Analysis of Nonlinear Phase Noise in Dispersion Unmanaged Fiber-Optic Systems

An analytical expression for the linear and nonlinear phase noise variance in dispersion unmanaged fiber optic systems has been derived using a first-order perturbation theory. Some numerical examples have been provided to illustrate the behavior of the developed phase noise variance in terms of dispersion and distance. The results show that in dispersion unmanaged systems, nonlinear interaction between the amplified spontaneous emission and the signal does not grow as much as in dispersion managed systems, because this interaction is different in each fiber-amplifier span and the noise contributions from various fiber spans do not add up coherently. Therefore, the nonlinear phase variance in a dispersion unmanaged system is much lower than the corresponding noise variance in a dispersion managed system.