We propose a simple and cost-effective technique that can reduce the electrical bandwidth for Brillouin frequency-shift sensors with heterodyne detection without the need for expensive instruments or a complicated system. With this technique we use only a reference fiber. The reference Brillouin scattering light in the reference fiber is used as a local light for heterodyne detection. We confirm that this method can be used for measuring the Brillouin scattering spectrum distribution with a much lower frequency bandwidth (0.2 GHz) than that employed for conventional heterodyne detection (11 GHz). The method operates in a way similar to conventional Brillouin optical time domain reflectometry with comparable accuracy. Moreover, we successfully demonstrate temperature distribution sensing and show that we can compensate for temperature variation in the reference fiber.
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