Interferometer phase error and chromatic dispersion effects on the performances of 40 Gbit/s optical DPSK transmission systems

The performance limitations due to interferometer phase error (IPE) and Chromatic Dispersion (CD) in a 40 Gbit/s optical Differential Phase-Shift-Keying (DPSK) transmission system are investigated through simulations. Two different optical filters (Fabry-Perot filter (FP) or Fiber Bragg Grating filter (FBG)) and both return-to-zero (RZ) and non-return-to-zero (NRZ) codings were assumed to find out whether these different configurations showed better performances. By means of numerical simulations, we optimize the bandwidths of the optical and electrical receiver´s filters. Then, the impact of the IPE on the Bit Error Rate (BER) performance is analyzed when the received signal is filtered by two types of optical filter. The optical power penalties caused by the IPE impact at BER of 10^-9 in the presence of CD are evaluated. Simulation results show that, without CD the system suffer a significant amount of power penalties due to the IPE, and the optical filter has an influence on the power penalties, i.e. the system with FBG filter has the better performances than the one with FP filter, while NRZ-DPSK modulation format exhibit almost the same power penalty that RZ-DPSK. However, it is found that with CD, the system which uses FP filter performs better than the one which uses FBG filter, i.e. owing to the presence of CD, the better performances switch from FBG filter to FP filter, whereas RZ-DPSK modulation format is more robust to IPE than NRZ-DPSK while FP optical filter is employed. This provides the basis for a tradeoff between FP & FBG Filters and NRZ-DPSK & RZ-DPSK modulations format through a careful selection of a suitable optical filter and an appropriate modulation format.