对全入射角负折射二维光子晶体结构和电磁参量的研究

利用二维光子晶体的等频线分析原理和平面波展开方法,得到了使二维光子晶体产生全入射角负折射(All-Angle Negative Refraction,AANR)现象时,入射电磁波的频率取值范围.同时,分析了AANR频率范围随着结构参量(晶格类型、介质棒半径与晶格周期的比值)和电磁参量(介质柱介电常量、本底介电常量、入射电磁波偏振方向)变化的行为.结果表明:固定组成光子晶体的一种介质的介电常量,另一介质的介电常量只有达到一定阈值,才有可能使光子晶体出现AANR现象.在给定两种介质介电常量的条件下,存在使AANR频率范围最大化的结构参量和电磁参量.     

改变光子晶体表面结构对负折射透射光强的影响

以砷化镓圆形介质柱在空气中构成二维六边形排列结构的光子晶体为例,利用时域有限差分法模拟研究了光子晶体表面结构改变对负折射透射光强的影响.模拟结果表明:针对同一结构光子晶体,在可产生负折射现象的入射光频率范围,改变光子晶体表面两侧圆形介质柱的半径和顺向侧移两侧表面最外层圆形介质柱都会均对负折射透射光强产生影响.     

改变光子晶体表面结构对负折射透射光强的影响

以砷化镓圆形介质柱在空气中构成二维六边形排列结构的光子晶体为例,利用时域有限差分法模拟研究了光子晶体表面结构改变对负折射透射光强的影响.模拟结果表明：针对同一结构光子晶体,在可产生负折射现象的入射光频率范围,改变光子晶体表面两侧圆形介质柱的半径和顺向侧移两侧表面最外层圆形介质柱都会均对负折射透射光强产生影响.     

基于硅柱-磁性液体体系的光子晶体的可调谐负折射特性研究

本文研究了硅柱在MnFe₂O₄磁性液体背景中排列成六边形结构的二维光子晶体的可调谐负折射特性. 利用平面波展开法和时域有限差分法理论研究了硅柱-磁性液体体系二维光子晶体的带隙结构、等频曲线和负折射现象随外磁场强度的变化关系. 模拟结果表明, 硅柱-磁性液体体系二维光子晶体工作在TE模式时, 其负折射特性可由外磁场调节. 在固定背景溶液的磁性颗粒体积分数和入射光频率时, 所研究的折射光束的偏转角和光子晶体的负折射率绝对值随外磁场的增大而增大, 而在固定背景溶液的磁性颗粒体积分数和外磁场强度时, 负折射角和负折射率的绝对值随入射光归一化频率增大而减小. 固定外场强度和入射光频率时, 所研究结构的负折射特性随背景溶液的磁性颗粒体积分数增大而变弱.     

二维空气环型光子晶体的负折射成像特性

采用平面波展开法和时域有限差分法研究了由空气环组成的二维三角晶格光子晶体平板的负折射成像特性.研究结果表明对于外半径为 0.4 a,内半径 0—0.13a的空气环型光子晶体,第二能带中归一化频率为 0.3 的电磁波可以实现有效折射率为-1的负折射成像.通过光子晶体有效折射率的计算,得到了有效折射率为-1的电磁波频率随空气环内径由0—0.2 a变化的规律,并由对应等频曲线的变化解释了结构参数对光子晶体平板成像的影响. 关键词： 光子晶体 空气环 负折射 等频曲线     

高斯波束在光子晶体中的负折射特性分析

为了研究光子晶体中的负折射行为,我们应用2维TM模时域有限差分方法,数值模拟了高斯波束从自由空间垂直入射和斜入射到二维三角晶格光子晶体平板后的折射现象,并给出了平板内外的电场强度分布.模拟结果显示:垂直入射时,光子晶体平板对高斯波束具有汇聚作用,汇聚特性随着波源到晶体的距离的改变而发生显著的变化;斜入射时,折射波束与入射波束也均在法线的同一侧.结果证明了高斯波束在光子晶体和空气的交界面发生了负折射.模拟结果有望在制作聚焦透镜、带通滤波器、耦合器等光子晶体器件方面得到重要应用.     

