Dissertations / Theses on the topic 'Nanophotonic method'

Benzo[a]pyrene is the representative of polycyclic aromatic hydrocarbons family, the substance of the first hazard class. In present work for the development of novel nanophotonic assay method as a PAH representative benzo[a]pyrene was choose.

Polycyclic aromatic hydrocarbons (PAHs) are the widespread environmental contaminants that can be found in atmosphere, water, soil, sediment and organisms. Among most dangerous PAHs is benzo[a]pyrene (BP). The effects of BP on health are: short-term when people are exposed to it at levels above the maximum contaminant level (MCL) (0.2 ppm) for relatively short periods of time leading to red blood cells damage, anemia ect; suppression of immune system and long-term, when human beings are exposured do BP influence at levels above the MCL namely effects on reproducibility and high probability of cancer illnesses. There are known methods for PAHs detection, such as chromatography, immuno-chemistry, biological and chemical ones. However, they have several disadvantages, including high cost, duration and complexity of the analysis procedure, the high detection limit and low selectivity. So at present a development of a new method of PAHs detection based on modern technologies and materials such as nanotechologies and nanomaterials. Belonging to above mentioned is nanophotonic method of PAHs assay. Nanophotonic method for PAHs detection in particular BP in water is a combination of electrochemical and electrochemiluminescence analysis with the application of nanomaterials and nanotechnologies. This method can be carried out using nanophotonic sensor based on nanomaterials such as semiconductor quantum dots (QDs).

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental agents commonly believed to contribute significantly to human cancers pathologies. PAHs are formed in the process of incomplete combustion of organic material and are found widely in the environment, for example, in water, food, soil etc. so human exposure to PAHs is unavoidable. Like many other carcinogens, polycyclic aromatic hydrocarbons are metabolized enzymatically to various metabolites, of which some are highly reaction active. One of the most dangerous organic PAHs carcinogens is benzo[a]pyrene (BP). There are known methods for PAHs detection in water objects, such as chromatography, immuno-chemical, biological and chemical ones. However, they have several disadvantages, including high cost, duration and complexity of the analysis procedure, high detection limit, low selectivity and some others. So at present a development of new methods of PAHs detection based on modern technologies and materials such as nanotechologies and nanomaterials is a rather relevant and important task.

Anthropogenic pollution of environmental water is a huge problem for humanity today as it leads to an increase of incurable diseases. For example, the penetration into the organism of organic carcinogens such as polycyclic aromatic hydrocarbons (PAHs) can lead to the development of cancer tumors. Among PAHs the most dangerous is 3,4-benzopyrene (BP). There are a number of analytical methods for BP detection such as chromatographic, immuno-chemical, spectroscopic, luminescent and biological methods. But these methods beside their advantages have a number of significant shortcomings such as high detection limit (immuno-chemical and biological method), insufficient selectivity of PAHs detection, complexity and duration of sample preparation and analysis, high cost of device. Therefore development of new methods and tools for PAHs detecting using modern nanotechnology and nanomaterials remains urgent. So this work is devoted to the development of nanophotonic method and sensor device construction for the PAH in particular BP detection in water environment objects. Nanomaterials such as spherical quantum dots (QDs) are perspective object of nanophotonics can be used for development of optical sensors as sensor’s detector elements. They have a high luminescence quantum yield, possibility of optical and non-optical excitation, narrow luminescence spectrum and its wavelength dependence on the QDs diameter, high selectivity. This defined the perspective of their use instead of the well known organic luminophores.

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental agents commonly believed to contribute significantly to human cancer pathologies. One of the most dangerous organic PAHs carcinogens is benzo[a]pyrene (BP). Like many other carcinogens, PAHs are metabolized enzymatically to various metabolites, some of which are highly reaction active. Proposed nanophotonic analytical method is based on the process of QDs transfer to ionic forms in an EC process and their subsequent reactions with oppositely charged ionic forms of the analyte – PAHs (BP) inside ECL cell, resulting in the formation of emitter and emission of an analytical optical signal.

