 mbar and ablation process lasted 30 min. In order to study the structural as well as linear and nonlinear properties, the films were deposited in the substrate temperature range of room temperature (RT)\u2014600 \u00b0C.\n", "question": "What is the repetition rate of the XeCl excimer laser beam?", "answers": {"text": "10 Hz", "answer_start": [308]}}
{"id": "10.1007#s11082-016-0536-8.html_2", "title": "10.1007#s11082-016-0536-8.html", "context": "Time distribution of ablated species inside the plasma plume is very important for understanding the PLD processes and the thin films deposition. The experimental apparatus for laser ablation process is shown in Fig. 1. A pulsed XeCl excimer laser beam (\u03bb = 308 nm, pulse duration = 10 ns, repetition rate = 10 Hz) was incident on the rotating target at an angle of 45\u00b0 with a spot diameter around 0.1 mm. A step motor was used for rotation of the target and the frequency was equal to 10 turns per minute. The distance between the target and substrate was around 4 cm. Quartz substrates were thoroughly cleaned to remove the surface native pollutions before loading into the chamber. The MgO ion\u2013atomic plume was produced by irradiation of the MgO target by the excimer laser beam (Zawadzka et al. 2015a; Rumianowski and P\u0142\u00f3ciennik 2006; Zieli\u0144ski et al. 2000). A constant field for time-of-flight (TOF) mass spectrometer was used to investigate the expansion dynamics of the ionic species ejected during ablation process (Zawadzka et al. 2015a; Rumianowski and P\u0142\u00f3ciennik 2006). Pressure within the vacuum chamber was kept at 5 \u00d7 10\u22126 mbar and ablation process lasted 30 min. In order to study the structural as well as linear and nonlinear properties, the films were deposited in the substrate temperature range of room temperature (RT)\u2014600 \u00b0C.\n", "question": "What was used for rotation of the target?", "answers": {"text": "step motor", "answer_start": [408]}}
{"id": "10.1007#s11082-016-0536-8.html_3", "title": "10.1007#s11082-016-0536-8.html", "context": "Time distribution of ablated species inside the plasma plume is very important for understanding the PLD processes and the thin films deposition. The experimental apparatus for laser ablation process is shown in Fig. 1. A pulsed XeCl excimer laser beam (\u03bb = 308 nm, pulse duration = 10 ns, repetition rate = 10 Hz) was incident on the rotating target at an angle of 45\u00b0 with a spot diameter around 0.1 mm. A step motor was used for rotation of the target and the frequency was equal to 10 turns per minute. The distance between the target and substrate was around 4 cm. Quartz substrates were thoroughly cleaned to remove the surface native pollutions before loading into the chamber. The MgO ion\u2013atomic plume was produced by irradiation of the MgO target by the excimer laser beam (Zawadzka et al. 2015a; Rumianowski and P\u0142\u00f3ciennik 2006; Zieli\u0144ski et al. 2000). A constant field for time-of-flight (TOF) mass spectrometer was used to investigate the expansion dynamics of the ionic species ejected during ablation process (Zawadzka et al. 2015a; Rumianowski and P\u0142\u00f3ciennik 2006). Pressure within the vacuum chamber was kept at 5 \u00d7 10\u22126 mbar and ablation process lasted 30 min. In order to study the structural as well as linear and nonlinear properties, the films were deposited in the substrate temperature range of room temperature (RT)\u2014600 \u00b0C.\n", "question": "What was used to investigate the expansion dynamics of the ionic species ejected during ablation process?", "answers": {"text": "A constant field for time-of-flight (TOF) mass spectrometer", "answer_start": [863]}}
{"id": "10.1007#s11082-016-0536-8.html_4", "title": "10.1007#s11082-016-0536-8.html", "context": "Time distribution of ablated species inside the plasma plume is very important for understanding the PLD processes and the thin films deposition. The experimental apparatus for laser ablation process is shown in Fig. 1. A pulsed XeCl excimer laser beam (\u03bb = 308 nm, pulse duration = 10 ns, repetition rate = 10 Hz) was incident on the rotating target at an angle of 45\u00b0 with a spot diameter around 0.1 mm. A step motor was used for rotation of the target and the frequency was equal to 10 turns per minute. The distance between the target and substrate was around 4 cm. Quartz substrates were thoroughly cleaned to remove the surface native pollutions before loading into the chamber. The MgO ion\u2013atomic plume was produced by irradiation of the MgO target by the excimer laser beam (Zawadzka et al. 2015a; Rumianowski and P\u0142\u00f3ciennik 2006; Zieli\u0144ski et al. 2000). A constant field for time-of-flight (TOF) mass spectrometer was used to investigate the expansion dynamics of the ionic species ejected during ablation process (Zawadzka et al. 2015a; Rumianowski and P\u0142\u00f3ciennik 2006). Pressure within the vacuum chamber was kept at 5 \u00d7 10\u22126 mbar and ablation process lasted 30 min. In order to study the structural as well as linear and nonlinear properties, the films were deposited in the substrate temperature range of room temperature (RT)\u2014600 \u00b0C.\n", "question": "How long did the ablation process last?", "answers": {"text": "30 min", "answer_start": [1170]}}
{"id": "10.1007#s11082-016-0536-8.html_5", "title": "10.1007#s11082-016-0536-8.html", "context": "Ions, electrons and uncharged molecules were produced in the laser radiation interaction region at the MgO target inside the vacuum chamber. The COMSTOCK, model TOF 101 (Dygda\u0142a et al. 2000) mass spectrometer allowed us to distinguish the positive magnesium oxide ions. The positive ions were extracted into the spectrometer by an accelerating voltage between the target and the conical aperture of the spectrometer (Dygda\u0142a et al. 2009). The magnesium oxide ions were detected shot-to-shot by the tandem multichannel plate detector. The signal composed of a train of pulses was amplified and supplied to the input of the real time multichannel scaler (RTMS) (Zieli\u0144ski et al. 2000; Zielinski et al. 1998). The RTMS was triggered by a fast photodiode which detects a reflection from the laser. The computer was used additionally for registering the laser power from the pulse energy meter for each laser shot.", "question": "How were the magnesium oxide ions detected?", "answers": {"text": "tandem multichannel plate detector", "answer_start": [498]}}
{"id": "10.1007#s11082-016-0536-8.html_6", "title": "10.1007#s11082-016-0536-8.html", "context": "In present laser ablation process absorbed (from the laser beam) energy was sufficient to excite and ionize magnesium oxide molecules but not sufficient to break chemical bonds of the molecules. As a result, a supersonic jet of particles was ejected normal to the target surface giving rise a plasma plume. The plume was spreading towards the substrate with a strong forward-directed velocity distribution of the particles. Typical shape of the plasma plume during PLD process is shown in Fig. 2a. Figure 2b shows the TOF spectrum for MgO as a target material. The strong peaks assigned to MgO+ and MgO2+ have been observed.\n", "question": "What was enjected normal to the target surface to give rise a plasma plume?", "answers": {"text": "a supersonic jet of particles", "answer_start": [208]}}
{"id": "10.1007#s11082-016-0536-8.html_7", "title": "10.1007#s11082-016-0536-8.html", "context": "Figure 3 shows the XRD measurement results of ablated MgO thin films as a function of the substrate temperature during the deposition process. All measurements were carried out by diffractometer using CuK\u03b1 (\u03bb = 0.1542 nm) radiation. Two peaks attributed to diffraction from surfaces (111) and (200) were observed in most cases of XRD spectra for sample deposited at the room temperature (without heating of the substrate). Intensity of the peak (111) is about four times higher than peak (200). This result indicates that the growth of the films showed preferential orientation of crystallization. Intensity of this peak attributed to diffraction from surfaces (111) increased with increasing of the substrate temperature during ablation process, what leads to conclusion, that higher substrate\u2019s temperature causes the higher level of the internal structure orientation. This phenomenon can be explained by various molecules\u2019 mobility as a function of the substrate\u2019s temperature. The MgO molecules have higher surface mobility at higher temperature and they can move across the substrate surface and form. Hence, orientation of the internal structure obtained at higher temperature is more arranged. For lower temperatures this orientation is more accidental and weaker particles\u2019 mobility counteracts crystallization of the film.\n", "question": "Why does the higher substrate\u2019s temperature cause the higher level of the internal structure orientation?", "answers": {"text": "various molecules\u2019 mobility", "answer_start": [908]}}
