Search

Perovskite material has many advantages: excellent optoelectronic properties, low raw material costs and a wide range of deposition techniques. This makes it a promising candidate for photovoltaic applications. Perovskite solar cells have seen their efficiency increase from 6% to 25% in less than 10 years. However, the perovskites present a direct gap, and the absorption in this material drops suddenly when the wavelength passes above λgap. Using photonic crystals based on periodic structures allow, to improve the absorption around the gap of the material. The objective of this thesis is to study the integration of a photonic crystal in a perovskite solar cell.We have first optimized the perovskite deposition process in order to obtain a uniform and continuous layer. Then, we have carried out different imprint tests on the layers. This process, by applying a pressure, makes it possible to structure a material according to the inverted shape of a mold. Two types of imprint have been studied and optimized: flat compression, which, using a flat mold, makes the perovskite less rough and allows to obtain a better crystallization; and nanoimprint, using a nano-structured mold. An increase in grain size compared to simple annealing of perovskite without imprint has also been noticed. For nanoimprint, we have tested and optimized the impact of pressure and temperature on the perovskite structuration. After development and optimization of this technique on perovskite, we have shown that it is applicable to a wide range of molds, with patterns of different sizes and dimensions. We were able to make a photonic crystal in the perovskite layer to improve its absorption. Finally, we have realized solar cells using the imprint process (flat compression and nanoimprint) applied on the perovskite layer. By obtaining a conversion efficiency for the two types of cells, we have demonstrated the feasibility of such cells.; Le matériau pérovskite présente de nombreux avantages : excellentes propriétés optoélectroniques, faibles coûts des matières premières et vaste éventail de techniques de dépôt. Ceci en fait un candidat prometteur pour les applications photovoltaïques. Les cellules solaires en pérovskite ont ainsi vu leurs rendements de conversion progresser de 6 % à 25 % en moins de 10 ans. Cependant les pérovskites présentent un gap direct, et leur absorption chute brusquement lorsque la longueur d’onde passe au-dessus de λgap. Les cristaux photoniques sont des structures périodiques permettant, en fonction de leurs paramètres, d’améliorer l’absorption aux alentours du gap du matériau. L’objectif de ce travail de thèse est d’étudier l’intégration d’un cristal photonique dans une cellule solaire pérovskite. Nous avons dans un premier temps optimisé le dépôt de pérovskite pour obtenir une couche uniforme et continue. Nous avons ensuite réalisé différentes étapes d’impression sur les couches. Ce procédé, grâce à l’application d’une pression, permet de structurer un matériau suivant la forme inversée d’un moule. Deux types d’impression ont été étudiés et optimisés : la compression plane, permet d’aplanir la pérovskite et d’obtenir une couche de très faible rugosité tout en améliorant la cristallisation de la pérovskite ; la nanoimpression, qui s’effectue avec un moule structuré. Les paramètres des deux procédés ont été optimisés, nous avons démontré qu’elle est applicable à une large gamme de moules, avec des motifs de tailles et de dimensions différentes. Nous avons pu réaliser un cristal photonique dans la couche de pérovskite permettant d’améliorer l’absorption de celle-ci. Finalement, nous avons réalisé des cellules solaires en utilisant le procédé d’impression (compression plan et nanoimpression) sur la couche de pérovskite. En obtenant un rendement de conversion pour les deux types de cellules, nous avons montré la faisabilité de telles cellules.

Upon illumination by ultraviolet light, many animal species emit light through fluorescence processes arising from fluorophores embedded within their biological tissues. Fluorescence studies in living organisms are however relatively scarce and so far limited to the linear regime. Multiphoton excitation fluorescence analyses as well as non-linear optical techniques offer unique possibilities to investigate the effects of the local environment on the excited states of fluorophores. Herein these techniques are applied for the first time to the study of insects' natural fluorescence. The case of the male Hoplia coerulea beetle is investigated because the scales covering the beetle's elytra are known to possess an internal photonic structure with embedded fluorophores, which controls both the beetle's colouration and the fluorescence emission. An intense two-photon excitation fluorescence signal is observed, the intensity of which changes upon contact with water. A Third-Harmonic Generation signal is also detected, the intensity of which depends on the light polarisation state. The analysis of these non-linear optical and fluorescent responses unveils the multi-excited states character of the fluorophore molecules embedded in the beetle's elytra. The anisotropy of the photonic structure, which causes additional tailoring of the beetle's optical responses, is confirmed by circularly polarised light and non-linear optical measurements., Comment: 12 pages, 4 figures, 1 table, 1 SI file

