Abstract

The impact of interchannel stimulated Raman scattering (SRS) on optimization of channel powers to maximize the minimum channel margin is examined using a discrete Gaussian noise model for the Kerr nonlinearity. The simultaneous consideration of these two nonlinear effects is found to be incompatible with the goal of a convex SNR expression that can be optimized globally. A sequence of convex optimizations is employed to obtain a locally optimal solution, along with a bound on the degree of suboptimality. Optimization results obtained are most accurate for Gaussian-distributed signals, such as probabilistically shaped high-order-modulated signals. In a dispersion-uncompensated 4000-km fiber system utilizing the full C-band with perfect per-span SRS gain compensation, power optimization yields benefits of 0.25 to 2 dB over optimal spectrally flat power allocations. In systems including both C- and L-band, an optimization method that accounts for both SRS and Kerr nonlinearity effects provides a 0.23 to 0.60 dB margin benefit over a method compensating for SRS gain alone. In a system spanning only the C-band, per-span SRS gain compensation is not critical, as the maximum benefit is a 0.14 dB gain in minimum margin for optimized power allocations. By contrast, in a system spanning both C- and L-band, per-span SRS gain compensation provides a gain of up to 1.23 dB with optimized power allocations and larger gains with suboptimal power allocations.