Enhanced DFE-MLSE structure for high-performance optical channel equalization

Combining a channel memory-shortening filter with maximum likelihood sequence estimation (MLSE) effectively reduces MLSE complexity in low-bandwidth optical fiber communication systems. In this paper, we propose an enhanced decision feedback equalizer (DFE)-MLSE for high-speed fiber optic communication systems. This enhanced algorithm builds on our previous work by introducing a dispersion filter that adjusts channel memory length and by directly applying feedback filter coefficients in MLSE branch metric calculations. These advancements improve channel equalization performance, which we experimentally validate in a pulse-amplitude modulation level-4 (PAM-4) system. At a transmission rate of 112 GBd and a distance of 2 km, the enhanced DFE-MLSE achieves an approximate 0.5 dB improvement over the previous DFE-MLSE at a bit error rate of 3.8·10^-3, demonstrating its potential for 200 Gbps transmission in short-reach optical networks.