Made available in DSpace on 2014-06-12T18:07:26Z (GMT). No. of bitstreams: 2 arquivo7889_1.pdf: 1145740 bytes, checksum: b7623fb36e68590fae65b78367a8ac79 (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2004 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Estudamos a conversão ascendente de freqüências em nanocristais de zirconia dopados com íons de érbio (Er3+), usando diferentes esquemas de excitação (bombeando com 488, 650, 980 e 1420 nm). As amostras estudadas foram nanocristais de óxido de zirconia ( ZrO2 ) (com tamanhos típicos ~ 50 nm) dopados com 0,05 e 2,00 mol% de íons de Er3+, preparados pelo método sol-emulsão-gel. Linhas de emissão de conversão ascendente de freqüências centradas em 525, 550 e 670 nm foram observadas. As linhas de emissão correspondem a transições dos níveis 2H11/2, 4S3/2 e 4F9/2 ao estado fundamental. Observamos que a forma do espectro de luminescência muda com a concentração de ío ns de Er3+ e o comprimento de onda de excitação. Equações de taxa foram usadas para descrever o comportamento da emissão quando as amostras são excitadas com 1420 nm. Neste esquema de bombeamento determinou-se que o parâmetro de transferência de energia ma is importante é relacionado com as interações entre triades de íons de Er3+ . A dinâmica de emissão fluorescente foi também estudada. O tempo de decaimento do estado 4S3/2 foi determinado. A curva de decaimento da amostra dopada com 0,05mol% foi ajustada com uma exponencial simples, enquanto que o comportamento da amostra dopada com 2 mol% foi ajustado usando o modelo de Inokuti-Hirayama com a finalidade de estudar a origem do processo de transferência de energia. Os resultados indicam que a interação ent re os íons de Er3+ é do tipo dipolo-dipolo

Titre de l'écran-titre (visionné le 11 janvier 2024) / Le multiplexage par répartition spatiale (SDM) est une solution intéressante à la demande insatiable en capacité de transfert de données des réseaux de communications par fibres optiques. Ce type de multiplexage peut se diviser en deux approches majeures qui sont l'utilisation de fibres multicœurs et l'utilisation de fibres multimodes. Nous adressons des signaux multimodes. Une composante nécessaire au fonctionnement des réseaux de communications par fibres optiques est l'amplificateur optique qui sert à combattre les pertes de transmission du signal. Dans ce mémoire, on présente le développement de fibres optiques multimodes dopées à l'erbium pour des amplificateurs optiques pompés par la gaine. Dans le premier chapitre, la théorie derrière les amplificateurs optiques à fibre dopée à l'erbium (EDFAs) est abordée afin de présenter ultérieurement un simulateur construit sur MATLAB permettant d'émuler le comportement d'un EDFA à quelques modes (FM-EDFA). Dans le second chapitre, on explore le développement de telles fibres en utilisant un algorithme d'optimisation par essaims particulaires (PSO). Le PSO est utilisé afin d'optimiser la distribution d'erbium dans le cœur de la fibre pour minimiser la différence de gain modal (DMG) tout en maximisant le gain, et ce, en nécessitant moins de puissance de calcul par rapport aux modèles traditionnels. Dans le troisième chapitre, on présente le développement de fibres à l'aide de deux nouveaux critères d'optimisation basés sur la physique d'un FM-EDFA. Ces critères permettent de rapidement optimiser un profil d'erbium pour avoir une faible DMG. Dans le quatrième chapitre, on effectue un retour vers le PSO justifié par l'intégration des critères de design du troisième chapitre. On compare l'utilisation du PSO avec les nouveaux critères et l'utilisation du PSO avec les modèles traditionnels. Dans le cinquième chapitre, on documente le travail réalisé pour fabriquer avec succès une fibre optique développée au cours de ce projet. Au total, 6 préformes ont été fabriquées. Par contrainte de temps, aucun test n'a été effectué sur ces fibres dans le cadre de ce mémoire. / Spatial division multiplexing (SDM) is an interesting solution to the ever-growing demand in terms of data transfer capacity in optical fiber networks. This type of multiplexing can be described by two strategies which are using multicore fibers or using multimode fibers; we focus on multimode signals. Optical amplifiers are a critical component to the operation of SDM networks due to their ability to offset the propagation losses of the transmitted signals. In this master's thesis, we present the development of multimode erbium-doped optical fibers for cladding-pumped optical amplifiers. In the first chapter, we present the theory and modelling of erbium-doped fiber amplifiers (EDFAs) as well as a simulator built in MATLAB which permits us to emulate a few-mode EDFA (FM-EDFA). In the second chapter, we showcase the design of such fibers with a particle swarm optimization algorithm (PSO). We used the PSO to optimize the erbium doping profile in the core of the fiber to minimize the differential modal gain (DMG) while maximizing the gain and; our solution is more computationally efficient than traditional simulation methods. In the third chapter, we develop fibers for FM-EDFAs using two novel physics-based optimization criteria. These criteria allow us to rapidly optimize erbium doping profiles to achieve low DMG. In the fourth chapter, we use the knowledge acquired in the previous two chapters to integrate the novel optimization criteria into the PSO, and we compare the effectiveness of the PSO utilizing the two criteria of chapter three, versus the PSO with traditional simulation methods. In the final and fifth chapter, we document our work done on the fabrication of the optical fibers developed in this project. During this project, a total of 6 preforms were fabricated, but they were not tested due to time constraints.

