3．0μm～4．0μm全角度反射镜

分析了一维光子晶体的光子能带结构和禁带特性;然后利用光子禁带特性,设计了3.0～4.0μm全角度反射镜,给出了其反射光谱.     

一维光子晶体完全光子禁带与结构的关系

阐述了完全光子禁带的概念.用光学特征矩阵方法,通过数值模拟计算,讨论了一维光子晶体出现完全光子禁带与晶体结构和介质材料的折射率的密切关系.具体计算了用同样两种介质材料组成3种不同结构的一维光子晶体,对于TM及TE电磁模式在不同入射角下的透射率谱,从中找出它们的完全光子禁带,发现3种结构的完全光子禁带的波长范围及宽度各不相同.另外,研究结果表明组成光子晶体的两种材料的折射率差别越大,两种电磁模的禁带越宽,越容易产生完全光子禁带.简单讨论了完全光子禁带出现的条件.     

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。     

三维光子晶体光学性能分析及结构色模拟

以面心立方密堆积结构的三维光子晶体为研究对象,利用等体积原则将其等效为一维光子晶体结构,采用传输矩阵法计算晶体微球粒径、晶体堆积厚度对光子晶体反射率、带隙位置及宽度的影响,并通过CIE标准色度系统得到色品坐标,在CIE色度图直观地反映光子晶体结构色变化。控制微球粒径尺度可以调节光子禁带,进而调控光子晶体结构色。微球粒径增大,光子带隙中心波长增大,对应的结构色波长也增大,对于粒径分别为200nm、250nm、300nm、350nm的二氧化硅胶体光子晶体,其对应结构色分别为蓝色、绿色、黄色、红色。晶体堆积厚度在一定范围内增大有利于反射率增大、带隙宽度变窄,从而影响颜色但不引起色相发生变化。     

波导光子晶体的态密度

令方形波导内的电介质介电常数沿波导方向周期变化,实际上是非周期方向受限的一维光子晶体,不妨称为波导光子晶体。本文利用经典电动力学的方法计算了波导光子晶体的态密度,发现当波导宽度与其内部一维光子晶体晶的格常数可比拟时,会出现光子带隙;而且,波导宽度对系统的态密度有明显影响,随着波导宽度的增大光子带隙逐渐闭合。     

基于p型多孔硅的一维光子晶体的微结构分析

经由阳极氧化实现了p型硅基的60周期(120层)反射结构,并在此基础上成功制作了基于一维光子晶体的全反射镜,其中心反射波长位于1.6μm左右,反射率几乎为100%的禁带带宽约为0.25μm.     

二维旋转直柱光子晶体的频率带隙结构分析

设计了一种二维方形旋转正四边形直柱光子晶体,利用平面波展开方法计算了其光子频率带结构,发现在低频和高频区域,该类光子晶体的光子频率禁带明显增大.计算了空气中Al材料的旋转四边形直柱光子晶体的带结构和态密度,当填充比等于0.5时存在绝对带隙,旋转角度为45°时绝对带隙最大,旋转角度为0时,光子频率禁带位于高频区域.利用FDTD方法检验了计算结果,并分析了旋转角度为45°时,正四边形直柱光子晶体的波导特性以及TM模的电场分布.     

一维光子晶体的带隙特性研究

一维光子晶体是指介质只在一个方向成周期性排列的材料。利用薄膜光学的特征矩阵法研究了一维光子晶体的禁带特性,分析了填充率变化、厚度的随机扰动对光子带隙的影响。结果表明,随着填充率的变化,各能级的带隙率变化,并且存在一个极大值;厚度的随机扰动对光子带隙也有一定的影响,随机度不同,对光子带隙的影响也不一样。本研究对一维光子晶体的设计与制备有一定的参考价值。     

多通道光子晶体器件设计

一维光子晶体缺陷模的光谱特性与缺陷模的结构紧密相关.当缺陷模中包含有多个缺陷时,将导致光子禁带中出现多个分立的缺陷能级,形成多个透射光通道.利用一维光子晶体缺陷模这一光谱特性设计了红外谱段的三通道光子晶体器件.     

基于有限元法的一维光子晶体光学特性分析

运用电磁学的里兹变分法,建立一维光子晶体理论分析的有限元模型.通过建立的有限元模型,采用有限元方法对一维光子晶体进行研究.数值模拟出完整一维光子晶体的透射谱、含缺陷层的一维光子晶体TE偏振光和TM偏振光的透射谱以及缺陷层厚度对一维光子晶体的透射特性的影响.     