光频段多频率域负折射率材料的数值研究

利用电介质材料周期性排列构成二维六角结构光子晶体,用平面波展开法研究了二维光子晶体材料各个能级的等频率曲线图,发现此结构光子晶体在多个频段上存在负折射特性,用时域有限差分(finite difference time domain,FDTD) 数值计算模拟也得到了相同的结果. 关键词： 光子晶体 左手化媒质 负折射 多频段     

二维光子晶体的特殊色散特性研究

为了研究光场在二维光子晶体中的传播特性,本文应用平面波展开法,得到了二维三角晶格光子晶体的能带结构,在此基础上,运用时域有限差分法,分析了在一定入射角度下,特定频率的光束在光子晶体中的负折射现象,由于应用光子晶体的自准直效应,光束束腰在传播过程中展宽较小。研究了由于能带交折、重叠而产生的特殊色散特性和超棱镜效应,给出了光子晶体内外的磁场强度的分布,得到了极高的角色散度。文章的研究结果对研究基于光子晶体超棱镜效应的波分复用器,具有指导意义。     

液晶光子晶体的负折射特性研究

可调光子晶体由于其潜在的应用价值成为现今光子晶体研究中的一个热点.本文提出了通过光诱导液晶来调节光子晶体负折射效应的方法,采用平面波展开法、等频图分析法和推广的斯涅尔定理分析了二维液晶正方晶格光子晶体负折射的可调节性.提出了一种新型的液晶光子晶体结构, 数值模拟结果表明:通过偏振光改变液晶指向矢可以调节该液晶光子晶体的负折射.与电场调制方法相比,该光控液晶取向技术具有响应速度快、结构简单的优点.这种可调光子晶体可用于制作光控路由或者应用于全光网络.     

二维平板光子晶体的等效负折射率测量EI北大核心CSCD

光子晶体特殊的色散特性能导致负折射现象发生。用波束位移法对二维光子晶体平板的负折射现象进行理论计算和实验测量,得到了入射光经平板光子晶体折射后的二维光场分布。测量结果表明,横电(TE)光在光子晶体中发生负折射,出射光沿出射面产生了反方向的横向位移,由此计算出来的负折射率约为-0.44,而横磁(TM)光没有发生负折射。实验结果与仿真结果吻合较好。     

Frequency bands of negative refraction in finite one-dimensional photonic crystals

We have discussed theoretically the negative refraction in finite one-dimensional (1D) photonic crystals (PCs) composed of alternative layers with high index contrast. The frequency bands of negative refraction are obtained with the help of the photonic band structure, the group velocity and the power transmittance, which are all obtained in analytical expression. There shows negative transverse position shift at the endface when negative refraction occurs, which is analysed in detail.     

正方介质柱光子晶体中异常传输现象研究

研究了电磁波在二维正方介质柱光子晶体中的传输,发现处于第一频带部分带隙的电磁波在不同界面切割方向上不同角度入射时可分别产生全反射及复杂异常折射现象如自准直现象、负折射现象.首先利用平面波展开法从理论上研究正方介质柱正方晶格光子晶体的频带结构及等频线,然后通过时域有限差分法来仿真研究光子晶体在第一频带部分带隙的传输特性.当光子晶体的界面切割沿着ΓX方向时,由于光子晶体内无本征模能够被有效地激发,入射波束被完全反射,这与光子带隙导致的全反射具有本质的不同;当光子晶体的界面切割方向沿着ΓM时,归因于其扁平的等频线,一定角度范围内入射的波束在光子晶体内几乎沿同方向传输即产生自准直现象.     

