Planar optics at visible wavelengths based on titanium dioxide

We present a new platform that realizes high performance metasurfaces in the visible spectrum. This platform is based on atomic layer deposition of titanium dioxide and allows molding incident light wavefront to desired shapes including holographic images, optical vortices, and Bessel beams. The focus of this work will be on the design and demonstration of planar metalenses. We report on our recent experimental realization of high numerical aperture metalenses with efficiency as high as 86%. These metalenses can focus light into a diffraction-limited spot and can be employed for imaging purposes to provide sub-wavelength imaging resolution. In addition, by the judicious design of metalens building blocks, one can achieve a multispectral chiral metalens (MCML) within a single metasurface layer. The MCML can simultaneously resolve chiral and spectral information of an object without the requirement of additional optical components such as polarizers, wave-plates, or even gratings. Using this MCML, we map the chiroptical properties of a macroscopic chiral biological specimen across the visible range. Finally, since many applications require polarization insensitive planar lenses, we discuss the experimental realization of such metalenses with numerical apertures as high as NA=0.85. These metalenses can focus incident light to a spot as small as ~0.6lambda with efficiencies up to 70%. The straightforward and CMOS-compatible fabrication process of this platform is promising for a wide range of optics-based applications in multidisciplinary science and technology.