Simultaneous distributed acoustic and temperature sensing system based on ultra-weak chirped fiber Bragg grating array

The quasi-static temperature and dynamic acoustic signals based on ultra-weak chirped fiber Bragg grating (CFBG) array is proposed and experimentally demonstrated, which can be employed to detect distributed acoustic and temperature signals simultaneously. Distributed temperature sensing (DTS) was realized by cross-correlation operation to measure the spectral drift of each CFBG, and distributed acoustic sensing (DAS) was achieved by gauging the phase difference between adjacent CFBG. Using CFBG as the sensor unit can protect acoustic signals from the fluctuations and drifts induced by temperature change without deterioration of signal-to-noise ratio (SNR). Applying least square mean adaptive filter (AF) can enhance harmonic frequency suppression ratio and increase the SNR of system. In the proof-of-concept experiment the SNR of acoustic signal is higher than 100 dB after the digital filter and frequency response is from 2 Hz to 1.25 kHz with repetition frequency of laser pulses of 10 kHz. Temperature measurement from 30°C to 100°C is achieved with demodulation accuracy of ±0.8°C. The spatial resolution (SR) of two-parameter sensing is 5 m.