{"id": "10.1007#s11082-016-0536-8.html_8", "title": "10.1007#s11082-016-0536-8.html", "context": "Our results are in good agreement with that reported by Zhu et al. (2006), who found that MgO film grown at the temperature of the substrate equal to 400 \u00b0C under low oxygen atmosphere had a preferred orientation attributed to diffraction from surfaces (100) and (111). Magnesium oxide has a NaCl type crystal structure with face-centered-cubic Mg and O sublattices. The (100) planes are the cleavage planes of MgO, they are charge neutral and naturally occurring orientation, and have the lowest surface energy. Orientation attributed to surfaces (111) can be the fastest growing direction for a material with the NaCl structure (Mahieu et al. 2005). At low pressures or vacuum, the growth seems to be kinetically limited and (111) oriented grains have the largest perpendicular growth rate over (100) oriented grains. Therefore, (111) out-of-plane orientation can develop in an evolutionary way. It is suggested that the kinetic energy of the ablated species in the plume can be changed by controlling the pressure during the deposition process, which allows the energy of the incident particles to be adjusted to obtain the expected orientations.", "question": "How to change the kinetic energy of the ablated species in the plume?", "answers": {"text": "controlling the pressure during the deposition process", "answer_start": [992]}}
{"id": "10.1007#s11082-016-0536-8.html_9", "title": "10.1007#s11082-016-0536-8.html", "context": "Our results are in good agreement with that reported by Zhu et al. (2006), who found that MgO film grown at the temperature of the substrate equal to 400 \u00b0C under low oxygen atmosphere had a preferred orientation attributed to diffraction from surfaces (100) and (111). Magnesium oxide has a NaCl type crystal structure with face-centered-cubic Mg and O sublattices. The (100) planes are the cleavage planes of MgO, they are charge neutral and naturally occurring orientation, and have the lowest surface energy. Orientation attributed to surfaces (111) can be the fastest growing direction for a material with the NaCl structure (Mahieu et al. 2005). At low pressures or vacuum, the growth seems to be kinetically limited and (111) oriented grains have the largest perpendicular growth rate over (100) oriented grains. Therefore, (111) out-of-plane orientation can develop in an evolutionary way. It is suggested that the kinetic energy of the ablated species in the plume can be changed by controlling the pressure during the deposition process, which allows the energy of the incident particles to be adjusted to obtain the expected orientations.", "question": "What can be changed by controlling the pressure during the deposition process?", "answers": {"text": "kinetic energy of the ablated species in the plume", "answer_start": [923]}}
{"id": "10.1007#s11082-016-0536-8.html_10", "title": "10.1007#s11082-016-0536-8.html", "context": "A half-width (FWHM) of these peaks decreased slightly with increasing temperature of the substrate. This finding indicated that the samples had a certain crystalline quality. The measured FWHMs of the sample deposited at room temperature were 0.43 and 0.78 for (111), and (200) respectively. The FWHMs of the film deposited at 600 \u00b0C were 0.29 for (111). Thus, increasing of the substrate temperature causes that the grain size becomes larger and the film exhibits a crystal structure due to the enhancement of the atomic migration ability. Therefore, the optical quality of the MgO thin films is improved by heating of the substrate during the deposition process. The temperature equal to 600 \u00b0C appears the best substrate temperature for the MgO thin films\u2019 deposition on the quartz plate by using laser ablation process. At higher temperatures, the quartz substrate is getting more plastic and the re-evaporation process occurs, which leads to re-reduce the size of grains.", "question": "What causes the grain size becoming larger and the film exhibiting a crystal structure?", "answers": {"text": "enhancement of the atomic migration ability", "answer_start": [496]}}
{"id": "10.1007#s11082-016-0536-8.html_11", "title": "10.1007#s11082-016-0536-8.html", "context": "A half-width (FWHM) of these peaks decreased slightly with increasing temperature of the substrate. This finding indicated that the samples had a certain crystalline quality. The measured FWHMs of the sample deposited at room temperature were 0.43 and 0.78 for (111), and (200) respectively. The FWHMs of the film deposited at 600 \u00b0C were 0.29 for (111). Thus, increasing of the substrate temperature causes that the grain size becomes larger and the film exhibits a crystal structure due to the enhancement of the atomic migration ability. Therefore, the optical quality of the MgO thin films is improved by heating of the substrate during the deposition process. The temperature equal to 600 \u00b0C appears the best substrate temperature for the MgO thin films\u2019 deposition on the quartz plate by using laser ablation process. At higher temperatures, the quartz substrate is getting more plastic and the re-evaporation process occurs, which leads to re-reduce the size of grains.", "question": "What process leads to re-reduce the size of grains?", "answers": {"text": "re-evaporation", "answer_start": [901]}}
{"id": "10.1007#s11082-016-0536-8.html_12", "title": "10.1007#s11082-016-0536-8.html", "context": "For most optical applications high transmittance in the UV\u2013Vis\u2013NIR range is very important. A relatively high transmittance in this spectral range and clear absorption edges of the films were observed for all films irrespective of the annealing process. All investigated magnesium oxide thin films have average transmittances >87 % in the investigated range. As the temperature of the annealing process has been increased the value of the transmittance slightly increased and reached a maximum (>91 %) after the process. The slightly weaker transmittance of the samples deposited at room temperature of the substrate results from the lower kinetic energy of the ablated species inside the plasma plume. The high transmittances of the films are attributed to larger-sized crystallites what eliminates light scattering. Investigated wavelength range did not allow determining the absorption edge of MgO films which is of about 160 nm.", "question": "In what wavelength range is the high transmittance important for most optical applications?", "answers": {"text": "UV\u2013Vis\u2013NIR", "answer_start": [56]}}
{"id": "10.1007#s11082-016-0536-8.html_13", "title": "10.1007#s11082-016-0536-8.html", "context": "For most optical applications high transmittance in the UV\u2013Vis\u2013NIR range is very important. A relatively high transmittance in this spectral range and clear absorption edges of the films were observed for all films irrespective of the annealing process. All investigated magnesium oxide thin films have average transmittances >87 % in the investigated range. As the temperature of the annealing process has been increased the value of the transmittance slightly increased and reached a maximum (>91 %) after the process. The slightly weaker transmittance of the samples deposited at room temperature of the substrate results from the lower kinetic energy of the ablated species inside the plasma plume. The high transmittances of the films are attributed to larger-sized crystallites what eliminates light scattering. Investigated wavelength range did not allow determining the absorption edge of MgO films which is of about 160 nm.", "question": "How high could the value of the transmittance reach after the process?", "answers": {"text": "91 %", "answer_start": [496]}}
{"id": "10.1007#s11082-016-0536-8.html_14", "title": "10.1007#s11082-016-0536-8.html", "context": "For most optical applications high transmittance in the UV\u2013Vis\u2013NIR range is very important. A relatively high transmittance in this spectral range and clear absorption edges of the films were observed for all films irrespective of the annealing process. All investigated magnesium oxide thin films have average transmittances >87 % in the investigated range. As the temperature of the annealing process has been increased the value of the transmittance slightly increased and reached a maximum (>91 %) after the process. The slightly weaker transmittance of the samples deposited at room temperature of the substrate results from the lower kinetic energy of the ablated species inside the plasma plume. The high transmittances of the films are attributed to larger-sized crystallites what eliminates light scattering. Investigated wavelength range did not allow determining the absorption edge of MgO films which is of about 160 nm.", "question": "What is the absorption edge of MgO?", "answers": {"text": "about 160 nm", "answer_start": [919]}}
{"id": "10.1007#s11082-016-0536-8.html_15", "title": "10.1007#s11082-016-0536-8.html", "context": "Photoluminescence (PL) experiments were carried out under pulse excitation. Nitrogen laser (\u03bb = 337.1 nm, FWHM = 5 ns, power in pulse 20 kW and 10 Hz repetition rate) was used as excitation source. Photoluminescence signal was registered by using photomultiplier (HAMAMATSU R928) and the boxcar averager (162/164 PAR) (Zawadzka et al. 2014b). Measurements of the PL process were performed within temperature range from 13 to 300 K. Samples were placed in vacuum chamber and cooled to temperature equal to 13 K. Experimental spectra were registered after 30 min from reaching desirable temperature. Photoluminescence spectra of the MgO thin film on quartz plates recorded at different substrate\u2019s temperature equal to RT and 600 \u00b0C are shown in Fig. 5a, b.\n", "question": "What is the power in pulse of the Nitrogen laser?", "answers": {"text": "20 kW", "answer_start": [134]}}
