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.     

偏振模色散和非线性效应对光纤传输特性的综合影响

本文采用变分法,研究多色色散、偏振模色散(PMD)以及非线性效应对单模光纤中光脉冲传输的综合影响.模拟分析结果表明,非线性对偏振模色散具有一定的抑制作用;但它们的综合作用所导致的脉冲展宽比PMD或非线性单独作用时要大.     

二阶偏振模色散矢量致脉冲展宽的理论分析

我们首次提出了消偏矢量的概念，并用它来描述二阶偏振模色散中偏振模色散矢量方向的变化。本文导出了由于二阶偏振模色散所引起的脉冲展宽的解析表达式，结论指出，偏振相关的本征色散总是使脉冲展宽加剧；而偏振模色散矢量方向的变化（消偏矢量），却是使脉冲展宽减弱。二阶偏振模色散对脉冲的展宽，不仅与偏振相关的本征色散和消偏矢量有关，而且还与信号的传输速率以及初始一阶偏振模色散的大小有关。信号速率的提高，将明显的使二阶偏振模色散的影响增强。在偏振相关的本征色散不为零的情况下，通过调整初始偏振态矢量、初始一阶偏振模色散矢量以及消偏矢量三者的方向，使它们互相平行，可以获得最佳的色散补偿。但是却不能获得完全的色散补偿。在最佳色散补偿时的最小脉冲展宽为σ= (2^1/2/4)( DCF/T₀).     

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。     

偏振模色散影响下飞秒孤子的传输特性研究

以Maxwell电磁场理论为基础，在综合考虑了高阶色散、高阶非线性、自相位调制、交叉相位调制、自变陡、脉冲内喇曼散射及偏振模色散等因素的基础上，推导了飞秒孤子脉冲在双折射光纤中传输的耦合非线性薛定谔方程，并利用分步傅里叶方法对该方程进行了数值计算，研究分析了偏振模色散对飞秒孤子传输的影响。结果发现：当Dp≤0.1ps/km1/2时，偏振模色散对系统的影响很小，随着偏振模色散值的增大，系统的传输性能迅速恶化，当偏振模色散值达到0.3ps/km1/2时，系统的传输距离已经不到无偏振模色散时的1/3；若同时考虑光纤的高阶效应，以飞秒孤子作为载体的系统已经不能实现高速长距离的传输。     

二阶偏振模色散对高速高斯光脉冲在单模光纤中传输的影响

研究二阶偏振模色散（PMD）对高斯光脉冲在单模光纤中传输产生的影响，给出输出光脉冲的时域表达式。分析表明，输出光脉冲在每个基本偏振态上仍保持高斯形状，但其频率啁啾及脉宽等特性都已改变，文中对这些变化与二阶偏振模色散之间的关系进行了讨论。通过比较10Gb/s和40Gb/s的光传输系统中二阶偏振模色散的影响，可以发现，若规定脉冲展宽不能超过脉宽的十分之一，40Gb/s系统所能容忍的二阶偏振模色散极限值比10Gb/s系统小一个数量级。     

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.     

单模光纤折射率分布对偏振模色散的影响

利用将任意非圆柱等效为椭圆的方法分析和计算了单模光纤中包层和芯层折射率分布不同心导致的偏振模色散，得到了两个偏振模式的传输常数差△β和偏振模色散△τ与偏心比、入射光的波长、芯层半径、相对折射率差的关系曲线，为实践中昼减小单模光纤的偏振模色散提供理论上的指导。与椭圆度引起的偏振模色散相比，不同心引起的偏振模色散具有相同的数量级。     

High-birefringence fiber effects on transmitted pulses and mitigated by pulses’ reshaper

The transmission performance of Gaussian pulses over a high-birefringence fiber (HBF) has been studied. The Gaussian pulses are broken into a series of deformed pulses in the experiment. The simulation and transmission experiments were performed with HBF. The result of simulation is consistent with that of the experiment. Mitigation of birefringence effect by pulses reshaper, which is made of fiber Bragg grating (0.4 nm of 3 dB bandwidth) and high nonlinear dispersion shifted fiber (about  1 ps/nm km), has also been done. The badly distributed Gaussian pulses are restored well after the pulses’ reshaper.     

偏振模色散对多信道光纤通信系统信号的影响

利用耦合非线性薛定谔方程,计算了考虑PMD和非线性效应情况下8×40 Gb/s波分复用光纤通信系统中的波形及频谱.与不考虑PMD结果的比较表明:由于PMD的影响使得波形变宽,频谱分裂,同时通过比较还发现PMD对各信道的影响是不同的,这将有利于开发WDM系统中PMD补偿系统.     

