阶跃光纤的模间色散

利用全反射所产生的相移角导出了全反射光在光纤包层中的横向偏移和光在光纤包层中的渡越时间.考虑光在光纤包层中的渡越时间后导出了模间色散时延差的修正公式,通过模拟计算分析了模间色散随入射角的变化规律.     

偏振模色散矢量的研究

研究了无损光纤的密勒矩阵,进而得出了偏振模色散矢量的解析表达式、主偏振态对应的斯托克斯矢量的解析表达式,以及高阶偏振模色散矢量的解析表达式.这些解析表达式是由光纤参数决定的.讨论了局部偏振模色散矢量与整体偏振模色散矢量的关系,讨论了利用偏振模色散矢量进行偏振模色散补偿的原理.引入了偏振模色散补偿元件的偏振模色散补偿矢量C,具体计算了正规的非圆光波导类的补偿元件的C.从理论上证明了仅仅利用一个正规的非圆光波导类的补偿元件,例如一根保偏光纤或是一个双折射晶体,是不能实现偏振模色散补偿 关键词： 偏振模色散 密勒矩阵 色散补偿 主偏振态斯托克斯矢量     

光纤偏振效应导致脉冲展宽的解析模型

在10Gb／s,尤其是40Gb／s以上高速光纤通信系统中,光纤的偏振特性已成为限制系统传输距离的主要因素之一。光纤的偏振效应主要包括偏振模色散和偏振依赖损耗。而脉冲均方根展宽是判断信号传输性能的一个主要物理量。本文讨论了光纤线路偏振模色散与偏振相关损耗的相互作用及对信号脉宽的影响。给出了线路偏振模色散矢量和偏振相关损耗矢量之间的关系式,并基于严格的数学方法,导出了在光纤偏振模色散和偏振相关损耗共同作用下的信号均方根脉宽变化的解析形式,同时考虑了光纤色散,啁啾等。该模型可用于分析高阶偏振模色散和偏振相关损耗,任意线性光纤通信系统脉冲展宽分析。     

旋转光纤对二阶偏振模色散的影响

论述了单模光纤生产过程中旋转光纤对二阶偏振模色散的影响. 从理论上指出虽然旋转光纤 有助于减小一阶偏振模色散，但是同时会使二阶偏振模色散增大，这对10 Gb/s以上速率的 光纤通信系统是个重要的问题. 关键词： 二阶偏振模色散 旋转光纤 动态方程     

单模光纤中偏振模色散的仿真模型

利用琼斯矩阵法研究了长单模光纤中偏振模色散的仿真模型.考虑到偏振模色散的随机性,该模型中单模光纤被看作是一系列短双折射光纤段的级联,相邻两段之间耦合角是随机的.研究结果表明,当短双折射光纤段等长时,偏振模色散呈现随波长周期性变化的特点;不符合实际情况.当短双折射光纤段不等长且服从高斯分布时,周期性逐渐消失;当其长度均方差为均值的20%,周期性完全消失.最后比较了偏振模色散的时域统计特性.取短双折射光纤段的长度服从高斯分布且均方差为均值的20%,偏振模色散的统计特性接近于实际分布.因此得出结论:为了正确估计偏振模色散的影响,在单模光纤的级联模型中,短双折射光纤段的长度应服从高斯分布,均方差为其均值的20%.     

双折射光纤中偏振复用技术的三阶色散抑制和补偿

针对三阶色散对零色散波长附近光脉冲偏振复用技术的破坏作用，提出了使用色散平坦光纤来抑制三阶色散的影响。然而用色散平坦光纤只能在脉冲短距离传输时有效，故提出用正负三阶色散交替的光纤补偿三阶色散对光脉冲偏振复用技术的影响。研究发现该补偿方案能有效地抵消线路的总三阶色散，实现了偏振脉冲长距离稳定传输。     

双折射光纤中偏振模色散的抑制

利用双折射光纤中孤子自捕获现象可以抑制偏振模色散,但这种抑制技术对传输参量有严格的限制.本文提出在双折射光纤中周期性地改变快慢轴的方法来抑制偏振模色散. 研究发现,这种方法在一定程度上能有效地抑制偏振模色散,并且光纤间偏振轴的夹角偏差有利于对偏振模色散的进一步抑制.     