M.Phil. (Electrical and Electronic Engineering) / A numerical model of an Erbium-Ytterbium co-doped distributed feedback (DFB) fiber laser is developed. The DFB fiber laser is a short length fiber laser whose feedback is distributed throughout the cavity. Its main advantage is its single longitudinal mode operation. The amplifying medium of a DFB fiber laser is a few centimetres long rare earth doped fiber. The feedback is obtained by a fibre Bragg grating printed in the core of the rare earth doped fiber. This type of laser emits naturally in two longitudinal modes. To obtain the single longitudinal mode operation, a π phase shift is introduced in the middle of the grating. Erbium doped DFB fiber lasers present the advantage of emitting single frequency light in the 1550 nm region where telecommunication fibers present the minimum loss. However due to the relatively short length of the gain medium, the number of available Erbium ions is small; as a result pump power absorption is low and the efficiency of the fiber laser is strongly reduced. The straightforward solution to this problem could be increasing the concentration of Erbium ions. This solution however has the disadvantage of increasing the Erbium ions interactions, thus leading to detrimental effect like cooperative upconversion and excited state absorption, which in term reduce considerably the laser efficiency. The best solution is to use Ytterbium ions as sensitizers along with Erbium ions to enhance the pump absorption, hence the efficiency of the laser. A model of the DFB fiber laser is an indispensable tool for its design, because it allows one to predict characteristic behaviour that would be both difficult and costly to deduce in laboratory conditions. The model developed in this project is based on rate equations of the Er3+-Yb3+ gain medium and coupled mode equations describing the laser field propagation in the fibre Bragg grating structure. The equations are solved using a quasi-analytical iterative method along with transfer matrix method with appropriate boundary conditions. The quasianalytical method used in this thesis is more robust than numerical solutions because it does not require providing an initial guess on the solution. Furthermore this method is hundreds time faster than the exact numerical solution while giving almost similar results.

by Wong Ho Man, Bruce. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references (leaves [60-61]). / Text in English; abstracts in English and Chinese. / by Wong Ho Man, Bruce. / Acknowledgements --- p.i / Abstract --- p.ii / 摘要 --- p.iii / Table of Contents --- p.iv / List of figures --- p.vi / Chapter Chapter1 --- Introduction --- p.1 / Chapter Chapter 2 --- Fabrication of erbium-doped sol-gel derived silica --- p.4 / Chapter 2.1 --- Introduction to the sol-gel process --- p.4 / Chapter 2.1.1 --- The procedure for silica formation - ´ؤ --- p.7 / Chapter 2.1.2 --- Changes during the sol-gel process --- p.11 / Chapter 2.2 --- Factors affecting the fluorescence --- p.15 / Chapter 2.2.1 --- Clustering of Er3+ ions in the silica samples --- p.15 / Chapter 2.2.2 --- Retention of hydroxyl group OH/absorbed water in silica - --- p.16 / Chapter 2.3 --- The role of Aluminum in dissolving Er3+ ions in Si02 network --- p.18 / Chapter 2.4 --- Thermal dehydroxylation --- p.20 / Chapter 2.5 --- Characterization of the Erbium-doped silica samples --- p.24 / Chapter 2.5.1 --- Absorption spectrum --- p.24 / Chapter 2.5.2 --- "Refractive index, density and microhardness" --- p.29 / Chapter Chapter 3 --- Fluorescence spectroscopy --- p.35 / Chapter 3.1 --- Introduction --- p.35 / Chapter 3.2 --- Experimental set-up --- p.36 / Chapter 3.3 --- "Fluorescence spectrum with variation in Er3+ concentration, Al/Er molar ratio and annealing temperature" --- p.38 / Chapter Chapter 4 --- Decay lifetime measurements of the 4S3/2 energy level --- p.47 / Chapter 4.1 --- Introduction --- p.47 / Chapter 4.2 --- Experimental set-up --- p.48 / Chapter 4.3 --- Increase in decay lifetimes with Aluminum-codoping --- p.49 / Chapter Chapter 5 --- Conclusions and further works --- p.58 / References

