Fig. 1. Diagram of subwavelength structure simulation model

Fig. 2. Variations of level 0 transmissivity with structure height under different periods. (a) Period of 50 nm; (b) period of 100 nm;

Fig. 3. AFM images of LiNbO₃ sample surface after etching with different incident energies, where the lower left corner is Fourier transform (FFT) image and the arrow indicates ion beam incidence direction (incident angle is 70°, etching time is 60 min and ion beam current is 40 mA). (a) Incident energy is 400 eV; (b) incident energy is 600 eV; (c) incident energy is 800 eV; (d) incident energy is 1000 eV

Fig. 4. PSD curves, height and RMS roughness of nanostructure on LiNbO₃ sample surface after etching with different incident energies (incident angle is 70°, etching time is 60 min and ion beam current is 40 mA). (a) PSD curves; (b) height and RMS roughness of nanostructure

Fig. 5. AFM images of LiNbO₃ sample surface after etching with different ion beam currents, where the lower left corner is FFT image and the arrow indicates ion beam incidence direction (incident angle is 70°, etching time is 60 min and incident energy is 1000 eV). (a) Ion beam current is 20 mA; (b) ion beam current is 30 mA; (c) ion beam current is 40 mA; (d) ion beam current is 50 mA

Fig. 6. PSD curves, height and RMS roughness of nanostructure on LiNbO₃ sample surface after etching with different ion beam current (incident angle is 70°, etching time is 60 min and incident energy is 1000 eV). (a) PSD curves; (b) height and RMS roughness of nanostructure

Fig. 7. AFM images of LiNbO₃ sample surface after different etching time, where the lower left corner is FFT image and the arrow indicates ion beam incidence direction (incident angle is 70°, ion beam current is 40 mA and incident energy is 1000 eV). (a) Etching time is 20 min; (b) etching time is 40 min; (c) etching time is 60 min; (d) etching time is 80 min; (e) etching time is 100 min; (f) etching time is 120 min

Fig. 8. PSD curves, height and RMS roughness of nanostructure on LiNbO₃ sample surface after etching with different time (incident angle is 70°, ion beam current is 40 mA and incident energy is 1000 eV). (a) PSD curves; (b) height and RMS roughness of nanostructure

Fig. 9. Transmissivity curves of LiNbO₃ sample surface and height and RMS roughness of conical nanostructure. (a)-(c) Transmissivity curves of LiNbO₃ sample surface after etching with different ion beam parameters at 70° incident angle; (d)-(f) height and RMS roughness of conical structure

Fig. 10. Transmissivity of LiNbO₃ surface ( incident angle is 70°, incident energy is 1000 eV and ion beam current is 40 mA).

Fig. 11. Comparison between simulated and measured transmissivity of LiNbO₃ samples under different etching time (incident angle is 70°, ion beam current is 40 mA and incident energy is 1000 eV)