Spectral-Shaping Technique Based on Nonlinear-Coded-Modulation for Short-Reach Optical Transmission

The amount of data center traffic is rapidly increasing, and it is necessary for short-reach optical transmission such as Ethernet to realize a higher capacity data link. Therefore, the next-generation Ethernet links will require the higher data rate. In such a situation, transmission distance is limited by the bandwidth limitation due to optical and electrical devices in the Ethernet transceiver. In this article, we propose a nonlinear-coded-modulation which shapes the signal spectrum in order to realize the higher tolerance to bandwidth limitation. We apply this technique to a 92-Gbaud PAM4 signal and confirm that the proposed technique achieves the 7% HD-FEC threshold in 184-Gb/s transmission with the bandwidth limitation of 20 GHz through an O-band 10-km transmission experiment. We also investigate the applicability of MLSE to the proposed technique and show that the KP4-FEC threshold can be achievable with 2-memory MLSE and 5-tap channel-shortening filter. In addition, we study the applicability of the proposed technique to a QAM signal which is conventionally utilized in coherent systems. We compare the proposed nonlinear-coded QAM to the conventional duobinary QAM and show that the performance of the proposed QAM signal is greater than that of the duobinary QAM signal with MLSE where the signal degradation is induced by additive white Gaussian noise.