Effect of polarization mode dispersion on a coherent optical system with pilot carrier

The effect of fiber polarization mode dispersion (PMD) on a coherent optical system with pilot carrier is twofold. First, the PMD causes state of polarization (SOP) mismatch between the message signal and the pilot carrier. Second, the degrees of polarization (DOPs) of the message signal and pilot carrier are degraded by PMD. Because coherent reception relies both on the SOPs and DOPs of the waves, system performance is degraded by PMD. The effect of SOP mismatch causes intermediate frequency (IF) signal amplitude degradation, whereas DOP variation not only results in IF signal amplitude degradation but further induces IF noises. Analytical expressions are derived to evaluate the performance degradation. It is shown that there is no performance degradation if only one principle state of polarization is excited and maximum degradation occurs when both principle states of polarization are equally excited. It is found that significant degradation may happen when large differential group delay exists