Synthetic-Dimensions-Engineered Fiber-Optic Tamm Plasmon Metatips Enabling High-Dimensional Manipulation for Enhanced Hydrogen Sensing

Tamm plasmon polariton (TPP) multilayer nanofilms have drawn significant interest for their strong light field localization enhancement and fabrication scalability, yet conventional one-dimensional geometric configurations restrict the degrees of freedom for light field manipulation. Herein, we propose a synthetic-dimensions-engineered fiber-optic TPP (S-FOTPP) sensing metatip, which enables flexible control over the resonance and sensing characteristics of the TPP in a physically constrained two-dimensional parameter space, surpassing the limits of conventional structural optimization. When the TPP resonance in the synthetic-dimensions space approaches twice the Bragg wavelength, corresponding to the characteristic optical scale of the supercell, the mode is driven into a phase-sensitive regime in which hydrogenation-induced phase perturbations in the Pd layer are converted more efficiently into measurable wavelength shifts. As a result, the H2 sensing sensitivity is significantly enhanced compared with conventional TPP and FP structures, with a limit of detection (LOD) at the ppm level. Meanwhile, by leveraging the photocatalytic effect to regulate the reaction kinetics, the response and recovery time of the H2-sensitive system are optimized to 7.7 and 8.8 s. Additionally, the relative contributions of the thermal and nonthermal effects in the photocatalysis process are analyzed by investigating the dependence of the response and recovery time of S-FOTPP metatips with different Pd thicknesses on the pump laser power. This work presents a metatip that integrates high sensitivity from synthetic-dimensions engineering, rapid response from photocatalytic effects, and scalable fabrication via thin-film deposition, while highlighting the potential of photocatalysis for further improving photonic device performance.