Semiconducting nanostructures are promising as components in high performance metasurfaces. We show that single crystal silicon can be used to realize efficient metasurface devices across the entire visible spectrum, ranging from 480 to 700 nanometers. Alternative forms of silicon, such as polycrystalline and amorphous silicon, suffer from higher absorption losses and do not yield efficient metasurfaces across this wavelength range. To demonstrate, we theoretically and experimentally characterize the resonant scattering peaks of individual single crystal silicon nanoridges. In addition, we design high efficiency meta-gratings and lenses based on nanoridge arrays, operating at visible wavelengths, using a stochastic optimization approach. We find that at wavelengths where single crystal silicon is effectively lossless, devices based on high aspect ratio nanostructures are optimal. These devices possess efficiencies similar to those made of titanium oxide, which is an established material for high efficiency visible wavelength metasurfaces. At blue wavelengths, where single crystal silicon exhibits absorption losses, optimal devices are instead based on coupled low aspect ratio resonant nanostructures and are able to provide reasonably high efficiencies. We envision that crystalline silicon metasurfaces will enable compact optical systems spanning the full visible spectrum.
Jonathan A. Fan, Jianji Yang, David Sell, Sage Doshay, and Kai Zhang, "Silicon-based visible light meta-devices (Conference Presentation)," Proc. SPIE 10113, High Contrast Metastructures VI, 101130J (Presented at SPIE OPTO: February 01, 2017; Published: 28 April 2017); https://doi.org/10.1117/12.2255825.5395679939001.
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