精确的一维光子晶体的带隙

半导体材料的折射率是光频率的函数,所以在计算光子晶体的能带结构时必须考虑到色散关系。光子晶体存在光子禁带在反射谱上表现为高反射率带。本文已GaAs基材料为例,利用传输矩阵方法计算了考虑色散后的一维光子晶体的反射谱,计算结果表明考虑色散后的光子晶体禁带的宽度较不考虑色散关系的光子晶体的带隙要窄,如果光子晶体中存在缺陷则考虑色散后的光子晶体缺陷态的位置较不考虑色散关系时红移,且光子损耗较小。     

Nonlinear finite-volume time-domain analysis of photonic crystal-based resonant cavities

An accurate analysis of nonlinear photonic crystal (PhC) based resonant cavities is carried out. The nonlinearity considered for this analysis is a third-order nonlinearity with media composed of Kerr-like dielectric materials with an instantaneous nonlinearity. The analysis is performed with a robust and accurate finite-volume time-domain (FVTD) technique that for the first time has been extended in order to simulate nonlinear material with a Kerr-like instantaneous nonlinearity. From the analysis, interesting properties are revealed from the exploit of nonlinear characteristics of the PhC-based resonant cavities, properties that can be usefully applied for the realisation of all-optical circuits and specifically for optical switches.     

Numerical study of two-dimensional metamaterial composites: the existence of a stop band

Two-dimensional metamaterial photonic crystals composed of dispersive left-handed materials and a right-handed medium were investigated. The existence of a stop band was studied by finite-difference time-domain calculations incorporated into an auxiliary differential equation (FDTD-ADE) method. The existence of a stop band was studied in the case of Drude-type dispersion responses for the dielectric permittivity and magnetic permeability of the metamaterial. A distinct stop band appears when the dispersive left-handed metamaterials are embedded in a positive-refractive-index medium and spatially isolated from each other. In contrast, the stop band is absent when the metamaterials span the entire photonic crystal.     

Synthesis,crystal structure,optical and third order nonlinear optical properties of phosphoric acid pyridine-1-ium-2-carboxylate

A semi-organic nonlinear optical material phosphoric acid pyridine-1-ium-2-carboxylate (PAPC) crystal has been synthesized and grown. Vibrational spectral analysis and NMR spectral analysis has been carried out. Mechanical studies on the grown crystal has been performed which disclose the material belongs to soft materials category. The thermal behaviour of the grown crystal has been investigated by thermogravimetric and differential thermal analysis. UV–Visible spectral analysis has been carried out which reveals that the grown crystal is transparent in the entire visible region with the lower cut-off wavelength of 298 nm and the derived optical constant attests the suitability of this material for non-linear optical applications. The third order nonlinearity has been studied by z-scan method and the enhanced third-order nonlinearity shows PAPC is a potential material for device applications. Second harmonic generation efficiency has been studied by Kurtz and Perry powder test and is found as 0.14 times greater than the KDP.     

Development of NLO tunable band gap organic devices for optoelectronic applications

This paper, presents a preliminary guide to tune the band gap of photonic crystals for optoelectronic applications. This study includes the theoretical calculations to determine the optical constants of a material, synthesis of a new photonic crystal, and a technique for photonic band gap tuning which is minimally required for developing the optoelectronic device. It is observed from the optical studies that the band gap can be tuned by the replacement of the functional group in the compound. It is confirmed that this new crystal has the maximum transparency in the entire visible region and hence it should exhibit a non-linear optical property. The presence of moieties with intermolecular hydrogen bonding in the lattice of such compounds is responsible for the second harmonic generation (SHG).     

Mode tuning in dispersive and non-dispersive photonic crystals by defects

Transmission spectrum of two-dimensional photonic crystal for dispersive and non-dispersive photonic crystals (PhC) is calculated. Calculations show that by considering defect electromagnetic waves can propagate in PhC band gap. Transmission spectrum for different types of defects is compared together. The number and position of transmission modes in PhC waveguide depend on host PhC and type of defects. By selecting suitable PhC material and defect type, the number and position of transmission modes can be controlled.     

Symmetry properties of two-dimensional anisotropic photonic crystals

A theoretical study of two-dimensional photonic crystals made of anisotropic material is presented. Detailed computation principles including a treatment of the TE and TM polarizations are given for a photonic crystal made of either uniaxially or biaxially anisotropic materials. These two polarizations can be decoupled as long as any one of the principal axes of the anisotropic material is perpendicular to the periodic plane of the photonic crystal. The symmetry loss due to the anisotropy of the material and the variation of the Brillouin zones relative to the tensor orientations are also analyzed. Furthermore, the symmetry properties of the two-dimensional photonic band structure are studied, and the resulting effect on the photonic bandgap and the dispersion properties of photonic crystal are analyzed as a function of the orientation of the anisotropic material.     

