Orientador: Luis Vicente de Andrade Scalvi / Coorientador: Julio Ricardo Sambrano / Banca: Margarida Juri Saeki / Banca: Tomaz Catunda / Banca: Valeria Moraes Longo / Resumo: Este trabalho apresenta uma abordagem teórico-experimental na investigação de filmes finos de dióxido de estanho (SnO2) não dopado, de SnO2 dopado com antimônio (Sb), de dióxido de titânio (TiO2) e também de heteroestrutura Tio2/SnO2, produzidos pelo processo sol-gel-dip-coating. O conhecimento dos mecanismos de transporte elétrico de SnO2:Sb é fundamental para o desenvolvimento de dispositivos opto-eletrônicos. Neste sentido, a contribuição deste trabalho está principalmente no estudo das propriedades elétricas de SnO2:Sb, no qual foi analisado a captura de elétrons fotoexcitados por centros de Sb e/ou vacâncias de oxigênios termicamente ativados. Os resultados, surpreendentemente, mostraram que a taxa de variação da condutividade diminui com o aumento temperatura, independente da energia da fonte de excitação (acima ou abaixo da energia do bandgap). Este comportamento está provavelmente relacionado à mobilidade eletrônica, que é dominado pelo espalhamento de portadores de carga na região do contorno de grão. Quanto à heterojunção TiO2/SnO2, o conhecimento do tipo de estrutura cristalina dos semicondutores óxidos é fundamental para sua utilização em determinadas aplicações tecnológicas. A avaliação das propriedades estruturais de filmes finos de TiO2 apresentada nesta tese mostrou que o substrato de quartzo, utilizado para deposição dos filmes, exerce influência na temperatura de transição de fase anatásio-rutilo. De modo geral, apresentamos aqui uma avaliação das propriedades ópticas, estruturais, elétricas e eletrônicas de filmes finos de SnO2 e de SnO2:SB e também das propriedades ópticas, estruturais e eletrônicas de TiO2 e heterojunção TiO2/SnO2. As propriedades eletrônicas foram obtidas a partir de simulações computacionais de SnO2 SnO2:Sb e TiO2 desenvolvidas com o programa CRYSTAL06, baseadas na Teoria do Funcional da Densidade / Abstract: This work presents a theoretical-experimental approach in the investigation of undoped and Sb-doped SnO2 thin flims, TiO2 thin films and also the heterostructure TiO2/SnO2 deposited through the sol-gel-dip-coating technique. The knowledge of the electrical transport mechanisms in SnO2:Sb is fundamental towards the devolping of optoelectronic devices. Then, our contribution concerns the analysis of the electronic structure and, mainly, the investigation of the electrical properties of SnO2:Sb, where the electron capture by thermally activated Sb centers and/or oxygen vacancies was proposed. Results, surpisingly, show that the conductivity variation rate increases with temperature, independent on excitation source energy (above or below the gandgap energy). This behavior is probaly related to the electronic mobility, which is dominated by the charge carrier scattering at boundary layer. Concerning the heterojunction TiO2/SnO2, the determination of the crystalline structure type of oxide semiconductors if fundamental for application in specific technologies. The evalution of structural properties of TiO2 films show that the quartz substrate, used for film deposition, influences the transition temperature of the anatase-rutile phases. In summary, we present an evalution of optical, structural, electrical and electronic properties of SnO2 and SnO2:Sb as well as optical, structured, and electronic properties of TiO2/SnO2. Electronic properties were obtained from computacional simulations of SnO2, SnO2:Sb, TiO2 and TiO2/SnO2, developed with the program CRYSTAL06, through the Density Functional Theory / Doutor

Several applications require the detection of terrestrial UV-C signatures. Efficiency, compactness, environmentally friendly and cost-effective requirements for UV-C–detectors resulted in a research interest in wide-bandgap (WBG) semiconductor-based photovoltaic diodes with a 280 nm cut-off wavelength. Advances in producing group-III-nitride materials allowed the growth of high quality Al[x]Ga[1−x]N, a direct-WBG ternary semiconductor in which the Al mole fraction (x) could be varied, allowing for a tuneable bandgap that made the semiconductor intrinsically 'blind' to longer wavelengths and responsive to selected wavelengths shorter than 360 nm. This dissertation reports on the development and characterization of a tuneable AlGaN-based solar-blind UV-sensitive Schottky photodiode. A fabrication procedure was established using optimized metallization techniques derived from literature. This included metallization schemes, metal thicknesses and annealing methods for metallization of both the ohmic and Schottky contacts for a front-irradiated photodiode. Characterization was done