Fig. 1. (a) Schematic of the metasurface structure that can exhibit EOT, TIR, or EOD, depending on the incident angle. The index of the upper layer, slit area, and lower layer is n1=2, n2=1.4, and n3=1, respectively. (b) Diffraction order chart in k-vector space of the structure in (a). Solid lines represent the RWAs with orders ±0, ±1, and ±2, while the dashed lines represent TWAs with orders ±0, ±1.

Fig. 2. Analytical results of (a) zeroth reflectance R0, (b) zeroth transmittance T0, and (c) −1st reflectance R−1, respectively, of the metasurface for varying incident angle θ and wavelength λ. The three abrupt color changing contours in (a) automatically show the critical angles for TIR, the −1st RWA, and the −1st TWA, respectively, as marked in the figure, and they split the whole phase map into different subareas that contain combinations of different propagating channels (also denoted in the figure). In subarea ①, there are r0 and t0 channels; R0 exhibits a dip in (a), while T0 exhibits a peak in (b) under the resonance condition of the slit cavity mode. In subarea ②, there is only a r0 channel; R0 is unity in the whole subarea. In subarea ③, there are r0 and r−1 channels; R0 exhibits a dip in (a), while R−1 exhibits a peak in (c) under the resonance condition of the slit cavity mode.

Fig. 3. Reflection (R0,R−1) and transmission (T0) spectra of the metasurface composed of real metal (silver), for different incident angles (a) θ=0°, (b) θ=15°, (c) θ=35°, (d) θ=45°, and (e) θ=60°, respectively. Dashed curves show the corresponding analytical results of the PEC metasurface for comparison.

Fig. 4. (a) Reflection (R0, R−1) and transmission (T0) as a function of the incident angle θ at the working wavelength λ=3.3  μm for the periodic slit array of which the zoom-in structure is shown in the upper panel. Dashed curves show the corresponding analytical results of PEC metasurface for comparison. (b)–(f) Field patterns (|Hz|) of a Gaussian beam with λ=3.3  μm illuminating the metasurface (the area marked by the red dashed frame) with different incident angles: (b) 0°, (c) 15°, (d) 35°, (e) 45°, and (f) 55.6°, respectively.

Fig. 5. (a) Schematic of the modulated metasurface with a gradient grating profile with a zoomed-in structure on the upper panel. (b)–(f) Field patterns (|Hz|) of a Gaussian beam with λ=3.3  μm illuminating the modulated metasurface (the area marked by the red dashed frame) with different incident angles: (b) 0°, (c) 15°, (d) 35°, (e) 45°, and (f) 55.6°, respectively. In (b) and (c), the incident beam also undergoes EOT. In (d), the incident beam still undergoes TIR. In (e) and (f), the incident beam undergoes the focusing capability, with near-total suppression of the zeroth diffraction order.