The effect of propagation nonlinearities on the information capacity of WDM optical fiber systems: cross-phase modulation and four-wave mixing

The information capacity of a wavelength-division multiplexed optical fiber communication system is estimated in a model incorporating the nonlinear propagation effects of cross-phase modulation (XPM) and four-wave mixing (FWM). Physical models for propagation are used to calculate statistical properties of the conditional probability distribution relating input and output in a single WDM channel. A rigorous lower bound to the information capacity is found for coherent communication, in which both the signal phase and amplitude encode information. An approximate lower bound is computed for incoherent communication, in which only the amplitude is used. The results provide physical insight into the manner in which nonlinearities degrade the information capacity.