with a newly constructed optoelectronic characterization system. Electrical characterization was performed inside a light-tight shielded enclosure and a software routine aided in applying current–voltage and capacitance–voltage measurements on a Schottky diode. Spectral characterization made use of either a UV source or a visible-to-near-infrared source that was coupled to a monochromator that allowed for wavelength selection. The monochromatic electromagnetic radiation was guided by an optical fibre from the monochromator into the enclosure where the photodiode was irradiated. An additional software routine was developed that allowed for the automation of the spectral characterization. The system was calibrated against standards traceable to the National Institute of Standards and Technology (NIST) by following the photodetector substitution method. The study concluded with the manufacturing of an epoxy wire-bonded front-irradiated four-quadrant detector that was mounted on a commercial microchip carrier. Metal depositions were done through physical contact masks. The quadrants were surrounded with optimized layered ohmic contacts and a quadrant consisted of a thin-film iridium(IV) oxide (IrO₂) as Schottky contact that is UV transmissive with a Au contact on top to which a wire was bonded. Optoelectronic characterization verified that the four-quadrant detector was intrinsically solar-blind and showed good uniformity across the quadrants. Electrical parameters obtained included an average ideality factor of 1.97 ± 0.09, a Schottky barrier height of (1.22 ± 0.08) eV, a reverse leakage current density of (2.1 ± 3.3) nA/cm² and a series resistance of (120 ± 30) Ω. Spectral parameters obtained included a (275 ± 5) nm cut-off wavelength, an average current responsivity at 250 nm of (28 ± 1.0) mA/W with a quantum efficiency of (14 ± 0.5) % and an UV-to-visible and near-infrared rejection ratio between 10³ and 10⁵ for 400 nm to 1100 nm wavelengths. These characteristics allowed for the detector to be used in demonstrating a working solar-blind UV-sensitive electro-optic device. / Dissertation (MSc)--University of Pretoria, 2015. / Physics / Unrestricted

Ce mémoire présente la conception d'un radar Ultra Large Bande à déclenchement optoélectronique dédié au rayonnement d'impulsions ultra-courtes dans une bande de travail comprise entre 300MHz et 3GHz pour réaliser des opérations de détection à courte et moyenne portée. A l'émission, ce radar est composé de plusieurs sources de rayonnement élémentaires constituées d'une antenne au sein de laquelle un générateur optoélectronique est intégré, d'un générateur de haute tension pulsée et d'un système commande optique. Des mesures de validation ont été menées pour s'assurer du bon fonctionnement d'une source. Cette association garantit une excellente synchronisation entre les sources et autorise un balayage électromagnétique autonome rapide en ajustant les fréquences de répétition (quelques dizaines de MHz) de chaque générateur de manière à décaler proportionnellement à l'angle visé, l'instant d'alimentation. A la réception, une antenne ou plusieurs antennes sont utilisées pour récupérer les signaux diffractés par les cibles et un traitement de signal est appliqué pour reconstruire l'image. Ce traitement spécifique permet de s'affranchir de la limite de détection en distance imposée par la fréquence de répétition en utilisant une association entre des calculs de corrélation et une déconvolution itérative. Un des vecteurs d'amélioration de la qualité de l'image a également été développé. Il concerne la génération de forme d'ondes et plus particulièrement le façonnage spectral par profilage temporel en utilisant un algorithme d'optimisation évolutionnaire. / This thesis presents the design of an Ultra Wide Band radar triggered by an optoelectronic generator which is dedicated to ultra short pulses radiation for short and medium range detection. The emitting part of this radar is based on transmitting array composed of several UWB antennas with an integrated photoswitch device triggered using optical pulses and a receiving UWB antenna. A specific signal processing method has been proposed and implemented for UWB optoelectronic radar involving autonomous beam scanning capability in order to overcome the limitation in the depth of detection encountered while using standard imaging algorithm. Indeed, this hybrid correlation/CLEAN algorithm considers the whole measured burst and finds the relevant information to rebuilt a radar map with a very good accuracy. In order to improve the radar map quality, the waveform generation technique has been discussed and, more precisely, the temporal shaping method to obtain specific spectrum using evolutionary algorithm.

