Analysis of impact of receiver imperfections on performance of optical DQPSK systems

The effects of key receiver impairments on the performance of differential quadrature-phase shift keying (DQPSK) are analysed. While the sensitivity to photodetector responsivity imbalance is low and comparable to the case of binary DPSK, the constraints on the maximum tolerable detuning for the interferometers are very tight. In a 40 Gbit/s system, a 1 dB penalty is already incurred with a 0.7 GHz detuning.