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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.
181

Etude de cavités optiques formées de miroirs de Bragg à réseaux à pas variable : application aux filtres et lasers. / Study of optical cavities formed by chirped bragg mirrors : Application of filters and lasers

Wu, Xunqi 11 January 2012 (has links)
L'objectif de cette thèse vise à l'étude d'un laser à cavité étendue et/ou filtre optique, dont le miroir externe est un réseau de Bragg à pas variable linéairement. En ce qui concerne le milieu à gain dans le résonateur, l’amplificateur optique à semiconducteur (SOA, Semiconductor Optical Amplifier) peut offrir toutes les caractéristiques et avantages classiques et typiques tels que large bande passante spectrale de 50 nm, faible consommation, haute rapidité de commutation électro-optique etc.... Par conséquent, ce type de laser et/ou filtre optique offre de nombreuses applications intéressantes dans le domaine des télécommunications optiques.Dans cette recherche, les premiers travaux sont la conception de la cavité continuum passive à l'aide d’un réseau de Bragg à pas variable. A l’intérieur de cette cavité continuum, formée entre un miroir et un réseau de Bragg chirpé, toutes les longueurs d'onde de Bragg oscillent simultanément ; la phase après un aller-retour de chaque longueur d'onde doit rester constante. La largeur de bande passante du spectre de transmission peut être ajustée dans la bande C (entre 1525 nm et 1565 nm) pour répondre aux besoins des systèmes de multiplexage en longueur d'onde (WDM, Wavelength-Division Multiplexing). On appliquera dans un premier temps ce concept de cavité continuum à la conception et la réalisation d’un filtre optique à bande passante variable. Puis dans un deuxième temps on rajoute un amplificateur optique à semi-conducteur (SOA) dans cette cavité pour réaliser un laser dit continuum. On s’attend à une émission sur un large spectre défini par la bande de réflexion du réseau chirpé. Le contrôle et la compréhension des phénomènes liés à cette émission lumineuse feront l’objet de cette étude. La cavité laser dite continuum sera étudiée en régime d’injection optique. L’idée est d’utiliser cette source comme amplificateur résonant fonctionnant en régime d’injection locking. La contribution dans cette thèse couvre à la fois la modélisation numérique, et les manipulations expérimentales. La conception du filtre ainsi que des mesures expérimentales de validation ont été complètement réalisés sur une structure hybride constituée d’une cavité à fibre optique incluant les réseaux de Bragg. Un bon accord entre théorie et expérience a été obtenu. Par contre, les calculs ont montré qu’un filtre optique intégré sur semi-conducteur utilisant ce concept de cavité n’avait pas d’intérêt. Les propriétés spectrales du filtre réalisé montrent en effet qu’on ne pourra obtenir qu’un faible taux de réjection et une qualité médiocre de forme de filtre en version intégrée. La réalisation expérimentale d’une cavité laser continuum a pu être démontrée et les propriétés spectrales enregistrées. En particulier une émission laser avec une largeur de spectre de 10 nm a été observée. Même si il reste un grand travail de caractérisation et de modélisation pour comprendre totalement les mécanismes qui gouvernent le fonctionnement d’une telle structure, c’est un résultat totalement nouveau que l’on a obtenu ici. Cette structure a par ailleurs été testée en régime d’injection optique. Un fonctionnement d’injection locking est obtenu qui permet à cette structure de jouer le role d’amplificateur à faible bruit. / The aim of this thesis is focused on the study of an extended cavity laser or/and optical filter, whose external mirror is the linearly chirped Bragg grating. As for the gain medium in the resonant, SOA (Semiconductor Optical Amplifier) can act as optical gain device. It can offer all of the classic and typical characteristics and advantages like large spectral passband of 50 nm, low power consumption, high-speed electro-optical commutation and so on. Therefore, this type of laser or/and optical filter have many interesting applications in the field of optical telecommunications.In this research, the first works are the design of passive continuum resonant cavity using linearly chirped Bragg grating. Inside this so-called continuum cavity, formed between mirror and chirped grating, all of the Bragg wavelengths oscillate at the same time, so the round-trip phase of each oscillated wavelength should keep constant. Then there is a passband spectrum at the transmission side. The bandwidth of transmission could be varied in C band (from 1525 nm to 1565 nm) to satisfy the needs of wavelength-division multiplexing (WDM) systems. This project is separated by two cases, one is about the external cavity applying chirped fiber Bragg grating as an external mirror, and the other is about the integrated cavity on InP chip, where the Bragg grating is already lithographed. Anyway, the first works of the thesis consist of numerical modeling, computational simulations and experimental manipulations.During the second works, the first step we add SOA as gain medium between two chirped fiber Bragg gratings for the purpose of generating laser. There are reflectors and active part in the passive cavity, so there is lasing far and away. It emits the typical F-P multimode light at the intersection of SOA gain band and reflection band of chirped grating. Then the second step is that a seed laser, whose frequency is nearby one of the longitudinal modes, is injected into the cavity in order to lock this mode. So there is only one emitted laser mode because of injection locking. This lasing resonant cavity could also be formed between mirror and linearly chirped Bragg grating.
182

