Performance of different modulation formats in 40 Gb/s optical systems in the presence of polarization mode dispersion and nonlinear effects

We simulated different modulation formats in optical fiber systems in the presence of polarization mode dispersion (PMD) and fiber nonlinearities. Non-return-to-zero (NRZ), return-to-zero (RZ), chirped RZ (CRZ), carrier suppressed RZ (CSRZ), duobinary, differential phase shift keying (DPSK), differential quadrature phase shift keying (DQPSK) and CSRZ-DQPSK formats are simulated. The maximum data rate used in the system is 40 Gb/s and the length of the fiber is kept fixed at 100 km. Standard communication fiber models are used. Monte Carlo simulation method is used for high and low PMD coefficients and for varied nonlinear coefficients. The performance of different formats is compared in terms of differential group delay (DGD). The results show that RZ-DQPSK is better PMD tolerant in the presence of nonlinearities.