Hafez Hemmati

ORCID Identifier(s)

0000-0002-0270-1287

Graduation Semester and Year

2020

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Materials Science and Engineering

Department

Materials Science and Engineering

First Advisor

Yaowu Hao

Abstract

Since the emergence of diffraction gratings containing periodic unit cells, innumerable advances in theoretical studies and practical applications have emerged. Recently, these classic structures have been categorized as subsets of “meta-surfaces” or “meta-materials” in which periodically aligned wavelength-scale features manipulate all key properties of the electromagnetic waves in a desired manner for a wide variety of applications. This includes manipulating of amplitude, phase, spectral distribution, polarization state, and local mode structure of light in the various available spectral expressions. Among the significant characteristic properties of metasurfaces is the coupling of incident light to laterally propagating leaky Bloch modes in the subwavelength regime when the periodicity of the unit cell is moderately smaller than the free-space wavelength. This property, which manifests itself as a resonance at certain wavelengths, is called “guided mode resonance (GMR)” or “leaky mode resonance (LMR)”. These structures offer novel properties and functionalities in ultra-thin device dimensions which make them potential replacements for conventional and bulky optical devices. Extensive studies have been conducted to realize the periodic structures in different materials (metals, dielectric, and semiconductors or their hybrid compositions) employing various fabrication methods for different wavelength ranges in 1D or 2D configuration. Thus, on account of the wide variety of material compositions and lattice architectures, the design space is vast. Various numerical techniques such as rigorous coupled-wave analysis (RCWA), finite element method (FEM), and finite-difference time-domain (FDTD) can be used to implement simulations and obtain the precise optical responses of the metasurfaces. In addition, inverse optimization methods, efficiently provide optimized physical parameters in order to obtain a particular desired spectral response. However, these computational methods which are based on solving heavy and complicated equations and do not always provide comprehensive insight into underlying physics of the numerically obtained optical spectra. In this dissertation, we present a comprehensive physical description of resonant metasurfaces based on exact solutions of the Rytov formulation. We define a clear transition wavelength between the resonance subwavelength region and the deep-subwavelength region. This transition point, analytical in a special case, is not available presently in the literature. In addition, we design, fabricate, and characterize various novel GMR-based optical devices such as metamaterial polarizers, nanoimprinted nanocomposite filters, multipart unit-cell metasurfaces, ultrahigh-Q resonant dual-grating metamembranes, and fiber-facet integrated optical filters and sensors.

Keywords

Nanophotonics, Metasurfaces, Guided-mode resonances, Photolithography, Polarizers, Sensors, Bound states in the continuum, Optical fibers, Nanocomposites

Disciplines

Engineering | Materials Science and Engineering

Comments

Degree granted by The University of Texas at Arlington

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