Abstract-We discuss an all-optical wavelength converter based on nonlinear polarization rotation in a single semiconductor optical amplifier. We show that inverted and noninverted wavelength conversion can be realized. We also demonstrate this wavelengthconversion concept can operate over a large wavelength range. Experiments show that error-free wavelength conversion can be obtained at a bit rate of 10 Gb/s.Index Terms-All-optical wavelength converter, birefringence, nonlinear polarization rotation, semiconductor optical amplifier (SOA).