{"id": "10.1007#s11082-016-0536-8.html_16", "title": "10.1007#s11082-016-0536-8.html", "context": "Photoluminescence (PL) experiments were carried out under pulse excitation. Nitrogen laser (\u03bb = 337.1 nm, FWHM = 5 ns, power in pulse 20 kW and 10 Hz repetition rate) was used as excitation source. Photoluminescence signal was registered by using photomultiplier (HAMAMATSU R928) and the boxcar averager (162/164 PAR) (Zawadzka et al. 2014b). Measurements of the PL process were performed within temperature range from 13 to 300 K. Samples were placed in vacuum chamber and cooled to temperature equal to 13 K. Experimental spectra were registered after 30 min from reaching desirable temperature. Photoluminescence spectra of the MgO thin film on quartz plates recorded at different substrate\u2019s temperature equal to RT and 600 \u00b0C are shown in Fig. 5a, b.\n", "question": "What is the repetition rate of the Nitrogen laser?", "answers": {"text": "10 Hz", "answer_start": [144]}}
{"id": "10.1007#s11082-016-0536-8.html_17", "title": "10.1007#s11082-016-0536-8.html", "context": "Photoluminescence (PL) experiments were carried out under pulse excitation. Nitrogen laser (\u03bb = 337.1 nm, FWHM = 5 ns, power in pulse 20 kW and 10 Hz repetition rate) was used as excitation source. Photoluminescence signal was registered by using photomultiplier (HAMAMATSU R928) and the boxcar averager (162/164 PAR) (Zawadzka et al. 2014b). Measurements of the PL process were performed within temperature range from 13 to 300 K. Samples were placed in vacuum chamber and cooled to temperature equal to 13 K. Experimental spectra were registered after 30 min from reaching desirable temperature. Photoluminescence spectra of the MgO thin film on quartz plates recorded at different substrate\u2019s temperature equal to RT and 600 \u00b0C are shown in Fig. 5a, b.\n", "question": "Within what temperature range was the PL process measured?", "answers": {"text": "13 to 300 K", "answer_start": [419]}}
{"id": "10.1007#s11082-016-0536-8.html_18", "title": "10.1007#s11082-016-0536-8.html", "context": "Photoluminescence (PL) experiments were carried out under pulse excitation. Nitrogen laser (\u03bb = 337.1 nm, FWHM = 5 ns, power in pulse 20 kW and 10 Hz repetition rate) was used as excitation source. Photoluminescence signal was registered by using photomultiplier (HAMAMATSU R928) and the boxcar averager (162/164 PAR) (Zawadzka et al. 2014b). Measurements of the PL process were performed within temperature range from 13 to 300 K. Samples were placed in vacuum chamber and cooled to temperature equal to 13 K. Experimental spectra were registered after 30 min from reaching desirable temperature. Photoluminescence spectra of the MgO thin film on quartz plates recorded at different substrate\u2019s temperature equal to RT and 600 \u00b0C are shown in Fig. 5a, b.\n", "question": "Where were the samples placed in to be cooled to temperature equal to 13 K?", "answers": {"text": "vacuum chamber", "answer_start": [455]}}
{"id": "10.1007#s11082-016-0536-8.html_19", "title": "10.1007#s11082-016-0536-8.html", "context": "Intensities of the photoluminescence process for all investigated samples were very low regardless of the applied substrate temperature. Photoluminescence spectra at different measuring temperature contained various emission features, which changed their intensity and positions with the temperature. The optical properties of thin films are depending on both intrinsic and extrinsic effects. Photoluminescence measurements give the possibility to determine the optical quality and the presence of impurities in the material. Precious data of the energy transport and other processes occurring within the film structure can be deducted from temperature dependent photoluminescence spectra. In the case of this study, measurements of the PL were carried out within temperature range from 13 to 300 K.", "question": "How to determine the optical quality and the presence of impurities in the material?", "answers": {"text": "Photoluminescence measurements", "answer_start": [393]}}
{"id": "10.1007#s11082-016-0536-8.html_20", "title": "10.1007#s11082-016-0536-8.html", "context": "Intensities of the photoluminescence process for all investigated samples were very low regardless of the applied substrate temperature. Photoluminescence spectra at different measuring temperature contained various emission features, which changed their intensity and positions with the temperature. The optical properties of thin films are depending on both intrinsic and extrinsic effects. Photoluminescence measurements give the possibility to determine the optical quality and the presence of impurities in the material. Precious data of the energy transport and other processes occurring within the film structure can be deducted from temperature dependent photoluminescence spectra. In the case of this study, measurements of the PL were carried out within temperature range from 13 to 300 K.", "question": "Where can we obtain the data of the energy transport and other processes occurring within the film structure?", "answers": {"text": "temperature dependent photoluminescence spectra", "answer_start": [641]}}
{"id": "10.1007#s11082-016-0536-8.html_21", "title": "10.1007#s11082-016-0536-8.html", "context": "To reconstruct the spectrum and to determine the individual peak position and its intensity within the spectrum standard multiple Gaussian fitting procedure was used. One main and five smaller bands were identified. The peak positions of the six Gaussian bands are located at about 395, 423, 464, 580, 660 and 760 nm. Intensities of the first three peaks were much greater than the other three and these three bands overlap each other. Blue and blue-green emission may originate from the defects in MgO such as oxygen and magnesium vacancies (Kar and Chaudhuri 2006) and interstitials positions of the atoms, presumably being generated during the high-temperature ablation process. The similar blue (Deepak et al. 2006) and blue-green emission (Zhang and Zhang 2002) have been observed for various MgO nanostructures. The red bands with the peaks located at 600\u2013700 nm were reported by Zhang and Zhang (2002) and Chao (1971) and were assigned as vibrational sidebands lines in luminescence spectrum of bulk MgO with interstitials defects and/or or surface states. The band located at 760 nm may also be associated with the relaxation luminescence of the defect centers excited by mechanical stress. The relaxation luminescence of defect centers may exist because crack causes bond-breaking and nuclear motion, and promotes release of atoms and ions from the lattice sites, resulting in the creation of defects.", "question": "Who observed the blue emission for the MgO nanostructure?", "answers": {"text": "Deepak et al.", "answer_start": [700]}}
{"id": "10.1007#s11082-016-0536-8.html_22", "title": "10.1007#s11082-016-0536-8.html", "context": "To reconstruct the spectrum and to determine the individual peak position and its intensity within the spectrum standard multiple Gaussian fitting procedure was used. One main and five smaller bands were identified. The peak positions of the six Gaussian bands are located at about 395, 423, 464, 580, 660 and 760 nm. Intensities of the first three peaks were much greater than the other three and these three bands overlap each other. Blue and blue-green emission may originate from the defects in MgO such as oxygen and magnesium vacancies (Kar and Chaudhuri 2006) and interstitials positions of the atoms, presumably being generated during the high-temperature ablation process. The similar blue (Deepak et al. 2006) and blue-green emission (Zhang and Zhang 2002) have been observed for various MgO nanostructures. The red bands with the peaks located at 600\u2013700 nm were reported by Zhang and Zhang (2002) and Chao (1971) and were assigned as vibrational sidebands lines in luminescence spectrum of bulk MgO with interstitials defects and/or or surface states. The band located at 760 nm may also be associated with the relaxation luminescence of the defect centers excited by mechanical stress. The relaxation luminescence of defect centers may exist because crack causes bond-breaking and nuclear motion, and promotes release of atoms and ions from the lattice sites, resulting in the creation of defects.", "question": "When did Zhang and Zhang observe the blue-green emission of the MgO nanostructure?", "answers": {"text": "2002", "answer_start": [761]}}
{"id": "10.1007#s11082-016-0536-8.html_23", "title": "10.1007#s11082-016-0536-8.html", "context": "To reconstruct the spectrum and to determine the individual peak position and its intensity within the spectrum standard multiple Gaussian fitting procedure was used. One main and five smaller bands were identified. The peak positions of the six Gaussian bands are located at about 395, 423, 464, 580, 660 and 760 nm. Intensities of the first three peaks were much greater than the other three and these three bands overlap each other. Blue and blue-green emission may originate from the defects in MgO such as oxygen and magnesium vacancies (Kar and Chaudhuri 2006) and interstitials positions of the atoms, presumably being generated during the high-temperature ablation process. The similar blue (Deepak et al. 2006) and blue-green emission (Zhang and Zhang 2002) have been observed for various MgO nanostructures. The red bands with the peaks located at 600\u2013700 nm were reported by Zhang and Zhang (2002) and Chao (1971) and were assigned as vibrational sidebands lines in luminescence spectrum of bulk MgO with interstitials defects and/or or surface states. The band located at 760 nm may also be associated with the relaxation luminescence of the defect centers excited by mechanical stress. The relaxation luminescence of defect centers may exist because crack causes bond-breaking and nuclear motion, and promotes release of atoms and ions from the lattice sites, resulting in the creation of defects.", "question": "Why may the relaxation luminescence of defect centers exist?", "answers": {"text": "crack causes bond-breaking and nuclear motion", "answer_start": [1263]}}
