Photonic crystal waveguide directional couplers as wavelength selective optical filters

Waveguide directional couplers, formed by two closely spaced linear defect waveguides in a two-dimensional photonic crystal of air holes in a semiconductor matrix, are numerically studied using plane wave expansion and finite difference time domain methods. The coupling lengths are on a wavelength scale and show a strong wavelength dependence, allowing for the design of compact wavelength selective optical filters. Applications as a channel interleaver for the 1.55 μm wavelength range and as a micrometer sized 1.31/1.55 μm wavelength demultiplexer are presented.     

Analyzing integrated-optical inhomogeneous planar waveguides by Galerkin's method: A detailed comparison of two different basis functions

The trigonometric and Hermite-Gaussian basis functions for determining the modal characteristics of inhomogeneous optical waveguides by means of the Galerkin's method are presented and analyzed. The results obtained with each set of basis functions for mode spectra and field distributions are compared with other exact and approximate methods. The merits and problems arising with each set of basis functions are discussed.     

基于变量变换伽辽金法光波导半矢量分析

基于变量变换伽辽金法(VTGM),建立了半矢量分析光波导本征值问题的数理模型;获得了矩形光波导、脊形光波导的本征模的模场分布及归一化传播常数,计算结果和已发表的结果非常接近.半矢量VTGM采用平面映射边界条件,避免了边界截断,又能反映模场的偏振特性,是一种较为理想的光子器件分析方法.     

矩形槽光栅的矢量模式理论

本文引进满足均匀矢量Helmholtz方程的矢量波函数作为基矢,对矩形槽光栅的槽内和槽外的光场分别进行矢量平面波展开和矢量模式展开,并由耦合条件导出了求解展开系数的方程组,可进行数值计算.该方法可研究入射场的方向和偏振任意时的衍射效率、偏振特性变化等问题.在p偏振和s偏振的特殊情况下所得到的公式与用标量模式理论得到的结果一致.     

Modes of Bragg fiber with delta-function walls: Scalar approximation

An analytical theory of cylindrical low-contrast Bragg optical waveguides, i.e., Bragg fibers, was developed on the basis of the representation of thin diffuse layers by delta functions. A dispersion relation for the Bragg optical waveguide with a finite number of layers was derived in the scalar approximation. Mode fields and losses were numerically calculated for a fiber with parameters close to those of actual fiber known from the literature. A comparison with the planar model was performed, which showed significant qualitative similarity. The presented model of Bragg fibers is more realistic than the model with sharp layer boundaries.     

Analyzing integrated-optical inhomogeneous planar waveguides by Galerkin's method: A detailed comparison of two different basis functions

Abstract

The trigonometric and Hermite-Gaussian basis functions for determining the modal characteristics of inhomogeneous optical waveguides by means of the Galerkin's method are presented and analyzed. The results obtained with each set of basis functions for mode spectra and field distributions are compared with other exact and approximate methods. The merits and problems arising with each set of basis functions are discussed.     

On the problem of reconstruction of permittivity profiles for optical fibers and channel waveguides through the far field of fundamental mode emission

An algorithm for analytic continuation of the Fourier transform for the mode field in a three-dimensional waveguide from a finite region to the entire plane of spatial frequencies is proposed. It is demonstrated that this algorithm makes it possible to reconstruct the permittivity profiles of optical fibers and channel waveguides through the far field of fundamental mode emission with subwavelength resolution.     

A novel Fourier based 3D full-vectorial beam propagation method

In this paper a Fourier based full-vectorial beam propagation method (BPM) with perfectly matched layer (PML) absorbing boundary conditions is presented. The method starts with the slowly varying envelope coupled wave equations, including coordinate-stretching type PMLs, which are discretised using the Galerkin method with Fourier basis functions in the transversal direction. The proposed method is then assessed in a wide variety of situations, including 2D propagation of TE and TM waves and 3D full-vectorial situations. The obtained results show that good accuracy can be obtained even for complex strongly-guiding waveguides with a small number of basis functions.     

