Quasi-distributed acoustic sensing with interleaved identical chirped pulses for multiplying the measurement slew-rate

Abstract

Quasi-distributed acoustic sensing (Q-DAS) based on ultra-weak fiber Bragg grating (UWFBG) is currently attracting great attention, due to its high sensitivity and excellent multiplexing capability. Phase-sensitive optical time-domain reflectometry (Φ-OTDR) based on phase demodulation is one of the most promising interrogation schemes for Q-DAS. In this article, a novel interleaved identical chirped pulse (IICP) approach is proposed on the basis of pulse compression Φ-OTDR with coherent detection. Different from the frequency-division-multiplexing (FDM) method, the identical pulses are used for multiplexing in the IICP scheme, and the mixed reflection signals can be demodulated directly, so the inconsistent phase offsets in FDM can be avoided. As a result, this scheme can enlarge the measurement slew-rate (SR) of Q-DAS by times compared with traditional single pulse scheme. In the proof-of-principle experiment, the SR of 28.9 mɛ/s has been achieved with an 860 m sensing range, which is 5 times as that of the traditional single pulse scheme; meanwhile, the response bandwidth has been enlarged by 5 times. The 277 kHz response bandwidth has been achieved, with 5 m spatial resolution and 2.8 p ε / Hz strain sensitivity.

Optical fiber distributed acoustic sensing based on difference-frequency COTDR

“…Then, the traditional IQ demodulation method [8] for COTDR can be applied to the phase signal demodulation.…”

Improved Rotational Vector Summation Algorithm for Fade Suppression in Distributed Acoustic Sensing

“…Then, the conventional orthogonal demodulation method [14] of COTDR is applied to demodulating the raw phase signal.…”

Ultrasonic long range underwater acoustic sensing: going beyond the standard pulse repetition rate

“…The increase in interrogation rate can be combined with methods of pulse compression for enhancing the signal to noise ratio. Wang et al 1,2 implemented such Quasi Distributed Acoustic Sensing (Q-DAS) system along with pulse compression via chirped pulses. Our group demonstrated Q-DAS at ultrahigh interrogation rates combined with Perfect Periodic Autocorrelation (PPA) codes.…”