BER Calculation of the optical coherent DPOLSK based on Gaussion approximation of the pdf's

In the DPOLSK transmission system the state of polarisation (SOP) of the lightwave is the information carrying parameter. The receiver calculates the Stokes parameters of the incomming lightwave, which completely characterize the SOP. Exact expressions for the pdfs of the relevant parameters are derived implicitely. Explicit evaluation of those expressions is quite cumbersome and gives little insight in the analysis process. It is shown that for SNR's which are not too small, all relevant variables may well be approximated by gaussian distributions. It is shown how the non-linear operations in the receiver change the signal and noise spectra, in this way enabling to study the influence of phase noise on the performance of the receiver as well. The results of the analysis show that describing the pdfs by gaussian distributions approximates the BER's within tens of a dB compared with the exact analysis. Our method is much less involved and gains more insight in the signal and noise processing.