1、Low-Contrast Dielectric Metasurface OpticsAlan Zhan,Shane Colburn,Rahul Trivedi,Taylor K.Fryett,Christopher M.Dodson,and Arka Majumdar*,Department of Physics andDepartment of Electrical Engineering,University of Washington,Seattle,Washington 98122,UnitedStatesDepartment of Electrical Engineering,Ind

2、ian Institute of Technology,Delhi 110016,India*SSupporting InformationABSTRACT:The miniaturization of current image sensors islargely limited by the volume of the optical elements.Using asubwavelength-patterned quasi-periodic structure,also knownas a metasurface,one can build planar optical elements

3、 basedon 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 andexperimentally characterize several silicon nitride

4、-based lensesand vortex beam generators.The fabricated lenses achievedbeam spots of less than 1 m with numerical apertures as highas 0.75.We observed a transmission efficiency of 90%and focusing efficiency of 40%in the visible regime.Our results pave theway toward building low-loss metasurface-based

5、 optical elements at visible frequencies using low-contrast materials and extendthe range of prospective material systems for metasurface optics.KEYWORDS:diffractive optics,dielectric metasurface,silicon nitride photonics,lens,vortex beam generatorConventional transmissive macroscopic optical elemen

6、tsprimarily depend on refraction to control lightpropagation.Refraction relies heavily upon the exact curvatureof the surface and the spatial extent of the element in order toachieve gradual phase accumulation.This imposes a funda-mental limitation on the miniaturization of optical sensors andelemen