光子晶体应用于浓度检测的模拟研究

采用平面波展开法数值计算二维光子晶体在TE和TM偏振态下的带隙,给出了光子晶体中的禁带存在的理论依据,选择二维三角晶格光子晶体（GaAs）作为基底,在气孔内填充浓度为一定的待测溶液硫酸铜材料,计算温度为298K情况下介电常数在71．917～62．530变化时,光子晶体在不同偏振模式下的光子禁带结构,结果表明,以硫酸铜的水溶液作为空气圆孔中的介质材料,当溶液质量百分浓度不同时光子带隙（PBG）发生显著变化。     

Measurement of valence band structure in arbitrary dielectric films

A new way of measuring the band structure of various dielectric materials using the secondary electron emission from Auger neutralization of ions is introduced. The first example of this measurement scheme is the magnesium oxide (MgO) films with respect to the application of the films in the display industries. The density of state in the valence bands of MgO film and MgO film with a functional layer (FL) deposited over a dielectric surface reveals that the density peak of film with a FL is considerably less than that of film, thereby indicating a better performance of MgO film with functional layer in display devices. The second example of the measurement is the boron-zinc oxide (BZO) films with respect to the application of the films to the development of solar cells. The measurement of density of state in BZO film suggests that a high concentration of boron impurity in BZO films may enhance the transition of electrons and holes through the band gap from the valence to the conduction band in zinc oxide crystals; thereby improving the conductivity of the film. Secondary electron emission by the Auger neutralization of ions is highly instrumental for the determination of the density of states in the valence band of dielectric materials.     

Investigation of TE-polarized photonic band gap properties in matallodielectric photonic crystals composed of metal coated dielectric cylinders

Using the Dirichlet-to-Neumann map method and generalization of this method, we have been able to calculate the photonic band structure of two-dimensional (2D) metallodielectric photonic crystals composed of metal-coated circular dielectric rods. The rods are embedded in an air background with a square array. We are interested in considering transverse electric (TE) mode of electromagnetic waves. The resulting band structures show the existence of photonic band gaps as well as some flat band regions. We theoretically study the effect of the dielectric constant and radius of the dielectric core on the photonic band structures. There are some interesting results compared to the case of solid metallic rods (without dielectric core) such as appearing the new photonic band gaps and a flat band region with the characteristic of cavity modes.     

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.     

光子晶体调制下的光电材料

光子带隙的存在不仅产生出一大批新型材料和器件,也能够提供一种特殊的物理环境-具有波长尺度的介电周期场.这种物理环境为各种光电材料中光物理过程和光电性质的调制提供一种新的可能性.本文综合分析了光子晶体调制下光功能材料的自发辐射、能量传递、太阳能电池的光电转换效率、光催化等几个方面研究现状及其应用.     

Investigation of Absolute Photonic Band Gaps in Two-dimensional Dielectric Structures

Abstract

We examine the photonic band structure of two-dimensional (2D) arrays of dielectric holes using the coherent microwave transient spectroscopy (COMITS) technique. Such 2D hole arrays are constructed by embedding low-index rods (air) in a dielectric background of higher-index Stycast material (n = 3·60). The dispersion relation for electromagnetic wave propagation in these photonic crystals is directly determined using the phase sensitivity of COMITS. We find that both the square and triangular lattice structures exhibit photonic band gaps that are common to both polarizations for all wave-vectors along major symmetry axes. In addition, the connectivity of the high-index dielectric and the opening of a large gap for propagation with E field perpendicular to the hole cylinders are found to be important criteria for generating a large absolute photonic band gap.     

Symmetry reduction for maximization of higher-order stop-bands in two-dimensional photonic crystals

A large absolute higher-order stop-band is achieved in two-dimensional (2D) photonic crystals of square lattice. A genetic algorithm is used to search through a large number of possible structures. In this algorithm, the unit cell is divided into a grid of square pixels and a 2D binary chromosome is assigned to each filling pattern of the pixels. An initial structure with a small higher-order stop-band is included in the initial population to accelerate the search procedure. This initial structure is formed by breaking the symmetry of the supercell of a photonic crystal having a square lattice of square dielectric rods in air. In the optimization process, the effect of reducing the symmetry of the unit cell on the photonic band-gap is investigated. A structure showing an absolute higher-order band-gap as large as 0.1522(2πc/a) is obtained, which is larger than the values reported so far for photonic stop-bands.     

带隙可调光子晶体的研究进展

介绍了近几年带隙可调光子晶体的研究进展。带隙调节的机制主要有改变晶体材料的平均折射率和改变晶体的结构参数两种。综述了通过电场调制、磁场调制、压力调制、光照调制、温度调制和复合调制等实现带隙实时可调的研究进展,提出了目前存在的问题及研究方向。     

Genetic optimization of two-dimensional photonic crystals for large absolute band gaps under light line

A binary genetic algorithm with floating crossover and mutation probabilities is used to design two-dimensional photonic crystals for large absolute band gaps under a light line. The unit cell is composed of a small number of round rods and is arranged in a square lattice. The photonic band structure of each chromosome is calculated by the plane-wave expansion method. Starting from randomly generated photonic crystals, the genetic algorithm finally yielded a photonic crystal with an absolute common band gap of 0.0618(2πc/a) at the mid-frequency of 0.4084(2πc/a).