Compensation of the frequency fluctuations of light sources in distributed Brillouin sensor

Distributed sensor based on stimulated Brillouin scattering, especially Brillouin optical time-domain analysis (BOTDA) technique, attracts much interest recently due to its good performance of long sensing distance and high precision. In BOTDA system, the frequency fluctuation of the light sources is a serious problem, which will cause severe error of the measured Brillouin frequency shift (BFS), considering the narrow bandwidth of Brillouin spectrum. In this paper, a simple and low-cost method to compensate the error induced by frequency fluctuations of laser sources in a BOTDA system is proposed, by use of a local reference fiber which is loose and temperature monitored. The reference fiber, with several ten-meters long, can be part of the sensing fiber. Referring to the measured BFS of the reference fiber, one can obtain the errors induced by frequency fluctuations of light sources, and thus eliminate those errors. The proposed method is demonstrated by preliminary experiment.