非线性平板光波导中TM波的网络分析

用横向等效网络方法分析了非线性平板波导中TM的色散关系和场分布.这种方法基于传输线理论,把非线性介质波导中复杂的电磁场问题等效于电路网络问题,用横向谐振技术得到色散方程.用数值方法计算了不同非线性机制下三层平板非线性波导中的TM波传输特性.     

加载异向介质非辐射介质波导中的慢波传输及应用

将开口谐振环作为加载单元,分析了含有开口谐振环结构非辐射介质波导的新型传输特性.由于异向介质的双各向异性效应,纵剖面磁波型和纵剖面电波型在此新型非辐射介质波导中的传输速度能够减慢,甚至达到零速度.对于波导中的能量关系也进行了分析,研究表明,在一定情况下,慢波传输将引起功率流动的增强.这些特性使得此新型非辐射介质波导更能满足小型化的设计要求. 关键词： 开口谐振环 异向介质 非辐射介质波导 慢波传输     

关于波导管的格林张量函数

本文以本征函数展开的方法,研究了波导管中格林函数的一般性质和形式。为了得到波导管的本征函数(简正波)和格林张量函数的一些关系,我们首先对格林函数作富氏变换,它的象函数在各向同性介质波导中以并矢形式作为最简单的表达方法,而在充有各向异性介质波导中可以表为ABA⁺e^-ikz₀的形式,这里A是坐标矩阵。用这种方法详细推导了均匀各向同性介质波导中的并矢格林函数。 关键词：     

转移矩阵法在负折射率介质材料平板波导中的应用研究

利用严格电磁理论,推导出了适用于负折射率介质材料光波导的转移矩阵,分析讨论了转移矩阵的性质和应用.利用转移矩阵方法,推导出导波层为负折射率介质材料、覆盖层和衬底为右手材料的三层对称介质光波导的本征色散方程.用图解法研究了负折射率介质波导中TE波的异常色散特性.在负折射材料介质波导中没有零阶模,最低阶为1阶模,并且有截止频率,只有波导参量满足一定条件的时候才会存在,导模的横向波数可以为实数和纯虚数,而正折射率介质波导导模的横向波数只能为实数.     

纵向非均匀介质波导中超短光脉冲演化方程

本文利用约化摄动方法,从非线性介质中的原始Maxwell方程出发,首次导出了纵向非均匀介质波导中超短光脉冲演化方程,给出了描述飞秒光脉冲波包演化方程的两种等价表达式。     

有损耗介质中非线性光导波的数值模拟

发展了一种以有限元法为基础的数值方法，用它分析由损耗任意大小材料构成的平面非线性波导结构所传导的非线性有损耗光波。在这种方法中，从给出的非线性有损耗波导直接得到ＴＥ和ＴＭ波与功率有关的复传播常数和局域电磁场分布。     

高功率激光束波前空间频率划分研究

基于衍射理论和非线性小尺度自聚焦的纹波理论,推导了不同频率下的纹波经过非线性介质传输后的解析式.通过解析分析,得到了不同空间频率波前畸变的非线性增长特性.结合驱动器装置对打靶焦斑的要求,研究了波前空间频率的划分方法,并根据国内装置的特点划分了波前空间频率高中低频分界点.     

微结构固体中的孤立波及其存在条件

根据Mindlin理论,考虑宏观尺度非线性效应、二次和三次微尺度非线性效应以及微尺度频散效应,建立了描述一维微结构固体中纵波传播的一种新模型.用动力系统定性分析理论,分析了微结构固体中孤立波的存在条件及其几何特征,证明了当介质参数和孤立波传播速度满足适当条件时,在二次微尺度非线性效应的影响下微结构固体中可以形成一种非对称孤立波,在三次微尺度非线性效应的影响下微结构固体中可以形成一种对称孤立波.最后,用数值方法进一步验证了上述结论.     

