Rayleigh-Brillouin hybrid distributed acoustic sensing for high-sensitivity ultra-low frequency detection

We propose a Rayleigh-Brillouin hybrid distributed acoustic sensing that employs a pre-written Brillouin dynamic grating (BDG) in a polarization-maintaining fiber and a single-shot chirped pulse. Rayleigh backscatter (RBS) and BDG reflection are excited simultaneously, and theoretical analysis shows that both channels can be demodulated via time-to-frequency mapping. The recovered acoustic signals are then combined using an adaptive filtering algorithm that leverages the high sensitivity of the RBS channel and the large measurement range of the BDG channel. This strategy provides high dynamic range and sensitivity across the entire acoustic detection bandwidth, overcoming the low-frequency sensitivity limitations of RBS. Experiments demonstrate a minimum detectable strain of 2.6 nε at 1 mHz with temperature compensation.