LETTER TO THE EDITOR Phase detection in optical communication systems through phase conjugation

Abstract. A novel phase-detection scheme based on phase conjugation is proposed. Its use has all the advantages offered by the conventional heterodyne detection technique but simplifies the receiver design considerably since neither a balanced receiver nor a polarization-diversity receiver are required. The use of homodyne or heterodyne detection has not become practical for optical communication systems in spite of the advantages offered by such coherent lightwave systems [1, 2]. The major reason behind it is related to the complexity of coherent optical receivers, resulting from the need to counteract the effects of intensity, phase and polarization fluctuations [1]. In this letter I propose an alternative technique for phase detection that is similar to coherent detection from the standpoint of functionality, but allows us to overcome some of its practical limitations. The basic idea is to use four-wave mixing [3] (FWM) to generate a spectrally inverted, phase-conjugated wave, interfere it with the received signal, and detect the resulting interference pattern. The use of phase conjugation for dispersion compensation through midspan spectral inversion has attracted considerable attention recently [4–6]. The proposed scheme can be implemented in a similar way, wit