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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

Développement et exploitation scientifique d’un nouvel instrument interférométrique visible en optique guidée / Development and scientific exploitation of a new guided optics visible in interferometric instrument

Martinod, Marc-Antoine 14 December 2018 (has links)
L'interférométrie visible longue base est une technique d'observation en astronomie permettant de sonder les objets avec une résolution spatiale qu'il est impossible d'atteindre avec un télescope seul. La mise en œuvre au sol de cette méthode est limitée en sensibilité et précision de mesure à cause de la turbulence atmosphérique. Or les nouveaux besoins scientifiques, tels que la détermination des paramètres fondamentaux, l'étude de l'environnement proche ou de la surface des étoiles, requièrent la capacité d'observer des objets de moins en moins brillants et de faire des mesures de plus en plus précises, en interférométrie visible. Pour s'affranchir de la turbulence, l'interférométrie multimode a été développée en reprenant le concept de l'interférométrie des tavelures utilisée sur un seul télescope. Aujourd'hui, pour améliorer davantage les performances des futurs instruments, cette instrumentation évolue vers l'utilisation de la nouvelle génération de détecteur, l'Electron Multiplying Charge-Coupled Device (EMCCD), et de l'emploi des fibres optiques interfacées avec des optiques adaptatives. Cette avancée est motivée par le succès de l'utilisation conjointe de l'optique adaptative et du suivi de franges pour s'affranchir partiellement de la turbulence en interférométrie infrarouge, en 2017 avec l'instrument GRAVITY (Gravity Collaboration et al. 2017). Le prototype FRIEND (Fibered and spectrally Resolved Interferometer - New Design) a été conçu pour caractériser et évaluer les performances de la combinaison de ces éléments, dans le domaine visible. L'amélioration de la précision des instruments interférométriques est apportée par les fibres optiques et par la dynamique du signal délivré par une EMCCD. L'inconvénient de l'emploi des fibres dans le visible est une perte de la sensibilité du fait que le taux d'injection du flux dans celles-ci est très faible à cause de la turbulence atmosphérique. Mais il se trouve que l'optique adaptative et l'EMCCD permettent d'améliorer la sensibilité. En effet, l'optique adaptative maximise l'injection en réduisant l'influence de la turbulence atmosphérique, et l'EMCCD est capable de détecteur de faibles flux. FRIEND prépare ainsi le développement du futur instrument SPICA, recombinant jusqu'à six télescopes (Mourard et al. 2017, 2018). Celui-ci devra explorer la stabilisation des interférences grâce au suivi de franges. Cet aspect n'est pas abordé dans cette thèse. Je présente dans cette thèse le prototype FRIEND, capable de recombiner jusqu'à trois télescopes, opérant dans la bande R en franges dispersées. Il est doté de fibres optiques gaussiennes monomodes à maintien de polarisation et d'une EMCCD. Il est installé sur l'interféromètre visible Center for High Angular Resolution Astronomy (CHARA), au Mount Wilson, en Californie, qui est en train de s'équiper d'optiques adaptatives. J'ai développé des estimateurs de visibilité et de clôture de phase, la méthode de réduction des données de ce prototype et une stratégie d'observation. Grâce à ces outils, j'ai montré que les optiques adaptatives améliorent le taux d'injection dans les fibres. Il est alors apparu que la stabilisation de l'injection est importante pour maximiser le rapport signal-à-bruit dans chaque image. La biréfringence des fibres dégrade les performances de l'instrument mais elle a pu être compensée. J'ai montré qu'un instrument, basé sur la conception de FRIEND, permet d'accéder à des mesures de visibilité faibles avec une précision, inatteignable avec la génération actuelle, grâce au développement et l'utilisation d'un modèle de rapport signal-à-bruit. L'instrument a enfin été testé dans son intégralité sur le système binaire connu ζ Ori A. Cette observation montre la fiabilité et la précision des mesures interférométriques obtenues avec ce prototype, montrant l'intérêt de cette association de technologies pour les futurs interféromètres visibles. / Long baseline visible interferometry in astronomy is an observing technique which allows to get insights of an object with an outstanding angular resolution, unreachable with single-dish telescope. Interferometric measurements with ground-based instrumentation are currently limited in sensitivity and precision due to atmospheric turbulence. However, the new astrophysical needs, particularly the determination of fundamental parameters or the study of the closed environment and the surface of the stars, require to observe fainter objects with a better precision than now in visible interferometry. Ought to overcome the atmospheric turbulence, multispeckle interferometry has been developed by adapting speckle imaging technics used on single-dish telescope. Today, in order to improve the performance of the future combiners, instrumentation progresses to the use of a new generation detector called EMCCD, and the use of optical fibers which are coupled with adaptive optics. This path is chosen thank to the success of the use of the adaptive optics with the fringe tracking in the infrared interferometry in 2017 (Gravity Collaboration et al. 2017), in order to compensate turbulence. FRIEND prototype (Fibered and spectrally Resolved Interferometer - New Design) has been designed to characterize and estimate the performance of such a combination of technologies, in the visible spectral band. The improvement of the precision of the measurements from interferometric instruments is due to optical fibers and the dynamical range of the EMCCD. The counterpart of using the optical fibers is a loss in sensitivity due to a low injection rate of flux into the fibers because of the atmospheric turbulence. On the other hand, sensitivity is improved thanks to adaptive optics and EMCCDs. Indeed, adaptive optics increases the injection rate and EMCCDs can measure low fluxes. Lastly, FRIEND is a pathfinder for the future instrument SPICA which should recombine up to 6 telescopes (Mourard et al. 2017, 2018). Fringe-tracking aspects will have to be studied for SPICA; this topic is not dealt with in this thesis. In this work, I present the FRIEND prototype, which can recombine up to three telescopes and operates in the R band with dispersed fringes. It has Gaussian polarization-maintaining single mode optical fibers and an EMCCD. It is set up at the Center for High Angular Resolution Astronomy (CHARA), at Mount Wilson, in California. CHARA is currently being equipped with adaptive optics. I develop estimators of visibility modulus and closure phase, the data reduction software and an observing strategy. Thanks to that, I am able to show that adaptive optics improves the injection rate. I also demonstrate how important the stabilization of injection is to maximize the signal-to-noise ratio (SNR) per frame. Birefringence of the fibers decreases the performance of the instrument but we manage to compensate it. I show how such an instrument can measure low visibility with a better precision than now by developing and using a SNR model of FRIEND. Finally, FRIEND has entirely been tested on the known binary system ζ Ori A. These observations demonstrate how reliable and accurate the measurements of FRIEND are.
32

