In this work, two distinct types of Diffractive Optical Elements (DOEs) are designed to laterally distribute the solar spectrum across multiple photovoltaic (PV) cells. Each PV cell receives a spectral band near its bandgap energy to maximize overall solar-to-electric conversion efficiency of the system. The first DOE is an off-axis volume holographic lens. Design parameters include lateral grating period and slant angle, index modulation, film thickness, and control of swelling and index modulation attenuation in the film development process. Diffraction efficiency across the holographic lens is simulated using Rigorous Coupled Wave Analysis (RCWA). A full system model is created, and non-sequential raytracing is performed. Performance is evaluated under AM 1.5 conditions and annual insolation in Tucson, AZ, and Seattle, WA. A proof-of-concept off-axis holographic lens is fabricated and its performance is measured to confirm the optical properties of this system. The second DOE is an algorithmically-designed freeform surface relief structure. The Gerchberg-Saxton design algorithm is expanded to consider multiple wavelengths, resulting in a Broadband Gerchberg-Saxton (BGS) algorithm. All design variables are evaluated in a parametric study of the algorithm. Several DOE designs are proposed for spectrum splitting, and two of these designs are fabricated and measured. Additional considerations, such as finite sampling of the discrete Fourier transform, fabrication error, and solar divergence are addressed. The dissertation will conclude with a summary of spectrum splitting performance of all proposed DOEs, as well as a comparison to ideal spectrum splitting performance and discussion of areas for improvement and future work.

The main objective of the present research work is to fabricate three dimensional photonic nanostructures in photo-sensitive polymers using a novel diffractive optical element (DOE) based lithography technique. A diffractive optical element is a promising alternative device for 3D fabrication where one DOE creates multiple laser beams in various diffraction orders that are inherently phase-locked and stable for reproducible creation of 3D near-field diffraction patterns from a single laser beam. These near-field patterns are captured inside a photosensitive material like photoresist to fabricate 3D photonic crystal templates. We have demonstrated fabrication of a wide range of 3D structures having different crystal symmetries and different relative crystal axis ratios. The present work has provided 3D photonic crystal nanostructures with uniform optical and structural properties over large sample area (~3-4 mm diameter) and through large 15-50 micron thickness with large number of layers (> 40) having period 550 nm - 650 nm and feature sizes between 200 nm and 300 nm. The short exposure time and small number of process steps shows promise for scaling to very large volume fabrication, dramatically improving the throughput, quality and structural uniformity of 3D periodic nanostructures, especially over that provided by tedious and costly semiconductor processing technology. The diffractive optics lithography is a parallel processing method that is easily scalable to generate centimeter-scale 3D nanostructures having large number of layers in several seconds. Due to low refractive index contrasts these polymer templates possess partial stopgaps along several crystallographic directions which can be practically used in several device or sensor applications where complete bandgap is not necessary. The potential usefulness of these partial stopbands for refractive index sensing of liquids has been demonstrated. These low refractive index polymer structures have been inverted with amorphous silica to convert a "soft" polymer structure to a robust "hard" structure. Further, few preliminary tests were done in fabricating 3D nanostructures into micro-fluidic channels for potential chromatography applications. The practical merits of this 3D fabrication technique will enable new practical manufacturing methods for optical and MEMS applications of 3D micro and nano structures.

