Enhancement of single mode operation in coaxial optical waveguide using DB boundary conditions

In this study, a competent numerical strategy to compute the dispersion of optical waveguides is presented and propagation of electromagnetic waves in a coaxial optical waveguide with DB boundary conditions is instigated. For this intend, cylindrical coordinates are here being used to derive the DB boundary conditions and to obtain field components for the modes. The propagation constant for the waveguide to be studied is determined by solving the Bessel and the modified Bessel functions. The cutoff frequencies for various lower order modes have been calculated and their dispersion characteristics are plotted correspondingly. The behavior of the coaxial optical waveguide under DB boundary conditions is shown to be significantly different from that of coaxial optical waveguide and conventional optical waveguide under traditional or tangential boundary conditions. Finally, the effect of waveguide dimensions on the mode cutoff frequencies and fabrication issues are also addressed.     

A coupled-mode sound propagation model with complex effective depth

A coupled-mode sound propagation model with complex effective depth is presented,in order to involve the effect of branch line integral for acoustic field in a range-dependent waveguide.The equations of motion and continuity are used to obtain the coupled equations,which satisfy boundary conditions in the waveguide with varying topography and contain one coupling matrix.Meanwhile,the couplings between discrete and continuous spectrum are dealt with based on complex effective depth theory.Numerical simulations show that the accuracy of transmission loss is improved by the coupled mode model when eigenvalues of trapped modes are located near the branch point.The acoustic field in a non-horizontally stratified waveguide can be calculated efficiently and accurately by this model,and the energy corresponding to trapped modes,leaky modes and branch line integral can be considered adequately.     

Guided modes in asymmetric graphene waveguides

An asymmetric quantum well in graphene can act as a slab waveguide for electron waves in a manner analogous to the electromagnetic waves in dielectrics. Guided modes and the probability current density are analyzed in the graphene electron waveguide induced by asymmetric electrostatic potential. The modes in an asymmetric graphene waveguide include guided modes, “cover modes”, “substrate modes” and “radiation modes”. The conditions for a guided mode are quantified. It is found that the fundamental mode is absent when both the Klein tunneling and classical motion are present. The confinement of electrons for lower order mode is stronger than for higher order mode. We hope that these characteristics in asymmetric graphene waveguide can provide potential applications in graphene-based waveguide devices.     

复等效深度耦合简正波模型

为了考虑海底地形随距离变化的非水平分层介质中割线积分对声场的贡献,提出了复等效深度耦合简正波模型。该耦合简正波模型由介质运动方程和连续性方程推导得到了耦合微分方程组,此方程组满足海底地形随距离变化情况下的边界条件且仅包含一个耦合矩阵,并通过引入复等效深度理论处理连续谱和离散谱之间的相互耦合。仿真计算表明,复等效深度耦合简正波模型提高了波导简正波本征值位于割线枝点附近情况下声传播损失的计算精度,充分考虑了波导简正波、非波导简正波和割线积分对声场的贡献,可快速而准确地计算非水平分层介质中的声场。      

左手材料薄板波导中模式之间的正交关系

基于电磁场理论,采用直接计算的方法证明了左手材料薄板波导中各个模式是相互正交的,即不同传播模之间、传播模与辐射模以及不同辐射模之间是相互正交的.这为研究左手材料薄板波导中的模式耦合奠定了基础. 关键词： 左手材料 薄板波导 模式 正交关系     

Nondegenerate mirrorless oscillation in silicon waveguide

We propose nondegenerate four-wave mixing mirrorless oscillation in a multimode silicon nonlinear waveguide. Thanks to the large modal dispersion between two spatial modes caused by the high-index-contrast waveguide structure, two counterpropagating pumps of one spatial mode can generate two new optical waves of the other spatial mode at different frequencies. The phase-matching condition can be satisfied with the higher-order modes involved; therefore, frequencies of the newly generated light can be tuned by simply changing the pump frequency. The threshold power and conversion efficiency of the proposed mirrorless oscillation are investigated under different waveguide parameters.     

Reflection of Lamb waves obliquely incident on the free edge of a plate

The reflection of obliquely incident symmetric and anti-symmetric Lamb wave modes at the edge of a plate is studied. Both in-plane and Shear-Horizontal (SH) reflected wave modes are spawned by an obliquely incident in-plane Lamb wave mode. Energy reflection coefficients are calculated for the reflected wave modes as a function of frequency and angle of incidence. This is done by using the method of orthogonal mode decomposition and by enforcing traction free conditions at the plate edge using the method of collocation. A PZT sensor network, affixed to an Aluminum plate, is used to experimentally verify the predictions of the analysis. Experimental results provide support for the analytically determined results.     

