Improved Weighted Volterra DFE for C-Band 100-Gbit/s PAM-4 Transmission Over 60-km SSMF

To cope with the nonlinear distortions and the chromatic dispersion (CD) induced power fading in double-side band (DSB) intensity modulation and direct detection (IM/DD) transmission systems, high-performance Volterra decision-feedback equalizers (VDFEs) are widely applied. However, similar as linear DFE, the VDFEs suffer from error propagation in the case of wrong decisions. In this letter, to reduce the error propagation probability of VDFEs, we propose and experimentally demonstrate a diagonally-pruned improved weighted VDFE (DP-IWVDFE) in a C-band 4-level pulse amplitude modulation (PAM-4) transmission system. By replacing the hard-decision output by the soft-decision feedback symbol based on a compressed sigmoid nonlinear function in DP-IWVDFE, the error propagation probability can be significantly reduced, which lowers the bit error ratio (BER) by a factor of around two as compared to the DP-VDFE. Besides, 100-Gbit/s PAM-4 transmission over 60-km standard single-mode fiber (SSMF) using DP-IWVDFE is realized with the achieved BER below 3.8 $\times 10^{-3}$ , achieving around 3.8-dB, 1.5-dB, and 1-dB improvements of the receiver sensitivity over the polynomial DFE (PDFE), improved weighted PDFE (IWPDFE), and DP-VDFE, respectively.