Fiber Nonlinearity Mitigation in 32-Gbaud 16QAM Nyquist-WDM Systems

Fiber nonlinearity distortion limits the achievable transmission distance and channel capacity of optical transmission systems. In this paper, we demonstrate an experiment of 1400-km standard single mode fiber transmission of 11 × 32 Gbaud 16-ary quadrature amplitude modulation signals with an emphasis on nonlinearity mitigation. Based on the first-order perturbation theory, we present the nonlinearity mitigation principle of the conjugate data repetition (CDR) scheme in a polarization division multiplexed wavelength division multiplexed scenario. Then, we apply several nonlinearity mitigation methods such as CDR, phase-conjugated twin waves (PCTW), digital back propagation (DBP), and the recursive least-squares (RLS) algorithm based filtering to the experiment, respectively. Optical Kerr effects of self-phase modulation, intra- and interchannel cross-phase modulation are considered. The experimental results show that CDR demonstrates similar performance to PCTW. By introducing the CDR scheme, the average bit error rate is reduced from 1.92 × 10
^-2
to 1.76 × 10
^-3
at the cost of halving the data rate. This corresponds to 3.2-dB Q
²
factor promotion, including 1.5 dB improvement in nonlinearity mitigation. In contrast, 1.0-dB Q
²
factor promotion is achieved by employing RLS-based filtering and DBP together without sacrificing the data rate.