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.
© 2003 IEEE
Hoon Kim and Peter J. Winzer, "Robustness to Laser Frequency Offset in Direct-Detection DPSK and DQPSK Systems," J. Lightwave Technol. 21, 1887- (2003)