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.

Benzo[a]pyrene (BaP) is representative of polycyclic aromatic hydrocarbons (PAHs) family, the substance of the first hazard class. In an environmental, BaP accumulates mainly in a soil and less in a water. It comes from soil to plants and human tissues and continues to move on in the food chain in living organisms where at each stage the BaP concentration is increasing sufficiently. To human organism BaP can come through skin, respiratory organs, digestive system and transplacental infections. Besides that BaP is the most typical chemical carcinogen in environmental, it is dangerous to humans even at low concentrations, since its metabolites are mutagenic and highly carcinogenic and has the property for bioaccumulation. Being chemically relatively stable, BaP can migrate for a long time from one object to another. As a result, many objects and process in the environmental objects which do not have the ability to synthesize the BaP, are the secondary sources of its production. Content control of BaP in environmental can be accomplished by different assay among which the most wide-spread is liquid chromatography. Known methods possess both positive and negative characteristics the last are connected with assay complexity, not allowing of their used in a field conditions, duration, high cost. So new technologies especially based on nanotechnologies and nanomaterials are in great demand both for BaP and other hazardous organic PAHs compounds. Having in mind that BaP as most of PAH has high fluorescence yield in visible spectrum and is capable to emit electrogenerated chemiluminescence (ECL), it is quite possible to use this well-known assay method for both direct and indirect definition [1]. At the same time mentioned ECL methods of BaP definition provide not enough low limit of detection (LOD). Using luminescent nanomaterials such as semiconductor quantum dots (SCQD) as highly efficient detector elements in appropriate nanophotonic sensor can provide assay for BaP detection in surrounding objects water in the first turn with rather low LOD (10 nmol/l). The proposed combined photonic (electrochemiluminescent), nanotechnology (sensor’s electrode modification) and electrochemical (analytical signal excitation) techniques are possessing a number of advantages which are discussed in the given paper.

Interest in nanophotonics continues to grow as integrated optics provides an affordable platform for areas like telecommunications, quantum information processing, and biosensing. Designing and characterizing integrated photonics components and circuits, however, remains a major bottleneck. This is especially true when complex circuits or devices are required to study a particular phenomenon.To address this challenge, this work develops and experimentally validates a novel machine learning design framework for nanophotonic devices that is both practical and intuitive. As case studies, artificial neural networks are trained to model strip waveguides, integrated chirped Bragg gratings, and microring resonators using a small number of simple input and output parameters relevant to designers. Once trained, the models significantly decrease the computational cost relative to traditional design methodologies. To illustrate the power of the new design paradigm, both forward and inverse design tools enabled by the new design paradigm are demonstrated. These tools are directly used to design and fabricate several integrated Bragg grating devices and ring resonator filters. The method's predictions match the experimental measurements well and do not require any post-fabrication training adjustments.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2010.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 127-132).
Fast surface integral equation (SIE) solvers seem to be ideal approaches for simulating 3-D nanophotonic devices, as these devices generate fields both in an interior channel and in the infinite exterior domain. However, many devices of interest, such as optical couplers, have channels that cannot be terminated without generating reflections. Generating absorbers for these channels is a new problem for SIE methods, as the methods were initially developed for problems with finite surfaces. In this thesis, we show that the obvious approach for eliminating reflections, making the channel mildly conductive outside the domain of interest, is inaccurate. We propose a new method in which the absorber has gradually increasing surface conductivity; such an absorber can be easily incorporated in fast integral equation solvers. We present two types of PMCHW-based formulations to incorporate the surface conductivity into the SIE method. The accuracy of the two-type formulations are examined and discussed using an example of the scattering of a Mie sphere with surface conductivities. Moreover, we implement two different FFT-accelerated algorithms for the periodic non-absorbing region and the non-periodic absorbing region. In addition, we use perturbation theory and Poynting's theorem, respectively, to calculate the field decay rate due to the surface conductivity. We show a saturation phenomenon when the electrical surface conductivity is large. However, we show that the saturation is not a problem for the surface absorber since the absorber typically operates in a small surface conductivity regime. We demonstrate the effectiveness of the surface conductive absorber by truncating a rectangular waveguide channel. Numerical results show that this new method is orders of magnitude more effective than a volume absorber. We also show that the transition reflection decreases in a power law with increasing the absorber length. We further apply the surface conductive absorber to terminate a waveguide with period-a sinusoidally corrugated sidewalls. We show that a surface absorber that can perform well when the periodic waveguide system is excited with a large group-velocity mode may fail when excited with a smaller group-velocity mode, and give an asymptotic relation between the surface absorber length, transition reflections and group velocity. Numerical results are given to validate the asymptotic prediction.
by Lei Zhang.
Ph.D.

