High-performance D-shaped photonic quasi-crystal fiber SPR sensor with Ag-TiO₂ gratings

A D-shaped photonic quasi-crystal fiber (PQF) surface plasmon resonance (SPR) sensor is numerically designed and analyzed. By patterning a silver-titanium dioxide (Ag-TiO₂) composite film into a grating structure, the localized surface plasmon resonance (LSPR) is enhanced and the full width at half-maximum (FWHM) is narrowed. The finite element method (FEM) is employed to optimize the structural parameters. In the refractive index (RI) range of 1.36-1.425, the sensor obtained a wavelength sensitivity of 15,800 nm/RIU and a maximum figure of merit (FOM) of 929.02RIU^-1. A maximum amplitude sensitivity (AS) of 11,709.8RIU^-1 is also obtained. With its excellent FOM and AS, the proposed sensor holds great application potential in chemistry, biomedicine, and environmental monitoring. These results demonstrate a promising strategy for designing high-performance SPR RI sensors.