{"id": "10.1007#s11082-016-0536-8.html_24", "title": "10.1007#s11082-016-0536-8.html", "context": "To reconstruct the spectrum and to determine the individual peak position and its intensity within the spectrum standard multiple Gaussian fitting procedure was used. One main and five smaller bands were identified. The peak positions of the six Gaussian bands are located at about 395, 423, 464, 580, 660 and 760 nm. Intensities of the first three peaks were much greater than the other three and these three bands overlap each other. Blue and blue-green emission may originate from the defects in MgO such as oxygen and magnesium vacancies (Kar and Chaudhuri 2006) and interstitials positions of the atoms, presumably being generated during the high-temperature ablation process. The similar blue (Deepak et al. 2006) and blue-green emission (Zhang and Zhang 2002) have been observed for various MgO nanostructures. The red bands with the peaks located at 600\u2013700 nm were reported by Zhang and Zhang (2002) and Chao (1971) and were assigned as vibrational sidebands lines in luminescence spectrum of bulk MgO with interstitials defects and/or or surface states. The band located at 760 nm may also be associated with the relaxation luminescence of the defect centers excited by mechanical stress. The relaxation luminescence of defect centers may exist because crack causes bond-breaking and nuclear motion, and promotes release of atoms and ions from the lattice sites, resulting in the creation of defects.", "question": "Where does the defects come from?", "answers": {"text": "release of atoms and ions from the lattice sites", "answer_start": [1323]}}
{"id": "10.1007#s11082-016-0536-8.html_25", "title": "10.1007#s11082-016-0536-8.html", "context": "In the THG technique, an incident laser beam of high intensity at the frequency \u03c9 interacts with a nonlinear medium and generates an additional beam at a frequency 3\u03c9. The third harmonic beam corresponds to a pure coherent electronic nonlinearity. This technique is one of the most informative methods for evaluating the electronic contribution of the real part of the third order nonlinear optical susceptibilities \u03c7 elec \u30083\u3009 . The THG technique is sensitive to ultrafast electronic mechanisms of nonlinear response within femtosecond relaxation times and it is almost insensitive to slower effects such as thermal relaxation. Moreover, THG is a much more accurate technique because it allows to directly measure the nonlinear susceptibility and the result is undisturbed by the wavelength of fundamental laser beam. In the case of the DFWM technique, nonlinear signal from the sample is observed as an intensity decrease of the fundamental beams (all waves are focused on the sample and have the same wavelength).", "question": "What technique is one of the informative methods for evaluating the electronic contribution of the real part of the third order nonlinear optical susceptibilities?", "answers": {"text": "THG technique", "answer_start": [7]}}
{"id": "10.1007#s11082-016-0536-8.html_26", "title": "10.1007#s11082-016-0536-8.html", "context": "In the THG technique, an incident laser beam of high intensity at the frequency \u03c9 interacts with a nonlinear medium and generates an additional beam at a frequency 3\u03c9. The third harmonic beam corresponds to a pure coherent electronic nonlinearity. This technique is one of the most informative methods for evaluating the electronic contribution of the real part of the third order nonlinear optical susceptibilities \u03c7 elec \u30083\u3009 . The THG technique is sensitive to ultrafast electronic mechanisms of nonlinear response within femtosecond relaxation times and it is almost insensitive to slower effects such as thermal relaxation. Moreover, THG is a much more accurate technique because it allows to directly measure the nonlinear susceptibility and the result is undisturbed by the wavelength of fundamental laser beam. In the case of the DFWM technique, nonlinear signal from the sample is observed as an intensity decrease of the fundamental beams (all waves are focused on the sample and have the same wavelength).", "question": "What is the THG technique sensitive to?", "answers": {"text": "ultrafast electronic mechanisms of nonlinear response within femtosecond relaxation times", "answer_start": [463]}}
{"id": "10.1007#s11082-016-0536-8.html_27", "title": "10.1007#s11082-016-0536-8.html", "context": "A few theoretical models, using various approximations, have been described in order to determine the value of \u03c7   elec  3  from the shape of the experimental curves of Maker fringes (Maker et al. 1962; Zawadzka et al. 2013b, 2015b) obtained by the THG technique. We used comparative model for explanation of our experimental results. This model compares (Lee et al. 2001) directly the maximum of light intensities amplitudes for the third harmonic of nonlinear medium with those of the reference material used for its calibration of the experimental setup. The value of the third order nonlinear susceptibility \u03c7   elec  3  is derived by comparing third harmonic peak intensities of the sample and reference material (fused silica glass).", "question": "What reference material was used to derive the third order nonlinear susceptibility?", "answers": {"text": "fused silica glass", "answer_start": [719]}}
{"id": "10.1007#s11082-016-0536-8.html_28", "title": "10.1007#s11082-016-0536-8.html", "context": "Figure 7a, b show experimental results of the third harmonic intensity of two samples deposited on 1 mm thick quartz substrate at different substrate temperature: RT and 600 \u00b0C. THG signal were measured for two linear (S, vertical and P, horizontal) polarizations of the fundamental laser beam. To determine the third order optical susceptibility of the sample, the analysis of the experimental results was carried out by using Maker fringes technique. Detailed analyses of the spectra show many fringes, which become tighter with the increase of incidence angle \u03b8, because the length of interaction L in sample increases nonlinearly with the angle. When the thickness of the material d is higher than the coherence length L  CRM , the wave\u2019s constraint and free interfere to each other, and the intensity of third harmonic signal can pass through a series of maxima and minima.\n", "question": "What polarizations of the fundamental laser beam were used to measure the THG signal?", "answers": {"text": "S, vertical and P, horizontal", "answer_start": [219]}}
{"id": "10.1007#s11082-016-0536-8.html_29", "title": "10.1007#s11082-016-0536-8.html", "context": "This paper was focused on the growth and optical properties of magnesium oxide (MgO) thin films fabricated by laser ablation process. The improvement of the structure and the emission characteristics for MgO thin films by application proper substrate temperature during ablation process has been established. XRD spectra showed that the substrate temperature influences the FWHM of the diffraction peaks therefore also grain growth. The Photoluminescence spectra in wide range of temperatures: 13\u2013300 K also showed improvement in optical properties of the magnesium oxide films deposited at higher temperature of the substrate. Experimental results of TRPL shed new light on the controversial issue of the interpretation of the luminescence spectra of MgO thin films. Various physical mechanisms and their impact on observed spectra were depicted. THG experiments were performed and the values of the third order nonlinear susceptibility (electronic part) were found to be similar for well oriented crystal samples than those with the polycrystalline structure. This difference in THG intensities for the MgO thin films prompts that the well oriented crystalline thin films play a very important role as an intermediate films for various multilayer structures. Obtained results confirmed good structural and optical films\u2019 quality and the substrate temperature was crucial to controlling structure and preparing high-quality MgO thin films with a smooth surface.", "question": "What controversial issue could be possibly resolved by the experimental results of TRPL?", "answers": {"text": "interpretation of the luminescence spectra of MgO thin films", "answer_start": [706]}}
