Broadband high-efficiency dielectric metasurfaces for the visible spectrum

Significance Metasurfaces are optical elements that can mimic and expand on the functionality of refractive optics with a comparatively thin and planar profile. Transmissive metasurfaces suffer from high optical loss at visible wavelengths because of currently used materials and fabrication techniques. This work introduces metasurfaces that operate across the visible spectrum with high efficiencies. As the basis of our metasurfaces, we used a common material, titanium dioxide, and a fabrication method based an atomic layer deposition that creates highly anisotropic nanostructures. The results presented here provide an important advance for realizing optical components at visible wavelengths—e.g., lenses, holograms, and phase shifters—with orders of magnitude reduction in thickness compared with traditional refractive optics. Metasurfaces are planar optical elements that hold promise for overcoming the limitations of refractive and conventional diffractive optics. Original dielectric metasurfaces are limited to transparency windows at infrared wavelengths because of significant optical absorption and loss at visible wavelengths. Thus, it is critical that new materials and nanofabrication techniques be developed to extend dielectric metasurfaces across the visible spectrum and to enable applications such as high numerical aperture lenses, color holograms, and wearable optics. Here, we demonstrate high performance dielectric metasurfaces in the form of holograms for red, green, and blue wavelengths with record absolute efficiency (>78%). We use atomic layer deposition of amorphous titanium dioxide with surface roughness less than 1 nm and negligible optical loss. We use a process for fabricating dielectric metasurfaces that allows us to produce anisotropic, subwavelength-spaced dielectric nanostructures with shape birefringence. This process is capable of realizing any high-efficiency metasurface optical element, e.g., metalenses and axicons.