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Abstract Metasurfaces are planar metamaterials exhibiting certain inhomogeneous phase distributions for transmitted or reflected waves, which can efficiently reshape the wave‐fronts of incident beams in desired manners based on the Huygens principle. Due to their exotic abilities to freely manipulate electromagnetic (EM) waves on a flat and ultrathin platform, metasurfaces have attracted intensive attention recently, resulting in numerous new concepts and effects that could possibly find applications in many different aspects. In this article, the key achievements in this field are briefly summarized, with focus put on the efficiency issue of metasurfaces. After introducing the basic concept of metasurfaces and their early realizations, successively the mechanisms and realizations of high‐efficiency metasurfaces are described: for manipulating linearly polarized EM waves in reflection and transmission geometries, and for manipulating circularly polarized EM waves based on the geometric‐phase concept, using plasmonic materials as well as dielectric ones. Then, several important applications of high‐efficiency metasurfaces are summarized, including polarization control, metaholograms, metalenses, and surface wave couplers. Finally, this review is concluded with personal perspectives on the future directions of this rapidly growing research field.
He et al. (Sun,) studied this question.