Imbalanced Digital Back-Propagation for Nonlinear Optical Fiber Transmissions

In the canonical digital back-propagation (CDBP) of compensating for optical fiber nonlinearity, the aim is to invert the nonlinear Schrödinger equation (NSE). Therefore, the virtual link mirrors the fiber link for all the deterministic parameters. In theory, it can eliminate the deterministic linear and nonlinear impairments. However, the CDBP inherently does not consider the random noise along the fiber link. Meanwhile, the ultimate aim of optical receivers is to lower the BER or increase the SNR. To this aim, the CDBP may become sub-optimum in the presence of random noise. In this paper, we explicitly prove that the performance of CDBP can be improved by simply adjusting the power map in the virtual link. We call it imbalanced DBP (iDBP), since the parameters in the virtual link do not mirror those in the fiber link. Then by tuning the signal power in the virtual link, we derive the closed-form expressions of iDBP for single-span transmissions, and show that the SNR and information capacity can be increased, compared with CDBP. For multi-span transmissions, we demonstrate the improved performance of iDBP by simulation.