Theses Doctoral

Nonlocal Metasurfaces for Active and Multifunctional Wavefront Shaping

Malek, Stephanie Claudia

Metasurfaces are nanostructured interfaces capable of manipulating the phase, amplitude, or polarization of free-space light. ‘Local’ metasurfaces typically control the wavefront shape of spectrally broadband light to generate devices such as flat lenses, holograms, and beam steerers. In contrast, ‘nonlocal’ metasurfaces, such as photonic crystals, support spatially-extended optical modes that govern the transmission or reflection spectrum. Therefore, local metasurfaces typically offer spatial control over incident light but not spectral control, while nonlocal metasurfaces impose spectral but not spatial control. This thesis explores nonlocal dielectric metasurfaces with simultaneous spatial and spectral control such that they shape the wavefront only for spectrally narrowband resonant modes but act like an unpatterned substrate for non-resonant light. These devices are formulated from a rational design scheme based on symmetry arguments. Chapter 1 reviews the theoretical basis for these devices.

Chapters 2 and 3 discuss experimental demonstrations of nonlocal wavefront-shaping metasurfaces in the near-infrared and visible wavelength regions, respectively. Our initial experimental demonstrations in the near-infrared in silicon metasurfaces were the first verification of their theoretical proposal. In the visible, experimental results of metasurfaces made of silicon-rich silicon nitride suggest potential applications in transparent displays, augmented reality headsets, and quantum optics. Significantly, our nonlocal metasurfaces form a versatile platform for multifunctional and multicolor meta-optics that shape the wavefront distinctively at several different resonant wavelengths, which we have experimentally demonstrated in both the near-infrared and the visible.

Chapters 4 and 5 discuss conceptualization and experimentally demonstration of thermally-tunable nonlocal wavefront-shaping metasurfaces. Reconfigurable photonic devices such as zoom lenses and dynamic holograms have posed a substantial challenge and captured the interest of the optics community. We leverage the enhanced light-matter interaction in our nonlocal wavefront-shaping metasurfaces to realize tunable wavefront-shaping using conventional dielectric materials and standard nanofabrication procedures. The operating principle of these devices is that tuning the refractive index of the device with the thermo-optic effect can align or detune the resonant wavelength of a mode from the wavelength of a narrowband incident light source, and the wavefront is shaped only when the optical resonance is spectrally aligned with the incident light. Experimentally, we have demonstrated nonlocal metasurfaces based on structured germanium thin films whose functionality can be thermally switched between that of two different lenses. The thesis is concluded with a section on future prospects.


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More About This Work

Academic Units
Materials Science and Engineering
Thesis Advisors
Yu, Nanfang
Ph.D., Columbia University
Published Here
July 26, 2023