自适应偏振模色散补偿中控制信号的研究

文章比较了两种在自适应偏振模色散（PMD）补偿设备中控制信号的控制方法,即前馈（Feed Forward）检测控制和反馈（Feedback）检测控制;分析比较了各种可用作控制的信号,包括偏振度（DOP）、信号频率分量、眼开代价、两正交主极态（PSP）上光信号分量间的相位差和副载波信号等。     

PMD自适应补偿控制模块自启动的实现

为解决偏振模色散自适应补偿控制模块的自启动问题,提出了一种使用R0M引导、完全利用C语言进行程序烧写的自启动方案.首先分析了该模块的自启动过程,其次进行了自启动的硬件接口设计,最后重点介绍了自启动的C语言编程过程,给出了自启动的C语言源程序、cmd文件和Flash烧写流程图.     

Analysis of PMD compensators with fixed DGD using importancesampling

In this letter, we use importance sampling to analyze polarization-mode dispersion compensators with a constant differential group delay (DGD) element. We optimize the value of the fixed DGD element of the compensator with respect to the outage probability. We show that the optimum value of the fixed DGD element of the compensator can reduce the outage probability by several orders of magnitude, even though it does not provide a substantial reduction of the average penalty due to polarization-mode dispersion in the cases that we studied. By contrast, choosing the fixed DGD element to maximally reduce the average penalty may lead to an outage probability that is orders of magnitude larger than the optimal choice     

Theoretical evidence of dynamical limitations in practical single-stage PMD compensators

Dynamical effects in polarization-mode dispersion compensators are investigated. A typical compensator can actually work in two different operating modes. Dynamic evolution of the input signal can require a continuous switch between these modes, producing significant performance degradation. We introduce a numerical procedure to simulate dynamical effects, which confirms the occurrence of critical configurations.     

Performance limits of first-order PMD compensators using fixed andvariable DGD elements

In this letter, we analyze optical polarization-mode dispersion compensators using a single differential-group-delay (DGD) element that is either fixed or variable. We evaluate the upper-bound performance limits, and quantify the compensator performance under dynamic operations. We show that the variable-delay compensator can reduce the risk of feedback loops trapping a locally optimized state. Moreover, the variable-delay approach provides superior performance as compared to a fixed-delay compensator by increasing the optimal system tolerance for a 10-Gb/s nonreturn-to-zero signal from 28 to 33 ps of average link DGD     

Statistical analysis of the performance of PMD compensators using multiple importance sampling

In this letter, we evaluate the performance of fixed and variable differential group delay (DGD) polarization-mode dispersion (PMD) compensators as the first- and second-order PMD varies using multiple importance sampling. We show that importance sampling yields estimates of the average penalty with low variance over the entire region of interest of first- and second-order PMD. We also show that there is little advantage in using a compensator with a variable-DGD element and that the performance of a compensator that minimizes the residual DGD at the central frequency of the channel is considerably worse than a compensator that maximizes the eye opening.     

光纤偏振模色散的测量

介绍了时域法与频域法的几种偏振模色散(PMD)的测量方法，其中包括了一种新的测量方法——调制相移法。分别介绍了它们测量原理，并对各种方法进行了比较，概括了各种方法的优缺点。     

Practical considerations for optical polarization-mode dispersion compensators

For transmission systems at 10 Gb/s and beyond, polarization-mode dispersion (PMD) is one of the limiting factors. Optical PMD compensators aim at increasing the PMD value tolerated by the system; however, they do not cancel out its effects. Therefore, the performance of a PMD compensator is assessed statistically. Requirements for optical PMD compensators include a response time in the range of 1 ms in order to follow polarization fluctuations over the line. The system design should account for the interaction of other transmission impairments with the PMD compensator operation. For instance, transmitter chirp and residual chromatic dispersion have a deleterious impact on the compensator performance. While self-phase modulation is harmless, cross-phase modulation greatly reduces the compensator efficiency. System design rules have been applied to a one-year field trial, showing the compensator's efficiency and reliability. However, reducing their cost is the next challenge that will bring optical PMD compensators to be used in installed systems.     

Comparison of different feedback signals used in one stage PMD compensators for different modulation formats

As PMD compensation has become a very intense subject of research in recent years, the achievement of simple PMD compensators based on a feedback signal is a key issue. As PMD compensation uses a feedback indicator for system performance evaluation, such feedback signals must reproduce the DGD variations with time. In this paper, the correlation between DGD and different feedback signals is studied with a new method. This method is applied for various modulation schemes, leading to well-known results. By applying the method to the electrical and optical duobinary formats, it is shown that for duobinary signals, the DOP feedback signal shows the best correlation with instantaneous DGD value. Such a behavior of duobinary format is very interesting since duobinary modulation schemes are now considered for systems upgrades or mixed architectures (10 Gbit/s-40 Gbit/s on the same link). In such systems, PMD compensation has to be bit-rate independent which is available with the DOP as feedback indicator.     

RZ码和NRZ码的偏振模色散自适应补偿特性比较

建立了自适应偏振模色散补偿系统,利用偏振度作为反馈信号,对40 Gb/s的RZ和NRZ码分别进行了PMD补偿的数值模拟,结果显示,采用DOP作反馈信号、用二段补偿器和三段补偿器对二种码型的PMD补偿均是有效的.但由于高阶PMD的影响对NRZ码的补偿效果要优于RZ码,特别是存在偏振相关色散的影响时,对RZ码的补偿的影响在明显大于NRZ码,这说明,对于RZ码补偿偏振相关色散是必要的.     

