Inverse-Designed Volumetric Metaoptics for Multifunctional Nanophotonics

Author: Foo, Ian M.

Year: 2027

Degree: Dissertation (Ph.D.)

Advisor: Faraon, Andrei

Committee Members: Vahala, Kerry J.; Scherer, Axel; Atwater, Harry Albert; Faraon, Andrei

Option: Applied Physics

DOI: 10.7907/tyr2-fe77

Abstract

Optical metasurfaces have emerged as a powerful platform for compact, multifunctional light control, but the finite propagation length available within a single-layer metasurface fundamentally limits simultaneous and efficient control over multiple degrees of freedom such as phase, dispersion, polarization, and angular response. Multilayer and volumetric metaoptics overcome these limits through the use of multiple patterned surfaces or a full three-dimensional structured volume at the cost of a greatly enlarged design space and substantially increased fabrication complexity.

We develop an adjoint-based framework for fabrication-aware inverse design of volumetric permittivity distributions and apply it to design and experimentally demonstrate simultaneous control of polarization and dispersion in broadband metaoptic beam-splitters. We also characterize the performance of volumetric metaoptic Bayer-type spectral sorters under realistic fabrication constraints and address the challenges of operating these in sensor arrays under non-collimated illumination. Metaoptic spectral sorters in the mid-infrared are experimentally demonstrated using TiO2 nanopillars in-scaffold to approximate a gradient refractive index. Separately, we realize ten-layer metaoptic color sorters in the visible wavelength regime using a novel Sb2S3 fabrication platform. The results presented here establish an experimental foundation for volumetric metaoptic devices capable of multifunctional control with high efficiency under practical fabrication constraints.

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