Fiber-based distributed sensing laser interferometer enabled by mirror-image correlation method

Distributed fiber-optic sensing (DFOS) can turn the worldwide fiber network into a sensing array, which may immensely extend the sensing range and approaches for hazard assessment, earth observation, and human activity measurement. However, most existing DFOS schemes cannot simultaneously give dual attention to the detection ability (for example, sensing distance) and multipoint localizing function. A mirror-image correlation method is proposed and can precisely extract the time delay between two original signals from their composite detected signal. This method enables the distributed vibration sensing function of the laser interferometer and maintains its high detection ability. We demonstrate its feasibility by simultaneously localizing multiple knocking vibrations on a 250-km round-trip fiber and distinguishing traffic vibrations at two urban positions in a field test. The localizing precision is analyzed and satisfies the requirements for fiber network sensing.