Analytical evaluation of the effect of self-phase modulation on coherent optical CPFSK system

An analytical approach is presented to evaluate the effects of self-phase modulation (SPM) on the bit error rate performance of an optical heterodyne CPFSK transmission system. The signal phase distortion induced by SPM at the output of the fiber is determined by using the beam propagation method (BPM). The bit error rate performance is evaluated by using Gauss quadrature rule using the moments of the random phase fluctuations at the receiver output. The results show that the performance of a heterodyne CPFSK system is highly degraded due to the effect of fiber dispersion and self-phase modulation and the power penalty increases with the increase in input power level. Compared to direct detection CPFSK, the effect of SPM is found to be more pronounced in case of heterodyne receiver.