Piecewise Linear and Nonlinearity-aware Complex-valued Decision Feedback Equalization for DML-DD Link at C Band

Directly modulated laser with direct detection (DML-DD) is a low-cost solution for short-reach transmission, but it suffers from severe nonlinear impairment coupled by laser chirp and fiber dispersion. In this work, we propose a piecewise linear (PWL) with nonlinearity-aware complex-valued decision feedback equalizer (CDFE) scheme to compensate for the impairments in dispersion-unmanaged C-band short-reach link. By mapping neighboring symbol pair into 2-dimensional constellation, error propagation is suppressed by K-means and subsequently assist feedback equalization. The proposed PWL-CDFE exhibits 0.5dB receiver sensitivity improvement, compared with the joint PWL, feed forward equalizer (FFE) and decision feedback equalizer (DFE). With the help of proposed PWL-CDFE, 72 Gb/s 4-ary pulse amplitude modulation (PAM-4) signal is experimentally transmitted over 40km standard single-mode fiber (SSMF), with a BER below the 14% hard detection forward error correction (HD-FEC) threshold.