Multiplication-free error corrector for partial response equalization in 256-Gb/s PAM4 IM/DD systems

Partial response equalization (PRE) is a spectral shaping technique that enhances robustness to the inter-symbol interference (ISI) due to bandwidth limitation in the high-speed intensity modulation and direct detection (IM/DD) systems. The simple 1/(1 + D) decoder can be used to decode the PR-equalized signal. However, it suffers from error propagation, leading to performance degradation. In this Letter, we propose a multiplication-free error corrector (MF-EC) to suppress the error propagation resulting from the 1/(1 + D) decoder of second-order PRE. The proposed method can effectively locate the beginning and end of burst errors with only additive operations. We experimentally demonstrate the performance of the proposed method in 256-Gb/s 4-ary pulse amplitude modulation (PAM-4) IM/DD systems. The results show that the PRE with MF-EC can effectively eliminate the error propagation of the 1/(1 + D) decoder, reducing the maximum length of burst errors from 15 to seven. Moreover, the proposed method outperforms the PRE with precoding and error-correlation based DFE (EC-DEF). As for the 500-m transmission scenario, the PRE with MF-EC exhibits similar performance to the PRE-MLSE decoder at the KP4-FEC threshold but can reduce the complexity.