Nonlinear Phase Noise Reduction of DQPSK Signals by a Phase-Preserving Amplitude Limiter Using Four-Wave Mixing in Fiber

It is experimentally shown that phase-preserving amplitude regeneration by an all-optical amplitude limiter using saturation of four-wave mixing in a highly nonlinear fiber can enhance differential quadrature phase-shift keying (DQPSK) transmission performance. The limiter suppresses amplitude fluctuations of the signal, by which the nonlinear phase variance caused by self-phase modulation in the transmission fiber is reduced. The 10-GSymbol/s short-pulse DQPSK transmission experiment over densely dispersion-managed fiber shows that the amplitude limitation after an imperfect transmitter increases maximum transmitted signal power by 5 dB.