Ultra-Long Ultra-Broadband Distributed Acoustic Sensing With Zadoff-Chu Nonlinear Frequency Modulation and LEAF

The performances of fiber-optic distributed acoustic sensing (DAS) systems are fundamentally limited by the trade-off between the sensing distance and response bandwidth (RB), constraining the effectiveness of the DAS for long-haul sensing applications greatly. To break such a limitation, this paper proposes a novel Zadoff-Chu (ZC) based nonlinear frequency modulation (ZC-NLFM) scheme that combines the zero-correlation property of the ZC method with the chirp diversity of NLFM. The generated ZC-NLFM pulses exhibit excellent sidelobe and inter-pulse interference suppression, enabling high-sensitivity DAS demodulation even under low signal-to-noise ratio conditions. Furthermore, by employing the large-effective-area fiber (LEAF) with the lower attenuation, higher stimulated Brillouin scattering threshold, and Raman amplification, a wide-frequency-range, long-distance, and low-noise DAS (WLL-DAS) with high strain sensitivity of 94.34 $\text{p}\mathsf{\epsilon }/\phantom{\text{p}\mathsf{\epsilon }\sqrt{\text{Hz}}}\sqrt{\text{Hz}}$ over a wide RB of up to 7 kHz and an ultralong sensing distance of 148 km at the spatial resolution of 10 m is achieved simultaneously. Compared to the conventional DAS, the proposed WLL-DAS achieves a 22-fold increase in the RB over an ultralong distance of >140 km, significantly extending the performance boundary and application range of the DAS.