Diese Arbeit befasst sich mit der theoretischen Beschreibung nichtlinearer optischer Phänomene in Hinblick auf das (numerische) unstetige Galerkin-Zeitraumverfahren. Insbesondere werden zwei Materialmodelle behandelt: das hydrodynamische Modell für Metalle und das Modell für Raman-aktive Materialien. Im ersten Teil der Arbeit wird das hydordynamische Modell für Metalle unter Verwendung eines störungstheoretischen Ansatzes behandelt. Insbesondere wird dieser Ansatz genutzt, um die nichtlinearen optischen Effekte, Erzeugung zweiter Harmonischer und Summenfrequenzerzeugung, mit Hilfe des unstetigen Galerkin-Verfahrens zu studieren. In diesem Zusammenhang wird demonstriert, wie das optische Signal zweiter Ordnung von Nanoantennen optimiert werden kann. Hierzu wird ein hier erarbeitetes Schema für die Abstimmung des eingestrahten Lichtes angewandt. Zudem führt eine intelligente Wahl des Antennendesigns zu einem optimierten Signal. Im zweiten Teil dieser Arbeit wird das Modell für Raman-aktive Dielektrika behandelt. Genauer wird die nichtlineare Antwort dritter Ordnung für stimulierte Raman-Streuung hergeleitet. Diese wird dazu genutzt, um ein System aus Hilfsdifferentialgleichungen für das unstetige Galerkin-Verfahren zu konstruieren. Die Ergebnisse des erweiterten numerischen Verfahrens werden im Anschluss gezeigt und diskutiert.
This thesis is concerned with the theoretical description of nonlinear optical phenomena with regards to the (numerical) discontinuous Galerkin time-domain (DGTD) method. It deals with two different material models: the hydrodynamic model for metals and the model for Raman-active dielectrics. In the first part, we review the hydrodynamic model for metals, where we apply a perturbative approach to the model. We use this approach to calculate the second-order nonlinear optical effects of second-harmonic generation and sum-frequency generation using the DGTD method. In this context, we will see how to optimize the second-order response of plasmonic nanoantennas by applying a deliberate tuning scheme for the optical excitations as well as by choosing an intelligent nanoantenna design. In the second part, we examine the material model for Raman-active dielectrics. In particular, we see how to derive the third-order nonlinear response by which one can describe the process of stimulated Raman scattering. We show how to incorporate this third-order response into the DGTD scheme yielding a novel set of auxiliary differential equations. Finally, we demonstrate the workings of the modified numerical scheme.

