Large vibration response bandwidth and high spatial resolution FDM φ-OTDR system based on Optical Pulse Compression and Compressive Sensing

Heterodyne coherent distributed acoustic sensing (DAS) system has witnessed substantial expansion in applications due to its specific advantages like long sensing distance, real-time response and high accuracy. However, the trade-off between vibration response bandwidth and sensing distance limits the broader deployment. The frequency-division-multiplexing (FDM) technique is a well-known solution. But, to avoid the inter-channel crosstalk, it requires wide system bandwidth (like photodetector and modulator) or compromises in spatial resolution by enhancing pulse duration, which increases the system cost or degrading system performance, respectively. In this work, we propose to combine optical pulse compression (OPC) and compressive sensing (CS) in traditional FDM φ-OTDR. Experimental results demonstrate the detection of a 30 kHz vibration signal over a 5.2 km sensing fiber and the identification of two vibration regions spaced 8 m apart, achieving a spatial resolution beyond the pulse duration limit. This proposed method breaks the trade-offs between vibration response bandwidth, sensing distance and spatial resolution in conventional FDM φ-OTDR without upgrading hardware which broadens the application of DAS system in long distance monitoring.