Broadband Metasurfaces with Simultaneous Control of Phase and Amplitude

Metamaterials have continuously attracted enormous interest due to their unusual electromagnetic properties, which can be utilized for engineering the electromagnetic space and controlling light propagation, with prominent examples including negative and zero refraction, [ 1‐7 ] sub-diffraction imaging, [ 8‐10 ] and invisibility cloaking. [ 11‐13 ] Despite the success of metamaterials in ushering an array of new fundamental physics and potential applications, devising metamaterials for practical applications, however, still remains a big challenge. In particular, the material loss and fabrication challenges have roadblocked their transition to real world applications. For bulk metamaterials, this usually cannot be avoided due to the fact that metals are the primary constituent materials, whereby the ohmic loss of metals at optical frequencies is quite signifi cant. Moreover, volumetric metamaterials very often require precise alignment between different layers, which poses a great challenge even with the most state-of-the-art nanofabrication tools. Recently, metasurfaces consisting of a monolayer of plasmonic structures, capable of controlling the wavefront of light, serve as an alternative approach to bypass the loss and fabrication issues, and open doors for bridging the gap between the fundamental research of the artifi cial structures and their device applications. [ 14‐41 ] Being as thin as only a fraction of the wavelength, the optical loss is not a major concern. In addition, the complex and time-consuming alignment process necessary