含曲面介质结构复杂目标电磁散射计算的射线追踪方法

针对含曲面介质结构的电大复杂目标电磁散射计算问题, 提出一种基于平面元网格模型曲率重构与射线密度归一化概念相结合的快速射线追踪方法.该方法通过曲率重构计算复杂目标表面的主曲率半径, 考虑从光疏介质到光密介质和从光密介质到光疏介质时电磁波照射凹凸曲面所具有的不同扩散或聚焦效应, 并利用射线密度归一化计算射线追踪过程中每一根射线对总散射场的贡献.当射线与介质表面的碰撞点位于焦散处时, 通过引入功率追踪成功克服了传统几何射线管在焦散处的奇异性.仿真结果验证了该方法的正确性和高效性.     

光线入射角和晶体光轴取向对晶体折射光线的影响研究

基于平面光波在晶体中传播的电磁理论特性,推导了光波在晶体表面折射时,双折射光波中e光线透过晶体出射点的位置受到任意光轴取向、任意入射角影响的关系式;利用MAT-LAB对关系式进行了数值计算分析,绘出双折射e光与任意光轴取向、任意入射角关系曲线,并给出了对应的定量关系式;实验验证了该公式是正确的.     

光学各向异性介质折射率的简易测量方法

在各向同性透明介质光学中,常以测布儒斯特角的方法来实现折射率的简易测量.电矢量处于入射面的p偏振光,当入射角等于布儒斯特角时,在试件表面不发生反射.     

对消色差相位延迟器全反射相变的探讨

由菲涅耳公式出发，推导了在介质内全反射时电矢量相互垂直的两个分量的相位变化方程。并用理论分析加图解的方法，多方面深入探讨了相变方程对消色差性及器件对于入射角的灵敏性的影响，对优化相位延迟器的消色差性、抗入射角变化的干扰性提供了理论依据。     

直角棱镜的保偏反射膜设计及分析

光波经过光学位移反射器后,由于全反射的存在,入射光的s偏振分量和p偏振分量在相位上将产生一个额外的常量差值,这将导致出射光相对于入射光的偏振状态发生变化。通过分析高反膜的反射机理及其结构特征,同时结合直角棱镜的几何结构,提出了基于高反膜膜系结构的直角棱镜保偏膜设计方法,该方法通过将设计膜系镀制到直角棱镜的两直角面上,使光束经过直角棱镜平行反射后,偏振状态保持不变。同时,对该方法进行了可行性研究和误差分析。结果表明,该方法结合目前成熟的高反膜制作工艺,理论可行,易于实现商业化应用;对于光波的小角度入射误差而言,方案所述镀膜直角棱镜的保偏特性表现出良好的稳定性。     

基于平面光波导技术的阵列波导光栅发展概况

1 平面光波导技术 平面光波导(PLC)是使光沿其纵向传输而在横向上受到限制的光导体,能将光波束缚在光波长量级尺寸的介质中,波导只能传播某些特定模式的光,其作用机理是光波的全内反射,在光波导中传播的光波,不是纯粹的电磁辐射,而是入射光与波导中的光耦合的结果.     

光束反射中的若干新奇现象

本文对有限宽度的光束在两种不同光学性质的平面界面上反射中的若干新奇现象进行了系统的介绍．这里所说的反射中的新奇现象，指的是与经典几何光学反射定律不相一致的一切现象，主要介绍当光束从光密介质入射到光疏介质的界面上时的反射现象．本文就三种典型光束(平行光束、高斯光束与发散光束)的反射现象分述如下：     

用于光导板的亚微米光栅衍射特性研究

提出了利用亚微米光栅制作光导板的方法,用严格耦合波理论计算分析了亚微米光栅从光密介质到光疏介质的1级透射衍射效率与光栅槽深、入射角度的关系。讨论了在满足基底全反射条件的入射角时对应于R、G、B三原色光的亚微米光栅（0．651μm、0．508μm、0．405μm）在导波条件下的光场衍射特性,并用实验证明在导波条件下1级衍射效率率与光栅槽深关系的可靠性。给出亚微米光栅型光导板的初始结构,并进行了误差分析。     

