Compensation of Phase Noise Induced by Higher–Order Codirectional Raman Amplifiers

Codirectional Raman amplification with higher–order pumping is a promising solution for improving performance of commercial unrepeatered submarine links and thus to allow for an upgrade to advanced modulation formats offering larger capacity. However, power fluctuations of the involved high–power pump induce phase shifts in phase modulated signals via the nonlinear Kerr effect that destroy the theoretically possible performance improvement. A technique for reducing the impact of this effect on system performance by jointly processing signals of neighboring channels and evaluating the phase of both channels at a time for symbol detection is presented and evaluated.