Fig. 1. Flowchart of the automated design of guided mode resonance filters

Fig. 2. Schematic diagram of the silicon grating under normal incidence. (a) Schematic diagram of cross section; (b) top view of the grating

Fig. 3. Transmission and electromagnetic field distributions of silicon grating. (a) Transmission of silicon grating calculated by CST under TE polarization; (b) transmission of silicon grating calculated by CST under TM polarization; (c) transmission of silicon grating calculated by RCWA under TE polarization; (d) transmission of silicon grating calculated by RCWA under TM polarization; (e) electric field distribution of Fig. 3(a) at 0.6522 THz; (f) magnetic field distribution of Fig. 3(a) at 0.6522 THz

Fig. 4. Schematic and design result of the metasurface grating. (a) Three-dimensional view; (b) square cell structure; (c) transmission distribution between 0.55 THz and 0.65 THz; (d) cross section electric field distribution at 0.6 THz

Fig. 5. Photographs of silicon grating sample. (a) Photograph of silicon grating; (b) SEM of the central sample

Fig. 6. 8F terahertz time domain spectroscopy system. (a) Terahertz beam path diagram; (b) picture of experimental facility

Fig. 7. Measurement results of the central sample of silicon grating. (a) Time domain THz signal; (b) its corresponding amplitude spectrum; (c) comparison between simulation results (dot line) and experimental results (solid line)

Fig. 8. Influence of size error on the resonance frequency. (a) Influence of horizontal error; (b) influence of depth error

Fig. 9. Spectra of the silicon grating at 0°, 4°, and 8° incident angles. (a) Simulation result; (b) experimental results

Table 1. Parameters and resonance frequencies of the gratings optimized by CST and RCWA