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 (21) interferometric acoustic sensor array, constructed using 21 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 lambda 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 dBrad/root Hzat at 1 kHz and a cross talk level lower than -70 dB at 1 kHz are achieved. (C) 2021 Optical Society of America