Direct Detection With High Spatial Resolution Based on Distributed Vibration Sensor by Precise Signal Delay

A novel and cost-effective method of quantitative vibration demodulation with high spatial resolution based on a direct detection distributed vibration sensor (DVS) is proposed. It is mainly done by connecting dual radio frequency lines (RFLs) with a length difference smaller than the sampling interval of the data acquisition card (DAQ) to the output of the photodetector in the DVS system, and two interference signals with different initial phases and the same vibration signal can be acquired. The experimental results show that the phase demodulation of two different vibrations with a spatial resolution of 1 m can be achieved using dual RFLs with a length difference of 10 cm. The proposed method indirectly increases the sampling rate of the DAQ and shifts the spatial resolution determined by the larger bottom width of pulsed light to that determined by the smaller sampling spacing of the DAQ in two adjacent vibrations. And it overcomes the disadvantage of deterioration of spatial resolution caused by two vibration interference signals that must be selected from two adjacent sampling points of DAQ and expands the prospect of direct detection DVS systems for infrastructure security monitoring.