OBSERVATION OF COHERENT RAYLEIGH NOISE IN SINGLE-SOURCE BIDIRECTIONAL OPTICAL FIBER SYSTEMS

The authors report noise in a bidirectional optical fiber system that they believe arises from the interference of the signal light with the Rayleigh backscattered light. This noise, called coherent Rayleight noise (CRN), is the dominant noise source in this system. The interference provides a mechanism for translation of laser phase fluctuations into receiver photocurrent fluctuations. A number of noise reduction schemes are proposed. The authors demonstrate that CRN can be reduced, but not eliminated, by providing a small drive current modulation signal to the source laser to broaden its linewidth. Systems using this single-source-bidirectional architecture must take this noise source into account.