单频偏振激光干涉仪中波片对非线性误差的影响

研究了用于纳米测量的激光干涉仪中光学波片对非线性误差的影响,基于琼斯矩阵理论建立了多波片的误差分析模型,分析了λ/2和λ/4波片引起的干涉仪非线性误差,对波片位置引起的非线性误差进行了实验研究.结果表明,波片位置调整精度对干涉仪测量影响巨大,在0～5°范围内,λ/2波片和λ/4波片引起的非线性误差分别为6.5 nm和9...     

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     

Long Time Behaviour of Marginally Stable Magnetomodulational Perturbation

The long time behaviour of magnetomodulational perturbation has been investigated by using multiple time scale perturbation method. If the perturbation field is purely potential, it is found that unlike ordinary modulational unstability the magnetomolulational instability persists in the nonlinear stage of evolution. The exact analytical solution obtained for the marginally stable mode of the linear theory exhibits explosively unstable behaviour in the slow time scale. When both potential and solenoidal components of perturbation are present the transverse exerts a stabilising influence. Different kinds of long time behaviour may occur as medicated by the results of the numerical integration of the coupled nonlinear evolution equations for the Langmuir and transverse fields.     

Inclined periodic homoclinic breather and rogue waves for the (1+1)-dimensional Boussinesq equation

A new method, homoclinic (heteroclinic) breather limit method (HBLM), for seeking rogue wave solution to nonlinear evolution equation (NEE) is proposed. (1+1)-dimensional Boussinesq equation is used as an example to illustrate the effectiveness of the suggested method. Rational homoclinic wave solution, a new family of two-wave solution, is obtained by inclined periodic homoclinic breather wave solution and is just a rogue wave solution. This result shows that rogue wave originates by the extreme behaviour of homoclinic breather wave in (1+1)-dimensional nonlinear wave fields.     

Das Verhalten des Koppelmann-Bogens im Unterschallbereich

A system of nonlinear partial integral-differential equations will be given which satisfies the single fluid model and describes the behaviour of electric arcs. A method to solve these equations simultaneously is outlined. The method is applied to an arc with Koppelmann geometry (radial gas injection into a wall stabilized arc). The behaviour of this arc is discussed on the basis of the numerical results obtained.     

Influence of optical-damage-resistant dopants on the nonlinear optical properties of lithium niobate

Using the chemical-bond method, nonlinear optical properties of lithium niobate containing different dopants are calculated. In crystals with stoichiometric composition the second order nonlinear susceptibility decreases approximately linearly with increasing dopant concentration. Among the dopants studied – Mg, Zn and In – this behaviour is most highly expressed for In doping. In contrast to that, congruently grown crystals show a different behaviour; only a weak dependence on the dopant concentration is found for, for example, Mg-doped material. Received: 24 October 2000 / Published online: 21 March 2001     

Switching behaviour of a nonlinear Mach-Zehnder interferometer

In the present paper, a detailed investigation on the switching behaviour of a nonlinear Mach-Zehnder interferometer (NMZI) has been carried out using beam propagation method (BPM). A thorough investigation on input vs. output characteristic has been carried out by varying different parameters like length of the arms, refractive index of the linear/nonlinear arm, wavelength of the input beams and nonlinear coefficient of the material of the nonlinear arm. The input vs. output characteristic has also been investigated by shifting the balance point of the NMZI. The present paper provides a physically intuitive understanding of the effect of change in different parameters of the NMZI on its switching behaviour.     

Nonlinear stability of cylindrical shells subjected to axial flow: Theory and experiments

This paper, is concerned with the nonlinear dynamics and stability of thin circular cylindrical shells clamped at both ends and subjected to axial fluid flow. In particular, it describes the development of a nonlinear theoretical model and presents theoretical results displaying the nonlinear behaviour of the clamped shell subjected to flowing fluid. The theoretical model employs the Donnell nonlinear shallow shell equations to describe the geometrically nonlinear structure. The clamped beam eigenfunctions are used to describe the axial variations of the shell deformation, automatically satisfying the boundary conditions and the circumferential continuity condition exactly. The fluid is assumed to be incompressible and inviscid, and the fluid–structure interaction is described by linear potential flow theory. The partial differential equation of motion is discretized using the Galerkin method and the final set of ordinary differential equations are integrated numerically using a pseudo-arclength continuation and collocation techniques and the Gear backward differentiation formula. A theoretical model for shells with simply supported ends is presented as well. Experiments are also described for (i) elastomer shells subjected to annular (external) air-flow and (ii) aluminium and plastic shells with internal water flow. The experimental results along with the theoretical ones indicate loss of stability by divergence with a subcritical nonlinear behaviour. Finally, theory and experiments are compared, showing good qualitative and reasonable quantitative agreement.     

