Terahertz metalens for multifocusing bidirectional arrangement in different dimensions

Abstract

Metasurface lenses are typically investigated for a lot of characteristics, but the design method for conventional devices is comparatively simple in terms of controlling the quantity, position, and size of focal spots. Herein, ultra-thin-phase metasurface structures based on complementary square-split-ring (SSR) nanoantennas have been proposed to achieve terahertz (THz) optical metalenses with multidimensionality and multifocusing. The principle of beam propagation and efficient transmission can be effectively explained through the Fabry-Pérot resonance mode. The THz metalens can efficiently transfer linear cross-polarization under the effects of gratings in the incident plane. By locally tailoring edge lengths and opening the angles of the split rings, full control over abrupt phase changes can be achieved. Two symmetrically distributed parallel focal spots and two vertical focal spots with arbitrary distance can be obtained by arranging the SSR units on the metalenses. Furthermore, we apply the concept of a partitioned-phase mode to realize a double-focusing metalens in the longitudinal direction, which provides a flexible and convenient method to achieve the desired focusing properties. The simulation results are expected to pave the way for practical use of metasurfaces in optical holography, optical-information coding, and parallel-particle trapping.