Fig. 1. Structural diagram of detection system of methane

Fig. 2. Infrared adsorption spectrum of methane

Fig. 3. Transmittance curves of germanium wafer and silicon wafer

Fig. 4. Predesigned spectral curves of front layers. (a) 3-10 μm; (b) 3.7~6 μm

Fig. 5. Refractive index dispersion curves of ZnS under different process parameters

Fig. 6. Final theoretical spectral curves of front layers. (a) 3~10 μm; (b) 3.7~6 μm

Fig. 7. Theoretical spectral curves of back layers

Fig. 8. Layer sensitivity of back layers

Fig. 9. Theoretical spectral curves of double-side design

Fig. 10. Tested spectral curves of filter with front-surface-coated film

Fig. 11. Tested spectral curves of filter with double-side-coated film. (a) 3~10 μm; (b) 7~8.5 μm