BER Performance Evaluation for CPFSK Phase and Polarization Diversity Coherent Optical Receivers

The following methods of CPFSK signals demodulation are compared for phase and polarization diversity receivers: single filter, dual filter, delay and multiply. BER values are obtained in each case showing that for negligible laser linewidths the delay demodulation method outperforms the dual-filter method by approximately 3 dB, and the single-filter method by 6 dB. Since the noise bandwidth for MSK and delay demodulation is approximately twice as small as for the other methods, one should add another 3 dB to get the gain for that modulation/demodulation method. The influences of nonzero laser linewidth, noise correlation, and non-Gaussian character of the probability density functions of the noise at the sampler have been taken into account.