偏振模色散模拟器产生二阶PMD的理论研究

对基于保偏光纤（PMF）级联的偏振模色散模拟器（PMD emulator)产生的二阶PMD进行了数值模拟，结果表明，采用偏振控制器（PC）连接明显优于可旋转连接器（FC）连接，当级联段数N＝8时，PC连接的模拟器产生的二阶PMD与理论曲线基本符合；PMF的长度对PMD模拟器模拟二阶PMD并没有明显影响。     

单模光纤中椭圆双折射下偏振模色散特性研究

为了分析椭圆双折射对偏振模色散的影响,将模型中的偏振模色散(PMD)矢量及极化相关损耗(PDL)矢量设定为椭圆偏振矢量,应用保偏光纤(PMF)级联模型和蒙特卡罗仿真方法,研究在PDL影响下的PMD统计特性。研究表明,PMD和PDL矢量的椭圆偏振程度对PMD的统计分布和均值大小均会有影响;在椭圆偏振和PDL的联合影响下,PMD的统计分布为Maxwell和Gaussian分布的合分布。研究结果对偏振模色散的测试、补偿和系统设计均具有参考价值。     

白光扫描干涉仪用于保偏光纤偏振耦合检测

采用白光扫描干涉法,利用Michelson干涉仪中移动臂的移动补偿保偏光纤中产生的光程差,从而实现对保偏光纤绕组中偏振耦合点的耦合强度及空间位置分布的有效检测。分析了白光干涉仪的原理、结构以及干涉条纹特点,进行了保偏光纤环的扫描测量。结果表明,第一个保偏光纤环的质量优于其他各环,证明了仪器设计理论和实验结果相符。     

Effect of cabling on polarization mode dispersion in optical fiber ribbon cables

This paper theoretically and experimentally investigates an effect of cabling on polarization mode dispersion (PMD) in ribbon fibers helically stranded in optical fiber ribbon cables aimed at designing low PMD ribbon cables. Based on the birefringence model focused on the change in the birefringence when ribbon fibers are cabled, the helical pitch of optical fiber ribbon cables is designed to minimize the maximum PMD in the cables. A low PMD characteristic is confirmed in optical fiber ribbon cable with approximately the optimal helical pitch.     

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。     

频谱傅立叶法测量偏振模色散研究

对频谱傅立叶分析法测量偏振模色散进行了理论、模拟与实验研究。利用这种方法,分别对由一段、两段、三段保偏光纤组成的PMD模拟器进行了数值模拟．并对保偏光纤、单模光纤以及商用模拟器进行了实验测量,得到了很好的结果。将这种方法和波长极值计数测量法进行了比较,研究表明,由于考虑了偏振模色散的统计特性,频谱傅立叶分析法适于测量强耦合光纤。     

高速光通信系统中偏振模色散的补偿

光纤中偏振模色散已成为高速光通信系统增容的主要障碍,文章对现有的各种偏振模色散补偿方法进行了综合评述。认为用偏振控制器与保偏光纤构成的夺模色散自动补偿系统是一种首选方案。     

Loop-synchronous polarization scrambling technique for simulating polarization effects using recirculating fiber loops

A loop-synchronous polarization-scrambling technique has been proposed for the purpose of simulating polarization effects in straight-line systems using recirculating loops. This technique uses a fast polarization controller within a fiber loop. The polarization controller changes its transmission matrix after each round trip of the optical signal circulating through the loop; thus, the periodic polarization transform of the loop is avoided. Moreover, the polarization controller generates a series of random uncorrelated transmission matrixes. Therefore, the mean-square value of differential group delay (DGD) or polarization-dependent loss (PDL) increases linearly with the number of circulations. The matrix expression for a random polarization transform that scatters the state of polarization (SOP) uniformly on the Poincare sphere for any input SOP was also found. Experiments were performed for a 94-km fiber loop that contains a fixed DGD or PDL element. The histograms of polarisation mode dispersion (PMD) induced power penalties at 10/sup -9/ bit error rate (BER) were measured. There is a good agreement between experimental and theoretical results. Using loop-synchronous polarization scrambling, accurate reproduction of the Maxwellian distribution of DGD can be realized when the background PMD of transmission fiber is much smaller than the PMD intentionally introduced into the loop.     

