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.     

二阶偏振模色散高速光纤通信的影响及补偿

讨论了二阶偏振模色散对光脉冲的影响,模拟结果表明,二阶偏振模色散对信号影响起主要作用的是去偏振项,使得信号波形边缘出现能量过冲;同时也讨论了二阶偏振模色散补偿的方法,利用二段偏振模色散补偿器对二阶偏振模色散进行了有效的补偿,并给出了补偿的实验结果.     

利用两段PMF的PMD补偿法

提出了利用两段保偏光纤补偿偏振模色散的补偿方法,该方案能够提供足够的带宽,实现密集波分复用系统的多路同时补偿。该系统能够补偿差分群时延可变的光纤的一阶偏振模色散,并且对高阶偏振模色散有一定的抑制作用。     

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。     

高速光纤通信系统中偏振模色散的补偿方法

偏振模色散(PMD)已成为高速光纤通信系统发展的严重障碍。文章介绍了偏振模色散的概念,对现有的主要偏振模色散的补偿方法进行了分析和比较。指出用保偏光纤(PMF)和偏振控制器(PC)来补偿PMD是目前比较可行的方法,而用光子晶体光纤(PCF)进行PMD补偿的方法也在进一步研究之中。     

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.     

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。     

Fast Tracking Algorithm for Adaptive Compensation of High-Speed PMD Variation Caused by SOP Change in Milliseconds

We propose a tracking algorithm based on the steepest descent method for adaptive polarization-mode-dispersion (PMD) compensation. Transmission simulations at 160 Gb/s are conducted under the condition that the PMD fluctuates with a sequential random state of polarization change at a rate of 0.13 rad per 4 ms on average. The results show that our algorithm can successfully compensate PMD variations at speeds where a conventional hill-climbing-based tracking algorithm cannot maintain effective PMD compensation.     

The Second Order PMD in Optic Fiber and Compensation Experiment

1　Introduction　Inhigh speed /long distanceopticalfibertransmissionsystem ,PMDisoneofthemainfactorslimitingthebitrateandthetransmissiondistance ,becomingespeciallyimportantasthebitrateincreaseshigherthan 2 5Gb/s .TheinstantaneousPMDoftransmissionlineischangingfromtimetotimeandfromfrequencytofre quencyrandomly .InfrequencydomainPMDcanbeex pressedbytheTaylorexpansionatcenterfrequencyanddividedintofirstorder ,secondorder ,…ofwhichhigh erthansecondareallcalledhighorderPMD[1] .Fromfrequenc…     

Theoretical basis of polarization mode dispersion equalization upto the second order

We introduce a theoretical basis of polarization mode dispersion (PMD) equalizers based on the operator representation of PMD using Taylor's expansion. The two types of configuration of PMD equalizers are derived as the inverse of diagonalization operators and delay time difference compensation. One is a type using physical rotation of quarter wave phase plates. The other is a type using variable phase shifters suitable for PLC integration. Waveform comparison algorithm was simulated to show the existence of multiple equivalent optimum points due to the symmetry and periodicity of optical circuits. The second order PMD equalization is discussed briefly on the case of cascading the first and the second PMD equalizing circuits with two different polarization state converters     

Analysis of signal degree of polarization degradation used ascontrol signal for optical polarization mode dispersioncompensation

The basic property of degree of polarization (DOP) degradation of optical signal induced by polarization mode dispersion (PMD) in high-speed optical fiber transmission is investigated in detail. The DOP of the optical signal reflects the degree of waveform degradation caused by PMD, therefore, it is proposed to be used as the control signal judging the best compensation point for the optical adaptive PMD compensation techniques. However, the signal DOP is not only affected by PMD, but also by various factors, such as the modulation format, modulator chirp, fiber nonlinearity, amplified spontaneous emission (ASE), and so on. We use numerical simulations and experiments to explore the basic DOP property to detect PMD with these factors. We also show that using the signal DOP as control signal is especially useful for the optical duo-binary modulation because of its high sensitivity and wide PMD detection range     

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。     

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。     

Some enabling techniques for polarization mode dispersion compensation

Progress toward 40-Gb/s polarization-mode dispersion (PMD) compensation is presented in several areas. A single-waveplate polarization scrambler that generates Stokes' parameters with just three harmonics has been realized. Together with an arrival-time detection scheme, it allows the detection of about 1 ps of PMD within 2.4 /spl mu/s in a 40-Gb/s nonreturn-to-zero transmission setup. A scrambler that operates independent of its input polarization has also been realized. Both scramblers can be shared among a number of wavelength-division-multiplexed (WDM) channels for which PMD is to be detected. Furthermore, an inverse scattering technique has been implemented to determine differential group-delay profiles of an improved distributed PMD compensator in X-cut, Y-propagation LiNbO/sub 3/. In this context, the most common kind of higher order PMD is identified, which typically persists after compensation of first-order PMD. In a fiber link with polarization scrambling, it is shown to be measurable in a most efficient manner by comparing the rising and falling slopes of the detected signal using two oppositely poled one-way rectifiers placed at the output of a differentiator.     