自适应伪装材料在军用服饰产品的设计应用研究

目的 总结和展望可见光波段自适应伪装材料和红外波段自适应伪装材料的发展趋势及应用现状,为进一步研究和应用提供参考.方法 基于军用服饰对抗的不同波段,总结归纳了光致变色材料、电致变色材料、热致变色材料、相变材料、电致变发射率材料、电致变温材料和光子晶体材料的发展现状.结果 自适应伪装材料在军用服饰上的应用形式多,且相关产品在不断更新换代.结论 光学自适应伪装材料可适应不同场景不同要求下的变色需求,电致变发射率材料等红外自适应伪装材料可以用于军用红外伪装中,进一步完善可实现自适应红外隐身,人工光子晶体材料作为自适应伪装材料也可用于军用产品,目前已从多角度进行研发、实验,具有很大的应用前景及发展潜力.     

Temperature-dependent bending loss characteristics of W-type photonic crystal fibres: design and analysis

The temperature-dependent bending loss characteristics of two solid-core W-typephotonic crystal fibres have been reported by employing full-vectorial finite element method. The bending loss characteristics of W-type-I photonic crystal fibrestructure have been found better than that of the W-type-II photonic crystal fibre structure. The proposed photonic crystal fibrestructures show significant nonlinearity and hence can be used in telecommunication and nonlinear applications such as visible to near-infrared supercontinuum generation. Macro-bend insensitive nature of the proposed photonic crystal fibres makes them suitable candidates for fibre-to-the-home applications.     

Photonic and omnidirectional band gap engineering in stack of exponential graded index material and negative index material

We have investigated the photonic band gaps (PBG) and omnidirectional band gaps in one-dimensional photonic crystals made up of alternate layer of exponential graded index material and negative index material. We have considered the influence of material properties, geometrical parameters and material composition on the PBG and omnidirectional band gap. Results show that the parameters of exponential graded index material and negative index material can change the photonic and omnidirectional band structures remarkably. Number and bandwidth of PBG increases with increasing the negative index material layer thicknesses while thicknesses of graded index layer only have an effect on the bandwidth of PBGs. The bandwidth of PBG also depends on grading profile parameter of exponential graded index layers and bandwidth can be tuned with increase the value of grading profile parameter. This work can facilitate the design of filters and reflectors, and provide the basic understanding of the influence of graded index materials and metamaterials on the PBG properties.     

A simple perturbative tool to calculate plasmonic photonic bandstructures

We use first order perturbation theory to study the effect of surface plasmon polaritons on the photonic band structure of plasmonic photonic crystals. Our results are based on a simple numerical tool that we have developed to extend the standard frequency domain methods to compute the photonic band structure of plasmonic photonic crystals. For a two-dimensional honeycomb photonic crystal with a lattice constant of 500 nm placed on an aluminium substrate, we show that the band gap for TM modes is enhanced by 13%. Thus a slight variation in the effective dielectric function results in a plasmonic band structure that is not scale-invariant, which is reminiscent of the inherent non-linear properties of the effective dielectric constant.     

Coherent population trapping in photonic and dispersive band-gap materials

A theory of coherent population trapping (CPT) has been developed in photonic band-gap (PBG) and dispersive polaritonic band-gap (DPBG) materials when doped with an ensemble of five-level atoms. These materials have gaps in their photon energy spectra leading to unusual optical properties. The atoms are prepared as coherent superpositions of the two lower states and interact with a reservoir and two photon fields. The transition between the two lower states of an atom is dipole forbidden. The Schrödinger equation and the Laplace transform method are used to calculate the expressions for the number densities of the atomic states. Numerical simulations are performed for both PBG and DPBG materials with the phase factor between the coherent states chosen such that the number density of the upper state becomes zero when the photon fields have the same intensity. It is found that when the resonance energies lie away from the band edges and within the lower band, the CPT effect is observed in both materials when the fields have identical intensities. Similar results are also found when the resonance energies lie away from the band edges and within the upper band. When one of the resonance energies lies near the lower band edge, the number density vanishes at all intensities of the fields for both materials. This is an effect of the band structure of the materials and is not due to the CPT effect. A similar result is seen when one of the resonance energies lies near the upper band edge of a PBG material. However, for a DPBG material, the number density does not become zero when one of the resonance energies lies near the upper band edge, except due to the CPT effect brought on by the identical intensities of the photon fields. This is a very interesting phenomenon.     

Angle- and Thickness-Dependent Photonic Band Structure in?a?Superconducting Photonic Crystal

The angle- and thickness-dependent photonic band structures in a one-dimensional superconducting photonic crystal are theoretically investigated based on the transfer matrix method. The band structure is studied near and below the threshold frequency at which the superconducting material has a zero permittivity. The gap structure is analyzed as a function of the thicknesses of the two constituent superconducting and dielectric materials. In the angular dependence of the band structure, it is found that in the TM-polarization there exists a strongly localized superpolariton gap in the vicinity of the threshold frequency. This gap is shown to be enhanced as the angle increases.     