Polarization control method for suppressing polarization modedispersion influence in optical transmission systems

Recent progress in long-span optical repeater systems indicates that the polarization-mode dispersion (PMD) influence has become one of the main degradation factors in high speed and wideband systems. This paper discusses polarization-control methods for suppressing the PMD influence for both the coherent FDM system and the IM-DD optical repeater system. A principal-state transmission method, which can avoid PMD influence in coherent FDM common polarization control, has been proposed. In this scheme, FDM light is launched at one of the principal states in the fiber using two polarization controllers, located at both ends of the fiber. The feasibility of this scheme was confirmed through 2.5-Gb/s CPFSK, three-channel FDM transmission experiments. For a 150-km long fiber, a 700-GHz optical bandwidth can be used with the principal-state transmission method. This bandwidth is about three times wider than that for conventional common polarization control in a 150-km long fiber. The principal-state transmission method has been modified to apply to a long-span optical-repeater transmission system which includes optical isolators. In this method, small frequency modulation was added to the signal light to search for the principal state for the total transmission line. The modified method can avoid inter-symbol interference (ISI) degradation due to accumulated PMD in long-span optical fibers and optical components. Power-penalty-free operations were successfully demonstrated with up to one bit time PMD value in 5-Gb/s IM-DD, 1000-km transmission experiments. This method is expected to apply to a long-span undersea optical-repeater transmission system     

利用非线性偏振旋转效应的可调谐多波长光纤激光器

提出了一种基于非线性偏振旋转(NPR)效应的可调谐多波长掺铒光纤(EDF)激光器,非线性偏振旋转诱导的强度相关非均匀损耗有效地抑制了均匀加宽增益介质掺铒光纤中的模式竞争,使光纤激光器在室温下产生稳定的多波长输出。其中利用保偏光纤和偏振相关隔离器组成的等效Lyot 双折射光纤滤波器作为波长选择器件,该滤波器可以通过选择合适的双折射光纤长度改变波长间隔,调节偏振控制器改变偏振态实现对波长的精密调谐。实验采用10 m长的保偏光纤(PMF),得到了波长间隔为0.35 nm、最多17个波长的稳定激光输出,并且实现了输出波长在4 nm范围内的连续可调谐。分别采用10:90、30:70和50:50的输出耦合器,激光信号分别从10%、30%和50%的端口输出,得到了最多17、14和13个波长的输出,其波长功率浮动分别为13 dB、10 dB和7 dB,另外,其最大输出功率分别为-7 dBm、-3 dBm和0 dBm。实验结果表明,输出耦合器输出端比例越大,输出波长就越少,各波长激光输出功率越平坦,且输出功率越高。     

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.     

保偏光纤定轴技术的仿真及实验分析

根据保偏光纤侧视成像定轴原理,应用光线追迹方法,分析了保偏光纤侧视成像定轴过程,模拟考察了熊猫型保偏光纤侧视成像的光强分布与偏振轴方位角及物平面位置的关系.对比仿真结果和实验观测结果,对五指型光强分布特征值判断法进行了改进.比较了透镜效应侧视成像的不同定轴方法,发现改进的五指型光强分布特征值判断法的特征值在90°位置附近具有更高的定轴精度,更易于实现保偏光纤偏振主轴的定位.这种方法适用于制作保偏光纤耦合器和保偏光纤偏振器时,在偏振主轴0°或90°方位角时的高精度定轴.     

基于光子晶体光纤的偏振模色散的动态补偿

与普通保偏光纤相比,保偏光子晶体光纤(PM-PCF)具有高双折射、低温度偏振系数等优点.文章介绍了将PM-PCF作为偏振模色散(PMD)的补偿元件用于PMD的动态补偿实验,并通过对结果的分析,验证了该补偿系统的性能.     

