Regeneration of DPSK Signals in a Saturated SOA

We investigate and experimentally demonstrate a simple method for phase-preserving amplitude regeneration of constant envelope phase-coded signals. This scheme exploits nonlinear interaction between noisy data and a continuous wave beam at a different wavelength in a saturated semiconductor optical amplifier (SOA). We show that proper balancing of the input signals' power allows us to exploit the amplitude limiting effect of SOA saturated gain without introducing significant excess phase noise due to suppression of the α-factor in the amplifier. In a 10-Gb/s nonreturn-to-zero differential phase-shift-keying experiment, both four-wave-mixing (FWM) and pass-through signals are remarkably improved with respect to input data in terms of Q-factor and bit error ratio threshold margin, demonstrating wavelength preserving and wavelength converting regeneration. In particular, the FWM signal exhibits better regenerative performance over a broader range of degraded input data and for lower input overall power levels.