All-frequency PMD compensator in feedforward scheme

We present the architecture of a broad-band polarization mode dispersion (PMD) compensator in a feedforward PMD compensation scheme. It is comprised of four stages. The net effect of the first two stages is equivalent to a frequency dependent polarization rotation that aligns all PMD vectors into a common direction. The third stage compensates the frequency dependent variable differential group delay (DGD) and the last stage compensates for the isotropic dispersion created by the first three stages. In Stokes space formulation, we describe the algorithm to find the required rotation angles of each stage using the PMD concatenation rule, and show that these rotation angles can be synthesized using all-pass filters (APF) in a compact integrated optics circuit. Through numerical simulations, we show significant improvement of the signal quality as a result of the compensation.     

A Change of Perspective on Single- and Double-Stage Optical PMD Compensation

We present a rigorous investigation on how to optimize the degrees of freedom of optical polarization mode dispersion (PMD) compensators composed of differential group delay sections and polarization controllers, up to two stages. The analytical treatment relies on the extracted Jones matrices of the transmission and compensation fibers. The analysis of a single-stage compensator with two degrees of freedom (fixed DGD) is based on the maximization of the eye opening, as provided by the generalized Chen formula. The outage probability is quantified through a fast semi-analytical technique. It is shown how the benefits of single-stage compensation are strongly reduced and can lead to outage events, when certain critical input states of polarization are launched into transmission fibers with strong eigenmodes depolarization (i.e., strong higher order PMD). Focusing on such transmission fibers and input configurations, a novel algorithm is introduced for controlling a double-stage compensator with five degrees of freedom. The algorithm is based on an ideal equalization of the transmission fiber at half the bit-rate, realized resorting to spherical geometry. To this aim, we show that the first compensator stage must be a PMF fiber with very large DGD, equal to the bit period, in order to compensate the most critical configurations associated with outage events.      

Tracking and separation of time-varying principal states of polarization in optical fiber link for first-order PMD compensation and its filter-dependent performance

We propose a simple method for tracking and separating time-varying principal states of polarization (PSP) occurring in a fiber-optic transmission link with polarization mode dispersion (PMD) for use in PMD compensation. The proposed method uses as a feedback monitoring signal the bandpass-filtered RF power at bit-rate frequency for NRZ signal format. We demonstrated the operating principle of the method through theoretical simulation and experiment using an automatically adaptive PMD compensator employing a single polarization beam splitter (PBS). The effects of electrical filtering on the PSP tracking performance were also investigated by using three types of filters, i.e., a low-pass filter (LPF), a band-pass filter (BPF), and a high-pass filter (HPF). The simulation results showed that only a BPF centered at bit-rate frequency was found to allow for tracing and separation of two PSPs via PBS. The proposed method, when applied to a conventional PMD compensator that alternately controls a polarization controller and a delay line, enables separation of PSP control from differential-group-delay (DGD) control, thus allowing fast tracking of rapidly changing PSP in a PMD-impaired optical fiber link and reducing compensation time.     

Dispersion Compensation Configuration Applying a Combination of EDC and Tunable-ODC for Extended $L$-Band WDM Transmission

We propose effective polarization-mode dispersion (PMD) and chromatic dispersion (CD) compensation configuration for practical use in the field, taking into consideration the system cost and the field condition such as the CD changes due to fiber temperature dependence or transmission route change, and rapidly fluctuate state of polarization of the signal lightwave. Our configuration combines electric dispersion compensators (EDCs) with fixed taps in each channel with a multichannel tunable optical dispersion compensator (T-ODC) that can simultaneously compensate all channels' accumulated CD. We demonstrate widely extended $L$-band 43-Gb/s-based wavelength-division-multiplexing transmission over 450 km using our dispersion compensation configuration, and obtain effectiveness that the PMD penalty is suppressed by 2 dB at a differential group delay of 33 ps by using the EDC and that the CD penalty is improved by about 2 dB at the accumulated CD change of $+{/}-$ 30 ps/nm by using T-ODC and EDC.      

XPM对WDM系统中一阶PMD补偿的影响

介绍了交叉相位调制(XPM)效应的概念,数值分析了其对波分复用(WDM)系统中一阶偏振模色散(PMD)补偿性能的影响.文章基于两信道WDM系统PMD效应模型,数值模拟了XPM对一阶PMD补偿性能的影响,对比分析了考虑XPM前后系统的性能.文中给出了采用补偿后考虑XPM以及不考虑XPM时信道的眼图,可以看出XPM在一定程度上降低了眼图的张开度,削弱了一阶PMD补偿效果.     

Analytical calculation of pulse broadening in optical higher order PMD compensation

The system performances in second- and third-order polarization mode dispersion (PMD) compensations have been calculated analytically and a proper approach for the higher order PMD compensation has been investigated. The investigation has revealed that the frequency averaged higher order terms of the fiber link's PMD vector should be used as the coefficient vectors in emulating the frequency dependent compensation vector for higher order PMD compensation.