Improving the Achievable Rates of Optical Coherent Transmission With Back-Propagation

The power allocation in wavelength-division multiplexed (WDM) fiber-optic links with digital back-propagation (BP) is optimized in order to improve the achievable rates (AR). The power allocation is performed using a convex optimization technique based on a modulation-format-dependent time-domain model capable of including the nonlinear Kerr effects. In a fully loaded WDM link with heterogeneous (uneven) nonlinear interference noise (NLIN) spectrum, the AR gain of nonlinear BP over linear electronic dispersion compensation is 60% larger if per-channel power optimization is allowed than if all transceivers use an equal (flat) optimized power. The heterogeneous NLIN spectrum results from performing BP on a subset of the channels. However, the gain of per-channel power optimization disappears for the homogeneous (nearly flat) NLIN spectrum. Moreover, we show that the improvement obtained by joint channel power allocation is more pronounced for links with a larger number of spans.