Mitigation of Imperfect Carver-Induced Phase Distortions in a Coherent PM-RZ-QPSK Receiver

The impact of phase distortions caused by imperfect return-to-zero (RZ) pulse carving on 112 Gb/s polarization-multiplexed (PM)-RZ-quadrature-phase-shift-keying (QPSK) is investigated, and mitigation of the phase distortion is demonstrated by using digital signal processing technique. We show that carver-induced phase distortion causes an error in frequency offset estimation as well as sensitivity degradation. Based on the periodicity of distortion pattern, the phase distortion is compensated by estimating mean phase distortions for even and odd symbols after block phase estimation and subtracting these values from original symbols. The optical SNR penalty measured at 112 Gb/s PM-RZ-DQPSK signal is reduced from 3.8 to 1.1 dB with the help of correction algorithm.