Optimal Constellation Shaping in Optical Communication Systems

In optical communications systems, Shannon limit can be closely approached by properly chosen constellation shaping schemes. Both probabilistic shaping (PS) and geometric shaping(GS) can be applied to M-ary quadrature amplitude modulation (QAM) to obtain the shaping gain. In this invited paper, mutual information (MI) is used as a metric to analyze the performances of regular/GS/PS-8/16QAM formats. In a linear amplified spontaneous emission (ASE) noise dominated system, our numerical results show that the MI performances of the GS-8/16QAM are better than that of regular 8/16QAM and PS-8/16QAM. Then we experimentally compare the performances of regular/GS/PS-16QAM formats over a 100km fiber transmission link. Our numerical and experimental results are very useful in selection of the optimal constellation shaping for a given optical communication system.