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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.
1

The Study of All-optical Nonlinear Waveguide Devices

Tasy, Rong-Zhan 01 August 2003 (has links)
In the paper, the beam propagation method is used to analyze the characteristics and the applications of nonlinear optical waveguide structures. The nonlinear optical waveguide is a medium whose refractive index changes with the electric field intensity. Based on the mode theory, the propagating envelop of optical light waves in the three-layers nonlinear waveguide with the nonlinear cladding, the nonlinear substrate and the linear guiding film can be solved. Not only the dispersion relation curve is described, but also the affection of input power to the electric field distribution is observed. In the application of nonlinear optical waveguide structure, the three-layers nonlinear waveguide structure and the local nonlinear Mach-Zehnder waveguide interferometer structure will be discussed: In the three-layers nonlinear waveguide structure, by launching the symmetric and antisymmetric modes, various characteristics of spatial optical solitons will be observed. Based on the interaction property between spatial optical solitons, a new all-optical 1¡ÑN switching device will be proposed; In the local nonlinear Mach-Zehnder waveguide interferometer structure, by fixing the input signal power and changing the control power, output signal beam will show the switching property. Besides, by changing the local nonlinear distributions, the nonlinear Mach-Zehnder interferometer will show various logic functions. The numerical results show that the proposed structures could function as all-optical switch devices and all-optical logic gates.
2

Wet Etching Optical Fibers to Sub-micron Diameters for Sensing Application

Cui, Ziruo 05 June 2014 (has links)
No description available.
3

Método FD-BPM semivetorial de ângulo largo para a análise de estruturas tridimensionais utilizando a técnica ADI / not available

Nascimento, Valtemir Emerencio do 28 June 2002 (has links)
O projeto de dispositivos ópticos integrados é de fundamental importância no desenvolvimento de sistemas de comunicações ópticas. Por esse motivo, várias técnicas de modelamento para estes dispositivos tem surgido na literatura. Esta corrida em direção à sofisticação das ferramentas de modelamento decorre da evolução natural dos processos de fabricação, que tem permitido a construção de estruturas com geometrias bastante complexas. Dentre as várias técnicas utilizadas atualmente nas simulações de dispositivos fotônicos destaca-se o método da propagação do feixe (BPM). Este método apresenta como grande atrativo o fato de ser de fácil implementação e de apresentar baixa carga computacional. Inicialmente, a técnica BPM foi empregada utilizando a equação de onda escalar de Helmholtz. Esta abordagem é eficiente desde que a diferença entre os índices de refração dos materiais utilizados no guia de onda seja pequena e que a geometria da estrutura não apresente variações na direção de propagação. Entretanto, a luz é uma onda eletromagnética que possui propriedades intrinsecamente vetoriais. As propriedades vetoriais (efeitos de polarização) tornam-se importantes quando estruturas que apresentam elevado contraste de índices de refração precisam ser investigadas. Neste trabalho o fenômeno da polarização é avaliado através da utilização da equação de onda semivetorial de Helmholtz em três dimensões, a qual é desenvolvida