Abstract: The invention relates to a wavelength conversion apparatus for transmitting data carried by an incident pump wave beam of wavelength .lambda. to a probe wave of wavelength .lambda..sub.s. The apparatus has two semiconductor optical amplifiers and means for splitting the incident pump wave beam so as to inject a respective secondary pump wave beam into each of said optical amplifiers, said optical amplifiers are connected in series on the path of the probe wave so that each of them modulates said wave in intensity with the corresponding secondary pump wave beam by means of a crossover gain-saturation phenomenon.