Artificial metasurfaces are capable of completely manipulating the phase,amplitude, and polarization of light with high spatial resolutions. Theemerging design based on high-index and low-loss dielectrics has led to therealization of novel metasurfaces with high transmissions, but these devicesusually operate at the limited bandwidth, and are sensitive to the incidentpolarization. Here, for the first time we report experimentally thepolarization-independent and high-efficiency dielectric metasurfaces spanningthe visible wavelengths about 200 nm, which are of importance for novel flatoptical devices operating over a broad spectrum. The diffraction efficienciesof the gradient metasurfaces consisting of the multi-fold symmetricnano-crystalline silicon nanopillars are up to 93% at 670 nm, and exceed 75% atthe wavelengths from 600 to 800 nm for the two orthogonally polarizedincidences. These dielectric metasurfaces hold great potential to replaceprisms, lenses and other conventional optical elements.
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