Broadband and Wide-Angle Terahertz Metagrating Based on Fractal Structure

It is of great significance to achieve precise control of the diffraction wavefront in the teraherz band. Compared with phase-gradient metasurfaces, metagratings can avoid the efficiency reduction caused by phase discretization, so they have important applications in wavefront control. Here a type of metagrating based on fractal structure is proposed. By sweeping and optimizing parameters, the metagrating can achieve high efficient -1st order diffraction within a broadband and wide-angle range. According to the generalized KerKer effects, the mutual interference between multipoles determines the corresponding diffraction behavior. Multipole expansion reveals that compared with the rectangular metagrating, the multipoles excited by the proposed fractal metagrating can achieve stable phase difference in the broadband range. Therefore, the proposed fractal metagrating can achieve almost perfect one-way diffraction within a bandband and wide-angle range. This study provides new ideas for the design of metagratings, and has important application potential in the fields of communication, sensing, absorption and so on.