Enlargement of measurement range in a Brillouin optical correlation domain analysis system using double lock-in amplifiers and a single-sideband modulator

We demonstrate a novel technique to enlarge the measurement range of a correlation-based fiber Brillouin distributed sensing system using double lock-in amplifiers and a single-sideband (SSB) modulator. In our work, the lock-in detection is applied to both a probe and a pump waves at different frequencies to effectively remove the noise induced by the backward reflection of the pump waves, and the SSB modulator is used to purify the probe wave by suppressing the other first-order sideband component. A 300-m measurement range with a 20-cm spatial resolution is achieved successfully without any optical filter.