含负折射率光子晶体缺陷模偏振态的吸收特性

为了研究含负折射率掺杂光子晶体各缺陷模偏振态的吸收特性,引入复折射率并利用光学特征矩阵法进行分析,结果表明：杂质的消光系数对TE波和TM波的缺陷模均有影响,但对TE波的影响更为明显;当消光系数一定时,对TE波而言,中心波长相对较大的两个缺陷模透射峰值均随入射角的增加而迅速减小,而TM波的三个缺陷模透射峰均随入射角的增加而增加。利用这一特性可以设计双（多）通道光子晶体偏振滤波器。     

杂质吸收对光子晶体缺陷模偏振态的影响

引入复折射率并利用特征矩阵法,研究了杂质的吸收对TE波和TM波缺陷模透射峰的影响.得出:杂质的消光系数对TE波和TM波的缺陷模透射峰都有显著的影响,但对TE波缺陷模的影响比对TM波缺陷模的影响更为明显.当消光系数一定时,TE波的缺陷模透射峰随入射角的增大而迅速减小,而TM波的缺陷模透射峰随入射角的增大而增大.利用这一特性可以设计光子晶体偏振滤波器.     

一维多层掺杂光子晶体缺陷模的偏振特性

为了研究多层掺杂对一维光子晶体缺陷模偏振特性的影响,采用特征矩阵法计算了一维光子晶体双层掺杂和三层掺杂情况下缺陷模的偏振特征.结果表明:双层掺杂时,TE波和TM波都出现了两个缺陷模,两个缺陷模随入射角的增加向短波方向移动,TE波的两个缺陷模随入射角的增加而减弱,而TM波的两个缺陷模随入射角的增加而增强.三层掺杂时,TE波和TM波也都出现了两个缺陷模,但比两层掺杂的缺陷模要弱,TE波和TM波的两个缺陷模随入射角的变化特征与双层掺杂的情况相似.     

二维光子晶体偏振分束器的优化设计北大核心

为解决二维光子晶体在光束调整和光束偏转中的应用,采用有限时域差分法和完全匹配层吸收边界条件,通过在结构中引入消反层,从理论上实现基于二维光子晶体的偏振分束器。优化计算表明,通过随光频的改变调节消反层参数,可以实现TE模超过95%的光发生透射,TM模超过95%的光发生反射,从而使TM模与TE模分离。引入消反层的偏振分束器具有尺寸小、透射率高、分束角大和偏振分束率高等优点,在高密度集成光通信系统中有广泛的应用。     

负折射率缺陷层的一维各向异性光子晶体缺陷模特性

本文提出了负折射率缺陷层的一维各向异性光子晶体结构,利用传输矩阵的方法给出了TE波和TM波的透射率,结果表明在TE波中出现两个及多个缺陷模,TM波存在单缺陷模,两种偏振状态不同的透射波的缺陷模能分开,得出了光通过负折射率缺陷层的一维各向异性光子晶体后TE波和TM波随入射角的变化特性、随缺陷层厚度的的变化特性。这些特性用于光子晶体多通滤波、光子晶体偏振和激光谐振腔等器件的设计具有重要意义。     

基于两次衰减全反射结构的激光偏振控制器

为了实现激光偏振态的控制和提高两偏振态消光比,用由各向异性材料加工而成的耦合棱镜并采用两次衰减全反射方法,使具有相同入射角的TE和TM偏振态的共振激发条件不同,即当TE偏振态满足共振激发条件能量耦合进波导时,TM偏振态却不满足共振激发条件而被反射来实现其在空间上的分离.同时将电光系数较大、光学性能和热稳定性好的聚合物材料作为波导层,利用其电光效应来改变共振条件来实现输出光束偏振态的调谐.结果表明,反射型结构插入损耗小于0.2dB,器件的消光比高达27dB,驱动电压为19V.该方案预计在光信息存储、光路由、光开光以及图像处理等光学系统里有着极其广泛的应用.     

钛合金粗糙表面的偏振光及变温BRDF特性

基于红外光谱椭偏仪测得钛合金TC4在298~773 K范围的光学常数,结合Monte Carlo射线跟踪法对钛合金随机粗糙表面的双向反射分布函数(BRDF)进行了研究.分析了不同表面粗糙度、入射光偏振态及温度对钛合金表面BRDF分布的影响.结果表明:偏振光入射下钛合金的BRDF分布随入射角度及表面粗糙度的变化趋势与非偏振光相同;入射平面内粗糙钛合金表面的BRDF随光源偏振态变化与光滑平板具有相同趋势;TE波入射时的BRDF反射峰值大于TM波入射;钛合金粗糙表面的BRDF镜反射峰值随温度升高有下降趋势;在所研究的温度范围内(298~773 K),峰值变化在10.2%以内,温度变化对TM波下钛合金BRDF分布特性的影响大于TE波,且在入射角度增大时影响增大.     