{"id": "10.1007#s11082-016-0536-8.html_30", "title": "10.1007#s11082-016-0536-8.html", "context": "This paper was focused on the growth and optical properties of magnesium oxide (MgO) thin films fabricated by laser ablation process. The improvement of the structure and the emission characteristics for MgO thin films by application proper substrate temperature during ablation process has been established. XRD spectra showed that the substrate temperature influences the FWHM of the diffraction peaks therefore also grain growth. The Photoluminescence spectra in wide range of temperatures: 13\u2013300 K also showed improvement in optical properties of the magnesium oxide films deposited at higher temperature of the substrate. Experimental results of TRPL shed new light on the controversial issue of the interpretation of the luminescence spectra of MgO thin films. Various physical mechanisms and their impact on observed spectra were depicted. THG experiments were performed and the values of the third order nonlinear susceptibility (electronic part) were found to be similar for well oriented crystal samples than those with the polycrystalline structure. This difference in THG intensities for the MgO thin films prompts that the well oriented crystalline thin films play a very important role as an intermediate films for various multilayer structures. Obtained results confirmed good structural and optical films\u2019 quality and the substrate temperature was crucial to controlling structure and preparing high-quality MgO thin films with a smooth surface.", "question": "What plays an important role for various multilayer structures?", "answers": {"text": "well oriented crystalline thin films", "answer_start": [1137]}}
{"id": "10.1007#s11082-016-0539-5.html_0", "title": "10.1007#s11082-016-0539-5.html", "context": "In the past 30 years, optical trapping and manipulation (Ashkin 1970; Ashkin et al. 1986; Grier 2003; Neuman and Block 2004; Molloy and Padgett 2002; Dienerowitz et al. 2008; Marag et al. 2013; Ashkin 1997) has been a major tool for advances in biosciences (Khatibzadeh et al. 2014), physics (Gustavson et al. 2001) and chemistry (Misawa et al. 1991). In general, optical tweezers use forces based on the radiation pressure of laser light as a means to immobilise, rotate (Friese et al. 1998), Deufel et al. (2007) and guide small particles ranging from tens of nanometers to tens of micrometers in size (Grier 2003; Dienerowitz et al. 2008; Marag et al. 2013). They have been used in cutting edge research where small particles play a role. The applications of optical trapping include: the observation of the angular momentum of light (Yao and Padgett 2011), the transport of Bose\u2013Einstein condensates (Gustavson et al. 2001), the investigation of the DNA mechanics (Bustamante et al. 2003), spectroscopy and sensing (Cetin et al. 2011), cancer research (Cross et al. 2007), nanofabrication (Pauzauskie et al. 2006), tissue engineering (Kim et al. 1999; Matsuda and Sugawara 1996), the manipulation of single proteins (Pang and Gordon 2012) and single atoms (Yu et al. 2014) and study and manipulation of live cell dynamics in animals (Zhong et al. 2013).", "question": "Who firstly developed the optical trapping and manipulation?", "answers": {"text": "Ashkin", "answer_start": [57]}}
{"id": "10.1007#s11082-016-0539-5.html_1", "title": "10.1007#s11082-016-0539-5.html", "context": "The simulation results presented in this paper were produced using 3D-FDTD calculations (Taflove and Hagness 2005), namely the Lumerical and Meep packages, with a conformal mesh in x, y and z(i.e. a varying mesh size depending on sample dimensions) and a minimum step size of 0.25 nm in the mesh grid (in x, y and Z directions). A 500 nm perfectly matched layer (PML) was placed at the boundaries of the computational domain to prevent artifacts due to numerical reflections. A Drude\u2013Lorentz model (Palik parameters Palik 2012) was used to represent the real metal behaviour of the BNA (i.e. skin effect, dispersion etc.).", "question": "What packages were used in this paper to produce the simulation results?", "answers": {"text": "Lumerical and Meep packages", "answer_start": [127]}}
{"id": "10.1007#s11082-016-0539-5.html_2", "title": "10.1007#s11082-016-0539-5.html", "context": "The simulation results presented in this paper were produced using 3D-FDTD calculations (Taflove and Hagness 2005), namely the Lumerical and Meep packages, with a conformal mesh in x, y and z(i.e. a varying mesh size depending on sample dimensions) and a minimum step size of 0.25 nm in the mesh grid (in x, y and Z directions). A 500 nm perfectly matched layer (PML) was placed at the boundaries of the computational domain to prevent artifacts due to numerical reflections. A Drude\u2013Lorentz model (Palik parameters Palik 2012) was used to represent the real metal behaviour of the BNA (i.e. skin effect, dispersion etc.).", "question": "What model was used to represent the real metal behaviour of the BNA?", "answers": {"text": "Drude\u2013Lorentz", "answer_start": [478]}}
{"id": "10.1007#s11082-016-0539-5.html_3", "title": "10.1007#s11082-016-0539-5.html", "context": "The simulation results presented in this paper were produced using 3D-FDTD calculations (Taflove and Hagness 2005), namely the Lumerical and Meep packages, with a conformal mesh in x, y and z(i.e. a varying mesh size depending on sample dimensions) and a minimum step size of 0.25 nm in the mesh grid (in x, y and Z directions). A 500 nm perfectly matched layer (PML) was placed at the boundaries of the computational domain to prevent artifacts due to numerical reflections. A Drude\u2013Lorentz model (Palik parameters Palik 2012) was used to represent the real metal behaviour of the BNA (i.e. skin effect, dispersion etc.).", "question": "What is the thickness of the layer that was placed at the boundaries of the computational domain?", "answers": {"text": "500 nm", "answer_start": [331]}}
{"id": "10.1007#s11082-016-0539-5.html_4", "title": "10.1007#s11082-016-0539-5.html", "context": "Two conditions must be met to have a successful optical trap for Rayleigh particles. Firstly, the gradient force must be larger than the scattering force. Secondly, the trapping energy must dominate the thermal energy (in other words, the trapping forces must pull the particle in before the Brownian motion of the particle moves it out of the trap). As discussed earlier, the polarizability of the particle in the trap is the key factor in determining how easily it can be trapped (Svoboda and Block 1994). We know that laser induced heating is also proportional to the intensity (Seol et al. 2006) of the light. To trap nanosized particles, the gradient force should be increased while limiting the heating of the sample. For the trapping of biological samples, it is also important to keep the heating to a minimum to maintain the viability of the sample.", "question": "How many conditions are needed to meet to have a successful optical trap for Rayleigh particles?", "answers": {"text": "Two", "answer_start": [0]}}
{"id": "10.1007#s11082-016-0542-x.html_0", "title": "10.1007#s11082-016-0542-x.html", "context": "The multi-physics nature of optical heating is in this paper described as follows: The electromagnetic TLM model is used to model electromagnetic scattering of the optical wave in the plasmonic waveguide. The metal at optical frequencies cannot be assumed to be a perfect conductor and is highly lossy, dispersive and frequency dependent. As such the metal is described using the Drude model (Ramo et al. 1997) and the Z-transform that facilitates the translation between frequency responses of the filter to the time domain of the numerical method. The losses in the metal will give rise to the heating which is used as a heat source in solving the temporal heat diffusion using the thermal TLM. The coupling process is presented in Fig. 1b where coupling is done from the EM to thermal models at specified time intervals \u2206t  th  and where both EM and thermal simulations are run in parallel. The temporal time step of the EM simulation is fixed but the time step of the thermal simulation can in practice be much larger than that of the EM simulation; in the present model it can be m times larger where m is a positive integer.", "question": "What model is used to model electromagnetic scattering of the optical wave in the plasmonic waveguide?", "answers": {"text": "electromagnetic TLM model", "answer_start": [87]}}
{"id": "10.1007#s11082-016-0542-x.html_1", "title": "10.1007#s11082-016-0542-x.html", "context": "It is clear that the choice of the coupling interval which determines the thermal time steps would affect the stability, self-consistency and accuracy of the overall coupling method. This is investigated on an example of plasmonic Si waveguide utilizing a tapered nano-tip as a heat source, as shown in Fig. 2. The tapered part of the Si waveguide is submerged in a gold plate (Au). The fundamental TM mode, with the electric field polarised in y-direction, is excited in order to activate the plasmon mode at the Si\u2013gold interface. The strong confinement of the EM field at the waveguide tip will result in high ohmic losses and heating of the Au around the waveguide tip.\n", "question": "What will result in high ohmic losses and heating of the Au around the waveguide tip?", "answers": {"text": "strong confinement of the EM field", "answer_start": [537]}}
{"id": "10.1007#s11082-016-0542-x.html_2", "title": "10.1007#s11082-016-0542-x.html", "context": "where \u03c9\np is the plasma frequency in rad/s, \u03bdc is the plasma collision frequency, \u03b50 is the permittivity of free space, \u03c9 is the angular frequency, and \u03b5im(\u03c9) and \u03b5re(\u03c9) are the imaginary and real components of the plasma permittivity respectively. Complex dielectric constant is implemented in the TLM method using the Z-transform and digital filter method (Paul 1998) and will not be covered in detail here. The imaginary part of the complex dielectric index represents the material conductivity component that is responsible for the power dissipation in the metal. The heat source of the thermal model is obtained from the instantaneous power losses in the EM model as a consequence of the material conductivity. At optical frequencies the conductivity of a plasmonic material can be approximated to be (Ordal et al. 1985),\n", "question": "Why do the instantaneous power losses in the EM model exist?", "answers": {"text": "material conductivity", "answer_start": [476]}}
