Rozprawy doktorskie na temat „Nanophotonic devices”

In this thesis, we aim to explore several novel designs of nanostructures based on graphene to realize various functionalities. We briefly introduce the fundamental concepts and theoretical models used in this thesis in Chapter 1. Following the macroscopic analytical method outlined in the first chapter, in Chapter 2 we show that simple simulation methods allow us to accurately describe the optical response of plasmonic nanoparticles, including retardation effects, without the requirement of large computational resources. We then move to our proposed first type of device: optical modulators. We explore graphene sheets coupled to different kinds of optical resonators to enhance the light intensity at the graphene plane, and so also its absorption, which can be switched on/off and modulated through varying the level of doping, as explored in Chapter 3. Unity-order changes in the transmission and absorption of incident light are predicted upon electrical doping of graphene. Heat deposition via light absorption can severely degrade the performance and limit the lifetime of nano-devices (e.g., aforementioned optical modulators), which makes the manipulation of nanoscale heat sources/flows become crucial. In Chapter 4, we exploit the extraordinary optical and thermal properties of graphene to show that ultrafast radiative heat transfer can take place between neighboring nanostructures facilitated by graphene plasmons, where photothermally induced effects on graphene plasmons are taken into account. Our findings reveal a new regime for the nanoscale thermal management, in which non-contact heat transfer becomes a leading mechanism of heat dissipation. Apart from the damage caused by heat deposition, generated thermal energy can be in fact used as a tool for photodetection (e.g., silicon bolometers for infrared photodetection). In Chapter 5, we show that the excitation of a single plasmon in a graphene nanojunction produces profound modifications in its electrical properties through optical heating, which we then use to demonstrate an efficient mid-infrared photodetector working at room temperature based on theoretical predictions that are corroborated in an experimental collaboration with the group of Prof. Fengnian Xia in Yale University. Finally, in Chapter 6, we show through microscopic quantum-mechanical simulations, introduced in the first chapter, that both the linear and nonlinear optical responses of graphene nanostructures can be dramatically altered by the presence of a single neighboring molecule that carries either an elementary charge or a small permanent dipole. Based on these results, we claim that nanographenes can serve as an efficient platform for detecting charge- or dipole-carrying molecules.
En esta tesis, pretendemos explorar varios diseños novedosos de nanoestructuras basadas en grafeno, con diversas funcionalidades. Tras presentar brevemente los conceptos fundamentales y los modelos teóricos utilizados en esta tesis en el Capítulo 1, en el Capítulo 2 mostramos la posibilidad de describir la respuesta de nanopartículas plasmónicas (incluyendo efectos de retardo) mediante métodos de simulación semi-analíticos sencillos y sin la necesidad de emplear grandes recursos computacionales. Posteriormente, empleamos estos modelos en el desarrollo de un primer tipo de dispositivo: moduladores ópticos. Añadiendo láminas de grafeno acopladas a diferentes tipos de resonadores ópticos, podemos mejorar la intensidad de la luz en el plano del grafeno, y por lo tanto también su nivel de absorción, la cual puede ser modulada a voluntad mediante el nivel de dopado electrostático del grafeno, como se explora en el Capítulo 3. Los modelos empleados predicen cambios en la transmisión del orden de la unidad, produciendo así la absorción total por parte del dispositivo de la luz incidente. En esta clase de dispositivos, así como en todos los dispositivos nanofotónicos, la producción de calor mediante la absorción de la luz puede degradar severamente su rendimiento, así como limitar su vida útil, lo que hace que la manipulación de la fuente y el flujo de calor en la nanoescala sea una componente crucial del desarrollo. En el Capítulo 4, empleamos las extraordinarias propiedades ópticas y térmicas del grafeno para mostrar que puede tener lugar una transferencia ultrarrápida de calor radiativo entre nanoestructuras vecinas, facilitada por los plasmones del grafeno, los cuales a su vez experimentan efectos fototérmicos asociados con este proceso de disipación. Nuestros hallazgos revelan un nuevo régimen para la energía térmica a nanoescala, en la que la transferencia de calor radiativa se convierte en el mecanismo principal de disipación de calor. Además de los daños causados por la deposición de calor, la energía térmica generada puede ser de hecho usada como herramienta para la fotodetección: tal es el caso, por ejemplo, de los bolómetros de silicona, empleados para la fotodetección por infrarrojos. En el Capítulo 5, mostramos que la excitación de un solo plasmón en una unión de grafeno altera radicalmente sus propiedades eléctricas debido al calentamiento óptico. Este hecho puede ser empleado para demostrar el funcionamiento eficaz de un fotodetector en la región media de los infrarrojos a temperatura ambiente, tanto a través de predicciones teóricas como su corroboración experimental (en colaboración con el grupo del Prof. Fengnian Xia de la Universidad de Yale). Finalmente, en el Capítulo 6, mostramos a través de simulaciones mecánico-cuánticas (introducidas en el Capítulo 1), que tanto la respuesta óptica lineal como la no lineal de las nanoestructuras de grafeno pueden ser dramáticamente alteradas por la presencia de una sola molécula vecina que transporte o bien una carga elemental o un dipolo permanente. En base a estos resultados, afirmamos que las estructuras de grafeno nanoscópicas podrían ser una plataforma eficiente para detectar moléculas portadoras de carga o dipolos.

The emergence of optical applications, such as lasers, fiber optics, and semiconductor based sources and detectors, has created a drive for smaller and more specialized devices. Nanophotonics is an emerging field of study that encompasses the disciplines of physics, engineering, chemistry, biology, applied sciences and biomedical technology. In particular, nanophotonics explores optical processes on a nanoscale. This dissertation presents nanophotonic applications that incorporate various forms of the organic polymer N-isopropylacrylamide (NIPA) with inorganic semiconductors. This includes the material characterization of NIPA, with such techniques as ellipsometry and dynamic light scattering. Two devices were constructed incorporating the NIPA hydrogel with semiconductors. The first device comprises a PNIPAM-CdTe hybrid material. The PNIPAM is a means for the control of distances between CdTe quantum dots encapsulated within the hydrogel. Controlling the distance between the quantum dots allows for the control of resonant energy transfer between neighboring quantum dots. Whereby, providing a means for controlling the temperature dependent red-shifts in photoluminescent peaks and FWHM. Further, enhancement of photoluminescent due to increased scattering in the medium is shown as a function of temperature. The second device incorporates NIPA into a 2D photonic crystal patterned on GaAs. The refractive index change of the NIPA hydrogel as it undergoes its phase change creates a controllable mechanism for adjusting the transmittance of light frequencies through a linear defect in a photonic crystal. The NIPA infiltrated photonic crystal shows greater shifts in the bandwidth per ºC than any liquid crystal methods. This dissertation demonstrates the versatile uses of hydrogel, as a means of control in nanophotonic devices, and will likely lead to development of other hybrid applications. The development of smaller light based applications will facilitate the need to augment the devices with control mechanism and will play an increasing important role in the future.

L'information est devenue le bien le plus précieux au monde. Ce mouvement vers la nouvelle ère de l'information a été propulsé par la capacité à transmettre l'information plus rapidement, à la vitesse de la lumière. Il est donc apparu nécessaire de mener des recherches plus poussées pour contrôler plus efficacement les supports d'information. Avec les progrès réalisés dans ce secteur, la plupart des technologies actuelles de contrôle de la lumière se heurtent à certains obstacles tels que la taille et la consommation d'énergie et sont conçues pour être passives ou sont limitées technologiquement pour être moins actives (technologie Si-back). Même si rien ne voyage plus vite que la lumière, la vitesse réelle à laquelle les informations peuvent être transportées par la lumière est la vitesse à laquelle nous pouvons la moduler ou la contrôler. Ma tâche dans cette thèse visait à étudier le potentiel du VO2, un matériau à changement de phase, pour la nano-photonique, avec un accent particulier sur la façon de contourner les inconvénients du matériau et de concevoir et démontrer des dispositifs intégrés efficaces pour une manipulation efficace de la lumière à la fois dans les télécommunications et le spectre visible. En outre, nous démontrons expérimentalement que les résonances multipolaires supportées par les nanocristaux de VO2 (NC) peuvent être réglées et commutées dynamiquement en exploitant la propriété de changement de phase du VO2. Et ainsi atteindre l'objectif d'adaptation de la propriété intrinsèque basée sur le formalisme de Mie en réduisant les dimensions des structures de VO2 comparables à la longueur d'onde de fonctionnement, créant un champ d'application pour un métamatériau accordable défini par l'utilisateur
Information has become the most valuable commodity in the world. This drive to the new information age has been propelled by the ability to transmit information faster, at the speed of light. This erupted the need for finer researches on controlling the information carriers more efficiently. With the advancement in this sector, majority of the current technology for controlling the light, face certain roadblocks like size, power consumption and are built to be passive or are restrained technologically to be less active (Si- backed technology). Even though nothing travels faster than light, the real speed at which information can be carried by light is the speed at which we can modulate or control it. My task in this thesis aimed at investigating the potential of VO2, a phase change material, for nano-photonics, with a specific emphasis on how to circumvent the drawbacks of the material and to design and demonstrate efficient integrated devices for efficient manipulation of light both in telecommunication and visible spectrum. In addition to that we experimentally demonstrate the multipolar resonances supported by VO2 nanocrystals (NCs) can be dynamically tuned and switched leveraging phase change property of VO2. And thus achieving the target tailoring of intrinsic property based on Mie formalism by reducing the dimensions of VO2 structures comparable to the wavelength of operation, creating a scope for user defined tunable metamaterial

The research presented in the thesis includes the modelling and characterization of the novel devices based on graphene and carbon nanotube (CNT)-based buckypaper. The devices have great potential to be used in applications such as photovoltaics, optical communications/imaging and sensors for oil and gas industry. Graphene is a promising material with excellent optical and electrical properties. Research was carried out in utilizing graphene for photonic and plasmonic devices, including ultra-thin flat lens, plasmonic lens, and oil sensor. Buckypaper extends the applications of CNTs’ excellent properties from nanoscale to microscale. This opportunity was explored in the development of ultra-thin flat lens.

Thesis advisor: Michael J. Naughton
Thesis advisor: Michael J. Burns
Recent progress in the study of the brain has been greatly facilitated by the development of new measurement tools capable of minimally-invasive, robust coupling to neuronal assemblies. Two prominent examples are the microelectrode array, which enables electrical signals from large numbers of neurons to be detected and spatiotemporally correlated, and optogenetics, which enables the electrical activity of cells to be controlled with light. In the former case, high spatial density is desirable but, as electrode arrays evolve toward higher density and thus smaller pitch, electrical crosstalk increases. In the latter, finer control over light input is desirable, to enable improved studies of neuroelectronic pathways emanating from specific cell stimulation. Herein, we introduce a coaxial electrode architecture that is uniquely suited to address these issues, as it can simultaneously be utilized as an optical waveguide and a shielded electrode in dense arrays
Thesis (PhD) — Boston College, 2017
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Physics

Transformation optics (TO), which provides an elegant way of molding the flow of light to one's wishes, has become one of the most popular photonics research areas during the last few years. Owing to stringent material parameters of transformation media, TO is in general not favourable for designing practical applications. The recent proposal of carpet cloak, a device that optically hides an anomaly on an otherwise at reflective surface, simplifies material requirements due to the relaxed boundary condition on the cloak's reflective border, thus providing the prospect of realization at optical wavelength. In light of this approach, this thesis introduces a general procedure for transforming reflective optical devices, including in particular focal mirrors and diraction gratings. The curved or zigzagged surfaces of such devices are attened through a smooth coordinate mapping which makes convenient use of the loose boundary conditions on the reflective surface. The resulting devices are transformation media without extreme material parameters. For two-dimensional structures, it is even possible to attain an approximate dielectric-only implementation when considering only transverse-electric or transverse-magnetic incidence. The flattened reflective devices are finally adapted to operate in a transmission mode, creating focal lenses and transmissive diffraction gratings. It is illustrated through full-wave simulation that the performance of these transformation optical devices - under the right circumstances also for the dielectric only implementations - surpasses their traditional equivalents.

