理论上分析了相干光正交频分复用(COOFDM)系统中相位噪声(PN)和色度色散(CD)对星座图的影响, 并详细探讨了COOFDM系统中基于导频的直接判决均衡器(DDE)的原理, 还对其性能进行了仿真分析。仿真结果表明：在不同的传输距离下, DDE的误码率都能呈瀑布状下降至10-3这一公认的前向纠错(FEC)门限, 使得后续的FEC模块可以让误码率迅速降低。此外, 在激光器线宽小于100kHz时, DDE的误码性能并没有大幅度的提升。因此, 在选择DDE作为均衡器的COOFDM系统中, 应折中考虑激光器线宽和误码性能的关系, 基于成本考虑建议采用100kHz激光器。

The theory model of phase noise (PN) and Chromatic Dispersion (CD) in Coherent Optical Orthogonal FrequencyDivision Multiplexing (COOFDM) systems is theoretically analyzed and the effect of PN and CD on the constellation is also given. Based on the analysis, the principles and design of pilotbased decisiondirected equalizer of COOFDM systems are probed in detail. Then numerical simulations on the performance of Decisiondirected Equalizer (DDE) were implemented. The simulation results show that the bit error ratio (BER) performance of the DDE can always achieve 10-3 which is the commonlyreported Forward Error Correction (FEC) threshold, and this can make the following FEC module reduce the BER rapidly. Furthermore, the performance of DDE is not improved obviously when the laser linewidth is smaller than 100kHz. Therefore, the laser with 100kHz linewidth is recommended in COOFDM systems with DDE for the consideration on tradeoff between cost and BER performance.