Photonic crystal bends and power splitters based on ring resonators

In this paper, theoretical and numerical analysis of low-loss right angle waveguide bends and T-junctions based on ultra-compact photonic crystal ring resonators (PCRR) is presented. Desirable characteristics are obtained by designing the waveguide bends and T-junctions as low-Q resonant cavities with certain symmetries and small radiation loss. A simple analysis, based on coupled mode theory (CMT) in time, is used to explain the operation principles which agree qualitatively with the numerical results. These structures have high transmission efficiency over a large bandwidth in third communication window. Also effects of changing the ring size on power splitter transmission characteristics are discussed. The perfect transmission and zero reflection conditions are discussed by applying coupled mode theory. Results obtained by the finite difference time domain (FDTD) simulations are consistent with those from the coupled mode theory.     

The design of low-loss curved waveguides

A procedure for the design of low-loss continuous curvature waveguide bends, for use in integrated photonic circuits, is presented. The design employs the scalar finite element method and a technique for drawing waveguide bends based on their curvature. The finite difference beam propagation method is used to determine the power lost along the length of the waveguide structures. This new method allows the design of waveguide bends with lower loss than can be obtained by conventional methods.     

浅海波导中目标散射的边界元方法

提出了一种计算三维散射体在声速剖面随深度变化、距离无关浅海波导中散射声场的数值方法波导边界元方法。当散射体不十分靠近波导界面因而边界多次散射可以忽略时,在边界元计算中可以用自由场格林函数近似波导格林函数。应用镜像法和球波函数加法定理推导了理想波导中球体散射声场的解析解,用来验证波导边界元方法的计算精度,证明该数值方法是准确的。对浅海波导中水下潜器散射声场数值模拟的结果表明,浅海波导海面、海底界面反射、声速剖面等对目标散射声场的幅值和方向性都有很大的影响。      

光波导等参元分析

本文提出一套用于分析任意介质光波导的等参元算法,它基于严格的E_z-H_z变分公式,采用八节点曲边四边形单元。这种类型的等参元分析法尤其适用于研究各种具有曲边边界的复杂光波导和光波导器件。作为例子,文中把这一方法用于分析阶跃型光纤,渐变型光纤、各向同性以及各向异性光纤耦合器。     

Full-vectorial analysis of bending waveguides using finite difference method based on H-fields in cylindrical coordinate systems

A full-vectorial (FV) analysis of optical dielectric waveguide bends by using finite difference (FD) method in terms of magnetic field components is developed in a local cylindrical coordinate system. The perfectly matched layer absorbing boundary conditions via the complex coordinate stretching technique are incorporated into the FV wave equations for effectively demonstrating the leaky nature of waveguide bends, and a six-point FD scheme is constructed to approximate the cross-coupling terms for improving the convergent behavior. The leaky modes of a typical rib waveguide bend are calculated and the complex propagation constants and the field patterns for TE- and TM-like modes are obtained. Solutions are good agreement with those from the film mode matching method, which shows the validity and utility of the established method.     

平面光波导结构的FDTD分析

将各向异性理想匹配层(APML)吸收边界条件用于平面光波导结构的时域有限差分法(FDTD)分析中,导出了APML媒质中适用于角域和边缘的通用差分方程,并对平行介质带定向耦合器进行了数值模拟和验证,所得数值解与解析解非常一致.该方法可用于任意复杂结构的平面光波导的计算机辅助设计与分析.     

基于广角FD-BPM的PML边界处理方法

本文提出了基于三阶Padé近似广角有限差分光束传输法(FD-BPM)的简单有效的完美匹配层(PML)边界处理方法.分别给出了该方法应用于斜波导和多模干涉(MMI)数值模拟的结果,并与用完全透明边界条件处理的模拟计算结果进行了比较.本文最后对基于广角FD-BPM的PML边界处理方法进行了优化.     