光纤光栅偏振模色散的测量及补偿研究

介绍了光纤光栅的偏振模色散测量，并利用一段偏光纤对光纤光栅的偏振模色散进行补偿，效果良好。在40Gb/s、60km光纤光栅色散补偿系统中，加入保偏光纤对光纤光栅的偏振模色散进行补偿前后的测试结果表明，误码率为10^-10时，系统的功率代价由1.21dB改善为0.46dB。     

导管PS-OCT系统中双态数值色散补偿方法

导管光纤偏振敏感光学相干层析成像(PS-OCT)系统在心血管斑块定量分析上具有显著优势,搭建了基于保偏光纤成像深度复用的双偏振态导管PS-OCT系统。由于保偏光纤具有较强的双折射色散,因此难以利用一套色散系数实现双输入态色散补偿。针对这一难点问题,提出了一种用于导管PS-OCT系统的双态数值色散补偿方法。这种方法可对不同输入偏振态的色散系数进行调整,以补偿由保偏光纤双折射色散引起的不同输入偏振态色散的差异。实验结果表明,所提方法可以有效地解决材料色散、双折射色散带来的脉冲展宽、图像模糊、偏振对比度差等问题,保证了导管PS-OCT实现高质量的生物样品双折射相位延迟成像。     

高双折射光子晶体光纤偏振模色散测量

对一种高双折射光子晶体光纤的偏振模色散进行了测量.实验用26 m长光子晶体光纤使皮秒光脉冲的两个正交偏振模产生了108 ps时延.运用脉冲时延法和固定分析仪法对这种高双折射光子晶体光纤的偏振模色散进行了实验测量，测量得到其偏振模色散参量可达4154 ps/km，对应的模式双折射度为1.25×10－3.这种新型的高双折射光纤可用于补偿光纤通信系统中的偏振模色散.     

偏振模色散及非线性效应对40 Gbit/s密集波分复用系统的影响

高速率、大容量的密集波分复用系统是光纤通信系统的最终发展方向 ,单信道速率达到 4 0Gbit/s时 ,光纤的非线性效应、偏振模色散现象对系统的影响更加突出。在综合考虑群速度色散、自相位调制、交叉相位调制、四波混合、偏振模色散等因素的基础上 ,推导了密集波分复用系统中任意信道的耦合非线性薛定谔方程组。利用扩展的分步傅里叶方法对该方程进行了数值计算 ,通过对 8× 4 0Gbit/s密集波分复用系统的仿真 ,分别研究了非线性效应和偏振模色散对密集波分复用系统的影响。发现由于交叉相位调制和四波混合作用 ,多波长的密集波分复用系统比单波系统受非线性效应影响严重 ;系统受偏振模色散与非线性效应的影响程度与输入信号功率有关 ,在入射光单信道平均功率较低 0 .1mW时 ,偏振模色散是影响系统性能的主要因素 ;当入射光单信道平均功率较高1mW时 ,系统受非线性效应影响严重。而偏振模色散在使信号脉冲展宽的同时 ,类似于非零色散位移光纤中的微小色散 ,对非线性效应又有一定的抑制作用。     

A modified warping operator based on BDRM theory in homogeneous shallow water

In this paper, a modified warping operator for homogeneous shallow water based on the Beam-Displacement Ray-Mode (BDRM) theory is presented. According to the BDRM theory, the contribution of the beam displacement and the time delay to the group velocity can be easily considered in a shallow water waveguide. A more accurate dispersion formula is derived by using the cycle distance formula to calculate the group velocity of normal modes. The derived dispersion formula can be applied to the homogeneous shallow water waveguide. Theoretically, the formula is related to the phase of the reflection coefficient and suitable for various bottom models. Furthermore, based on the derived dispersion relation, the modified warping operator is developed to obtain linear modal structures. For the Pekeris model, the formulae for the phase of the reflection coefficient are derived in this work. By taking account of the effect of the bottom attenuation on the reflection coefficient, the formula for the phase of the reflection coefficient including the bottom attenuation is obtained for the Pekeris model with a lossy bottom. Performance and accuracy of different formulae are evaluated and compared. The numerical simulations indicate that the derived dispersion formulae and the modified warping operator are more accurate.     

Interaction of nonlinearity and polarization mode dispersion

The derivation of the coupled nonlinear Schrödinger equation and the Manakov-PMD equation is reviewed. It is shown that the usual scalar nonlinear Schrödinger equation can be derived from the Manakov-PMD equation when polarization mode dispersion is negligible and the signal is initially in a single polarization state as a function of time. Applications of the Manakov-PMD equation to studies of the interaction of the Kerr nonlinearity with polarization mode dispersion are then discussed.     

