2020 Theses Doctoral

Multivariate Optical Wavefronts Generated by Dielectric Metasurfaces

Overvig, Adam Christopher

Diffractive optical elements (DOEs) are thin, light-weight devices capable of shaping light both spatially and spectrally. Classical light is a multivariate vector field: at each wavelength and at each point in space, it is characterized an amplitude and phase for two orthogonal polarizations. “Metasurfaces” are a class of DOEs composed of subwavelength structures engineered to alter a featureless wavefront into a custom wavefront; a multivariate metasurface may control several parameters simultaneously and independently. If limited to low-loss dielectric materials, metasurfaces promise functionalities and efficiencies unparalleled in other DOEs, and are manufacturable by mature micro- and nanofabrication methods.

Here, we expand the capabilities of metasurfaces to generate multivariate wavefronts. By engineering both the phase and the phase dispersion, we experimentally demonstrate metasurfaces focusing light to a single point independently of wavelength or polarization. By tuning the structural birefringence and in-plane orientation angle of rectangular nanostructures, we experimentally demonstrate arbitrary control of both phase and amplitude, enabling holography as it was originally envisioned. By maximizing the in-plane Bragg scattering of a Photonic Crystal Slab, and then successively adding symmetry-breaking perturbations to the otherwise perfect lattice, we may control angular dependence, optical lifetime, and polarization dependence of up to four optical resonances simultaneously and independently (which we study using Group Theory and fullwave simulations). By spatially varying the perturbations, the wavefronts at the resonance frequencies may be spatially tailored while the non-resonant frequencies are unaffected, promising DOEs uniquely suitable for augmented reality applications.