Digital Compensation of Residual Pump Dithering in Optical Phase Conjugation of High-Order QAM

We develop a new two-stage digital scheme to suppress the phase distortion due to residual pump dithering in the dual-pump fibre-based optical phase conjugation of high-order (64/256) QAM signals. We show more than 5-dB SNR improvement relative to conventional phase-noise compensation at high pump-phase mismatch levels.