Metasurfaces are arrays of subwavelength meta-atoms that shape waves in a compact and planar form factor. During recent years, metasurfaces have gained a lot of attention due to their compact form factor, easy integration with other devices, multi functionality and straightforward fabrication using conventional CMOS techniques. To provide and evaluate an efficient metasurface, an optimized design, high resolution fabrication and accurate measurement is required. Analysis and design of metasurfaces require accurate methods for modeling their interactions with waves. Conventional modeling techniques assume that metasurfaces are locally periodic structures excited by plane waves, restricting their applicability to gradually varying metasurfaces that are illuminated with plane waves. In this work, we will first provide a novel technique that enables the development of accurate and general models for 1D metasurfaces. This approach can be easily extended to 2D metasurfaces. Due to the remarkable importance of accurate characterization of metasurfaces, we will provide a rigorous method to characterize 1D metasurfaces. Finally, we will provide an accurate approach to fabricate and characterize 2D metasrufaces.

Photonic metasurfaces obtain their unique optical properties from the periodic arrangement of sub-wavelength building blocks and can manipulate light in ways that differ significantly from bulk materials. Until recently, metasurfaces have been fabricated using top-down methods on a limited surface area. With the development of directed self-assembly methods and utilization of nanoscale colloids, metasurfaces can be fabricated on a larger scale and with reasonable efforts. In particular, soft nanoimprint lithography, based on the controlled drying of the colloidal solution within a structured template, allows for the precise placement of versatile colloidal building blocks on a substrate of choice. In this dissertation, the material and optical properties of self-assembled plasmonic and photoluminescent nanoparticles are systematically studied in terms of their short- and long-range interactions. It is shown that 1D plasmonic lattices exploit the intrinsic anisotropy and substrate-dependent collective resonant coupling. Likewise, semiconductor nanoparticles organized into linear gratings, result in light-emitting metasurfaces, featuring geometry-dependent amplification of the photoluminescence that can be further promoted to a non-linear amplification regime. Moreover, on flexible substrates, these self-assembled light-emitting metasurfaces can be stacked and twisted, inducing remarkably strong chiral effects and subsequently used for directional light sources, nanolasers, sensing, and labeling applications. Supported by theoretical modeling, this work provides a novel approach to realize anisotropic and non-linear optical properties on centimeter-scaled surface area using soft-lithography and directed self-assembly methods. It bridges the gap between nanoscale colloids and optoelectronics while advancing the integration of metasurfaces into functional devices. / Photonische Metaoberflächen erhalten ihre einzigartigen optischen Eigenschaften durch die periodische Anordnung von Bauelementen im Sub-Wellenlängenbereich und können Licht auf eine Weise manipulieren, die sich deutlich von Ausgangsmaterialien unterscheidet. Bis vor kurzem wurden Metaoberflächen mit Top-Down-Methoden auf einer begrenzten Oberfläche hergestellt. Mit der Entwicklung von Methoden der gerichteten Selbstorganisation und der Nutzung von Kolloiden im Nanomaßstab können Metaoberflächen in größerem Maßstab und mit angemessenem Aufwand hergestellt werden. Insbesondere die Soft-Nanoimprint-Lithographie, die auf der kontrollierten Trocknung der kolloidalen Lösung innerhalb einer strukturierten Template basiert, ermöglicht die präzise Platzierung vielseitiger kolloidaler Bauelemente auf einem Substrat der Wahl. In dieser Dissertation werden die materiellen und optischen Eigenschaften selbstorganisierter plasmonischer und photolumineszenter Nanopartikel im Hinblick auf ihre Kurz- und Langstreckenwechselwirkungen systematisch untersucht. Es wird gezeigt, dass plasmonische 1D-Gitter die intrinsische Anisotropie und die substratabhängige kollektive Resonanzkopplung ausnutzen. Ebenso führen Halbleiter-Nanopartikel, die in linearen Gittern organisiert sind, zu lichtemittierenden Metaoberflächen, welche eine geometrieabhängige Verstärkung der Photolumineszenz aufweisen, die bis zu einem nichtlinearen Verstärkungsregime weitergeführt werden kann. Außerdem können diese selbstorganisierten, lichtemittierenden Metaoberflächen auf flexiblen Substraten gestapelt und verdreht werden, was zu bemerkenswert starken chiralen Effekten führt und anschließend für gerichtete Lichtquellen, Nanolaser, Sensor- und Beschriftungsanwendungen genutzt werden kann. Unterstützt durch theoretische Modellierung bietet diese Arbeit einen neuartigen Ansatz zur Realisierung anisotroper und nichtlinearer optischer Eigenschaften auf zentimetergroßen Oberflächen unter Verwendung von Softlithographie und Methoden der gerichteten Selbstmontage. Sie überbrückt die Lücke zwischen Kolloiden im Nanomaßstab und der Optoelektronik und treibt gleichzeitig die Integration von Metaoberflächen in funktionale Geräte voran.