We propose a novel approach for wide-field fluorescence imaging based on dielectric multilayers on glass coverslides. It is demonstrated that the fluorescence radiated by emitters in proximity to the multilayer surface can couple to Bloch Surface Waves and subsequently leaks into the glass. The coupled fluorescence is beamed with low divergence according to the Bloch Surface Waves spectral/angular dispersion and then collected with a low-magnification imaging system. Since the coupling between emitter and surface modes is dependent on the surface local morphology, we find a strong spectral deformation of the collected fluorescence spectrum depending on the corresponding surface relieves imaged.

Four-wave mixing can be stimulated or occur spontaneously: the latter effect, also known as parametric fluorescence, can be explained only in the framework of a quantum theory of light, and it is at the basis of many protocols to generate nonclassical states of the electromagnetic field. In this work we report on our experimental study of spontaneous four wave mixing in microring resonators and photonic crystal molecules integrated on a silicon on insulator platform. We find that both structures are able to generate signal and idler beams in the telecom band, at rates of millions of photons per second, under sub-mW pumping. By comparing the experiments on the two structures we find that the photonic molecule is an order of magnitude more efficient than the ring resonator, due to the reduced mode volume of the individual resonators.

El comportamiento de la propagación de ondas electromagnéticas en diferentes medios posee gran relevancia debido a sus amplias aplicaciones actualmente en telecomunicaciones, electrónica y demás campos de la ingeniería y la ciencia. Conocer el comportamiento de los campos electromagnéticos al pasar a través de un material brinda información importante para su caracterización y posterior uso, así como el descubrimiento de nuevos fenómenos aprovechables. El Método de Matriz de Transferencia (MMT) es un método ampliamente usado en óptica, mecánica cuántica y acústica, con el fin de analizar la propagación de ondas (electromagnéticas, funciones de onda, acústicas) a través de medios estratificados. En el presente trabajo se realiza el estudio de la propagación de la radiación electromagnética en materiales dieléctricos, metálicos, semiconductores y en los dispositivos conocidos como cristales fotónicos dieléctricos 1D (DPC), mediante MMT se determinan los los coeficientes de transmisión y reflexión para la caracterización del material, además de establecer relaciones importantes para el cambio de la radiación al interior del material. Abstract. The behavior of the propagation of electromagnetic waves in different media has great significance due to its broad applications currently in telecommunications, electronics and other fields of engineering and science. Knowing the behavior of electromagnetic fields by passing through a material provides important information for characterization and subsequent use as well as the discovery of new exploitable phenomena. The Transfer Matrix Method (TMM ) is a method widely used in optical , acoustic and quantum mechanics, in order to analyze the propagation of waves ( electromagnetic , wave functions , acoustic ) through stratified media , in this paper studying the propagation of electromagnetic radiation in dielectric materials, metal , semiconductor and dielectric devices known as photonic crystals 1D (PhC), by the MMT the transmission and reflection coefficients are determinate for material characterization also to establish important relations to the changes of the radiation into the material Maestría

Effect of relaxation time on the performance of photonic crystal optical bistable switches based on Kerr nolinearity is discussed. This paper deals with optical pulses with the duration of about 50 ps. In such cases the steady state response of the optical device can be used to approximate the pulse evolution if the nonlinearity is assumed instantaneous, hence analytical solutions such as the coupled mode theory can be used to obtain the time evolution of the electromagnetic fields. However if the relaxation time of the material nonlinear response is also considered, changes in the power levels and in the shape of the hystersis loop is observed. In this case, we use the nonlinear finite difference time domain method (NL-FDTD) to follow the system dynamics and get the bistability hystersis loop. Codes are developed to analyze the instantaneous Kerr materials and the Kerr materials with finite response times. Depending on the material, the relaxation times of the order of 1-10fs should be considered in studying bistability to obtain the right shape of the output pulses. It is observed that the relaxation leads to larger input power and threshold and hence degrades the performance of the switch in pulse shaping.

