Combined metagratings for efficient broad-angle scattering metasurface

Spectrally controlled diffusion and reflection of light are key operations for light management in many optical devices. Integration of this operation in complex nanophotonic devices requires a 2D interface that provides tailored spectrum and directivity control. Here, we present a metagrating superstructure that realizes a resonant light reflector with tailored angular scattering profile. Millimeter-sized metasurfaces are built from arrays of combined supercells of 20-50 μm, composed of 5-7 differently pitched metagratings that tailor at will and with large efficiency the angular response. Each supercell is composed of one or more Si Mie resonators, arranged in a periodic array above a Ag back plane and tailored to resonantly scatter light at 650 nm into only the ±1 diffraction orders with very high efficiency. By varying the pitch and supercell design, we can tailor the overall metasurface reflection profile with large flexibility, realizing a broad-angle Lambertian-type scattering metasurface, as well as a large-angle (35-75°) scattering metasurface, both with resonant optical scattering efficiencies above 70%. These ultra-thin structures, fabricated using thin-film deposition, electron beam lithography and reactive ion etching, can find applications for light trapping and spectrum splitting in solar cells and other devices.

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