Differential quadrature phase shift keying with close to homodyne performance based on multi-symbol phase estimation

We discuss an improved detection scheme for differential phase shift keying (DPSK) and differential quadrature phase shift keying (DQPSK), based on multi-symbol phase estimation (MSPE) through electrical signal processing. Using a recursive electrical signal processing algorithm, close to homodyne performance is obtained without a local oscillator at the receiver. In the presence of only Gaussian noise the proposed scheme yields a 0.5 dB and 1.8 dB sensitivity improvement over self-homodyne detection, for DPSK and DQPSK respectively. It furthermore improves robustness against impairments due to the influence of a finite laser linewidth and nonlinear phase noise. (7 pages)