Le domaine du photovoltaïque en couches minces s’attache à réduire le coût de l’énergie photovoltaïque, en réduisant considérablement la quantité de matières premières utilisées. Dans le cas du silicium cristallin en couches minces, la réduction de l’épaisseur de la cellule s’accompagne d’une baisse drastique de l’absorption, notamment pour les plus fortes longueurs d’onde. Nombreuses sont les techniques aujourd’hui mises en œuvre pour lutter contre cette baisse de performance, dont l’utilisation des effets plasmoniques induits par des nanostructures métalliques qui permettent un piégeage de la lumière accru dans la couche absorbante. Dans ces travaux, nous étudions l’influence de nanostructures d’argent organisées suivant un réseau périodique sur l’absorption d’une couche de silicium. Ces travaux s’articulent autour de deux axes majeurs. L’influence de ces effets plasmoniques sur l’absorption est d’abord mise en évidence à travers différentes simulations numériques réalisées par la méthode FDTD. Nous étudions ainsi les cas de réseaux périodiques finis et infinis de nanostructures d’argent situés sur la face arrière d’une couche mince de silicium. En variant les paramètres du réseau, nous montrons que l’absorption au sein du silicium peut être améliorée dans le proche infrarouge, sur une large plage de longueurs d’onde. Le second volet de la thèse concerne la réalisation des structures modélisées. Pour cela, deux voies de fabrication ont été explorées et développées. Pour chacune d’entre elles, trois briques élémentaires ont été identifiées : (i) définition du futur motif du réseau grâce à un masque, (ii) réalisation de pores dans le silicium et (iii) remplissage des pores par de l’argent pour former le réseau métallique. La première voie de fabrication développée fait appel à un masque d’alumine, réalisé par l’anodisation électrochimique d’une couche d’aluminium, pour définir les dimensions du réseau métallique. Une gravure chimique assistée par un métal est ensuite utilisée pour former les pores, qui seront alors comblés grâce à des dépôts d’argent par voie humide. La seconde voie de fabrication utilise un masque réalisé par lithographie holographique, une gravure des pores par RIE et un remplissage des pores par dépôt d’argent electroless. Les substrats plasmoniques fabriqués sont caractérisés optiquement, au moyen d’une sphère intégrante, par des mesures de transmission, réflexion et absorption. Pour tous les substrats plasmoniques caractérisés, les mesures optiques montrent une baisse de la réflexion et de la transmission et une hausse de l’absorption pour les plus grandes longueurs d’onde. / Thin-film photovoltaics focus on lowering the cost reduction of photovoltaic energy through the significant reduction of raw materials used. In the case of thin-films crystalline silicon, the reduction of the thickness of the cell is linked to a drastic decrease of the absorption, particularly for the higher wavelengths. This decrease of the absorption can be fought through the use of several different light trapping methods, and the use of plasmonic effects induced by metallic nanostructures is one of them. In this work, we study the influence of a periodic array of silver nanostructures on the absorption of a silicon layer. This work is decomposed into two main axes. First, the influence of the plasmonic effects on the silicon absorption is highlighted through different numerical simulations performed by the FDTD method. Both finite and infinite arrays of silver nanostructures, located at the rear side of a thin silicon layer, are studied. By varying the parameters of the array, we show that the silicon absorption can be improved in the near infrared spectral region, over a wide range of wavelengths. The second part of the thesis is dedicated to the fabrication of such modeled structures. Two different approaches have been explored and developed inside the lab. For each of these two strategies, three major building blocks have been identified: (i) definition of the future array pattern through a mask, (ii) etching of the pattern in the silicon layer and (iii) filling of the pores with silver in order to form the metallic array of nanostructures. In the first fabrication method, an anodic alumina mask, produced by the electrochemical anodization of an aluminium layer, is used in order to define the dimensions of the metallic array. A metal assisted chemical etching is then performed to produce the pores inside the silicon, which will then be filled with silver through a wet chemical process. The second fabrication method developed involves the use of holographic lithography to produce the mask, the pores in silicon are formed by reactive ion etching and they are filled during an electroless silver deposition step. The fabricated plasmonic substrates are optically characterized using an integrating sphere, and transmission, reflection and absorption are measured. All the characterized plasmonic substrates shown a decrease of their reflection and transmission and an absorption enhancement at the largest wavelengths.