Etude du guidage et du confinement de la lumière dans les guides optiques nanostructurés : application au filtrage spectral ultra-sélectif / Guiding and confinement of light inside nanostructured optical waveguides : application to the ultra selective spectral filtering

Rassem, Nadège 20 January 2017 (has links)
Un CRIGF (pour Cavity Resonator Integrated Grating Filter) est un filtre spectral nanophotonique présentant une bande passante étroite (inférieure au nanomètre) fonctionnant avec un faisceau relativement focalisé. Cette structure, introduite récemment (2010), est composée d'un réseau à résonance de mode guidé (ou réseau résonnant, ou encore réseau coupleur) inséré entre deux réseaux de Bragg. Les réseaux à résonance de mode guidé sont connus pour présenter dans leur spectre en réflexion (ou transmission) des pics très étroits, dus à l'excitation, via un ordre de diffraction, d'un mode guidé de la structure. Ce phénomène de résonance correspond à une anomalie de Wood. Mais leur majeure limitation reste leur très faible tolérance angulaire, et le CRIGF permet de lever ce problème.Dans la littérature, numériquement le CRIGF a été modélisée par la FDTD seulement avec d’importants temps de calculs. Nous avons utilisé la RCWA pour modéliser numériquement le CRIGF en apportant une possibilité de recherche des modes propres. Nous avons surtout montré grâce aux calculs que le comportement angulaire extraordinaire du CRIGF est très différent de celui des réseaux infinis. Nous avons prouvé grâce à la théorie des modes couplés étendue à quatre modes que cette large tolérance angulaire est due à l'existence d'un couplage additionnel qui n’existait pas dans les réseaux infinis. Grâce à une approche basée sur la cavité de Fabry-Pérot, nous avons confirmé que le CRIGF se comporte comme une cavité de Fabry-Pérot à pertes, ce qui nous a permis de définir des règles de conception simples comme le contrôle de la largeur spectrale et le repositionnement de la longueur d’onde de centrage / A CRIGF (Cavity Resonator Integrated Grating Filter) is a nanophotonic spectral filter with a narrow bandwidth (less than a nanometer) using a relatively focused beam. This structure, introduced recently (2010), is composed of a guided mode resonance grating filter (or resonant grating, or coupler grating) inserted between two Bragg gratings. Guided mode resonance gratings are known to exhibit very narrow peaks in their reflection spectrum (or transmission), due to the excitation of one guided mode of the structure via one diffraction order. This resonance phenomenon corresponds to an anomaly of Wood. But their major limitation remains their very low angular tolerance, and the CRIGF allows to overpass this problem.In literature, the numerical modeling of CRIGF was done only by FDTD with an important calculations time. We have used RCWA to model numerically the CRIGF by bringing a possibility of research of the eigen-modes. We have mainly shown thanks to calculations the extraordinary angular behavior of the CRIGF is very different from that of infinite gratings. We have proved thanks to the coupled modes theory extended to four modes that this large angular tolerance is due to an additional coupling that did not occur in infinite gratings.With an approach based on the Fabry-Perot cavity, we confirmed that the CRIGF behaves as a lossy Fabry-Perot cavity, which allowed us to define simple design rules such as the control of the spectral width and tuning the centering wavelength.
183

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.
184

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.
185

Hybrid lithography fabrication of single mode optics for signal redistribution and coupling

Weyers, David, Nieweglowski, Krzysztof, Bock, Karlheinz 10 May 2024 (has links)
This paper describes advances in hybrid-lithography process, combining UV-lithography for planar, single mode redistribution layer (RDL) and 2-photon-polymerization direct-laser-writing (2PP-DLW) for micro-mirrors inside RDL-opening. Improvements to multi-layer direct patterning of OrmoCore/-Clad material system using UV-lithography and need for broadband UV-LED source are presented. Near square core cross sections and smooth sidewalls are achieved. Openings in full stack with steep sidewalls without residual layer are patterned. To optimize 2PP-DLW-process processing window for both OrmoComp and IP-DIP is thoroughly characterized. Roughness measurements prove feasibility even of coarsely printed structure as reflective μ-mirror for 1550 nm wavelength. Finally these results are applied to periscope probe for wafer-level-testing of edge emitting lasers and proof of concept is shown. Outlook to further research on UV-lithography of multi-layer waveguide stack and alignment with μ-mirror printing is given.
186

The Medieval Reception of Firdausī's Shāhnāma: The Ardashīr Cycle as a Mirror for Princes

