Probabilistic shaping PAM8 based on Huffman coding distribution matching in optical interconnection

We propose and experimentally verify a Huffman coding distribution matching (HCDM) scheme in intensity modulation and direct-detection (IM/DD) optical interconnection applying low-density parity-check-coded (LDPC) probabilistic shaping 8-level pulse amplitude modulation (PS-PAM8). Not only superior to that of conventional PS methods in view of arithmetic distribution matching (ADM) as well as constant composition distribution matching (CCDM) with much lower computational complexity, the HCDM can also enable arbitrary symbol probability distribution (SPD) by utilizing an optimal Huffman binary tree. The binomial coefficients required for SPD can be precomputed and stored in a lookup table. The experimental results show that the HCMD PS-PAM8 shows remarkably promoted receiver power sensitivity and improved system tolerance to optical fibre nonlinear effects compared to the uniformly distributed signal with the same effective net rate.