Chaotic behaviour of nonlinear coupled reaction–diffusion system in four-dimensional space

In recent years, nonlinear coupled reaction–diffusion (CRD) system has been widely investigated by coupled map lattice method. Previously, nonlinear behaviour was observed dynamically when one or two of the three variables in the discrete system change. In this paper, we consider the chaotic behaviour when three variables change, which is called as four-dimensional chaos. When two parameters in the discrete system are unknown, we first give the existing condition of the chaos in four-dimensional space by the generalized definitions of spatial periodic orbits and spatial chaos. In addition, the chaotic behaviour will vary with the parameters. Then we propose a generalized Lyapunov exponent in four-dimensional space to characterize the different effects of parameters on the chaotic behaviour, which has not been studied in detail. In order to verify the chaotic behaviour of the system and the different effects clearly, we simulate the dynamical behaviour in two- and three-dimensional spaces.     

A second-order discretization of the nonlinear Poisson–Boltzmann equation over irregular geometries using non-graded adaptive Cartesian grids

In this paper we present a finite difference scheme for the discretization of the nonlinear Poisson–Boltzmann (PB) equation over irregular domains that is second-order accurate. The interface is represented by a zero level set of a signed distance function using Octree data structure, allowing a natural and systematic approach to generate non-graded adaptive grids. Such a method guaranties computational efficiency by ensuring that the finest level of grid is located near the interface. The nonlinear PB equation is discretized using finite difference method and several numerical experiments are carried which indicate the second-order accuracy of method. Finally the method is used to study the supercapacitor behaviour of porous electrodes.     

Multivalued phase conjugate reflectivity in the reflection-type photorefractive four-wave mixing; strong coupling regime

Optical multistability based on the theory of four-wave mixing (FWM) is considered for the case of reflection geometry in photorefractive crystals. The resultant nonlinear algebraic equation obtained from the initial nonlinear coupled differential equations, is solved numerically by using a successive bisection method which can predict repeated zeros (roots) as well as discontinuities (jumps). We show that apart from the effects of photorefractive phase shift, the strong nonlinear coupling itself is sufficient to bring about multivalued branching behaviour of the phase conjugate reflectivity (PCR). As the coupling strength increases, the solutions become richer and more complex. We find that for certain values of pump and probe ratios and owing to the nature of strong nonlinear coupling the appearance of multiple solutions has a close connection with the phenomenon of bistability and self-oscillation.     

Nd0.7Sr0.3MnO3陶瓷EPIR效应的起源

用两线法和四线法对球磨合成后热处理的Nd_0.7Sr_0.3MnO₃陶瓷样品的电脉冲诱导电阻转变(EPIR)效应进行了测试.结果表明:在Nd_0.7Sr_0.3MnO₃块体中用四线法测得的I-V曲线为非线性,说明Nd_0.7Sr_0.3MnO₃样品在晶(相)界处存在空间电荷层和界面电阻.但用四线法测量EPIR效应时,没有EPIR效应发生,表明晶(相)界处的空间电荷层和肖特基势垒不能产生EPIR效应;对同一样品采用直流两线法测量,其I-V曲线也为非线性,但却发生明显的EPIR效应.说明在Nd_0.7Sr_0.3MnO₃陶瓷中发现的EPIR效应起源于样品与电极之间的接触界面,块体内的晶(相)界处虽能产生相似I-V特性,但却不能发生EPIR效应. 关键词： 电脉冲诱导电阻转变(EPIR) 亚锰酸盐 空间电荷层 I-V非线性')" href="#">I-V非线性