Ding, Meng, Wu, William, Kelly, Thomas William, Jasion, Gregory, Davidson, Ian, Masoudi, Ali, White, Paul, Poletti, Francesco and Slavík, Radan (2026) Towards Low-Frequency Acoustic sensing using Antiresonant Hollow-Core Fibers. Photonics Research. (In Press)
Abstract
Low-frequency acoustic waves exhibit low attenuation and strong penetration, enabling propagation over long distances in water and the solid Earth. This capability underpins applications in natural-hazard monitoring and early warning (earthquakes, tsunamis, volcanic activity), long-range marine sensing and surveillance, and structural and equipment-health monitoring in harsh environments. Traditional piezoelectric hydrophones suffer from high self-noise and electro-magnetic interference, motivating the exploration of fiber optic solutions. However, the operation of fiber solutions at low frequencies suffers from temperature cross sensitivity due to the inherent thermal sensitivity of conventional optical fibers. Hollow-core fibers (HCFs), that guide light in air/vacuum, provide lower thermal and higher acoustic sensitivity than conventional solid core fibers, however, extent to which they could address this limitation has never been studied. Here, we present a comprehensive study of the acoustic and thermal sensitivities of HCFs, combining theoretical modelling and experimental validation, aiming for high acoustic sensitivity while keeping thermal sensitivity low, hence reducing unwanted crosssensitivity. We validate its results experimentally on three HCFs with different structural compositions, quantifying the trade-off between acoustic and temperature sensitivities. Besides, we demonstrate a substantial improvement in temperature–acoustic decoupling by employing an HCF made from Ti-doped ultralow-expansion (ULE) glass, achieving a reduction in thermal sensitivity by more than three orders of magnitude compared with standard single-mode fiber while maintaining comparable acoustic sensitivity. Further, based on the theoretical model we have developed, we show that more optimal coating material could improve the performance of ULE-HCF by another two orders of magnitude. This work thus guides comprehensive design of thermally stable and acoustically sensitive HCF sensors for low-frequency acoustic sensing.
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