The dispersion property of periodic structures is a hot research topic in the last decade. By exploiting dispersion properties, one can manipulate the propagation of electromagnetic waves, and produce effects that do not exist in conventional materials. This thesis is devoted to two important dispersion effects: negative refraction and designed surface plasmons. First, we introduce negative refraction and designed surface plasmons, including a historical perspective, main areas for applications and current trends. Several numerical methods are implemented to analyze electromagnetic effects. We apply the layer-KKR method to calculate the electromagnetic wave through a slab of photonic crystals. By implementing the refraction matrix for semi-infinite photonic crystals, the layer-KKR method is modified to compute the coupling coefficient between plane waves and Bloch modes in photonic crystals. The plane wave method is applied to obtain the band structure and the equal-frequency contours in two-dimensional regular photonic crystals. The finite-difference time-domain method is widely used in our works, but we briefly discuss two calculation recipes in this thesis: how to deal with the surface termination of a perfect conductor and how to calculate the frequency response of high-Q cavities more efficiently using the Pad\`{e} approximation method. We discuss a photonic crystal that exhibits negative refraction characterized by an effective negative index, and systematically analyze the coupling coefficients between plane waves in air and Bloch waves in the photonic crystal. We find and explain that the coupling coefficients are strong-angularly dependent. We first propose an open-cavity structure formed by a negative-refraction photonic crystal. To illuminate the physical mechanism of the subwavelength imaging, we analyze both intensity and phase spectrum of the transmission through a slab of photonic crystals with all-angle negative refraction. It is shown that the focusing properties of the photonic crystal slab are mainly due to the negative refraction effect, rather than the self-collimation effect. As to designed surface plasmons, we design a structured perfectly conducting surface to achieve the negative refraction of surface waves. By the average field method, we obtain the effective permittivity and permeability of a perfectly conducting surface drilled with one-dimensional periodic rectangle holes, and propose this structure as a designed surface plasmon waveguide. By the analogy between designed surface plasmons and surface plasmon polaritons, we show that two different resonances contribute to the enhanced transmission through a metallic film with an array of subwavelength holes, and explain that the shape effect is attributed to localized waveguide resonances. / QC 20100817

This thesis introduces spatial filtering, which is a technique to extend the time step size beyond the conventional stability limit for the Finite-Difference Time-Domain (FDTD) method, at the expense of transforming field nodes between the spatial domain and the discrete spatial-frequency domain and removing undesired spatial-frequency components at every FDTD update cycle. The spatially-filtered FDTD method is demonstrated to be almost as accurate as and more efficient than the conventional FDTD method via theories and numerical examples. Then, this thesis combines spatial filtering and an existing subgridding scheme to form the spatially-filtered subgridding scheme. The spatially-filtered subgridding scheme is more efficient than existing subgridding schemes because the former allows the time step size used in the dense mesh to be larger than the dense mesh CFL limit. However, trade-offs between accuracy and efficiency are required in complicated structures.

This thesis introduces spatial filtering, which is a technique to extend the time step size beyond the conventional stability limit for the Finite-Difference Time-Domain (FDTD) method, at the expense of transforming field nodes between the spatial domain and the discrete spatial-frequency domain and removing undesired spatial-frequency components at every FDTD update cycle. The spatially-filtered FDTD method is demonstrated to be almost as accurate as and more efficient than the conventional FDTD method via theories and numerical examples. Then, this thesis combines spatial filtering and an existing subgridding scheme to form the spatially-filtered subgridding scheme. The spatially-filtered subgridding scheme is more efficient than existing subgridding schemes because the former allows the time step size used in the dense mesh to be larger than the dense mesh CFL limit. However, trade-offs between accuracy and efficiency are required in complicated structures.