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The goal of this project was to design a lens utilisinga glide symmetric periodic structure. A Lüneburg lens forantennas with a center frequency of 8 GHz has been designed.The structure was constructed using a unit cell in the shape ofan angular Bowen knot. This unit cell was then etched on themetallic surface of a parallel plate waveguide. Two symmetrycases for the unit cell were studied, the mirror symmetry andthe glide symmetry. Mirror symmetry is when the unit cell wasmirrored on the opposite metallic sheet, and glide symmetrywhen the cell was mirrored and shifted half a period. Theglide symmetric case was found to be less dispersive and moreisotropic. Further, we study the influence on the refractive indexwhen changing the geometry of the unit cell. A sufficient rangeof refractive index for realising the lens was found. These resultswere used to construct a full lens. Simulation of the complete lensshows the desired point to planar wave behavior of a Lüneburglens. In conclusion, the angular Bowen knot with glide symmetryhas the potential to construct a functioning Lüneburg lens. / Målet för detta projekt var att konstrueraen lins med glidsymmetriska periodiska strukturer. En Lüneburg-lins för antenner med en centerfrekvens på 8 GHz har de-signats. Strukturen byggdes med en enhetscell i formen avett sankthanskors etsat på en metallisk plattkondensator fylldmed ett dielektriskt substrat. Två symmetrifall betraktades,spegelsymmetri, då enhetscellen speglades på motstående me-tallskikt, och glidsymmetri där den även var förskjuten en halvperiod. Glidsymmetrin fanns ha mindre spridning och störreisotropi. Därtill undersöktes förändringarna i brytningsindex dåenhetscellens geometri förändrades. En tillräcklig räckvidd avbrytningsindex kunde uppnås. Dessa resultat användes för attkonstruera en fullständig lins. Simulering av den kompletta linsenvisade det önskade punkt till planvågbeteendet hos en Lüneburglins. Slutsatsen är att enhetsceller i formen av ett sankthanskorsmed glidsymmetri har potentialen att konstruera fungerandeLüneburg-linser. / Kandidatexjobb i elektroteknik 2020, KTH, Stockholm

Yes / In this letter a novel on-chip array antenna is investigated which is based on CMOS 20μm Silicon technology for operation over 0.6-0.65 THz. The proposed array structure is constructed on three layers composed of Silicon-Ground-Silicon layers. Two antennas are implemented on the top layer, where each antenna is constituted from three sub-antennas. The sub-antennas are constructed from interconnected dual-rings. Also, the sub-antennas are interconnected to each other. This approach enhances the aperture of the array. Surface waves and substrate losses in the structure are suppressed with metallic via-holes implemented between the radiation elements. To excite the structure, a novel feeding mechanism is used comprising open-circuited microstrip lines that couple electromagnetic energy from the bottom layer to the antennas on the top-layer through metasurface slot-lines in the middle ground-plane layer. The results show the proposed on-chip antenna array has an average radiation gain, efficiency, and isolation of 7.62 dBi, 32.67%, and -30 dB, respectively. / H2020-MSCA-ITN-2016 SECRET-722424 and the financial support from the UK Engineering and Physical Sciences Research Council (EPSRC) under grant EP/E0/22936/1

Yes / An effective method is presented for suppressing mutual coupling between adjacent radiating elements which is based on metasurface isolation for MIMO and synthetic aperture radar (SAR) systems. This is achieved by choking surface current waves induced over the patch antenna by inserting a cross-shaped metasurface structure between the radiating elements. Each arm of the cross-shaped structure constituting the metasurface is etched with meander-line slot (MLS). Effectiveness of the metasurface is demonstrated for a2×2antenna array that operates over six frequency sub-bands in X, Ku and K-bands. With the proposed technique, the maximum improvement achieved in attenuating