In recent years, metasurfaces have shown promising abilities to control and manipulate electromagnetic (EM) waves through modified surface boundary conditions. These surfaces are electrically thin and comprise an array of spatially varying sub-wavelength scattering elements (or meta-atoms). Metasurfaces can transform an incident EM wave into an arbitrarily tailored transmitted or reflected wavefront through carefully engineering each meta-atom. Recent developments in metasurfaces have opened exciting new opportunities in antenna design, sensing, and communications systems. In particular, reconfigurable metasurfaces - wherein meta-atoms are embedded with active components - lead to the development of low-cost, lightweight, and compact systems capable of producing programmable radiation patterns and jointly performing multi-function communications, and enable advanced sensors for next-generation platforms. This research introduces reconfigurable metasurfaces and their various applications in designing simplified communications systems, wherein the RF aperture and transceiver are integrated within the metasurface. Finally, we will present our recent work on reconfigurable metasurfaces control, metasurface-enabled direct signal modulation, and deep learning-based metasurface design. / Doctor of Philosophy / Metasurfaces are a promising new technology to enhance the capacity and coverage of wireless communication networks by dynamically reconfiguring the wireless propagation environment. These low-profile artificial electromagnetic surfaces, consisting of subwavelength resonant elements, are capable of tailoring electromagnetic waves controllably. In this dissertation, we control the transmission or reflection properties of the surface using digital codes by embedding tunable elements within each subwavelength element. Furthermore, metasurface antennas are a promising candidate for reducing the cost and hardware footprint of wireless sensor systems, such as radar or imaging. Using a digital microcontroller, we program the metasurface to steer the antenna beam in the direction of interest, modulate the radio wave, or change the polarization of an incoming signal. In addition to dynamic beamforming capabilities, we program the metasurface to reduce the scattering of an incoming signal, thereby reducing its perturbations on the radio environment. Still, the design of metasurfaces for specific applications remains complex and technically challenging. Lastly, we present innovative deep learning techniques to simplify metasurface design.

Metasurfaces have presented themselves as next generation optical platforms with an unprecedented capability to exert designer amplitude, phase, and polarization control on incoming electromagnetic (EM) waves. Existing works have focused on demonstrating simple optical functionalities (lensing, beam steering, holography) at longer wavelengths (microwave, infrared), and the design methodology has largely been empirical. In this work, we demonstrate next generation metasurface applications in near infrared and visible wavelengths. The purpose of such applications evolves from imaging to complex machine vision applications, and as such calls for a updated design paradigm that combines traditional, empirical based methods with modern inverse design tools based on machine learning. We expand the potential of metasurfaces by demonstrating their interdisciplinary applications in complex imaging, quantum optics and optical computation. A homebrew fabrication and testing pipeline is developed to support the challenging mission of near infrared and visible frequency usage. Furthermore, we propose a new design paradigm that combines physics informed intuitions with modern machine learning to simulate and design metasurface in an accurate and time-efficient way. In conclusion, I will discuss the outlook of metasurfaces in real-world applications, whose unique combination of performance and form factor make them ideal candidates for next-generation optical devices.

<p>Metasurfaces are broadly defined as artificially engineered material interfaces that have the ability to determinately control the amplitude and phase signatures of an incident electromagnetic wave. Subwavelength sized optical scatterers employed at the planar interface of two media, introduce abrupt modifications to impinged light characteristics. Arbitrary engineering of the optical interactions and the arrangement of the scatterers on plane, enable ultra-compact, miniaturized optical systems with a wide array of applications (e.g. nanoscale and nonlinear optics, sensing, detection, energy harvesting, information processing and so on) realizable by the metasurfaces. However, maturation from the laboratory to industry scale realistic systems remain largely elusive despite the expanding reach and vast domains of functionalities demonstrated by researchers. A large part of this multi-faceted problem stems from the practical constraints posed by the commonly used plasmonic materials that limit their applicability in devices requiring high temperature stability, robustness in varying ambient, mechanical durability, stable growth into nanoscale films, CMOS process compatibility, stable bio-compatibility, and so on. </p> <p>Aiming to create a whole-some solution, my research has focused on developing novel, high-performance, functional plasmonic metasurface devices that utilize the inherent benefits of various emerging and alternative material platforms. Among these, the two-dimensional MXenes and the refractory transition metal nitrides are of particular importance. By exploiting the plasmonic response of thin films of the titanium carbide MXene (Ti₃C₂T_x) in the near infrared spectral window, a highly broadband metamaterial absorber has been designed, fabricated and experimentally demonstrated. In another work, high efficiency photonic spin Hall Effect has been experimentally realized in robust phase gradient metasurface devices based on two different refractory transition metal nitrides –titanium nitride (TiN) and zirconium nitride (ZrN). Further, taking advantage of the refractory nature of these plasmonic nitrides, a metasurface based temperature sensor has been developed that is capable of remote, optical sensing of very high temperatures ranging up to 1200^oC.</p>

