Figure 4:

Determination of the MPD initial position. (a) Schematic diagram of determining the MPD initial position. The yellow and green circles on the ground represent the correct initial position and the coarsely determined initial position, respectively. The yellow and green triangles on CMOS represent the correct center of metalens and the coarsely determined center of metalens, respectively. (b) When the MPD position and the metalens center are not determined correctly, the curves of LED viewing angles θ and the image point distances F(θ) in four quadrants would be irregular. (c) When the MPD position and the metalens center are determined correctly, the curves of LED viewing angles θ and the image point distances F(θ) in four quadrants would completely overlap.