Mitigation of MIMO equalizer-enhanced noise in long-haul coupled-core multicore fiber transmissions by an advanced...

Commonly used linear equalizers in optical transmissions may induce in-band noise enhancement in the high-frequency region, degrading signaling performance. In this Letter, we propose for the first, to our knowledge, time, to mitigate the multi-input-multi-output (MIMO) equalizer-enhanced noise (EEN) in coupled-core multicore fiber (CC-MCF) systems by utilizing the spectral shaping (SS) filter and maximum likelihood sequence detection (MLSD), which have shown effective EEN mitigation in SMF systems. However, CC-MCF systems feature multiple spatial channels, each requiring separate coefficient optimization for SS filters corresponding to each output of MIMO. To streamline this process, we introduce a simplified coefficient optimization method using the overall averaged MIMO response, demonstrating no obvious performance degradation. In experiments, a more significant Q-factor improvement was achieved with the proposed technique for higher baud rate signals, which experienced more severe bandwidth limits and thus exhibited higher EEN effects. This result indicates that the proposed DSP technique can effectively suppress MIMO-induced EEN in CC-MCF transmissions. Additionally, we conducted a multi-loop CC-4CF transmission to evaluate the feasibility of the proposed DSP scheme in long-haul transmissions. Q-factor improvements of 0.45 dB were successfully achieved after a 1000-km transmission. Experimental results demonstrated the effectiveness of the proposed technique in mitigating MIMO-induced EEN and show promise for enhancing the signaling performance of long-haul CC-MCF transmissions.