Limitations to first-order PMD compensation in WDM systems due to XPM-induced PSP changes

We show both numerically and experimentally that the nonlinear phase change due to cross-phase modulation (XPM) induces a bit-pattern-dependent change in the state-of-polarization that translates to uncertainty in the principal states of polarization (PSP). This effect severely limits the effectiveness of first-order polarization mode dispersion (PMD) post-compensation and suggests the use of in-line compensation.