64-Gb/s SSB-PAM4 Transmission Over 120-km Dispersion-Uncompensated SSMF With Blind Nonlinear Equalization, Adaptive Noise-Whitening Postfilter and MLSD

Abstract

A novel low-complexity digital signal processing solution is presented to compensate the impairments of limited bandwidth and nonlinearity. It is based on the equalizer, adaptive noise-whitening postfilter, and maximum likelihood sequence detection (MLSD). The system performance loss is induced by higher noise power at the signal band edges after the equalizer can be mitigated by the postfilter and MLSD. Given the above structure, it is possible to enrich the equalizer by providing nonlinear compensation capability. A memory polynomial equalizer (MPE), instead of Volterra equalizer (VE), is applied as the equalizer to compensate the nonlinearity impairments in order to make a tradeoff between complexity and performance. For the adaption of MPE, the blindly adaptive multistep-size decision-directed least-mean-square algorithm is selected. By using a dual-drive Mach–Zehnder and direct detection, 64-Gb/s single-sideband 4-ary pulse amplitude modulation (SSB-PAM4) transmission over 120-km dispersion-uncompensated standard single-mode fiber (SSMF) with 10-dB bandwidth roughly 13.5 GHz is experimentally demonstrated. Given a 20% overhead soft-decision forward-error correction with bit error rate threshold of $2\times 10^{{-2}}$ , the dispersion-uncompensated SSMF transmission distance can be significantly increased from 40 to 120 km with the proposed receiver side solution. The optical signal noise ratio performances for different fiber reach and receiver structure are investigated. Furthermore, we compare the computational complexity of MPE with VE and conclude that MPE can substantially reduce computation complexity with negligible performance loss.