Non-uniformly periodical sampling in phase-sensitive OTDR

The maximum detectable frequency response of phase-sensitive optical time domain reflectometry is limited by the sensing fiber length, which is a challenging issue in long-haul distributed vibration sensing. The vibration measurement in φ-OTDR system can be regarded as a discrete sampling process, and the sampling rate is the repetition rate of probe pulses. In this paper, we propose a method to enhance the detected frequency response range of φ-OTDR system by using non-uniformly periodical sampling, which is known for the ability of sub-Nyquist sampling for band-limited signals. The non-uniformly periodical probe pulses are injected into the sensing fiber to sample vibrations on the fiber. Experimental results show that the maximum detected frequency response is 2.3 kHz with ∼2397 Hz averaging frequency. The system can realize high frequency vibration measurement with low repetition rates of probe pulses in long-haul vibration measurement.