一种新的自适应偏振模色散补偿前馈方法

提出了一种新偏振模色散（PMD）补偿的方法，直接从被补偿光纤中提取偏振色散矢量的大小和方向信息，根据算法调节偏振模色散补偿器的各参量，使得补偿器的快轴与被补偿光纤的慢轴对准，从而使得偏振模色散得到补偿。这种方法的优点是减少了搜索的自由度。建立了40Gb／s偏振模色散前馈补偿系统，并通过数值模拟．对40Gb／s的非归零（NRZ）码的偏振模色散进行了自适应补偿。通过对补偿前后的眼图、偏振度（DOP）和Q值进行对比和分析，结果表明，这种偏振模色散补偿的前馈方法是非常有效的。     

高速光纤通信系统中高阶PMD补偿技术研究

随着光放大器和色度色散补偿技术的不断提高，光纤的偏振模色散（PMD）已经成为超高速、超长距离光纤通信系统发展的主要障碍，在40Gbit/s或更高速率的光纤通信系统中，PMD的影响已不可忽略，必须考虑PMD的补偿问题，从高阶PMD对40Gbit/s NRZ系统影响的数值模拟发现，当光纤中PMD高阶效应比较明显时，将严重劣化一阶PMD补偿的效果，另外，通过对两种高阶PMD补偿器的比较介绍，认为两段级联的高队PMD补偿系统是一种比较现实的补偿方法。     

40Gb／s光通信系统中光域偏振模色散补偿的实验研究

在40Gb/s归零码(RZ)大Polarization Mode Dispersion(PMD)光通信系统中，采用两级四自由度光域PMD(偏振模色散)补偿器，以信号的DOP(偏振度)为反馈信号，利用自适应优化算法，实现了一阶及高阶PMD动态自适应补偿．最大一阶PMD补偿能力为35ps，二阶PMD补偿能力为200ps^2，PMD动态自适应补偿器的优化补偿时间小于10ms．     

偏振相关损耗对偏振模色散补偿系统性能的影响

数值分析了40Gb／s占空比50％的归零码（RZ）、占空比38％的RZ和载波抑制归零码（CSRZ）3种不同码型系统中偏振相关损耗（PDL）对偏振模色散（PMD）补偿的性能，并和不考虑PDL的情况作了比较。结果表明，由于PDL的存在，导致补偿系统的补偿性能恶化严重，使得损耗概率增加，眼图张开度减小；3种码型中，CSRZ码型系统的缓解性能比其他两种码型要好。     

优化算法在偏振模色散自适应补偿技术中的应用

介绍了10Gb/s的光纤通信系统中,优化算法在偏振模色散(PMD)自适应补偿技术中的应用。偏振模色散在线监测技术建立在偏振度(DOP)的基础上,偏振度随着微分群时延(DGD)的增加而减小。为了使用DOP做为PMD的监测反馈信号,需要在传输线路中模拟DGD的状态,为此设计了一个PMD仿真器。在光纤输入复用器端使用一个偏振控制器(PC)来调整光信号的偏振态,在光纤输出复用器端使用一个起偏器。随后信号到达控制计算机,优化程序运行,寻找全局最优点并通过PC来控制PMD。对现代非线性优化算法进行了讨论,比较了它们在PMD自适应补偿技术中的优缺点。在实验过程中选择遗传算法,取得良好效果。在很短时间内一阶二阶PMD能达到最大补偿效果,其动态补偿时间不超过10ms。     

高双折射取样啁啾光纤光栅的研究与应用

为实现高速光纤通信系统中的偏振模色散(PMD)补偿,提出了基于高双折射线性啁啾光纤光栅(Hi-BiLCFBG)的线性应变梯度悬臂梁作为PMD补偿器,同时考虑到波分复用(WDM)系统中不同信道PMD值不同,提出了取样啁啾(CSP)与周期啁啾(CGP)的等效,利用带有CSP的高双折射取样光纤光栅(Hi-Bi SFBG)制成多信道PMD补偿器,不同信道等效的啁啾系数不同,从而可同时实现多个信道的PMD补偿。实验中,实现了40Gb/s的传输系统中最大58.6 ps的差分群时延(DGD)补偿,补偿后,信号眼图张开度有明显改善,从而证明了该PMD补偿器的有效性与可行性。     

40 Gb/s光纤通信系统中一阶PMD对信号频谱的影响

首先给出了受一阶偏振模色散(PMD)影响的40 Gbit/s高斯脉冲信号功率谱的数学表达式,并分析了脉冲波形、分光比、监测频率以及差分群延时(DGD)对接收信号功率谱的影响.实验测量了在分光比为0.5时的40 Gbit/s归零(RZ)码伪随机信号在接收频率为12 GHz处的电功率谱密度随DGD变化的关系,实验结果与理论计算一致.这表明,对于40 Gb/s的光纤通信系统,可以通过简单地检测某一特定频率的电信号功率,动态跟踪系统中PMD的变化情况,从而为补偿一阶PMD提供了重要依据.     