GaN基蓝光发光二极管分布布拉格反射器设计研究

采用传输矩阵法对GaN基蓝光发光二极管分布布拉格反射器（DBR）反射光谱进行研究。计算发现正入射时S偏振(TE模)与P偏振(TM模)反射带是一致的;S偏振和P偏振反射带随着入射角的增大都向高频(短波)方向移动,且两者之间的差别也随之增大,DBR反射带蓝移快慢与入射介质相关;低折射率入射介质时DBR具有更宽角度响应。通过修改结构参数多次计算表明：入射角修正的方法能较快的找到提高全方向反射的结构。复合DBR以降低反射率或者成倍增加膜层厚度为代价实现大角度范围的反射。复合DBR比传统DBR有更好的光谱特性,这对提高发光二极管的出光效率有现实意义。     

基于金属包覆波导结构的偏振选择器的研究

把具有各向异性的耦合棱镜和具有电光效应的晶体材料引入到双面金属包覆波导结构中,让两种偏振态的TE和TM以相同的入射角入射,实现不同偏振光束的空间分离;同时通过电控改变波导的参数,进而实现输出光束偏振态的调谐。     

入射角度对一维光子晶体禁带的调制研究

利用特征矩阵法,分别研究了不同偏振方式的波入射到光子晶体时,光子晶体的禁带随入射角度的变化.结果表明:不论是TM波入射还是TE波入射,随着入射角度的增大,光子晶体的带隙都向短波方向移动;TM波入射时,光子晶体的带隙随入射角度的增大而减小,而以TE波入射光子晶体时,随着入射角度的增大,光子晶体的带隙逐渐增大.     

Propagation Characteristics of a Partially Filled Cylindrical Waveguide for Light Beam Modulation

Propagation characteristics of a cylindrical waveguide partially filled with a cylindrical dielectric light modulation material is analyzed and numerical computation is performed for a few typical cases. This type of traveling-wave structure supports a TE or TM mode, and therefore is useful for light beam modulation applications requiring a longitudinal magnetic or electric field. Numerical analysis indicates that for the TM case, a broadband region occurs near a crossover point and broadband synchronization between the modulating microwave and the parallel-launched light beam can be obtained by a suitable choice of the dielectric medium surrounding the central dielectric.     

基于二氧化硅薄膜夹层式亚波长金属光栅的宽波段太赫兹偏振分束器

设计出一种结构新颖的宽波段太赫兹偏振分束器,这种偏振分束器由夹层式亚波长金属光栅制成。亚波长金属光栅偏振分束器可以将入射的任意自然光分成两束偏振状态垂直的线偏振光。其中,TE模反射而TM模透射。设计的偏振分束器在3.5~5.5 THz波段可以达到很高的衍射效率与消光比。但是,在光栅的实际制作过程中,加工技术的缺陷引起的误差大大影响了光栅的性能,比如衍射效率,消光比等。因此文中对一些结构参数进行了计算,从计算结果可以看出这种偏振分束器也有很好的工艺容差。当覆盖层厚度D1与底层介质厚度D3的变化范围分别为1~1.2 m和2.8~3 m时,T0TM大于96.9%,R0TE大于98.7%。Tc和Rc分别大于31 dB和33.4 dB。结果显示,设计的偏振分束器在2 THz的带宽10的大角度范围内,衍射效率高于90%,消光比大于20 dB。因此文中设计对于太赫兹调制器件的研究,以及太赫兹通信系统的集成都有很大的参考价值。     

Design of a compact photonic-crystal-based polarizing beam splitter

A compact polarizing beam splitter based on a photonic crystal (PC) directional coupler with a triangular lattice of air holes is designed and simulated. In the employed PC structure, transverse-electric (TE) light is confined with the photonic bandgap effect, while transverse-magnetic (TM) light is guided through an index-like effect. Due to the different guiding mechanisms, TM and TE light have strikingly different beat lengths, which is utilized to separate the two polarizations in a directional coupler no longer than 24.2 /spl mu/m. The two-dimensional finite-difference time-domain method of computation is used to evaluate the device performance. The extinction ratios are found to be around 20 dB for both TE and TM polarized light.     

金属银掺杂光子晶体的缺陷模

引入消光系数并利用特征矩阵法,研究了一维银掺杂光子晶体的反射光和透射光中TE波和TM波的缺陷模随入射角和银的光学厚度的变化规律.得出:在反射光中TE波和TM渡都出现了明显的缺陷模,缺陷模随入射角的增加而减弱,而缺陷模不随银的光学厚度的变化而变化.在透射光中TE波和TM波出现了很弱的缺陷模,缺陷模随银的光学厚度的增加而迅速消失.

