Fig. 1. Cross-section of the PQF-SPR sensor

Fig. 2. Dispersion relationships of the X-polarized core mode and SPP mode, confinement loss spectra, and electric field distributions forC_H₂=2.5%: (a) X-polarized core mode at 1875 nm, (b) X-polarized core mode at the phase matching point, and (c) X-polarized SPP mode at 1875 nm.

Fig. 3. Dispersion relationships of the Y-polarized core mode and SPP mode, confinement loss spectra, and electric field distributions for C_CH₄=2.5%: (a) Y-polarized core mode at 1570 nm, (b) Y-polarized core mode at the phase matching point, and (c) Y-polarized SPP mode at 1570 nm.

Fig. 4. CL spectra of the core mode for (a) hydrogen and (b) methane with different concentrations

Fig. 5. Relationship between the gas concentration and wavelength shift for hydrogen and methane

Fig. 6. (a) CL spectra of the core mode for different air hole diameters d when the hydrogen concentration is 3.0%. (b) Resonance wavelength versus hydrogen concentration (t₁=t₂=30 nm, h₁=1.5 μm, h₂=2.17 μm, and C_H₂=3%)

Fig. 7. (a) CL spectra of the core mode for different air hole diameters d when the methane concentrations are 2.0% and 2.5%. (b) Resonance wavelength versus methane concentration and average sensitivity (t₁=t₂=30 nm, h₁=1.5 μm, and h₂=2.17 μm).

Fig. 8. (a) CL spectra of the core mode for different metal film thicknessest₁ at a hydrogen concentration of 3.0%. (b) Resonance wavelength versus hydrogen concentration and average sensitivity (d=1.58 μm, t₂=30 nm, h₁=1.5 μm, and h₂=2.17 μm).

Fig. 9. (a) CL spectra of the core mode for different metal film thicknesses t₂ when the methane concentrations are 2.0% and 2.5%. (b) Resonance wavelength versus methane concentration and average sensitivity (d=1.58 μm,t₁=30 nm, h₁=1.5 μm, and h₂=2.17 μm).

Fig. 10. (a) CL spectra of the core mode for the methane gas channel with different height h₂ when the methane concentrations are 2.0% and 2.5%. (b) Resonance wavelength versus methane concentration and average sensitivity (d=1.58 μm, t₁=t₂=30 nm, and h₁=1.5 μm).