Journal
NANO LETTERS
Volume 15, Issue 3, Pages 1615-1621Publisher
AMER CHEMICAL SOC
DOI: 10.1021/nl5041572
Keywords
Metamaterials; plasmonics; gradient metasurface; broadband; anomalous reflection; surface plasmon
Categories
Funding
- AFOSR [FA9550-12-1-0280]
- McCormick School of Engineering and Applied Sciences at Northwestern University
- Institute for Sustainability and Energy at Northwestern (ISEN) through ISEN
- Materials Research Science and Engineering Center (NSF-MRSEC) of Northwestern University [DMR-1121262]
- NSF-NSEC
- NSF-MRSEC
- Keck Foundation
- State of Illinois
- NUFAB deanroom facility at Northwestern University
- U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-AC02-06CH11357]
- Ryan Fellowship
- Northwestern University International Institute for Nanotechnology
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Ultrathin metasurfaces have recently emerged as promising materials that have huge potential to enable novel, flat optical components, and surface-confined, miniature photonic devices. Metasurfaces offer new degrees of freedom in molding the optical wavefronts by introducing abrupt and drastic changes in the amplitude, phase, and/or polarization of electromagnetic radiation at the wavelength scale. By carefully arranging multiple subwavelength anisotropic or gradient optical resonators, metasurfaces have been shown to enable anomalous transmission, anomalous reflection, optical holograms, and spin-orbit interaction. However, experimental realization of high-performance metasurfaces that can operate at visible frequency range has been a significant challenge due to high optical losses of plasmonic materials and difficulties in fabricating several plasmonic resonators of subwavelength size with high uniformity. Here, we propose a highly efficient yet a simple metasurface design comprising of a single, anisotropic silver antenna in its unit cell. We demonstrate broadband (450-850 nm) anomalous reflection and spectrum splitting at visible and near-IR frequencies with high conversion efficiency. Average power ratio of anomalous reflection to the strongest diffraction mode was calculated to be on the order of 103 and measured to be on the order of 10. The anomalous reflected photons have been visualized using a charge-coupled device camera, and broadband spectrum splitting performance has been confirmed experimentally using a free space, angle-resolved reflection measurement setup. Metasurface design proposed in this study is a clear departure from conventional metasurfaces utilizing multiple, anisotropic and/or gradient optical resonators and could enable high-efficiency, broadband metasurfaces for achieving flat high signal-to-noise ratio optical spectrometers, polarization beam splitters, directional emitters, and spectrum splitting surfaces for photovoltaics.
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