With the progression towards lighter but larger-display self-sustainable mobile devices, device efficiency becomes increasingly important, owing to the higher power display consumption but at the same time more limitation on the size and volume of energy storage. In this thesis, selected aspects regarding to efficiency of three types of optoelectronic devices, indoor photovoltaics (IPVs), perovskite thin-film transistors (TFTs) and organic light-emitting diodes (OLEDs) have been investigated. IPVs can make off-grid devices self-sustainable by harvesting ambient light energy. Its weak irradiance necessitates high-efficiency IPVs to generate sufficient power. Our work addresses the need of knowing the limit of the device parameters for correct evaluation and understanding the efficiency loss for developing clinical tactics. We delivered a general scheme for evaluating the limiting efficiency and the corresponding device parameters of IPVs under various lights, illuminance and material bandgap. In contrast to the AM1.5G conditions, a maximum power conversion efficiency (PCE) of 51-57 % can be achieved under the optimal bandgap of 1.82-1.96 eV. We also propose using the second thickness peak of interference instead of the first as a better optimal absorber thickness after identifying the finite absorption as the major source of efficiency loss. The work provides insights for device evaluation and material design for efficient IPV devices. The novel hybrid organic-inorganic perovskites have gained enormous research interest for its various excellent optoelectronic properties such as high mobility. TFT as an alternative application to the majorly focused photovoltaics is realized in this work. There are few reports on perovskite TFTs due to wetting issues. By employing polymethacrylates with ester groups and aromatic substituents which provide polar and cation-π interactions with the Pb2+ ions, quality films could be fabricated with large crystals and high electron mobility in TFTs. We further improved the performance by resolving interfacial mixing between the perovskite and the polymer using the crosslinkable SU-8, achieving the highest mobility of 1.05 cm2 V−1 s−1. Subsequently, we cured the grain boundaries using methylamine solvent vapor annealing, suppressing the TFT subthreshold swing. The work provides a map for the improvement of perovskite TFTs. It has been revealed that molecular orientations of the emitters in OLEDs with the transition dipole moment lying in plane enhances light outcoupling efficiency. Multiple experimental techniques are needed to provide complementary orientation information and their physical origin. Here, we propose using TFT to probe the orientation of the phosphorescent emitters. Homoleptic fac-Ir(ppy)3 and heteroleptic trans-Ir(ppy)2(acac) and trans-Ir(ppy)2(tmd) were deposited on polystyrene (PS) and SiO2 substrates. Compared to the PS surface inducing isotropic orientation as the control, trans-Ir(ppy)2(acac) and trans-Ir(ppy)2(tmd) possessed decreased carrier mobilities on SiO2. With the study of initial film growth, we infer that preferred orientation induced by the polar SiO2 surface led to an increase in energetic disorder in the well-stacked trans-Ir(ppy)2(acac) and hopping distance in the amorphous trans-Ir(ppy)2(tmd). The highly symmetric fac-Ir(ppy)3 remained its isotropic orientation despite the dipolar interaction. Surprisingly, the TFT technique gives much higher sensitivity to surface-induced orientation, and thus may potentially serve as a unique electrical probe for molecular orientation.

