Performance improvement of DPSK signal transmission by a phase-preserving amplitude limiter

It is theoretically and experimentally shown that phase-preserving amplitude regeneration by an all-optical amplitude limiter using saturation of four-wave mixing in a nonlinear fiber can enhance DPSK transmission performance. The limiter suppresses amplitude fluctuations of the signal, by which the nonlinear phase noise caused by self-phase modulation of the transmission fiber is reduced. A 10-Gbit/s short-pulse DPSK transmission experiment shows that the limiter inserted either after a transmitter or inside a recirculating transmission loop can enhance the performance. Theoretical expressions for the linear and nonlinear phase noise are derived, with which the influence of imperfections of the limiter is examined.