Design and simulation of magneto-optic Mach-Zehnder isolator

In this paper, we have designed, optimized and simulated the magneto-optic Mach-Zehnder isolator. The waveguide isolator is based on a nonreciprocal phase shift in the magneto-optic branch of the MZ isolator. We have used the finite difference beam propagation method for numerical solution of the scalar wave equation. We have also used the transparent boundary condition. The propagation constant has been achieved by using the effective index method. We have calculated the design parameters to decrease the insertion loss in the forward direction and increase return loss in the backward direction and achieved a 40 dB isolation ratio.     

Computation of the Reflection Coefficient of a Triangular Semiconductor Prism in a Rectangular Waveguide

In this paper we present a method to solve Maxwell's equations that enables to compute waveguide structure containing a semiconductor triangular prism. The numerical study has showed that the triangular prism in the waveguide has a wider frequency band in comparison with a square rod under equal conditions. The reflection coefficient dependencies on frequency, prism size and its permittivity have been computed. The algorithm and computer programme have been tested and compared with the numerical results and experimental data of the paper [1] with good agreement.     

二维Helmholtz边界超奇异积分方程解析研究

基于常规边界元法及超奇异边界积分方程复线性耦合的Burton-Miller方法应用于无限域声学问题的最大难点在于处理超奇异积分（二维问题）.目前,此类超奇异积分主要使用各种弱奇异/正则化方法求解,而这些弱奇异/正则化方法具有时间消耗大等弱点.基于围道积分定理,本文给出一种使用常值单元的二维Helmholtz边界超奇异积分的解析表达式.在有限部分积分意义下,所有的奇异和超奇异积分可以解析表达.数值算例表明该解析表达式是有效的.     

MRTD算法在集成平面光波导组件分析中的应用

将基于Daubechies紧支集尺度函数的时域多分辨分析（MRTD）算法用于集成平面光波导组件的时域分析中,实现了MRTD算法的各向异性理想匹配层（APML）吸收边界条件,并对平行介质带定向耦合器进行了数值模拟和验证,所得结果与解析解非常一致.与传统的FDTD算法相比,MRTD算法在不牺牲计算精度的前提下能够大大节省计算资源.     

Design of sharp bends with transformation plasmonics

We report a design method of surface plasmon polaritons sharp bends based on transformation optics. Plasmonic waveguide bends with different angles, which possess little radiation loss, are proposed. Transformation media can be simply achieved with homogeneous and nonmagnetic materials, which can be constructed by altering two different dielectric films. Electromagnetic simulations by a finite-element method on detailed examples have been performed to validate the designs.     

Analysis of the plasmonic power splitter and MUX/DEMUX suitable for photonic integrated circuits

In this paper, the metal-insulator-metal (MIM) plasmonic directional coupler (PDC) with 45° waveguide bends based on surface plasmon polaritons (SPPs) excitation has been analyzed by the finite-difference time-domain (FDTD) numerical method. Effects of the variations of the coupler length and the metal gap thickness on the output powers and the propagation loss at 1550 nm wavelength have been studied. By choosing proper coupler lengths, power splitters with various output power ratios at 1550 nm wavelength and multi/demultiplexers, as some applications of the directional couplers have been proposed and their performances have been simulated.     

楔形理想波导中球体散射的镜像方法

应用镜像原理和球波函数加法公式,把楔形理想波导中球体的散射声场等效为无界空间中多球体散射声场,镜像解析解与边界元数值结果相同,可以作为边界随水平距离变化波导中目标散射数值方法的标准解。比较无界空间和楔形理想波导中球体散射声场空间分布特征,结果表明:楔形理想波导中球体的散射声场在水平和倾斜边界反射;散射声场沿楔形理想波导下坡方向的衰减在相同的水平距离下小于无界空间的情况,散射声场在楔形理想波导上坡的空间分布受到限制。     

Study of transmission properties for waveguide bends by use of a circular photonic crystal

We study the transmission properties for the waveguide bends composed by a circular photonic crystal. Two types (Y and U type) of the waveguide bends utilizing the circular photonic crystal are studied. It has been shown, compared with the conventional photonic crystal waveguide bends, transmission properties for these bends can be significantly improved. Over a 6.4% bandwidth, less than 1-dB loss/bend are observed. U bent waveguide, i.e., 180° bend, can be easily realized with low loss using the circular photonic crystal.     

