Performance of line codes in optical direct detection continuous phase frequency shift keying transmission system impaired by polarization mode dispersion

Small deviations from perfect circular symmetry in the core region of single mode fiber (SMF) cause optical pulses to become broadened as they propagate. This phenomenon is referred to as polarization node dispersion (PMD), which leads to intersymbol interference and becomes a major impediment for the high speed long-haul fiber-optic links. We present here the theoretical complement for evaluating the performance of lincoded continuous phase frequency shift keying (CPFSK) optical transmission system with direct detection receiver. The analysis is carried out for two different line coding schemes, i.e., alternate mark inversion (AMI) and order-1 coding, to investigate the effectiveness of the line coding in counteracting the effect of PMD in CPFSK direct detection transmission system in presence of group velocity dispersion (GVD) and receiver noise in SMF. The average bit error rate (BER) performance are evaluated without and compared to that of line codes at a bit rate of 10 Gb/s considering Maxwellian distribution for the mean differential group delay (DGD). We found that the sensitivities of line coded systems are within 0.65 dB and 2.25 dB at a BER of 10^-9.