在线同步调制对偏振模色散补偿的研究

通过解在线同步调制的非线性耦合方程,揭示在线同步调制对偏振模色散补偿的原理;数值计算了在线同步调制对40Gbit/s脉冲传输的偏振模色散的补偿作用。结果表明,同步调制可使脉冲传输距离增大3倍,大大改善了脉冲传输性能,有效地对偏振模色散进行了补偿。     

基于光环形器的光传送网通信偏振模色散抑制

为了降低光传送网传输过程中产生的偏振模色散对传输信号质量的影响,采用将光环形器置于光传送网光放大器前端的方法,对光传送网通信传输中的偏振模色散效果进行了仿真。经过偏振模色散抑制后,传输眼图具有更加明显的张开状态,系统的传输性能有一定的提高,在一定程度上抑制了光传送网中存在的偏振模色散,有效改善了信号的质量。结果表明,从添加光环形器前后补偿偏振模色散的误比特率计算结果发现,误比特率的效率提高了约1倍,光环形器对光传送网通信的偏振模色散现象具有显著的抑制效果。该方案对不同传输速度的偏振态光信号延迟进行等效补偿,最终实现补偿偏振模色散的效果。     

100 Gbit/s级联交错相位调制码型信号的传输性能

介绍了一种应用于100 Gbit/s传输系统的新型光信号调制码型--交错差分相位调制码(SDPSK).该码型的解调仅通过一个1 bit延时的马赫曾德尔延时干涉仪和一个平衡接收机即可实现.与传统的4种级联相位调制码型进行长距离传输特性比较后证明:基于NRZ码和50%占空比RZ码的SDPSK码与相同包络的DPSK码具有几乎相同的色散容限和一阶偏振模色散容限;与有相同包络的DPSK信号和差分四相相移键控码(DQPSK)信号相比,基于NRZ码和RZ码的SDPSK信号具有更高的抵抗非线性负面效应的能力:经过90 km普通单模光纤传输并采用16 km色散补偿光纤进行后置色散补偿后,通过带宽值大于125 GHz的三阶高斯滤波器检测光信号,RZ-SDPSK信号的接收性能最佳.     

利用光脉冲传输特性抑制偏振模色散

基于双折射光纤中光脉冲传输方程,详细分析了二阶色散、自相位调制以及交叉相位调制在光脉冲传输过程中引起的啁啾。分析结果显示:通过合理选取入射功率,二阶色散引起的啁啾与自相位调制引起的啁啾在脉冲中心附近可以相互抵消,从而使脉冲展宽最小;交叉相位调制产生的两偏振分量的啁啾引起的频移,可使两偏振分量间产生互束缚,利用这种现象可以抑制偏振模色散。     

偏振模色散仿真系统研究

单模光纤内核圆对称结构的破坏而导致的缺陷会在传播时引起光学脉冲变形展宽,从而导致偏振模色散,且偏振模色散具有统计特性。本文通过计算机仿真偏振模色散系统。通过改变通信系统参数,研究一阶偏振模色散对不同通信系统的影响,分析在不同系统参数情况下的偏振模色散群时延差、信号脉冲展宽和信号眼图,并讨论了不同码型对偏振模色散的影响。     

10 Gbit/s的光纤通信系统中一阶偏振模色散自动补偿技术的研究

分析并通过实验验证了光纤通信系统中偏振模色散引起的脉冲展宽对接收信号频谱的影响 ,在此基础上提出了一种偏振模色散的补偿技术。在 10Gbit/s的传输线路中实现了一阶偏振模色散 (PMD)的自动补偿。     

超宽带信号的产生及光纤传输的研究

提出了一种新的超宽带(UWB)脉冲产生的方法,并对其产生的数学原理进行了分析和实验验证。经过高斯信号调制的偏振控制器(PC)可以产生两个相位互补的相位调制信号,先通过PC调节两个正交的相位调制信号的静态相移,再经过偏振分束器(DBS)检偏后可以得到两路相位互补的高斯信号或二阶高斯信号,最后将这两路信号延时然后再经过偏振合路器(PBC)就可以分别得到一阶或三阶高斯信号。由于这3种脉冲的产生方式不同,频带宽度不同,在光纤中传输时对色散的容忍度也不一样,因此仿真分析了色散对这3种UWB信号传输特性的影响,得出了三阶高斯信号最适合UWB传输。     

利用光脉冲传输特性抑制偏振模色散

基于双折射光纤中光脉冲传输方程，详细分析了二阶色散、自相位调制以及交叉相位调制在光脉冲传输过程中引起的啁啾。分析结果显示：通过合理选取入射功率，二阶色散引起的啁啾与自相位调制引起的啁啾在脉冲中心附近可以相互抵消，从而使脉冲展宽最小；交叉相位调制产生的两偏振分量的啁啾引起的频移，可使两偏振分量间产生互束缚，利用这种现象可以抑制偏振模色散。     

基于递阶粒子群优化径向基函数人工神经网络的光性能监控

为解决差错反向传输神经网络在透明可重构光网络光性能监测中精度不足的问题,提出一种基于优化的径向基函数人工神经网络的光性能监测方案。在该方案中,以信号眼图参数为网络输入,以光信噪比、色散和偏振模色散为网络输出;采用二进制与十进制相结合编码的递阶粒子群方法,用适应度函数引导粒子向小规模和小误差方向运动,进行神经网络的结构与参数自适应优化;分别以不同光信噪比,不同色散和偏振模色散水平仿真信道中传输速率为40 Gb/s差分相移键控仿真信号,进行网络训练和测试,并将测试结果与相同情形下基于差错反向传输法神经网络的光性能监测结果进行比较。结果表明,所提方案在保有人工神经网络方案优点的基础上,有着更好的监测精度。     

偏振模色散仿真系统研究

单模光纤内核圆对称结构的破坏而导致的缺陷会在传播时引起光学脉冲变形展宽，从而导致偏振模色散，且偏振模色散具有统计特性．本文通过计算机仿真偏振模色散系统．通过改变通信系统参数，研究一阶偏振模色散对不同通信系统的影响，分析在不同系统参数情况下的偏振模色散群时延差、信号脉冲展宽和信号眼图，并讨论了不同码型对偏振模色散的影响．     

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.     