With the progression towards lighter but larger-display self-sustainable mobile devices, device efficiency becomes increasingly important, owing to the higher power display consumption but at the same time more limitation on the size and volume of energy storage. In this thesis, selected aspects regarding to efficiency of three types of optoelectronic devices, indoor photovoltaics (IPVs), perovskite thin-film transistors (TFTs) and organic light-emitting diodes (OLEDs) have been investigated. IPVs can make off-grid devices self-sustainable by harvesting ambient light energy. Its weak irradiance necessitates high-efficiency IPVs to generate sufficient power. Our work addresses the need of knowing the limit of the device parameters for correct evaluation and understanding the efficiency loss for developing clinical tactics. We delivered a general scheme for evaluating the limiting efficiency and the corresponding device parameters of IPVs under various lights, illuminance and material bandgap. In contrast to the AM1.5G conditions, a maximum power conversion efficiency (PCE) of 51-57 % can be achieved under the optimal bandgap of 1.82-1.96 eV. We also propose using the second thickness peak of interference instead of the first as a better optimal absorber thickness after identifying the finite absorption as the major source of efficiency loss. The work provides insights for device evaluation and material design for efficient IPV devices. The novel hybrid organic-inorganic perovskites have gained enormous research interest for its various excellent optoelectronic properties such as high mobility. TFT as an alternative application to the majorly focused photovoltaics is realized in this work. There are few reports on perovskite TFTs due to wetting issues. By employing polymethacrylates with ester groups and aromatic substituents which provide polar and cation-π interactions with the Pb2+ ions, quality films could be fabricated with large crystals and high electron mobility in TFTs. We further improved the performance by resolving interfacial mixing between the perovskite and the polymer using the crosslinkable SU-8, achieving the highest mobility of 1.05 cm2 V−1 s−1. Subsequently, we cured the grain boundaries using methylamine solvent vapor annealing, suppressing the TFT subthreshold swing. The work provides a map for the improvement of perovskite TFTs. It has been revealed that molecular orientations of the emitters in OLEDs with the transition dipole moment lying in plane enhances light outcoupling efficiency. Multiple experimental techniques are needed to provide complementary orientation information and their physical origin. Here, we propose using TFT to probe the orientation of the phosphorescent emitters. Homoleptic fac-Ir(ppy)3 and heteroleptic trans-Ir(ppy)2(acac) and trans-Ir(ppy)2(tmd) were deposited on polystyrene (PS) and SiO2 substrates. Compared to the PS surface inducing isotropic orientation as the control, trans-Ir(ppy)2(acac) and trans-Ir(ppy)2(tmd) possessed decreased carrier mobilities on SiO2. With the study of initial film growth, we infer that preferred orientation induced by the polar SiO2 surface led to an increase in energetic disorder in the well-stacked trans-Ir(ppy)2(acac) and hopping distance in the amorphous trans-Ir(ppy)2(tmd). The highly symmetric fac-Ir(ppy)3 remained its isotropic orientation despite the dipolar interaction. Surprisingly, the TFT technique gives much higher sensitivity to surface-induced orientation, and thus may potentially serve as a unique electrical probe for molecular orientation.

