High-Sensitivity Fiber-Optic Hydrogen Sensor with Pd-Modified hBN Film

We present a compact Fabry-Perot fiber-optic hydrogen sensor employing a palladium-decorated hexagonal boron nitride ($\mathbf{P d} / \mathbf{h B N}$) film as the reflective membrane. The nanometer-thick hBN substrate offers high mechanical strength and low thermal expansion, enabling efficient transduction of Pd lattice expansion into optical wavelength shifts. The sensor achieves a sensitivity of$\mathbf{0. 5 8 ~ p m} / \mathbf{p p m}$over a hydrogen volume fraction range of$0.02 \%-0.50 \%$, with a response time of 60 s at$0.10 \% \mathrm{H}_{2}$and excellent repeatability without response memory. The proposed design combines high sensitivity, fast response, and structural robustness, which demonstrates strong potential for real-time hydrogen monitoring in harsh environments such as transformer oil.