Out-of-Plane Mirrors for Single-Mode Polymeric RDL using Direct Laser Writing

Mistry, Akash, Weyers, David, Nieweglowski, Krzysztof, Bock, Karlheinz 14 November 2023 (has links)
The growing demand for the Internet of Things (IoT) and Artificial Intelligence (AI) need high-speed commu-nication within short-range distances. In the Back-End-Of-Line (BEOL), Single-Mode Waveguide (SMW) with micro-mirror shows the promising application as an Optical Redistribution Layer (O-RDL) connecting photonic-chip at the interposer-level. The presented study shows the potential application of the 2-Photon-Polymerization (2PP) process for fabrication of out-of-plane coupling elements (micro-mirror) for SMW using low-loss Ormocer® hybrid polymers. This fabricated micro-mirror uses as a coupling element to connect the light from RDL to chips or for inter-layer connections at Interposer level. To evaluate the processing time, structural quality, and resolution of the printed micro-mirror, two types of lenses (63x and 25x) and Ormocer® polymers (OrmoComp and OrmoCore) were used. The optimization of the process flow for the micro-mirrors for SMW applications will be described in detail.
33

Studies of particle and atom manipulation using free space light beams and photonic crystal fibres

Gherardi, David Mark January 2009 (has links)
Light can exert optical forces on matter. In the macroscopic world these forces are minuscule, but on the microscopic or atomic scale, these forces are large enough to trap and manipulate particles. They may even be used to cool atoms to a fraction of a degree above absolute zero. This thesis details a number of experiments concerned with the optical manipulation of atoms and micron-size particles using free space light beams and photonic crystal fibres. Two atom guiding experiments are described. In the first experiment, a spatial light modulator is used to generate higher blue-detuned azimuthal Laguerre-Gaussian LG) beams, which are annular beams with a hollow core. These LG beams are then used to guide laser cooled rubidium-85 atoms within the dark core over a distance of 30 mm. The second atom guiding experiment involves attempting to guide laser cooled and thermal rubidium atoms through a hollow-core photonic crystal fibre using red-detuned light. Hollow-core photonic crystal fibres are fibres that are able to guide light with low attenuation within a hollow core. For this experiment a hot wire detection system was designed, along with a number of complex vacuum systems. The first dual-beam fibre trap for micron-size particles constructed using endlessly single-mode photonic crystal fibre (ESM-PCF) is described. The characteristics of dual-beam fibre traps are governed by the fibres used. As ESM-PCF has considerably different properties in comparison to conventional single- or multimode fibres, this dual beam ESM-PCF trap exhibits some novel characteristics. I show that the dual beam ESM-PCF trap can form trapping, repulsive and line potentials; an interference-free ‘white light’ trap; and a dual-wavelength optical conveyor belt.
34

