Nonlinear distortion equalization for 60-Gb/s 64QAM-Multi-band-SCM Fiber-Millimeter-Wave Integration System in W-band

In fiber-millimeter-wave integration systems, nonlinear distortion and inter-symbol interference (ISI) will degrade system performance, and post-equalization is an efficient method to compensate for them. In this paper, a 60 Gbit/s 64-quadrature amplitude modulation (QAM) fiber-millimeter-wave integration system based on multi-band subcarrier modulation (MSCM) at W-band is demonstrated. We design a comparative experiment to study equalization method for multi-band SCM nonlinear distortion compensation. Volterra-series based equalizer, artificial-neural-network (ANN)-based equalizer and Bi-directional gated recurrent unit (Bi-GRU)-based equalizer are compared for their ability to compensate for nonlinear distortion. Experiment results indicate that it is necessary to compensate nonlinear distortion in waveform level and Bi-GRU equalizer can compensate the nonlinear distortion the best. With post-equalization, a 60 Gbps data rate is achieved at a forward error correction (FEC) bit error rate (BER) threshold of 1×10
^-2
after 20-km fiber and 1-m wireless transmission.