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.