mutual coupling between neighbouring antennas is: 8.5 dB (8-8.4 GHz), 28 dB (9.6-10.8 GHz), 27 dB (11.7-12.6 GHz), 7.5 dB (13.4-14.2 GHz), 13 dB (16.5-16.8 GHz) and 22.5 dB (18.5-20.3 GHz). Furthermore, with the proposed technique (i) minimum center-to-center separation between the radiating elements can be reduced to 0.26λ0, where λ0 is 8.0 GHz; (ii) use of ground-plane or defected ground structures are unnecessary; (iii) use of short-circuited via-holes are avoided; (iv) it eliminates the issue with poor front-to-back ratio; and (v) it can be applied to existing arrays retrospectively. / H2020-MSCA-ITN-2016 SECRET-722424 and the financial support from the UK Engineering and Physical Sciences Research Council (EPSRC) under grant EP/E0/22936/1

Cette thèse s’inscrit dans le développement d’imageurs térahertz en technologie intégrée CMOS avec pour volonté de rendre ces derniers fiables et robustes, de permettre de réaliser de l’imagerie en temps réel, à température ambiante et à bas coût de production. L’ensemble doit être mené en parallèle de l’amélioration des réponses et sensibilités des capteurs actuels dans le but de rendre l’imageur fonctionnel et industrialisable. La caractérisation d’un imageur THz précédent réalisée au cours de la thèse a permis de redéfinir avec plus de rigueur cette caractérisation ainsi qu’une méthodologie de conception de la partie amont du pixel térahertz. Cette partie amont inclut l’antenne réceptrice et son environnement électromagnétique ainsi qu’un transistor à effet de champ redressant le signal THz reçu. Différentes parties amont de pixels THz, sensibles autour de 300 GHz, ont été développées. L’ensemble est monolithiquement intégré à l’aide du procédé CMOS standard dans un circuit complet et l’antenne est co-conçue avec le MOSFET de redressement afin de réaliser l’adaptation d’impédance. Chaque pixel inclut une antenne intégrée au niveau métallique supérieur avec un plan de masse parfois couplé à une métasurface afin d’isoler cette antenne du circuit de traitements du signal (non traité dans cette thèse) et du substrat de silicium localisés aux niveaux inférieurs du circuit. Finalement, 17 cas de test croisés (16 de 3 x 3 pixels et une matrice de 9 x 9 pixels) intégrant différentes topologies d'antenne et configurations de surfaces électromagnétiques (plan de masse et métasuface) ainsi que différents transistors de redressement sont conçus et fabriqués en fonderie CMOS. / This thesis deals with the development of terahertz imager in CMOS technology with the objectives to make it robust and reliable, with real-time imaging capacity at ambient temperature and with low-cost production. These objectives has to be developed at the same time as the improvement of responses and sensibilities to get the imager functional and ready for industrialization. The characterization of a previous THz imager, done during this thesis, brought the possibility to redefine in a more rigorous way this characterization and to develop a methodology for designing the THz front-end pixel. This front-end includes the reception antenna and its electromagnetic environment and a field effect transistor (FET) rectifying the received THz signal. Various front-end of THz pixels, design for 300 GHz reception, were developed. The whole structure has to be monolithically integrated with the standard CMOS process in a complete circuit and the antenna is co-design with the rectifying MOSFET in order to satisfy the impedance matching. Every pixel includes an antenna, integrated in higher metal levels with a ground plan sometimes coupled with a metasurface. This is in order to isolate the antenna from the signal processing circuit (not investigated in this thesis) and the silicon substrate botth located at the lower levels of the circuit. Finally, 17 crossed test cases (16 of 3 x 3 pixels and one matrix of 9 x 9 pixels) which integrate various antenna topologies and various configurations of electromagnetic surfaces (ground plane and metasurface) with various rectifying transistor were designed and manufactured in CMOS foundry.

