Increasing the frequency response of direct-detection phase-sensitive OTDR by using frequency division multiplexing

The frequency division multiplexing (FDM) technique is firstly introduced into a direct-detection phase-sensitive OTDR to improve the distributed fiber acoustic sensing performance by using a frequency step sweeping laser source and a dual probe pulse scheme. By using FDM technique, a 40 kHz sampling rate to vibration is realized with a 10 km measurement range, which implies the tradeoff between the frequency response and the measurement range is broken. In experiment, a 6 kHz vibration is successfully measured.