An Enhanced Distributed Acoustic Sensor Based on UWFBG and Self-Heterodyne Detection

We demonstrate an enhanced distributed acoustic sensing (DAS) system based on ultra-weak fiber Bragg grating (UWFBG) array and self-heterodyne detection. By using the interaction process between nearby UWFBGs, the distribution of acoustic field along the sensing fiber could be fully captured. Self-heterodyne detection was applied, leading to much lower noise density level for the proposed sensing system. The experimental results have shown that the acoustic field could be reconstructed with high fidelity even at the rear end of a 42 km long sensing fiber with the spatial resolution of 11.7 m. The proposed sensing system has a linear intensity response of R
²
= 0.9988, while the peak-to-peak value (V
_PP
) of dynamic strain was tuned from 9.28 nε to 176.96 nε. The root-mean-square (RMS) measurement error of our sensing system was less than 1.32 nε. The frequency response range of the proposed system was from 8 Hz to 1 kHz. The proposed sensing system offered a promising solution for the performance enhancement of DAS system that could achieve high spatial resolution, high sensing sensitivity, long sensing distance and dead zone free measurement at the same time.