Les propriétés optiques des nanomatériaux, tels que les cristaux photoniques ou les métamatériaux, ont reçu beaucoup d’attention dans les dernières années [1–9]. La dérivation numérique de ces propriétés se révèle pourtant très compliquée, en particulier dans le cas des structures métallo-diélectriques, qui comportent des résonances plasmoniques. C’est pourquoi des méthodes numériques avancées et des modèles semi-analytiques sont nécessaires. Dans cette thèse, nous montrerons que le formalisme de la matrice de diffraction peut satisfaire ces deux aspects. La méthode de la matrice de diffraction est un concept très général en physique. Dans le cas des structures périodiques, on peut dériver la matrice de diffraction à l’aide de la méthode modale de Fourier [10]. Pour la description exacte des géométries planes, nous avons développé la méthode des coordonnées adaptées [11], qui nous donne un nouveau système de coordonnées, dans lequel les interfaces des matériaux sont des surfaces de coordonnées constantes. En combinaison avec la méthode de la résolution spatiale adaptative, la méthode des coordonnées adaptées permet d’améliorer considérablement la convergence de la méthode modale de Fourier, de telle sorte qu’on peut calculer des structures métalliques compliquées très efficacement. Si on utilise la matrice de diffraction, il est non seulement possible de dériver les propriétés optiques en illumination de champ lointain, comme la transmission, la réflexion, l’absorption, et le champ proche, mais aussi de décrire l’émission d’un objet à l’intérieur d’une structure et d’obtenir les résonances optiques d’un sytème. Dans cette thèse, nous présenterons une méthode efficace pour la dérivation des résonances optiques tridimensionnelles, utilisant directement la matrice de diffraction [14]. Si on connaît les résonances d’un système isolé, il est aussi possible d’obtenir une approximation des résonances dans le cas d’un système combiné à l’aide de notre méthode du couplage des résonances [15, 16]. Cette méthode permet de décrire le régime de couplage des champs lointain et proche, y compris le couplage fort avec les résonances Fabry-Perot, pour des systèmes qui se composent d’un empilement de deux structures planes et périodiques. Pour cette raison, on peut étudier efficacement le couplage de ces systèmes. Cette thèse est écrite de manière à donner une idée d’ensemble du formalisme de la matrice de diffraction et de la méthode modale de Fourier. En outre, nous décrivons notre généralisation de ces méthodes et nous montrons la validité de nos approches pour différents exemples
The optical properties of nanostructures such as photonic crystals and metamaterials have drawn a lot of attention in recent years [1–9]. The numerical derivation of these properties, however, turned out to be quite complicated, especially in the case of metallo-dielectric structures with plasmonic resonances. Hence, advanced numerical methods as well as semi-analytical models are required. In this work, we will show that the scattering matrix formalism can provide both. The scattering matrix approach is a very general concept in physics. In the case of periodic grating structures, the scattering matrix can be derived by the Fourier modal method [10]. For an accurate description of non-trivial planar geometries, we have extended the Fourier modal method by the concept of matched coordinates [11], in which we introduce a new coordinate system that contains the material interfaces as surfaces of constant coordinates. In combination with adaptive spatial resolution [12,13], we can achieve a tremendously improved convergence behavior which allows us to calculate complex metallic shapes efficiently. Using the scattering matrix, it is not only possible to obtain the optical properties for far field incidence, such as transmission, reflection, absorption, and near field distributions, but also to solve the emission from objects inside a structure and to calculate the optical resonances of a system. In this work, we provide an efficient method for the ab initio derivation of three-dimensional optical resonances from the scattering matrix [14]. Knowing the resonances in a single system, it is in addition possible to obtain approximated resonance positions for stacked systems using our method of the resonant mode coupling [15, 16]. The method allows describing both near field and far field regime for stacked two-layer systems, including the strong coupling to Fabry-Perot resonances. Thus, we can study the mutual coupling in such systems efficiently. The work will provide the reader with a basic understanding of the scattering matrix formalism and the Fourier modal method. Furthermore, we will describe in detail our extensions to these methods and show their validity for several examples

