Statistical PMD and PDL effects emulator based on polarization maintaining optical fiber segments

Low cost statistical PMD/PDL emulator is presented. The emulator was initially designed as a classical PMD emulator. But PDL measurements of the designed emulator show that it can be also used as statistical PDL emulator. The emulator was constructed by concatenating 15 highly birefringence optical fiber segments and randomly varying the mode coupling between them, by rotating the polarization state between them. The achieved numerical and experimental results show that the designed emulator can mimic the polarization effects (PMD and PDL) of a real modern optical fiber link.     

Emulator with inverse trend in first-order and second-order polarisation mode dispersion

We design a polarisation mode dispersion (PMD) emulator through subdividing a polarisation maintaining fibre (PMF) of 22 m in length. The aim of this emulator design is to show that first-order and second-order PMD can be inversely proportional to each other. Furthermore, the emulator is also used to show that the magnitude of PMD is independent to whether its statistics approach theoretical distributions or not, of most importance is the degree of mode coupling. The same (as former) applies to its autocorrelation function (ACF). The PMD control mechanism for the emulator is not in real time.     

偏振模色散模拟器的特性

通过对微分群时延差(DGD)统计特性和偏振模色散(PMD)矢量自相关函数的数值模拟，分析比较了目前常用的三种PMD模拟器的性能. 结果表明：在DGD分布方面，由DGD发生器构成的模拟器，一个DGD发生器就可与实际光纤PMD的统计特性相符合，而由保偏光纤和可旋转的连接器构成的模拟器则至少需要15段. 在自相关函数方面，基于保偏光纤的模拟器取决于各段光纤的延时量，而基于DGD发生器的模拟器在中心频带外的自相关值很平稳，可视为常数. 关键词： 光纤通信 偏振模色散 偏振模色散模拟器 自相关函数     

PMD compensation using a fuzzy automatic polarization controller

A new first-order polarization mode dispersion (PMD) compensation technique is experimentally demonstrated in a 2.5 Gbit/s optical transmission system. It achieves adaptive compensation over a wide range of differential group delay (DGD) values, since it does not try to compensate it, but to eliminate one of the principal states of polarization by means of a liquid crystal polarization controller and a polarizer. The PMD parameters of the received signal are measured in real time through its spectrum analysis, and used as the feedback signal in a fuzzy logic algorithm controlling the liquid crystal device. The algorithm achieves a response time faster than the PMD variations in real links, also featuring endless operation. Moreover, a deterministic compact PMD emulator has been implemented in order to test the PMD compensator system.     

三类偏振模色散模拟器的多阶特性和频率统计相关性分析

对现有三类偏振模色散模拟器：旋转晶体型、偏振控制器型和加热器型模拟器,进行了详尽的相关群时延、高阶偏振模色散的统计分布和频率自相关函数三大统计特性的数值模拟和性能比较.以级联段数作为主要参量的分析结果表明：相关群时延分布的产生准确度,旋转晶体型模拟器略优于偏振控制器型,而加热型模拟器相对最差;在产生精确的高阶偏振模色散分布方面,偏振控制器型模拟器最为优越,加热型模拟器略优于旋转晶体型;而对于产生较低的频率自相关本底水准方面,加热型模拟器则优于偏振控制器型和旋转晶体型.综合而言,偏振控制器型模拟器的性能最为优越;十段左右的偏振控制器型模拟器就可以产生合格的模拟效果,其效果等价于十五段以上旋转晶体型,或二十段以上加热型模拟器.     

光纤偏振模色散对信号偏振度的影响

采用一种简化的线路传输模型，详细讨论了在高速光纤通信系统中，线路偏振模色散（PMD ），尤其是二阶PMD、输入信号偏振态等对信号偏振度（DOP）的影响，并指出以信号DOP做 反馈控制信号适合于一阶PMD优化补偿系统，但在较大二阶PMD的影响下，将增加控制算法的 复杂性，使系统可能陷入局部最优解. 关键词： 信号偏振度 偏振模色散 信号偏振态     

A deeper analysis of the second order polarization mode dispersion in optical communications systems