Power of entanglement in quantum communication

A communication channel is a physical system that transfers information from one place to another. Examples of communication channels include wires, optical fibers, and chains of spins that propagate spin waves through a medium. This Letter shows that the power-limited communication capacity of a multimode optical fiber or a set of parallel spin chains can be enhanced by introducing nonlinear couplings between the modes or chains. In particular, M coupled, entangled modes can send M bits in the same time it takes a single mode to send a single bit, and in the same time it takes M uncoupled, unentangled modes to send sqrt[M] bits.     

Three-mode coupling in a passive dielectric waveguide with index modulation

The characteristics of a three-mode coupling in a passive dielectric waveguide are investigated for the case of even TE modes. The index is assumed to have a doubly periodic harmonic variation in the propagation direction. By a singular perturbation procedure using multiple space scales, the coupled-mode equations governing the Bragg interactions are systematically deduced. The three-mode coupling causes a stop band in frequency and the characteristics of the resulting evanescent mode are analyzed. For a periodic dielectric waveguide of finite length, the three coupled-mode equations are solved subject to suitable boundary conditions to obtain the reflection and the transmission coefficients. The frequency response of the reflection and the transmission coefficients are investigated and compared with the results of the pair of corresponding two-mode couplings. Representative numerical results are presented to illustrate the characteristics of the interaction of the three modes.     

对称单负介质包层平面波导的模式特征

系统研究了负μ材料(MNG)作为包层的对称三层平板波导的传输特性. 研究发现,这种波导既支持快波的传播,又支持TE₀,TE₁模式的慢波传输. 其模式特性不同于左手介质波导和传统介质波导,导模存在的模折射率范围要比它们的大. MNG波导的TE₀快波模缺失,且TE_m模(m>1)的传播常数大于TM_m模的传播常数. TE_m模具有双模特征,且与波导的结构参数密切相关,导致波导中的净能流出现负值. 关键词： 单负介质 平板波导 快波与慢波 传播常数     

Dichroic optical waveguides and lasers

The transverse structure of modes in optical waveguides and resonators filled with dichroic media is investigated. Two families of Hermite-Gaussian modes, corresponding to two orthogonal polarizations of radiation, are found for transversely one-dimensional field distributions and for approximating the characteristics of the medium by quadratic functions of the transverse coordinate. Angular selectivity is displayed by extraordinary waves and is manifested in a decrease in the increment of the mode upon an increase in the mode number. With account of the absence of deformation in the lowest mode due to selection, this implies that resonators containing dichroic media (including photon crystals) are promising for reducing the angular divergence of laser beams.     

On the cyclotron maser instability in a waveguide

The cyclotron maser instability is conventionally treated as a pure electromagnetic instability⁽⁵⁾. Waveguide modes can'be equivalent to plane waves reflected slantingly upon the two sides of the waveguide. According to the principles of plasma physics(⁶) the electromagnetic and the electrostatic modes can't be decoupled when the wave vector isn't strictly perpendicular or parallel to the d-c magnetic field. Therefore the conventional treatment is incomplete and invalid in the case of intense beams.Vlasov kinetic theory of the cyclotron maser instability taking into account the space-charge wave is presented. It is found that the respective couplings between the negative-energy cyclotron mode and the RHCP waveguide mode as well as the fast space-charge mode are responsible for the wave-guide maser instability.     

X波段高功率微波TE11模圆极化器

 基于圆波导TE₁₁模的模式简并特性和微波在椭圆波导中传输两个正交TE11模式相速不同的性质,研制了一种带有椭圆波导结构的圆波导TE₁₁模圆极化器。该圆极化器通过圆波导到椭圆波导的过渡段,将输入的线极化TE₁₁模式分成两个等幅、正交的TE₁₁模,然后调整椭圆波导长度,使得两个正交的TE₁₁模式的相位差为90°,实现了TE₁₁模式微波线极化到圆极化的转换。利用时域有限差分软件优化设计了该圆极化器,并按照优化的结构尺寸加工了一套实验装置进行了实验测试,测试结果表明：在工作频率9～10 GHz范围内,该圆极化器轴比小于1 dB,驻波比小于1.1,且功率容量大于1.6 GW。     

