Phase distortion suppression for phase-sensitive OTDR using time-slotted pulse

Phase distortion influences the vibration demodulation effect of direct detection phase-sensitive optical time-domain reflectometer (Φ-OTDR) system. In this paper, a time-slotted pulsed direct detection Φ-OTDR is proposed. By using a double acousto-optic modulation device to generate the same-frequency phase-shifted time-slotted pulse, the phase distortion caused by the excessively long disturbance range can be effectively suppressed. The sliding window empirical modal decomposition (SWEMD) is introduced to solve the anisotropy problem of phase distortion and extract the correct signal. The phase demodulation performance of the single-pulse and time-slotted pulsed detection structures are compared and analyzed. The experimental results show that the vibration and sound signals from 50 Hz to 1300 Hz can be accurately demodulated along a 10040 m sensing fiber, and the amplitude fitting coefficients of demodulated vibration and sound signals in the repeatability experiments can be up to 0.9912 and 0.9906, respectively. The sampling rate of the system is as low as 50 MHz. It provides an effective solution for the direct detection Φ-OTDR with high-quality phase demodulation for weak signals.