  A correlated phase-and-additive-noise (CPAN) mismatched model is developed
for wavelength division multiplexing over optical fiber channels governed by
the nonlinear Schr\"odinger equation. Both the phase and additive noise
processes of the CPAN model are Gauss-Markov whereas previous work uses Wiener
phase noise and white additive noise. Second order statistics are derived and
lower bounds on the capacity are computed by simulations. The CPAN model
characterizes nonlinearities better than existing models in the sense that it
achieves better information rates. For example, the model gains 0.35 dB in
power at the peak data rate when using a single carrier per wavelength. For
multiple carriers per wavelength, the model combined with frequency-dependent
power allocation gains 0.14 bits/s/Hz in rate and 0.8 dB in power at the peak
data rate.
