偏振模色散动态补偿中色度色散影响的研究

Effect of Chromatic Dispersion on the Feedback Signal in Polarization Mode Dispersion Compensation

分析了色度色散(CD)对偏振模色散(PMD)动态补偿中偏振度(DOP)反馈的影响,模拟和实验验证了2.5Gb/s和10Gb/s非归零调制系统中光信号偏振度特性和系统误码率特性。表明有色度色散作用时信号偏振度值比仅受偏振模色散作用时要大,但误码率随色度色散量增加先轻度好转后就逐渐变差,偏振度值将不能如实反映偏振模色散对系统性能的影响。且信号两正交偏振分量间能量差别越小或差分群延迟越大,上述两种情况下信号偏振度值偏离就越远。这种偏离还随系统速率和色度色散量的增加而加剧。进一步探讨了实际偏振模色散补偿中减轻色度色散影响的措施,表明当系统中同时存在偏振模色散和色度色散影响时,必须在基于偏振度反馈的偏振模色散补偿前完成色度色散补偿。

The effect of chromatic dispersion (CD) on the degree of polarization (DOP) feedback signal in polarization mode dispersion (PMD) compensation is analyzed. Signal suffering from PMD and CD shows a larger DOP than that in the only PMD case, and their DOP deviations relate not only to the polarization splitting ratio or relative delay between the signal's two polarization components, but to the bit error rate and the CD values; But the system performance collapses after a firstly slight improvement with the increasing of CD, as the experiments in 2.5 Gb/s NRZ modulated system and the simulations in 10 Gb/s system show. Therefore DOP can no longer reflect the effect of PMD on system performance in presence of CD. The less the energy difference between two cross-polarization components, or the larger the differential group delay, the greater the signal DOP deviates, and the deviations increase rapidly with the system ratio and CD increase. Modifications to the DOP distortion in PMD compensation are proposed finally, which indicate that CD must be compensated before PMD in actual systems when the effects of PMD and CD simultaneously exist.