The main subject of this thesis is the synthesis and investigation of the properties and potential applications of a new class of hybrid compounds consisting of a rigid, electroactive 4,4’-bipyridinium core capped by nucleobase terminal groups with hydrogen bonding abilities. A new series of small molecules consisting in a 4,4’-bipyridinium unit carrying thymine or/and adenine as capping groups was synthetized. The synthesis strategy implied the regioselective alkylation of thymine and adenine bases respectively, followed by coupling of the alkylated precursors to 4,4’-bipyridine unit via Menschutkin reaction. Electrochemical, spectroelectrochemical and optical investigations revealed an intramolecular charge transfer (CT) relationship between nucleobases as donors and 4,4’-bipyridinium unit as acceptor which is accompanied by a change in color and a shift of the reduction potentials (approx. 60 mV). The viologen-nucleobase derivatives, particularly viologens capped by thymine, were used as building blocks to create self-assembled functional nanostructures in the presence of complementary templates such as oligonucleotides or ssPNA analogues via thymine-adenine interactions. The viologen-thymine derivatives were found to partially precipitate oligonucleotides or plasmid DNA by mean of coulombic interactions and form stable polyplexes that could be used as potential gene delivery vectors. It was found that the number of positive charges, as well as the number of thymine units per viologen-thymine derivative determines whether the interaction with DNA is dominated by electrostatic or by hydrogen bonding interactions. New electroactive ionic liquid crystals were prepared by ion pairing of viologen-nucleobase dicationic species with amphiphilic 3,4,5-tris(dodecyloxy)benzene sulfonate anion. The nucleobases with ability to self-associate by hydrogen bonding were found to influence not just the thermotropic behavior, by decreasing transition temperature from crystalline to mesophase state, but also the supramolecular arrangement in solution. A versatile approach to functionalize mesoporous TiO2 film with viologen-nucleobase derivatives was developed consisting of hydrogen bonding layer-by-layer deposition of viologen-nucleobase derivatives on TiO2 surface using the thymine-adenine molecular recognition as driving force for immobilization. This method is promising and represents an easy way to construct optoelectronic device components as was demonstrated with the construction of a switchable electrochromic device.

Nous avons développé et construit un imageur polarimétrique actif avec une illumination laser à la longueurd'onde 1:55 um. Il peut générer et analyser tous les états de polarisation de la sphère de Poincaré. Il permetde réaliser une optimisation polarimétrique du contraste en analysant la scène à l'aide d'un algorithme desegmentation ultra rapide basé sur des contours actifs. Cet imageur nous permet de comparer plusieursmodalités d'imagerie possédant des nombres de degrés de liberté polarimétrique différents. Nous effectuons ladétection d'objets manufacturés dans différents environnements avec l'imagerie polarimétrique active pourillustrer les capacités de ces modalités. Nous démontrons l'effcacité de l'imagerie polarimétrique active pourdes applications de décamouffage et de détection d'objets dangereux, et mettons en évidence lescaractéristiques qu'un imageur polarimétrique doit posséder pour ce type d'applications. Nous montrons quedans la majorité des scénarios étudiés, les matrices de Mueller sont presque diagonales, et que desperformances de détection satisfaisante peuvent être atteintes avec des imageurs polarimétriques plus simplesqui ont un nombre de degrés de liberté réduit. De plus, la normalisation de l'intensité des images est unecondition nécessaire pour mieux révéler le contraste polarimétrique. / We designed and built an active polarimetric imager with laser illumination at 1:55 um wavelength. It cangenerate and analyze any polarization state on the Poincaré sphere. It let us the possibility to perform apolarimetric contrast optimization by analyzing the scene with an ultrafast active-contour-based segmentationalgorithm. This imagins systeme allow to compare several imaging modes having different numbers ofpolarimetric degrees of freedom. We address the detection of manufactured objects in different types ofenvironments with active polarimetric imaging to illustrate the capabilities of the techniques. We demonstratethe effciency of active polarimetric imaging for decamouffage and hazardous object detection, and underlinethe characteristics that a polarimetric imager aimed at this type of application should possess. We show thatin most encountered scenarios the Mueller matrices are nearly diagonal, and suffcient detection performancecan be obtained with simple polarimetric imaging systems having reduced degrees of freedom. Moreover,intensity normalization of images is of paramount importance to better reveal polarimetric contrast.

