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Dielectric metasurfaces are quasi-two-dimensional nanostructured interfaces capable of spatially shaping an optical wavefront. By using only dielectric materials, the optical losses caused by metals are eliminated, but the strength of the light-matter interactions is reduced, making complete control of an optical wavefront a unique challenge. However, by careful rational design, dielectric metasurfaces may control more than one parameter simultaneously and independently, generating multivariate optical wavefronts with subwavelength spatial resolution. (1) We show that by controlling both the phase and the phase-dispersion, broadband achromatic focusing is possible within a single ultra-thin metasurface lens (called a “meta-lens”). (2) By introducing a polarization filter, anisotropic metasurfaces may control both the phase and amplitude of light simultaneously and independently, enabling “artifact-free” holograms. Adding dispersion control or a second metasurface extends this to more than one wavelength simultaneously, enabling multi-color phase-amplitude holograms. (3) We develop a design paradigm allowing simultaneous engineering of both the group velocity and radiative Quality factor by introducing symmetry-breaking into a high index contrast photonic crystal slab. The result is a device concentrating light in both space and time, greatly enhancing light-matter interactions; this enables compact optical modulators and high harmonic generation from monolithically fabricated dielectric structures.
Adam is expecting to receive his Ph.D from Columbia University in Fall of 2019, where he is advised by Professor Nanfang Yu. His anticipated dissertation is entitled “Dielectric Metasurfaces for Controlling the Complex Amplitude of Broadband and Narrowband Light,” and his research focuses on expanding the control of free-space optical wavefronts using nanostructured materials. His experimental work includes realizing the first broadband achromatic polarization-independent “metalenses”, and multi-color phase-amplitude holograms. His theoretical work has focused on developing a design paradigm for spatially and temporally confining light in symmetry-broken gratings, which was the subject he studied as a recipient of the NSF IGERT fellowship (2015-2016). Adam received his B.S. in Engineering Physics from Cornell University in 2013.