3D quantum transport solver based on the perfectly matched layer and spectral element methods for the simulation of semiconductor nanodevices

A 3D quantum transport solver based on the spectral element method (SEM) and perfectly matched layer (PML) is introduced to solve the 3D Schrödinger equation with a tensor effective mass. In this solver, the influence of the environment is replaced with the artificial PML open boundary extended beyond the contact regions of the device. These contact regions are treated as waveguides with known incident waves from waveguide mode solutions. As the transmitted wave function is treated as a total wave, there is no need to decompose it into waveguide modes, thus significantly simplifying the problem in comparison with conventional open boundary conditions. The spectral element method leads to an exponentially improving accuracy with the increase in the polynomial order and sampling points. The PML region can be designed such that less than −100 dB outgoing waves are reflected by this artificial material. The computational efficiency of the SEM solver is demonstrated by comparing the numerical and analytical results from waveguide and plane-wave examples and its utility is illustrated by multiple-terminal devices and semiconductor nanotube devices.     

一种水平变化波导中声传播问题的耦合模态法

针对介质参数及海底边界水平变化波导中的声传播问题,本文基于多模态导纳法提出一种能量守恒且便于数值稳定求解的耦合模态方法.将声压表示为一组正交完备的本地本征函数之和,对声压满足的Helmholtz方程在本地本征函数上作投影,推导出关于声压模态系数的二阶耦合模态方程组.耦合矩阵直观描述水平变化因素对模态耦合的贡献.为避免直接求解二阶耦合模态方程组可能遇到的数值发散问题,将其重构为两个耦合的一阶演化方程组,引入导纳矩阵并使用Magnus数值积分方法获得稳定的声场解.利用该耦合模态方法数值计算水平变化波导中的声场,并与COMSOL参考解比较,结果表明该耦合模态理论能够精确求解水平变化波导中的点源及分布源传播问题.     

具有同轴结构的高功率微波弯曲波导设计

 基于模式耦合理论,在理论推导出弯曲同轴波导TEM模和同轴TE11模之间耦合系数显式表达的基础上,报道了可传输同轴TE11模的弯曲同轴波导的设计方法和计算结果,并进行了实例研究。数值仿真结果表明：设计的具有同轴结构的弯曲波导,利用不同的同轴空间,在P,L,S波段中心频率0.680,1.575和3.75 GHz处TE11模单模传输效率超过了99.5%,单模传输效率超过90%的工作带宽分别为0.60～0.83,1.10～2.42和3.10～4.16 GHz。该结构的功率容量在各频段均达到了GW量级。     

Scattering by an E plane dielectric sheet in rectangular waveguide

A method for the computation of S-parameters associated with a rectangular waveguide with a rectangular dielectric obstacle is presented. The method uses the Method of Lines and discretization of the dielectric permittivity to treat the dielectric discontinuity along the discretization direction. In this way, the Method of Lines can be applied to analyze waveguide discontinuity with dielectric inhomogenousity along the discretization direction. The numerical results have been verified by both theoretical and experimental results.     

毫米波行波管电子光学系统的设计

 利用基于虚边界元法的VBGUN程序和基于边界元法的MOM程序，对一折叠波导毫米波行波管的电子光学系统进行了设计。设计过程中使用计算相关性系数的方法调节参数，通过计算敏感性系数以考察加工误差带来的影响。设计过程显示：低导流系数、小束腰、高压缩比的毫米波电子枪的层流性与电极尺寸相关性很大，易受到加工误差的影响；聚束系统的设计难点在于轴上峰值磁感应强度要受到漂移管半径的限制，这一点可以通过提高工作电压和降低电流来平衡，因此它的设计必须与慢波结构的设计同时进行。