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2017-09-04T20:55:30Z No. of bitstreams: 1 FelipeFerreiraDeAraujo_DISSERT.pdf: 2900111 bytes, checksum: 315d88ae28395a6225499dd53b02e23b (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2017-09-06T22:06:44Z (GMT) No. of bitstreams: 1 FelipeFerreiraDeAraujo_DISSERT.pdf: 2900111 bytes, checksum: 315d88ae28395a6225499dd53b02e23b (MD5) / Made available in DSpace on 2017-09-06T22:06:44Z (GMT). No. of bitstreams: 1 FelipeFerreiraDeAraujo_DISSERT.pdf: 2900111 bytes, checksum: 315d88ae28395a6225499dd53b02e23b (MD5) Previous issue date: 2017-01-30 / No Brasil e no mundo, a evolu??o do setor de telecomunica??es tem sido cada vez mais requisitada como uma clara consequ?ncia do crescimento exponencial da demanda por sistemas de comunica??o sem fio. Neste cen?rio, a integra??o de m?ltiplos padr?es wireless em uma ?nica plataforma, antena reconfigur?vel, tamb?m conhecida como antena sintoniz?vel, est? atraindo muita aten??o. Estruturas metasurfaces t?m sido extensivamente utilizadas nos ?ltimos anos para alcan?ar o aperfei?oamento de antenas, dentre eles, a reconfigura??o. Uma metasuperf?cie (tamb?m referida como um metafilm) ? o equivalente de uma superf?cie metamaterial. Mais precisamente, um metafilm ? uma superf?cie com uma distribui??o de pequenos dispersores arranjados ao longo de uma regi?o do espa?o, de modo a obter comportamentos eletromagn?ticos desej?veis. Para muitas aplica??es, metasuperf?cies podem ser usadas no lugar de metamateriais, pois possuem como vantagem principal ocupar menos espa?o f?sico do que as estruturas tridimensionais dos metamateriais, oferecendo a possibilidade de perdas reduzidas, o que tem gerado grande interesse. Neste contexto, esta disserta??o de mestrado apresenta a simula??o, o projeto e a implementa??o de estruturas de antenas planares acopladas a estruturas de metasurfaces a fim de realizar reconfigura??o de antenas em frequ?ncia, polariza??o e multibanda, para aplica??es em comunica??es sem fio. A an?lise das estruturas das antenas ? realizada com o aux?lio de ferramentas computacionais. Prot?tipos s?o constru?dos e medidos, para fins de comprova??o experimental. Os resultados obtidos em medi??es e simula??es apresentam uma boa concord?ncia. / All over the world, the evolution of the technological apparatus for telecommunications systems has been increasingly required, as a clear consequence of the exponentially growth in the demand for wireless communication services. Therefore, the integration of multiple wireless standards on a single platform, like a reconfigurable antenna, also known as tunable antenna, is attracting much attention. Metasurfaces structures have been extensively used in recent years to improve the performance of planar antennas for wireless applications, including reconfiguration. A metasurface (also referred to as a metafilm) is the equivalent of a metamateriaI surface. More precisely, one metafilm is a surface with a distribution of small scatterers arranged along a region of space, to achieve desirable electromagnetic behaviors. For many applications, metasurfaces can be used in place of metamaterials because they have the advantage of taking up less physical space than the three-dimensional structures of metamaterials, offering the possibility of reduced losses, which has generated great interest. Therefore, this master thesis presents the simulation, design and implementation of planar antenna structures coupled to metasurfaces structures in order to reconfigure frequency, polarization and multiband antennas for wireless communications applications. The analysis of the antenna structures is performed with the aid of computational tools. Prototypes are fabricated and measured for experimental verification purpose. Simulations and measurements results are in good agreement.

