Properties of wavelength converters based on semiconductor optical amplifiers in the arms of a Mach-Zehnder interferometer

The results of a detailed experimental characterization of a three-port, all-active SOA-MZI wavelength converter are presented. It is shown that for counter-propagating input signals, the ASE noise is intensity modulated due to gain saturation in the output SOA. Consequently, the waveform for the wavelength-converted signal is determined by both cross-phase modulation and self-gain modulation. Time- and frequency-domain measurements are used to characterize the properties of the modulated ASE noise, wavelength-converted signal and total signal. For both co- and counter-propagating signals, the small-signal chirp properties of the wavelength converter along the conversion curve are considered. The measured results for the small-signal chirp and optical conversion are incorporated into a device model that can be used to obtain the large-signal pulse response. Based on this model, good agreement is demonstrated between calculated and measured results for the time dependence of the intensity and chirp of the wavelength-converted signal.