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Ce travail porte sur l'étude expérimentale et numérique de jets coaxiaux de rapports de vitesses débitantes intérieure/extérieure) inférieurs à l’unité, présentant une rotation dans le jet annulaire. Dans un premier temps, des visualisations par tomographie laser ont été réalisées dans les plans méridien et transversaux permettant une description tridimensionnelle de l'écoulement. Pour différents nombres de Reynolds, de rapport de vitesses et de nombre de Swirl, un inventaire des modes dominants a pu être établi. Les champs instantanés de vitesses ont ensuite été mesurés par Vélocimétrie par Imagerie de Particules (PIV). Les résultats de mesures de vitesses longitudinales et azimutales moyennées en temps sont présentés. Une comparaison avec les structures observées par tomographie est proposée. Une décomposition de Fourier a été effectuée permettant d'identifier les modes dominants ainsi que leur position dans la direction radiale. L'approche expérimentale a été suivie par une analyse de stabilité linéaire. Une attention particulière est portée sur l'état de base stationnaire reconstruit à partir des profils de vitesses mesurées par PIV à la sortie du jet. Étant donné que l'écoulement est non parallèle, une approche globale de la stabilité est utilisée. L'étude de la stabilité est basée sur la résolution numérique des équations de Navier-Stokes par des méthodes pseudo-spectrales. L'objectif de cette analyse est de retrouver la carte en mode de Fourier azimutaux observée expérimentalement. Nous nous sommes donc intéressés au taux de croissance le plus élevé de la perturbation pour chaque mode azimutal ainsi qu'à la nature convective/ absolue des modes. Pour finir, une com / This work concerns the experimental and numerical study of coaxial jets with outer to inner velocity ratio lower than unity, presenting a rotation in the annular jet. At first, flow visualizations by tomography laser were used in the meridian and transverse plans in order to provide a spatial description of the flow. For various values of the nondimensional parameters : numbers of Reynolds, outer to inner velocity ratio and Swirl number, an inventory of the dominant modes was be established. Instantaneous velocity fields were then measured by Particle lmaging Velocimetry (PIV). The results of longitudinal and azimuthal time-averaged Velocity fields are presented. A comparison with the structures observed by tomography is proposed. A Fourier decomposition was made allowing to identify the dominant modes as well as their position in the radial direction. Experimental investigation was followed by a linear stability analysis. Special attention is paid to the steady base-flow solution reconstructed from the velocity profiles measured by PIV at the end of the nozzle. Given that the is not parallel, a global approach was used. Study of the stability is based on the numerical solution of the incompressible Navier-Stokes equations with pseudo-spectral methods. The objective of this analysis is to the map of azimuthal Fourier modes observed experimentally. We were thus interested in the most amplified growth rate of the disturbance for every azimuthal mode as well as in the absolute/convective nature of the modes. To conclude, a comparison of the results obtained in both numerical and experimental approaches is proposed.

Cette thèse constitue un ensemble de travaux et de réflexions sur la question de la modélisation d’expériences en nano-optique utilisant la méthode des différences finies dans le domaine fréquentiel (FDFD) et la méthode des différences finies dans le domaine temporel (FDTD). D’abord, un code FDFD bidimensionnel, dédié au calcul de modes propres de guides d’ondes optiques, a été mis en œuvre et testé à travers une comparaison avec des résultats publiés. Dans une deuxième grande partie, nous étudions le piégeage optique de petites particules (de taille microscopique) à l’aide d’une antenne à nano-ouverture papillon (BNA) gravée à l’extrémité d’une sonde de microscope optique métallisée. Le confinement de lumière obtenue à la résonance de la nano-antenne permet un piégeage 3-D des nanoparticules de latex. Une étude systématique a été menée pour quantifier la puissance de la lumière incidente nécessaire pour un piégeage stable. Un bon accord entre les résultats expérimentaux et numériques a été obtenu dans le cas d’une BNA opérant dans l’eau à _ = 1064 nm pour le piégeage de particules de latex de 250 nm de rayon. En outre, les résultats numériques pour de plus petites particules sont présentés et montrent qu’une telle configuration est capable de piéger des particules avec des rayons aussi petits que 30 nm. Troisièmement, nous avons étudié le processus de piégeage optique basé sur l’amélioration du confinement, non seulement du champ électrique comme dans le cas de la BNA, mais aussi du magnétique que peut exhiber l’antenne métallique type diabolo (DA). Cette dernière a été récemment proposée car elle présente une résonance avec un fort confinement magnétique. Nous avons amélioré le design afin qu’une double résonance, électrique et magnétique, ait lieu au centre de la nano-antenne. Ce double confinement a ensuite été exploité pour exalter le gradient de champ au voisinage de l’antenne et ainsi aboutir à de meilleures efficacités de piégeage (moindre puissance). De plus, les résultats des simulations montrent que le processus de piégeage dépend fortement des dimensions des particules et que, pour des géométries particulières, un piégeage sans contact peut être réalisé. Cette structure doublement résonnante ouvre la voie à la conception d’une nouvelle génération de nano-pinces optiques à forte efficacit / This thesis is a set of work and reflections on modeling the experiments in nano-optics by using the finite difference method in the frequency domain (FDFD), and in time domain (FDTD). First, a two-dimensional code FDFD, dedicated to the calculation the eigenmodes of optical waveguides, has been implemented and tested through a comparison with results found in the literature. In a second large part, we study the optical trapping of small particles (of microscopic size) by using a bowtie nanoaperture antenna (BNA) engraved at the end of a metal-coated near-field optical microscope tip. The confinement of light obtained at the resonance of the nano-antenna allows 3-D trapping of latex nanoparticles. A systematic study was conducted to quantify the power of incident light necessary for stable trapping. Good agreement between the experimental and numerical results was obtained in the case of a BNA operating in water at _ = 1064 nm for the trapping of latex particles having a radius of 250 nm-radius. In addition, numerical results for smaller particles are presented and show that such configuration is capable of trapping particles with radii reaching 30 nm. Third, we studied the optical trapping process based on improved confinement of the electric field as in the case of the BNA, but also of the magnetic field, by using a metallic diabolo shape antenna (DA). This latter has been recently proposed because it exhibits resonance with a strong magnetic field confinement. We have improved the design in such a way that a double resonance, electric and magnetic, takes place in the center of the nano-antenna. This dual confinement was then used in order to enhance the field gradient in its vicinity and thus obtain better efficiencies of the trapping (less power). In addition, the simulation results show that the trapping process is greatly dependent of the particles size, and also show that, for specificl geometries, a trapping without contact can be achieved. This doubly resonant structure opens the way to the conception of a new generation of optical nano-tweezers with high efficiency.

