Single-carrier 400G unrepeatered WDM transmission using nonlinear compensation and DD-LMS with FEC feedback

In this paper, we investigate the performance of unrepeatered optical transmission using nonlinear compensation, and dynamic equalization enhanced by forward error correction (FEC) feedback. The digital back-propagation (DBP) algorithm is used for nonlinear compensation, while error correction is provided by spatially-coupled low-density parity-check (SC-LDPC) codes. The technique is experimentally evaluated by the unrepeatered WDM transmission of 16×400 Gb/s single-carrier channels (66 GBd DP-16QAM) within a 75 GHz grid over 403 km (64.7 dB span loss), achieving 2.58 Pb/s km. The results indicated Q ² margins to the FEC limit of up to 0.4 and 0.5 dB for 3 and 6-dBm average launch powers, respectively, exhibiting a tangible improvement compared with previous works.