Robustness to laser frequency offset in direct-detection dpsk and dqpsk systems

Abstract

We assess, both by measurement and simulation, the receiver performance degradation caused by frequency offsets between the optical source and the delay interferometer for nonreturn-to-zero (NRZ) and return-to-zero (RZ) differential-phase-shift-keying (DPSK) and differential-quadrature-phase-shift-keying (DQPSK) systems. We find that NRZ- and RZ-DQPSK systems are about six times more sensitive to frequency offsets than NRZ- and RZ-DPSK systems operating at the same bit rate. We explain the reason for this behavior by means of eye aperture considerations.