Ce travail de thèse porte sur l’étude de deux éléments au cœur d’un système de nanopositionnement et de micromanipulation : a) un capteur interférométrique intégré sur puce ; ses caractéristiques, particularités et potentiels sont étudiés en détails ; b) un élément utilisable en capteur et actionneur : un polymère électro-actif à flexions.L'interféromètre PicoMove est le résultat de l'étroite collaboration entre LISV et l’entreprise TeemPhotonics. Cet interféromètre, qui fonctionne dans le domaine de l'infrarouge moyen (1,55 µm) est basé sur la technologie des guides d'ondes optique lui offrant une plus grande robustesse vis-à-vis de l'environnement extérieur. son architecture est basée sur une structure Michelson-Young modifiée. Des expérimentations ont été mises en œuvre pour caractériser ses performances. Il a été démontré une résolution sub-nanométrique et un très faible niveau de bruit. Une densité spectrale de puissance de 100 fm/√Hz a été atteinte en condition statique.En outre, sa robustesse aux conditions environnementales est démontrée, et ses sources d’erreurs et spécificités métrologiques sont discutées au travers d’une application sur un étage de nanopositionnement, fonctionnant avec un moteur à bobine mobile et un guidage flexible.Le second point de cette thèse concerne l’étude des propriétés électro-mécaniques d'un polymère électro-actif ionique (IEAP) en configuration poutre encastrée. Il est capable de fonctionner en mode actionneur et en mode capteur. Pour la partie actionneur, sa raideur et fréquence propre sont déterminées. Pour la partie capteur, sa bande passante, sa résolution et sa fonction de transfert sont étudiées expérimentalement.Les capacités micrométriques de ce polymère en mode actionneur et en mode capteur sont démontrées et discutées. / This work concerns the study of two elements of a system of nanopositioning and micromanipulation: a) integrated on-chip interferometric sensor; its characteristics, peculiarities and potential are studied in detail; b) an element usable in sensor and actuator mode: an electro-active flexural polymer.The PicoMove interferometer is the result of the collaboration between LISV and the company TeemPhotonics. This interferometer, which operates in the mid-infrared range (1.55 μm), is based on optical guide technology that gives a high degree of robustness to the external environment. Its architecture is based on a modified Michelson-Young structure. Experiments have been implemented to characterize its performance. It has been demonstrated nanometric resolution and very low noise level. A spectral power density of 100 fm/√Hz was reached under static conditions.In addition, its robustness to the environmental conditions is demonstrated, and the metrological specificities are discussed with details about the specific error sources. It is applied to a nanopositioning stage using mobile coil and flexible guidance.The second point of this PhD work concerns the study of electromechanical properties of an ionic electroactive polymer (IEAP) in a flexible cantilever configuration. It is able to operate in actuator mode and in sensor mode. For the actuator part, its stiffness and its natural frequency are studied. For the sensor part, its bandwidth, resolution and transfer function are experimentally studied.The micrometric capabilities of this polymer in actuator and sensor mode are demonstrated and discussed.

Le développement technologique dans le domaine des télécommunications, ainsi que des systèmes de détection, a accru ces dernières années la nécessité de signaux de référence présentant une très haute pureté spectrale. L'augmentation des débits, la saturation des bandes de fréquence ainsi que les performances imposées pour la détection radar ont ouvert la voie à la génération micro-onde par l'optique. Ces références de fréquence sont souvent issues d'oscillateurs optoélectroniques (OEO). Ces oscillateurs intègrent un élément de stockage de l'énergie au travers de résonateurs ou de longues lignes à retard fibrées afin d'augmenter leur facteur qualité et permettant ainsi d'atteindre des performances supérieures aux signaux multipliés à partir de sources basses fréquences ou directement à partir d'oscillateurs micro-ondes à résonateur diélectrique (DRO). Une topologie originale d'oscillateurs optoélectroniques a été proposée à la fin des années 1990 par une équipe américaine : il s'agit de remplacer le résonateur passif nécessitant un verrouillage du laser sur ce dernier par un résonateur actif, intégrant un amplificateur optique. Ce résonateur actif, un laser à blocage de modes, permet un couplage entre l'oscillation optique du laser et l'oscillation optoélectronique. On parle alors d'oscillateur optoélectronique couplé (COEO). Les performances du COEO sont étroitement liées à la pureté spectrale du signal issu du laser à blocage de modes. Ce travail de thèse traite de l'étude et de l'optimisation de ces systèmes. Une étude