Fig. 1. (a) Schematic of focusing of the bifocal metalens; (b)-(c) Side and top views of silicon microbricks with height H, length L and width W, and the unit cell size is P; (d) Top view of the silicon microbrick with rotation angle θ; (e) Top view of the constructed bifocal metalens

Fig. 2. Intensity distribution of the bifocal metalens under the RCP (a), LCP (b) and XLP (c) incidence light, respectively; (d) Intensity distribution curve along the x-axis through the focal point under the RCP (blue line) and LCP (red line) incidence light, respectively

Fig. 3. Intensity distribution of the focusing field when the incident light is (a)， (b)， (c) and (d), respectively 当入射光分别为 (a)， (b)， (c) 和 (d) 时，聚焦场的强度分布

Fig. 4. Intensity distribution of the focusing field when the RCP light incidence with the angle of 10° (a) and 20° (c), respectively; Intensity distribution of the focusing field when the LCP light incidence with the angle of 10° (b) and 20° (d), respectively

Fig. 5. [in Chinese]

Fig. 5. Intensity distribution of the focusing field when the RCP (a) and LCP (b) light incidence with the frequency of 0.8 THz; Intensity distribution of the focusing field when the RCP (c) and LCP (d) light incidence with the frequency of 1.2 THz