Resonant devices are an integral component of the integrated silicon photonics platform, with applications in filters, switches, modulators, delays, sensors etc. High index contrast SOI waveguides can be used to form compact micro-ring resonators with bend radii on the order of micro-meters. This work describes the application of micro-ring resonators in linear and nonlinear silicon photonics. We describe the use of higher-order coupled resonators for use as ultra-high contrast pass-band filters with close to 100 dB extinction. Using the spontaneous four-wave mixing process, a third-order nonlinear Kerr effect, coupled resonator waveguides are shown to be a useful source of heralded single photons, as well as other unique quantum states of light. We also describe four-wave mixing results in silicon micro-resonators, where nonlinear loss effects are mitigated by reverse biased p-i-n diodes, showing potential for high-speed optical signal processing.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 107-123).
The nitrogen vacancy (NV) center in diamond has in recent years emerged as a promising solid state system for quantum information processing and sensing applications. However, using NV centers to build up quantum networks for these applications faces several challenges, such as the lack of efficient interface between NVs and photons, difficulty of maintaining spin coherence times, and scalable techniques for fabrication of NV-photon networks. This thesis focuses on overcoming these challenges by fabricating diamond devices to improve the collection efficiency of NV photon emission, especially from the zero phonon line (ZPL), while maintaining long spin coherence times after fabrication. After an introduction to the subject matter in Chapter 1, Chapter 2 discusses a fabrication technique to produce vertical membranes out of bulk diamond plates. This work showed that after reactive ion etching, the spin properties of isolated NVs in diamond nanostructures were largely preserved. We also observed increased photoluminescence collection from shallow implanted NV centers in these slabs. In Chapter 3, we describe a versatile nanofabrication method based on re-usable silicon membrane hard masks, patterned using standard lithography and mature silicon processing technology. These masks are transferred precisely onto targeted regions of diamond membranes, where photonic devices can be realized without the need for spin coating, wet etching or electron beam exposure. Chapter 4 describes and demonstrates an alternative technique for fabricating one-dimensional photonic crystal (PC) cavities in single-crystal diamond by a combination of reactive ion etching (RIE) and focused ion beam milling. We compare it to transferred silicon hard mask lithography with RIE. Chapter 5 demonstrate NV-nanocavity systems in the strong Purcell regime with consistently high Q factors while preserving the long spin coherence times of NVs. These systems enable coherent spin control of cavity-coupled semiconductor qubits with coherence times exceeding 200 [mu]s - an increase by two orders of magnitude over previously reported optical cavity-coupled solid-state qubits. Chapter 6 introduces a circular diamond "bullseye" grating that achieves the highest reported photon collection rate from a single NV center of 4.56 0.08 Mcps at saturation when fitted with the widely-used background counts subtraction method. We also quantified the emission by a g(²)-corrected saturation curve measurement which gives a rigorous single photon count rate of 2.7 ± 0.09 Mcps. By using dynamical decoupling sequences, we measured a spin coherence time of 1.7 ± 0.1 ms, which is comparable to the highest reported spin coherence times of NVs under ambient conditions and also indicates that the bullseye fabrication process does not degrade the spin properties noticeably. The planar architecture allows for on-chip integration, and the circular symmetry supports left- and right-handed circularly polarized light for spin-photon entanglement. In Chapter 7, we demonstrate a top-down fabrication process using a porous metal mask and a self-guiding RIE process that enables rapid nanocrystal creation across the entirety of a high-quality chemical vapor deposited (CVD) diamond substrate. High-purity CVD nanocrystals produced in this manner exhibit single NV phase coherence times reaching 210 ps and magnetic field sensitivities of 290 nT.Hz⁻¹/² without compromising the spatial resolution of a nanoscale probe.
by Luozhou Li.
Ph. D.

Group- III nitride based semiconductors have emerged as the leading material for short wavelength optoelectronic devices. The InGaN alloy system forms a continuous and direct bandgap semiconductor spanning ultraviolet (UV) to blue/green wavelengths. An ideal and highly efficient light-emitting device can be designed by enhancing the spontaneous emission rate. This thesis deals with the design and fabrication of a visible light-emitting device using GaN/InGaN single quantum well (SQW) system with enhanced spontaneous emission. To increase the emission efficiency, layers of different metals, usually noble metals like silver, gold and aluminum are deposited on GaN/InGaN SQWs using metal evaporator. Surface characterization of metal-coated GaN/InGaN SQW samples was carried out using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Photoluminescence is used as a tool for optical characterization to study the enhancement in the light emitting structures. This thesis also compares characteristics of different metals on GaN/InGaN SQW system thus allowing selection of the most appropriate material for a particular application. It was found out that photons from the light emitter couple more to the surface plasmons if the bandgap of former is close to the surface plasmon resonant energy of particular metal. Absorption of light due to gold reduces the effective mean path of light emitted from the light emitter and hence quenches the quantum well emission peak compared to the uncoated sample.

This project is focused on the application of new electronic and optical materials. In particular it involves examining the use of chalcogenide thin films as phase change and ion conducting glasses for emerging optoelectronic applications. The ability of this group of materials to easily change their state from glass to crystal has meant that they have been widely used in CD's and DVDs. However, their ability to also conduct electrons and ions, promises novel solutions for next generation logic and memory devices which will take us in the short term beyond the limits of the silicon chip and, into the world of neuromorphic cognitive computing (computers that think and adapt). Additionally, this reversible change in the structure of these thin films allows their utilisation in ultra-high speed optical and optoelectronic switches to power the internet and future computers. Three main goals are pursued within this research. First, next generation phase change (PCRAM) and nano-ionic resistive (ReRAM) memory is pursued for faster, non-volatile high density data storage. Secondly, the design of novel processing elements like next generation logic gates enabling neuromorphic cognitive processing and data storage in one structure based on material properties. Finally, the integration of phase change thin films with metamaterial arrays to produce electro-optic and all optical switches for future photonic computers and communication networks.

III-V optoelectronic device integration in a CMOS post-process compatible manner is important for the intimate integration of silicon-based electronic and photonic integrated circuits. The low temperature, self-catalyzed growth of high crystalline quality Wurtzite-phase InP nanopillars directly on silicon presents a viable approach to integrate high performance nano-optoelectronic devices.

For the optical transmitter side of the photonic link, InGaAs quantum wells have been grown in a core-shell manner within InP nanopillars. Position-controlled growth with varying pitch is used to systematically control emission wavelength across the same growth substrate. These nanopillars have been fabricated into electrically-injected quantum well in nanopillar LEDs operating within the silicon transparent 1400–1550 nm spectral window and efficiently emitting micro-watts of power. A high quality factor (Q ~ 1000) undercut cavity quantum well nanolaser is demonstrated, operating in the silicon-transparent wavelength range up to room temperature under optical excitation.

We also demonstrate an InP nanopillar phototransistor as a sensitive, low-capacitance photoreceiver for the energy-efficient operation of a complete optical link. Efficient absorption in a compact single nanopillar InP photo-BJT leads to a simultaneously high responsivity of 9.5 A/W and high 3dB-bandwidth of 7 GHz.

For photovoltaic energy harvesting, a sparsely packed InP nanopillar array can absorb ~90% of the incident light because of the large absorption cross section of these near-wavelength nanopillars. Experimental data based on wavelength and angle resolved integrating sphere measurements will be presented to discuss the nearly omnidirectional absorption properties of these nanopillar arrays.

Hybrid plasmonic-photonic structures were introduced as novel platforms for on-chip biochemical sensing and spectroscopy. By appropriate coupling of photonic and plasmonic modes, a hybrid architecture was realized that can benefit from the advantages of integrated photonics such as the low propagation loss, ultra-high Q modes, and robustness, as well as the advantages of nanoplasmonics such as extreme light localization, large sensitivities, and ultra-high field enhancements to bring about unique performance advantages for efficient on-chip sensing. These structures are highly sensitive and can effectively interact with the target biological and chemical molecules. It was shown that interrogation of single plasmonic nanoparticles is possible using a hybrid waveguide and microresonator-based structure, in which light is efficiently coupled from photonic structures to the integrated plasmonic structures. The design, implementation, and experimental demonstration of hybrid plasmonic-photonic structures for lab-on-chip biochemical sensing applications were discussed. The design goal was to achieve novel, robust, highly efficient, and high-throughput devices for on-chip sensing. The sensing scenarios of interest were label-free refractive index sensing and SERS. Nanofabrication processes were developed to realize the hybrid plasmonic-photonic structures. Silicon nitride was used as the material platform to realize the integrated photonic structure, and gold was used to realize plasmonic nanostructures. Special optical characterization setups were designed and implemented to test the performance of these nanoplasmonic and nanophotonic structures. The integration of the hybrid plasmonic-photonic structures with microfluidics was also optimized and demonstrated. The hybrid plasmonic-photonic-fluidic structures were used to detect different analytes at different concentrations. A complete course of research from design, fabrication, and characterization to demonstration of sensing applications was conducted to realize nanoplasmonic and integrated photonic structures. The novel structures developed in this research can open up new potentials for biochemical sensors with advanced on-chip functionalities and enhanced performances.