偏振模色散后补偿器的工作方式分析

从理论上研究了一阶和高阶偏振模色散（PMD）后补偿器工作时补偿光纤与被补偿光纤的PMD矢量在Stokes空间中的相对位置关系，由此提出了其在小PMD和大PMD情况下可能的工作方式，以故障概率为指标，数值结果表明补偿器在这些工作方式下的补偿性能与实际补孙器所能达到的最佳性能一致。     

用于40 Gb/s系统的可编程光纤挤压式PMD模拟器

用于40Gb/s系统的可编程全光纤偏振模色散(PMD)模拟器,采用一个电控光纤挤压式偏振控制器(PC)连接两段高双折射光纤的方案,该方案结构简单,PMD变化周期为1ms,输出偏振态在邦加球上均匀分布。能产生0～22ps的群时延差(DGD)以及0～121ps^2的二阶PMD。通过程序控制,可以产生各种均值的Maxwell分布。脉冲展宽实验和10 Gb/s系统眼图实验证明该模拟器性能良好。     

利用高双折射啁啾光纤光栅补偿偏振模色散

利用具有光敏性的保偏光纤，制成高双折射啁啾光纤光栅(FBG)。将其作为偏振模色散(PMD)补偿器的关键器件，进行了一阶PMD补偿实验，补偿量为40～50ps，具有很好的补偿效果。     

Adaptive PMD compensation experiment in 40 Gb/s CSRZ system

In 40 Gb/s systems with low polarization-mode dispersion(PMD) fibers,first-order PMD is the dominate factor with quite small value. An adaptive PMD compensator consisting of an electrical polarization controller(PC) ,a section of polariza-tion maintaining fiber(PMF) ,a degree of polarization(DOP) detector and a feedback control module is employed in 40 Gb/s NSFCNet. This compensator has a simple structure and high speed,which can compensate up to 20 ps first-order PMD adaptively and the average searching time is 2 ms.     

Analysis of feedback for higher order polarization-mode dispersion mitigation of NRZ 40-Gb/s optical transmission

First-order polarization-mode dispersion (PMD) compensation by means of a polarization controller and a differential delay line is not sufficient to guarantee error-free transmission for 40-Gb/s channels when higher order effects severely increase signal distortion. Higher order mitigation is possible by cascading more than one first-order block. However, only two-stage or three-stage devices remain simple enough to be actually controlled. The performance of such higher order PMD compensators is evaluated by means of numerical simulations. Two different feedback signals have been used, demonstrating that first-order and higher order PMD distortion of nonreturn-to-zero (NRZ) pulses at 40 Gb/s can be strongly mitigated for instantaneous values of the differential group delay (DGD) up to the bit slot, when the compensator is properly controlled.     

Large PMD Compensated by Four Free Degrees in OTDM System

By introducing a two-stage polarization mode dispersion (PMD) compensator after a optical fiber link with a large PMD,over 270 ps first-order and 2 000 ps2 high-order PMD was compensated. The results show that the two-stage compensator can be used to PMD compensation in the 20 Gb/s optical time division multiplexing system with 60 km high PMD fiber. After compensating, the 270 ps DGD is changed into max. 7 ps. Moreover,the tunable FBG has a function of dispersion compensation.     

Dynamic PMD compensator for 40 Gb/s PM-DQPSK system

The adaptive polarization mode dispersion(PMD) compensation in high-speed transmission system has become more and more necessary for the link PMD causing strong signal distortions.A dynamic adaptive PMD compensator in 40 Gb/s polar-multiplex differential quadrature phase shift keying(PM-DQPSK) system is reported.Experimental results show that the PMD compensator can track the average polarization state variation at 65 rad/s without any lost of the optimum tracking.The 1st-order PMD compensation is demonstrated experimentally,and the compensator can increase the maximal tolerable PMD value by 26 ps from 17 ps to 43 ps in an optical transmission system.     

