C-band 120-Gb/s PAM-4 transmissions over a 100-km dispersion-uncompensated SSMF using joint combined pulse shaping and low-complexity nonlinear equalization

In C-band intensity modulation and direct detection (IM/DD) systems, the frequency-dependent power fading induced by chromatic dispersion (CD) and square-law detection limits the transmission capacity and distance, espe-cially for beyond 100-Gb/s transmissions over a 100-km dispersion-uncompensated link. To reach this goal, we pro-pose a scheme of nonlinear pre-distortion, novel, to the best of our knowledge, combined pulse shaping, and post nonlin-ear equalization for four-level pulse amplitude modulation (PAM-4)-based IM/DD systems. At the transmitter, the non-linear pre-distortion is used to generate unequally spaced PAM-4 symbols for pre-compensating the nonlinearities. While the novel pulse shaping, simply shaped by the lin-ear combination of two inter-symbol interference (ISI)-free pulses, alters the frequency-domain power distribution of the PAM-4 signal and results in performance improvement. At the receiver, low-complexity post nonlinear equaliza-tion using an absolute-term based nonlinear equalizer with weight sharing (AT-NLE-WS) is performed to eliminate CD -induced power fading and residual nonlinear impairments. With the cooperation of these techniques, record 120-Gb/s PAM-4 signals are successfully transmitted over a 100-km standard single-mode fiber (SSMF) with the measured bit error ratio (BER) below 3.8 x 10-3, achieving >9% improve-ment of system capacity in comparison with the conventional pulse shaping schemes. (c) 2022 Optica Publishing Group