The main objective of the present research work is to fabricate three dimensional photonic nanostructures in photo-sensitive polymers using a novel diffractive optical element (DOE) based lithography technique. A diffractive optical element is a promising alternative device for 3D fabrication where one DOE creates multiple laser beams in various diffraction orders that are inherently phase-locked and stable for reproducible creation of 3D near-field diffraction patterns from a single laser beam. These near-field patterns are captured inside a photosensitive material like photoresist to fabricate 3D photonic crystal templates. We have demonstrated fabrication of a wide range of 3D structures having different crystal symmetries and different relative crystal axis ratios. The present work has provided 3D photonic crystal nanostructures with uniform optical and structural properties over large sample area (~3-4 mm diameter) and through large 15-50 micron thickness with large number of layers (> 40) having period 550 nm - 650 nm and feature sizes between 200 nm and 300 nm. The short exposure time and small number of process steps shows promise for scaling to very large volume fabrication, dramatically improving the throughput, quality and structural uniformity of 3D periodic nanostructures, especially over that provided by tedious and costly semiconductor processing technology. The diffractive optics lithography is a parallel processing method that is easily scalable to generate centimeter-scale 3D nanostructures having large number of layers in several seconds. Due to low refractive index contrasts these polymer templates possess partial stopgaps along several crystallographic directions which can be practically used in several device or sensor applications where complete bandgap is not necessary. The potential usefulness of these partial stopbands for refractive index sensing of liquids has been demonstrated. These low refractive index polymer structures have been inverted with amorphous silica to convert a "soft" polymer structure to a robust "hard" structure. Further, few preliminary tests were done in fabricating 3D nanostructures into micro-fluidic channels for potential chromatography applications. The practical merits of this 3D fabrication technique will enable new practical manufacturing methods for optical and MEMS applications of 3D micro and nano structures.

The demand for high optical resolution has brought researchers to explore the use of beam shaping diffractive optical elements (DOEs) for improving performance of high numerical aperture (NA) optical systems. DOEs can be designed to modulate the amplitude, phase and/or polarization of a laser beam such that it focuses into a targeted irradiance distribution, or point spread function (PSF). The focused PSF can be reshaped in both the transverse focal plane and along the optical axis. Optical lithography, microscopy and direct laser writing are but a few of the many applications in which a properly designed DOE can significantly improve optical performance of the system. Designing DOEs for use in high-NA applications is complicated by electric field depolarization that occurs with tight focusing. The linear polarization of off-axis rays is tilted upon refraction towards the focal point, generating additional transverse and longitudinal polarization components. These additional field components contribute significantly to the shape of the PSF under tight focusing and cannot be neglected as in scalar diffraction theory. The PSF can be modeled more rigorously using the electromagnetic diffraction integrals derived by Wolf, which account for the full vector character of the field. In this work, optimization algorithms based on vector diffraction theory were developed for designing DOEs that reshape the PSF of a 1.4-NA objective lens. The optimization techniques include simple exhaustive search, iterative optimization (Method of Generalized Projections), and evolutionary computation (Particle Swarm Optimization). DOE designs were obtained that can reshape either the transverse PSF or the irradiance distribution along the optical axis. In one example of transverse beam shaping, all polarization components were simultaneously reshaped so their vector addition generates a focused flat-top square irradiance pattern. Other designs were obtained that can be used to narrow the axial irradiance distribution, giving a focused beam that is superresolved relative to the diffraction limit. In addition to theory, experimental studies were undertaken that include (1) fabricating an axially superresolving DOE, (2) incorporating the DOE into the optical setup, (3) imaging the focused PSF, and (4) measuring aberrations in the objective lens to study how these affect performance of the DOE.

No description available.

Dois tipos diferentes de hologramas (Fresnel e Fourier) foram gerados por computador. O holograma de Fresnel foi escolhido para fazer parte de um arranjo experimental que teve como objetivo estimar a rugosidade de amostras metálicas. Para isso, um novo método de aplicação de um correlator óptico foi desenvolvido. Hologramas de Fourier geralmente fazem parte do correlator óptico de VanderLugt, o qual é muito utilizado no reconhecimento de padrões. A reconstrução numérica de hologramas de Fresnel gerados por computador, "distorcidos" por superfícies metálicas (também simuladas), serviram de base para que a reconstrução óptica de um holograma de Fresnel fosse utilizada, de forma inédita, no reconhecimento de padrões para estimar a rugosidade de amostras metálicas. / Two different types of holograms (Fresnel and Fourier) have been computer-generated. The Fresnel hologram has been chosen as part of an experimental set, which meant to estimate the roughness of the metalic samples. A new method for the aplication of an optical correlator has been developed. Fourier holograms are, generally, part of the VanderLugt optical correlator, that is very used for pattern recognition. The numerical reconstruction of the computer-generated Fresnel holograms, "distorted" by metalic surfaces (simulated as well), worked as the base for the utilization, in an original way, of the optical reconstruction of a Fresnel hologram, at the pattern recognition to estimate the roughness of the metalic samples.

