Nonlinearity tolerance of optical modulation formats in nonzero dispersion fibers

This letter addresses the issue of the choice of optical modulation format in a multipan wavelength-division-multiplexing system using G.655 fiber. Various modulation formats are assessed by numerical simulation in the presence of fiber nonlinearities with four-wave mixing being the dominant effect. It is shown that the various amplitude modulation alternatives result in more or less the same performance. Phase modulation schemes such as differential phase-shift keying drastically increase the system performance leading to an increase of the Q-factor by almost 3 dB.