Les structures nanophotoniques sont généralement simulées par des méthodes de volumes, comme la méthode des différences finies dans le domaine temporel (FDTD), ou la méthode des éléments finis (FEM). Toutefois, pour les grandes structures, ou des structures plasmoniques métalliques qui nécessitent, la mémoire et le temps de calcul requis peuvent augmenter de façon spectaculaire.Les méthodes de surface, comme la méthode des éléments de frontière (BEM) ont été développées afin de réduire le nombre d'éléments de maillage. Ces méthodes consistent à exprimer le champ formé dans tout l'espace en fonction des courants électrique et magnétique à la surface de l’objet. Combinées avec la méthode multipôle rapide (FMM) qui permet une accélération du calcul de l'interaction entre les éléments lointain du maillage, de grands systèmes peuvent ainsi être manipulés.Nous avons développé, pour la première fois à notre connaissance, une FMM sur un nouveau formalisme BEM, basé sur les potentiels scalaire et vectoriel au lieu de courants électriques et magnétiques. Cette méthode a été montrée pour permettre une simulation précise des systèmes plasmoniques métalliques, tout en offrant une réduction significative des besoins de calcul. Des systèmes nanophotoniques complexes ont été simulés, comme une lentille plasmonique composé d'un ensemble de nanotubes d'or
Nanophotonic structures are generally simulated by volume methods, as Finite-difference time-domain (FDTD) method, or Finite element method (FEM). However, for large structures, or metallic plasmonic structures, the memory and time computation required can increase dramatically, and make proper simulation infeasible.Surface methods, like the boundary element method (BEM) have been developed to reduce the number of mesh elements. These methods consist in expressing the electromagnetic filed in whole space as a function of electric and magnetic currents at the surface of scatterers. Combined with the fast multipole method (FMM) that enables a huge acceleration of the calculation of interaction between far mesh elements, very large systems can thus be handled.What we performed is the development of an FMM on a new BEM formalism, based on scalar and vector potentials instead of electric and magnetic currents, for the first time to our knowledge. This method was shown to enable accurate simulation of metallic plasmonic systems, while providing a significant reduction of computation requirements, compared to BEM-alone. Several thousands of unknowns could be handled on a standard computer. More complex nanophotonic systems have been simulated, such as a plasmonic lens consisting of a collection of gold nanorods

L’objectif de cette thèse est de développer une méthode Galerkine discontinue d’ordre élevé capable de prendre en considération des simulations réalistes liées à la nanophotonique. Au cours des dernières décennies, l’évolution des techniques de lithographie a permis la création de structure géométriques de tailles nanométriques, révélant ainsi une large gamme de phénomènes nouveaux nés de l’interaction lumière-matière à ces échelles. Ces effets apparaissent généralement pour des objets de taille égale ou (très) inférieure à la longueur d’onde du champ incident. Ce travail repose sur le développement et l’implémentation de modèles de dispersion appropriés (principalement pour les métaux), ainsi que sur un large éventail de méthodes computationnelles classiques. Deux développements méthodologiques majeurs sont présentés et étudiés en détails: (i) les éléments courbes, et (ii) l’ordre d’approximation local. Ces études sont accompagnées de plusieurs cas-tests réalistes tirés de la nanophotonique
The goal of this thesis is to develop a discontinuous Galerkin time-domain method to be able to handle realistic nanophotonics computations. During the last decades, the evolution of lithography techniques allowed the creation of geometrical structures at the nanometer scale, thus unveiling a variety of new phenomena arising from light-matter interactions at such levels. These effects usually occur when the device is of comparable size or (much) smaller than the wavelength of the incident field. This work relies on the development and implementation of appropriate models for dispersive materials (mostly metals), as well as on a large panel of classical computational techniques. Two major methodological developments are presented and studied in details: (i) curvilinear elements, and (ii) local order of approximation. This work is complemented with several physical studies of real-life nanophotonics applications

