Computational nanooptics in hyperbolic metamaterials and plasmonic structures

This dissertation concerns several problems in the fields of light interaction with nanostructured media, metamaterials, and plasmonics. We present a technique capable of extending operational bandwidth of hyperbolic metamaterials based on interleaved highly-doped InGaAs and undoped AlInAs multilayer stacks. The experimental results confirm theoretical predictions, exhibiting broadband negative refraction response in mid-infrared frequency. We propose a new class of nanofocusing structures, named hypergrating, combining hyperbolic metamaterials with Fresnel optics, able to achieve extremely subwavelength focal spots (up to 50 times smaller than free-space wavelength) in the far field of the input interface. Several experimental realizations of hypergratings for visible and infrared frequencies are presented. We further develop a new technique capable of imaging subwavelength objects with far-field measurements. The approach utilizes a diffraction grating, placed at the object plane, to convert subwavelength information of objects into propagating waves and project this information into far-field. The set of far-field measurements is used to deconvolute the images. The resolution of the proposed method can surpass 1/20-th of the free-space limit, strongly overperforming other subwavelength imaging technology. We develop a new mode matching approach for analysis of scattering and propagation of surface and volume modes in multiple multilayered-stack structures. Our theory relies on the complete spectrum of free-space and guided electromagnetic modes to solve Maxwell's equations in the extended systems that have relatively few interfaces. We demonstrate the convergence of this technique on a number of plasmonic and metamaterial structures. Finally, we consider the problem of plasmonic beam-steering structures consisting of a single slit flanked by a periodic set of metallic corrugations. We show that the light emitted by the structures forms a prolonged focal range that may extend for hundreds of wavelength from the plasmonic interface and eventually splits into two plasmonic beams. We develop a quantitative theory to physically describe the beam formations and evolution of field pattern. The numerical and analytical results presented here can be applied to several nanooptics applications including deep-subwavelength imaging, nanolithography, on-chip communications, high-density energy focusing, and beaming devices, and can be used for metamaterial and plasmonic composites operating across ultraviolet, visible, infrared, or terahertz spectra

Mode patterns in quadrupole resonator with anisotropic core

This thesis deals with applications of uniaxial anisotropic crystals for microcavity resonators with partially chaotic underlying ray dynamics. We develop an implementation of the scattering matrix formalism, and relate the eigenvalues and eigenvectors of the scattering matrix to the field distribution of inside the system. Using the developed technique, we analyze the evolution of spatial structure of modes as functions of dielectric permittivities and shape of the resonator boundary. Numerical errors emanating are identified and discussed. The applications of this work lie in polarization control, negative refraction, and other optical phenomena

Plasmons in electrostatically doped graphene

Graphene has raised high expectations as a low-loss plasmonic material in which the plasmon properties can be controlled via electrostatic doping. Here, we analyze realistic configurations, which produce inhomogeneous doping, in contrast to what has been so far assumed in the study of plasmons in nanostructured graphene. Specifically, we investigate backgated ribbons, co-planar ribbon pairs placed at opposite potentials, and individual ribbons subject to a uniform electric field. Plasmons in backgated ribbons and ribbon pairs are similar to those of uniformly doped ribbons, provided the Fermi energy is appropriately scaled to compensate for finite-size effects such as the divergence of the carrier density at the edges. In contrast, the plasmons of a ribbon exposed to a uniform field exhibit distinct dispersion and spatial profiles that considerably differ from uniformly doped ribbons. Our results provide a road map to understand graphene plasmons under realistic electrostatic doping conditions.Comment: 9 pages, 9 figure

Total light absorption in graphene

We demonstrate that 100% light absorption can take place in a single patterned sheet of doped graphene. General analysis shows that a planar array of small lossy particles exhibits full absorption under critical-coupling conditions provided the cross section of each individual particle is comparable to the area of the lattice unit-cell. Specifically, arrays of doped graphene nanodisks display full absorption when supported on a substrate under total internal reflection, and also when lying on a dielectric layer coating a metal. Our results are relevant for infrared light detectors and sources, which can be made tunable via electrostatic doping of graphene.Comment: 4 figure

Quasi-planar optics: computing light propagation and scattering in planar waveguide arrays

We analyze wave propagation in coupled planar waveguides, pointing specific attention to modal cross-talk and out-of-plane scattering in quasi-planar photonics. An algorithm capable of accurate numerical computation of wave coupling in arrays of planar structures is developed and illustrated on several examples of plasmonic and volumetric waveguides. An analytical approach to reduce or completely eliminate scattering and modal cross-talk in planar waveguides with anisotropic materials is also presented

Graphene Plasmonics

Plasmons in doped graphene provide an ideal platform for strong light‐matter interaction, perfect light absorption in an atomically thin layer, and ultra‐large field enhancement, well beyond conventional plasmonics, and tunable through electrostatic doping

Graphene Plasmon Waveguiding and Hybridization in Individual and Paired Nanoribbons

Plasmons in doped graphene exhibit relatively large confinement and long lifetime compared to noble-metal plasmons. Here, we study the propagation properties of plasmons guided along individual and interacting graphene nanoribbons. Besides their tunability via electrostatic gating, an additional handle to control these excitations is provided by the dielectric environment and the relative arrangement of the interacting waveguides. Plasmon interaction and hybridization in pairs of neighboring aligned ribbons are shown to be strong enough to produce dramatic modifications in the plasmon field profiles. We introduce a universal scaling law that considerably simplifies the analysis an understanding of these plasmons. Our work provides the building blocks to construct graphene plasmon circuits for future compact plasmon devices with potential application to optical signal processing, infrared sensing, and quantum information technology

The magnetic response of graphene split-ring metamaterials

We report an experimental realization of a visible range planar diffraction grating, formed by sub-wavelength elements, with periodically variable parameters. At normal incidence the grating exhibits asymmetric diffraction into the positive and negative first diffraction orders and operates at visible wavelengths with peak efficiency at 736 nm wavelength