摘要
Electromagnetic or optical metasurfaces, as a kind of quasi-twodimensional artificial interface, are patterned subwavelength structures within ultrathin thickness that interact strongly with electromagnetic waves. The history of metasurface was traced back to the two-dimensional electromagnetic bandgap structure [1], which may be regarded as the beginning of metasurface research. Such metasurface with high impedance has been widely used in reducing the size of antennas and improving their performance. Recently, generalized Snell’s laws [2] have been coined and widely applied to various designs of metasurfaces [3], which pave a clearcut physical foundation for metasurfaces. Thereby, the metasurfaces have been widely deployed in designing new devices to regulate and control the electromagnetic wavefronts. For example, 600-nm-thick TiO2 metalens have been demonstrated to focus the light [4], 105 times thinner than the optical traditional lens with similar performance. Such a metasurface lens is believed promising to replace the traditional optical lens in the future. Hence, functional structured surfaces have become the subject of several rapidly-growing research areas, and demonstrated a lot of useful properties of structure-based devices with customized electric and magnetic responses.