{"id": "10.1007#s11082-016-0542-x.html_3", "title": "10.1007#s11082-016-0542-x.html", "context": "Typically, the time step of the thermal model that satisfies Eq. 13 is many orders of magnitude higher than the time step of the EM model, which means that that the overall timescales of EM and thermal models are different. The choice of thermal time step is thus important for stable coupling between the EM and thermal models. Generally setting the thermal time step to be equal to the electrical time step will guarantee the stability of the thermal model due to the fact that thermal diffusion is much slower than the interaction of the EM waves. However, this choice would increase the computational resources of the model. It would be desirable to increase the thermal time step and coupling intervals so that both the accuracy and the stability of the method are ensured and both EM and thermal simulations are effectively running in parallel over the same time frame as shown in Fig. 1b. In the following section the choice of the thermal time step is discussed in terms of the accuracy and stability of the coupled method.", "question": "Why will setting the thermal time step to be equal to the electrical time step guarantee the stability of the thermal model?", "answers": {"text": "thermal diffusion is much slower than the interaction of the EM waves", "answer_start": [480]}}
{"id": "10.1007#s11082-016-0542-x.html_4", "title": "10.1007#s11082-016-0542-x.html", "context": "In this section the coupled EM-thermal model is used to simulate the EM field propagation and conduction heat diffusion for the 2D nanotip waveguide structure shown in Fig. 2. The silicon slab waveguide has a width of 1 \u03bcm and a length of 3 \u03bcm. The triangular tapered area has a base of 0.45 \u03bcm and a length of 1 \u03bcm with the nanotip of 20 nm diameter to focus the light at the end of the waveguide. The silicon waveguide core has an effective refractive index of 3.3917 at the operating frequency of 1.55 \u03bcm and the air as the cladding material. The material parameters for gold are \u03c9p = 1.36734 \u00d7 1016 rad/s and \u03bdc = 6.46 \u00d7 1013 Hz (Ordal et al. 1985). The silicon is considered to be lossless in this model as silicon conductivity is negligible at the operating frequency. All EM material parameters are kept constant in the model.", "question": "What is the width of the silicon slab waveguide?", "answers": {"text": "1 \u03bcm", "answer_start": [218]}}
{"id": "10.1007#s11082-016-0542-x.html_5", "title": "10.1007#s11082-016-0542-x.html", "context": "In this section the coupled EM-thermal model is used to simulate the EM field propagation and conduction heat diffusion for the 2D nanotip waveguide structure shown in Fig. 2. The silicon slab waveguide has a width of 1 \u03bcm and a length of 3 \u03bcm. The triangular tapered area has a base of 0.45 \u03bcm and a length of 1 \u03bcm with the nanotip of 20 nm diameter to focus the light at the end of the waveguide. The silicon waveguide core has an effective refractive index of 3.3917 at the operating frequency of 1.55 \u03bcm and the air as the cladding material. The material parameters for gold are \u03c9p = 1.36734 \u00d7 1016 rad/s and \u03bdc = 6.46 \u00d7 1013 Hz (Ordal et al. 1985). The silicon is considered to be lossless in this model as silicon conductivity is negligible at the operating frequency. All EM material parameters are kept constant in the model.", "question": "What is the length of the silicon slab waveguide?", "answers": {"text": "3 \u03bcm", "answer_start": [239]}}
{"id": "10.1007#s11082-016-0542-x.html_6", "title": "10.1007#s11082-016-0542-x.html", "context": "In this section the coupled EM-thermal model is used to simulate the EM field propagation and conduction heat diffusion for the 2D nanotip waveguide structure shown in Fig. 2. The silicon slab waveguide has a width of 1 \u03bcm and a length of 3 \u03bcm. The triangular tapered area has a base of 0.45 \u03bcm and a length of 1 \u03bcm with the nanotip of 20 nm diameter to focus the light at the end of the waveguide. The silicon waveguide core has an effective refractive index of 3.3917 at the operating frequency of 1.55 \u03bcm and the air as the cladding material. The material parameters for gold are \u03c9p = 1.36734 \u00d7 1016 rad/s and \u03bdc = 6.46 \u00d7 1013 Hz (Ordal et al. 1985). The silicon is considered to be lossless in this model as silicon conductivity is negligible at the operating frequency. All EM material parameters are kept constant in the model.", "question": "At what operating frequency does the silicon waveguide core display an effective refractive index of 3.3917?", "answers": {"text": "1.55 \u03bcm", "answer_start": [500]}}
{"id": "10.1007#s11082-016-0542-x.html_7", "title": "10.1007#s11082-016-0542-x.html", "context": "In order to investigate the convergence of the coupled-method results with the mesh size Fig. 7a, b shows the temperature distribution along the middle of the plasmonic waveguide, i.e., in the y = 2.5 \u03bcm plane, for different mesh sizes, namely \u2206x = 25, \u2206x = 20 and \u2206x = 10 nm. The time steps of the EM and thermal models are kept the same as \u2206t  EM  = \u2206t  th  = 2.3586 \u00d7 10\u221217 s. Two different cases are considered, namely (a) an uncoupled EM-thermal where a complete EM simulation is done until the field reaches steady state and the power losses at the end of simulation are used as an input to the thermal model, and (b), where the power losses of the EM model are used as an input to the thermal at every time step. The input optical source power in both cases is taken to be 10 mW.\n", "question": "What is the power of the input optical source in the two case studies?", "answers": {"text": "10 mW", "answer_start": [780]}}
{"id": "10.1007#s11082-016-0542-x.html_8", "title": "10.1007#s11082-016-0542-x.html", "context": "To further investigate the thermal profile, Fig. 8a, b plots the thermal field distribution after 82.78 ps of the simulation time for the uncoupled and coupled EM-thermal models using \u2206x = 20 nm and an input optical power of 10 mW. The uncoupled model results show a wider spatial spread but lower maximum temperature (~8 \u00b0C) due to the fact that all the thermal energy is given once at the beginning of the modelling process as shown in Fig. 8a. Figure 8b shows that thermal profile of the coupled EM-thermal model results in a more focused profile with higher maximum temperature compared to Fig. 8b. In the case of the coupled model the regular application of the input thermal source resulting from the EM simulation leads to higher temperatures and temperature distribution more focused at places where the EM field is strongest as shown in Fig. 7. The result of Fig. 7b compares very well with the simulations and measurements of (Desiatov et al. 2014) where the maximum temperature rise is ~15 \u00b0C. The small differences might occur due to the fact that a 2D model is considered in this paper.\n", "question": "How long did the simulation time last?", "answers": {"text": "82.78 ps", "answer_start": [98]}}
{"id": "10.1016#j.ijleo.2013.02.006.xml_0", "title": "10.1016#j.ijleo.2013.02.006.xml", "context": "In this paper the design, implementation and performance analysis of four wave mixing (FWM) in optical communication system for different number of input channels is presented using various values of channel spacing. Here, all the input channels have been spaced evenly at various values like 6.25 GHz, 12.5 GHz, 25 GHz, 40 GHz, 50 GHz with the different number of channels at the input i.e. with 2, 4, 6, 8, 12 input channels. The simulation results reveal that the four wave mixing is minimum when the channel spacing is maximum i.e. 50 GHz with minimum number of channels i.e. 2 input channels. It is observed that on increasing the channel spacing, the interference between the input frequencies decreases and hence the four wave mixing also decreases. Also, on increasing the number of input channels/users, the interference between the input frequencies increases and thus, the four wave mixing also increases.", "question": "On what condition will the four wave mixing decrease?", "answers": {"text": "increasing the channel spacing", "answer_start": [621]}}
{"id": "10.1016#j.ijleo.2013.02.006.xml_1", "title": "10.1016#j.ijleo.2013.02.006.xml", "context": "In this paper the design, implementation and performance analysis of four wave mixing in optical communication system for different number of input channels at various values of channel spacing is presented. It has been observed that on increasing the number of input channels/users, the interference increases and thus, the four wave mixing effect also increases. The eye opening decreases as the number of channels increases. Increasing the number of channels causes the Q-factor to decrease. Moreover, as the number of channels increases, the BER increases. Thus, it can be concluded that the four wave mixing is least when less number of channels are used but in today's technology, it is important for the circuit to handle wavelength division multiplexing i.e. different users can use the bandwidth at the same time without any interference so this drawback of four wave mixing should be minimized.", "question": "What causes the Q-factor to decrease?", "answers": {"text": "Increasing the number of channels", "answer_start": [428]}}
