Background: Metamaterials (MMs) are smartly engineered structures with rationally designed, nanostructured building blocks that allow us to build devices with distinct responses to light, acoustic waves, and heat flows that are not attainable with naturally available materials. Advances: The latest developments have shown that optical metasurfaces comprising a class of optical MMs with a reduced dimensionality can exhibit exceptional abilities for controlling the flow of light; achieve the anomalously large photonic density of states; and, similar to their bulk analog, provide superresolution imaging. Such a planar photonics technology is expected to facilitate new physics and enhanced functionality for devices that are distinctly different from those observed in their three-dimensional MM counterparts. As a result, this technology will enable new applications in imaging, sensing, data storage, quantum information processing, and light harvesting. Outlook: The recent progress in optical metasurfaces can address the major issues hampering the full-scale development of MM technology, such as high loss, cost-ineffective fabrication, and challenging integration. The studies of new, low-loss, tunable plasmonic materials—such as transparent conducting oxides and intermetallics—that can be used as building blocks for metasurfaces will complement the exploration of smart designs and advanced switching capabilities. This progress in metasurface design and realization will lead to novel functionalities and improved performance and may result in the development of new types of ultrathin metasurface designs with unparalleled properties, including increased operational bandwidths and reduced losses. These new designs would also be compatible with planar, low-cost manufacturing. In turn, these advances will lead to ultrathin devices with unprecedented functionalities, ranging from dynamic spatial light modulation to pulse shaping and from subwavelength imaging or sensing to novel quantum optics devices.

Holography, a revolutionary 3D imaging technique, has been developed for storing and recovering the amplitude and phase of light scattered by objects. Later, single-beam computer-generated phase holography was proposed for restoring the wavefront from a given incidence. However, because the phase modulation depends on the light propagation inside the material, the thickness of phase holograms usually remains comparable to the wavelength. Here we experimentally demonstrate ultra-thin metasurface holograms that operate in the visible range whose thickness is only 30 nm (approximately 1/23 of the operational wavelength). To our knowledge, this is the thinnest hologram that can provide both amplitude and phase modulation in the visible wavelength range, which generates high-resolution low-noise images. Using this technique, not only the phase, but potentially the amplitude of the incident wave can be efficiently controlled, expanding the route to new applications of ultra-thin and surface-confined photonic devices.

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A plasmonic antenna array is used to control the propagation of a light beam across an interface.