Askari, Nasrin 02 August 2013 (has links)
Based on a broad survey of the reception of Firdausī’s Shāhnāma in medieval times, this dissertation argues that Firdausī’s oeuvre was primarily perceived as a book of wisdom and advice for kings and courtly élites. The medieval reception of the Shāhnāma is clearly manifested in the comments of medieval authors about Firdausī and his work, and in their use of the Shāhnāma in the composition of their own works. The production of ikhtiyārāt-i Shāhnāmas (selections from the Shāhnāma) in medieval times and the remarkable attention of the authors of mirrors for princes to Firdausī’s opus are particularly illuminating in this regard. The survey is complemented by a close textual reading of the Ardashīr cycle in the Shāhnāma in comparison with other medieval historical accounts about Ardashīr, in order to illustrate how history in the Shāhnāma is reduced to only a framework for the presentation of ideas and ideals of kingship. Based on ancient Persian beliefs regarding the ideal state of the world, I argue that Ardashīr in the Shāhnāma is represented as a Saviour of the world. Within this context, I offer new interpretations of the symbolic tale of Ardashīr’s fight against a giant worm, and explain why the idea of the union of kingship and religion, a major topic in almost all medieval Persian mirrors for princes, has often been attributed to Ardashīr. Finally, I compare the Ardashīr cycle in the Shāhnāma with nine medieval Persian mirrors for princes to demonstrate that the ethico-political concepts contained in them, as well as the portrayal of Ardashīr, remain more or less the same in all these works. Study of the Shāhnāma as a mirror for princes, as this study shows, not only reveals the meaning of its symbolic tales, but also sheds light on the pre-Islamic roots of some of the ethico-political concepts presented in the medieval Perso-Islamic literature of wisdom and advice for kings and courtiers.
187

The Medieval Reception of Firdausī's Shāhnāma: The Ardashīr Cycle as a Mirror for Princes

Askari, Nasrin 02 August 2013 (has links)
Based on a broad survey of the reception of Firdausī’s Shāhnāma in medieval times, this dissertation argues that Firdausī’s oeuvre was primarily perceived as a book of wisdom and advice for kings and courtly élites. The medieval reception of the Shāhnāma is clearly manifested in the comments of medieval authors about Firdausī and his work, and in their use of the Shāhnāma in the composition of their own works. The production of ikhtiyārāt-i Shāhnāmas (selections from the Shāhnāma) in medieval times and the remarkable attention of the authors of mirrors for princes to Firdausī’s opus are particularly illuminating in this regard. The survey is complemented by a close textual reading of the Ardashīr cycle in the Shāhnāma in comparison with other medieval historical accounts about Ardashīr, in order to illustrate how history in the Shāhnāma is reduced to only a framework for the presentation of ideas and ideals of kingship. Based on ancient Persian beliefs regarding the ideal state of the world, I argue that Ardashīr in the Shāhnāma is represented as a Saviour of the world. Within this context, I offer new interpretations of the symbolic tale of Ardashīr’s fight against a giant worm, and explain why the idea of the union of kingship and religion, a major topic in almost all medieval Persian mirrors for princes, has often been attributed to Ardashīr. Finally, I compare the Ardashīr cycle in the Shāhnāma with nine medieval Persian mirrors for princes to demonstrate that the ethico-political concepts contained in them, as well as the portrayal of Ardashīr, remain more or less the same in all these works. Study of the Shāhnāma as a mirror for princes, as this study shows, not only reveals the meaning of its symbolic tales, but also sheds light on the pre-Islamic roots of some of the ethico-political concepts presented in the medieval Perso-Islamic literature of wisdom and advice for kings and courtiers.
188

Zjištění doby potřebné pro řidiče k vyhodnocení situace za vozidlem při odbočování a předjíždění / Determination of duration that driver needs to assess the situation behind the vehicle in course of turning or overtaking manoeuvres.

Belák, Michal January 2020 (has links)
The dissertation thesis deals mainly with determining of the duration that driver needs to assess the situation behind his vehicle at manoeuvers of turning and overtaking, based on the measurements made in real road traffic. These are common and frequent driving manoeuvers, which the driver performs while driving the vehicle in regular road traffic. For their safe execution the driver needs to have sufficient amount of information about the situation around the vehicle and especially behind the vehicle. This information can driver usually gain from devices for indirect vision, most often rear view mirrors. The time thus defined, suitable e.g for the needs of forensic engineering applications for the analysis of road accidents, has not been studied in detail yet. For the purpose of its determination, therefore, an extensive analysis of the current state of problematics related to the indirect vision from the vehicle was carried out. There were formulated influences on the time duration and with this related characteristics of humans as a part of the driver-vehicle-environment system in the thesis. The characteristics of human perception were investigated and the problematics of reaction time was discussed. Existing research focused on the duration of rear view mirrors glances was analyzed and possible methods of its measurement in detail were presented by author. Based on this, an experiment was designed and realized, the time necessary for rear view mirror glances was defined by the author. The results enable to quantify the time that the driver needs for assessing the situation behind the vehicle in connection of turning, overtaking and other driving manoeuvers when the driver needs to change the driving direction. The conclusions showed that the time needed to evaluate the situation behind the vehicle by means of the rear-view mirrors does not normally exceed duration 1 second.

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