Performance of multilevel modulation formats in 92 Gb/s systems in the presence of PMD and nonlinear effects

We simulated two multilevel modulation formats in optical fiber systems in the presence of varying polarization mode dispersion (PMD) and fiber nonlinearities. Carrier suppressed return-to-zero differential quadrature phase shift keying (CSRZ-DQPSK) and polarization shift keying (PolSK) formats are simulated. The maximum data rate used in the system is 92 Gb/s and the length of the fiber is kept fixed at 100 km. Dispersion compensated standard communication fiber models are used in the simulations. Monte Carlo method is used for the simulation where the PMD coefficients are varied from 0 to 2 ps/sqrt(km). For simulating nonlinear coefficients, 0.1 and 1.0 1/W/km are used for the low and high nonlinearities respectively. The performances of the modulating formats are compared in terms of bit error rate (BER). The results show that the PolSK system possesses better PMD tolerance in the presence of nonlinearities.