Effects of nonlinear crosstalk in optical PMD compensation

We report on the effects of nonlinear crosstalk on the optical polarization-mode dispersion (PMD) compensation in wavelength-division-multiplexing (WDM) systems. An analytical model is presented to describe the effect of nonlinear crosstalk on the first-order PMD compensation. We also experimentally show that the performance of WDM systems could be degraded by nonlinear birefringence, even when the first-order PMD is completely compensated.     

Performance of turbo equalizers for optical PMD channels

This paper investigates the performance of iterative (turbo) equalization to mitigate the effects of a polarization-mode dispersion (PMD) in nonreturn-to-zero (NRZ) intensity-modulated optical-fiber transmission systems. A PMD can lead to severe distortions in the received electrical signal and is a key limiter for the development of high-bit-rate transmission over currently used fibers. In order to reduce the distortions due to a PMD, the performance of symbol-by-symbol maximum a posteriori (sbs-MAP) soft-in/soft-out (SISO) decoders is studied. The SISO algorithms are adapted to the noise statistics of the optical channel where the photo detector leads to a non-Gaussian signal-dependent noise at the receiver side. The modified SISO algorithms are successfully employed for turbo equalization and results show that iterative (turbo) equalization and decoding for the compensation of a PMD can lead to a tremendous reduction in the bit error ratio (BER). Moreover, it is shown that, due to the robustness of mutual information, the extrinsic information transfer (EXIT) chart can be applied for the design of iterative receivers in optical transmission systems even with a non-Gaussian noise.     

高速光传输系统中自适应偏振模色散补偿

偏振模色散(PMD)是影响高速光传输系统性能的关键因素之一,如何构建一个适合有效的偏振模色散补偿器极具挑战性.新型光偏振模补偿(PMC)系统利用DSP和CPLD平台实现逻辑控制单元.该系统中引入了高速控制模块,使得每个周期的补偿时间缩短了将近100 μ s.利用粒子群优化(PSO)算法,整个系统能够完成一阶和二阶的偏振...     

减小光纤PMD的新方案

首先介绍了几种从生产工艺上减小光纤偏振模色散的措施,并指出了各自的缺点。然后重点介绍在拉丝过程中加入了搓动轮,使光纤来回旋转,从而减小光纤的PMD的原理。对拉出的光纤的PMD进行了测试,给出了测试结果,同时对测试结果加以探讨,最后得出搓动轮的搓动次数与PMD的关系。     

Adaptive PMD compensation by electrical and optical techniques

Adaptive polarization-mode dispersion (PMD) compensation in 10 and 40 Gb/s transmission systems might become necessary if the link PMD causes strong signal distortions, which results in an unacceptable high system outage. The application of PMD compensation has the potential to lead to a drastic improvement of system robustness. Optical and electrical compensators will be reported, their operation principle explained, and their benefits will be quantified. The discussion is focused on the most important structures for practical system application including adaptive feedback loops. Experimental investigations proof compensator concepts which performance conforms with simulations. The electronical feed forward equalizer and the decision feedback equalizer are assessed in comparison to the optical simple and the two-stage compensator and the differences in performance are discussed for statistical PMD limited systems.     

Performance of MSE configured PLC optical equalizers for chromatic dispersion compensation

In this letter, we propose a mean square error (MSE) strategy to control a planar lightwave circuit (PLC) optical equalizer. We show by simulation that MSE is a suitable criterion to exploit the PLC programmability for realizing an adaptive optical equalizer. When controlled through the MSE criterion, a PLC equalizer for chromatic dispersion compensation performs better than with other control strategies and turns out to be effective even with few component elements.     

DWDM光纤通信系统中PMD及补偿的研究

文章分析了密集波分复用(DWDM)光纤通信系统中偏振模色散(PMD)的特点,并讨论了单信道PMD补偿法在DWDM多信道系统PMD补偿中所遇到的困难,提出了基于最坏通道补偿法来补偿DWDM多信道系统中PMD以及多信道PMD监测法,并讨论了这种方案的可行性.     

Optimal design for direct-detection system with optical amplifiersand dispersion compensators

System performances of direct detection optical fiber communication systems with optical amplifiers and dispersion compensators are investigated theoretically and confirmed by experimental results for several different configurations. The experimental results agreed well with the calculated results. The theoretical calculation predicts that a 120-km repeaterless transmission of 10 Gb/s is possible through the standard single-mode fiber using only one commercial fiber amplifier and a dispersion compensation fiber at the receiving end     

基于LNAFSA算法的WDM系统PMD自适应补偿

提出了一种可应用于波分复用(WDM)系统的偏振摸色散(PMD)自适应补偿方案.该方案以偏振度(DOP)为反馈信号,采用局部邻域结构的人工鱼群算法(LNAFSA)为控制算法,对低于设定阈值的一个或多个信道同时进行PMD自适应补偿.补偿后各补偿信道的DOP均大于0.96,眼图张开度明显增大,系统性能得到了改善.     

多信道动态色散补偿器的研究进展

文章对光的多信道动态色散补偿器(CTODC)的原理进行了阐述,并介绍了基于微电子机械系统(MEMS)和硅基液晶(LCOS)的CTODC的最新发展动态.对其工作机制、结构特征和指标参数进行分析和比较,指出了其中的关键技术及存在的问题.探讨了未来高速动态全光网络中CTODC的发展趋势.