Optical spectral inversion without frequency shift by four-wave mixing using two pumps with orthogonal polarization

We propose a method to obtain spectral inversion of a signal without shifting its frequency. We use four-wave mixing (FWM) in a semiconductor optical amplifier (SOA) with two pumps of orthogonal polarization. A conjugate field is generated with a polarization orthogonal to that of the incoming signal and is selected at the amplifier output by a polarizer. Using a commercially available pig-tailed SOA of 1.5-mm length, we obtain after the polarizer 21.5 dB of intensity ratio between conjugate and amplified incoming signal.