Frequency Response Enhancement of f-OTDR Using Interval-Sweeping Pulse Equivalent Sampling Based on Compressed Sensing

An interval-sweeping pulse equivalent sampling (ISPES) method based on compressed sensing technique is proposed to enhance the frequency response of phase-sensitive optical time-domain reflectometry (phi-OTDR). The proposed method achieves an equivalent high-sampling-rate acquisition of Rayleigh backscattered signals along each sensing point of the fiber by the interval-sweeping pulse sampling and compressed sensing reconstruction. Meanwhile, based on the Whittaker-Shannon interpolation formula, the observation matrix corresponding to the interval-sweeping pulse sampling is successfully constructed and proved, which is easy to implement in hardware. In experiments, an ultrasonic signal with a frequency up to 28 kHz at the end of a 4.4-km sensing fiber is accurately identified by using this method, which outperforms other compressed-sensing-based methods. And multi-frequency vibration signals are also accurately detected. Besides, this method performs signal compression while sampling. The number of samples is only 13.3% of the reconstructed data, significantly reducing the amount of data acquisition/transmission/storage. Therefore, the proposed method can effectively enhance the frequency response of phi-OTDR to sparse-wideband vibration signals without any hardware modification. It also has great advantages in reducing the hardware burden and improving the response speed.