Long-Range DAS Utilizing Cascaded Acousto-Optic Modulators and Frequency-Shifting Loop

A long-distance, high-spatial-resolution distributed acoustic sensor (DAS) based on cascaded acousto-optic modulators (AOMs) in frequency-shifting loop (FSL) was proposed. The system achieves a vibration frequency response bandwidth of 1 kHz over a detection range of 50 km. Experimental results demonstrate successful recovery of a 600 Hz vibration waveform at a distance of 40 km, with a signal-to-noise ratio (SNR) of 25 dB, a spatial resolution of 3 m, and a strain sensitivity of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$116 p \varepsilon / \sqrt{H z}$</tex>.