Compensating Large PMD by Four Free degrees in an OTDM System

In this paper, by introducing a two-stages polarization mode dispersion (PMD) compensator after a optical fiber link with a large PMD, we compensated over 270ps first-order and 2000ps2 high-order PMD in a optical fiber link with super high PMD. Our experimental results shows that, the compensators based on the two-stages of compensator can be used to PMD compensation in a 20Gb/s OTDM system with 60 km high PMD fiber. Before compensation,270ps DGD is became into max. 7ps after compensation. At simultaneity, the tunable FBG have a function of dispersion compensation.     

一种可编程PMD模拟器

为了研究光纤通信中的偏振模色散(PMD)及其对高速光通信系统的影响和补偿技术,研制了一种可编程控制的PMD模拟器,它由6组双折射晶体和磁光晶体组成,群时延差(DGD)变化范围为±(0.3~35) ps,可设为不同平均值的Maxwell统计分布随机变化,也可以设为其它要求的数学分布.实验证明,该模拟器测量值与理论符合得很好,且具有较高的重复性和稳定性,响应时间小于1 ms.这种模拟器可用于10 Gb/s和40 Gb/s光传输系统PMD问题的研究.     

Analysis and Compensation of Polarization Mode Dispersion in Single Channel,WDM and 32-channel DWDM Fiber Optic System

One of the most serious impairments which limit the data rate in long distance and high speed transmission systems is Polarization Mode Dispersion (PMD). PMD is negligible when data rate is low (i.e. in Mb/s or few Gb/s) but it will affect the high data rate transmission systems (10^s of Gb/s, Tb/s etc.), as the pulse broadening severely distorts the signal during transmission. Thus it is necessary to compensate the PMD in both single and multichannel fiber optic transmission system due to increase in the traffic demand. This paper deals with a Deterministic Differential Group Delay (DDGD) method to compensate the PMD in single channel, by delaying the fast polarization component and wavelength independent Polarization Maintaining Fiber (PMF) method for multichannel PMD compensation. The DDGD method efficiently compensates the PMD upto 45 ps in single channel 40 Gb/s transmission systems. The State of Polarization (SOP) before and after the PMD and after compensation is analyzed by means of Poincare Sphere. By using PM Fiber method, simultaneous and effective compensation of PMD in multichannel system is achieved. Here, the simulation has been carried out for 4-channel (40 Gb/s), 8-channel (80 Gb/s), 16-channel (160 Gb/s) WDM systems and 32-channel (320 Gb/s) DWDM fiber optic system with each channel having the data rate of 10 Gb/s and the results of PMD compensation for all the channels are analyzed. It is seen that the PMD compensation is achieved upto 90 ps 87 ps, 84 ps and 80 ps in 4-channel, 8-channel, 16-channel WDM systems and 32-channel DWDM systems respectively. As very high data rate of 100 Gb/s and above are in practice now-a-days, compensation of PMD is enhanced to 1.6 Tb/s (16 × 100 Gb/s) data rate for 16-channel by PMF method and 74 ps of broadening is compensated effectively.     

Dependence of polarization mode dispersion of slotted core NZDF ribbon on cable design and environmental conditions

Non-zero dispersion fiber (NZDF) ribbon cable has recently become a considerable alternative in long-haul high-speed network construction. Since long-distance high-bit rate transmission requires low polarization mode dispersion (PMD), it is very important to know the PMD performance of this type of optical fiber cables. In this paper, we report experimental analysis of effects of the cable design and environmental parameters, in particular ribbon thickness, positions of fibers in the ribbon, flexing and vibration, on PMD performances of several slotted-core fiber ribbon cables. Results show that ribbon thickness and positions of fibers in the ribbon alter the PMD values of NZDF ribbon cables. Also, 23% and 11% PMD variations have been determined in flexing and vibration experiments, respectively. Moreover, it has been observed that vibration amplitude has significant effects and vibration frequency has little effects (14% and 6% variations, respectively) on fiber PMD. Results are important for understanding effects of installation conditions and wind, especially for aerial fibers, on PMD values of cables.     

Polarization Mode Dispersion in High-Speed Optical Communication Systems

We review the research progress concerning some fundamental issues related to polarization-mode dispersion (PMD) in high-speed fiber-optic transmission systems. We pay particular attention to issues such as the PMD-induced pulse broadening, PMD measurement and emulation, as well as PMD compensation. An electrical equalization technique based on a transversal filter and an optical technique based on a nonlinear chirped fiber Bragg gratings for PMD compensation will be discussed.     

Polarization Mode Dispersion in High-Speed Optical Communication Systems

Abstract

We review the research progress concerning some fundamental issues related to polarization-mode dispersion (PMD) in high-speed fiber-optic transmission systems. We pay particular attention to issues such as the PMD-induced pulse broadening, PMD measurement and emulation, as well as PMD compensation. An electrical equalization technique based on a transversal filter and an optical technique based on a nonlinear chirped fiber Bragg gratings for PMD compensation will be discussed.