| We evaluate the performance of optical fiber communication systems using binary and quaternary differential phase-shift-keying (DPSK) modulation and interferometric demodulation, focusing on its resilience to transmission impairments, which include chromatic dispersion (CD), first-order polarization-mode dispersion (PMD) and fiber nonlinearity, and to receiver imperfections, which include inteferometer phase error and non-optimum optical and electrical filtering. In order to precisely evaluate the system bit-error-ratio (BER) taking account of CD, PMD, optical noise and receiver imperfections, we propose a novel model for DPSK systems and compute the BER using Karhunen-Loeve series expansion (KLSE) method and eigenfunction expansion (EFE) method, which both were originally proposed for optical systems using on-off keying (OOK) modulation. We show that when properly applied, both methods yield highly accurate results for DPSK systems. Using KLSE method, we evaluate the power penalties caused by CD, PMD and receiver imperfections in DPSK systems and compare them to those in OOK systems. When fiber nonlinearity is taken into account, we model the accumulated optical noise at the receiver as additive non-white Gaussian noise and employ the EFE method to compute the BER. Monte-Carlo simulation verifies that the combination of non-white Gaussian noise model and EFE method yields accurate BER results for nonlinear DPSK and OOK systems using chirped return-to-zero pulses. We also investigate the resilience of offset DPSK, a variant of DPSK, to dispersion effects. |