The widespread adoption of photonic circuits requires the economics of volume manufacturing offered by integration technology. A Complementary Metal-Oxide Semiconductor compatible silicon material platform is particularly attractive because it leverages the huge investment that has been made in silicon electronics and its high index contrast enables tight confinement of light which decreases component footprint and energy consumption. Nevertheless, there remain challenges to the development of photonic integrated circuits. Although the density of integration is advancing steady and the integration of the principal components – waveguides, optical sources and amplifiers, modulators, and photodetectors – have all been demonstrated, the integration density is low and the device library far from complete. The integration density is low primarily because of the difficulty of confining light in structures small compared to the wavelength which measured in micrometers. The device library is incomplete because of the immaturity of hybridisation on silicon of other materials required by active devices such as III-V semiconductor alloys and ferroelectric oxides and the difficulty of controlling the coupling of light between disparate material platforms. Metamaterials are nanocomposite materials which have optical properties not readily found in Nature that are defined as much by their geometry as their constituent materials. This offers the prospect of the engineering of materials to achieve integrated components with enhanced functionality. Metamaterials are a class of photonic crystals includes subwavelength grating waveguides, which have already provided breakthroughs in component performance yet require a simpler fabrication process compatible with current minimum feature size limitations. The research reported in this PhD thesis advances our understanding of the structure-property relations of key planar light circuit components and the metamaterial engineering of these properties. The analysis and simulation of components featuring structures that are only just subwavelength is complicated and consumes large computer resources especially when a three dimensional analysis of components structured over a scale larger than the wavelength is desired. This obstructs the iterative design-simulate cycle. An abstraction is required that summarises the properties of the metamaterial pertinent to the larger scale while neglecting the microscopic detail. That abstraction is known as homogenisation. It is possible to extend homogenisation from the long-wavelength limit up to the Bragg resonance (band edge). It is found that a metamaterial waveguide is accurately modeled as a continuous medium waveguide provided proper account is taken of the emergent properties of the homogenised metamaterial. A homogenised subwavelength grating waveguide structure behaves as a strongly anisotropic and spatially dispersive material with a c-axis normal to the layers of a one dimensional multi-layer structure (Kronig-Penney) or along the axis of uniformity for a two dimensional photonic crystal in three dimensional structure. Issues with boundary effects in the near Bragg resonance subwavelength are avoided either by ensuring the averaging is over an extensive path parallel to boundary or the sharp boundary is removed by graded structures. A procedure is described that enables the local homogenised index of a graded structure to be determined. These finding are confirmed by simulations and experiments on test circuits composed of Mach-Zehnder interferometers and individual components composed of regular nanostructured waveguide segments with different lengths and widths; and graded adiabatic waveguide tapers. The test chip included Lüneburg micro-lenses, which have application to Fourier optics on a chip. The measured loss of each lens is 0.72 dB. Photonic integrated circuits featuring a network of waveguides, modulators and couplers are important to applications in RF photonics, optical communications and quantum optics. Modal phase error is one of the significant limitations to the scaling of multimode interference coupler port dimension. Multimode interference couplers rely on the Talbot effect and offer the best in-class performance. Anisotropy helps reduce the Talbot length but temporal and spatial dispersion is necessary to control the modal phase error and wavelength dependence of the Talbot length. The Talbot effect in a Kronig-Penny metamaterial is analysed. It is shown that the metamaterial may be engineered to provide a close approximation to the parabolic dispersion relation required by the Talbot effect for perfect imaging. These findings are then applied to the multimode region and access waveguide tapers of a multi-slotted waveguide multimode interference coupler with slots either in the transverse direction or longitudinal direction. A novel polarisation beam splitter exploiting the anisotropy provided by a longitudinally slotted structure is demonstrated by simulation. The thesis describes the design, verification by simulation and layout of a photonic integrated circuit containing metamaterial waveguide test structures. The test and measurement of the fabricated chip and the analysis of the data is described in detail. The experimental results show good agreement with the theory, with the expected errors due to fabrication process limitations. From the Scanning Electron Microscope images and the measurements, it is clear that at the boundary of the minimum feature size limit, the error increases but still the devices can function.