Reconfigurable photonic metamaterials

Abstract

This thesis reports on the development of a new class of switchable nanostructured photonic metamaterials, Reconfigurable Photonic Metamaterials (RPMs). Over the last decade, fascinating material properties including negative refraction, optical magnetism, invisibility, asymmetric transmission, perfect lenses and many more were demonstrated in metamaterials. Inspired by pioneering work on micro-electro mechanical metamaterials for the terahertz and microwave spectral regions with feature sizes from millimeters to tens and hundreds microns, I develop reconfigurable photonic metamaterials for the optical spectral range that have sub-micron meta molecules and nanoscale design features.In particular, for the first time I developed:

Novel fabrication processes for manufacturing reconfigurable photonic metamaterials based on the platform of elastic silicon nitride membranes using focused ion beam lithography, film deposition, precise alignment, etching and annealing techniques. These fabrication techniques have allowed the manufacturing of a wide range of reconfigurable metamaterials consisting of bi-layer (gold/silicon nitride) or tri-layer (gold/silicon nitride/gold) structured membranes suitable for applications as plasmonic RPMs.

Novel RPMs tunable by ambient temperature that operate in the optical and near infrared parts of the spectrum. With such metamaterials exploiting the change in plasmonic response due to differential thermal expansion in bimorph nanostructures I have demonstrated 50% changes in optical transmission at the wavelength of 1735 nm when the temperature is ramped from 76 K to 270 K.

Novel RPMs operating in the near-infrared part of the spectrum that can be controlled by electric signals. These types of metamaterials harness electrostatic forces on the nanoscale and offer up to 20 MHz modulation bandwidth. At a threshold level of stimulation these metamaterials exhibit non-volatile switching with up to 250% transmission change. As a part of this research I developed a characterization technique that allows imaging and recording of the electrostatic switching under a scanning electron microscope.

Novel optically controlled RPMs exploiting near-field optical forces induced by light and optical heating for reconfiguration. Such metamaterials show a new type of optomechanical nonlinearity leading to intensity-dependent transmission that exceeds the cubic nonlinearity of GaAs by seven orders of magnitude. Using CW diode lasers operating at telecommunication wavelengths of 1.3 µm and 1.55 µm I have demonstrated cross-wavelength optical modulation with amplitude of about 1 % that can be achieved at only about 1 mW of average power of the control beam. I also developed the numerical analysis of thermo-opto-mechanical properties of the structures and calculated eigenmodes and cooling constants of the RPMs under modulated laser irradiation.

Overall, the development of reconfigurable photonic metamaterials provides a new and flexible platform for the control of metamaterial properties "on demand". Such metamaterials can find applications in sensors, tunable spectral filters, switches, modulators, programmable transformation optics devices and any other application where tunable optical properties are required.

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Identifiers

ORCID for Jun-Yu Ou: orcid.org/0000-0001-8028-6130

ORCID for E. Plum: orcid.org/0000-0002-1552-1840

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