The phase estimation based on M-th power algorithm is employed in a differential quadrature phase-shift keying (DQPSK) coherent optical fiber communication system, and the system performance improvement is investigated through numerical simulations. It is found that the application of phase estimation algorithm can restrain the phase noise induced by laser linewidth and fiber nonlinear effects, and recover the carrier phase, so the transmission distance of a 40 Gb/s DQPSK-RZ system can be extended to more than 1300 km with the BER below 10-12.