{"id": "10.1016#j.ijleo.2013.02.007.xml_0", "title": "10.1016#j.ijleo.2013.02.007.xml", "context": "In this paper, the optical effects on the characteristics of GaAs FinFET with Gaussian doping profile in the vertical direction of the channel considering quantum mechanical effects (QME) have been theoretically examined and analyzed. The device characteristics are obtained using self-consistent solution of 3D Poisson\u2013Schr\u00f6dinger equations using interpolating wavelet method and Simpson's one-third rule. This method provides more accurate results by dynamically adjusting the computational mesh and scales the CPU time linearly with the number of mesh points using polynomial interpolation, hence reducing the numerical cost. The results obtained are compared with uniformly doped Si FinFET photodetector characteristics and used to examine the performance of the device for its suitable use as a photodetector in Opto-Electronic Integrated Circuit (OEIC) receivers.", "question": "Why could the numerical cost of the mentioned method be reduced?", "answers": {"text": "dynamically adjusting the computational mesh and scales the CPU time linearly with the number of mesh points using polynomial interpolation", "answer_start": [453]}}
{"id": "10.1016#j.ijleo.2013.02.007.xml_1", "title": "10.1016#j.ijleo.2013.02.007.xml", "context": "In order to optimize the performance of double gate devices, self-aligned processes and structures are proposed, with FinFET being one of the most promising . The FinFET is a symmetric three gate structure, which means that all its three gates have the same work function and also at the same potential. The three dimensional (3-D) structure requires 3-D analysis. The potential variation in the channel used to calculate the subthreshold current and threshold voltage of FinFETs with doped and undoped channels has been reported . Two dimensional (2-D) models can only be used to study the operation of the device along certain plane sections of the channel. The 3-D analytical modeling of FinFET by solving the Poisson's equation has also been reported . The existing literatures reported on analytical modeling have shown the complexity in evaluating various device characteristics including QM effects. In addition, it has been found that many assumptions and approximations have to be incorporated while the device is analytically modeled. Quantum mechanical modeling is important for many reasons, e.g., the tunneling current through ultra-thin gate oxide adds to the low limit of the off-state current. In FinFET devices, quantum effects and non-equilibrium, ballistic or near-ballistic transport has large impact on device performance . For channel length comparable to the carrier scattering length, carriers transport ballistically .", "question": "What is reported in this study?", "answers": {"text": "self-aligned processes and structures", "answer_start": [61]}}
{"id": "10.1016#j.ijleo.2013.02.007.xml_2", "title": "10.1016#j.ijleo.2013.02.007.xml", "context": "In our previous work, a 3D numerical modeling of optical effects on the characteristics of the nanoscale Si FinFET considering quantum mechanical effects has been obtained . It is also proved that the interpolating wavelet method provides better accuracy with reduced simulation time . The simulation results obtained using interpolating wavelet has been validated with device simulator results and experimental values . A two-dimensional model for the potential distribution and threshold voltage of short-channel double-gate metal-oxide-semiconductor field-effect transistors with a vertical Gaussian-like doping profile has also been reported . It may be mentioned that ion implantation method is an established technique that can be used to maintain the doping distribution in doped devices in an accurately controlled manner. Since, ion implantation provides a Gaussian profile for the doping distribution in the doped region of any device and the Gaussian distribution is the most general doping profile from which a number of different doping profiles can be derived by varying the projected range, RP, and straggle, \u03c3p of the Gaussian function, it may be an important issue in the near future to characterize the nanoscale FinFET with such a non-uniform doping profile . Although Si FinFET are suitable for high speed applications , GaAs FinFETs provides better performance than Si FinFET.", "question": "What has the simulation results obtained using interpolating wavelet been validated with?", "answers": {"text": "device simulator results and experimental values", "answer_start": [370]}}
{"id": "10.1016#j.ijleo.2013.02.008.xml_0", "title": "10.1016#j.ijleo.2013.02.008.xml", "context": "Titanium dioxide (TiO2) is widely studied by researchers in the basic sciences as well as in engineering. Its phase transformation has been widely studied for optical and electronic applications. This material shows properties that are of special interest in wide range technological of applications such as: photo catalysis, solar cells, gas sensors, hard coating, self-cleaning windows , optical wave guiding, optical coatings and microelectronics , antireflective coatings , and thin film capacitors . Besides, these films are extensively used in optical thin film devices, because of their good transmittance in the visible region, high refractive index and chemical stability . For fabricating TiO2 thin films, many methods have been applied, such as chemical-vapor deposition (CVD) , sol\u2013gel deposition , electron beam evaporation , magnetron sputtering, pulsed laser deposition (PLD) , molecular beam epitaxy (MBE) , and biomimetic approaches .", "question": "Why are the titanium dioxide films extensively used in optical thin film devices?", "answers": {"text": "good transmittance in the visible region, high refractive index and chemical stability", "answer_start": [594]}}
{"id": "10.1016#j.ijleo.2013.02.008.xml_1", "title": "10.1016#j.ijleo.2013.02.008.xml", "context": "TiO2 films of 33 nm thickness were produced, using resistive heat deposition of TiO2 powder (98% purity) at 300 K temperature. Titanium dioxide thin films were transparent in visible light wavelength range. Optical properties of TiO2 thin films at different deposition angles, were obtained using Kramers\u2013Kronig relations. All the optical properties showed deposition angle dependence. There was a good agreement between the void formation on layers and the optical properties. By increasing the deposition angle, more voids formed on layers. That tends to change in the optical properties. By increasing deposition angle real part of refractive index (n) increases and imaginary part of refractive index (k) decreases. Also real part of dielectric constant increases and imaginary part of dielectric constant decreases. Therefore real part of conductivity constant decreases and imaginary part of conductivity constant increases.", "question": "What is the purity of the TiO2 powder that is used in this study to produce the TiO2 films?", "answers": {"text": "98%", "answer_start": [93]}}
{"id": "10.1016#j.ijleo.2013.02.008.xml_2", "title": "10.1016#j.ijleo.2013.02.008.xml", "context": "TiO2 films of 33 nm thickness were produced, using resistive heat deposition of TiO2 powder (98% purity) at 300 K temperature. Titanium dioxide thin films were transparent in visible light wavelength range. Optical properties of TiO2 thin films at different deposition angles, were obtained using Kramers\u2013Kronig relations. All the optical properties showed deposition angle dependence. There was a good agreement between the void formation on layers and the optical properties. By increasing the deposition angle, more voids formed on layers. That tends to change in the optical properties. By increasing deposition angle real part of refractive index (n) increases and imaginary part of refractive index (k) decreases. Also real part of dielectric constant increases and imaginary part of dielectric constant decreases. Therefore real part of conductivity constant decreases and imaginary part of conductivity constant increases.", "question": "How to form more voids on layers?", "answers": {"text": "increasing the deposition angle", "answer_start": [481]}}
{"id": "10.1016#j.ijleo.2013.02.010.xml_0", "title": "10.1016#j.ijleo.2013.02.010.xml", "context": "The post-processing of LPGs is actually used to adjust or stabilize the spectral transmission, as well to improve the sensitivity of the rejection bands in the LPGs. Typically the amount of hydrogen present in an optical fiber for grating manufacture is far in excess of that required to achieve a given refractive index change . Thus following the completion of the writing process there is a finite amount of unused hydrogen remaining in the cladding that can significantly influence the grating transmission spectrum. LPG spectrum can be stabilized by annealing it at high temperatures . LPGs can be produced in various types of fibers, from standard telecommunication fibers to micro structured ones . LPGs with two different grating periods (415 \u03bcm and 550 \u03bcm) written into the cores of standard telecommunication fibers (SMF-28e, Corning) have been utilized for our studies. We first discuss the spectral variation during the fabrication process and then the impact of annealing and temperature variations on the attenuation bands of LPGs.", "question": "What are the two grating periods of the LPGs that have been utilized for our studies?", "answers": {"text": "415 \u03bcm and 550 \u03bcm", "answer_start": [747]}}
