Performance degradation due to polarisation dependent gain and loss in lightwave systems with optical amplifiers

Analytic expressions for the degradation of the mean system performance due to polarisation dependent loss (PDL) and polarisation dependent gain (PDG) are derived. For PDL values lower than 0.5 dB only a negligible change in the mean system performance is expected. PDG, on the other hand, is shown to cause a significant degradation of the system performance.