Effect of Polarization Mode Dispersion on Direct Detection CPFSK Optical Transmission System in a Single Mode Fiber

An analytical approach is developed to evaluate the bit error rate (BER) performance degradation of an optical direct detection CPFSK system caused by signal phase distortion due to polarization mode dispersion (PMD) in a single mode fiber. The average BER performance results are evaluated at a bit rate of 10 Gb/s considering Maxwellian distribution for the differential group delay (DGD). The results show that the performance of optical direct detection system suffers power penalty of 0.15 dB, 1.0 dB, 3.40 dB and 6.40 dB corresponding to mean DGD of 20 ps, 40 ps, 60 ps and 80 ps respectively at a BER of 10^-9 operating at 10 Gb/s and modulation index of 0.5. Furthermore, at increased values of the 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