Fig. 1. Structural diagrams of periodic silver nanoring array. (a) Plan of structure；(b) 3D diagram of structure

Fig. 2. Spectra, mode fields and current densities of silver nanoring array calculated when P＝690 nm, r＝100 nm, R＝225 nm, H＝50 nm, and t＝60 nm. (a) Reflection, transmission and absorption spectra; mode field distributions in XOZ plane corresponding to two resonant wavelengths of (b) 415 nm and (c) 691 nm in reflection spectrum; surface current density distributions in XOZ plane corresponding to two resonant wavelengths of (d) 415 nm and (e) 691 nm in reflection spectrum

Fig. 3. Spectral responses of silver nanorings with different structural parameters. (a) Different film thicknesses; (b) different structural heights

Fig. 4. Reflectance spectra under different conditions. (a) Reflectivity versus R when r is fixed; (b) reflectivity versus P for silver nanorings with same structural parameters

Fig. 5. Operation schematic of PS film transferred to glass slide surface

Fig. 6. Flow chart of preparation of silver nanoring. (a) Single layer PS microsphere array on surface of glass slide; (b) spin coating silica gel; (c) oxygen etching PS microspheres; (d) magnetron sputtering silver nano films; (e) spin coating NOA; (f) NOA template; (g) silver nano films prepared by magnetron sputtering with NOA template

Fig. 7. Characterization diagrams of structure. (a) Physical picture of silver nanoring sample; (b)(c) SEM images of NOA nanoring array; (d) AFM image of silver nanoring array sample; (e) AFM line height profile of structure in Fig.7(d) indicated by white line

Fig. 8. Schematic of spectral acquisition system

Fig. 9. Experimental and simulated reflectance spectra of silver nanoring structure after parameter optimization

Fig. 10. Reflectance spectra of structures under different refractive index environments. (a) Results obtained from experiment; (b) results obtained from calculation; (c) offset line diagram of refractive index decline in low refractive index environment

Fig. 11. Refractive index sensitivity at resonance wavelength λ₂. (a) Under different H; (b) under different P