High‐Efficiency Ultrathin Dual‐Wavelength Pancharatnam–Berry Metasurfaces with Complete Independent Phase Control

Abstract

AbstractMetasurfaces are planar structures that can offer unprecedented freedoms to manipulate electromagnetic wavefronts at deep‐subwavelength scale. The wavelength‐dependent behavior of the metasurface could severely reduce the design freedom. Besides, realizing high‐efficiency metasurfaces with a simple design procedure and easy fabrication is of great interest. Here, a novel approach to design highly efficient meta‐atoms that can achieve full 2π phase coverage at two wavelengths independently in the transmission mode is proposed. More specifically, a bilayer meta‐atom is designed to operate at two wavelengths, the cross‐polarized transmission efficiencies of which reach more than 70% at both wavelengths. The 2π phase modulations at two wavelengths under the circularly polarized incidence can be achieved independently by varying the orientations of the two resonators constructing the meta‐atom based on Pancharatnam–Berry phase principle. As proof‐of‐concept demonstrations, three dual‐wavelength meta‐devices employing the proposed meta‐atom are numerically investigated and experimentally verified, including two metalenses (1D and 2D) with the same focusing length and a vortex beam generator carrying different orbital angular momentum modes at two operation wavelengths. Both the simulation and experimental results satisfy the design goals, which validate the proposed approach.