Abstract：

By leading into the extinction coefficient and making use of the characteristic matrix method,the defect mode of TE wave and TM wave of Ag doping photonic crystal are studied in reflected light and refracted light.In reflected light,there are obvious defect modes of TE wave and TM wave,and the defect modes decrease with the increment of incident angle,but does not change with the optical thickness of Ag.In refracted light,there are very weak defect modes of TE wave and TM wave,and they decrease quickly with the increment of the optical thickness of Ag.     

Sequential TE/TM polarization emission from a tunable externalcavity diode laser

A tunable external cavity diode laser that emits in a closely spaced sequence of alternating TE and TM wavelength intervals in the range between 1256 and 1282 nm is reported. In each interval, stable single longitudinal mode TE and then TM emission occurs that can be tuned in wavelength. Two consecutive intervals are separated by a wavelength region where emission instabilities are observed. The wavelength spacing between two successive intervals belonging to the same polarization state corresponds to the mode spacing of the solitary diode laser. As the laser is tuned beyond 1282 nm and up to 1316 nm, the emitted radiation is only TM polarized. The above-mentioned phenomena are based on the composite cavity gain modulation with the wavelength, and on the comparable losses of the system for the TE and TM polarization     

Reflection and transmission at the surface of a chiral negative refractive medium

Electromagnetic fields at the surface of a chiral negative refraction medium (the chirality parameter is larger than the refractive index) are analyzed theoretically. For obtaining chirality parameter,the normalized reflected and transmitted powers as a function of the incident angle are given for the perpendicular (TE) and parallel (TM) polarized incident wave.Brewster angle and total internal reflection angle are discussed. Due to the negative refraction of one eigen-wave in the chiral medium, the reflection, transmission and Brewster angle characteristics are very different from those in the normal chiral medium.     

Performance of an array of circular waveguides with strip-loadeddielectric hard walls

An infinite planar periodic antenna array of radiating open-ended circular waveguides is considered. The conducting waveguide walls are covered with dielectric layers loaded with longitudinal conducting strips for providing the hard wall boundary condition. Analysis of the array is carried out by the mode-matching method. The waveguide modes involved in the method are calculated by using the asymptotic strip boundary condition. It is shown that they are split into an independent subsystem of TE modes for the whole cross section and two independent subsystems of TM modes: one is for the central region and another is for the layer region. The calculations show that the operation of the hard waveguides in an array with small element spacing is similar to that of the multimode smooth wall waveguides completely filled with dielectric. For large diameters and element spacing, the hard waveguides have significant advantages over the smooth ones. It is shown that unlike an individual hard waveguide, the aperture efficiency of such a waveguide in the array has a nonmonotonic dependence on the waveguide radius. The results characterizing the behavior of the aperture efficiency and cross-polarization level in a frequency band as well as the contribution of certain waveguide modes in the reflected power are presented and discussed. The examples of the element patterns corresponding to minimal cross polarization are also given     

Effects of leaky-wave propagation in metamaterial grounded slabs excited by a dipole source

In this paper, dispersive propagation and radiation properties of leaky waves on metamaterial grounded slabs are investigated. The proper or improper nature of leaky modes supported by such structures is shown to be related to the metamaterial being /spl epsi/-negative, /spl mu/-negative, or double-negative, and to field polarization, giving rise to backward or forward radiation depending on the frequency range of operation. These spectral features and the associated frequency scan of the radiated beam are illustrated by considering the field excited by a dipole source in the presence of an infinite metamaterial grounded slab. The possibility to achieve nearly equal values for the phase constants of a TE and a TM leaky mode on a large frequency range is shown; this allows us to obtain a conical radiation pattern and, also, for suitable values of the attenuation constants, the radiation of a pencil beam at broadside. Conditions for achieving maximum power density at broadside are derived, when one constitutive parameter is much smaller than the other. In order to illustrate these novel features, numerical results based on experimentally tested dispersion models for permittivity and permeability of the metamaterial media are provided, concerning leaky-wave modal properties and near and far fields excited by a dipole source.     

具有光束偏转功能的亚波长光栅偏振分束器

针对亚波长光栅偏振分束器无法实现垂直出射光 、集成耦合效率低的问题,本文设计了 一种具有光束偏转功能的亚波长光栅偏振分束器,可实现偏振分束且能获得垂直出射光。器 件上 层采用光栅衍射理论设计了可实现偏振分束的周期亚波长光栅,下层通过严格耦合波法与波 前相 位控制理论设计了具有光束偏转功能的非周期亚波长光栅。基于有限元软件COMSOL对设计 的器 件进行仿真分析,结果表明该器件可分开TE与TM混合偏振光且能实现光束垂直出射,两种 偏振 光的总透射率在1550nm处超过了76.5%,偏振 消光比为14.0 dB。因此通过该偏振分束器不但可 以获得垂直出射的单偏振光,而且能有效提高垂直耦合型器件的工作效率,有望应用在面向 光纤通信的集成光电器件中。