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Combining Stokes and anti-Stokes interactions to achieve ultra-low noise dynamic Brillouin strain sensing

Brillouin based fiber sensors are susceptible to a range of technical and environmental noise sources that can degrade the sensor performance or introduce unacceptable levels of crosstalk. Here, we introduce a new measurand that combines information from the complex Stokes and anti-Stokes interactions to extract the Brillouin frequency shift while suppressing noise and crosstalk originating from fluctuations in the power, frequency, or polarization state of the pump and probe beams. We then present a modified slope-assisted Brillouin optical time domain analysis (BOTDA) architecture capable of simultaneously recording the gain, loss, and phase associated with both the Stokes and anti-Stokes interactions. We experimentally confirm that the sensor is able to reject noise due to laser frequency jitter, intensity noise, or polarization fading and is immune to crosstalk due to effects such as pump depletion. By suppressing these noise sources, the sensor is able to achieve a minimum detectable strain of only 15.6 ne/Hz1/2 in ∼1 km of fiber with 4 m spatial resolution and a sensor bandwidth of 25 kHz, representing a significant noise improvement compared to state-of-the-art BOTDA systems.