approfondie sur le bruit dans les amplificateurs optiques a tout d'abord été menée afin de déterminer quel type d'amplificateur choisir pour le COEO et sous quelles conditions l'amplification optique apporte un bruit de phase minimal. Ensuite, un COEO à 10 GHz a été réalisé, présentant un très faible bruit de phase atteignant - 132 dBc/Hz à 10 kHz de la porteuse. Un modèle a par ailleurs été implémenté, permettant de déterminer a posteriori l'efficacité du couplage et ainsi la bande de verrouillage entre l'oscillation optoélectronique et le laser à blocage de modes. Ce couplage interne dépend fortement de la dynamique du système. Cependant, les différents effets non linéaires qui ont lieu dans l'amplificateur à semiconducteur et les fibres ne permettent pas d'obtenir un modèle analytique. Un modèle itératif a alors été proposé afin d'obtenir les propriétés de l'enveloppe complexe lentement variable du peigne de fréquence généré en sortie du laser dont la photodétection conduit à la puissance RF générée par le COEO. Le COEO génère un peigne de fréquence suffisamment large pour produire des harmoniques RF supérieurs à la fréquence de répétition du laser à blocage de modes, si les modes longitudinaux espacés de plusieurs intervalles spectraux libres (ISL) sont en phase. Le modèle itératif développé permet, à partir des paramètres expérimentaux de déterminer le spectre optique ainsi que la distribution de phase à l'intérieur de celui-ci. Il est possible alors d'augmenter la puissance d'une harmonique en sortie de la photodiode par un ajout d'éléments dispersifs. Cette multiplication de fréquence permet la génération de signaux à haute pureté spectrale en bande millimétrique. Une démonstration expérimentale à 90 GHz a été proposée, basée sur un COEO fonctionnant à 30 GHz. Ces résultats sont prometteurs et une intégration du COEO dans un boîtier thermalisé ainsi qu'une gestion plus fine de la dispersion des fibres peut permettre des améliorations significatives sur le bruit de phase du système. / The important rise of telecommunication systems in the past decades, together with the sensitivity improvement of radar systems, has increased the necessity for high spectral purity frequency references at high frequencies. The saturation of classical microwave bandwidths motivated the search of frequency references at higher frequencies, such as K-band. Frequency multiplication from highly stable sources, such as quartz sources, is limited by the increase of the noise floor, which is often prohibitive at millimeter wave frequencies. On the contrary, microwave generation using optics becomes a very efficient technique in this frequency range. Indeed, passive optical resonators or delay lines feature a high Q factor which can be used to stabilize the microwave frequency. The best phase noise performance is today obtained with long delay line oscillators. However, a spurious mode suppression technique has to be implemented in this type of OEOs. The use of an active optical resonator is a third solution, which avoids any locking technique between the laser and the passive resonator. The first architecture of this type has been proposed at the end of the 1990's. In such a system, a mode-locked laser is coupled to a microwave oscillator (COEO). COEO phase noise performances are strongly dependent on the spectral purity of the mode locked laser signal. This thesis work focus on the study and the optimization of this system. Optical amplifiers noise is firstly investigated, in order to determine the optimal conditions to minimize their phase noise contribution to the COEO. A 10 GHz SOA based COEO has been realized and features a low phase noise level reaching - 132 dBc/Hz at 10 kHz from the carrier. An analytical model has also been developed to obtain the locking range of the coupled oscillations. This frequency range is strongly dependent on the coupling efficiency between optical oscillation and the optoelectronic oscillation. This parameter cannot be calculated analytically and an iterative model has been proposed to determine the amplitude and phase of the optical spectrum. Therefore, one can calculate the RF power on the photodiode, on which the coupling efficiency is depending. Since COEO features a large optical frequency comb where each tooth of the comb is phase locked thanks to the mode locked laser, harmonic generation from COEO is possible. Wide frequency comb from high frequency COEO allow millimeter wave generation. The iterative model developed in this work enable to determine the RF power of one specified harmonic from experimental parameters. Harmonic selection can also be performed through the management of the chromatic dispersion. Such frequency multiplication has been implemented to generate a high purity 90 GHz signal from a 30 GHz COEO.These results are promising and an integration of the system in a thermalized box is under process.

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