We demonstrate an easy-to-implement scheme for fluorescence enhancement and observation volume reduction using photonic crystals (PhCs) as substrates for microscopy. By normal incidence coupling to slow 2D-PhC guided modes, a 65 fold enhancement in the excitation is achieved in the near field region (100 nm deep and 1 μm wide) of the resonant mode. Such large enhancement together with the high spatial resolution makes this device an excellent substrate for fluorescence microscopies. Fil: Estrada, Laura Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina Fil: Martínez, Oscar Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina Fil: Brunstein, Maia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Centre National de la Recherche Scientifique; Francia Fil: Bouchoule, S.. Centre National de la Recherche Scientifique; Francia Fil: Le Gratiet, L.. Centre National de la Recherche Scientifique; Francia Fil: Talneau, A.. Centre National de la Recherche Scientifique; Francia Fil: Sagnes, I.. Centre National de la Recherche Scientifique; Francia Fil: Monnier, P.. Centre National de la Recherche Scientifique; Francia Fil: Levenson, J. A.. Centre National de la Recherche Scientifique; Francia Fil: Yacomotti, A. M.. Centre National de la Recherche Scientifique; Francia

By a periodic space structuring at wavelength scale, photonic crystals allow for efficient light control. Our work is on the exploitation of these crystals' properties in order to define a planar cavity for a laser diode, with controlled emission properties. The first part presents the study of the waveguide, which is defined by bi-dimensional photonic crystals in a semi-conductor heterostructure, obtained by hole etching. The modal characteristics are analyzed for chosen operating points. We show that a DFB (Distributed Feedback)-like single-mode emission can be obtained. The second part consists in the experimental demonstration of a working, electrically pumped photonic crystal laser diode. Its spectral and modal characteristics are analyzed, validating the theoretical study. A single-mode emission with a secondary mode suppression ratio higher than 35dB has been obtained. In the last part, we propose a novel approach for spectral control by deformation of the photonic crystal lattice, along the lateral axis of the laser cavity. It is shown that by means of this deformation, the emission wavelength can be accurately controlled with a precision close to 0.4nm, while remaining compatible with the technological constraints involved in photonic crystal fabrication. Furthermore, we demonstrate experimentally that this kind of deformations may be used to improve the emission characteristics of the studied devices by photonic band-gap engineering.; Par une structuration périodique de l'espace à l'échelle de la longueur d'onde, les cristaux photoniques permettent un contrôle efficace de la lumière. Nos travaux concernent l'exploitation des propriétés de ces cristaux pour définir une cavité planaire de diode laser et pour en proposer un contrôle de l'émission. Une première partie présente l'étude de guides définis par des cristaux photoniques bidimensionnels obtenus dans une hétérostructure semi-conductrice par la réalisation de trous. Différents comportements modaux sont analysés selon le point de fonctionnement choisi. Nous montrons qu'une émission monomode de type DFB (Distributed Feedback) peut être obtenue. La deuxième partie concerne la démonstration expérimentale de diodes laser à cristaux photoniques bidimensionnels fonctionnant sous pompage électrique. Les caractéristiques spectrales et modales sont analysées et elles permettent de valider l'étude théorique. Une émission monomode avec un taux de réjection des modes secondaires supérieur à 35 dB a été obtenue. Dans la dernière partie, nous proposons une approche originale du contrôle spectral basée sur une déformation de la maille du cristal photonique selon l'axe latéral de la cavité laser. Il est alors montré qu'une telle déformation permet d'accéder à un contrôle de la longueur d'onde d'émission à 0,4 nm près, tout en restant compatible avec les contraintes technologiques liées à la réalisation d'un cristal photonique. D'autre part, nous démontrons expérimentalement que ce type de déformations peut être mis à profit pour améliorer les caractéristiques d'émission laser des dispositifs étudiés grâce à une ingénierie de la bande interdite photonique.