Optical self-homodyne coherent system using elliptically or circularly polarized laser light

Abstract

Coherent detection, as a process for demodulation of an optical signal, is used to a great extent in modern optical communications. In some configurations of this technique, the information which exists in the frequency or the phase of the optical signal can be derived by using the same beam as a carrier and as a local-oscillator signal too. In this communication, we present a theoretical analysis of such a self-homodyne system, which is composed of a laser source, an electrooptic modulator, a photodetector and all the necessary optical components. The whole analysis is accompanied with a PC-supported program, which offers the possibility to study the system for various kinds of optical polarization but with the same incident optical power on the photodetector, independently of the various optical components.Furthermore, this program provides the possibility of changing the respective values at will, after we have introduce direct and alternating voltage as a signal. Finally, the study of the various harmonics of the output signal's spectrum gives the possibility to discover the advantages that the circular polarization offers compared with other kinds of polarization.