Cette thèse contribue au domaine mathématique de l’optimisation de forme et explore deux sujets:l’une concerne la détermination automatique du design de composant nanophotonique et l’autre l’obtention de la forme optimale des conditions aux limites permettant de définir une équation au dérivées partielles (EDP).• Dans le cadre mathématique des équations de Maxwell tridimensionnelles et harmoniques dans letemps, nous proposons un algorithme d’optimisation de forme combinant la méthode d’Hadamard etune représentation des formes par la méthode level-set. Une attention particulière est accordée à larobustesse des dispositifs optimisés par rapport à des petites incertitudes sur les données physiques ougéométriques du problème. À cet égard, nous nous appuyons sur un algorithme provenant du domainede l’optimisation multi-objectifs pour traiter les deux principales sources d’incertitudes affectant desdispositifs nanophotoniques, à savoir les incertitudes sur la longueur d’onde de la lumière injectée ainsique les incertitudes géométriques liées au procédé de fabrication par lithographie-gravure. Plusieursexemples numériques sont présentés permettant d’évaluer l’efficacité de la méthode proposé.• La deuxième application concerne l’optimisation de la forme des régions affectées à différentes condi-tions limites dans la définition d’une EDP d’un problème “physique”. L’étude de ce problème s’avèreêtre délicate dans le cas d’une transition Dirichlet-Neumman car elle nécessite une analyse précise dela singularité des solutions d’une EDP à la transition entre deux régions supportant ces conditionslimites. Nous proposons d’une part une étude mathématique complète de ce problème dans le casde l’équation du Laplacien et d’autre part une méthode numérique basée sur une régularisation desconditions aux limites pour optimiser la forme de ces régions. Différents exemples numériques sontprésentés afin d’évaluer l’efficacité de notre méthode
This thesis focuses on the mathematical field of shape optimization and explores two topics:one concerns the systematic determination of the design of nanophotonic components and the other one the optimal shape and location of boundary conditions defining partial differential equations (PDE).• In the mathematical setting of the three-dimensional, time-harmonic Maxwell equations, we proposea shape and topology optimization algorithm combining Hadamard’s boundary variation methodwith a level set representation of shapes and their evolution. A particular attention is devotedto the robustness of the optimized devices with respect to small uncertainties over the physical orgeometrical data of the problem. In this respect, we rely on a simple multi-objective formulation todeal with the two main sources of uncertainties plaguing nanophotonic devices, namely uncertaintiesover the incoming wavelength, and geometric uncertainties entailed by the lithography and etchingfabrication process. Several numerical examples are presented and discussed to assess the efficiencyof our methodology.• The second application concern the optimization of the shape of the regions assigned to different typesof boundary conditions in the definition of a “physical” PDE. This problem proves to be difficult inthe case of a Dirichlet-Neumann transition since it requires a precise study of the singular nature ofPDE solutions at the transition between two regions supporting these boundary conditions. On theone hand a full mathematical study is carried out on this theoretical problem and on the other handa numerical method based on a regularization of the boundary conditions is proposed to optimizethese regions. Various numerical examples are eventually presented in order to appraise the efficiencyof the proposed process

L’objectif de cette thèse est l’étude numérique du piégeage de la lumière dans des cellules solaires nanostructurées. Le changement climatique est devenu une problématique majeure nécessitant une transition énergétique à court terme. Dans ce contexte, l'énergie solaire semble être une source énergétique idéale. Cette ressource est à la fois scalable à l’échelle planétaire et écologique. Afin de maximiser sa pénétration, des travaux visant à augmenter la quantité de lumière absorbée et à réduire les coûts liés à la conception des cellules sont nécessaires. Le piégeage de la lumière est une stratégie qui permet d’atteindre ces deux objectifs. Son principe consiste à utiliser des texturations nanométriques afin de focaliser la lumière dans les couches de semi-conducteur absorbantes. Dans ce travail, la méthode de Galerkine Discontinue en Domaine Temporel (DGTD) est introduite. Deux développements méthodologiques majeurs, permettant de mieux prendre en compte les caractéristiques des cellules solaires, sont présentés. Tout d'abord, l’utilisation d’un ordre d’approximation local est proposé , basé sur une stratégie de répartition particulière de l’ordre. Le deuxième développement est l’utilisation de maillage hybride mixant ses élements hexahédriques structurés et tétrahédriques non structurés. Des cas réalistes de cellules solaires issus de la littérature et de collaborations avec des physiciens du domaine du photovoltaïque permettent d'illustrer l' apport de ces développements. Un cas d’optimisation inverse de réseau de diffraction dans une cellule solaire est également présenté en couplant le solveur numérique avec un algorithme d’optimisation bayésienne. De plus, une étude approfondie des performances du solveur a également été réalisée avec des modifications méthodologiques pour contrer les problèmes de répartition de charge. Enfin, une méthode plus prospective, la méthode Multiéchelle Hybride-Mixte (MHM) spécialisée dans la résolution de problème très fortement multiéchelle est introduite. Un schéma en temps multiéchelle est présenté et sa stabilité prouvée
The objective of this thesis is the numerical study of light trapping in nanostructured solar cells. Climate change has become a major issue requiring a short-term energy transition. In this context, solar energy seems to be an ideal energy source. This resource is both globally scalable and environmentally friendly. In order to maximize its penetration, it is needed to increase the amount of light absorbed and reduce the costs associated with cell design. Light trapping is a strategy that achieves both of these objectives. The principle is to use nanometric textures to focus the light in the absorbing semiconductor layers. In this work, the Discontinuous Galerkin Time-Domain (DGTD) method is introduced. Two major methodological developments are presented, allowing to better take into account the characteristics of solar cells. First, the use of a local approximation order is proposed, based on a particular order distribution strategy. The second development is the use of hybrid meshes mixing structured hexahedral and unstructured tetrahedral elements. Realistic cases of solar cells from the literature and collaborations with physicists in the field of photovoltaics illustrate the contribution of these developments. A case of inverse optimization of a diffraction grating in a solar cell is also presented by coupling the numerical solver with a Bayesian optimization algorithm. In addition, an in-depth study of the solver's performance has also been carried out with methodological modifications to counter load balancing problems. Finally, a more prospective method, the Multiscale Hybrid-Mixed method (MHM) specialized in solving very highly multiscale problems is introduced. A multiscale time scheme is presented and its stability is proven