Recently, developments in novel and high-purity materials allow for the presence of a single, solitary crystalline defect to define the electronic, magnetic, and optical functionality of a device. The discrete nature of the active dopant, whose properties are defined by a quantum mechanical description of its structure, enables radically new quantum investigations and applications in these arenas. Finally,there has been significant development in large-scale device engineering due to mature semiconductor manufacturing techniques. The diverse set of photonic device architectures offering light confinement, guiding, and extraction is a prime example. These three paradigms – solitary dopant photonics and optoelectronics (solotronics), quantum science and technology, and device engineering – merge in the development of novel quantum photonic devices for the next generation of information processing systems. We present in this thesis a series of investigations of optical nanostructures for single optically active spins in single crystal diamond. Chapter 1 introduces the Nitrogen-Vacancy (NV) color center, summarizes its applications, and motivates the need for their integration into photonic structures. Chapter 2 describes two prototype nanobeam photonic crystal cavities for generating strong light-matter interactions with NV centers. The first device consists of a silicon nitride photonic crystal nanobeam cavity with high quality factor \(Q \sim 10^5\) and small mode volume \(V \sim 0.5*(\lambda/n)^3\). The second device consists of a monolithic diamond nanobeam cavity fabricated with the focused ion beam (FIB) directly in a single crystal diamond sample. Chapter 3 presents a high-efficiency source of single photons consisting of a single NV center in a photonic diamond nanowire. Early FIB prototypes are described, as is the first successful realization of the device achieved via reactive ion etching nanowires in a single crystal diamond containing NV centers, and finally a variation of this approach based on incorporation of NV centers in pure diamond via ion implantation. In chapter 4 we consider the optimal design of photonic devices offering both collection efficiency and cavity-enhancements and extend the model of the NV center to include photonic effects. In chapter 5 we briefly introduce a novel optically active spin discovered in a diamond nanowire. Finally, in chapter 6 we conclude with several proposals to extend this research program.
Engineering and Applied Sciences

Die vorliegende Forschungsarbeit widmet sich der Entwicklung und Untersuchung neuartiger photonischer Kristallstrukuren für Anwendungen in den Gebieten der Nanophotonik und Optofluidik. Dabei konzentriert sich eine erste Serie von Experimenten auf die Charakterisierung und Optimierung photonischer Kristallresonatoren im sichtbaren Spektralbereich, wobei bisher unerreichte Resonatorgüten von bis zu 3400 gezeigt werden können. Diese Strukturen werden anschließend als Plattformen zur Herstellung von hybriden nanophotonischen Bauelementen verwendet, indem externe Partikel (wie z.B. Diamant-Nanokristalle und Metall-Nanopartikel) in kontrollierter Art und Weise an die Resonatoren gekoppelt werden. Zu diesem Zweck wird eine Nanomanipulationsmethode entwickelt, welche Rastersonden zur gezielten Positionierung und Anordnung von Partikeln auf den photonischen Kristallstrukturen benutzt. Verschiedene Arten solcher Hybridelemente werden realisiert und untersucht, einschließlich diamant-gekoppelter Resonatoren, plasmon-gekoppelter Resonatoren und Metall-Diamant Hybridstrukturen. Außer für Anwendungen auf dem Gebiet der Nanophotonik werden verschiedene photonische Kristallstrukturen auch hinsichtlich ihres Leistungsvermögens als biochemische Sensorelemente erforscht. Zum ersten Mal wird eine umfassende numerische Analyse der optischen Kräfte auf Objekte im Nahfeld photonischer Kristallresonatoren durchgeführt, welche neue Möglichkeiten zum Einfang sowie zur Detektion und Untersuchung biologischer Partikel in integrierten optofluidischen Bauteilen bieten. Weiterhin werden unterschiedliche photonische Kristallfasern bezüglich ihrer Detektionssensitivität in Absorptions- und Fluoreszenzmessungen untersucht, wobei sich eine klare Überlegenheit von selektiv befüllten Hohlkern-Designs im Vergleich zu Festkern-Fasern offenbart.
This thesis deals with the development and investigation of novel photonic crystal structures for applications in nanophotonics and optofluidics. Thereby, a first series of experiments focuses on the characterization and optimization of photonic crystal cavities in the visible wavelength range, demonstrating unprecedented cavity quality factors of up to 3400. These structures are subsequently employed as platforms for the creation of advanced hybrid nanophotonic elements by coupling external particles (such as diamond nanocrystals and metal nanoparticles) to the cavities in a well-controlled manner. For this purpose, a nanomanipulation method is developed, utilizing scanning probes for the deterministic positioning and assembly of particles on the photonic crystal structures. Various types of such hybrid elements are realized and investigated, including diamond-coupled cavities, plasmon-coupled cavities, and metal-diamond hybrid structures. Apart from applications in nanophotonics, different types of photonic crystal structures are also studied with regard to their performance as biochemical sensing elements. For the first time a thorough numerical analysis of the optical forces exerted on objects in the near-field of photonic crystal cavities is conducted, providing novel means to trap, detect, and investigate biological particles in integrated optofluidic devices. Furthermore, various types of photonic crystal fibers are studied with regard to their detection sensitivity in absorption and fluorescence measurements, revealing a clear superiority of selectively infiltrated hollow-core designs in comparison to solid-core fibers.

Les nanostructures métalliques permettent de confiner la lumière à des échelles sub-longueur d’onde grâce à l'excitation de plasmons de surface. Elles ouvrent la voie à de nombreuses applications que ce soit en imagerie, en élaboration de composants photoniques ou en information quantique. Cette thèse porte sur l’étude de nanostructures métalliques, semi-continues ou constituées par des réseaux de trous au désordre contrôlé, et à leur interaction avec des nanocristaux semi-conducteurs colloïdaux particulièrement photostables. En associant plusieurs approches expérimentales complémentaires (spectroscopie en champ lointain, microscopie de champ proche optique, microscopie avec une sonde active de champ proche, caractérisation par microscopie confocale de l’émission de nanocristaux couplés aux surfaces métalliques), nous avons pu mettre en évidence les caractéristiques spécifiques des modes plasmons de ces différentes structures. Pour les réseaux au désordre contrôlé, nous avons en particulier analysé l’apparition progressive de modes localisés intenses et déterminé l’influence de paramètres tels que l’épaisseur de la couche d’or, le diamètre des trous ou la périodicité initiale du réseau. Les résultats expérimentaux obtenus se sont révélés en très bon accord avec les simulations numériques réalisées par FDTD
Metallic nanostructures allow to confine light at subwavelength scales by the excitation of surface plasmon. They open the way for many applications in imaging, photonic components development and quantum information. This thesis deals with the study of metallic nanostructures, semi-continuous or based on holes gratings with a controlled disorder, and their interaction with colloidal semiconductor nanocrystals that are very photostable. Combining several complementary experimental approaches (far-field spectroscopy, near-field optical microscopy, near-field active probe microscopy, characterization by confocal microscopy of the emission of nanocrystals coupled to the metallic surfaces), we were able to highlight specific characteristics of the plasmon modes of these different structures. For the gratings with a controlled disorder, we have in particular analyzed the emergence of intense localized modes and determined the influence of parameters such as the thickness of the gold layer, the diameter of the holes or the initial periodicity of the grating. The experimental results are in very good agreement with the numerical simulations carried out by FDTD

The aim of this thesis is to develop a technique which can be used in the reliable modelling, design and optimisation of practical suboptical wavelength sized photonic/plasmonic devices, which may involve arbitrary geometries on various scales. The technique involves the application of numerical electromagnetic simulation led by theoretical knowledge and physical insight to determine, design and optimise the operating mechanism of such devices. The work in this thesis contains a variety of problems/devices which involve arbitrary structures of different scales. This poses difficulties in both the fabrication and the modelling aspects of the design. The problems range in difficulty from those which can be simply and perfectly described via an analytical solution, to those which would be impractical to design using any other technique. The nature of the problems considered, i.e. the complicated geometry and the range of scales, necessitates the use of a flexible modelling technique. Finite Element Method (FEM) was found to be a valuable tool in the design and optimisation of the devices throughout this thesis, owing its success mainly to its versatility and flexible meshing abilities which allowed its operation in different length scales in an efficient manner. Three nanophotonic/plasmonic devices are considered in an effort to demonstrate the implementation and the application of the developed technique. The devices considered in this thesis demonstrate different challenges in the modelling and design while being of considerable interest in their own right as nanostructures for sensing and measurement. These devices are: A self-calibrated plasmon sensor, a plasmon resonator and an ultrahigh frequency optical acoustic surface wave detector. Whilst the first two devices are important as an application of plasmonics, the third device links the mechanical and optical processes together.

Recent impactful advances in integrated photonics undoubtedly owe much to silicon and its associated enabling platform (SOI). Although silicon has proved to be an indispensable element in many photonic systems yet it seems that it is not the ultimate solution to address all the challenges facing the photonics community. Therefore, integration of silicon with other optical materials featuring diverse properties is highly desirable. Such integration will be conducive to platforms which are naturally more capable and are suited for implementation of a wider range of optical devices and diverse functionalities. This dissertation is dedicated to design and implementation of integrated optical elements for hybrid material platforms. The basic theoretical foundation of integrated photonics is laid out in Chapter 2. In Chapter 3, an interlayer grating coupler for a specific hybrid material platform is designed, and demonstrated. Considering the fact that in almost all integrated photonic platforms, fabrication imperfections lead to an unpredictable shift in the wavelength of operation of individual devices, post fabrication tuning/trimming is inevitable. A number of widely used post fabrication trimming/tuning methods are briefly reviewed in Chapter 4 with special emphasis on a method based on electron beam exposure. In Chapter 5, an ultra-fast, low-power, and self-trimmable electro-optic modulator in demonstrated on a Si-based multilayer platform. Due to its remarkable optical and electronic properties, graphene has become a valuable material for opto-electronic applications. Integration of this novel 2D material with SOI platform is investigated in Chapter 6. Graphene-based electro-optic modulation through absorption and refractive-index change is successfully demonstrated using electrostatic gating mechanism. Chapter 7 is devoted to demonstration of a field-programmable 2 by 2 optical switch on a vertically stacked Si/SiO2/SOI platform. In Chapter 8, the peak-dragging phenomenon in a nanobeam photonic crystal cavity is studied. The optical bistability associated with this nonlinear phenomenon is of great interest for all-optical processing and sensing application. Future directions of this thesis are also discussed in the last Chapter.

Thesis (Ph.D)--Electrical and Computer Engineering, Georgia Institute of Technology, 2010.
Committee Chair: Prof. Ali Adibi; Committee Member: Prof. Joseph Perry; Committee Member: Prof. Stephen Ralph; Committee Member: Prof. Thomas Gaylord. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Reflection measurements on nanoparticle arrays fabricated using electron-beam lithography confirm the predicted particle-grating interaction. An unexpected polarization-dependent splitting of the film-mediated collective resonance is successfully attributed to the existence of out-of plane polarization modes of the metal nanoparticles. In order to distinguish between the excitation of propagating surface plasmons and localized nanoparticle plasmons, spectrally resolved leakage radiation measurements are presented. Based on these measurements, a universally applicable method for measuring the wavelength dependent efficiency of coupling free-space radiation into guided surface plasmon modes on thin films is developed. Finally, it is shown that the resonantly enhanced near-field coupling the nanoparticles and the propagating surface plasmons can lead to optimized coupler device dimensions well below 10 micrometers].; The current thrust towards developing silicon compatible integrated nanophotonic devices is driven by need to overcome critical challenges in electronic circuit technology related to information bandwidth and thermal management. Surface plasmon nanophotonics represents a hybrid technology at the interface of optics and electronics that could address several of the existing challenges. Surface plasmons are electronic charge density waves that can occur at a metal-dielectric interface at optical and infrared frequencies. Numerous plasmon based integrated optical devices such as waveguides, splitters, resonators and multimode interference devices have been developed, however no standard integrated device for coupling light into nanoscale optical circuits exists. In this thesis we experimentally and theoretically investigate the excitation of propagating surface plasmons via resonant metal nanoparticle arrays placed in close proximity to a metal surface. It is shown that this approach can lead to compact plasmon excitation devices. Full-field electromagnetic simulations of the optical illumination of metal nanoparticle arrays near a metal film reveal the presence of individual nanoparticle resonances and collective grating-like resonances related to propagating surface plasmons within the periodic array structure. Strong near-field coupling between the nanoparticle and grating resonances is observed, and is successfully described by a coupled oscillator model. Numerical simulations of the effect of nanoparticle size and shape on the excitation and dissipation of surface plasmons reveal that the optimum particle volume for efficient surface plasmon excitation depends sensitively on the particle shape. This observation is quantitatively explained in terms of the shape-dependent optical cross-section of the nanoparticles.
ID: 028917015; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2010.; Includes bibliographical references (p. 111-119).
Ph.D.
Doctorate
Optics and Photonics

