Consideration of the Separated Polarization Optical Frequency Domain Reflectometry using Serrodyne Modulation.

Abstract

A multi-channel system Optical Frequency Domain Reflectometry(OFDR) based on serrodyne modulation has been developed. OFDR that uses a stepped optical-frequency sweep utilizes heterodyne interference, so the developed system uses serrodyne modulation produced by vibration of an optical path with a saw-tooth waveform. The degree of serrodyne phase modulation is expressed in terms of the serrodyne coefficient K(br)-derived from the ratio (br) of the beat frequency to the serrodyne frequency. It is shown that even if the amount of serrodyne phase modulation is not 2π, there is no effect on the spectral distribution (which expresses the optical reflection position), but there is on spectral level. The effect on the spectral level can then be compensated according to the serrodyne coefficient. This paper describes the effect of this frequency ratio on position finding as well as the reflective position measurement (performed by multi-channel digital-signal-processing equipment) corresponding to each polarization direction.