em termos das componentes transversais de campo magnético (Formulação H). A solução da equação de onda semivetorial de Helmholtz é obtida pelo método BPM expandido em diferenças finitas (FD). Os aproximantes de Padé de ordem (1,0), equivalentes à propagação no limite paraxial, e de ordem (1,1), equivalentes à propagação em ângulo largo, são implementados e seus resultados discutidos ) A propagação do campo no FD-BPM tridimensional proposto aqui se dá através da utilização da técnica implícita das direções alternadas (ADI), a qual proporciona uma ótima estabilidade com baixo esforço computacional. A validação deste método é feita através da simulação de guias de onda tipo rib, avaliando parâmetros numéricos como: passo de propagação longitudinal, largura da gaussiana de excitação inicial, passo de discretização transversal, número de iterações e índice de referência. Adicionalmente, também é investigada uma fibra óptica com geometria tipo D. Estes resultados serão comparados com os resultados existentes na literatura para estas estruturas a fim de garantir a eficácia do método. / It is well known that finite difference beam propagation methods have been a valuable tool for the simulation of a large variety of optical waveguides structures such as: Mach-Zehnder, Y junctions, directional couplers, switches, etc. The increasing complexity of these structures, either in terms of geometry or material composition, requires more accurate modeling techniques. Among the several techniques available nowadays the beam propagation method (BPM) is maybe the most celebrated one. This method has attracted a great deal of attention by virtue of its ease of implementation and low computational effort. Initially, the BPM was applied to solve the scalar Helmholtz equation. This approach can be quite efficient for waveguides exhibiting low refractive index contrast and no variation along the longitudinal direction. Light, by its turn, is an electromagnetic wave with intrinsically vectorial properties. The vectorial properties (polarization effects) become very important when high contrast and longitudinally varying structures are involved. In this work the polarization phenomenon is evaluated by means of the three-dimensional semivectorial Helmholtz equation, which is solved in terms of its transverse magnetic field components (H formulation). The solution of this semivectorial equation is obtained via the finite difference BPM method expanded in terms of the following Padé approximants: Padé(1,0), equivalent to the semivectorial equation in the paraxial limit, and Padé (1,1), the wide angle solution. The field propagation dynamics in both cases is performed via alternate direction implicit method (ADI), which provides good numerical stability and low computational effort. As far as the authors know, this is the first time that a wide-angle formalism based on Padé(1,1) and ADI technique is proposed to solve the semivectorial Helmholtz equation. The validation of this new wide-angle method is performed for three well known rib waveguides structures available in the literature, and its accuracy measured in terms of the following parameters: longitudinal step size, initial field (gaussian) width, transversal step size, iteration number, and reference refractive index. A D-shaped fiber is also investigated with this method for comparison purposes. The results obtained in all cases are checked against those available in the literature in order to guarantee the efficiency of the method.
4