In 2000, a controversial paper by John Pendry surmised that a slab of negative index material could act as a perfect lens, projecting images with resolution detail beyond the limits of conventional lensing systems. A thin silver slab was his realistic suggestion for a practical near-field superlens - a 'poor-mans perfect lens'. The superlens relied on plasmonic resonances rather than negative refraction to provide imaging. This silver superlens concept was experimentally verified by the author using a novel near-field lithographic technique called Planar Lensing Lithography (PLL), an extension of a previously developed Evanescent Near-Field Optical Lithography (ENFOL) technique. This thesis covers the computational and experimental efforts to test the performance of a silver superlens using PLL, and to compare it with the results produced by ENFOL. The PLL process was developed by creating metal patterned conformable photomasks on glass coverslips and adapting them for use with an available optical exposure system. After sub-diffraction-limited ENFOL results were achieved with this system additional spacer and silver layers were deposited onto the masks to produce a near-field test platform for the silver superlens. Imaging through a silver superlens was achieved in a near-field lithography environment for sub-micron, sub-wavelength, and sub-diffraction-limited features. The performance of PLL masks with 120-, 85-, 60-, and 50-nm thick silver layers was investigated. Features on periods down to 145-nm have been imaged through a 50-nm thick silver layer into a thin photoresist using a broadband mercury arc lamp. The quality of the imaging has been improved by using 365 nm narrowband exposures, however, resolution enhancement was not achieved. Multiple layer silver superlensing has also been experimentally investigated for the first time; it was proposed that a multi-layered superlens could achieve better resolution than a single layer lens for the same total silver thickness. Using a PLL mask with two 30-nm thick silver layers gave 170-nm pitch sub-diffraction-limited resolution, while for a single layer mask with the same total thickness (60 nm) resolution was limited to a 350-nm pitch. The proposed resolution enhancement was verified, however pattern fidelity was reduced, the result of additional surface roughness. Simulation and analytical techniques have been used to investigate and understand vi ABSTRACT the enhancements and limitations of the PLL technique. A Finite-Difference Time- Domain (FDTD) tool was written to produce full-vector numerical simulations and this provided both broad- and narrowband results, allowing image quality as a function of grating period to be investigated. An analytical T-matrix method was also derived to facilitate computationally efficient performance analysis for grating transmission through PLL stacks. Both methods showed that there is a performance advantage for PLL over conventional near-field optical lithography, however, the performance of the system varies greatly with grating period. The advantages of PLL are most prominent for multi-layer lenses. The work of this thesis indicates that the utilisation of plasmonic resonances in PLL and related techniques can enhance the performance of near-field lithography.

Nowadays, silicon photonics is a widely studied research topic. Its high-index-contrast and compatibility with the complementary metal-oxide-semiconductor technology make it a promising platform for low cost high density integration. Several general problems have been brought up, including the lack of silicon active devices, the difficulty of light coupling, the polarization dependence, etc. This thesis aims to give new attempts to novel solutions for some of these problems. Both theoretical modeling and experimental work have been done. Several numerical methods are reviewed first. The semi-vectorial finite-difference mode solver in cylindrical coordinate system is developed and it is mainly used for calculating the eigenmodes of the waveguide structures employed in this thesis. The finite-difference time-domain method and beam propagation method are also used to analyze the light propagation in complex structures. The fabrication and characterization technologies are studied. The fabrication is mainly based on clean room facilities, including plasma assisted film deposition, electron beam lithography and dry etching. The vertical coupling system is mainly used for characterization in this thesis. Compared with conventional butt-coupling system, it can provide much higher coupling efficiency and larger alignment tolerance. Two novel couplers related to silicon photonic wires are studied. In order to improve the coupling efficiency of a grating coupler, a nonuniform grating is theoretically designed to maximize the overlap between the radiated light profile and the optical fiber mode. Over 60% coupling efficiency is obtained experimentally. Another coupler facilitating the light coupling between silicon photonic wires and slot waveguides is demonstrated, both theoretically and experimentally. Almost lossless coupling is achieved in experiments. Two approaches are studied to realize polarization insensitive devices based on silicon photonic wires. The first one is the use of a sandwich waveguide structure to eliminate the polarization dependent wavelength of a microring resonator. By optimizing the multilayer structure, we successfully eliminate the large birefringence in an ultrasmall ring resonator. Another approach is to use polarization diversity scheme. Two key components of the scheme are studied. An efficient polarization beam splitter based on a one-dimensional grating coupler is theoretically designed and experimentally demonstrated. This polarization beam splitter can also serve as an efficient light coupler between silicon-on-insulator waveguides and optical fibers. Over 50% coupling efficiency for both polarizations and -20dB extinction ratio between them are experimentally obtained. A compact polarization rotator based on silicon photonic wire is theoretically analyzed. 