Tato dizertční práce se zabývá výrbou a charakterizací plasmonických nanostruktur. Její první část začíná krátkým úvodem do plasmoniky s navazujícím přehledem metod, které jsou v dnešní době nejčastěji používány k výrobě a charakterizaci plasmonických nanostruktur. Druhá část se pak zaměřuje na samotný výzkum, který byl v rámci PhD studia realizován. Cílem prvních experimentů bylo prozkouat možnosti použití elektronové litografie za variabilního tlaku v procesní komoře pro výrobu plasmonických nanostruktur na nevodivých substrátech jako je např. sklo. Jelikož se jedná o materiály, které jsou velice často používány k přípravě plasmonických struktur pacujících v oblasti viditelného světla. Druhá sekce pak diskutuje některé specifické aspekty přípravy plasmonických mikrostruktur elektronovou litografií pro THz oblast. Poslední část se pak zaměřuje na funkční vlastnosti plasmonických nanostruktur, převážně pak na kvantitativní charakterizaci fáze dalekého pole indukovaného plasmonickými nanostrukturami a jejich aplikacemi v oblasti optických metapovrchů - uměle připravených povrchů, které mohou být použity jako planární optické komponenty. Práce demonstruje a diskutuje různé experimentální přístupy použití mimoosové holografické mikroskopie pro jejich charakterizaci.

Der rapide Anstieg der Bevölkerung führt zu einer dramatischen Zunahme des Brennstoff- und Energiebedarfs. Längerfristig kann die nachhaltige Energieversorgung der Menschheit nur durch erneuerbare Energiequellen gewährleistet werden. Dies motiviert die Bemühungen um alternative, sauberere Brennstofftechnologien wie z.B. die Erzeugung von Wasserstoff. Diese Arbeit untersucht die Verbesserung der optoelektronischen Eigenschaften von Silizium Photokathoden, durch optische Nanostrukturen, die die Reflexion mittels optischer Resonanzen reduzieren. Wir konzentrieren uns dabei auf die Entwicklung von Nanostrukturen , die optische Konzepte wie Mie-Resonanzen und periodische Indexprofilierung nutzen. Um diese optischen Nanostrukturen zu realisieren, verwenden wir zwei Herstellungsverfahren. Die Verfahren werden durch einen iterativen Ansatz optimiert, um zu den Nanostrukturen mit den gewünschten optischen Eigenschaften zu gelangen. Die erste Art von Nanostrukturen gehört zur Klasse der Meta-Oberflächen (Metasurfaces) und wird durch Elektronenstrahl- Lithographie und Top-Down-Herstellung implementiert. Die optischen Spektren dieser Strukturen werden dann mit Hilfe von Simulation und Experimenten eingehend untersucht. Die zweite Art von Nanostrukturen basiert auf Änderungen des Brechzahlprofils von dielektrischen periodischen Nanostrukturen. Diese Strukturen werden durch Maskenlithographie mittels Polystyrol-Kugeln hergestellt. Auch bei diesen Strukturen werden die optischen Eigenschaften vermessen und ihre physikalischen Bedeutung mit Hilfe von numerischen Simulationen analysiert. Um den Einfluss dieser Strukturen auf die Kurzschlussstromdichten von Silizium Photokathoden zu demonstrieren, charakterisieren wir den Photostrom, der über einen Silizium-Elektrolyt-pn-Übergang mit und ohne Nanostrukturen gemessen wird. Zusammenfassend stellen wir einen Vergleich der Antireflexionseigenschaften der beiden entwickelten Strukturen sowie eine Verbesserung der photoelektrochemischen Funktionalität vor. Daraus leiten wir Ideen für zukünftige Oberflächendesigns ab, welche die noch bestehenden Nachteile beider Strukturen überwinden. / Global fuel and energy demands continue to increase due to the rapid rise in population and the dependence of this increasing population on exisiting energy resources for its sustainance. This has led to efforts in developing cleaner fuel sources such as hydrogen generation. This thesis focuses on demonstrating the optical benefit of nanostructures to improve the optoelectronic functioning of silicon photocathodes which aid in hydrogen generation via nanostructured antireflection. We lay our focus on the development of nanostructures which utilise optical concepts such as Mie type resonances based on metasurfaces and periodic index profiling. Computational design is used to obtain structure parameters for achieving desired effects. To implement these optical effects we take aid of two methods of fabrication. These fabrication methods are optimised via iterative trials to arrive at nanostructures of high quality. The first type of nanostructures belong to the metasurface class. These are implemented by e-beam lithography and top down processing. The optical spectra are then comapred with aid of simulation and experiments. The second type of nanostructures belong to the class of gradually varying periodic nanostructures. We obtain these via iterative fabrication using colloidal mask lithography. In a subsequent step we analyse experimentally their optical spectra and with aid of simulations analyse their physical implication. To demonstrate an optical benefit of these structures on enhancing the short circuit current densities of silicon photocathodes, we characterise the photocurrent measured across the silicon-electrolyte pn-junction with and without nanostructures and evaluate this increase. In conclusion, we provide a comparison of the antireflection properties offered by the two developed structures as well as in terms of improving photoelectrochemical environment. As an outlook, we propose ideas to overcome the existing drawbacks of both structures.

