Performance evaluation of coherent CPFSK lightwave systems

The receiver sensitivity of continuous phase frequency shift keyed lightwave systems with differential detection is determined using a technique which combines computer simulation, to determine a probabilistic characterization of the signal at the receiver output, with a formula-based method for evaluating the bit error ratio, based upon maximum entropy probability density functions. This approach permits consideration of laser phase noise, local oscillator intensity noise, nonlinear signal processing, and nonideal components within a general framework. In particular, the technique captures the asymmetry in the probability density function of the sampled signal at the receiver output. The usefulness of this technique is demonstrated by assessing the performance implications of photodetector responsivity mismatch and time delay mismatch in balanced receivers