Analysis and Experiment of Equilateral Triangular Uniaxial-Anisotropic Dielectric Resonator Antennas

The design procedure of a uniaxial anisotropic equilateral triangular dielectric resonator antenna (ETDRA) is presented for the first time. The uniaxial material is realized by a periodic stack of sheets of two dissimilar materials with different dielectric constants. It is proven that the increase of the boresight gain and impedance bandwidth of the ETDRA is possible by using the uniaxial material for the antenna prism. The gain improvement is due to the increase in the sidewall radiations and the bandwidth enhancement is owing to the lowering of the effective permittivity of the structure. The fabricated anisotropic ETDRA offers an impedance bandwidth of 27.7% between 3.025 and 4 GHz with a measured gain above 8 dB. The simulation results agree well with the experimental ones

Parametric Optimization of Visible Wavelength Gold Lattice Geometries for Improved Plasmon-Enhanced Fluorescence Spectroscopy

The exploitation of spectro-plasmonics will allow for innovations in optical instrumentation development and the realization of more efficient optical biodetection components. Biosensors have been shown to improve the overall quality of life through real-time detection of various antibody-antigen reactions, biomarkers, infectious diseases, pathogens, toxins, viruses, etc. has led to increased interest in the research and development of these devices. Further advancements in modern biosensor development will be realized through novel electrochemical, electromechanical, bioelectrical, and/or optical transduction methods aimed at reducing the size, cost, and limit of detection (LOD) of these sensor systems. One such method of optical transduction involves the exploitation of the plasmonic resonance of noble metal nanostructures. This thesis presents the optimization of the electric (E) field enhancement granted from localized surface plasmon resonance (LSPR) via parametric variation of periodic gold lattice geometries using finite difference time domain (FDTD) software. Comprehensive analyses of cylindrical, square, star, and triangular lattice feature geometries were performed to determine the largest surface E-field enhancement resulting from LSPR for reducing the LOD of plasmon-enhanced fluorescence (PEF). The design of an optical transducer engineered to yield peak E-field enhancement and, therefore, peak excitation enhancement of fluorescent labels would enable for improved emission enhancement of these labels. The methodology presented in this thesis details the optimization of plasmonic lattice geometries for improving current visible wavelength fluorescence spectroscopy

Antennas and Propagation

This Special Issue gathers topics of utmost interest in the field of antennas and propagation, such as: new directions and challenges in antenna design and propagation; innovative antenna technologies for space applications; metamaterial, metasurface and other periodic structures; antennas for 5G; electromagnetic field measurements and remote sensing applications

Efficient PML boundaries for anisotropic waveguide simulations using the finite element method

The application of integrated optics has broadened from well established areas, such as high-speed modulators for communication over optical fibre, to such diverse areas as radio frequency (RF) signal processing and antenna beam forming. Simulation tools that are general enough to model a wide range of RF and photonic devices, yet efficient enough to be used trivially are required. The aim of this thesis is to investigate the use of the perfectly matched layer (PML) boundary condition as a means of improving the efficiency of eigenvalue simulations, and to extend their range of applicability to radiating waveguides. This work focuses in particular on the simulation of waveguides using the biaxial material Lithium Niobate. Major contributions made by this work include the derivation of a generalised PML suitable for matching biaxial materials, extension of analysis of numerical dispersion and reflection in the finite element method to biaxial media and derivation of closed form expressions for the numerical reflection from a PML interface. These expressions are used to investigate the major contributions to numerical errors in the implementation of the PML boundary and hence a significantly more efficient technique for enhancing the PML's performance with a minimal increase in unknowns is suggested and demonstrated in a practical simulation. Finally, the generalised PML is applied to three eigenvalue simulations, including a radiating waveguide bend, with greatly improved efficiency and accurate simulation of propagation loss. In summary, the PML has been extended to biaxial materials and the sources of numerical errors in its implementation have been identified and an efficient means of reducing them devised. The new PML and implementation technique have been demonstrated in eigenvalue simulations of both lossless and lossy waveguides with accurate and efficient results being achieved

Simulation of continuous-wave solid-state laser resonators using field tracing and a fully vectorial fox-li algorithm

In this PHD thesis the scalar Fox and Li algorithm for the dominant transversal resonator eigenmode calculation is generalized to a fully vectorial field tracing concept. Therefore Fox and Li’s scalar integral equation is reformulated to a set of coupled operator equations. The introduction of a field tracing round trip operator concept shows that, in principle, any modeling technique which can be formulated to operate for electromagnetic fields can be used to simulate light propagation through the different subdomains of the resonator. This allows a flexible, fast, and accurate simulation of the fully vectorial dominant transversal resonator eigenmode. Several examples are presented to demonstrate the flexibility and accuracy of the field tracing approach

