High dynamic range distributed acoustic sensing based on dual-wavelength fiber Bragg grating pairs

A high dynamic range distributed acoustic sensing (DAS) system is demonstrated based on a dual-wavelength ( 2 λ ) interferometric acoustic sensor array, constructed using 2 λ fiber Bragg grating pairs (FBGPs). Each FBGP is composed of two weak FBGs presenting − 30 -dB reflectivity and center wavelengths of 1535 nm and 1565 nm. With the phase demodulation results from the two wavelengths, 2 λ linear regression phase unwrapping is implemented, which significantly enhances the dynamic range of the DAS system. By examining the four time-division-multiplexed sensors, an average background noise level of − 105.2 d B r a d / H z at 1 kHz and a cross talk level lower than − 70 d B at 1 kHz are achieved.