DMD衍射特性及其在红外场景仿真中的应用

为了提高基于数字微镜器件(DMD)的红外场景仿真系统输出图像对比度,分析了DMD的结构及工作原理,利用其类似闪耀光栅的结构特点,建立仿真模型.利用傅里叶光学分析其衍射特性,并用MATLAB进行仿真.当单色平行光入射,通过改变输入光波波长,分析衍射光强分布变化,得出入射光波波长与微镜片越相近,衍射效果越显著;通过改变入射角,分析衍射光强变化,得出在一定范围内改变入射角,衍射光强发生偏移,对输出图像影响发生变化.在红外场景仿真系统中,可以通过改变光源入射角提高输出图像的的对比度.     

四频差动激光陀螺法拉第片最佳入射角的研究

为了探究入射光偏振态对四频差动激光陀螺法拉第片最佳入射角的影响,建立四频差动激光陀螺法拉第片三光束干涉的琼斯矩阵,利用计算机进行数值计算,模拟圆偏振光和椭圆偏振光在陀螺仪内的传播方程,并通过搜索不同入射角情况下-40℃~80℃温度范围内磁圆二向色性差分损耗的振幅最小值来选取最佳入射角。结果表明,圆偏振模式下和椭圆偏振模式下法拉第片的最佳入射角有一定差别,这种差别足以影响到激光陀螺仪的测量精度,因此在安装法拉第片时应考虑入射光偏振态对其最佳入射角的影响;此外,法拉第片的最佳入射角与入射光s分量(垂直于入射面)、p分量(平行于入射面)在反射镜上的反射相位差以及反射镜的反射系数均有关。     

圆形周期介质内艾里光束的传输特性

为了研究无衍射光波在特异材质内的传输特性，实现更优良的光波通信，将传统右手材料和双负折射率材料相结合，提出了一种轴向阶跃变化周期圆形介质结构。基于广义惠更斯-菲涅耳光学积分公式，结合光学传输矩阵，分析了艾里光束在这种传输媒质中出射表面光强分布特性和侧面传输光强分布图；分析了负折射率参量对这类光波演变的影响及其补偿机理；分析了实现输出光波完美还原时，负折射率大小同介质单元长度的定量关系。结果表明，当介质孔径逐渐减小时，有限艾里光束衍射效应越来越严重，并且出射光强外形轮廓逐渐从艾里光束过渡到高斯光束；当双负折射率材料的折射率n_l的绝对值大于右手材料的折射率n_r时，出射表面实现光波完美还原的双负折射率材料单元层越长，反之则越短。该研究对分析周期或准周期轴向阶跃变化的圆形平板介质光波通信是有帮助的。     

Plane wave reflection from a rectangular-mesh ground screen

The theory of scattering of electromagnetic plane waves of arbitrary incidence and polarization from an infinite rectangular-mesh ground screen is treated. The screen is composed of thin wires of circular cross section, and is parallel to the interface between two homogeneous media. The theoretical results for parallel-wire screens are obtained in the limit of large wire spacing for one dimension of the mesh screen. Results presented for incident parallel polarized plane waves indicate that both the parallel-wire and mesh screens may exhibit a change in reflecting properties as the plane of incidence is varied from the wire axis direction. In addition, it is shown that the parallel-wire screen can produce appreciably higher cross-polarized fields than a square-mesh screen of the same wire spacing.     

Scattering by thin dielectric strips

A plane wave incident on a thin dielectric strip with infinite length is considered, letting the incident electric field vector be parallel with the edges of the strip. The field is expanded in the dielectric region as the sum of three plane waves (the forced wave and two surface waves). Thex-axis andy-axis propagation constants are known for each wave, and Galerkin's method is employed to determine the amplitudes of these waves. Finally, the far-zone scattered field is determined by considering the polarization currents radiating in free space. Numerical data are presented to illustrate the scattering properties of lossless and lossy dielectric strips as a function of the angle of incidence and the width of the strip. The calculations show excellent agreement with an earlier moment method using pulse bases and point matching.     

