Dual-carrier 400G solutions based on 8/16/32-QAM modulation formats

The performance of dual-carrier 400G solutions based on three high-order quadrature amplitude modulation (QAM) formats (8/16/32-QAM) is investigated on the same platform. We first study the benefit and penalty differences of Gray and differential coding, and then experimentally compare OSNR sensitivities and transmission performance using flexible transceiver configuration and the same EDFA-only SSMF link. Experimental results show the implementation penalties are 1.85 dB for 42-GBaud PM-8QAM, which is 1 dB and 1.5 dB better than 32-GBaud PM-16QAM and 25-GBaud PM-32QAM at 5.92-dB Q2-factor (corresponding to a BER of 2.4E-2), respectively. It is also found that maximum reaches of 2460 km for 42.6-GBaud PM-8QAM, 1640 km for 32-GBaud 16QAM, and 820 km for 25-GBaud PM-32QAM are achieved. Furthermore, the performances of cascaded multi-modulus algorithm (CMMA) and decision-directed least mean square (DD-LMS) algorithms are also compared. The improvement by addition of one sample/symbol based DD-LMS digital filter is investigated as well.