No description available.

Artificiels structurés, présentent des propriétés inédites et des aptitudes uniques pour la manipulation d’ondes en général. L’avènement de ces nouveaux matériaux a permis de dépasser les limites classiques dans tout le domaine de l’acoustique-physique, et d’élargir l’horizon des recherches fondamentales. Plus récemment, une nouvelle classe de structures artificielles, les métasurfaces acoustiques, présentant une valeur ajoutée par rapport aux métamatériaux, avec des avantages en termes de flexibilité, de finesse et de légèreté de structures, a émergé. Inspirés par ces propriétés et fonctionnalités sans précédent, des concepts innovants pour la collecte d’énergie acoustique avec ces deux types de structures artificielles ont été réalisés dans le cadre de cette thèse. Tout d’abord, nous avons développé un concept à base d’un métamatériau en plaque en se basant sur le de l’approche de bande interdite et des modes de défaut permis par le mécanisme de Bragg. Dans la deuxième partie de cette thèse, des métasurfaces d’épaisseur sublongueur d’onde et ultra-minces composées d’unités labyrinthiques ou de résonateurs de Helmholtz ont été conçues et étudiées pour s’atteler à la focalisation et au confinement de l’énergie acoustique. Cette thèse propose un nouveau paradigme de collecte d’énergie des ondes acoustiques à base des métamatériaux et métasurfaces. La collecte de cette énergie acoustique renouvelable, très abondante et actuellement perdue, pourrait particulièrement être utile pour l’industrie de l’aéronautique, de l’automobile, du spatial, de l’urbanisme / Phononic crystals (PCs) and acoustic metamaterials (AMMs), well-known as artificially engineered materials, demonstrate anomalous properties and fascinating capabilities in various kinds of wave manipulations, which have breached the classical barriers and significantly broaden the horizon of the whole acoustics field. As a novel category of AMMs, acoustic metasurfaces share the functionalities of AMMs in exotic yet compelling wave tailoring. Inspired by these extraordinary capabilities, innovative concepts of scavenging acoustic energy with AMMs are primarily conceived and sufficiently explored in this thesis. Generally, a planar AMM acoustic energy harvesting (AEH) system and acoustic metasurfaces AEH systems are theoretically and numerically proposed and analyzed in this dissertation. At first, taking advantage of the properties of band gap and wave localization of defect mode, the AEH system based on planar AMM composed of a defected AMM and a structured piezoelectric material has been proposed and sufficiently analyzed. Secondly, subwavelength (λ/8) and ultrathin (λ/15) metasurfaces with various lateral configurations, composed of labyrinthine and Helmholtz-like elements, respectively, are designed and analyzed to effectively realize the acoustic focusing and AEH. This thesis provides new paradigms of AEH with AMMs and acoustic metasurfaces, which would contribute to the industries of micro electronic devices and noise abatement as well