Plane wave diffraction by a thin dielectric half-plane

Expressions that apply for all observation points are derived for the field produced by a plane wave incident on a thin dielectric half-plane when the electric vector of the incident wave is parallel to the edge. Away from shadow boundaries the total field comprises an edge wave and a surface wave in addition to the transmitted and reflected waves of geometrical optics. The nature of the edge wave differs from that of a perfectly conducting half-plane in that both the amplitude and phase vary with the observation angle, for a given angle of incidence.     

Generalized soft-and-hard surface

Soft-and-hard surface (SHS) is a mathematical idealization of the tuned corrugated boundary. The boundary conditions are defined by a single real vector parallel to the corrugations. The SHS boundary was recently generalized by replacing the real vector by a complex vector and its conjugate (see Lindell, I.V., Proc. Inst. Elect. Eng. Microw. Antenna Propagat., vol.147, p.495-9, 2000). The SHS boundary is generalized one step further by defining it in terms of two complex vectors tangential to the surface. It is shown that, analogous to the previous special cases, there exist two eigenpolarizations, TE and TM with respect to the two vectors for plane waves of any angle of incidence. These two specially polarized waves see the boundary as a simple perfect magnetic or electric conductor surface, respectively. Because the same is true for TE and TM parts of fields radiated by finite sources, it is possible to apply the classical image theory for the computation of fields in the presence of a planar generalized SHS boundary. A principle of realization of such a boundary is briefly discussed. If the two vectors defining the boundary can be realized in practice, a device transforming any given polarization to any other polarization in reflection appears feasible.     

Negative Index Materials With Gain Media for Fast Optical Modulation

We discuss the origin of negative index behavior that is observed in certain artificial structures known as metamaterials that are periodic structures supporting backward optical waves with generally antiparallel phase and group velocities. Slab-like metamaterials, metal-dielectric, and purely dielectric ones support surface-plasmon polaritons that may be coupled into by an incident field. When this is the case, these surface waves can be pumped by the source, lead to pumping of the evanescent waves, and, as a result, enable subwavelength resolution. The main limiting factors for subwavelength resolution are losses and surface imperfections. Metal-dielectric metamaterials and systems are of special interest to nanophotonics, the focus of this paper, since they obviously provide high dielectric contrast, much larger than all-dielectric/semiconductor systems. This makes them promising for applications in dense integrated optical systems, since the mode volume is small. We consider various ways of combining metallic materials for negative dielectric constant and a gain medium to compensate for optical losses. Ultimately, one would like to make Si-compatible subwavelength optical components using metamaterials.     

基于IQ/CD的单光子载波矢量信号传输系统设计

提出并验证了一种使用单光子载波、基于 IQ 调制和相干检测的新方法来传输两个矢量信号,单光子载波上的同一个偏振态光携带 IQ 调制信号,具有正交偏振状态的光载波直接通过光波调制光波传输,两个正交极化波的光发送到相干检测器中解调。仿真实验了在25 km 单模光纤两个 QPSK 信号以数据率为1 Gbps 传输时的传输性能。     

基于并行BP神经网络的近红外光断层图像重建方法基础研究

提出一种基于并行BP神经网络的近红外光断层成像(Near-infrared optical tomography,NIR OT)图像重建算法,利用BP神经网络来表征生物组织内部光学参数的空间分布和边界光强之间的非线性映射关系.该方法将一个复杂的模型分解成简单的模型分别建立并行的神经网络.利用Femlab软件完成基于有限元的稳态扩散方程的两个简单模型的正向问题求解,根据提出的平均优化散射系数和正向问题训练的大量数据集合,建立并训练并行神经网络,通过对两个网络结果的分析,实现快速获得更复杂模型的光学参数的重构.算法能够快速识别特异组织的位置和准确反映热疗过程中生物组织的优化散射系数的变化趋势.     

A vector beam propagation method for guided-wave optics

A vector beam propagation method (BPM) for the modeling and simulation of electromagnetic wave propagation in optical guided-wave devices is proposed. The vector BPM is based on a finite-difference scheme which takes into account the boundary conditions of the transverse electric fields over the waveguide cross section. By incorporating the vector boundary conditions in the finite-difference scheme, the polarization property of the propagation electromagnetic waves is included in the analysis. The method is applied to a directional coupler made of parallel slabs, and is shown to be in excellent agreement with the exact solutions.<>