Signal-and-Kernel Phase Noise Compensation Method for Distributed Acoustic Sensors

Distributed acoustic sensing (DAS) is a transformative tool for applications involving dense dynamic strain measurements. Coherent detection, and matched filtering, are two effective approaches promoting the evolution of DAS technology. In the current stage, laser with linewidth of sub-kilohertz is considered to be mandatory in phase-sensitive optical time-domain reflectometry ( $\Phi$ -OTDR) with coherent detection and matched filtering, which restricts its further popularization in some degree. In this work, an effective phase noise compensation method for $\Phi$ -OTDR with coherent detection and matched filtering is proposed, which significantly relaxes the laser linewidth limitation in DAS. The phase noise of light source is obtained by an auxiliary interferometer, and is then used to separately compensate the coherent detection signal of Rayleigh backscattering light, and the kernel function for matched filtering demodulation. In the demonstrational experiment, such signal-and-kernel phase noise compensation method is introduced into linear-frequency-modulation-pulsed $\Phi$ -OTDR with 100 kHz linewidth integrable tunable laser assembly (ITLA), achieving 50 km measurement range, 68 $\mathbf {p} {\varepsilon } /\sqrt\mathbf {{Hz}}$ strain resolution, and 4.2 m spatial resolution at the same time.