Low-Contrast Dielectric Metasurface Optics

The miniaturization of current image sensors is largely limited by the volume of the optical elements. Using a subwavelength-patterned quasi-periodic structure, also known as a metasurface, one can build planar optical elements based on the principle of diffraction. Recent demonstrations of high quality metasurface optical elements are mostly based on high refractive-index materials. Here, we present a design of low contrast metasurface-based optical elements. We fabricate and experimentally characterize several silicon nitride-based lenses and vortex beam generators. The fabricated lenses achieved beam spots of less than 1 pm with numerical apertures as high as similar to 0.7S. We observed a transmission efficiency of 90% and focusing efficiency of 40% in the visible regime. Our results pave the way toward building low-loss metasurface-based optical elements at visible frequencies using low-contrast materials and extend the range of prospective material systems for metasurface optics.