Investigation of Chiral Metamaterial Characteristics Under Dielectric Losses with Applications to Thin Film Resonator Arrays
Date of Award
12-12-2024
Degree Name
Ph.D. in Electrical and Computer Engineering
Department
Department of Electrical and Computer Engineering
Advisor/Chair
Monish Chatterjee
Abstract
This dissertation investigates p-polarized electromagnetic (EM) wave propagation through chiral metamaterials using Fresnel coefficients (FCs), examining thereby such characteristics as possible emergence or mitigation of Brewster phenomena, total internal reflection (TIR) or the more unusual inverse TIR (ITIR) effect at a chiral-achiral (CAC) boundary, and the behavior of chiral Fabry-Perot type slabs (especially in the thin film limit) with particular attention to their resonance characteristics. Chiral materials belong among the broader group of metamaterials known for their ability to interact with polarized light, leading to bimodal propagation of right- and left-circularly polarized (RCP and LCP) states with interesting and potentially useful optical properties. In this dissertation, the propagation of a parallel (p-) polarized plane wave across an achiral/chiral (ACC) interface is investigated under different material index assumptions (rarer to denser (R→D) and denser to rarer (D→R) configurations). Subsequently, a chiral/achiral (CAC) interface was investigated using the transmitted circularly polarized waves out of the first interface as incident waves for the second interface. Multiple optical phenomena have been found to be tunable and/or controllable by adjusting the material parameters such as dimensionless chirality factor, medium index, and/or material thickness. These optical phenomena include Brewster effect, TIR and ITIR, evanescence and tunable critical angles. Since chiral materials are inherently lossy material, following an initially lossless analysis with some related results, the problem was extended to include dielectric losses (defined via the imaginary part of the complex chiral dielectric permittivity). With dielectric losses present, it turns out that the EM boundary conditions with complex material parameters and the related phase matching led to entirely modified algebraic results (several of which, as with the lossless cases) are considerably complicated. A modified Snell’s law is derived under loss which carries information based on both the real and imaginary parts of the complex permittivity and thereby the reflected and transmitted phasor fields are derived indicating multiple loss conditions (dielectric- and evanescence-based). Investigating the propagation across an ACC and CAC lead to investigating the chiral slab resonator by combining both interfaces. Chiral slabs were examined under many assumptions of different chirality factors, slab thickness and/or frequency operating bands. Chiral slabs could be examined further under very thin thickness (100 to 10 nm) which is the thickness of the thin films. Investigating a thin film resonator in the presence of chirality is analytically challenging. Thin film devices may be designed so that the electromagnetic fields are strongly confined within a small region and work with applications in fields ranging from molecular sensing and high-gain antennas to optical filters and smart solar cell grids. In this dissertation, we study the mode distribution and spectral characteristics of chiral thin films under p-polarized propagation. We examine Fabry-Perot type thin film resonators in different frequency bands (the visible and near-infrared) to show that chirality may offer tunability and improvements to the optical properties of thin film resonators including higher transmitted power over wider (or narrower) spectral bands for real-life applications. More recently in the investigations, thin film resonator array configurations have been examined for the total composite response of the arrays under p-polarized wave propagation. The studies have involved regular polygonal arrays and also a horizontal array of symmetrically spaced thin film resonators. These arrays of chiral thin film resonators are aligned in polygonal and linear geometries and illuminated by a linear, p-polarized plane wave incident normally on each thin film resonator. Each resonator is analyzed using standard numerical simulation of chiral thin film slabs analyses, evaluating the corresponding mode spectra for the right- (RCP) and left-circular (LCP) modes for variable chirality coefficients, film thickness and substrate placement conditions as a function of the (monochromatic) mode frequency. To determine the effect of superposing peak modal responses at a single spatial point (chosen as the center/centroid of the polygonal array and a point along the vertical axis relative to the center of the horizontal resonator array). It is interesting that due to spatial phase differences, the field vectors superposed at the centroid yield non-zero, complex phasor interference patterns controlled by the phases. Earlier work with polygonal arrays had involved the use of photodetectors resulting in intensity-dependent photocurrents added at the centroid, resulting in a scalar summation of the transmitted intensities. The updated approach dispenses with the photodetectors and uses vector superposition of the transmitted fields from each resonator. For the horizontal resonator array, the transmitted fields resulting from a single collimated p-polarized incident illumination are deflected towards the point of superposition using mechanically controlled mirrors as deflectors. The resulting spectral behavior of (2n+1) resonator outputs (thereby finding wideband, narrowband, and also band-reject regimes within specific modes) superposed at a vertical point is studied in some detail (the work is ongoing) under different chirality coefficients, resonator thickness and resonator length.
Keywords
Electrical Engineering
Rights Statement
Copyright © 2024, author.
Recommended Citation
Muntaser, Akram, "Investigation of Chiral Metamaterial Characteristics Under Dielectric Losses with Applications to Thin Film Resonator Arrays" (2024). Graduate Theses and Dissertations. 7481.
https://ecommons.udayton.edu/graduate_theses/7481