La plasmonique basée sur les matériaux 2D est un domaine en plein essor dans la photonique, avec des implications technologiques potentielles révolutionnaires dans des domaines aussi variés que le diagnostic, l'énergie et la communication. Le graphène, un matériau 2D unique et doté d'excellentes propriétés plasmoniques, est une alternative prometteuse aux métaux nobles conventionnels dans le domaine de la plasmonique, notamment en raison de ses propriétés accordables en fréquence. Le graphène est modélisé dans cette thèse comme une feuille conductrice infiniment mince dans le cadre des éléments finis (vectoriels) de Galerkin, par opposition aux modèles plus conventionnels où la feuille de graphène est considérée comme ayant une épaisseur finie. Une seconde étude 2D rigoureuse du comportement du champ électromagnétique le long de la direction de propagation dans un guide d'ondes ouvert est réalisée en modélisant le graphène comme un diffuseur (1D) qui agit comme une perturbation locale au guide. Enfin, l'important décalage d’indice effectif qui existe entre le mode du guide d'ondes dielectrique et le mode plasmonique du graphène altère le couplage. Pour surmonter ce problème, un coupleur est conçu à l'aide du formalisme direct en champ diffracté développé. Des études approfondies du phénomène de battement observé dans le coupleur sont également réalisées. Plusieurs études impliquant les différents ordres de diffraction du réseau coupleur, l'épaisseur du guide d'ondes, etc. sont menées. Les paramètres du coupleur sont ensuite optimisés pour obtenir un coupleur à réseau compact et intégré à base de graphène dont l'efficacité atteint 80% à dans l’infrarouge
Plasmonics based on 2D materials is a burgeoning field in photonics with potential groundbreaking technological implications for diagnostics, energy and data communication. Graphene, a unique 2D material with excellent plasmonic properties is a promising alternative to conventional noble metals in plasmonics notably due to its tunable properties. Graphene is modelled in this thesis as an infinitesimally thin current-carrying sheet in a fully vectorial finite element Galerkin framework as opposed to more conventional models where graphene is considered to be of finite thickness. A rigorous study of the behaviour of the electromagnetic field along the propagation direction in an openridge waveguide is carried out by modelling graphene as a 1D conductive scatterer which acts as a local perturbation. The scattering model is verified through a full energy balance in different geometries. The large momentum mismatch that exists between the waveguide mode and the graphene plasmon mode in a graphene-based waveguide severely alters the coupling between these two modes. To overcome this, a coupler is designed using the developed scattering field formalism. Elaborate studies of the beating phenomenon observed in the coupler are performed. The designed waveguide coupler is apt for graphene of lengths equal to or shorter than the order of the wavelength. Several studies involving the various diffraction orders of the grating coupler, waveguide thickness, etc. are conducted. The parameters of the coupler are then optimized to yield a compact and integrated graphene-based grating coupler of efficiency as high as 80% in the infrared region

Avec les avantages significatifs de stockage, de traitement et de transmission des informations, la science de l’information quantique a attiré des études abondantes lors des dernières décennies, par lesquelles de nombreuses preuves de principe ont été faite en utilisant des techniques expérimentales macro-photoniques. Cependant, l'applicabilité de ces technologies dépend fortement de la miniaturisation du système, i.e. l'intégration « sur-puce » des fonctionnalités photoniques quantiques. Les conditions prérequis générales d'une puce quantique intégrée sont la génération, le transport et la détection localisée et efficace de photons. Des efforts ont été réalisés avec succès comportant une ou deux fonctions nécessaires. Cependant, l'intégration complète reste encore inachevée. Basé sur des éléments nano-photoniques de semiconducteurs et des techniques de nano-fabrication simples, cette thèse vise à fournir une stratégie d'intégration « sur-puce ». Une excitation efficace et locale d'une source de photon unique par un guide d'onde inférieure à l'échelle de la longueur d'onde est d'abord démontrée. Ensuite, nous étudions l’échange efficace de la lumière entre les nanostructures et les guide d'onde, qui peuvent servir le bloc de liaison entre les dispositifs dans un système d'intégration. La fabrication et la caractérisation d'un photo-détecteur sensible basé sur un nanofil unique sont présentées, qui présente un grand potentiel pour la détection de photons uniques. A la fin, une perspective de l'intégration ultime de toutes ces fonctionnalités est fournie
With the significant advantages in storing, processing and transmitting information, quantuminformation science has attracted abundant studies in the last few decades, by which many proofs ofprinciple have been made using macro-photonic experimental techniques. However, the applicabilityof this technology still strongly depends on the miniaturization of the system, i.e. the on-chip integration of quantum photonic functionalities. The general prerequisites of an integrated quantumchip are localised and efficient generation, transportation and detection of photons. Some effortshave been made successfully involving one or two necessary features. However, the full integration still remains unaccomplished. Based on semiconductor nanophotonic elements and simple nanofabrication techniques, this thesis aims to provide a strategy for on-chip quantum photonic integration. An efficient and local excitation of a single photon source with a subwavelengthwaveguide is firstly demonstrated. Then we investigate the efficient light exchange betweennanostructures and waveguides that can serve as linking blocks between devices in an integrationsystem. The fabrication and characterisation of a sensitive photodetector based on a single nanowireis also presented, which exhibits great potential in single-photon detection. At the end, an outlook ofthe ultimate integration of all these functionalities is provided

A la fin des années 80, ont été introduits les cristaux photoniques et les métamatériaux, permettant de concevoir des dispositifs avec des propriétés optiques très intéressantes. La découverte de ces propriétés artificielles est considérée comme l’une des avancées les plus spectaculaires de la photonique moderne, avec des applications importantes telles que la création de matériaux à réfraction négative, ou la conception de lentilles plates parfaites. Ces structures présentent néanmoins des pertes optiques dues aux métaux qui rendent plus difficile l’obtention de lentilles super-résolues. Une nouvelle approche, basée sur l’anisotropie du métamatériau, a alors été proposée comme une alternative très intéressante pour la conception de lentilles plates à super-résolution. Parallèlement les limites du modèle de Drude pour la description de la réponse optique des métaux ont été mises en évidence expérimentalement. Ce manuscrit de thèse présente une étude théorique et numérique d’empilements de couches minces métallo-diélectriques se comportant dans certains domaines de fonctionnement comme des milieux hyperboliques. Après avoir étudié le lien existant entre la réfraction négative et les décalages géants, le manuscrit se concentre sur la conception de lentilles plates permettant d’obtenir de la super-résolution : des images offrant une meilleure résolution que celle permise par les lois de la diffraction classique. Pour répondre à ces objectifs, nous avons développé une théorie basée sur l’approximation du milieu hyperbolique (obtenue avec un empilement métallo-diélectrique) par un milieu isotrope effectif à l’aide d’un développement parabolique du vecteur d’onde de Bloch. Les outils nécessaires pour toute étude de l’influence de la non-localité intrinsèque des métaux sur les propriétés optiques des structures sont ensuite développés et appliqués aux métallo-diélectriques
In the early 80’s, planar or periodic photonics crystals have been introduced in order to control light and to obtain entirely new optical properties. The unrivalled properties of these metamaterials are of tremendous interest for advanced photonic systems, with some important applications such as materials with negative refraction or flat lenses. However, these structures present optical losses induced by metals defects and experimental fabrication at nanometric scales that prevent them to reach the expected performances. A new approach based on describing metallo-dielectric as anisotropic materials has then been proposed as an alternative description. In parallel, the limits of the Drude model have been experimentally highligthed. In this context this manuscript presents a theoretical and numerical study of metallo-dielectric multilayers that can be considered as homogeneous media with a hyperbolic dispersion relation. We first present the link between negative refraction and large negative lateral shifts, and then focus on the design of flat lenses with subwavelength resolution : structures allowing a better resolution than the classical diffraction limit. We thus developed a theory based on the approximation of the hyperbolic medium, by a homogeneous and isotropic medium with a parabolic development of the vector of wave of Bloch. Finally, the tools required to study the influence of the intrinsic nonlocality of metals on the optical properties of multilayers are developped and the formalism is applied to metallo-dielectric lenses

Dislocation-free semiconductor nanowires are an extremely promising route towards compound semiconductor integration with silicon technology. However, precise control over nanowire doping, together with the surface charge properties, has remained a near-universal material challenge to date. In this regard, we have investigated the molecular beam epitaxial growth and the correlated surface electrical and optical properties of InN nanowires, a promising candidate for future ultrahigh-speed nanoscale electronic and photonic devices and systems, on Si platform.By dramatically improving the epitaxial growth process, intrinsic InN nanowires are achieved, for the first time, both within the bulk and on the non-polar InN surfaces. The near-surface Femi-level is measured to locate below the CBM, suggesting the absence of surface electron accumulation. Such intrinsic InN nanowires can possess an extremely low free carrier concentration of ~1e13 /cm3, as well as a close-to-theoretically-predicted electron mobility in the range of 8,000 to 12,000 cm2/V·s at room temperature. This result is in direct contrast to the universally observed 2DEG on the InN grown surfaces. Furthermore, the surface charge properties of InN nanowires, including the formation of 2DEG and the optical emission characteristics can be precisely tuned, for the first time, through the controlled n-type doping.More importantly, p-type doping into InN nanowires is also realized, for the first time. The presence of Mg-acceptors is clearly demonstrated by the PL spectra. Furthermore, p-type surface is observed from the XPS experiments, indicating the presence of free holes. Additionally, p-type conduction is directly measured by single nanowire field effect transistors.In the end of this thesis, InN nanowire p-i-n photodiodes are fabricated, with a light response up to the telecommunication wavelength range at low temperatures. This thesis work provides a vivid example, and paves the way for the rational “materials by design” development of silicon integrated InN-based device technology in the nanoscale.
Les nanofils semi-conducteurs sans dislocations sont une voie très prometteuse vers l'intégration des semi-conducteurs composés avec la technologie silicium. Cependant, un contrôle précis de dopage des nanofils, ainsi que les propriétés de charge de surface, reste un défi universel à ce jour. À cet égard, nous avons étudié la croissance épitaxiale par faisceau moléculaire et les propriétés de surface corrélés électriques et optiques des nanofils de InN sur du substrat de silicium, qui ont émergé comme candidat prometteur pour l'avenir des dispositifs électroniques et photoniques à très haute vitesse et à échelle nanométriques.Pour la première fois, en améliorant le processus de croissance épitaxiale, InN intrinsèque est atteint, à la fois dans le volume et sur les surfaces non polaires de InN. Le niveau de Fermi à la surface est mesuré et localisée sous le CBM, ce qui suggère l'absence d'accumulation d'électrons en surface. Ces nanofils InN intrinsèques possédent une concentration de porteurs libres très faible ~1e13 /cm3, ainsi que d'une mobilité proche de le théoriquement prédite d'électrons entre 8000 à 12000 cm2/V·s à température ambiante. Ce résultat est en contraste direct avec les 2DEG observés sur les surfaces d'InN. En outre, les propriétés de charge de surface de nanofils InN, y compris la formation de 2DEG et les caractéristiques d'émission optiques, peut être réglé avec précision, pour la première fois, par l'intermédiaire du contrôle d'incorporation de dopants de type n.Plus important encore, dopage de type p dans les nanofils InN est également réalisé pour la première fois. La présence de niveaux d'énergie Mg-accepteur est démontrée par les spectres de PL. Dans ces nanofils dopés de Mg, il n'y a pas d'accumulation d'électrons de surface et le niveau de Fermi dans le volume est proche de la VBM, ce qui indique un matériau de type p.En fin, la jonction p-i-n basé sur des nanofils InN photodétecteurs qui peut être utilisé en mode photovoltaïque est démontrée, avec une réponse à la lumière jusqu'à la longueur d'onde des télécommunications à de basses températures. Ce travail de thèse fournit un exemple frappant, ainsi que prépare le terrain pour le développement "matériaux par conception" de la technologie des dispositifs en silicium intégrée à base InN à l'échelle nanométrique.

