Design of hybrid metagrating microstructures with high efficiency and large angle focusing

The traditional gradient metasurface is limited on the low efficient focusing for designed metalens due to the small angle steering. Generally, metasurface has advantage for controlling beams at the small angles, but there are low efficiency at larger angles. In order to improve the focusing efficiency of the gradient metasurface lens, a hybrid metagrating design scheme is proposed, in which the gradient metasurface structure is used in the central region of the lens, and the metagrating structure is used in the edge of the lens. The electric field distribution and diffraction characteristics of the gradient metasurface are demonstrated. The element structure of the metagrating is designed with asymmetric type to suppress the unnecessary diffraction order, so that the outgoing light energy propagates along the expected direction. In order to verify whether hybrid metagratings can improve the focusing effect, we compared the electric field distribution of hybrid metagratings and conventional gradient metasurface lenses and discuss their focusing effect. It is found that the focusing effect of hybrid metagrating is improved by 8% compared with the traditional gradient metasurface lens.