Wurtzite GaN epilayers grown by metal organic chemical vapor deposition on sapphire substrates were subsequently ion implanted with Er to a dose of 5×10¹⁵ cm⁻². The implanted samples were annealed in nitrogen atmosphere at different temperatures to facilitate recovery from implantation related damage. In this paper we report the annealing behavior of Erbium implanted GaN by using micro Raman spectroscopy and optimized annealing condition. We have observed almost full damage recovery of the crystalline quality of Er implanted GaN after annealing at 1000°C for 2 minute. This observation is further confirmed by using AFM images. / Singapore-MIT Alliance (SMA)

Fiber Fabry-Perot Interferometers (FFPI) are optical sensors which can be used to measure changes in stress or temperature, but efforts continue to improve them. Calculations show that the response can be dramatically altered with a gain inducing medium in the cavity. In order to induce gain, a highly doped Erbium (Er) fiber is incorporated in the FFPI. A pump wavelength of 1480 nm is used with a wavelength near 1550 nm. The pump must be at a significantly higher power level than the signal for gain. In order to correctly interpret responses, it is necessary to characterize the response of the measurement equipment. This includes everything from the laser and photodetector to system losses and the titanium oxide coated fibers. Fabrication of FFPIs involves fusing titanium oxide coated fibers to standard single mode fibers. Directly fusing an Er - doped fiber to a titanium oxide coated fibers was not possible because of incompatible splice conditions required in each case. Instead, an intermediate standard single mode fiber was spliced between them. This lengthened the cavity. Experimental results from the Er - doped Fiber Fabry-Perot Interferometer verified the hypothesis that improvements are obtainable. Overall, the measurements showed a 1.3 dB improvement in the maximum-to-minimum Insertion Loss Ratio.

Selectively erbium (Er) doped titanium (Ti) in-diffused optical waveguide amplifiers on lithium niobate (LiNbO3) substrate have been fabricated and characterized in the wavelength regime around λ = 1.53μm using counter-directional pumping at λP = 1.48μm. LiNbO3 waveguide amplifiers are desirable for providing gain in optical circuit chips through integration with other optical elements on a single substrate. A prerequisite for achieving useful gain rests on the optimization of overlap between the incident guided optical signal mode distribution and the evolving emission from excited Er ions. The extent of overlap can be controlled by adjusting fabrication parameters. Fabrication parameters for Er-doped Ti in-diffused waveguide amplifiers of useful optical gain have been optimized by diffusing selective patterns of vacuum-deposited 17nm-thick erbium film at 1100˚C for 100 hours into LiNbO3, and integrating with 7μm-wide single mode straight channel waveguides formed by diffusing 1070Å thick titanium film into the LiNbO3. Small-signal gain characterization was carried out with a -30 dBm of transmitted input signal power at λS=1531nm with counter-directionally launched pump power ranging between 0 to 119mW at λP=1488nm, using TM polarization for both the signal and pump beams. At a maximum launched pump power of 119mW, a signal enhancement of 8.8dBm for 25mm-long erbium doped region, and 11.6dBm for 35mm-long erbium doped region were obtained. The corresponding calculated net gain values are 1.8dB and 2.8dB, for the 25mm-long and 35mm-long Er-doped regions, respectively.

Proefschrift Universiteit van Amsterdam. / Met lit. opg. - Met samenvatting in het Nederlands.

Thesis (MS)--Montana State University--Bozeman, 2008. / Typescript. Chairperson, Graduate Committee: Richard Wolff. Includes bibliographical references (leaves 48-49).

Universiẗat, Diss.--Paderborn, 1994.