单轴各向异性异向介质平板波导中的导模特性

 推导了介电常数张量和磁导率张量中各分量带有不同符号的单轴各向异性异向介质平板波导的导行条件。根据分量符号的正负组合,分情况讨论了导行TE波的偶模特性,画出了平板波导中为实横波数时的布里渊图。结果表明,在特定条件下此平板波导中有无穷多导模,这与传统介质波导及各向同性异向介质平板中只有有限数量模式存在有很大不同。此外,还发现当分量参数满足一定条件时,出现了多个虚横波数的传输模式解,并且该模式存在高频截止。     

Transformation of surface magnetostatic waves channeled by a step bias field

The propagation of magnetostatic waves in a waveguide ferromagnetic channel formed by exposing a ferromagnetic film to a step bias is simulated. Both weak and strong channel couplings are considered. The dispersion characteristics and the distributions of wave functions are calculated. It is shown that the amplitudes of “half-waves” fitting into the channel width alternately increase and decrease with increasing frequency and the half-waves pass into the channel with the largest bias.     

Analysis of non-linear multilayer waveguides with Kerr-like permittivities

This paper presents a semi-analytical method for calculating the dispersion relationships for stationary non-linear TE waves guided by general multilayer waveguides with Kerr-like permittivities. The non-linear wave equations are solved rigorously for each layer, and the mode index and field distribution are systematically determined so as to satisfy the boundary conditions at all interfaces. To verify the validity of the present method, a non-linear graded-index waveguide is approximated by a number of step layers and the resultant multilayer waveguide is analysed numerically. The convergence properties of mode index and total power flow are presented, and these are compared with direct solutions of the non-linear wave equation by the numerical integration method. The dispersion relationships for a non-linear multiple-quantum-well waveguide have also been investigated under two simple permittivity models. The present method is useful for the analysis of non-linear graded-index waveguides in addition to non-linear multilayer waveguides such as the multiple-quantum-well structure.     

Strain field manipulation in ultrafast laser inscribed BiB3O6 optical waveguides for nonlinear applications

A novel technique was used to control the spatial overlap of the orthogonal linearly polarized waveguide modes in ultrafast laser inscribed BiB(3)O(6) waveguides. We report that the strain fields induced by the expansion of material in the laser focus can be considered independently in the design of "type II" waveguides guiding orthogonal linearly polarized light. The waveguide with the optimal mode overlap was used for type I birefringently phase-matched second-harmonic generation of a continuous wave laser source at 1047 nm.     

电磁波在负折射材料填充的3层平板波导中的传播特性

从电磁场理论出发对负折射材料填充的3层平板波导的传播特性进行研究,并进行了数值计算,分析TE和TM波在平板中传播的性质,得到了电磁波的模式方程,与电磁波在右手材料填充的平板波导中的传播特性做了对比,考察了TE模式的能流密度,进行了归一化计算。结果分析表明：基模、一阶模不存在,且任何模式都存在一个截止厚度,随着厚度的增大,模式数量也增多;在一定的入射频率下,平板薄膜厚度趋向一定数值时,可以同时传播多种模式的波,并且入射波频率越高,波导同时存在多种模式的可能性越大;与右手材料相比,左手材料填充相同尺寸的3层平板波导可以传播更高能量的电磁波,导波效果更好。     

Guided modes in a rectangular waveguide filled with single-negative materials

Based on classical electromagnetic theory, characteristics of guided modes in a rectangular waveguide filled with a pair of single-negative layers are studied. The results show that only surface waves of TE mode can propagate in this peculiar waveguide, no TM mode in any forms can propagate in it. In addition, TE waveguide modes will be affected by permeability ratio μ₁/μ₂ and dielectric layer thickness ratio P. Finally, from the electric field distribution of TE mode, we find the amplitude and location of the electric field can be adjusted by changing the thickness ratio P.     

Magneto-optical effects for detection of in-plane magnetization in plasmonic crystals

Methods for magneto-optical detection of the in-plane magnetization in a magnetic film due to the deposition of a one-dimensional metallic diffraction grating on the film have been considered. This structure is a magnetoplasmonic crystal, in which the excitation of the waveguide and plasmon modes leads to the appearance of five resonant magneto-optical effects that consist in a change of the intensity, the polarization, and the phase of the transmitted and reflected waves. The conditions responsible for the origin of these effects and their magnitude are determined by the configuration of the incident light, the parameters of the metallic grating, and the chemical composition of the magnetic layer. It has been found that the magnetophotonic intensity effects are the most optimal for the detection of the in-plane magnetization. The influence of the parameters of the metallic grating on the magneto-optical effects has been analyzed and the most optimal conditions for the observation of these effects have been determined. It has also been found that an increase in the concentration of bismuth in a magnetic dielectric material can lead to a weakening of the optical and magneto-optical responses.