2-bit coding metasurface with a double layer random flip structure for wide band diffuse reflection and reciprocity protected transmission

Coding metasurfaces based on random-flip structures have attracted great attention due to their ability to achieve distortion-free transmission and diffuse reflection simultaneously. However, previous implementation based on 1-bit coding metasurface has a narrow bandwidth and insufficient bandwidth coverage in the near infrared region. Here, we propose a novel vertical 2-bit coding metasurface composed of double-layer random-flip meta-atoms (DLRFM). while the main transmission lobe is unchanged, the zero-order diffraction intensity of DLRFM's reflection direction is less than 10% of the total reflection in the range of 0°∼ 30° incidence angle, which proves its excellent diffuse reflection and distortion-free transmission effect. Such design strategy can be extended to multiple wide band coverage in near-infrared regime by tailoring the geometric parameters, which indicates good application potential in advanced display and lens designs.