This article presents a new approach to the combined analysis of the first and second-order polarization mode dispersion (SOPMD) and shows their importance in optical communication systems performance. How it affects the relation between second-order polarization mode dispersion (PMD) and the differential group delay (DGD) in a single mode fiber is discussed. The analysis is based on time or wavelength and temperature variations changing/impacting PMD and DGD measured values. We present long term statistical characteristics of second-order PMD over a PMD emulator, and investigate the correlation between SOPMD, depolarization (DEP) and polarization dependent chromatic dispersion (PCD). Some authors calculate these modes from measurements obtained from the first order polarization mode dispersion, assuming a positive correlation between these effects, but this not the real relationship between them. A new interpretation of SOPMD was used to analyze the problem of the spectral stability in terms of the temperature. Actual techniques for determination SOPMD, consequently DEP and PCD, use the variation in time and/or wavelength. In some studies the results obtained for SOPMD are correlated to first-order PMD (FOPMD). This paper shows, based on measurements, that the correlation between first and second order Polarization Mode Dispersion (PMD) in the case where the last one is a function of the temperature can assume positive or negative values.     

A polarization mode dispersion (PMD) emulator with tuneable first-order PMD and constant second-order PMD

We design a polarization mode dispersion (PMD) emulator with fixed second-order polarization mode dispersion (SO-PMD) but varying first-order PMD (FO-PMD). The emulator constitutes of an optical delay line (ODL), a polarization controller (PC) and a fixed number of randomly concatenated polarization maintaining fibre (PMF) segments. An understanding of the SO-PMD equation is the first vital step to consider before designing such an emulator. The control of the differential group delay (DGD) statistics with wavelength proves to be the key measure for this design. Results show that the mean DGD (or the mean magnitude of the FO-PMD vector ()) of the emulator is biased towards the dominant wavelength-independent of the ODL. This is provided the dominant is by far greater than FO-PMD contributions from the other cascaded sections. Experimentally it is shown that when the DGD (Δτ) is wavelength-independent due to the absence of mode coupling, or when the wavelength-dependent DGD spectra do not change with time due to fixed mode coupling, there is negligible influence on the SO-PMD. The PC angle is controlled at an angle θ to ensure that the sub-emulator is always parallel to the ODL . Thus by rotating the mode coupling angle θ, we change the wavelength-dependent DGD spectra thereby ensuring SO-PMD variation.     

能够补偿二阶偏振模色散的三阶段偏振模色散补偿器

简要分析了偏振相关色散对光通信系统性能的影响,提出了一种三阶段高阶偏振模色散补偿方案,从理论上分析了它同时补偿偏振相关色散和偏振主态旋转的可能性,并提出了其可能存在的两种工作方式.通过数值模拟与两阶段补偿方案进行了性能比较,其偏振模色散容限比两阶段补偿提高约17%个比特周期 关键词： 光通信 光偏振 光纤色散     

Study of the stability of polarization mode dispersion in fibre

Polarization mode dispersion (PMD) is the ultimate limitation to high bit-rate fibre communication system. The stability of PMD is very important to its measurement and compensation. This paper puts forward a method to measure the stability of PMD by measuring the stability of the state of polarization (SOP) and introduces the conception of time evolution vector (TEV) of SOP. We observe the fact that the regularity of the principal state of polarization changing with time is the same as other SOPs‘‘, if we neglect the dependence of TEV on wavelength. We also measure the SOP‘‘s stability of some fibres with different lengths, and obtain results of PMD changing with time.     

Introduction to polarization mode dispersion in optical systems

This introduction covers concepts important to the understanding of polarization mode dispersion (PMD), including optical birefringence, mode coupling in long optical fibers, the Principal States Model, and the time and frequency domain behavior of PMD. Other topics addressed include the concatenation rules, bandwidth of the Principal States, PMD statistics and scaling, PMD system impairments, and PMD outage probability calculations.     

Jones matrix for second-order polarization mode dispersion

A Jones matrix is constructed for a fiber that exhibits first- and second-order polarization mode dispersion (PMD). It permits the modeling of pulse transmission for fibers whose PMD vectors have been measured or whose statistics have been determined by established PMD theory. The central portion of our model is a correction to the Bruyère model.     