By down-sizing noble metals to the nanoscale, striking new optical properties arise—investigated in the scientific field of plasmonics. The steady rise of developments, innovations, and interest in plasmonics is directly linked with the much broader field of (colloidal) nanotechnology and its breakthroughs. In order to harvest the full potential of colloidal plasmonics, optimizing the synthesis of colloidal nanoparticles, controlling the subsequent assembly of them into complex architectures, and fully understanding the emerging plasmonic properties is inevitable. Wet-chemical seed-mediated growth of colloidal building blocks and colloidal self-assembly offer the tool-sets to tackle the challenges of plasmonic applications. Due to the intrinsic properties of colloids and the resulting (coupled) assemblies, distinct differences are evident in comparison to top-down fabrication based plasmonics. Among these properties, this thesis focuses on the true three-dimensionality of colloids—in vast contrast, top-down processes always rely on stacking of layered architectures. Strong plasmonic coupling interactions are predominantly defined by the inter-particle distances and the geometry of the cross section area by which adjacent particles interact. Consequently, unique plasmonic features emerge from the three-dimensional structure of colloids and the possibility to tune the dielectric environment by surface functionalization. The objective of this work is to investigate and understand the plasmonics of coupled colloidal systems. Following this scope, the first part of this thesis introduces a new synthetic concept, which thereby aims to provide colloidal building blocks for plasmonic assemblies. The optical quality and spectral range can be boosted by applying silver nanoparticles instead of gold as plasmonic material. Herein, a general synthetic concept is introduced resulting in monodispersed and shape-pure silver nanoparticles in a highly controlled manner. By transferring the concept of living polymerization reactions to nanoparticle growth, secondary nucleation is successfully suppressed and the particle dimensions are freely tunable. Finally, chemical stability toward oxidation and functionalization reactions is obtained by covering silver particles with a sub-skin depth gold shell. The second part summarizes the plasmonic properties arising from coupled particle assemblies fabricated by colloidal self-assembly. Therefore, the complexity of the coupled systems was systematically increased to observe the transition from local to collective coupling interactions. Starting from metallic film-coupled gold nanorods, the presence of a highly sensitive magnetic mode and its impact on the magnetic permeability were investigated. Next, the transition from local to collective coupling was observed by stepwise increase of the number of particles in a linear gold nanoparticle chain revealing the formation of a plasmon band in quasi-infinite particle chains. Consequently, this work aims to advance the field of colloidal metasurfaces by optimizing the building blocks and by further comprehending the plasmonic coupling effects in colloidal assemblies. / Durch das Herunterskalieren von (Edel-)Metallen in den Nanometerbereich entstehen neue optische Eigenschaften, die im Wissenschaftsfeld der Plasmonik untersucht werden. Die stetige Weiterentwicklung, Innovation, und das steigende Interesse an der Plasmonik ist direkt mit dem weiter gefassten Gebiet der (kolloidalen) Nanotechnologie verbunden. Um das Potenzial der kolloidalen Plasmonik voll ausschöpfen zu können, ist es unumgänglich, die Synthese kolloidaler Nanopartikel zu optimieren, deren anschließende Anordnung zu komplexen Architekturen gezielt zu steuern, und die entstehenden plasmonischen Effekte vollständig zu verstehen. Das nasschemische Keim-vermittelte Wachstum kolloidaler Bausteine und die kolloidale Selbstanordnung bieten die geeigneten Werkzeuge für plasmonische Anwendungen. Aufgrund der intrinsischen Eigenschaften kolloidaler Partikel und den daraus resultierenden optischen Eigenschaften ihrer Anordnungen, ergeben sich deutliche Unterschiede zur Plasmonik von Top-down Systemen. Im Gegensatz zu diesen Systemen, die immer aus geschichteten Architekturen bestehen, handelt es sich bei kolloidalen Systemen um echte dreidimensionale Objekte. Starke plasmonische Kopplungswechselwirkungen werden hauptsächlich durch die Abstände zwischen Partikeln und die Geometrie des Querschnitts definiert, über die benachbarte Partikel interagieren. Folglich ergeben sich aus der dreidimensionalen Struktur von kolloidalen Nanopartikeln und der Möglichkeit, diese mit verschiedenen dielektrischen Umgebung zu funktionalisieren, einzigartige plasmonische Effekte. Das übergeordnete Ziel dieser Arbeit besteht darin, die plasmonischen Effekte gekoppelter kolloidaler Systeme zu untersuchen und besser zu verstehen. Diesem Ziel folgend, wird im ersten Teil der Arbeit ein neues Synthesekonzept vorgestellt, das darauf abzielt geeignete kolloidale Bausteine für plasmonische Anordnungen zur Verfügung zu stellen. Verglichen