The Analysis, Simulations, and Applications of the Structure of the Nonlinear Waveguide

Lin, Jyh-Shiuan 10 July 2002 (has links)
In this paper, we used the beam propagation method to analyze the characteristics of nonlinear optical waveguides. Refractive indexes of media in planar optical waveguides are changed with the electric field intensity called nonlinear planar optical waveguides. We use the modal theory to solve the three-layer planar optical waveguide with the guiding film is nonlinear. We not only obtained dispersion relation curves, but also observed the affections of the input power to field distributions. By the basic theory of this, we proposed a novel method to analyze multi-layer planar optical waveguides with nonlinear or localized nonlinear guiding films.By the theory and novel method we pointed out, on the other hand, we proposed an all-optical switch and analyze the all-optical device by the beam propagation method.
5

Método FD-BPM semivetorial de ângulo largo para a análise de estruturas tridimensionais utilizando a técnica ADI / not available

Valtemir Emerencio do Nascimento 28 June 2002 (has links)
O projeto de dispositivos ópticos integrados é de fundamental importância no desenvolvimento de sistemas de comunicações ópticas. Por esse motivo, várias técnicas de modelamento para estes dispositivos tem surgido na literatura. Esta corrida em direção à sofisticação das ferramentas de modelamento decorre da evolução natural dos processos de fabricação, que tem permitido a construção de estruturas com geometrias bastante complexas. Dentre as várias técnicas utilizadas atualmente nas simulações de dispositivos fotônicos destaca-se o método da propagação do feixe (BPM). Este método apresenta como grande atrativo o fato de ser de fácil implementação e de apresentar baixa carga computacional. Inicialmente, a técnica BPM foi empregada utilizando a equação de onda escalar de Helmholtz. Esta abordagem é eficiente desde que a diferença entre os índices de refração dos materiais utilizados no guia de onda seja pequena e que a geometria da estrutura não apresente variações na direção de propagação. Entretanto, a luz é uma onda eletromagnética que possui propriedades intrinsecamente vetoriais. As propriedades vetoriais (efeitos de polarização) tornam-se importantes quando estruturas que apresentam elevado contraste de índices de refração precisam ser investigadas. Neste trabalho o fenômeno da polarização é avaliado através da utilização da equação de onda semivetorial de Helmholtz em três dimensões, a qual é desenvolvida em termos das componentes transversais de campo magnético (Formulação H). A solução da equação de onda semivetorial de Helmholtz é obtida pelo método BPM expandido em diferenças finitas (FD). Os aproximantes de Padé de ordem (1,0), equivalentes à propagação no limite paraxial, e de ordem (1,1), equivalentes à propagação em ângulo largo, são implementados e seus resultados discutidos ) A propagação do campo no FD-BPM tridimensional proposto aqui se dá através da utilização da técnica implícita das direções alternadas (ADI), a qual proporciona uma ótima estabilidade com baixo esforço computacional. A validação deste método é feita através da simulação de guias de onda tipo rib, avaliando parâmetros numéricos como: passo de propagação longitudinal, largura da gaussiana de excitação inicial, passo de discretização transversal, número de iterações e índice de referência. Adicionalmente, também é investigada uma fibra óptica com geometria tipo D. Estes resultados serão comparados com os resultados existentes na literatura para estas estruturas a fim de garantir a eficácia do método. / It is well known that finite difference beam propagation methods have been a valuable tool for the simulation of a large variety of optical waveguides structures such as: Mach-Zehnder, Y junctions, directional couplers, switches, etc. The increasing complexity of these structures, either in terms of geometry or material composition, requires more accurate modeling techniques. Among the several techniques available nowadays the beam propagation method (BPM) is maybe the most celebrated one. This method has attracted a great deal of attention by virtue of its ease of implementation and low computational effort. Initially, the BPM was applied to solve the scalar Helmholtz equation. This approach can be quite efficient for waveguides exhibiting low refractive index contrast and no variation along the longitudinal direction. Light, by its turn, is an electromagnetic wave with intrinsically vectorial properties. The vectorial properties (polarization effects) become very important when high contrast and longitudinally varying structures are involved. In this work the polarization phenomenon is evaluated by means of the three-dimensional semivectorial Helmholtz equation, which is solved in terms of its transverse magnetic field components (H formulation). The solution of this semivectorial equation is obtained via the finite difference BPM method expanded in terms of the following Padé approximants: Padé(1,0), equivalent to the semivectorial equation in the paraxial limit, and Padé (1,1), the wide angle solution. The field propagation dynamics in both cases is performed via alternate direction implicit method (ADI), which provides good numerical stability and low computational effort. As far as the authors know, this is the first time that a wide-angle formalism based on Padé(1,1) and ADI technique is proposed to solve the semivectorial Helmholtz equation. The validation of this new wide-angle method is performed for three well known rib waveguides structures available in the literature, and its accuracy measured in terms of the following parameters: longitudinal step size, initial field (gaussian) width, transversal step size, iteration number, and reference refractive index. A D-shaped fiber is also investigated with this method for comparison purposes. The results obtained in all cases are checked against those available in the literature in order to guarantee the efficiency of the method.
6

Método da propagação de feixe de ângulo largo para análise de guias de ondas ópticos não-lineares / not available

