A semiconductor optical amplifier (SOA) based double-stage wavelength converter working with an assist light is considered. The principle of operation consists of injecting the pump and the assist light simultaneously in all amplifiers, while the CW probe crosses in series the amplifiers. The effects of probe and pump wavelengths on the achievement of a given extinction ratio on the probe signal are studied. In comparison with a single SOA, this wavelength converter shows a shorter recovery time, a double extinction ratio and low pump powers.