基于均匀光纤光栅的DWDM系统PMD补偿方法

提出一种基于均匀光纤Bragg光栅(FBG)的透射型密集波分复用(DWDM)系统多信道偏振模色散(PMD)补偿方案。当FBG受到横向挤压时，会产生双折射现象。当一波长的光信号从光栅带隙附近透射时，就会在快轴和慢轴之间产生时延差(DGD)。通过改变外力的大小来调节DGD的大小可以实现对PMD的补偿。通过将多个补偿光栅级联，就可以实现对DWDM系统多信道PMD的补偿。在100N外力作用下，5cm长的光栅最大可以补偿121ps的PMD，而对相邻0．8nm的信道，只引入0．2ps的DGD。     

A DOP feedback controlling multi-stage electrical PMD compensator in digital coherent receiver

We proposed a degree of polarization (DOP) controlling multi-stage electrical polarization mode dispersion (PMD) compensator in digital coherent receiver. The compensator is modulation format independent and can mitigate both first order and higher order PMD. We evaluated this PMD compensator in both 100-Gb/s 16-QAM and QPSK signal transmission systems with 15 ps and 20 ps average differential group delay (DGD) respectively. The results show that, for both two cases, less than 0.2 dB optical signal to noise ratio (OSNR) penalty at 1e^?3 symbol error rate (SER) can be achieved after 4-stage PMD compensation.     

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     

Density-matrix-formalism based scheme for polarization mode dispersion monitoring and compensation in optical fiber communication systems

We propose a density-matrix-formalism based scheme to study polarization mode dispersion (PMD) monitoring and compensation in optical fiber communication systems. Compared to traditional monitoring and compensation schemes based on the PMD vector in the Stokes space, the scheme we proposed requires no auxiliary matrices and can be handily extended to any higher-dimensional modal space, which is advantageous in mode-division multiplexing (MDM) systems. A 28 GBaud polarization division multiplexing quadrature phase-shift keying (PDM-QPSK) coherent simulation system is built to demonstrate that our scheme can implement the monitoring and compensation of 170 ps large differential-group-delay (DGD) that far exceeds the typical DGDs in practical optical communication systems. The results verify the effectiveness of the density-matrix-formalism based scheme in PMD monitoring and compensation, thus pave the way for further applications of the scheme in more general MDM optical communication systems.     

An IIR adaptive electronic equalizer for polarization multiplexed fiber optic communication systems

An electronic digital equalizer for polarization multiplex coherent fiber optic communication systems is designed to compensate polarization mode dispersion (PMD) and residual chromatic dispersion (CD) of transmission channel. The proposed equalizer is realized with fraction spaced infinite impulse response (IIR) butterfly structure with 21 feedforward taps and 2 feedback taps. Compared with finite impulse response (FIR) structure, this structure can reduce implementation complexity of hardware under the same condition. To keep track of the random variation of channel characteristics, the filter weights are updated by least mean square (LMS) algorithm. The simulation results show that the proposed equalizer can compensate residual chromatic dispersion (CD) of 1600 ps/nm and differential group delay (DGD) of 90 ps simultaneously, and also can increase the PMD and residual CD tolerance of the whole communication system.     

Performance of a 46-Gbps Dual-Polarization QPSK Transceiver With Real-Time Coherent Equalization Over High PMD Fiber

We report experimental results on the transmission performance of a coherent dual-polarization quadrature phase-shift-keyed (DP-QPSK) transceiver with real-time electronic equalization over fiber having 50-ps mean polarization mode dispersion (PMD). Both single-channel, single-span and multi-channel, multi-span measurements were performed over the high PMD fiber, which has near Maxwellian statistics for the differential group delay (DGD) as well as higher order PMD as expected for a long, mode-coupled fiber. Transmission of eighty channels was achieved over 8$, times ,$100 km of TrueWave Reduced Slope fiber plus distributed high PMD fiber, where individual channels had instantaneous DGD as high as 127 ps. The dependence of the OSNR penalty on the launch state of polarization was evaluated and found to be minimal, and the contribution of fiber nonlinearities to the transmission penalty was evaluated for two different per-channel launch powers. Finally, using a transceiver equipped with forward-error-correction, error-free transmission over the 800-km link was demonstrated over a 10-day period; during this time the DGD of the measured channel varied from 13 to 116 ps.      

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.     

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.     

偏振副载波调制在光纤色散与PMD监测技术中的应用

利用偏振副载波调制(SCM)的方法,协同监测光纤通信系统的色散(CD)和偏振模色散(PMD).通过发送端叠加2个不同频率的副载波、接收端监测2副载波对应的功率和功率比值的方法协同监测光纤通信系统的CD和PMD.接收端副载波功率随CD和PMD的增加而增加,其比值随CD的增加而增加、随PMD的增加而减小,通过监测2副载波的功率和其比值,可以实现CD与PMD的协同监测.