▎ 摘　　要

Directional beaming of light from a subwavelength slit surrounded with phase-gradient metasurfaces can be realized with very high efficiencies, but the available optical proposals suffer from narrow bandwidth after the fabrication process and cannot be reconfigured dynamically with switchable frequencies. Here we demonstrate reconfigurable multifrequency directional beaming by placing a graphene ribbon array at two sides of a subwavelength metallic slit. Each graphene ribbon works with the metallic film to fulfill the magnetic response, and the resultant reflection phase can cover full 0-2 pi range by changing the chemical potential of graphene. The on-axis and off-axis directional beams can be formed by properly arranging the chemical potentials of graphene ribbons to serve as meta-couplers between surface waves and propagating waves. Thanks to the negligible interaction between vertically stacked graphene sheets, the beaming frequencies and angles can be broadened by use of double layers of the graphene ribbon array. (C) 2020 Optical Society of America