La microscopie en champ proche optique permet d'analyser les phénomènes optiques avec une résolution spatiale sublongueur d'onde comme par exemple la localisation et la propagation de la lumière dans des cristaux photoniques. D'une manière générale, les méthodes de microscopie en champ proche optique reposent sur le positionnement à l'échelle nanométrique d'une sonde locale à proximité de l'échantillon à analyser, puis sur la détection du signal diffusé et collecté lors du balayage de la sonde. En fonction du type de détection optique mise en oeuvre ou du type de sonde utilisée, les grandeurs physiques communément accessibles par ces méthodes sont les distributions spatiales de l'amplitude et de la phase ou de l'intensité des composantes électriques ou magnétiques du champ sondé.Ce travail de thèse est consacré à la mise en place d'une détection hyperstectrale en champ proche optique dans le but de comprendre et de caractériser, à des échelles sublongueurs d'onde, les propriétés spectrales et spatiales de systèmes optiques miniaturisés. L'imagerie hyperstectrale fournit en une seule acquisition, une série d'image à chaque longueur d'onde dans les gammes spectrales visibles, infrarouges et aux longueurs d'onde des télécommunications optiques. Cette nouvelle technique d'imagerie a permis l'observation, sur une large bande spectrale, de phénomènes électromagnétiques dépendant de la longueur d'onde tels que les effets superprisme et mirage dans les cristaux photoniques et la mise en forme de faisceaux de Bessel plasmoniques

