▎ 摘　　要

A method for designing a metalens with electrically tunable focal length is proposed and analyzed. Metasurfaces are defined as low-thickness devices to initiate and generate the abrupt electromagnetic wavefront variation. However, there is no way to control them actively. Our research proposes the design of a metalens that consists of cross-shaped apertures (CSAs) in a gold film and a graphene layer. The CSAs have different lengths and rotation angles. By applying bias voltage to graphene, the focal length can be varied and controlled electrically. When the Fermi energy of the graphene changes from 0.1 to 0.5 eV, the focal length changes from 10.5 to 12.67 mm. The structure is simulated by the finite-difference time-domain numerical method. By splitting graphene layers to several parts and biasing each of them with different bias voltages, the transmitted focused beam could be rotated up to 35 deg. As an application of the metalens device, a refractive index sensor with sensitivity of 80 pm per refractive index unit (pm/RIU) is proposed. (C) 2020 Society of Photo-Optical Instrumentation Engineers (SPIE)