A simple model for approximate bandgap structure calculation of all-solid photonic bandgap fibre based on an array of rings is proposed. In this model calculated are only the potential modes of a unit cell, which is a...A simple model for approximate bandgap structure calculation of all-solid photonic bandgap fibre based on an array of rings is proposed. In this model calculated are only the potential modes of a unit cell, which is a high-index ring in the low-index background for this fibre, rather than the whole cladding periodic structure based on Bloch＇s theorem to find the bandgap. Its accuracy is proved by comparing its results with the results obtained by using the accurate full-vector plane-wave method. High speed in computation is its great advantage over the other exact methods, because it only needs to find the roots of one-dimensional analytical expressions. And the results of this model, mode plots, offer an ideal environment to explore the basic properties of photonie bandgap clearly.展开更多
Phase effect on the guided resonances in photonic crystal slabs is analysed. We present an analysis in the case of a mirror symmetric system and an asymmetric system irradiated from both sides, as well as the more rea...Phase effect on the guided resonances in photonic crystal slabs is analysed. We present an analysis in the case of a mirror symmetric system and an asymmetric system irradiated from both sides, as well as the more realistic and interesting case of a system bounded from one side by a perfect mirror. Gain is incorporated in the system, mainly to exemplify the results. Finally we find that phase effects persist in the asymmetric system resulting in a periodic response for the reflectivity versus the distance from the mirror, which is the main parameter controlling the phase relationship between the two incident waves.展开更多
In this work, we study the photonic band of cumulative Fibonacci lattices, of which the structure is composed of all generated units in a Fibonacci sequence. The results are compared with distributed Bragg reflector(D...In this work, we study the photonic band of cumulative Fibonacci lattices, of which the structure is composed of all generated units in a Fibonacci sequence. The results are compared with distributed Bragg reflector(DBR)structures with the same numbers of layers. Photonic bandgaps are found at two characteristic frequencies, symmetrically separated from the central bandgap in the DBR counterpart. Field amplitude and phase distribution in the Fibonacci lattice indicates an interferential origin of the bandgaps. Fourier transform on the refractive index profile is carried out, and the result confirms a determinate long-range periodicity that agrees well with the photonic band structure.展开更多
In the past decade,molybdenum ditelluride(MoTe2)has received significant attention from the scientific community due to its structural features and unique properties originate from them.In the current review,the prope...In the past decade,molybdenum ditelluride(MoTe2)has received significant attention from the scientific community due to its structural features and unique properties originate from them.In the current review,the properties,various preparation approaches,and versatile applications of MoTe2 are presented.The review provides a brief update on the state of our fundamental understanding of MoTe2 material and also discusses the issues that need to be resolved.To introduce MoTe2,we briefly summarize its structural,optoelectronic,magnetic,and mechanical properties in the beginning.Then,different preparation meth-ods of MoTe2,such as exfoliation,laser treatment,deposition,hydrothermal,microwave,and molecular beam epitaxy,are included.The excellent electri-cal conductivity,strong optical activity,tunable bandgap,high sensitivity,and impressive stability make it an ideal contender for different applications,includ-ing energy storage,catalysis,sensors,solar cells,photodetectors,and transistors.The performance of MoTe2 in these applications is systematically introduced along with mechanistic insights.At the end of the article,the challenges and possible future directions are highlighted to further modify MoTe2 material for the numerous functionalities.Therefore,the availability of different phases and layer structures implies a potential for MoTe2 to lead an era of two-dimensional materials that began from the exfoliation of graphene.展开更多
We perform a comprehensive analysis of uniform-velocity bilayer spacetime crystals,combining concepts of conventional photonic crystals and special relativity.Given that a spacetime crystal consists of a sequence of s...We perform a comprehensive analysis of uniform-velocity bilayer spacetime crystals,combining concepts of conventional photonic crystals and special relativity.Given that a spacetime crystal consists of a sequence of spacetime discontinuities,we do this by solving the following sequence of problems:(1)the spacetime interface,(2)the double spacetime interface,or spacetime slab,(3)the unbounded crystal,and(4)the truncated crystal.For these problems,we present the following results:(1)an extension of the Stokes principle to spacetime interfaces,(2)an interference-based analysis of the interference phenomenology,(3)a quick linear approximation of the dispersion diagrams,a description of simultaneous wavenumber and frequency bandgaps,and(4)the explanation of the effects of different types of spacetime crystal truncations and the corresponding scattering coefficients.This work may constitute the foundation for a virtually unlimited number of novel canonical spacetime media and metamaterial problems.展开更多
Silicon carbide nanosheets(SiCNSs)have a very broad application prospect in the field of new two-dimensional(2D)materials.In this paper,the interlayer interaction mechanism of bilayer SiCNSs(BL-SiCNSs)and its effect o...Silicon carbide nanosheets(SiCNSs)have a very broad application prospect in the field of new two-dimensional(2D)materials.In this paper,the interlayer interaction mechanism of bilayer SiCNSs(BL-SiCNSs)and its effect on optical properties are studied by first principles.Taking the charge and dipole moment of the layers as parameters,an interlayer coupling model is constructed which is more convenient to control the photoelectric properties.The results show that the stronger the interlayer coupling,the smaller the band gap of BL-SiCNSs.The interlayer coupling also changes the number of absorption peaks and causes the red or blue shift of absorption peaks.The strong interlayer coupling can produce obvious dispersion and regulate the optical transmission properties.The larger the interlayer distance,the smaller the permittivity in the vertical direction.However,the permittivity of the parallel direction is negative in the range of 150-300 nm,showing obvious metallicity.It is expected that the results will provide a meaningful theoretical basis for further study of SiCNSs optoelectronic devices.展开更多
基金Project supported by the National High Technology Research and Development Program of China (Grant No 2004AA31G200)Beijing Jiaotong University Foundation, China (Grant No 2005SM002)
文摘A simple model for approximate bandgap structure calculation of all-solid photonic bandgap fibre based on an array of rings is proposed. In this model calculated are only the potential modes of a unit cell, which is a high-index ring in the low-index background for this fibre, rather than the whole cladding periodic structure based on Bloch＇s theorem to find the bandgap. Its accuracy is proved by comparing its results with the results obtained by using the accurate full-vector plane-wave method. High speed in computation is its great advantage over the other exact methods, because it only needs to find the roots of one-dimensional analytical expressions. And the results of this model, mode plots, offer an ideal environment to explore the basic properties of photonie bandgap clearly.
