Spectrally efficient pilot tone-based compensation of inter-channel cross-phase modulation noise in a WDM coherent transmission using injection locking

We propose the precise and wideband compensation of the nonlinear phase noise caused by cross-phase modulation (XPM) among WDM channels using a pilot tone (PT) and injection locking for short-reach, higher-order QAM transmission. A high spectral efficiency is maintained by sharing a single PT among multiple channels. We describe a 60 ch, 3 Gbaud PDM−256 QAM transmission over 160 km, where the bit error rate was improved from 6 × 10−3 to 2 × 10−3 by employing the proposed XPM compensation technique, with a spectral efficiency of 10.3 bit/s/Hz. We also analyze the influence of the group delay caused by fiber chromatic dispersion that determines the compensation range achievable with a single PT. We obtained good agreement with the experimental results.