Numerical Analysis of Multi-Layer Grating Assisted SPR-Based D-Shaped Optical Fiber

A novel D-shaped fiber optic surface plasmon resonance (SPR) refractive index (RI) sensor with a bimetallic superimposed double-layer metal oxide grating structure is proposed. Ag/Au layers are coated with ZnO and Ta2O5 to considerably increase the electric field strength on the grating surface. The finite element method is used to calculate and analyze the influence of structural parameters, including grating period and the number of gratings, on the performance of the D-shaped fiber grating sensor. The parameters are optimized to achieve the maximum sensor sensitivity. The analyte RI detection range is 1.34–1.41, with a maximum sensitivity of 15,600 nm/RIU.