Metasurfaces, which consist of tailor-made two-dimensional arrays of resonant structures, are promising for achieving planar and compact optical devices capable of shaping optical waves. Their performance is based on the design of the scattering phase of the individual resonant structures. While a variety of functions, such as optical vortex generation or focusing, have been reported separately, finding designs allowing the integration of multiple functions on a single metasurface is needed. This will further stimulate the development of metasurfaces for practical applications in high-speed data communication.

In this work, Li and coauthors report a silicon-based metasurface for realizing superposition states and multi-channel transmission of vortex and spherical waves at terahertz frequencies. Two orthogonally positioned elliptical silicon bars are chosen as the unit structure of the metasurface for independent phase control of the linearly polarized incident waves by tuning the sizes of the axes. The superposition states and multi-channel transmission of spherical and vortex waves (with different charges) are demonstrated theoretically and experimentally by exploring the full range phase control of the silicon structures, as shown in Fig.1. The related work has published in Photonics Research Issue Vol.11 Issue.3: Fuyu Li, Yuanxun Li, Tingting Tang, Yongcheng Lu, Xinyan Liu, Yulong Liao, Qiye Wen. All-dielectric terahertz metasurface for linearly-polarized multichannel transmission and superposition states of spherical and vortex waves[J]. Photonics Research, 2023, 11(3): 485

Caption: Researchers created metasurface devices for linear polarization multichannel transmission and superposition states of spherical and vortex waves. (a) Superposition state of spherical wave and vortex wave under 45° polarized wave incidence. (b) Four-channel transmission of two spherical waves and two vortex waves can be carried under 45° polarized wave incidence. (c) Superposition states of spherical wave and vortex under x and y polarized wave incidence, respectively. (d) Two-channel transmission of a spherical wave and a vortex wave can be carried under x (or y) polarized wave incidence.

The reported metasurface for superposition states and multi-channel transmission of terahertz waves may inspire multi-functional metasurface designs for terahertz information encryption and vortex-based high-speed communication.