Impact of Polarization Mode Dispersion on CPFSK Transmission Systems using MZI Based Direct Detection Receiver

摘要

An analytical approach is presented to determine the impact of signal phase distortion due to polarization mode dispersion (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 for different values of the mean differential group delay (DGD) and also by considering Maxwellian distribution of it at a bit rate of 10 Gbit/s. The computed results show that the direct detection CPFSK system suffers a significant amount of power penalty and occurrence of BER floor due the effect of PMD. At a modulation index of 0.5, the amount of power penalty at a BER of 10~(-9) is found to be 0.5 dB, 1.10 dB, 2.10 dB and 3.50 dB when the mean DGD is 20 ps, 30 ps, 40 ps and 50 ps respectively for a fiber length of 100 km. At modulation index of 1.0, the penalty is approximately 4.10 dB for a mean DGD of 40 ps. Furthermore, while considering Maxwellian distribution for mean DGD, there occur BER floors above 10~(-9), which cannot be lowered by further increasing the signal power. It is noticed that BER floors occur at about 10~(-4) and 10~(-8) for modulation index of 0.50 and 1.0 respectively to a corresponding mean DGD of 90 ps. The effect of PMD is found to be more detrimental at higher modulation index and bit rate.