Sensitivity-enhanced dual-parametric hydrogen and temperature sensing with thin-clad optical fiber sensors and palladium-gold nanocoatings

Hydrogen monitoring requires accurate, thermally stable sensors for detecting low hydrogen concentrations under variable environmental conditions. We demonstrate a multi-parametric hydrogen and temperature sensor based on dual-FBG Fabry–Pérot etalons integrated into thin-clad optical fibers and functionalized with palladium–gold nanofilms. Two sensitivity-enhancement strategies were combined: reducing the fiber cross-section to improve strain transfer between nanocoating and fiber, and alloying palladium with gold to increase hydrogen solubility and reduce the miscibility gap. The optimized Pd 85 :Au 15 coating (86 nm) on a 5 0 μ ⁢ m fiber achieved 24 pm/%(H 2 ) at 20 °C. We introduce the normalized sensitivity, accounting for the coating-to-fiber cross-sectional ratio, to compare the intercalation-mediated strain sensing effect across platforms in a thorough review. The sensor enabled ISO-26142-compliant simultaneous read-out from 10–60 °C and 100–20,000 ppm in nitrogen. In air, the lowest measurable concentration was 3000 ppm, with transferable calibration above this threshold and excellent repeatability over 260 h of cyclic hydrogen loading.