研究一阶、二阶偏振模色散（PMD）对10 Gb/s和40 Gb/s的光传输系统性能的影响，考虑PMD的统计特性，基于基本偏振态（PSP）理论数值模拟了非归零码（NRZ）和归零码（RZ）在传输过程中产生的脉冲畸变以及系统Q值的变化。结果表明，传输速率越高PMD对系统性能的影响越显著，二阶PMD也将不可忽略。另外，RZ码传输性能明显优于NRZ码并且可通过预啁啾进行改善。

The first and second-order polarization mode dispersion (PMD) effect on the performance of 10 Gbit/s and 40 Gbit/s systems is studied. The statistical behavior of PMD is considered by simulating the nonreturn-to-zero (NRZ) and return-to-zero (RZ) pulses distortion and the system's Q-factor based on principal states of polarization (PSP) theory. It is found that the effect of PMD is significant in higher bit rate systems and the second-order PMD cannot be neglected. Furthermore, the RZ format is more tolerant to PMD than is the NRZ format, and the system performance is improved if the input pulses are appropriately chirped.