Actualment el diagnòstic de Tuberculosi (TB) es realitza en laboratoris centralitzats, emprant equips voluminosos, reactius complexos i personal capacitat, augmentant els costos i el temps per obtenir els resultats. Per aquesta raó, l’objectiu d’aquesta tesi doctoral és el desenvolupament d’una plataforma point-of-care (POC) capaç d’oferir una resposta ràpida i fiable en el diagnòstic de TB. Per dur a terme aquest objectiu, la plataforma POC integra un nou sensor fotònic incorporat en un cartutx de micofluídica d’un sol ús. El sensor fotònic consisteix en un conjunt de interferòmetres Mach-Zehnder que ofereixen una alta sensibilitat. En primer lloc, es va dur a terme una caracterització òptica per estudiar el rendiment de la plataforma POC i la seva capacitat per a ser emprada en aplicacions biosensoras. Un cop caracteritzada òpticament, es van avaluar diferents estratègies de biofuncionalització per incorporar anticossos específics com a bioreceptors a la superfície del sensor. Després d’un estudi en profunditat, es va seleccionar i es va emprar l’estratègia de biofuncionalització òptima per l’anàlisi dels biomarcadors de TB. Els biomarcadors de TB es van avaluar tant en solució tampó com en mostres biològiques, particularment en orina humana. El biomarcador més prometedor i conegut de TB és el lipoarabinomanan (LAM), un component de la paret cel·lular bacteriana. En concret, la detecció d’aquest biomarcador va ser validada amb mostres clíniques de pacients amb TB i donants sans, mostrant la capacitat de la nostra plataforma POC per discriminar aquells pacients amb tuberculosi activa. A més, el disseny del sensor fotònic permet la detecció simultània de sis biomarcadors diferents. Tenint en compte això, hem dut a terme una prova de concepte de l’ús de la plataforma biosensora POC per a la detecció d’un panell de biomarcadors de TB utilitzant nanolitografía Dip-Pen per a la deposició de cada bioreceptor en cada sensor. Els nostres resultats, validats en estudis clínics més amplis, podrien tenir importants implicacions diagnòstiques. A més, el nostre biosensor POC ofereix una sèrie d’avantatges en comparació amb els mètodes recomanats per l’Organització Mundial de la Salut.
Actualmente el diagnóstico de Tuberculosis (TB) se realiza en laboratorios centralizados, empleando equipos voluminosos, reactivos complejos y personal capacitado, aumentando los costes y el tiempo para obtener los resultados. Por esta razón, el objetivo de esta Tesis Doctoral es el desarrollo de una plataforma point-of-care (POC) capaz de ofrecer una respuesta rápida y fiable en el diagnóstico de TB. Para llevar a cabo este objetivo, la plataforma POC integra un novedoso sensor fotónico incorporado en un cartucho de micofluídica desechable. El sensor fotónico consiste en un conjunto de interferómetros Mach-Zehnder que ofrecen una alta sensibilidad. En primer lugar, se llevó a cabo una caracterización óptica para estudiar el rendimiento de la plataforma POC y su capacidad para ser empleada en aplicaciones biosensoras. Una vez caracterizada ópticamente, se evaluaron distintas estrategias de biofuncionalización para incorporar anticuerpos específicos como bioreceptores a la superficie del sensor. Después de un estudio en profundidad, se seleccionó y empleó la estrategia de biofuncionalización óptima para el análisis de los biomarcadores de TB. Los biomarcadores de TB se evaluaron tanto en solución tampón como en muestras biológicas, particularmente en orina humana. El biomarcador más prometedor y conocido de TB es el lipoarabinomanano (LAM), un componente de la pared celular bacteriana. En concreto, la detección de este biomarcador fue validada con muestras clínicas de pacientes con TB y donantes sanos, mostrando la capacidad de nuestra plataforma POC para discriminar a aquellos pacientes con Tuberculosis activa. Además, el diseño del sensor fotónico permite la detección simultánea de seis biomarcadores distintos. Teniendo esto en cuenta, hemos llevado a cabo una prueba de concepto del empleo de la plataforma biosensora POC para la detección de un panel de biomarcadores de TB utilizando nanolitografía Dip-Pen para la deposición de cada bioreceptor en cada sensor. Nuestros resultados, validados en estudios clínicos más amplios, podrían tener importantes implicaciones diagnósticas. Además, nuestro biosensor POC ofrece una serie de ventajas en comparación con los métodos recomendados por la Organización Mundial de la Salud.
Nowadays, Tuberculosis (TB) diagnosis is carried out at centralised laboratories, employing bulky equipment, complex reagents, and trained staff, increasing costs and the time to obtain the results. For that reason, the aim of this Doctoral Thesis is to develop a point-of-care (POC) platform able to deliver a prompt and reliable response to TB diagnosis, taking advantage of a highly sensitive evanescent wave optical sensor. The POC platform integrates a novel photonic sensor consisting of a Mach-Zehnder Interferometer transducer array incorporated in a disposable microfluidic cartridge. Firstly, an optical characterisation was carried out to study the new POC performance and its ability to be employed for biosensing applications. Once the POC platform was optically characterised, diverse biofunctionalisation strategies were tested in order to incorporate specific antibodies as bioreceptors to the sensor surface. After an in-depth study, the optimal biofunctionalisation strategy was selected and employed for the analysis of the TB biomarkers. The TB biomarkers were evaluated in both buffer and biological samples, particularly human urine. The most promising and well-known TB biomarker was lipoarabinomannan (LAM), a bacterial cell wall component. In particular, this biomarker detection was validated with clinical samples from TB patients and healthy donors, showing the ability of our POC platform to discriminate those patients with active TB. Moreover, taking advantage of the photonic sensor design, which allows the simultaneous detection of six different biomarkers, we initiated the proof-of-concept of the POC platform for a TB biomarker panel detection using Dip-Pen Nanolithography for each corresponding bioreceptor deposition. Our results, if validated with larger clinical studies, could have important diagnostic implications taking into account the advantages added by our POC biosensor in comparison with the methods recommended by the World Health Organisation.
Universitat Autònoma de Barcelona. Programa de Doctorat en Biotecnologia

La plasmónica es la ciencia que estudia la interacción, a escala nanométrica, entre la luz y los electrones libres de los metales, dando lugar a la propagación de ondas altamente confinadas a su superficie. La plasmónica tiene multitud de aplicaciones en nanotecnología, como son el sensado biológico y químico, espectroscopía, nanolitografía, comunicaciones de banda ultra ancha integradas en chips, nanoantenas para luz, filtrado, y manipulación de señales ópticas, entre muchas otras. Una de las aplicaciones más novedosas es la creación de metamateriales: estructuras artificiales diseñadas para controlar la propagación de la luz, con aplicaciones fascinantes como la lente perfecta o la capa de invisibilidad. La plasmónica y los metamateriales están al frente de la investigación actual en fotónica, gracias al auge de la nanotecnología y la nanociencia, que abre las puertas a una gran cantidad de nuevas aplicaciones. Esta tesis, desarrollada en el Centro de Tecnología Nanofotónica de Valencia de la UPV, en colaboración con la University of Pennsylvania y King's College London, trata de aportar nuevas ideas, estructuras y dispositivos a los campos de la plasmónica y los metamateriales, tratando de realizar su fabricación y medida experimental cuando sea posible. La tesis no se ciñe a una única aplicación o dispositivo, sino que realiza una extensiva exploración de los diversos sub-campos de la plasmónica en busca de fenómenos novedosos. Los resultados descritos son los siguientes: En el campo de los metamateriales de índice negativo se presentan dos estructuras: nanocables en forma de U, y guías coaxiales plasmónicas. En el campo del sensado plasmónico se presenta el diseño y la prueba experimental de un sensor se sustancias químicas de altas prestaciones con nanocruces metálicas. También se detallan teóricamente: un novedoso dispositivo para luz lenta e inversión temporal de pulsos basada en metamateriales y cristales fotónicos, un metamaterial para conversión de polarización sintonizable mediante pérdidas, un análogo plasmónico al efecto de levitación Meissner en superconductores y un método de reducción de pérdidas en guías plasmónicas mediante interferencia en guías multimodo. Por último se presenta teórica y experimentalmente un nuevo ejemplo fundamental de interferencia de campo cercano, logrando la excitación unidireccional de modos fotónicos ---ya sean plasmónicos o no--- mediante los campos cercanos de un dipolo circularmente polarizado.
Rodríguez Fortuño, FJ. (2013). Design and implementation of plasmonic metamaterials and devices [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/31207
TESIS
Premiado

Les systèmes optiques intégrés ont été largement utilisés dans la détection et la caractérisation de substances biochimiques. Aussi, le développement de nouvelles technologies permettant la fabrication de structures intégrées à l’échelle nanométrique, ouvre un horizon dans la conception d'une nouvelle génération de capteurs biochimiques. Sur la base de plasmons de surface localisés, au cours des dernières années ont été proposés différentes configurations de systèmes optiques pour concentrer le champ électromagnétique dans une petite région de l'espace, ce qui favorise son interaction avec des substances biochimiques. En utilisant la méthode modale de Fourier, dans la présent thèse est présentée une analyse exhaustive de la propagation des modes dans un réseau périodique de nanoparticules métalliques intégrés avec une guide d'ondes diélectrique. Deux géométries des nanoparticules ont été étudiées: des réseaux périodiques de nanofils et de nanocônes métalliques. Il est démontré que pour les nanocônes métalliques le champ optique est fortement exalté au sommet des nanocônes quand ils sont excités à leur résonance LSP via une guide d'onde diélectrique. Pour valider les résultats numériques, on a fabriqué et caractérisé expérimentalement un réseau périodique de nanofils d’or placée sur une guide d’onde à échange d’ions. La caractérisation de l'échantillon a été réalisée dans le champ lointain en mesurant des spectres de transmission et dans le champ proche en utilisant la microscopie en champ proche optique de balayage (NSOM). Les résultats obtenus montrent que les dispositifs intégrés plasmoniques proposées peuvent être appliquées dans la détection de substances biochimiques
Localized surface plasmons (LSP) are used to control and concentrate the electromagnetic field in small volumes of matter. This is a very interesting property in the context of biophotonics. Indeed, it allows an enhancement of the light-matter interaction at the cell scale, or even at a single molecule scale. The technological challenge is to propose optical devices able to efficiently couple light into localized plasmonic modes and to improve the detection of signals resulting from the interaction between the confined light and the analyte under detection.In this thesis work, we theoretically and experimentally study the guiding and confinement properties of light in periodic arrays of metallic nanowires of rectangular and triangular (nanocones) cross section that support localized plasmons. These nanowires are integrated in a photonic circuit that enables an efficient light coupling. The extinction spectra of the plasmonic resonances are directly obtained by analyzing the transmitted light in the device. By making use of the Fourier modal method, we perform an exhaustive theoretical study of the plasmonic Bloch modes that propagate due to the near-field coupling of the localized plasmons resonances. It is demonstrated that for the metallic nanocones, the optical field can be strongly enhanced by a controllable tip effect and remarkably intense