100% polarization conversion is achievable and the fabrication tolerance is relatively large by using a compensation method. A novel integration platform based on nano-epitaxial lateral overgrowth technology is investigated to realize monolithic integration of III-V materials on silicon. A silica mask is used to block the threading dislocations from the InP seed layer on silicon. Technologies such as hydride vapor phase epitaxy and chemical-mechanical polishing are developed. A thin dislocation free InP layer on silicon is obtained experimentally. / QC20100705

Strongly localised plasmons in metallic nano-structures offer exciting characteristics for guiding and focusing light on the nano-scale, opening the way for the development of new types of sensors, circuitry and improved resolution of optical microscopy. The work presented in this thesis focuses on two major areas of plasmonics research - nano-focusing structures and nano-sized waveguides. Nano-focusing structures focus light to an area smaller than the wavelength and will find applications in sensing, efficiently coupling light to nano-scale devices, as well as improving the resolution of near field microscopy. In the past the majority of nano-focusing structures have been nano-scale cones or tips, which are capable of focusing light to a spot of nano-scale area whilst enhancing the light field. The alternatives are triangular nano-focusing structures which have received far less attention, and only one type of triangular nano-focusing structure is known – a sharp V-groove in a metal substrate. This structure focuses light to a strip of nano-scale width, which may lead to new applications in microscopy and sensing. The difficulty with implementing the V-groove is that the structure is not robust and is quite difficult to fabricate. This thesis aims to develop new triangular nano-focusing devices which will overcome these difficulties, whilst still producing an intense light source on the nano-scale. The two proposed structures presented in this thesis are a metallic wedge submerged in uniform dielectric and a tapered metal film lying on a dielectric substrate, the latter being the easier to fabricate and the more structurally sound and robust. The investigation is performed using the approximation of continuous electrodynamics, the geometrical optics approximation and the zero-plane method. The second aim of this thesis is to investigate plasmonic waveguides and couplers for the development of nano-optical circuitry, more compact photonic devices and sensors. The research will attempt to fill the gaps in the current knowledge of the V-groove waveguide, which consists of a sharp triangular groove in a metal substrate, and the gap plasmon waveguide, which consists of a rectangular slot in a thin metal film. The majority of this work will be performed using the author’s in house finite-difference time-domain algorithm and FEMLAB as well as the effective medium method and geometric optics approximation. The V-groove may be used as either a nano-focusing or waveguiding device. As a waveguide the V-groove is one of the most promising plasmonic waveguides in the optical regime. However, there exist quite a number of gaps in the current knowledge of V-groove waveguides which this thesis will attempt to fill. In particular, the effect of rounded groove tip on plasmon propagation has been assessed for the V-groove. The investigation of rounded groove tip is important, as due to modern fabrication processes it’s not possibly to produce an infinitely sharp groove, and the existing literature has not considered the impact of this problem. The thesis will also investigate the impacts of the inclusion of dielectric filling in the groove on plasmon propagation parameters. This research will be important for optimising the propagation characteristics of the mode for certain applications, but it may also lead to easier methods of fabricating the V-groove device and prevent oxidation of the metal film. The gap plasmon waveguide is easier to fabricate than the V-groove, and is a new type of sub-wavelength waveguide which displays many advantages over other types of plasmon waveguides, including ease of fabrication, almost 100% transmission around sharp bends, sub-wavelength localisation and long propagation distances of the guided mode, etc. This waveguide may prove invaluable in the development of compact photonic devices. In the past the modes supported by this structure were not thoroughly analysed and the possibility of using this structure to develop sub-wavelength couplers for sensing and nano-optical circuits was not considered in detail. This thesis aims to resolve these issues. In conclusion, the results of this thesis will lead to a better understanding of Vgroove and gap plasmon waveguide devices for the development of nano-optical circuits, compact photonic devices and sensors. This thesis also proposes two new nano-focusing structures which are easier to fabricate than the V-groove structure and will lead to applications in sensing, coupling light efficiently into nano-scale devices and improving the resolution of near-field microscopy.