Flamino, Reinaldo de Sales 21 September 2001 (has links)
Este trabalho propõe uma extensão do método de propagação de feixe (BPM - Beam Propagation Method) para a análise de guias de ondas ópticos e acopladores baseados em materiais não-lineares do tipo Kerr. Este método se destina à investigação de estruturas onde a utilização da equação escalar de Helmholtz (EEH) em seu limite paraxial não mais se aplica. Os métodos desenvolvidos para este fim são denominados na literatura como métodos de propagação de feixe de ângulo largo. O formalismo aqui desenvolvido é baseado na técnica das diferenças finitas e nos esquemas de Crank-Nicholson (CN) e Douglas generalizado (GD). Estes esquemas apresentam como característica o fato de apresentarem um erro de truncamento em relação ao passo de discretização transversal, &#916x, proporcional a O(&#916x2) para o primeiro e O(&#916x4). A convergência do método em ambos esquemas é otimizada pela utilização de um algoritmo interativo para a correção do campo no meio não-linear. O formalismo de ângulo largo é obtido pela expansão da EEH para os esquemas CN e GD em termos de polinômios aproximantes de Padé de ordem (1,0) e (1,1) para CN e GD, e (2,2) e (3,3) para CN. Os aproximantes de ordem superior a (1,1) apresentam sérios problemas de estabilidade. Este problema é eliminado pela rotação dos aproximantes no plano complexo. Duas condições de contorno nos extremos da janela computacional são também investigadas: 1) (TBC - Transparent Boundary Condition) e 2) condição de contorno absorvente (TAB - Transparent Absorbing Boundary). Estas condições de contorno possuem a facilidade de evitar que reflexões indesejáveis sejam transmitidas para dentro da janela computacional. Um estudo comparativo da influência destas condições de contorno na solução de guias de ondas ópticos não-lineares é também abordada neste trabalho. / This work introduces an extension of the beam propagation method (BPM) for the analysis of optical waveguides and couplers based on Kerr-type nonlinear materials. This method is intended for the investigation of structures where the paraxial scalar Helmholtz equation (EEH) no longer holds. The numerical methods developed for this situation are known in the literature as wide-angle beam propagation methods. The formulation developed in this work is based on finite differences and on the Crank-Nicholson (CN) and Generalized Douglas (GD) schemes. These schemes are characterized by a truncation error with respect to the transverse discretization step, &#916x, proporcional to O(&#916x2) for the CN and to O(&#916x4) for the GD scheme. The convergence of the method for both schemes is optimized by the application of an iterative algorithm for the correction of the field in the nonlinear medium. The wide-angle formalism is obtained by the expansion of the EEH for the CN and GD schemes in terms of Padé approximant polynomials. The expansions addressed in this work utilize Padé approximants of order (1,0) and (1,1) for the CN and GD scheme, and (2,2) and (3,3) for the CN scheme. Approximants orders higher than (1,1) show serious stability problems. This problem is circumvented by rotating the approximants in the complex plane. Two boundary conditions on the edge of the computational window are also investigated: 1) transparent boundary condition (TBC) and 2) transparent absorbing boundary (TAB). These boundary conditions are necessary in order to avoid unwanted reflections back to computational domain. A comparative study of the influence of these boundary conditions on the solution of nonlinear optical waveguides is also addressed in this work.
7

Método da propagação de feixe de ângulo largo para análise de guias de ondas ópticos não-lineares / not available

