Self-Demodulated Heterodyne Frequency Domain Distributed Brillouin Fiber Sensor

We demonstrate a novel technique for Brillouin scattering-based distributed fiber sensing. The proposed technique is based on the use of two counterpropagating intensity-modulated optical signals, with their modulation frequencies differing by a small, fixed quantity. Stimulated Brillouin scattering leads to an optical demodulation of the probe signal, generating on its intensity spectrum a low-frequency component which is detected by a lock-in amplifier. As a proof of concept, measurement with a spatial resolution of 6 m is reported on a 230-m-long sensing fiber