Aujourd’hui l’Internet des Objets (IdO) est en pleine évolution, et le dispositif de détection optique tel que présenté ici pourrait être utilisé dans ce domaine. En effet ces dispositifs pourraient être utilisé pour faire des tests pour une analyse comme la surveillance de la santé d'une personne en faisant un test sanguin ou d'autres analyses médicales et utilisés pour surveiller l'environnement en testant l'eau ou de l'air dans les villes, les montagnes, les usines, les rivières. Pour créer le dispositif, on a utilisé une combinaison du spectromètre nommé Spectromètre d'échantillonnage bi-directionnel couplé (CoBiSS) [Brevet WO2009127794A1] et une puce à résonance de Plasmon de Surface (SPR).Dans le but de l’intégration optique, une nouvelle analyse de l’échantillonnage dans le spectromètre CoBiSS est présentée, suivie de l'intégration du système électronique et optique pour supprimer les pièces mobiles. Il était nécessaire de rendre l'appareil petit et portable. Pour faciliter l'utilisation, une interface graphique a été développée. Pour la détection, une puce SPR a été ajouté à CoBiSS et une nouvelle puce à résonance de plasmon de surface localisée (LSPR) a été modélisé pour maximiser sa sensibilité. Une nouvelle définition du calcul de sensibilité a été proposée.Cet appareil nécessite l'ajout de fonctionnalisation sur (L)SPR Chip pour la détection et une application finale. Cet appareil pourrait être un « objet » idéale dans l’IdO
As the world is moving towards Internet of Things, an optical detection device is presented that can be utilized in this domain. This device can be used to do tests that use optical detection for analysis like monitoring of Health of a person by doing a blood test or other medical analysis and also be used to monitor environment by testing water or air in cities, mountains, factories, rivers and so on for a practical purpose. To create this optical detection device, a combination of spectrometer named Coupled Bi-Directional Sampling Spectrometer (CoBiSS) [Patent number WO2009127794A1] and Surface Plasmon Resonance (SPR) Chip has been used. For the optical integration, a new analysis of the sampling in the spectrometer CoBiSS is presented. Followed by, Device and Optical Integration of CoBiSS has been done to remove all the moving parts. It was necessary to make the device small that can be handheld and portable. For ease of use a Graphical User interface was developed. For detection, CoBiSS was added with a chip of SPR. A modelisation of SPR chip was done to maximize its sensitivity. A new Localized Surface Plasmon Resonance (LSPR) chip has been proposed to work with CoBiSS. Optimization of LSPR chip has been performed to maximize the sensitivity. A new definition for the calculation of Sensitivity has been proposed. This device needs the addition of functionalization on (L)SPR Chip for detection and a final application. This device could be an ideal “Thing” in Internet of Things

Les besoins en matière d'analyse moléculaire portative sont croissants, comme dans le cadre de la médecine d'urgence, le dépistage médical précoce, ou encore le contrôle sanitaire des denrées alimentaires. Ces besoins mènent au développement de biocapteurs performants répondant aux critères du « Point-of-Care » (POC), c'est-à-dire la détection sur le lieu d'intervention, que ce soit au chevet du patient, dans un cabinet de médecin, etc. Les capteurs POC ont pour fonction principale de réduire le coût et la durée nécessaire aux analyses, afin d'être en mesure de prendre une décision thérapeutique la plus rapide. De plus, grâce à leur mobilité ils permettent de proposer des analyses médicales dans les zones éloignées des centres hospitaliers et des laboratoires d’analyses. L'objectif de cette thèse est de développer un dispositif de détection optique compatible avec les critères du POC et permettant de répondre aux besoins en matière de criblage moléculaire dans ce type d’analyses. Afin de répondre à ces critères, ce dispositif devra être portable, rapide, bas-coût, et capable de détecter plusieurs biomolécules en parallèle avec une puce jetable, tout en présentant de bonnes performances de détection. L'approche présentée dans ce manuscrit consiste en un dispositif d'imagerie sans lentille, utilisant une puce de cristaux photoniques en silicium, avec une illumination en incidence normale par une source lumineuse bas-coût. Les résultats phares de cette thèse sont d’une part la démonstration d’une détection spécifique de biomolécules à l'aide de nos capteurs à cristaux photoniques, et d’autre part la démonstration de puces à cristaux photoniques intégrant une fonction de spectrométrie pour une application de détection en imagerie sans lentille compatible avec les critères du POC
The needs for portable molecular analysis tools are growing, including in the fields of emergency care, early medical diagnosis, or food safety analysis. These needs lead to the development of performant biosensors, meeting the criteria of “Point-of-Care” (POC), that is, the detection in the field, whether at the patient’s place, the physician’s office, etc. POC sensors’ primary missions are to reduce the analysis time and cost, to allow for a quicker therapeutic decision. In addition, thanks to their portability, they can provide analysis availability in remote areas, far from hospitals or medical laboratories. The objective of this PhD work is to develop an optical sensing system, compatible with the POC criteria, and addressing the needs in terms of molecular screening. To meet these criteria, this sensing system should be portable, fast, low-cost, and able to detect multiple biomolecules in parallel on a disposable chip, while providing good sensing performances. The approach presented in this manuscript consists in a lens-less imaging system, exploiting photonic crystals on a silicon chip, with a normal incidence illumination by a low-cost light source. The main results of this PhD work are on one hand the demonstration of a specific detection of biomolecules, thanks to our photonic crystal sensors; and on the other hand the demonstration of the integration of an on-chip spectrometry functionality using photonic crystals, towards an application in lens-less imaging detection compatible with the POC criteria

Dottorato in Information and Communication Technologies, Ciclo XXXI
The purpose of this thesis research project has been the integration of photonic nanostructures on silicon substrate. In particular, three different devices have been developed, whose application fields fall within the main research topics of silicon photonics. Indeed, a plasmonic biochemical sensor, an all-dielectric metamaterial for all-optical switching applications and a 1D photonic crystal as an interconnecting device have been successfully integrated on silicon substrate. All of the proposed devices could lead to noticeable advances in silicon photonics, thanks to their potentiality for the development of integrated silicon-based nanodevices.
University of Calabria

A central topic in the research of nanophotonics is the geometrical optimization of the nanostructures since the geometries are deeply related to the Mie resonances and the localized surface plasmon resonances in dielectric and metallic nanomaterials. When many nanostructures are assembled to form a metamaterial, the tuning of the geometrical parameters can bring even more profound effects, such as bound states in the continuum (BIC) with infinite quality factors (Q factors). Moreover, with the development of nanofabrication technologies, there is a trend of integrating nanostructures in the vertical direction, which provides more degrees of freedom for controlling the device performance and functionality. The main topic of this dissertation is to explore some of the abovementioned tuning possibilities to enhance the performance of nanophotonic devices. The dissertation contains two major parts: In chapters 2 and 3, the vertical integration of metalenses is studied. We discover a phenomenon similar to the Moiré effect in the bilayer Pancharatnam-Berry phase metalenses and reveal the role of geometrical imperfections on the focusing performance of reflective metalenses. Novel multifocal and reflective metalenses, with smaller footprints and enhanced performance compared to their bulky conventional counterparts, are designed based on the theoretical findings. The study of geometrical imperfections also provides guidelines for analyzing and compensating the fabrication errors, which is vital for large scale production and commercialization of metalenses. In chapters 4 and 5, we use machine learning to harness the full tuning power of the complicated geometries, which is challenging with conventional design methods. Plasmonic metasurfaces with on-demand optical responses are designed by manipulating the coupling of multiple nanodisks using neural networks. An accuracy of ± 8 nm is achieved, which is higher than previous reports and close to the fabrication limits of nanofabrication technologies. We also demonstrate, for the first time, the control of multiple BIC states using freeform geometries with predefined symmetry. It is a new method to exploit the untapped potential of freeform photonics structures. The discoveries we have made in both dielectric and plasmonic nanophotonic devices could benefit applications such as imaging, sensing, and light-emitting devices.

Photonic Crystals, man-made periodic structures with a high refractive index contrast modulation, have recently become very interesting platform for the manipulation of light. The existence of a photonic bandgap, a frequency range in which propagation of light is prevented in all directions, makes photonic crystals very useful in applications where spatial localization of light is required. Ideally, by making a three-dimensional photonic crystal, propagation of light in all three dimensions can be controlled. Since fabrication of 3-D structures is still a difficult process, a more appealing approach is based on the use of lower dimensional photonic crystals. A concept that has recently attracted a lot of attention is a planar photonic crystal based on a dielectric membrane, suspended in the air, and perforated with a two-dimensional lattice of holes.

In this thesis theoretical and experimental study of planar photonic crystal nanolasers, waveguides and super-dispersive elements is presented. Room temperature operation of low-threshold nanolaser is demonstrated, both in air and in different chemical solutions. For the first time, we have demonstrated that photonic crystal nanocavity lasers can be used to perform spectroscopic tests on ultra-small volumes of analyte. Our porous cavity design permits the introduction of analyte directly into the high optical field of the laser cavity, and therefore it is ideally suited for the investigation of interaction between light and matter on a nanoscale level. We showed that small changes in refractive index of the ambient surrounding the laser can be detected by observing the shifts in emission wavelengths of the laser. Our lasers can be integrated into large arrays to permit the analysis of many reagents at the same time. The nanolasers can also be integrated with photonic crystal waveguides to form the integrated systems of higher complexities. Theoretical and experimental investigation of various photonic crystal waveguide designs is discussed. Details of the fabrication procedure used to realize nanophotonic devices in silicon on insulator as well as InGaAsP materials are presented.

