Distributed birefringence measurement with beat period detection of homodyne Brillouin optical time-domain reflectometry

We report a distributed optical fiber birefringence measurement method based on homodyne Brillouin optical time-domain reflectometry (BOTDR). Unlike conventional BOTDR, which requires scanning of the local oscillator to get the Brillouin spectrum, instead we propose the beat period measurement of fast and slow components of the backscattered Brillouin signal in single-mode fibers using homodyne detection. The beat period is measured by detecting the envelope of the Brillouin beat signal, which gives the beat length at different fiber locations, so that birefringence can be calculated accordingly. The distributed birefringence of a 1.7 km SMF-28 and a 4.3 km largeeffective- area fiber were measured with 0.6 m spatial resolution without frequency scanning of the Brillouin spectrum.