A High Response Bandwidth DAS System Based on Optical Loop Modulation

We propose a Distributed acoustic sensing (DAS) system with a high response based on sequential frequency division multiplexing (FDM). Pulse sequences with different frequencies and delays are modulated by an optical loop structure and injected into the sensing fiber. The vibration signals are discretely collected by Rayleigh backscattering light (RBS) signals with different delays and frequencies. After frequency demultiplexing of the RBS signal in the digital domain, the high-fidelity differential phase of the vibration region was extracted using the peak search method and interlacing according to the time delay order to achieve high-dense sampling of the vibration signal. Compared with the traditional sequential frequency division multiplexing scheme, the scheme using an optical loop structure to generate pulse sequence reduces the dependence on the bandwidth performance of the microwave signal source and the modulator, effectively controls the experimental cost, and provides a new scheme for sequential pulse sequence modulation.