mit Gold als Bausteinmaterial kann die optische Qualität und der Spektralbereich durch Nutzung der überlegenen plasmonischen Eigenschaften von Silbernanopartikeln gesteigert werden. Hier wurde ein allgemeines Synthesekonzept entwickelt, das auf kontrollierte Weise zu monodispersen und formreinen Silbernanopartikeln führt. Durch die Übertragung des Konzepts lebender Polymerisationsreaktionen auf das Nanopartikelwachstum, werden Nebenreaktionen (z.B. sekundäre Keimbildung) erfolgreich unterdrückt und die Partikelgröße wird dadurch genau einstellbar. Schließlich wurde durch die Überwachsung der Silberpartikel mit einer Goldschale unterhalb der Leitschichtdicke chemische Stabilität gegenüber Oxidations- und Funktionalisierungsreaktionen erhalten. Im zweiten Teil werden die plasmonischen Eigenschaften gekoppelter Partikelanordnungen untersucht. Dafür wurde die Komplexität der gekoppelten Systeme systematisch erhöht, um den Übergang von lokalen zu kollektiven Kopplungsinteraktionen zu beobachten. Ausgehend von Goldstäbchen, die mit einem Metallfilm gekoppelt sind, wurde eine hochempfindliche magnetische Mode nachgewiesen und deren Einfluss auf die magnetische Permeabilität untersucht. Desweiteren wurde der direkte Übergang von lokaler zu kollektiver Kopplung durch schrittweise Erhöhung der Anzahl der Partikel in einer linearen Goldnanopartikelkette beobachtet, was zur Bildung eines Plasmonenbandes für quasi-unendlich lange Partikelketten führt. Letztendlich ist das Ziel dieser Arbeit, kolloidale Metaoberflächen durch Optimierung der Bausteine und durch besseres Verständnis der plasmonischen Kopplungseffekte voranzubringen.

The aim of this project is to design a cost-effective planar Maxwell fish-eye lens in PCB technology operating at the center frequency 5 GHz with a bandwidth of 20 %. An approach to design a cost-effective lens is to use a metasurface, which is commonly realized as a periodic structure of unit cells. In this project, a study was made by comparing different unit cells and considering the effect of applying glide symmetry to the unit cells. Comparing different unit cells withand without glide symmetry demonstrates that glide symmetry is necessary to achieve a 20 % bandwidth. Introducing glide symmetry showed a reduction in dispersive behavior, an increaseof isotropy and effective refractive index. Simulations of the full lens show a functioning lens with a power transfer of 67 % at 5.46 GHz. In conclusion, glide symmetry will improve the performance of the lens and is necessary to fulfill the requirement of a 20 % bandwidth.

<p dir="ltr">Thermal radiation is the property that all forms of matter have, due to the intrinsic vibrations as a result of their temperature. This has spurred the desire to study and use this ever-present phenomena. Controlling and detecting thermal radiation has relevance in modern-world applications, ranging from high temperature thermal barriers used on airplanes to protect the turbines from overheating to energy conversion devices being improved with advances in solar cell design.</p><p dir="ltr">Control over the thermal radiation is achieved through the understanding of what the desired properties will be and then designing a material system that can fulfill the users’ criteria. The criteria that can be controlled vary depending on application and can range from having a broadband polarized emission, to having selective narrowband circular polarized emission at specific angles. The more distinctive the properties, the more degrees of control are needed to accomplish it. We will introduce the concept of symmetries of material systems that, when broken, allow for additional degrees of freedom to control the thermal radiation. We will also discuss how we perform the measurements, to demonstrate the methods used to verify that our control of the thermal radiation was valid. A spin-polarized angle-resolved spectroscopy (SPARTES) setup is used for the measurements to substantiate the claim that we can design structures that control their wavelength, angles of emission and polarization properties.</p><p dir="ltr">Thermal metamaterials designs are a great interest in high temperature applications. We explore various structured material surfaces that maintain their selective angular emission properties even when raised to high temperatures. Using different structures and materials, it is clear that our thermal radiation can be engineered to elicit different spectral responses at selective angles.</p><p dir="ltr">To explore the limits of our control, we observe the photon spin characteristics of thermal radiation. In general, objects in nature have little to no spin angular momentum. However, we can engineer a symmetry-broken metasurface that demonstrates this generation of circular polarized thermal emission without the presence of magnetic fields with high selectivity. We focus here on the affect that symmetry has on the spin-dependent polarization properties and how symmetry is a good metric to focus on when controlling the temporal, spatial and spin coherence of thermal radiation.</p>