异核偶极相互作用非久期项对交叉极化弛豫速率的影响

本文通过计入异核偶极相互作用的非久期项对交叉极化弛豫速率的影响而推广交叉极化理论。自旋系统内部的快运动可以使得异核偶极相互作用的非久期项对交叉弛豫的贡献变得可观。本文给出了交叉弛豫速率的一般公式,并讨论了本理论在交叉极化实验中的应用。     

Eigenmodes of index-modulated layers with lateral PMLs

Maxwell equations are solved in a layer comprising a finite number of homogeneous isotropic dielectric regions ended by anisotropic perfectly matched layers (PMLs). The boundary-value problem is solved and the dispersion relation inside the PML is derived. The general expression of the eigenvalues equation for an arbitrary number of regions in each layer is obtained, and both polarization modes are considered. The modal functions of a single layer ended by PMLs are found, and their orthogonality relation is derived. The present method is useful to simulate scattering problems from dielectric objects as well as propagation in planar slab waveguides. Its potential to deal with more complex problems such as the scattering from an object with arbitrary cross section in open space using the multilayer modal method is briefly discussed.     

掺Yb3+光纤F-P腔被动锁模激光器的实验研究

 掺镱(Yb³⁺光纤被动锁模激光器谐振腔采用线性腔结构，腔内插入二分之一波片和偏振分束器引入偏振旋转，结合半导体可饱和吸收镜的自起动，实现稳定的被动锁模运转。腔内插入光栅对，提供负的群速度色散，以补偿光纤所带来的正色散，达到压缩脉宽的目的。当泵浦功率为300 mW、光栅对的距离为10 cm时，获得稳定的锁模运转，锁模输出功率28 mW，脉冲重复频率20 MHz，输出光谱宽度达15 nm，按脉冲变换极限公式，其脉冲时间宽度与频带宽度的乘积为0.315计算，脉宽可达100 fs以下。     

Computing Eigen value equation and modal dispersion characteristics of an elliptical Bragg waveguide

Using the method of separation of variables in the elliptical coordinate system, a recursive formula for the electromagnetic fields in a new type of Bragg waveguide having elliptical core cross section with multilayered cladding is derived. The eigen equation is written in the form of Mathieu and the modified Mathieu functions and a dispersion relation is obtained for various modes supported by the proposed Bragg waveguide. The cutoff frequencies for several lower order even-odd modes have been calculated and their propagation characteristics are plotted. The results show that the dispersion curves are discontinuous and modes can exist only in particular wavelength bands. The effects of elliptical eccentricity on the mode cutoff values and mode transmission are addressed. Finally, the modal birefringence in the said waveguide is also estimated.     

An analytical formulation of CPMAS

An exact expression for the cross polarization between two spin-1/2 particles is derived from the quantum Liouville equation. This is given in the form of two integrodifferential equations. These can be solved exactly in the static case (no sample spinning) and a powder average easily performed numerically. With magic-angle spinning, the neglect of certain interference terms simplifies the numerical calculation. A further assumption decoupling the calculation of the sidebands gives a very simple formula that is capable of giving a qualitative interpretation of all experimental observations. Examples are given illustrating typical buildup curves and CPMAS matching profiles.     

基于色散偏振度的乳化油光谱检测系统研究

以色散偏振光谱检测技术为背景,着重研究了乳化油颗粒的偏振光学特性及米散射物理模型,构建了色散偏振度光谱检测系统。在400～700nm波长范围内,分别对四种样品进行了301个波段的光谱反射率采集。结合贝塞尔函数和汉克尔函数,推导出了入射光波长与散射光偏振振幅矢量的关系,提取了一个新的特征参数：色散偏振度(DODP)。在暗室条件下,对乳化油样品ND18和ND75进行测量,利用色散偏振公式计算出了样品在各测量波长处的偏振度值,验证了基于DODP值检测乳化油的可行性。研究发现,虽然米散射的解是由单个球体的衍射推导而来,但是只要它们的直径和组成相同,且彼此之间的距离比波长大,也同样可以用于任意数量的球的衍射。在这种情况下,被不同球体散射的光之间没有相干的相位关系,总散射能量等于被一个球体散射的能量乘以它们的整数。当观测平面与入射波电矢量振动方向之间的夹角φ=0或者φ=π/2时,散射光分量E⁽(s))_θ或者E⁽(s))_φ消失。由于ND18的粒径比ND75的粒径小,所以ND18的前向散射波瓣较大,前向散射与后向散...