LDPC-Coded Probabilistic Shaping PAM8 Employing a Novel Bit-Weighted Distribution Matching in WDM-PON

We propose and experimentally demonstrate a wavelength-division-multiplexing passive optical network (WDM-PON) employing low-density parity-check (LDPC) coded probabilistic shaping 8-level pulse amplitude modulation (PS-PAM8). In such a splitter-based WDM-PON system with direct detection, a novel probabilistic shaping (PS) method based on a bit-weighted distribution matching (BWDM) for near-Gaussian distribution (NGD) is proposed for the first time. For typical PS schemes based on typical arithmetic distribution matching (ADM) and constant composition distribution matching (CCDM), refining intervals continuously is needed to find the target symbol probability, which will necessarily introduce a plenty of additional redundant bits in the process of the target symbol probability distribution (SPD) emulation from data source. Different from ADM and CCDM, the PS scheme based on BWDM is realized by a simple bit-weight intervention algorithm with low hardware and calculation complexity, which only includes weight-marking bit insertion and bit inversion processes for adjustable SPD kurtosis. The experimental results show that by employing the proposed PS-PAM8, the receiver power sensitivity and system fiber nonlinear effect tolerance can be dramatically improved compared with the unshaped signal. Thus, the WDM-PON employing PS-PAM8 is of cost-effective advantage, which can serve more available optical network units due to the enlarged system loss budget for the optical distribution network.