A Novel Probabilistic Shaping PAM4 Employing Bit Weight Reconstruction for Optical Interconnection

In this letter, a novel probabilistic shaping (PS) scheme based on joint polar-coded modulation is proposed and experimentally demonstrated in an intensity modulation and direct-detection four-level pulse amplitude modulation (PAM4) optical interconnection. Different from the prevailing probability-oriented PS schemes like constant composition distribution matching (CCDM) and the symbol-oriented ones like many-to-one (MTO) mapping, the proposed bit-oriented one realizes PS through simple bit weight reconstruction (BWR) in joint systematic-like polar coded modulation with lower computational complexity. As a key process in BWR, two bit-permutation (BP) operations are employed to reuse the frozen bits for dynamic frozen bits shaping, to obtain the desired PS distribution by enhancing the probability weight of bit '0' with neither additional shaping bits nor extra FEC redundancy. The experimental results show that 1.7-dB receiver power sensitivity enhancement and 2.6-dB systematic tolerance improvement to optical fiber nonlinear effect can be achieved in a 5-km optical PAM4 interconnection system.