High-sensitivity quasi-distributed acoustic sensing system using dual linear-frequency-modulation pulses

In this paper, a direct-detection quasi-distributed acoustic sensing (QDAS) system using dual linear-frequency-modulation pulses is proposed, which achieves high-sensitivity sensing. Microwave photonic technology is used to generate two identical linear-frequency-modulation (LFM) pulses with a certain time interval as a probe signal. Compared with the previously proposed QDAS system based on a single LFM pulse, within the threshold of fiber nonlinear effects, the power of the probe signal is increased while avoiding the use of a matching interferometer. Experimental results show that under the same probe power, the received carrier power is increased by 6 dB. In addition, an improved phase-shift integration (IPSI) algorithm is proposed, combined with the empirical mode decomposition algorithm, which significantly improves the demodulation signal-to-noise ratio compared with the Hilbert algorithm. The noise floor is greatly suppressed, achieving a level of -90.6 dB rad²/Hz@10kHz.