Le transfert de chaleur est intimement lié à la propagation du son (transfert acoustique) dans les matériaux, par exemple dans les isolants et les semi-conducteurs, les principaux vecteurs d’énergie sont des phonons acoustiques. Le concept de présence d’interfaces a été largement exploité pour manipuler efficacement les phonons des longueurs d’onde macroscopiques aux longueurs d’onde nanométriques. Les derniers correspondent aux fréquences en régime THz, qui sont responsables du transport thermique à température ambiante. Dans cette thèse, la méthode des éléments finis est utilisée pour effectuer des analyses transitoires de la propagation des paquets d’ondes dans différents milieux à 2D. Elle est commencée par une étude paramétrique de l’atténuation des paquets d’ondes dans un système élastique semi-infini avec des interfaces circulaires périodiques. Trois paramètres clés sont étudiés, notamment le contraste de rigidité, la densité d’interface et la longueur d’onde des phonons. Différents régimes de transfert (propagatif, diffusif et localisé) sont identifiés, qui permettent d’identifier la contribution des phonons à la conductivité thermique. Outre les interfaces circulaires, la réponse mécanique et l’atténuation acoustique pour différents types d’interfaces sont également étudiées, telles que l’inclusion de forme dendritique, l’inclusion d’Eshelby, et les matériaux poreux avec des pores ordonnés / désordonnés. Afin d’étendre l’étude aux matériaux amorphes, j’ai également considéré un milieu hétérogène avec des rigidités aléatoires réparties dans l’espace selon une distribution gaussienne basée sur la théorie de l’élasticité de cisaillement hétérogène des verres. Enfin et surtout, deux versions de lois de comportement viscoélastiques sont proposées pour prendre en compte l’atténuation intrinsèque des phonons dépendant de la fréquence dans les verres, dans le but qu’un milieu visqueux homogène puisse reproduire cette atténuation intrinsèque. La simulation par éléments finis confirme qu’un modèle continu peut suivre strictement l’atténuation atomistique (G) avec une loi de comportement viscoélastique linéaire macroscopique bien calibrée. Par rapport aux données expérimentales de a-SiO2, notre deuxième loi de comportement reproduit qualitativement et quantitativement les trois régimes d’atténuation acoustique en fonction de la fréquence : successivement Γ ∝ ω^2,ω^4,ω^2
Heat transfer is actually intimately related to the sound propagation (acoustic transfer) in materials, as in insulators and semi-conductors the main heat carriers are acoustic phonons. The concept of the presence of interfaces has been largely exploited for efficiently manipulating phonons from long-wavelength to nanometric wavelengths, i.e., frequencies in THz regime, responsible for thermal transport at room temperature. In this thesis, the finite element method is used to perform transient analysis of wavepacket propagation in different mediums. I started with a parametric study of attenuation of acoustic wave-packets in a 2D semi-infinite elastic system with periodic circular interfaces. Three key parameters are investigated, including rigidity contrast, interface density and phonon wavelength. Different energy transfer regimes (propagative, diffusive, and localized) are identified allowing to understand the phonon contribution to thermal transport. Besides the circular interfaces, mechanical response and acoustic attenuation for different types of interfaces are also investigated, such as Eshelby’s inclusion, dendritic shape inclusion and porous materials with ordered/disordered holes. In order to extend the study to amorphous materials, I also considered a heterogeneous medium with random rigidities distributed in space according to a Gaussian distribution based on the theory of heterogeneous shear elasticity of glasses. Finally yet importantly, viscoelastic constitutive laws are proposed to take into account the frequency-dependent intrinsic phonon attenuation in glasses, with the aim of reproducing such intrinsic attenuation using a homogeneous viscous medium. Finite element simulation confirms that a continuum model may strictly follow the atomistic attenuation (G) for a well-calibrated macroscopic linear viscoelastic constitutive law. Compared with the experimental data in a-SiO2, our second constitutive law reproduces qualitatively and quantitatively the three regimes of acoustic attenuation versus frequency : successively Γ∝ω^2,ω^4,ω^2

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.

Optical whispering-gallery mode (WGM) cavities, which exhibit extraordinary spatial and temporal confinement of light, are one of the leading transducers for examining molecular recognition at low particle counts. With the advent of hybrid photonic-plasmonic and increasingly sophisticated forms of these resonators, the importance of supporting numerical methods has correspondingly become evident. In response, we adopt a full-vector finite difference approximation in order to solve for WGM's in terms of their field distributions, resonant wavelengths, and quality factors in the context of naturally discontinuous permittivity structure. A segmented Taylor series and alignment/rotation operator are utilized at such singularities in conjunction with arbitrarily spaced grid points. Simulations for microtoroids, with and without dielectric nanobeads, and plasmonic microdisks are demonstrated for short computation times and shown to be in agreement with data in the literature. Constricted surface plasmon polariton (SPP) WGM's are also featured within this document. The module of this thesis is devised as a keystone for composite WGM models that may guide experiments in the field.
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