20Gb/s系统中偏振模色散的偏振度反馈控制分析

基于主偏振态理论和一阶偏振模色散近似，推导出光信号偏振度的一个简洁解析表达式。并利用该解析表达式和快速傅里叶变换，对20Gb／s系统的偏振模色散补偿中，偏振度监测法的灵敏度和跟踪范围受多种因素(如脉冲啁啾、占空比、消光比、放大自发辐射噪声、自相位调制等)的影响程度进行了数值模拟分析。发现利用偏振度监测法反馈控制偏振模色散补偿时，监测灵敏度和跟踪范围是折中的，较小的占空比有利于提高偏振度监测法的灵敏度，而且总可以对高达1．5个位周期(75ps)的差分群延时进行跟踪，但当占空比低于0．5时，跟踪范围迅速缩小，消光比和放大自发辐射噪声不会明显改变偏振度监测法的跟踪范围，自相位调制效应显著地影响偏振度监测法的性能。

Analysis on Degree-or-Polarization Detection Used to Control Polarization-Mode-Dispersion Compensation for 20 Gb/s System

Based on the theory of the principal polarization state and first-order assumption, a compact analytical expression of the degree of polarization (DOP) of the optical signal is derived. Using this analytical expression and fast Fourier transform, the sensitivity and trackable differential group delay range of degree-of-polarization detection technique are investigated by numerical simulation in 20 Gb/s optical transmission system. The effects of various factors on signal DOP degradation are considered, such as the signal chirp, duty ratio, extinction ratio, amplified spontaneous emission (ASE), self-phase modulation (SPM), and so on. It is found that there exists a tradeoff between sensitivity and trackable differential group delay range for degree-of-polarization detection used as feedback control technique in polarization mode dispersion compensation. With smaller duty ratio, the DOP technique is more sensitive to the differential group delay (DGD) and able to detect DGD range from 0 to 1.5 bit period (75 ps). However, the trackable DGD will reduce sharply when the duty ratio is smaller than 0.5. Extinction ratio and ASE noise do not change greatly the trackable DGD range. The performance of DOP technique is affected remarkably by SPM.