Giving Metamaterials a Hand

The focus of this thesis is the interaction of electromagnetic fields with chiral structures in the microwave regime. Through this study, which focuses on three regimes of electromagnetic interactions, I aim to develop a deeper understanding of the consequences and manifestations of chiral interactions The structures are on the order of, or smaller than, the wavelength of the probing radiation. As the structures are chiral, they have broken inversion symmetry, and exist in two states where one is the mirror image of the other. The results in this thesis can have impacts on future optical communications technologies and methods of sensing biological molecules. To begin with, the manipulation of the circular polarisation of a propagating beam by bilayer chiral metasurfaces is investigated. The metasurfaces consist of two layers of stacked crosses with a twist between top and bottom layers, forming chiral metamolecules. A broad frequency region of dispersionless polarisation rotation appears between two resonances, due to alignment between electric and magnetic dipoles. The dependence of this effect on the layer separation is studied for two similar metasurfaces. Evanescent chiral electromagnetic fields are the focus of the next chapter. An array of chiral antennas produces chiral near-fields at their resonant frequency. Aligned and subwavelength helices placed within this field interact differently depending on the handedness of the field with respect to the handedness of the helices. This difference in interaction strength is measured for the helices and an effective medium model where multipolar interactions are forbidden. Comparison of these two systems leads to the conclusion that the contribution to a chiral interaction from multipolar modes is minimal, in contrast to previous publications. The third study concentrates on the electromagnetic wave bound to an "infinitely long" metal helix. The helix has infinite-fold screw symmetry, and this leads to interesting features in the energy-dispersion of the waves it supports. The broad frequency range of high, tunable, dispersionless index is interpreted using a geometrical approach, and the factors that limit the bandwidth explained. A modified geometry is suggested for increased bandwidth. The final part of the thesis is dedicated to future work, based on the results presented thus far. Three suggestions for future study are presented, including chiroptical signals from higher-order chiral arrangements, the effect of reflecting surfaces next to chiral objects and the possible use of orbital angular momentum for chiroptical measurements.Engineering and Physical Sciences Research Council (EPSRC

Topological Photonics

Topological photonics is a rapidly emerging field of research in which geometrical and topological ideas are exploited to design and control the behavior of light. Drawing inspiration from the discovery of the quantum Hall effects and topological insulators in condensed matter, recent advances have shown how to engineer analogous effects also for photons, leading to remarkable phenomena such as the robust unidirectional propagation of light, which hold great promise for applications. Thanks to the flexibility and diversity of photonics systems, this field is also opening up new opportunities to realize exotic topological models and to probe and exploit topological effects in new ways. This article reviews experimental and theoretical developments in topological photonics across a wide range of experimental platforms, including photonic crystals, waveguides, metamaterials, cavities, optomechanics, silicon photonics, and circuit QED. A discussion of how changing the dimensionality and symmetries of photonics systems has allowed for the realization of different topological phases is offered, and progress in understanding the interplay of topology with non-Hermitian effects, such as dissipation, is reviewed. As an exciting perspective, topological photonics can be combined with optical nonlinearities, leading toward new collective phenomena and novel strongly correlated states of light, such as an analog of the fractional quantum Hall effect.Comment: 87 pages, 30 figures, published versio

High Resolution Electron Energy Loss Spectroscopy of Plasmonic Nanostructures

This dissertation discusses developing fabrication techniques to study the plasmonic phenomena of nanostructures utilizing high spatial and energy resolution of monochromated aberration-corrected scanning transmission electron. While standard lithography has been widely used to create planar nanostructures, investigation into 3-dimensional nanostructures is lacking. A robust synthesis approach utilizing focused electron beam induced deposition, atomic layer deposition, and thin film sputter deposition to fabricate complex 3D plasmonic architectures is described and characterization of single nanoresonators is presented. Additionally, this dissertation discusses the use of high-resolution electron energy loss spectroscopy to investigate the hybridization of gold nanorod oligomers. Experiment and simulation resolve magnetic and electric dipole resonances in the cyclic assemblies. Finally, the hybridization of split ring resonators is discussed. Both planar and 3D SRR arrangements are investigated to reveal the coupling dynamics in the systems

Structural, Magnetic, Dielectric, Electrical, Optical and Thermal Properties of Nanocrystalline Materials: Synthesis, Characterization and Application

This book is a collection of the research articles and review article, published in special issue "Structural, Magnetic, Dielectric, Electrical, Optical and Thermal Properties of Nanocrystalline Materials: Synthesis, Characterization and Application"