Abstract
Implementation of abrupt phase discontinuities along a surface has been the theme of recent research on electromagnetic metasurfaces. Simple functionalities such as reflecting, refracting, or focusing plane waves have been demonstrated with devices featuring phase discontinuities, but optical surfaces allowing independent magnitude and phase control on the scattered waves have yet to emerge. In this paper, we propose the first true optical Huygens’ surface, which explicitly utilizes orthogonal electric and magnetic responses to realize total control on an optical surface’s local reflection coefficients. This extends the functionality of metasurfaces to an unprecedented level. We first demonstrate that a nanorod gap-surface plasmon resonator can act as a Huygens’ source. Thereafter, by properly tuning and rotating these resonators, we realize arbitrary reflection optical metasurfaces—surfaces for which the local reflection coefficients can be independently tailored in both magnitude and phase. We demonstrate the versatility of this approach through designs of a metasurface that asymmetrically reflects two copolarized beams and a Dolph-Tschebyscheff optical reflectarray.
- Received 23 June 2014
DOI:https://doi.org/10.1103/PhysRevX.4.041042
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Published by the American Physical Society
Popular Summary
Funny mirrors at amusement parks entertain by showing shortened, stretched, or exotic images of ourselves. We see distorted images from such mirrors because they are curved in such a way that the direction of the light scattered off the mirror’s surface differs from that of typical flat mirrors. Creating flat surfaces that offer arbitrary control of reflected light would have enormous implications in the field of nanophotonics. In order to arbitrarily control reflected light, one would need a surface where each point on the surface can independently tune the magnitude and phase of the reflected light. Recent advances in nanofabrication techniques have made it possible to build artificial surfaces known as metasurfaces in the hopes of controlling scattered light. These surfaces contain subwavelength-sized “meta-atoms” whose electrical response alone has been emphasized in recent metasurface research. As a result, no practical metasurface has been shown to fully control scattered light.
On the contrary, we rely on both the electric and magnetic responses of meta-atoms to independently tune the magnitude and phase of the surface’s local complex reflection coefficients. The meta-atom we employ consists of a gold nanorod separated from a gold substrate by a thin silica layer. The lengths and rotation angles of these nanorod resonators can be tuned to arbitrarily and locally tailor the reflection coefficients of optical light and therefore completely control the reflective properties of electromagnetic radiation. We use 800-nm incident light and are able to asymmetrically reflect a wave from the metasurface at any arbitrary direction with prescribed amplitudes.
We expect that these new metasurfaces, which are capable of reshaping scattered optical wave fronts, will also be useful for realizing complex optical antenna patterns.