(Al)GaAs/AlGaAs周期光波导中的等幅基模

本文应用周期介质光波导的模场分布函数和特征方程分析了(Al)GaAs/AlGaAs周期光波导中结构参量及介质折射率对模场分布形状的影响,研究了波导中形成等幅基模的条件,讨论了相应参量的优化选择。     

Fully vectorial eigenmode calculation of dielectric waveguides using a Rayleigh--Ritz method with rational basis functions

A fully vectorial Rayleigh--Ritz method for the eigenmode calculation of dielectric waveguides is presented. It uses the four transversal field components and takes rational functions as an orthonormal basis. This formalism is especially useful near the cutoff frequency and has been applied for the investigation of the polarization properties of the output waveguides in integrated spot-size transformers. This revised version was published online in November 2006 with corrections to the Cover Date.     

Planar low-contrast Bragg waveguide with periodically arranged delta-function walls

An analytical theory of planar low-contrast Bragg optical waveguides, based on representation of thin diffuse layers by delta functions, was developed. A dispersion relation for an optical waveguide with a small number of layers was derived. Losses were numerically calculated for an optical waveguide with parameters close to those of actual fiber, known from the literature. The presented model is more realistic than the model with sharp layer interfaces.     

用平面映射边界条件的伽辽金法分析耦合脊形光波导

用平面射映边界条件的伽辽金法分析耦合脊形光波导的结果表明，耦合脊形光波导的耦合能力随脊高增加而减小，随波导间距增加呈指数衰减。给出了耦合脊形光波导所承载的偶、奇模电场分布，其结果与采用其它方法得出的结果吻合得较好，可以优化波导光电子器件的结构参数。另外，平面映射边界条件避免了非物理反射，待求矩阵小，计算效率高。     

左手介质矩形波导导模和表面模的场分布

从麦克斯韦方程组出发,结合电磁场的边界条件,推导出介质矩形波导导模的一般色散方程.对普通介质矩形波导和左手介质矩形波导的导模场分布分别进行了数值模拟.通过对比两种介质矩形波导的导模场分布的模拟结果,发现左手介质矩形波导Ex22模的场分布比普通介质波导Ex00模的场更集中在波导中部.同时,根据处理普通介质矩形波导的Marcatili方法.类比得到左手介质矩形波导表面模的色散方程,并数值模拟了低阶模的场分布,结果表明,能量主要集中在波导的四个角区以及波导的边缘.     

Manipulation of subwavelength optical fields and resonant field enhancements of a silver-shell nanocylinder pair and chain waveguides with different core–shell patterns

Near field optical properties and surface plasmon resonances on a pair of silver-shell nanocylinder and nanochain waveguides with different core–shell patterns which interact with incident plane wave along chain axis are numerically investigated by using the finite element method. Simulation results show that the peak wavelengths and resonant field enhancements are highly tunable by using the nanoshell particles instead of solid ones, revealing a critical relationship among the wavelengths and illuminated direction of incident light, interparticle spacing, radii, and medium of dielectric holes and the patterns of chain waveguides. Besides, nanochain waveguides with different patterns of core–shell that are operated on resonant multipolar modes can provide higher propagation intensities and the transmission ability can be increased by decreasing the size of nanocylinders along the chain axis.     

Optical crosstalk influence in fiber imaging endoscopes design

Medical endoscopy constitutes a basic and powerful medical tool for the development of minimally invasive procedures for a wide range of medical applications. Fiber endoscopes show a high flexibility, but are severely limited by optical crosstalk. Although they have been manufactured for decades, some of their quality limiting factors have not been exhaustively studied yet, and no design curves have been published so far. In this work, we apply a theoretical model for the study of coupling between multimode optical waveguides to the analysis of crosstalk influence in fiber imaging endoscopes. The fundamental equations and novel design curves will be obtained, enabling the adjustment of the fiber endoscope parameters in order to fulfill the quality requirements for a certain application.     

