Phase Demodulation for Distributed Acoustic Sensing Based on Improved Phase-Locked Loop

The Distributed Acoustic Sensing (DAS) system based on phase-sensitive optical time-domain reflectometry (Φ-OTDR) uses optical fiber as a medium to detect external vibration information. To improve the noise immunity of phase demodulation in DAS systems, this paper introduces an enhanced phase-locked loop demodulation method. The approach incorporates a Kalman filter (KF) to optimize the Costas loop (CL) and employs a moving average filter (MAF) to further suppress noise in the phase demodulation process. In addition to significantly improving phase demodulation performance, the method effectively reduces the influence of random noise on the demodulation accuracy. Simulation and experimental results show that the proposed KF-CL-MAF algorithm reduces both phase demodulation distortion and mean square error by an order of magnitude, while increasing the output signal-to-noise ratio (SNR) by approximately 11 dB compared to existing demodulation methods. This improvement provides a more reliable technical solution for high-precision vibration monitoring with DAS systems in complex environments.