160 Gb/s-Based Field Transmission Experiments Using Polarizer-Based PMD Compensator With Optical Power Monitor

Higher bit-rate transmission is attractive for improving network resource efficiency and reducing the complexity of network management in future transmission systems. However, chromatic dispersion and polarization mode dispersion (PMD) are one of the most serious impairments. In particular, PMD should be compensated for dynamically because it changes rapidly according to environmental variations such as temperature change and mechanical vibration. Therefore, an adaptive PMD compensator is indispensable for higher bit-rate transmission systems. In this paper, we employed a simple and bit-rate independent PMD compensator based on a polarizer with an optical power monitoring scheme in 160 Gb/s-based field experiments. By using the PMD compensator, the single channel transmission of a 160 Gb/s return-to-zero differential phase-shift-keying modulation signal over an installed fiber link with buried and aerial cable routes was successfully achieved. Approximately 1 dB of Q-factor was improved by using the PMD compensator when PMD impairment was maximized. Through these experiments, the effectiveness of the PMD compensator in the higher bit-rate transmission systems was confirmed in the field environment. Furthermore, single-polarization 8times160 Gb/s wavelength division multiplexing transmission over the installed 200 km standard single mode fiber without polarization demultiplexing was successfully achieved by using the simple PMD compensator.     

Multichannel Adaptive Polarization Mode Dispersion Compensation with One Compensator in Dense Wavelength Division Multiplexing Transmission Systems

A simple two-section polarization mode dispersion(PMD) compensator is proposed for multichannel PMD compensation, which can compensate two or even more channels simultaneously. Because of the statistical characteristics and the frequency-dependence of PMD, for current single mode fiber with moderate PMD, the probability that all channels are severely degraded at the same time is extremely small, which makes it possible to compensate a dense wavelength division multiplexing(DWDM) transmission system with moderate PMD using this compensator. It is shown that the outage probability of a 40×43 Gb/s DWDM transmission system using this compensator is decreased significantly from 3.6×10-3 to 3.6×10-5.     

Polarization mode dispersion detected by arrival time measurementof polarization-scrambled light

Polarization mode dispersion (PMD) limits optical fiber capacity. PMD compensators usually minimize the associated eye closure. This measure scales with the square of the differential group delay (DGD) and makes it difficult to detect low DGDs. However, light with a low-speed polarization modulation suffers arrival time variations, in the presence of PMD, that are proportional to the DGD. These are detected by integrating the voltage-controlled oscillator (VCO) input signal of the clock recovery phase-locked loop (PLL). This novel method has been demonstrated for 40 Gb/s nonreturn-to-zero (NRZ) and for 2×40 Gb/s return-to-zero (RZ) polarization division multiplex transmission. PMD detection sensitivities range between 2 ps and 84 fs     

2.5 Gb/s偏振模色散自动补偿对偏振模色散容限值的影响

在我国现有的光纤通信骨干网中,绝大部分速率为2.5 Gb/s。今后如在我国现有的2.5 Gb/s网络系统上进行密集波分复用(DWDM)升级,亦需要考虑偏振模色散(PMD)对系统容量升级的影响。采用十段高双折射光纤级联而成的偏振模色散模拟器模拟实际光纤,从信号中提取基带频率分量作为反馈信号,对2.5 Gb/s系统进行了偏振模色散自动补偿实验,并对反馈前后的系统进行了系统代价的测量和比较。实验结果表明,偏振模色散自动补偿能较大幅度地提高系统的偏振模色散容限值。     

Automatic compensation of polarization-mode dispersion for 40 Gb/s transmission systems

We present an automatic compensator that effectively mitigates signal distortion due to polarization-mode dispersion (PMD). Accurate compensation is achieved by utilizing a degree of polarization (DOP) monitor with a measurement uncertainty of better than 1% achieved by applying a self-dependent precalibration procedure. The compensation performance at 43 Gb/s was evaluated systematically with respect to both first- and second-order PMD by using a crystal-optical PMD emulator. The compensator extended the tolerable differential group-delay (DGD) limit from 8 to 28 ps, while maintaining the Q penalty below 1 dB. In terms of the average of a Maxwellian-distributed DGD, the PMD compensator enabled transmission for up to 8 ps, or about three times higher than the level tolerated in the uncompensated case. In addition to the compensation performance, we demonstrate successful operation, even for distorted signals with high chromatic dispersion. We believe this capability will be a key enabler for a combined operation with adaptive chromatic dispersion compensators.