光子晶体应用研究进展

光子晶体是一种具有光子带隙的新型材料,其概念提出比较早,距今已经过了30年。由于光子晶体具有很多新颖的特性,使其成为微纳光子学和量子光学的重要研究领域。随着微加工技术的进步和理论的深入研究,光子晶体在信息光学以及多功能传感器等其他多个学科中也得到广泛应用。本文从理论上详细综述了光子晶体的各种奇异特性,并从各种特性出发,详细介绍近年来光子晶体在光子晶体光纤、反射镜、滤波器、波导、低阈值激光器、多功能传感器、腔量子电动力学、偏振器、量子信息处理等领域的应用研究,并与传统的器件进行性能比较得出光子晶体器件具有无可比拟的优势。最后提出,随着3D打印制造技术的成熟,光子晶体材料必然会推动信息技术的新一轮革命。     

Hydrogen gas sensor based on long-range surface plasmons in lossy palladium film placed on photonic crystal stack

Nanostructured plasmonic H₂ gas sensor has been designed and fabricated by palladium nanostructure onto one-dimensional photonic crystal. Our one dimensional photonic crystal has been designed and fabricated to have photonic band gap in visible spectrum and the palladium nanostructure has been designed and constructed as 11 nm thin film onto the above mentioned photonic crystal. All of fabrication processes have been done in vacuum chamber by the aid of electron gun and sputtering deposition methods. The ability of the devise as a Hydrogen gas sensor has been examined by recording the long range surface Plasmon resonance in different injection of H₂ gas and our results show that this sensor head can be used to sense very little amount of H₂ gas in ambient at room temperature. A reversible red shift of the reflectance deep of long range surface Plasmon resonance make this sensor as a good and useful device in medical, safety and energy related materials.     

Negative refraction in the visible range in water-infiltrated opal photonic crystals

A negative refraction effect has been found in opal photonic crystals in the visible range. We have calculated the dispersion branches of a photonic crystal and determined the position of its photonic band gap. The frequency range has been identified where the refractive index of the opal is negative. An experimental arrangement is proposed for focusing a light beam by passing it through a plane-parallel opal photonic crystal and experimental evidence is presented in favor of negative refraction in the visible range.     

Layer‐by‐Layer Approach to (2+1)D Photonic Crystal Superlattice with Enhanced Crystalline Integrity

Large‐area polystyrene (PS) colloidal monolayers with high mechanical strength are created by a combination of the air/water interface self‐assembly and the solvent vapor annealing technique. Layer‐by‐layer (LBL) stacking of these colloidal monolayers leads to the formation of (2+1)D photonic crystal superlattice with enhanced crystalline integrity. By manipulating the diameter of PS spheres and the repetition period of the colloidal monolayers, flexible control in structure and stop band position of the (2+1)D photonic crystal superlattice has been realized, which may afford new opportunities for engineering photonic bandgap materials. Furthermore, an enhancement of 97.3% on light output power of a GaN‐based light emitting diode is demonstrated when such a (2+1)D photonic crystal superlattice employed as a back reflector. The performance enhancement is attributed to the photonic bandgap enhancement and good angle‐independence of the (2+1)D photonic crystal superlattice.     

Local surface spectroscopy of magnetic photonic crystals

Visible reflection spectra of opal photonic crystals infiltrated with magnetic materials have been measured in different areas on the (111) surface of the crystals with a spatial resolution of ∼0.1 mm. The observed reflection band corresponds to the photonic band gap of the opal. The peak position of the reflection band depends on the nature of the magnetic material infiltrated into the opal pores and the position of the fiber-optic probe on the opal surface.     

Broadening of Photonic Band Gap in a One—Dimensional Superconductor Star Waveguide Structure

The present paper describes the theoretical investigation of enlarged reflection bands (photonic band gaps) in a 1D star waveguide (SWG) structure consists of superconductor and dielectric as its constituent materials. For the present study, we take the different combinations of superconductor and dielectric materials as a backbone and side branches of the SWG structure. In order to obtain the dispersion relation, Interface Response Theory (IRT) has been employed. Photonic band gaps of SWG structure having superconductor?Csuperconductor, superconductor?Cdielectric, and dielectric?Csuperconductor materials are compared with the band gaps of the conventional photonic crystal (PC) structure having superconductor?Csuperconductor and dielectric?Csuperconductor materials. Analysis of the dispersion characteristics shows that there exists no band gaps for conventional PC when both layers are made of the same superconducting materials (as the usual case) while the SWG structure shows forbidden bands of finite width even the backbone and side branches are made of same materials. Also, the SWG structure having superconductor?Cdielectric shows the wider reflection bands in comparison with the structure having dielectric?Csuperconductor as its constituent materials, while for the conventional PC structure it is same in both the cases. Further, the effect of temperature and the effect of variation of number of grafted branches on the photonic bands of SWG structure have been studied.     

Color tunability of upconversion emission in YBO3: Yb, Er inverse opal

Upconversion (C) light-emitting photonic band gap materials (YBO₃: Yb, Er) with inverse opal structure were prepared by a self-assembly technique in combination with a sol-gel method. The effect of the photonic stop-band on the upconversion luminescence of Er³⁺ ions has been investigated in the YBO₃: Yb, Er inverse opals. Significant suppression of the green or red UC emission was detected if the photonic band-gap overlaps with the Er³⁺ ions emission band. We successfully achieved the color tuning of the UC optical properties of the inverse opal by controlling the structure of the photonic crystal.