Full wave electromagnetic simulation of electrooptic high-speed probes

This paper outlines the process of modelling external electrooptic probes mounted on coplanar waveguides (CPW). The techniques used to describe the electromagnetic properties of the external probes are the finite difference time domain (FDTD) method and the finite difference transmission line method (FDTLM). These full wave techniques are time domain in nature that must be Fourier transformed to describe important frequency domain characteristics such as scattering parameters. The optical retardation of the probe is related to the full wave analysis through a commonly used grid size that results in a generalized basis for a complete electrooptic system analysis including a unique definition of an electrooptic transfer function,H(). Following the field simulation, the properties of the probe (invasiveness, retardation, signal distortion and group delay) are presented. Procedures for optimizing models for probe tips are discussed and related to a first-order model that has been developed. The results indicate that these probes can be simulated successfully on moderately sized Unix work stations and that the optimization of probe models must include the full wave simulation in the definition of the necessary gradients for the optimization process.     

Full-vectorial analysis of optical waveguides by the finite difference method based on polynomial interpolation

Based on the polynomial interpolation, a new finite difference (FD) method in solving the full-vectorial guided-modes for step-index optical waveguides is proposed. The discontinuities of the normal components of the electric field across abrupt dielectric interfaces are considered in the absence of the limitations of scalar and semivectorial approximation, and the present FD scheme can be applied to both uniform and non-uniform mesh grids. The modal propagation constants and field distributions for buried rectangular waveguides and optical rib waveguides are presented. The hybrid nature of the vectorial modes is demonstrated and the singular behaviours of the minor field components in the corners are observed. Moreover, solutions are in good agreement with those published early, which tests the validity of the present approach.     

Accuracy of three-point finite difference approximations for optical waveguides with step-wise refractive index discontinuities

A rigorous truncation error analysis of three-point finite difference approximations for optical waveguides with step-wise refractive index discontinuities is given. As the basis for the analysis we use the exact coefficients of the series that expresses the field value at a given finite difference node in terms of the field value and its derivatives at a neighbouring node. This series is applied to develop a rigorous formalism for the truncation error analysis of the three-point finite difference approximations used in the numerical modelling of light propagation in optical waveguides with step-wise discontinuities of the refractive index profile. The results show that the approximations reach O(h²) truncation error only asymptotically for sufficiently small values of the mesh size.     

Experimental research on the longitudinal field generated by a tightly focused beam

The longitudinal optical field is a peculiar physical phenomenon that is always involved with the domain of near-field optics. Due to its extraordinary properties, it has recently attracted increasing attention in research and application. In this work, the longitudinal fields generated by the evanescent illumination of tightly focused, different polarized hollow beams are investigated. The focused light fields are numerically simulated according to vector diffraction theory, and their vector analysis is also carried out. The longitudinal fields on the focal plane are demonstrated experimentally using tip-enhanced scanning near-field microscopy. The simulation and experimental results show that the tightly focused radially polarized beam is suited to generating a stronger and purer longitudinal optical field at the focus.     

光控液晶光子晶体微腔全光开关

设计了一种缺陷模迁移光子晶体微腔全光开关. 两条二维三角晶格空气孔光子晶体波导由一个光子晶体微腔连接, 在微腔的点缺陷中填充掺有少量偶氮聚合物的苯乙炔类液晶. 通过调节控制光的偏振态, 使偶氮聚合物发生顺-反异构化反应, 带动液晶分子重新取向, 从而改变光子晶体微腔的谐振波长, 进而实现光的通过与截止. 运用时域有限差分法和平面波展开法分析 了二维光控液晶光子晶体微腔全光开关的光学特性. 数值计算结果表明: 对于1.55 μ通信波段通过外界偏振光控制所填充的向列相液晶 的折射率可以实现对光波的导通与截止. 分析结果显示, 此开关具有阈值低, 消光比较大, 体积小等优点. 关键词： 二维光子晶体微腔 波导 时域有限差分(FDTD) 液晶