Distributed Acoustic Sensing Using an Ultra-stable Laser

Abstract

Distributed Acoustic Sensing (DAS) technology, which utilizes optical fibres to monitor vibrations and acoustic signals, has emerged as a powerful tool for applications ranging from structural health monitoring of bridges and pipelines to geophysical exploration and surveillance. This study investigates using an ultra-narrow linewidth ultra-stable continuous-wave (CW) laser operating at a wavelength of 1550 nm to enhance the performance and reliability of fiber-based DAS systems. The proposed system addresses the limitations of phase noise and frequency instability, delivering improved signal-to-noise ratio (SNR) and detection sensitivity. The CW laser, characterized by exceptional coherence properties, continuously interrogates the optical fibre, which serves as both the sensing element and the transmission medium. Environmental perturbations such as acoustic waves or vibrations induce phase changes in the fibre, which are captured through a beat-note signal between the stable laser and the propagated light. These variations are processed to accurately detect and localize disturbances with a spatial resolution of ±5 m. The system can detect frequencies from < 0.01 Hz up to 500 Hz. This system can be used for acceleration sensitivity/mass movement at peak-particle velocities (PPV) of sub-µm/s. By minimizing phase noise, the ultra-stable laser source ensures precise and reliable measurements, demonstrating significant potential for applications such as validating acoustic vibrations in gravitational wave detectors. The findings highlight the transformative impact of integrating ultra-narrow ultra-stable CW lasers into DAS systems, paving the way for advancements in acoustic sensing technologies across various industries with enhanced accuracy, sensitivity, and spatial resolution.