Non-Linear Phase Noise Mitigation over Systems using Constellation Shaping

This paper presents a modified soft-decoding strategy, which improves performance in the presence of strong phase noise. This can substantially increase the reach of systems that are severely affected by phase noise, generated by fiber non-linear Kerr effect. This strategy is applied to two different experimental scenarios employing constellation shaping, which is known to generate strong non-linear phase noise. In the first experiment, we show that the strategy significantly improves the performance of probabilistically shaped (PS) 64 quadratic-amplitude modulation (QAM) over low-dispersion fibers. In the second experiment, the strategy is used to optimize the position of the points of a 32-QAM constellation (geometrical shaping). This optimized constellation is then compared to standard 32-QAM and PS 64-QAM over standard single-mode fiber. Also in this case, the modified strategy is able to give significant reach gains.