波状结构二维光子晶体负折射现象的研究

结合波状结构二维(2D)光子晶体(PC)与入射介质两者的等频面结构分析了PC内部的负折射现象，采用时域有限差分(FDTD)方法模拟了高斯光束在波状结构2DPC内的负折射，分别得到了折射角/入射角以及折射角/入射波长之间的关系曲线，当入射角为45°，入射波段在1485—1530nm区域时，波状结构2DPC的负折射角与入射波长近似呈线性变化关系，并带有明显的PC超棱镜效应，采用端面投影方法对波状结构2DPC的入射端面和出射端面进行处理，改善了负折射时的透过率. 关键词： 光子晶体 负折射 等频面     

Optical and electro-optical properties of photonic crystals based on polymer-dispersed liquid crystals

Two-dimensional (2-D) square lattice (SL) photonic crystals (PCs) are fabricated, and their optical/electro-optical properties are studied. The PCs are based on polymer-dispersed liquid crystals (PDLC) that are formed using two-beam interference with double exposures. The PC structure that is observed using a scanning electron microscope matches with the calculated interference pattern. The results of optical/electro-optical studies demonstrate that superprism and negative refraction effects occur at certain incident angles over a range of frequencies and are consistent with the simulated ones. Moreover, the negative refraction efficiency is electrically controllable.     

Manipulating light flow with one-dimensional photonic crystals of an electromagnetically induced transparency medium

The band structures and equifrequency contours of one-dimensional photonic crystals (PCs), which consist of an electromagnetically induced transparency (EIT) medium and a common dielectric medium, can be dramatically changed by tuning the coupling field intensity (or coupling Rabi frequency, CRF) of the EIT medium. It is found that for a probe light at a fixed frequency, either positive or negative refraction in the EIT PC can be realized with a proper CRF. The behavior of a Gaussian beam (probe light) obliquely incident on such an EIT PC slab is simulated numerically. The probe light beam transmitted from the slab can be shifted transversely in a large range, and negative refraction enhances this effect. The present scenario can be applied in some areas such as quantum optical and photonic device designs.     

Amphoteric-like refraction in a two-dimensional photonic crystal

High-index contrast photonic crystals possess an intricate photonic band structure that is responsible for surprising phenomena as the surperprism effect, self-collimation, power splitting or negative refraction. Recently, it was reported that at the interface between an isotropic medium and a uniaxial crystal (or between two uniaxial crystals) a phenomenon known as amphoteric refraction, that is, positive as well as negative refraction, can take place. By means of a equifrequency contours analysis and finite-difference time-domain simulations, we show that a two dimensional photonic crystal can also present amphoteric refraction by properly choosing the lattice orientation and the termination. However, total transmission is difficult to achieve because a Bloch mode is excited inside the photonic crystal and the coupling efficiency from this mode to an external plane wave is lower than one.     

Realization of absolute negative refraction index by a photonic crystal using anisotropic dielectric material

A method to realize absolute negative refraction index -1 with a two-dimensional （2D） photonic crystal is presented by introducing dielectric anisotropy in the photonic crystal material. The band structures of E-polarization mode and H-polarization mode can be adjusted by changing the parameters of materials. Thus the two modes with different polarizations have the same negative refraction index -1 for the same frequency. The results are demonstrated by numerical simulation based on the finite-difference time-domain （FDTD） method.     

Analysis and optimization of a new photonic crystal filters in near ultraviolet band

Transmission characteristics of one-dimensional (1D) photonic crystals (PCs) heterostructures containing defective are studied using the transfer matrix method. The key is to search the best combination style for different 1D PCs to form heterostructures. It is shown that the non-transmission range over near ultraviolet and visible range can be substantially enlarged and the phenomenon of narrow band PC filter in near ultraviolet can be realized by adjusting the repeat cycle counts of various photonic crystals. The theoretical results on multiple heterostructures containing TiO₂/SiO₂ multilayer films are presented. With a perfect omni-directional and high peak transmission filters for TE modes, this structure opens a promising way to fabricate ultra-narrow band PC filters with wide non-transmission range in near ultraviolet and visible range.     

Negative refraction in photonic crystals

We demonstrate that light propagation in strongly modulated 2D/3D photonic crystals (PhCs) becomes refraction-like in the vicinity of the photonic bandgap, which is contrary to the fact that light propagation in weakly modulated PhCs is very different from refraction and thus the definition of refraction index becomes meaningless. Such a crystal behaves like a material having an effective refractive index controllable by the band structure. This situation is analogous to the effective-mass approximation in electron-band theory. The propagation states having a negative effective index exhibit unusual properties, such as mirror-like imaging effect, image-transfer effect. These properties are confirmed by finite-difference time-domain simulations.