Ce travail de thèse visait à concevoir, assembler, optimiser et tester des modules d’illumination structurée à base d’éléments optiques diffractifs (EODs) pour une application de reconnaissance faciale sur appareils mobiles (smartphones, tablettes). L’intégration des modules dans des smartphones impliquait de fortes contraintes de miniaturisation, de consommation énergétique, de coût, et de sécurité laser. L’élément clé de chaque module était un EOD de Fourier à angle de diffraction supérieur à la limite du modèle scalaire paraxial de la diffraction permettant d’illuminer la surface d’un visage à une distance d’une portée de bras. Afin de faciliter la conception (relâchement des contraintes angulaires), la fabrication (minimisation de l’efficacité de diffraction à l’ordre 0) et la réplication des EODs, le premier axe de travail a consisté à concevoir et à fabriquer des dispositifs hybrides « agrandisseurs d’angles » combinant des EODs et des optiques divergentes conventionnelles. Le second volet portait sur la conception des EODs qui devait prendre en considération à la fois les paramètres des systèmes bas coût d’illumination et d’acquisition d’images utilisés, notamment pour contrôler la présence de granularité laser (« speckle ») sur la figure de diffraction souhaitée (contrôle imposé par les algorithmes de reconnaissance faciale et de détection de fraudes utilisés). Le savoir-faire acquis dans le domaine de l’illumination structurée générée par des EODs a été étendu et transposé à trois autres applications dans les domaines de la vibrométrie, de l’aviation civile et commerciale, et de l’aviation militaire. / This thesis work aimed to design, assemble, optimize and test structured illumination modules based on diffractive optical elements (DOEs) for facial recognition application on mobile devices (smartphones, tablets). The integration of modules into smartphones involved significant constraints in terms of miniaturization, energy consumption, cost and laser safety. The key element of each module was a Fourier DOE with a diffraction angle greater than the limit of the paraxial scalar diffraction model to illuminate the surface of a face at a distance of an arm reach. In order to facilitate the design (relaxation of angular constraints), manufacturing (minimization of the zero order diffraction efficiency) and replication of DOEs, the first axis of research consisted in designing and manufacturing hybrid "angle enlarger" devices combining DOEs and conventional divergent optics. The second part concerned the design of the DOEs, which had to take into account both the parameters of the low-cost illumination and image acquisition systems used, in particular to control the presence of laser speckle on the desired diffraction pattern (control imposed by the facial recognition and fraud detection algorithms used). The know-how acquired in the field of structured illumination generated by DOEs has been extended and transposed to three other applications in the fields of vibrometry, civil and commercial aviation, and military aviation.

Dois tipos diferentes de hologramas (Fresnel e Fourier) foram gerados por computador. O holograma de Fresnel foi escolhido para fazer parte de um arranjo experimental que teve como objetivo estimar a rugosidade de amostras metálicas. Para isso, um novo método de aplicação de um correlator óptico foi desenvolvido. Hologramas de Fourier geralmente fazem parte do correlator óptico de VanderLugt, o qual é muito utilizado no reconhecimento de padrões. A reconstrução numérica de hologramas de Fresnel gerados por computador, "distorcidos" por superfícies metálicas (também simuladas), serviram de base para que a reconstrução óptica de um holograma de Fresnel fosse utilizada, de forma inédita, no reconhecimento de padrões para estimar a rugosidade de amostras metálicas. / Two different types of holograms (Fresnel and Fourier) have been computer-generated. The Fresnel hologram has been chosen as part of an experimental set, which meant to estimate the roughness of the metalic samples. A new method for the aplication of an optical correlator has been developed. Fourier holograms are, generally, part of the VanderLugt optical correlator, that is very used for pattern recognition. The numerical reconstruction of the computer-generated Fresnel holograms, "distorted" by metalic surfaces (simulated as well), worked as the base for the utilization, in an original way, of the optical reconstruction of a Fresnel hologram, at the pattern recognition to estimate the roughness of the metalic samples.