Measurement of polarization mode dispersion in single mode fibre

Polarization mode dispersion (PMD) in fibre seriously limits the high-capacity optical fibre communication system. The measurement of PMD was realized by three methods — wavelength scanning method, modified OTDR method and modified York S-38 dispersion meter method. Different types of fibres have been measured using the above three methods and the results have been found to be consistent. Finally, we also found that the measured results of longer non-polarization-maintaining fibre satisfied the Maxwellian probability density function and the results of polarization maintaining fibre were derived. Supported by The National Natural Science Foundations of P. R. China.     

Analysis of polarization mode dispersion fluctuations in single mode fibres due to temperature

We have studied the effect of temperature on the birefringence and polarization mode dispersion PMD in standard single mode fibre (SSMF) with elliptical core cross section by using numerical computations. On the basis of simulation we have concluded that PMD fluctuates more rapidly than the stress-induced birefringence. In addition, DGD is inversely proportional to temperature.     

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     

偏分复用系统中偏振模色散补偿与偏分解复用一体化方案

本文建立了偏分复用系统中偏振模色散与信号偏振态变化引起信道串扰的数学模型, 分析了偏振模色散对偏分复用信道射频功率的影响, 并提出了适用于偏分复用系统的光域偏振模色散补偿与偏分解复用同时进行的方案: 用信道的射频功率作为反馈控制信号, 监测链路中偏振模色散和偏振态变化引起的信道串扰的大小, 用改进的粒子群优化算法对偏振控制器进行自适应控制, 同时完成偏振模色散补偿与偏分解复用. 在112 Gb/s偏分复用-差分正交相移键控(PDM-DQPSK)传输系统中仿真验证了该方案的有效性. 结果表明该方案可以使112 Gb/s-PDM-DQPSK传输系统完成自适应偏分解复用的同时, 在1 dB的光信噪比代价下, 使系统对偏振模色散的容忍度提高20 ps. 关键词： 偏分复用系统 信道串扰 偏振模色散 偏分解复用     

A model to characterize the effect of cross phase modulation on polarization in an optical fiber transmission system

This paper presents a model that described the process of inter-influence between cross phase modulation (XPM) and polarization effects such as polarization mode dispersion (PMD) and polarization dependant loss (PDL) in an optical fiber communication system. Previous papers have discussed PMD-PDL and PMD-XPM effects in separate models, but in this work we developed a model that is capable of characterizing and evaluating PMD, PDL and XPM simultaneously. From the model, we found that PMD and PDL can be affected by XPM. The presence of XPM changed the vector directions of PMD and PDL in Stokes space.     

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.     

Impact of polarization dependent loss on degree of polarization as feedback signal of polarization mode dispersion

Polarization dependent loss (PDL) has been recognized as a critical issue because various inline optical components may have nonnegligible PDL effect that interacts with polarization mode dispersion (PMD).We investigated the impact of PMD-PDL interaction on degree of polarization (DOP), which is the most commonly used feedback signal in PMD compensation. The simulation results of a 40-Gb/s NRZ code optical transmission system show that the maximum PMD increases from approximately 40 ps to more than 45 ps, while minimum DOP declines from approximately 0.6 to approximately 0.2. The interaction of PMD and PDL also induces residual PMD underestimation of 5-8 ps, which causes degradation of PMD compensation performance.     

Statistics of polarization mode dispersion-induced gain fluctuations in Raman amplified optical transmissions

A systematic experimental evaluation of polarization mode dispersion (PMD) -induced polarization-dependent gain (PDG) in forward pumped Raman amplification in dispersion-shifted and in dispersion-compensating fiber was performed. Good agreement was obtained between the measured statistical parameters and the current analytical model for PDG fluctuation statistics. The probability distribution of the PDG was approximately Maxwellian within the range PMD >0.05 ps/km(1/2). The interplay between PMD and gain fluctuations is discussed; random birefringence strongly reduces PDG fluctuations. However, the trade-off between reduction of the power penalties for PDG and increase of the penalties for PMD distortion precludes the use of PMD instead of source depolarization techniques for reduction of PDG.