Performance Evaluation of an Optical Direct Detection CPFSK Transmission System Affected by Polarization Mode Dispersion

The effect of polarization mode dispersion (PMD) imposes serious restriction on the allowable distance and ultimate hurdle for the massive deployment of multi-gigabit transmission rate in an optical communication system. An analytical approach is presented to determine the impact of signal phase distortion due to PMD in a single mode fiber (SMF) on the bit error rate (BER) performance of an optical continuous phase FSK (CPFSK) transmission system with MZI based direct detection receiver. The probability density function (pdf) of the random phase fluctuation due to PMD and group velocity dispersion (GVD) at the output of the receiver is determined analytically. Based on the pdf of the random phase fluctuation the BER performance results are evaluated at a bit rate of 10 Gb/s fiber with dispersion co-efficient Dc=15 ps/km-nm for different values of the mean differential group delay (DGD). The computed results show that the direct detection CPFSK system suffers a significant amount of power penalty due the effect of PMD at a bit rate of 10 Gb/s. At a modulation index of 0.5, the penalty at a BER of 10^-9 is found to be 0.5 dB, 1.25 dB, 2.35 dB and 4.0 dB when the mean differential group delay (DGD) is 10 ps, 20 ps, 30 ps and 50 ps respectively for a fiber length of 100 km. At modulation index of 1.0, the penalty is approximately 5.25 dB for a mean DGD of 40 ps. The penalty is more significant at higher modulation index and bit rate