In a near future, the computation power will be widely used in endoscopy rooms. It will enable the augmented reality already implemented in some surgery. Before reaching this, a preliminary step is the development of a 3D reconstruction endoscope. In addition to that, endoscopists suffer from a lack of quantitative data to evaluate dimensions and distances, notably for the polyp size measurement.<p>In this thesis, a contribution to more a robust 3D reconstruction endoscopic device is proposed. Structured light technique is used and implemented using a diffractive optical element. Two patterns are developed and compared: the first is based on the spatial-neighbourhood coding strategy, the second on the direct-coding strategy. The latter is implemented on a diffractive optical element and used in an endoscopic 3D reconstruction device. It is tested in several conditions and shows excellent quantitative results but the robustness against bad visual conditions (occlusions, liquids, specular reflection,) must be improved. <p>Based on this technology, an endoscopic ruler is developed. It is dedicated to answer endoscopists lack of measurement system. The pattern is simplified to a single line to be more robust. Quantitative data show a sub-pixel accuracy and the device is robust in all tested cases. The system has then been validated with a gastroenterologist to measure polyps. Compared to literature in this field, this device performs better and is more accurate. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

Le domaine des couches minces optiques a vu les fonctions de filtrage se complexifier et les techniques de dépôt se perfectionner. Cependant, certains filtres requièrent des performances ultimes notamment en termes d’uniformité et de centrage de leur réponse spectrale. Atteindre ces spécificités requiert un contrôle précis de l'épaisseur optique des couches de l’empilement. Pour se faire, l’utilisation d’un matériau dont l’indice de réfraction peut être modifié localement après dépôt est une solution. Le candidat retenu est un verre de chalcogénures : l’AMTIR-1, un verre commercial, dont l’indice de réfraction décroit sous l’action d’un champ électrique lumineux. Des couches minces de ce matériau ont été déposées par évaporation par canon à électrons et leurs propriétés optiques ont été caractérisées par mesures spectrophotométriques. Des variations d’indice photo-induites de ~4.10-2 ont été enregistrées à λ = 1 μm. Ces variations d’indice ont ensuite été exploitées pour concevoir des composants à base de couches minces optiques spatialement structurés. En particulier, des composants optiques diffractifs binaires ont été enregistrés dans le volume d’une monocouche épaisse de chalcogénure par exposition structurée. Un accord quasi parfait entre théorie et expérience a ainsi été obtenu. L’insertion de ces couches photosensibles à base de chalcogénures dans des filtres optiques interférentiels multicouches a également été investiguée. Une démonstration du contrôle local de la réponse spectrale d’un filtre passe-bande de type Fabry-Perot a été réalisée, démontrant ainsi le potentiel de cette nouvelle approche pour la réalisation de composants optiques optimisés. / In recent years, there has been a tremendous progress in the complexity of thin film optical filters but also an important improvement in the deposition techniques. However, some filters require ultimate performances especially in terms of uniformity and absolute position of their spectral responses. Achieving these characteristics requires a precise and local control of the optical thickness of each of the layers. To overcome some of these fabrication constraints, the use of a material which index of refraction or thickness can be locally changed after deposition is an attractive solution. The chosen material is a chalcogenide glass : AMTIR-1, a commercial glass which refractive index decreases when exposed to light source. Thin films of this material were deposited by electron beam deposition and optical properties were characterized by spectrophotometric measurements. Photo-induced refractive index changes of ~ 4.10-2 were recorded at λ = 1 μm. These refractive index variations were then used to fabricate spatially structured thin films. In particular, diffractive optical elements were recorded in the volume of a thick chalcogenide single layer. This is performed by structured exposure using an optical arrangement based on a digital micromirror device. A close to perfect agreement between theory and experiment has been obtained. The insertion of these chalcogenide-based photosensitive layers in multilayer optical interference filters has also been investigated. A demonstration of the local control of the spectral response of a Fabry-Perot bandpass filter was performed, demonstrating the potential of this new approach for the production of optimized optical components