As optical interconnects make their paces to replace traditional electrical interconnects, implementing low cost optical components and hybrid optic-electronic systems are of great interest. In the research work described in this dissertation, we are making our efforts to develop several practical optical components using novel printing technologies including imprinting, ink-jet printing and a combination of both. Imprinting process using low cost electroplating mold is investigated and applied to the waveguide molding process, and it greatly reduces the surface roughness and thus the optical propagation loss. The imprinting process can be applied to photonic components from multi-mode waveguides with 50[mu]m critical dimension down to photonic crystal structures with 500nm hole diameter. Compared to traditional lithography process, imprinting process is featured by its great repeatability and high yield to define patterns on existing layers. Furthermore we still need an approach to deposit layers and that is the reason we integrate the ink-jet printing technology, another low-cost, low material consumption, environmental friendly process. Ink-jet printing process is capable of depositing a wide range of materials, including conductive layer, dielectric layer or other functional layers with defined patterns. Together with molding technology, we demonstrate three applications: proximity coupler, thermo-optic (TO) switch and electro-optic (EO) polymer modulator. The proximity coupler uses imprinted 50[mu]m waveguide with embedded mirrors and ink-jet printed micro-lenses to improve the board-to-board optical interconnects quality. The TO switch and EO modulator both utilize imprinting technology to define a core pattern in the cladding layer. Ink-jet printing is used to deposit the core layer for TO switch and the electrode layers for EO modulator. The fabricated TO switch operates at 1 kHz with less than 0.5ms switching time and the EO modulator shows V[pi][middle dot]L=5.68V[middle dot]cm. To the best of our knowledge, these are the first demonstrations of functional optical switches and modulators using printing method. To further enable the high rate fabrication of ink-jet printed photonic and electronic devices with multiple layers on flexible substrate, we develop a roll-to-roll ink-jet printing system, from hardware integration to software implementation. Machine vision aided real time automatic registration is achieved when printing multiple layers.
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Silicon is the dominant material in Microelectronics. Building photonic devices out of silicon can leverage the mature processing technologies developed in silicon CMOS. Silicon is also a very good waveguide material. It is highly transparent at 1550nm, and it has very high refractive index of 3.46. High refractive index enables building high index contrast waveguides with dimensions close to the diffraction limit. This provides the opportunity to build highly integrated photonic integrated circuit that can perform multiple functions on the same silicon chip, an optical parallel of the electronic integrated circuit. However, silicon does not have some of the necessary properties to build active optical devices such as lasers and modulators. For Example, silicon is an indirect band gap material that can’t be used to make lasers. The centro-symmetric crystal structure in silicon presents no electro-optic effect. By contrast, electro-optic polymer can be engineered to show very strong electro-optic effect up to 300pm/V. In this research we have demonstrated highly compact and efficient devices that utilize the strong optical confinement ability in silicon and strong electro-optic effect in polymer. We have performed detailed investigations on the optical coupling to a slow light waveguide and developed solutions to improve the coupling efficiency to a slow light photonic crystal waveguides (PCW). These studies have lead to the demonstration of the most hybrid silicon modulator demonstrate to date and a compact chip scale true time delay module that can be implemented in future phased array antenna systems. In the future, people may be able to realize a photonic integrated circuit for optical communication or sensor systems using the devices we developed in our research.
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This thesis investigates ways of improving the performance of fundamental silicon nanophotonic devices through post-fabrication processes. These devices include numerous optical resonator designs as well as slow-light waveguides. Optical resonators are used to confine photons both spatially and temporally. In recent years, there has been much research, both theoretical and experimental, into improving the design of optical resonators. Improving these devices through fabrication processes has generally been less studied. Optical waveguides are used to guide the flow of photons over chip-level distances. Slow-light waveguides have also been studied by many research groups in recent years and can applied to an increasingly wide-range of applications. The work can be divided into several parts: Chapter 1 is an introduction to the field of silicon photonics as well as an overview of the fabrication, experimental and computational techniques used throughout this work. Chapters 2, 3 and 4 describe our investigations into the precision tuning of nanophotonic devices using laser-assisted oxidation and atomic layer deposition. Chapters 5 and 6 describe our investigations into improving the sidewall roughness of silicon photonic devices using hydrogen annealing and excimer laser induced melting. Finally, Chapter 7 describes our investigations into the nonlinear properties of lead chalcogenide nanocrystals.

Microscale and nanoscale mechanical resonators have been used in advanced technological applications, from high precision time keeping and mass sensing, to processing high frequency signals in mobile communications. In the last few decades, they have been an important part of progress in the field of quantum information and metrology and have been proposed as quantum memories or transducers for measuring or connecting different types of quantum systems.

The field of cavity optomechanics and electromechanics is concerned with coupling the electromagnetic field of a resonant optical cavity or electrical circuit to mechanical motion. These systems provide potential means to control and engineer the state of a mechanical object at the quantum level. This thesis contains the description of mechanical systems in megahertz to a few hundred megahertz frequency range formed by nano-fabricating photonic, phononic, and electrical circuits on a chip. These structures are designed to provide a large radiation pressure coupling between mechanical motion and electromagnetic fields to address and manipulate motional degrees of freedom. Qualitatively novel quantum effects are expected when one takes a step beyond linear coupling and exploits higher order interactions. To that end, we integrate electrical, mechanical and photonic structures in a multimode photonic crystal structure to observe "x²-coupling", where the optical cavity frequency is coupled to the square of the mechanical displacement. Moreover, we have developed two integrated on-chip platforms based on Si₃N₄ and Si nanomembranes capable of interfacing superconducting qubits and optical photons and realizing reversible microwave-to-optical conversion. We employ radiation pressure to cool these mechanical resonators to their quantum ground state. Finally, we demonstrate a form of electromechanical crystal for coupling microwave photons and hypersonic phonons of frequency ω_m/2π = 0.425 GHz by capacitively coupling a phononic crystal acoustic cavity to a superconducting microwave resonator. Moving to higher frequency acoustic cavities not only facilitates the integration of electromechanical circuits and nanophotonic systems capable of operation in the resolved sideband limit of optomechanics for noise-free quantum signal conversion, but it opens up the possibility of using phonons as information carriers via phononic circuits. Utilizing a two-photon resonance condition for efficient microwave pumping and phononic bandgap shield to eliminate acoustic radiation, we achieve large cooperative electromechanical coupling (C ≈ 30) and intrinsic decay time of 2.3 ms. Moreover, electrical read-out of the phonon occupancy shows that the acoustic mode thermalizes close to its quantum ground-state of motion (phonon occupancy n_m=1.5) at a fridge temperature of T_f = 10 mK. We conclude by considering several designs and fabrication improvements to the hypersonic electromechanical crystals that would enable them to perform quantum conversion between the electrical and acoustic domain.

Silicon has become an increasingly important photonic material for communications, information processing, and sensing applications. Silicon is inexpensive compared to compound semiconductors, and it is well suited for confining and guiding light at standard telecommunication wavelengths due to its large refractive index and minimal intrinsic absorption. Furthermore, silicon-based optical devices can be fabricated alongside microelectronics while taking advantage of advanced silicon processing technologies. In order to realize complete chip-based photonic systems, certain critical components must continue to be developed and refined on the silicon platform, including compact light sources, modulators, routers, and sensing elements. However, bulk silicon is not necessarily an ideal material for many active devices because of its meager light emission characteristics, limited refractive index tunability, and fundamental limitations in confining light beyond the diffraction limit.

In this thesis, we present three examples of hybrid devices that use different materials to bring additional optical functionality to silicon photonics. First, we analyze high-index-contrast silicon slot waveguides and their integration with light-emitting erbium-doped glass materials. Theoretical and experimental results show significant enhancement of spontaneous emission rates in slot structures. We then demonstrate the integration of vanadium dioxide, a thermochromic phase-change material, with silicon waveguides to form micron-scale absorption modulators. It is shown experimentally that a 2-µm long waveguide-integrated device exhibits broadband modulation of more than 6.5 dB at wavelengths near 1550 nm. Finally, we demonstrate polymer-on-gold dielectric-loaded surface-plasmon waveguides and ring resonators coupled to silicon waveguides with 1.0±0.1 dB insertion loss. The plasmonic waveguides are shown to support a single surface mode at telecommunication wavelengths, with strong electromagnetic field confinement at the polymer-gold interface. These three device concepts show that diverse materials can be integrated with silicon waveguides to achieve enhanced light emission, broadband modulation, and strong confinement, all while retaining the advantages of the silicon photonics platform.

The sub-wavelength optical confinement and low optical loss of nanophotonic devices dramatically enhances the interaction between light and matter within these structures. When nanophotonic devices are combined with an efficient optical coupling channel, nonlinear optical behavior can be observed at low power levels in weakly-nonlinear materials. In a similar vein, when resonant atomic systems interact with nanophotonic devices, atom-photon coupling effects can be observed at a single quanta level. Crucially, the chip based nature of nanophotonics provides a scalable platform from which to study these effects.

This thesis addresses the use of nanophotonic devices in nonlinear and quantum optics, including device design, optical coupling, fabrication and testing, modeling, and integration with more complex systems. We present a fiber taper coupling technique that allows efficient power transfer from an optical fiber into a photonic crystal waveguide. Greater than 97% power transfer into a silicon photonic crystal waveguide is demonstrated. This optical channel is then connected to a high-Q (> 40,000), ultra-small mode volume (V < (λ/n)³) photonic crystal cavity, into which we couple > 44% of the photons input to a fiber. This permits the observation of optical bistability in silicon for sub-mW input powers at telecommunication wavelengths.

To port this technology to cavity QED experiments at near-visible wavelengths, we also study silicon nitride microdisk cavities at wavelengths near 852 nm, and observe resonances with Q > 3 million and V < 15 (λ/n)³). This Q/V ratio is sufficiently high to reach the strong coupling regime with cesium atoms. We then permanently align and mount a fiber taper within the near-field an array of microdisks, and integrate this device with an atom chip, creating an "atom-cavity chip" which can magnetically trap laser cooled atoms above the microcavity. Calculations of the microcavity single atom sensitivity as a function of Q/V are presented and compared with numerical simulations. Taking into account non-idealities, these cavities should allow detection of single laser cooled cesium atoms.