Les travaux présentés dans ce mémoire s’inscrivent dans la thématique de la transmission d’énergie sans fil, appliquée à l’alimentation à distance de capteurs, de réseaux de capteurs et d’actionneurs à faible consommation. Cette étude porte sur la conception,l’optimisation, la réalisation et la mesure de circuits Rectennas (Rectifying antennas)compacts, à faible coût et à haut rendement de conversion RF-DC.Un outil d’analyse globale, basé sur la méthode des Différences Finies dans le Domaine Temporel (FDTD), a été développé et utilisé pour prédire avec précision la sortie DC des rectennas étudiées. Les résultats numériques obtenus se sont avérés plus précis et plus complets que ceux de simulations à base d’outils commerciaux. La diode Schottky a été rigoureusement modélisée, en tenant compte de ses éléments parasites et de son boîtier SOT23, et introduite dans le calcul itératif FDTD.Trois rectennas innovantes, en technologie micro-ruban, ont été développées,optimisées et caractérisées expérimentalement. Elles fonctionnent à 2.45 GHz et elles ne contiennent ni filtre d’entrée HF ni vias de retour à la masse. Des rendements supérieurs à 80% ont pu être mesurés avec une densité surfacique de puissance de l’ordre de 0.21 mW/cm²(E = 28 V/m). Une tension DC de 3.1 V a été mesurée aux bornes d’une charge optimale de1.05 k_, lorsque le niveau du champ électrique est égal à 34 V/m (0.31 mW/cm²).Des réseaux de rectennas connectées en série et en parallèle ont été développés. Les tensions et les puissances DC ont été doublées et quadruplées à l’aide de deux et de quatre éléments, respectivement. / The work presented in this thesis is included within the theme of wireless power transmission, applied to wireless powering of sensors, sensor nodes and actuators with low consumption. This study deals with the design, optimization, fabrication and experimental characterization of compact, low cost and efficient Rectennas (Rectifying antennas).A global analysis tool, based on the Finite Difference Time Domain method (FDTD),has been developed and used to predict with a good precision the DC output of studied rectennas. The packaged Schottky diode has been rigorously modeled, taking into account the parasitic elements, and included in the iterative FDTD calculation.Three new rectennas, with microstrip technology, have been developed and measured.They operate at 2.45 GHz and they don’t need neither input HF filter nor via hole connections. Efficiencies more than 80 % have been measured when the power density is 0.21mW/cm² (E = 28 V/m). An output DC voltage of about 3.1 V has been measured with anoptimal load of 1.05 k_, when the power density is equal to 0.31mW/cm² (34 V/m).Rectenna arrays, with series and parallel interconnections, have been developed and measured. Output DC voltages and powers have been doubled and quadrupled using two andfour rectenna elements, respectively.

This work deals with techniques of time-domain analysis of interconnects. After a studying crucial issue of time-domain analysis of interconnects methods of modeling and simulation simple interconnects in electrotechnics are described. For transient effect analysis two elementary methods can be used: the state variable method and the FDTD (Finite - Difference Time - Domain) method. The FDTD method can be used to solve partial differential equations in time domain, for instance equations of transmission lines. The method is very effective and delivers satisfactory results in case of linear and non-linear lines with a single “live” conductor. The method can be easily programmed in Matlab.

