Regenerative Wavelength Conversion of DPSK Signals Through FWM in an SOA

We experimentally investigate broadband regenerative capability of four-wave mixing (FWM) in a semiconductor optical amplifier (SOA) for nonreturn-to-zero differential phase-shift keying signals at 10 Gb/s. This scheme exploits the amplitude-limiting properties of the FWM process, when proper SOA gain saturation and α-factor depletion result in almost negligible additional phase noise for the converted signal after delay-interferometer demodulation. We report characterization in both the wavelength down- and up-conversion operations, demonstrating sound Q-factor improvement (through a factor comprised between 1.4 and 2.4) over a conversion range of about 50 nm.