Antenna Shape Synthesis Using Characteristic Mode Concepts

Ethier, Jonathan L. T. 26 October 2012 (has links)
Characteristic modes (CMs) provide deep insight into the electromagnetic behaviour of any arbitrarily shaped conducting structure because the CMs are unique to the geometry of the object. We exploit this very fact by predicting a perhaps surprising number of important antenna metrics such as resonance frequency, radiation efficiency and antenna Q (bandwidth) without needing to specify a feeding location. In doing so, it is possible to define a collection of objective functions that can be used in an optimizer to shape-synthesize antennas without needing to define a feed location a priori. We denote this novel form of optimization “feedless” or “excitation-free” antenna shape synthesis. Fundamentally, we are allowing the electromagnetics to dictate how the antenna synthesis should proceed and are in no way imposing the physical constraints enforced by fixed feeding structures. This optimization technique is broadly applied to three major areas of antenna research: electrically small antennas, multi-band antennas and reflectarrays. Thus, the scope of applicability ranges from small antennas, to intermediate sizes and concludes with electrically large antenna designs, which is a testament to the broad applicability of characteristic mode theory. Another advantage of feedless electromagnetic shape synthesis is the ability to synthesize antennas whose desirable properties approach the fundamental limits imposed by electromagnetics. As an additional benefit, the feedless optimization technique is shown to have greater computational efficiency than traditional antenna optimization techniques.
35

Antenna Shape Synthesis Using Characteristic Mode Concepts

Ethier, Jonathan L. T. 26 October 2012 (has links)
Characteristic modes (CMs) provide deep insight into the electromagnetic behaviour of any arbitrarily shaped conducting structure because the CMs are unique to the geometry of the object. We exploit this very fact by predicting a perhaps surprising number of important antenna metrics such as resonance frequency, radiation efficiency and antenna Q (bandwidth) without needing to specify a feeding location. In doing so, it is possible to define a collection of objective functions that can be used in an optimizer to shape-synthesize antennas without needing to define a feed location a priori. We denote this novel form of optimization “feedless” or “excitation-free” antenna shape synthesis. Fundamentally, we are allowing the electromagnetics to dictate how the antenna synthesis should proceed and are in no way imposing the physical constraints enforced by fixed feeding structures. This optimization technique is broadly applied to three major areas of antenna research: electrically small antennas, multi-band antennas and reflectarrays. Thus, the scope of applicability ranges from small antennas, to intermediate sizes and concludes with electrically large antenna designs, which is a testament to the broad applicability of characteristic mode theory. Another advantage of feedless electromagnetic shape synthesis is the ability to synthesize antennas whose desirable properties approach the fundamental limits imposed by electromagnetics. As an additional benefit, the feedless optimization technique is shown to have greater computational efficiency than traditional antenna optimization techniques.
36

反射戻り光が動的単一モード半導体レーザのモード分配特性に及ぼす影響の研究

森, 正和 03 1900 (has links)
科学研究費補助金 研究種目:一般研究(C) 課題番号:03650275 研究代表者:森 正和 研究期間:1991-1992年度
37

Leadership styles employed at Zambia's colleges of education

Simango, Benson 02 1900 (has links)
This study is a collective case study grounded in the literature regarding leadership styles and leadership theories. It includes among others, an analysis of data from interviews of college Principals and middle Managers to identify the leadership styles at the three colleges of education. The purpose of the study was to analyse the leadership styles of college Principals and middle Managers operating in dual-mode environments. The colleges that were being studied are the Copperbelt College of Education; Mufulira College of Education and Malcom Moffat College of Education. There were sixteen (16) participants in this study drawn from three colleges. The researcher collected data using semi-structured individual and focused group interviews. In addition, policy documents such as ‗Open and Distance Learning Policy (draft) and National Policy on Education were analysed. The researcher employed qualitative methods in the collection and analysis of data. Triangulation was used in order to verify the information given during this study. The evidence from the literature review indicates that there is no single leadership style that may provide answers to all situations in institutions of higher education; rather, a blend of the leadership styles would be beneficial to college Principals. The research further revealed that, managing dual-mode colleges of education entails that Principals require tailor-made programmes in management and leadership of dual-mode institutions for them to improve quality of their products and enhance tenets of transparency, democracy and good governance in colleges of education in Zambia. They also must be excellent communicators and ensure understanding by students, employees, peers, and the many stakeholders involved in dual-mode colleges of education. The study was important as it hoped to shed some light on how to improve quality of leadership in dual-mode colleges of education in Zambia. The study will contribute scientific knowledge to all categories of Higher Education (HE) institutions especially colleges of education, be they face-to-face or distance mode, that are contemplating a move into dual-mode delivery. Finally, Information garnered from this study is expected to allow Principals and other middle Managers and administrators to evaluate their leadership styles in comparison to the effective styles revealed by this study. / Educational Leadership and Management / D. Ed. (Education Management)
38

