This article presents the development and characterization of a tilted fiber Bragg grating (TFBG) hydrogen sensor functionalised with a nanometre-scale multilayer thin film stack comprising tantalum (Ta), palladium-gold (Pd0.6Au0.4), and polytetrafluoroethylene (PTFE). Ta is introduced as a novel optical fiber sensing material for hydrogen detection, offering unique advantages in sensitivity, reversibility, and hysteresis-free behavior. The optical design of the TFBG ensures efficient coupling to cladding modes, enabling a stable and repeatable hydrogen-induced spectral response when coated with Ta. The sensor was tested over a wide hydrogen concentration range from 0.001% to 100% H ₂ at room temperature. Experimental results demonstrate a measurable and reversible optical response in the mean center wavelength of the cladding mode resonances, averaged over the 1520–1580-nm spectral envelope, with a minimum detection limit of 0.001% (~10 ppm) H ₂ and a maximum mean wavelength shift of approximately 15 pm at 100% H ₂. The Ta coating provides excellent optical performance, characterized by an absence of hysteresis and a large, nearly constant relative sensitivity across an exceptionally wide sensing range spanning at least five orders of magnitude in hydrogen concentration. Sensor stability and repeatability were further confirmed through extended cycling between 0.1% and 4% H ₂, validating the robustness of the cladding mode response. These results highlight both the unique TFBG-based optical architecture and the role of Ta as a highperformance coating, supporting the potential of the Ta-TFBG sensor for sensitive, low-level hydrogen detection in aerospace and energy applications.

Hydrogen is a cornerstone of the emerging net-zero carbon economy, and its widespread deployment demands sensitive, stable, and scalable detection technologies. In this study, we present a comparative performance analysis of Fibre Bragg Grating (FBG) sensors coated with nanometre-thick metal hydride-forming layers—tantalum (Ta), tantalum-palladium alloy (Ta_0.88 Pd_0.12), palladium (Pd), and palladium-gold alloy (Pd _0.6 Au_0.4)—for optical hydrogen sensing. The integration of Ta and Ta _0.88 Pd_0.12, two tantalum-based metal hydrides, with FBG sensors is introduced here for the first time, offering a promising alternative to conventional Pd-based materials. All coatings were deposited via magnetron sputtering and tested under controlled hydrogen exposure across concentrations ranging from 0.001% to 100% H₂. The Ta-based FBGs exhibited outstanding performance, showing a remarkably linear relative wavelength shift over the full tested range (0.001% to 100% H₂), with sensitivity detectable down to 10 ppm—the lowest concentration achievable in the current setup. Both Ta and Ta_0.88 Pd_0.12 sensors exhibited fully reversible and hysteresis-free response characteristics, with rapid response and recovery. Among them, the Ta_0.88 Pd_0.12 sensor with a 100 nm coating demonstrated the highest logarithmic sensitivity of ∼9 pm/decade(%H₂), corresponding to a 9 pm wavelength shift for every tenfold increase in hydrogen concentration between 0.001% and 100% H₂. In contrast, Pd and Pd _0.6 Au_0.4 sensors showed degraded performance at low concentrations and greater signal hysteresis. These results underscore the potential of Ta and Ta _0.88 Pd_0.12 coatings as robust and high-performance alternatives to conventional Pd-based materials for next-generation distributed fibre-optic hydrogen sensing systems.