文摘Phase effect on the guided resonances in photonic crystal slabs is analysed. We present an analysis in the case of a mirror symmetric system and an asymmetric system irradiated from both sides, as well as the more realistic and interesting case of a system bounded from one side by a perfect mirror. Gain is incorporated in the system, mainly to exemplify the results. Finally we find that phase effects persist in the asymmetric system resulting in a periodic response for the reflectivity versus the distance from the mirror, which is the main parameter controlling the phase relationship between the two incident waves.
基金National Natural Science Foundation of China(NSFC)(11574166)Science and Technology Foundation for Youth Talents of the Educational Commission of Hubei Province of China(Q2015002)
文摘In this work, we study the photonic band of cumulative Fibonacci lattices, of which the structure is composed of all generated units in a Fibonacci sequence. The results are compared with distributed Bragg reflector(DBR)structures with the same numbers of layers. Photonic bandgaps are found at two characteristic frequencies, symmetrically separated from the central bandgap in the DBR counterpart. Field amplitude and phase distribution in the Fibonacci lattice indicates an interferential origin of the bandgaps. Fourier transform on the refractive index profile is carried out, and the result confirms a determinate long-range periodicity that agrees well with the photonic band structure.
文摘In the past decade,molybdenum ditelluride(MoTe2)has received significant attention from the scientific community due to its structural features and unique properties originate from them.In the current review,the properties,various preparation approaches,and versatile applications of MoTe2 are presented.The review provides a brief update on the state of our fundamental understanding of MoTe2 material and also discusses the issues that need to be resolved.To introduce MoTe2,we briefly summarize its structural,optoelectronic,magnetic,and mechanical properties in the beginning.Then,different preparation meth-ods of MoTe2,such as exfoliation,laser treatment,deposition,hydrothermal,microwave,and molecular beam epitaxy,are included.The excellent electri-cal conductivity,strong optical activity,tunable bandgap,high sensitivity,and impressive stability make it an ideal contender for different applications,includ-ing energy storage,catalysis,sensors,solar cells,photodetectors,and transistors.The performance of MoTe2 in these applications is systematically introduced along with mechanistic insights.At the end of the article,the challenges and possible future directions are highlighted to further modify MoTe2 material for the numerous functionalities.Therefore,the availability of different phases and layer structures implies a potential for MoTe2 to lead an era of two-dimensional materials that began from the exfoliation of graphene.
文摘We perform a comprehensive analysis of uniform-velocity bilayer spacetime crystals,combining concepts of conventional photonic crystals and special relativity.Given that a spacetime crystal consists of a sequence of spacetime discontinuities,we do this by solving the following sequence of problems:(1)the spacetime interface,(2)the double spacetime interface,or spacetime slab,(3)the unbounded crystal,and(4)the truncated crystal.For these problems,we present the following results:(1)an extension of the Stokes principle to spacetime interfaces,(2)an interference-based analysis of the interference phenomenology,(3)a quick linear approximation of the dispersion diagrams,a description of simultaneous wavenumber and frequency bandgaps,and(4)the explanation of the effects of different types of spacetime crystal truncations and the corresponding scattering coefficients.This work may constitute the foundation for a virtually unlimited number of novel canonical spacetime media and metamaterial problems.
基金supported by Hebei Natural Science Foundation(Grant No.A2021203030)the National Natural Science Foundation of China(Grant No.11574261).
文摘Silicon carbide nanosheets(SiCNSs)have a very broad application prospect in the field of new two-dimensional(2D)materials.In this paper,the interlayer interaction mechanism of bilayer SiCNSs(BL-SiCNSs)and its effect on optical properties are studied by first principles.Taking the charge and dipole moment of the layers as parameters,an interlayer coupling model is constructed which is more convenient to control the photoelectric properties.The results show that the stronger the interlayer coupling,the smaller the band gap of BL-SiCNSs.The interlayer coupling also changes the number of absorption peaks and causes the red or blue shift of absorption peaks.The strong interlayer coupling can produce obvious dispersion and regulate the optical transmission properties.The larger the interlayer distance,the smaller the permittivity in the vertical direction.However,the permittivity of the parallel direction is negative in the range of 150-300 nm,showing obvious metallicity.It is expected that the results will provide a meaningful theoretical basis for further study of SiCNSs optoelectronic devices.