{"id": "10.1016#j.ijleo.2013.02.010.xml_1", "title": "10.1016#j.ijleo.2013.02.010.xml", "context": "where L is the length of LPG and km is the coupling coefficient for mth cladding mode. Therefore, the percentage of coupled power depends on L and km. The parameter km however depends on the specific cladding mode and also the amplitude of refractive index modulation (\u0394nco) induced in the fiber core. The resonance wavelength of LPGs is a function of strain, temperature , bending and SRI. The presence of these external perturbations affects the coupling strength between the core and cladding modes, which could cause the resonant wavelength shift (\u03bbm) and amplitude changes of the LPG attenuation bands. The shift of the center wavelength of the peaks can occur toward shorter or longer wavelengths.", "question": "The coupling strength between what will be affected by the presence of these external perturbations?", "answers": {"text": "core and cladding modes", "answer_start": [478]}}
{"id": "10.1016#j.ijleo.2013.02.010.xml_2", "title": "10.1016#j.ijleo.2013.02.010.xml", "context": "where L is the length of LPG and km is the coupling coefficient for mth cladding mode. Therefore, the percentage of coupled power depends on L and km. The parameter km however depends on the specific cladding mode and also the amplitude of refractive index modulation (\u0394nco) induced in the fiber core. The resonance wavelength of LPGs is a function of strain, temperature , bending and SRI. The presence of these external perturbations affects the coupling strength between the core and cladding modes, which could cause the resonant wavelength shift (\u03bbm) and amplitude changes of the LPG attenuation bands. The shift of the center wavelength of the peaks can occur toward shorter or longer wavelengths.", "question": "What could cause the resonant wavelength shift (\u03bbm) and amplitude changes of the LPG attenuation bands?", "answers": {"text": "presence of these external perturbations", "answer_start": [395]}}
{"id": "10.1016#j.ijleo.2013.02.010.xml_3", "title": "10.1016#j.ijleo.2013.02.010.xml", "context": "Two LPGs with grating periods of 415 \u03bcm and 550 \u03bcm, respectively, were fabricated for our experimental investigation. These LPGs were fabricated using a 248 nm KrF excimer laser source and employing point-by-point writing method. A great advantage of the point-by-point method is that it is a highly flexible technique, since the grating periodicity and length can be individually adjusted to meet the desired LPG specifications and corresponding spectral characteristics. The duty cycle of grating period was \u223c50%. The standard single-mode fiber (SMF-28e) used had a core diameter of 8.2 \u03bcm and cladding diameter of 125 \u03bcm. The core and the cladding refractive indices were 1.46145 and 1.456, respectively. To enhance the photosensitivity, the fibers were hydrogen loaded at 100 \u00b0C and 1500 psi of pressure for 24 h before the LPG fabrication. The fiber coating was removed just before exposure to the UV laser light.", "question": "What is the core diameter of the standard single-mode fiber?", "answers": {"text": "8.2 \u03bcm", "answer_start": [585]}}
{"id": "10.1016#j.ijleo.2013.02.010.xml_4", "title": "10.1016#j.ijleo.2013.02.010.xml", "context": "Two LPGs with grating periods of 415 \u03bcm and 550 \u03bcm, respectively, were fabricated for our experimental investigation. These LPGs were fabricated using a 248 nm KrF excimer laser source and employing point-by-point writing method. A great advantage of the point-by-point method is that it is a highly flexible technique, since the grating periodicity and length can be individually adjusted to meet the desired LPG specifications and corresponding spectral characteristics. The duty cycle of grating period was \u223c50%. The standard single-mode fiber (SMF-28e) used had a core diameter of 8.2 \u03bcm and cladding diameter of 125 \u03bcm. The core and the cladding refractive indices were 1.46145 and 1.456, respectively. To enhance the photosensitivity, the fibers were hydrogen loaded at 100 \u00b0C and 1500 psi of pressure for 24 h before the LPG fabrication. The fiber coating was removed just before exposure to the UV laser light.", "question": "What is the cladding diameter of the used standard single-mode fiber?", "answers": {"text": "125 \u03bcm", "answer_start": [617]}}
{"id": "10.1016#j.ijleo.2013.02.010.xml_5", "title": "10.1016#j.ijleo.2013.02.010.xml", "context": "Two LPGs with grating periods of 415 \u03bcm and 550 \u03bcm, respectively, were fabricated for our experimental investigation. These LPGs were fabricated using a 248 nm KrF excimer laser source and employing point-by-point writing method. A great advantage of the point-by-point method is that it is a highly flexible technique, since the grating periodicity and length can be individually adjusted to meet the desired LPG specifications and corresponding spectral characteristics. The duty cycle of grating period was \u223c50%. The standard single-mode fiber (SMF-28e) used had a core diameter of 8.2 \u03bcm and cladding diameter of 125 \u03bcm. The core and the cladding refractive indices were 1.46145 and 1.456, respectively. To enhance the photosensitivity, the fibers were hydrogen loaded at 100 \u00b0C and 1500 psi of pressure for 24 h before the LPG fabrication. The fiber coating was removed just before exposure to the UV laser light.", "question": "What is the refractive index of the core of the standard single-mode fiber?", "answers": {"text": "1.46145", "answer_start": [675]}}
{"id": "10.1016#j.ijleo.2013.02.010.xml_6", "title": "10.1016#j.ijleo.2013.02.010.xml", "context": "Two LPGs with grating periods of 415 \u03bcm and 550 \u03bcm, respectively, were fabricated for our experimental investigation. These LPGs were fabricated using a 248 nm KrF excimer laser source and employing point-by-point writing method. A great advantage of the point-by-point method is that it is a highly flexible technique, since the grating periodicity and length can be individually adjusted to meet the desired LPG specifications and corresponding spectral characteristics. The duty cycle of grating period was \u223c50%. The standard single-mode fiber (SMF-28e) used had a core diameter of 8.2 \u03bcm and cladding diameter of 125 \u03bcm. The core and the cladding refractive indices were 1.46145 and 1.456, respectively. To enhance the photosensitivity, the fibers were hydrogen loaded at 100 \u00b0C and 1500 psi of pressure for 24 h before the LPG fabrication. The fiber coating was removed just before exposure to the UV laser light.", "question": "What is the refractive index of the cladding of the standard single-mode fiber?", "answers": {"text": "1.456", "answer_start": [687]}}
{"id": "10.1016#j.ijleo.2013.02.010.xml_7", "title": "10.1016#j.ijleo.2013.02.010.xml", "context": "Two LPGs with grating periods of 415 \u03bcm and 550 \u03bcm, respectively, were fabricated for our experimental investigation. These LPGs were fabricated using a 248 nm KrF excimer laser source and employing point-by-point writing method. A great advantage of the point-by-point method is that it is a highly flexible technique, since the grating periodicity and length can be individually adjusted to meet the desired LPG specifications and corresponding spectral characteristics. The duty cycle of grating period was \u223c50%. The standard single-mode fiber (SMF-28e) used had a core diameter of 8.2 \u03bcm and cladding diameter of 125 \u03bcm. The core and the cladding refractive indices were 1.46145 and 1.456, respectively. To enhance the photosensitivity, the fibers were hydrogen loaded at 100 \u00b0C and 1500 psi of pressure for 24 h before the LPG fabrication. The fiber coating was removed just before exposure to the UV laser light.", "question": "How long were the fibers hydrogen loaded?", "answers": {"text": "24 h", "answer_start": [812]}}
{"id": "10.1016#j.ijleo.2013.02.010.xml_8", "title": "10.1016#j.ijleo.2013.02.010.xml", "context": " shows the transmission spectra of the LPG with grating period of 415 \u03bcm and various grating period numbers of 21, 36, 46 and 56. The appearance of attenuation dips in the transmission spectrum was first observed after the 21st period of the grating was created. Five loss peaks were detected in the wavelength range of 1240\u20131625 nm. They exhibited a slow initial growth rate followed by a progressively increasing growth rate. It can also be seen that, with an increase in the number of the grating period, the attenuation dip increases, and the 3 dB bandwidth of the transmission spectrum decreases. The increase in attenuation dip is due to the fact that, with increasing grating length the power coupling to different cladding modes increases [Eq. ]. After the writing of the 56th period, the power coupling to different cladding modes LP02, LP03, LP04, LP05 and LP06 were seen to occur at 1247.60, 1278.32, 1331.19, 1425.41, 1613.84 nm respectively. The maximum attenuation dip, corresponding to the LP06 cladding mode observed is about 31.21 dB.", "question": "What is the maximum attenuation dip that is observed?", "answers": {"text": "31.21 dB", "answer_start": [1042]}}