在光四相相移键控系统中,相位噪声主要源于激光器的线宽、激光器的相位偏移、同相支路(I路)和正交支路(Q路)相位不匹配、90°混频器的相位不平衡以及光纤和器件等引起的相位变化。这些相位噪声对相干光通信系统性能影响很大。提出一种改进的相位估计算法,采用前向反馈方法对信号取n次方后再取对数。仿真结果显示该方案可以消除7.5 MHz的激光器线宽、30°激光器相位偏移、20°调制器I路/Q路的相位偏移或90°混频器的相位不平衡对系统误码率的影响,并能提高1 dB的光信噪比,显著改善了系统性能。

Phase noise mainly comes from laser linewidth,laser phase offset,in/quadrature (I/Q) phase mismatch,90° hybrid phase imbalance,fiber channel and component in optical quadrature phase shift keyed (QPSK) transmission system. Those phase noise can affect system performance of coherent optical communication system seriously. To compensate the impairments introduced by these phase noise,a novel feed forward phase estimation techniques with n-th power operation and logarithm operation are proposed. The simulation results shown the new solution can eliminate bit error rate (BER) deteriorating due to 7.5 MHz laser linewidth,30° laser phase offset,20° I/Q phase mismatch of transmitter,or 20° of 90° hybrid phase imbalance,and can improve the optical signal to noise ratio requirements 1 dB,significantly improve system performance.