Impact of fiber birefringence on optical switching with nonlinear optical loop mirrors

We use a vector theory of cross-phase modulation to discuss how residual birefringence of the fiber loop affects the switching performance of a nonlinear optical loop mirror. It is found that the interaction between polarization-mode dispersion (PMD) and cross-phase modulation transfers spatial randomness of residual birefringence to temporal power fluctuations within the switching window. PMD reduces the switching contrast and the reduction depends on wavelength separation between the signal and control pulses as well as on the magnitude of the PMD parameter. Fluctuations in the switched power become worse for a wavelength separation for which the PMD diffusion length associated with birefringence fluctuations becomes comparable to the nonlinear length associated with cross-phase modulation.