Perturbation-Aided Fiber Nonlinearity Compensation in Subcarrier-Multiplexing Systems

A perturbation-aided advanced digital backpropagation (P-ADBP) is proposed for subcarrier-multiplexing (SCM) coherent systems. To improve the nonlinearity compensation (NLC) performance, for the first time, the first-order perturbation analysis is introduced into the conventional ADBP. Based on the fact that the perturbation-based self-subcarrier nonlinearity (PSSN) has a similar form as the cross-subcarrier nonlinearity (CSN), we approximate that PSSN and CSN can be calculated in parallel and the compensation of them can be fused together. This compensation fusion scheme saves the computational complexity effectively by sacrificing only a little performance. Furthermore, to realize the best performance, gradient descent is used to jointly optimize the perturbation coefficients and other necessary parameters in P-ADBP. Verified by 9×120-GBaud 1600-km wavelength-division multiplexing SCM systems with dual-polarization 16QAM modulation format, 1-Step P-ADBP provides identical Q $^{2}$ improvement as 5-Step ADBP but saves about 72.3% complexity. 5-Step P-ADBP and 10-Step P-ADBP also leapfrog into the NLC level of 10-Step ADBP and 20-Step ADBP, but save about 44.4% and 46.0% complexity, respectively. The proposed algorithm helps achieve an improved performance-complexity trade-off compared to the conventional ADBP and its state-of-the-art modifications.