一种新型的光纤光栅可调整偏振模色散补偿器

文章提出一种基于磁场变化对均匀周期光纤光栅(FBG)引入线性啁啾的特性来实现可调整偏振模色散(PMD)补偿的技术。这种全光型PMD补偿技术在实现调整的同时能保持中心波长固定不变，而且能够灵活方便地实现不同的微分群时延量(DGD)。针对10Gbit／s非归fig(NRZ)传输系统，采用这种技术对进行PMD补偿的模拟计算结果表明，接收信号的眼图在补偿后得到了显著改善。     

40 Gb/s CSRZ码系统下的自适应PMD补偿实验

在采用了新型光纤的40Gb／s系统中，通常只有很小的一阶偏振模色散（PMD）。本文在40Gb/s的国家自然科学基金网（NSFCNET）上，搭建了由电控偏振控制器（PC）、保偏光纤（PMF）、信号光偏振度（DOP）检测单元以及反馈控制单元组成的PMD补偿模块，具有结构简单、反应灵敏的特点，可以对小于20ps的一阶PMD进行自适应的补偿，平均搜索时间为2ms。     

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。     

A dynamical polarization mode dispersion emulator

A polarization mode dispersion (PMD) emulator is presented which accurately follows the dynamics of PMD in field optical fiber. A modification on a dynamic mode coupling wave-plate model is presented to model the emulator. It is found that the emulator and model can accurately describe the dynamical behavior of the state of polarization and thus PMD in a field fiber. The emulator is shown to be repeatable. Generally, the dynamical PMD emulator is shown to cause more realistic bit-error-rate degradation than a classical PMD emulator.     

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.      

Efficient Pump Depolarizer Analysis for Distributed Raman Amplifier With Low Polarization Dependence of Gain

This paper discusses a method of reducing the polarization dependence of gain (PDG) of a distributed Raman amplifier. Reducing its PDG is important for a Raman amplifier because it is higher than that of an erbium-doped fiber amplifier and can degrade transmission performance. Raman PDG is determined primarily by two factors, namely 1) polarization-mode dispersion (PMD) of the transmission fiber and 2) degree of polarization (DOP) of the pump source. The authors propose a simple analytical model to show the required pump light DOP for a given transmission fiber's PMD and the allowable PDG. For instance, a low pump DOP of 5% produces a low PDG of 0.2 dB under typical fiber PMD conditions, in which the analytical model agrees well with experiment. Subsequently, to achieve the required DOP, the pump source configuration is investigated in detail. The authors used one length of polarization-maintaining fiber (PMF) as an efficient pump depolarizer and evaluated its performance for various pump light spectra. It has been shown that the DOP following the depolarizer is determined simply by Fourier transformation of the pump light spectrum. The analysis in this paper has led to the important result that a Fabry-Perot laser diode pump with a short piece of PMF is effective in achieving a low pump DOP due to its multimode spectrum when the length of the PMF is properly adjusted for the longitudinal-mode spacing frequency. It has been verified that a Raman amplifier's PDG can be reduced by the proposed efficient depolarizer sufficiently for a PDG-reduced Raman amplifier repeater to be applicable to long-haul transmission systems     

基于保偏光纤模式干涉的温度传感技术

基于Sagnac光纤干涉仪偏振非互易的光纤温度传感器的理论、方案和相关技术,利用光强度直接测量的信号检测技术,实现了单点温度传感并进行了实验验证.实验和测试表明:这种温度传感器达到了0.01℃的温度分辨率和稳定性,通过改变温度传感头的长度和传感保偏光纤的双折射率,可方便地调节其测量范围.同时又提出了一种新的反射型保偏光纤温度传感方案并研制出微小型保偏光纤温度传感头.在此基础上,实现了多点温度测量,研制出大型变压器绕组温度监控用多点温度传感系统,在0～200 ℃的温度范围内达到了0.5℃的测量精度和分辨率,研制的传感头满足高电压绝缘和热油、热蒸汽的恶劣环境要求.