表面電漿是由貴金屬表面電荷密度漲落引起的沿著金屬表面傳播的電磁波。在過去十年裡，表面電漿效應因其在光子器件，傳感，表面增強螢光，尤其是表面增強拉曼散射(SERS) 方面的應用而引起了廣泛的關注.許多著作中的結論已經證實了的預期的SERS 強度，因此使得基於各種不同納米結構中的熱點的SERS變成一種下一代超敏感生物傳感平臺。因為表面電漿的波長和材料介電性質密切相闕，受f於此，難以進一步減小，所以對於進一步的各種應用來說，保證產生高強度的表面電漿使至關重要。同時，用電漿實現納米光子器件已經引起了研完者長久的興趣。例如，基於等問距規則排列的密置金屬納米顆粒之間突破衍射極限的的近場耕合已經被用於傳輸光信號。但是，輻射和吸收損耗在此類波導中是很嚴重的。因此，設計新概念的電漿器件是急需的。
有鑒於上述種種問題，本論文集中于總結構和材料兩方面剪裁表面電漿以期達到下面的要點和目的:
(1)基於傳播電漿(PSPs) ，或者傳播電漿同局域電漿(LPRs) 的結合而發展新的簡單的器件，由此提供顯著的聚焦、電磁場和場強增強。這種器件可以應用於很多方面，包括依賴強場的生物分子傳感探測，以及非線性光學效應。
(2) 設計基於增益介臂的低損耗的納米光子學器件，這種器件能夠為納米光子器件提供切實的可行性。針對表面電漿共振和電漿結構植于的介電環境之間聯繫，獲得其理論闡釋。這一工作將可以為傳感和器件設計提供深入的理解。
本論文中我們已經得到了如下的成果:
(1)一種基於將表面電漿聚焦到金屬盤中心孔而實現級聯放大增強的SERS 激勵源被提出和理論研究。這種器件提供了準均勻，水平偏振，較大面積的強SERS 激勵源。如時域有限差分(FDTD) 方法所揭試，強度譜線和波長範圍在650-1000 nm的近場性質展混出了一系列增強模式。在最佳的增強模式下，孔洞中的電場可以使得SERS 信號獲得四次方的進一步增強。同時一種解析模型也被提出來給FDTD結果以精確的解釋。我們的模型同時揭示了通過侵化金屬盤尺度而得到八次方場增強的可能性。我們的結果表明極強的電場增強，並且聚焦的電場是平行于金屬盤平面的效果，只能在中間包含一個孔洞的中空金屬盤(HMDs) 中才可能實現。這是因為金屬盤中間絶悸的問時的存在使得孔洞邊棒的電子不能流通間隙，進進而使得高強度的電場可以存在。另一方面，在實心的金屬盤的情形下，電子流會傾向於抑制到達中心的表面電漿的強度。除了產生高度優化的SERS 熱點，這種大面積的活性孔洞在螢光增強和非線性光學中也提供了一些潛在的應用。
除了中空金屬盤，基於經由增孟輔助下PSPs 的LPRs 之間的衍射共掠，我們開發了另一種一種高度侵化的熱點。由此得到的器件被理論上分析。衍射共振的過程是經由下述過程實現的:由LPRs 實現的光場局域化， LPRs 和PSPs 相互作用，以及通過PSPs 的能量傳遞。我們的研究表明通過給PSPs 引入光學增孟，可以從一種激光過程中的到LPRs 非常強的電磁場增強。我們發現通過現實的增豆豆水平，局域電場的增強引子可以達到10⁷。因此，我們為實現依賴強電場的單分子SERS提供了一種理想的方案，並且這種方案也是一種納米激光的新機制。
(2) 基於增孟輔助的電漿共振金屬納米顆粒鏈，我們提出了一種低損耗納米尺度的波導。我們證明通過引入增孟材料或者引入適當的介電材料作為周圍環境，波導的損耗可以顯著減小。為了得到低損耗傳翰的復介電譜，我們開發了一種高效的膺正交基展開(POBE) 方法。本徵模式分析揭示了低損耗模式的物理源頭，同時給出了除了基於單體偶極共振傳輸之外能量傳輸的可能性。我們提出一種基於電子書刻蝕和化學合成納米顆粒的一種製備方案。這種電漿波導可以構成納米光學器件的基石，尤其是用於集成納米光子學線路。同時，我們原創的揭示表面電漿的物理機理的POBE 方法可以用於進一步研究優化增豆豆輔助的電漿結構，進而設計良好的納米光子器件。
本論文始於一個古老問題:宏觀尺度下基於傳統介電材料光聚焦和傳導，并最後終結於納米尺度內經由增益材料和電漿結構的表面電漿的聚焦、和引導。論文結尾，本文給出了展望以及幾種可能的器件實現方案。
Surface plasmons (SPs) are electromagnetic waves that propagate along the surface of a noble metal via fluctuations in electron density. In the last decade, SPs effects gained widespread attention for their potential application in photonic devices, sensing, surface-enhanced fluorescence, especially Surface-Enhanced Raman Scattering (SERS). Many published results have confirmed the expected strengths of SERS, hence making it possible for SERS to become a next generation ultra-sensitive biosensing platform, which may take the form of various nano-structures in order to achieve optimized hot spots. While the wavelength of SPs is closely related to material dielectric properties and has limited scope for further reduction, it is of critical importance to ensure that SPs are being generated with the highest intensity before any further application advancement is possible. Meanwhile, plasmonics has aroused longstanding interests among researchers to realize nanophotonic devices. For example, ordered arrays of closely spaced metallic nanoparticles (MNP) have been employed to transport optical signals via near-field coupling below the diffraction limit. However, radiation and absorption losses in these waveguides can be serious. New concepts for novel plasmonic devices are essential.
In light of these issues, this thesis focuses on tailoring SPs from the viewpoints of structural and material properties with the following objectives:
(1) To develop a new class of simple plasmonic devices based on tailoring of propagating surface plasmons (PSPs) or cooperation between PSPs and localized plasmon resonance (LPRs) to offer significant field focusing and intensity enhancement. It can serve a wide range of applications, including high field related biomolecular sensing and detection as well as non-linear optical effects.
(2) To design low loss nanophotonic wave guides based on gain medium, which may offer real opportunity for practical nanophotonic devices. To obtain a theoretical interpretation of relationship between surface plasmon resonance and host environment where the plasmonic structure embedded. This study should provide further insight towards sensing and device design.
We have achieved the following results in this project:
(1) A novel SERS excitation source based on focusing of surface plasmons around the center hole of a metal disk for cascaded enhancement is put forward and studied theoretically. The device offers intense SERS excitation with quasi-uniformity and horizontal polarization over a comparatively large hole. As revealed by fmite-difference time-domain (FDTD) method, the intensity spectra and the characteristics of the near field for the wavelength range of 650-1 000 nm exhibit a number of enhancement modes. Electric field intensity of the optimal mode enhances the SERS signal inside the hole by over four orders. An analytical model was also developed to gain precise interpretation on FDTD results. Our model also reveals the possibility of achieving eight orders of enhancement by optimizing the scale of the disk. Our results indicate that much higher electric field enhancement in hollow metal disks (HMDs) can only be possible when we have a hole at the centre and the direction of the focusing field is parallel to the surface of the plasmonic device. This is because of the presence of an insulating gap at the center, that higher level of electric field can exist as electrons are not allowed to flow pass the gap. On the other hand, in the case of a solid metal disk, the flow of mobile electron will tend to dampen the amplitude of the arriving SPs. In addition to generation of highly optimized hot spots for SERS, the large active hole also offers potential applications in fluorescence enhancement and nonlinear spectroscopy.
In addition to HMDs, we also develop a kind of highly optimized hot spots based on diffraction coupling between LPRs via gain-assisted PSPs. Thus derived device was theoretically analyzed. The process of diffraction coupling is achieved via localization of light by LPRs, LPRs-PSPs interplay and PSPs transfer. Our study shows that by incorporating optical gain to PSPs, a very strong boost of the electromagnetic enhancement of LPRs can be expected from a lasing process. We find that with a practical gain level, the enhancement factor of local electric field intensity can be larger than 10⁷. Hence, we offer an ideal configuration to realize high-field dependent single molecule SERS and also a newly applied physical scheme for nano-Iaser.
(2) We propose a low-loss nanoscale wave guide based on gain-assisted plasmonic resonance MNP chain. We demonstrate that by employing a gain material or even an appropriate dielectric for the host environment, waveguide loss can be reduced dramatically. A highly efficient pseudo-orthonormal basis expansion (POBE) method for obtaining the complex dielectric spectra of the low-loss transmission has been developed. Eigenmode analysis revealed the physical origin of those low-loss wave guiding modes, which opens the possibility to achieve waveguiding other than using conventional dipolar resonances of individual particles. A scheme based on electron beam lithography and chemically synthesized nanoparticles has been proposed to fabricate the device. Such plasmonic waveguides may serve as building blocks for making nanoscale optical devices especially for integrated nanophotonic circuits. Meanwhile, the originally developed POBE method, which reveals the general physical mechanism of SPs, can be used to further explore optimized gain-assisted plasmonic structures to design favorable nanophotonic devices.
This thesis begins with an old problem: light focusing and guiding in macroscopic scale with traditional dielectric, and sum up finally with SPs focusing and guiding in nanoscale with gain material and plasmonic material. An outlook is presented at last with several potential schemes for the device realization.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Detailed summary in vernacular field only.
Zhang, Haixi.
"September 2011."
Thesis (Ph.D.)--Chinese University of Hong Kong, 2012.
Includes bibliographical references (leaves 124-139).
Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Abstract also in Chinese.
Chapter Chapter1 --- Introduction --- p.1
Chapter 1.1 --- Towards field intensity focusing and guiding of electromagnetic wave --- p.1
Chapter 1.2 --- Surface plasmons as a route to realize electromagnetic field focusing and waveguiding in nanoscale --- p.3
Chapter 1.3 --- Structure of this thesis --- p.10
Chapter Chapter2 --- Plasmonic near field engineering: structural and material aspects --- p.13
Chapter 2.1 --- Light focusing using near field oflocalized plasmon resonances --- p.13
Chapter 2.2 --- Plasmonic near field focusing through propagating surface plasmons --- p.30
Chapter 2.3 --- Various schemes for near field focusing through surface plasmons --- p.33
Chapter 2.4 --- Guiding surface plasmons in nanoscale --- p.35
Chapter 2.5 --- Gain-assisted surface plasmons: a different path to field enhancement and guiding --- p.38
Chapter Chapter3 --- Surface plasmons: characteristics and methodology --- p.42
Chapter 3.1 --- Characteristics of localized plasmon resonance --- p.42
Chapter 3.2 --- Localized plasmon resonance: Mie theory and its variations --- p.44
Chapter 3.3 --- Characteristics of propagating surface plasmons --- p.49
Chapter 3.4 --- Reflection Pole Method for studying propagating surface plasmons in multilayer structures --- p.55
Chapter 3.5 --- Pseudo-orthonormal basis expansion method: a new mathematical scheme for modeling surface plasmons --- p.58
Chapter Chapter4 --- High field generation through intensity focusing of propagating surface plasmons --- p.62
Chapter 4.1 --- Introduction --- p.62
Chapter 4.2 --- The hollow metal disk design and its characteristics --- p.64
Chapter 4.3 --- Quasi-uniform excitation source based on focusing of propagating surface plasmons for cascade enhancement of surface enhanced Raman scattering --- p.68
Chapter 4.4 --- Conclusions and outlook --- p.78
Chapter Chapter5 --- High field generation through intensity enhancement of localized plasmon resonance from gain-assisted diffraction coupling --- p.81
Chapter 5.1 --- Introduction --- p.81
Chapter 5.2 --- Diffraction excitation of localized plasmon resonance from propagating surface plasmons --- p.83
Chapter 5.3 --- Diffraction coupling of localized plasmon resonance through gain-assisted propagating surface plasmons --- p.89
Chapter Chapter6 --- Gain-assisted plasmonic waveguides based on nanoparticle chains: an effective device approach for achieving low loss in nanoscale dimensions --- p.97
Chapter 6.1 --- Introduction --- p.97
Chapter 6.2 --- Theoretical study of near-field particle interactions in active plasmon wave guides --- p.99
Chapter 6.3 --- Routing and splitting of electromagnetic energy in nanosphere plasmon waveguides --- p.103
Chapter 6.4 --- Conclusions --- p.107
Chapter Chapter7 --- Conclusions and outlook --- p.109
Appendix --- p.117
Bibliography --- p.124