Fig. 1. Four-layer Kretschmann prism coupling SPR sensing structure

Fig. 2. The Reflecting spectra for different prisms

Fig. 3. The influence of different Ag film thickness on SPR resonance spectra

Fig. 4. The effect of TiO₂ thickness on SPR resonance
(a): Ag=45 nm; (b): 50 nm

Fig. 5. The reflectance spectrum of the sensor under different environmental refractive indexes
(a): 45 nm Ag/110 nm TiO₂; (b): 50 nm Ag/110 nm TiO₂

Fig. 6. The relationship between the position of the SPR resonance valley and the refractive index of the environment

Fig. 7. (a) Schematic diagram of SPR resonance gas sensor based on waveleogth interrogation; (b) The experimental setup SPR resonance gas sensor

Fig. 8. Spectra of different hydrogen concentrations

Fig. 9. The relationship between the trough position and the hydrogen concentration

Fig. 10. Linear fitting diagram of SPR resonance valley wavelength and gas concentration