Research progress of electromagnetic properties of tunable chiral metasurfaces

Chiral metasurfaces are ultra-thin metamaterials composed of planar chiral cell structures with specific electromagnetic responses. They have attracted great attention due to their singular ability to control electromagnetic waves at will. With tunable materials incorporated into the metasurfaces design, one can realize tunable/reconfigurable metadevices with functionalities controlled by external stimuli, opening a new platform to dynamically manipulate electromagnetic waves. In this paper, we introduce some theoretical foundations of the electromagnetic properties of tunable/reconfigurable chiral metasurfaces. When a linearly polarized light enters a tunable chiral metasurface, it can be decomposed into left-handed circularly polarized (LCP) wave and right-handed circularly polarized (RCP) wave. By changing the dielectric constant and magnetic permeability of the medium through the external environment, the metadevices can dynamically control the response characteristics to various polarized lights, especially circularly polarized lights such as refractive index, dichroism, optical rotation, asymmetric transmission, etc. According to the properties of negative refractive index, circular dichroism, optical rotation, and asymmetric transmission controlled by the tunable chiral metasurfaces, we review the latest research progress. Finally, we put forward our own opinions on the possible future development directions and existing challenges of the rapidly developing field of the tunable chiral metasurface.