The presence of photonic band gap in an arbitrarily shaped photonic structure, particularly structures that are fabricated by exploiting rolled-up nanotechnology, can be understood from the density of optical states. In this thesis, the density of optical states and the local density of optical states in finite-sized photonic structures are calculated using the finite difference time domain method together with a parallelized message passing interface. With this approach, a software package suitable for high-performance computing on multi-platform was published under GNU GPL license. When light is guided to propagate along a rolled-up thin film, whispering gallery mode resonances can be formed in a microtubular structure. Dynamic probing and tuning via a plasmonic nanoparticle-coated glass tip are investigated to demonstrate the transition from dielectric-dielectric to dielectric-plasmonic coupling in the tubular microcavity. The competition of these two coupling mechanisms allow the tuning of the optical cavity modes towards lower and then higher energies in a single coupling system. Moreover, three dimensionally confined higher order axial modes can be selectively coupled and tuned by the glass tip due to their unique spatial distribution of the optical field along the tube axis. In addition, the interaction between sharp optical cavity modes and broad plasmonic modes supported by silver nanoparticles leads to the occurrence of Fano resonance. In particular, Fano resonances occurring at higher-order axial modes has been observed as well. The experimental results are supported by numerical simulations based on the finite difference time domain method. In photonic lattice structures, light propagation behavior can be influenced and defined by the photonic band structure. By designing the unit cell with glide mirror symmetry, topologically protected edge states operating in the visible spectral range have been proposed in two dimensional photonic crystals which can be made of feasible materials. Topological phenomena such as unidirectional waveguiding and/or effective zero refractive index are presented. In addition, a scheme to study topological phase transition in a single photonic crystal device is proposed and studied via unevenly stretching photonic lattice. Moreover, a new method is explored to distinguish the topological phase from the bulk modes. The research presented in this thesis concerns molding the flow of light in specially designed photonic devices for various potential applications. The software package can be used to design and investigate finite-sized photonic structures with an arbitrary shape, which is much faster in terms of computation than other reported techniques and software packages. The rolled-up microcavities can be employed to trap and store light in the way of whispering gallery mode resonances, and the resonant light can be tuned and modulated by a plasmonic nanoparticles-coated glass tip. This research is particularly interesting for optical signal processing, slowing light via Fano resonances, and high sensitive sensing. In addition, the topological photonic crystal design and examination scheme presented in this thesis provide a simplified yet more efficient way to obtain non-trivial topological phase from a tunable photonic crystal that can be verified not only by edge modes but also by bulk modes.:Bibliographic record 1 Abstract 1 LIST OF ABBREVIATIONS and Symbols 3 1 Introduction 9 1.1 Introduction and Motivation 9 1.2 Objectives 11 1.3 Organization of the thesis 12 2 Density of optical states in rolled-up photonic crystals and quasi crystals 15 2.1 Introduction 15 2.1.1 background 17 2.1.2 Infinitely extended ideal photonic crystal 17 2.2 Finite-sized photonic crystal, photonic quasicrystal, and arbitrary photonics structures 20 2.2.1 Numerical algorithm 25 2.2.2 Rolled-up photonic crystals and quasi crystals 30 2.3 Software package 33 2.3.1 Computational performance 33 2.3.2 FPS User interface 35 2.3.3 Detailed tutorial 37 2.3.4 Alternative rolled-up photonic crystals 47 2.3.5 Beyond 3D photonic crystals. 48 2.4 Conclusion 49 3 Rolled-up microesonator 51 3.1 Introduction 51 3.2 Rolled-up microresonators 52 4 Tip-assisted photon-plasmon coupling in three-dimensionally confined microtube cavities 57 4.1 Introduction 57 4.2 Tube and plasmonic particle preparation and characterization 60 4.3 Results and discussion 62 4.4 Axial mode tuning 64 4.5 Fano resonance 65 4.5.1 Background 65 4.5.2 Fano resonance in the tip assisted coupling setup 68 4.6 Conclusion 71 5 Topological photonics 73 5.1 Introduction and motivation 73 5.2 Topological phase transition point 77 5.2.1 Fundamental phase transition point 77 5.2.2 Zero refractive index material 79 5.3 Non-trivial topology in realistic materials 80 6 Topological phase transition in stretchable photonic crystals 85 6.1 Introduction and motivation 85 6.2 SSH model 88 6.3 Photonic crystal 91 6.4 Band structure and end modes of the photonic crystal 99 6.5 Conclusion 101 7 Summary and outlook 103 7.1 Summary 103 7.2 Outlook 104 Bibliography 111 List of figures 127 Publications 133 Acknowledgments 136 Selbständigkeitserklärung 137 Curriculum Vitae 138