Wavelength-tunable optical response from solid-state optoelectronic devices is a desired feature for a variety of applications such as spectroscopy, laser emission tuning, and telecommunications. Nonlinear optical response, on the other hand, has an important role in modern photonic functionalities, including efficient frequency conversions, all-optical signal processing, and ultrafast switching. This study presents the development of optical devices with wavelength tunable or nonlinear optical functionality based on plasmonic effects. For the first part of this study, widely wavelength tunable optical bandpass filters based on the unique properties of long-range surface plasmon polaritons (LR SPP) are presented. Planar metal stripe waveguides surrounded by two different cladding layers that have dissimilar refractive index dispersions were used to develop a wide wavelength tuning. The concept was demonstrated using a set of index-matching fluids and over 200nm of wavelength tuning was achieved with only 0.004 of index variation. For practical application of the proposed concept, a thermo-optic polymer was used to develop a widely tunable thermo-optic bandpass filter and over 220 nm of wavelength tuning was achieved with only 8 ºC of temperature variation. Another novel approach to produce a widely wavelength tunable optical response for free-space optical applications involves integrating plasmonic metasurfaces with quantum-electronic engineered semiconductor layers for giant electro-optic effect, which is proposed and experimentally demonstrated in the second part of this study. Coupling of surface plasmon modes formed by plasmonic nanoresonators with Stark tunable intersubband transitions in multi-quantum well structures induced by applying bias voltages through the semiconductor layer was used to develop tunable spectral responses in the mid-infrared range. Experimentally, over 310 nm of spectral peak tuning around 7 μm of wavelength with 10 ns response time was achieved. As the final part of this study, highly nonlinear metasurfaces based on coupling of electromagnetically engineered plasmonic nanoresonators with quantum-engineered intersubband nonlinearities are proposed and experimentally demonstrated. In the proof-of-concept demonstration, an effective nonlinear susceptibility over 50 nm/V was measured and, after further optimization, over 480 nm/V was measured for second harmonic generation under normal incidence. The proposed concept shows that it is possible to engineer virtually any element of the nonlinear susceptibility tensor of the nonlinear metasurface. / text

Plasmonic cavities confine optical fields at metal-dielectric interfaces via collective charge oscillations of free electrons within metals termed surface plasmon polaritons (SPPs). SPPs are confined in nanometre gaps formed between two metallic surfaces which creates an optical resonance. This optical resonance of the system is controlled by the geometry and the material of the nanogap. The focus of this work is to understand and utilize these confined optical modes to probe and manipulate the dynamics of single-molecules at room temperature. In this thesis, nanogap cavities are constructed by placing nanoparticles on top of a metal-film separated by molecular spacers. Such nanogaps act as cavities with confined optical fields in the gap. Precise position and orientation of single-molecules in the gap is obtained by supramolecular guest-host assembly and DNA origami breadboards. The interaction of light and single-molecules is studied in two different regimes of interaction strength. In the perturbative regime molecular light emission from electronic and vibrational states is strongly enhanced and therefore is used for the detection of single-molecules. In this regime the energy states remain unaltered, however profound effects emerge when the gap size is reduced to < 1 nm. New hybridized energy states which are half-light and half-matter are then formed. Dispersion of these energies is studied by tuning the cavity resonance across the molecular resonance, revealing the anti-crossing signature of a strongly coupled system. This dressing of molecules with light results in the modification of photochemistry and photophysics of single-molecules, opening up the exploration of complex natural processes such as photosynthesis and the possibility to manipulate chemical bonds.