Antenna Shape Synthesis Using Characteristic Mode Concepts

Ethier, Jonathan L. T. January 2012 (has links)
Characteristic modes (CMs) provide deep insight into the electromagnetic behaviour of any arbitrarily shaped conducting structure because the CMs are unique to the geometry of the object. We exploit this very fact by predicting a perhaps surprising number of important antenna metrics such as resonance frequency, radiation efficiency and antenna Q (bandwidth) without needing to specify a feeding location. In doing so, it is possible to define a collection of objective functions that can be used in an optimizer to shape-synthesize antennas without needing to define a feed location a priori. We denote this novel form of optimization “feedless” or “excitation-free” antenna shape synthesis. Fundamentally, we are allowing the electromagnetics to dictate how the antenna synthesis should proceed and are in no way imposing the physical constraints enforced by fixed feeding structures. This optimization technique is broadly applied to three major areas of antenna research: electrically small antennas, multi-band antennas and reflectarrays. Thus, the scope of applicability ranges from small antennas, to intermediate sizes and concludes with electrically large antenna designs, which is a testament to the broad applicability of characteristic mode theory. Another advantage of feedless electromagnetic shape synthesis is the ability to synthesize antennas whose desirable properties approach the fundamental limits imposed by electromagnetics. As an additional benefit, the feedless optimization technique is shown to have greater computational efficiency than traditional antenna optimization techniques.
39

Hybrid lithography approach for single mode polymeric waveguides and out-of-plane coupling mirrors

Weyers, David, Mistry, Akash, Nieweglowski, Krzysztof, Bock, Karlheinz 14 November 2023 (has links)
This paper describes technology and process development for a hybrid lithography approach pairing UV-lithography for planar single mode waveguides with 2-photon-polymerization direct-laser-writing for out-of-plane coupling mirrors. Improvements to multi-layer direct patterning of OrmoCore/-Clad material system using UV-lithography are presented. Near square core cross sections are achieved. Minimum alignment accuracy at ≈ 3 μm is observed. Cut-back measurement on single mode waveguides shows attenuation of 0.64 dB cm −1 and 1.5 dB cm −1 at 1310 nm and 1550 nm respectively. Up to 2.5-times increase of shear-strength after thermal exposure up to 300 ◦ C is found using shear tests and compared for various surface treatments. Mechanical compatibility to reflow soldering is derived. An extensive study on the pattering of ORMOCER® using 2-photon-polymerization is performed. Flat 45 ◦ -micro mirrors with sub-10 μm dimensions are 3D-printed both in OrmoCore and OrmoComp. Outlook to further research on hybrid lithography integration approach is given.
40

Advances in UV-lithographic patterning of multi-layer waveguide stack for single mode polymeric RDL

Weyers, David, Nieweglowski, Krzysztof, Bock, Karlheinz 14 November 2023 (has links)
This paper describes design and advances in process development for UV-lithography of planar single mode waveguides with openings for out-of-plane coupling µ-mirrors. Improvements to multi-layer direct patterning of OrmoCore/-Clad material system using UV-lithography are presented. Near square core cross sections are achieved. However, non uniformity across 4” wafer is shown due to varying proximity and UV-intensity. Openings in full stack with steep sidewalls without residual layer are patterned. Reduction in stack thickness for very small exposure doses due to inhibition even under inert atmosphere is shown. 45° -µ-mirrors are integrated in these openings to manufacture a U-link via a single mode waveguide and two adjacent micro-mirrors. Optical characterization of U-link demonstrates the feasibility of hybrid lithography approach. However, non-uniformity of core cross-section leads to cross coupling of planar waveguides. Outlook to further research on UV-lithography of multi-layer waveguide stack and alignment with µ-mirror printing is given.

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