Fig. 1. Preparation process and structure diagram of gap microstructure. (a) Preparation process of monolayer PS microsphere array; (b) SME image of large-area PS microsphere array (scale bar is 1 µm); (c) 3D schematic diagram of single-layer PS microsphere array and gap microstructure array; (d) SME image of large-area nano-gap array (scale bar is 1 µm); (e) top view SME image of nano-gap array (scale bar is 300 nm); (f) macro photos of samples (scale bar is 1 cm); (g) simulation section diagram of nano-gap array

Fig. 2. Optical properties obtained by FDTD simulation of nano-gap array. (a) Transmission spectra with polarization angle changing from 0° to 90°; (b)-(d) mode field diagrams in XOY and XOZ planes at wavelengths of 411 nm, 622 nm, and 1148 nm when polarization angle is 90°

Fig. 3. Effect of structural parameters on optical properties of nano-gap array. (a) Transmission spectra for different gap length L; (b) relationship between λ3 and gap length L; (c) transmission spectra for different gap width W; (d) relationship between λ3 and gap width W; (e) transmission spectra for different structural period P; (f) relationship between λ3 and structural period P

Fig. 4. Environment refractive index sensitivity of gap microstructure. (a) Transmission spectra varying with environment refractive index; (b) refractive index sensitivity obtained by fitting wavelength position of main transmission peak under different refractive indexes

Fig. 5. Polarization-controlled properties of nano-gap microstructure measured by experiment. (a) Line diagram; (b) map

Fig. 6. SEM of experimental sample