Fig. 1. Schematic diagram of fiber optic sensor structure

Fig. 2. Mode dispersion characteristics and confinement loss when analyte refractive index n_a=1.26. (a) SPP mode at 2.45 µm; (b) core mode at 2.45 µm; (c) coupled mode at 2.56 µm

Fig. 3. Confinement losses at different TiO₂ thicknesses

Fig. 4. Confinement losses under different conditions. (a) Different r₁; (b) different r₂; (c) different r₃; (d) different adjacent stomatal spacing Λ

Fig. 5. Confinement losses under different conditions. (a) Different r₄; (b) distance h from different sections to center of circle

Fig. 6. Confinement losses with different Au film thicknesses

Fig. 7. Sensing performance analysis. (a) Confinement losses for different analyte refractive indices; (b) fitting of resonance wavelength to corresponding refractive index