Reinaldo de Sales Flamino 21 September 2001 (has links)
Este trabalho propõe uma extensão do método de propagação de feixe (BPM - Beam Propagation Method) para a análise de guias de ondas ópticos e acopladores baseados em materiais não-lineares do tipo Kerr. Este método se destina à investigação de estruturas onde a utilização da equação escalar de Helmholtz (EEH) em seu limite paraxial não mais se aplica. Os métodos desenvolvidos para este fim são denominados na literatura como métodos de propagação de feixe de ângulo largo. O formalismo aqui desenvolvido é baseado na técnica das diferenças finitas e nos esquemas de Crank-Nicholson (CN) e Douglas generalizado (GD). Estes esquemas apresentam como característica o fato de apresentarem um erro de truncamento em relação ao passo de discretização transversal, &#916x, proporcional a O(&#916x2) para o primeiro e O(&#916x4). A convergência do método em ambos esquemas é otimizada pela utilização de um algoritmo interativo para a correção do campo no meio não-linear. O formalismo de ângulo largo é obtido pela expansão da EEH para os esquemas CN e GD em termos de polinômios aproximantes de Padé de ordem (1,0) e (1,1) para CN e GD, e (2,2) e (3,3) para CN. Os aproximantes de ordem superior a (1,1) apresentam sérios problemas de estabilidade. Este problema é eliminado pela rotação dos aproximantes no plano complexo. Duas condições de contorno nos extremos da janela computacional são também investigadas: 1) (TBC - Transparent Boundary Condition) e 2) condição de contorno absorvente (TAB - Transparent Absorbing Boundary). Estas condições de contorno possuem a facilidade de evitar que reflexões indesejáveis sejam transmitidas para dentro da janela computacional. Um estudo comparativo da influência destas condições de contorno na solução de guias de ondas ópticos não-lineares é também abordada neste trabalho. / This work introduces an extension of the beam propagation method (BPM) for the analysis of optical waveguides and couplers based on Kerr-type nonlinear materials. This method is intended for the investigation of structures where the paraxial scalar Helmholtz equation (EEH) no longer holds. The numerical methods developed for this situation are known in the literature as wide-angle beam propagation methods. The formulation developed in this work is based on finite differences and on the Crank-Nicholson (CN) and Generalized Douglas (GD) schemes. These schemes are characterized by a truncation error with respect to the transverse discretization step, &#916x, proporcional to O(&#916x2) for the CN and to O(&#916x4) for the GD scheme. The convergence of the method for both schemes is optimized by the application of an iterative algorithm for the correction of the field in the nonlinear medium. The wide-angle formalism is obtained by the expansion of the EEH for the CN and GD schemes in terms of Padé approximant polynomials. The expansions addressed in this work utilize Padé approximants of order (1,0) and (1,1) for the CN and GD scheme, and (2,2) and (3,3) for the CN scheme. Approximants orders higher than (1,1) show serious stability problems. This problem is circumvented by rotating the approximants in the complex plane. Two boundary conditions on the edge of the computational window are also investigated: 1) transparent boundary condition (TBC) and 2) transparent absorbing boundary (TAB). These boundary conditions are necessary in order to avoid unwanted reflections back to computational domain. A comparative study of the influence of these boundary conditions on the solution of nonlinear optical waveguides is also addressed in this work.
8

Génération et étude de guides d'onde dynamiques et reconfigurables induits par illumination latérale / Study of reconfigurable light-induced waveguides induced by lateral illumination

Gorram, Mohamed 25 June 2009 (has links)
La réalisation de réseaux optiques ne nécessitant pas l'intervention d'éléments électroniques pour la détection temporaire de signaux demande des éléments de routage et d'interconnexion optique, adaptables et reconfigurables en des temps courts, de l'ordre de la milliseconde dans le cas des réseaux de télécommunications. L'utilisation de guides d'onde optiques réalisés dans des matériaux actifs par des techniques conventionnelles telles que la diffusion d'ions, l'échange protonique ou l'implantation ionique se prêtent mal à ce but. Ces techniques donnent lieu exclusivement à des guides statiques, typiquement de surface qui ne sont pas facilement modifiables. La méthode de photo-inscription transversale développée dans le cadre de cette thèse permet de franchir un cap important vers la réalisation de dispositifs purement optiques dans les quels la lumière est utilisée pour guider et manipuler la lumière sans avoir recours à de complexes étapes de fabrication. L'avantage principal est que cet effet peut être effacé, donnant lieu à des structures dynamiques sans l'intervention d'endommagements permanents du matériau. Un autre avantage est la grande versatilité par rapport à la forme des guides qui est conditionnée par la structure imposée à l'illumination de contrôle perpendiculaire à la direction de propagation. La formation de guides d'onde reconfigurables planaires à une dimension (1D) transversale a été réalisée dans des cristaux ferroélectriques photoréfractifs comme le SrxBa1xNb2O6 (SBN) ou le Sn2P2S6 (SPS), dans les longueurs d'ondes du visible ([lambda] = 514 nm et [lambda] = 633 nm). Des temps de génération et de reconfiguration des guides de l'ordre de la milliseconde ont été atteints dans le SPS. La dynamique des guides a été étudiée en s'appuyant sur des traitements théoriques et des simulations numériques. Une nouvelle méthode pour la déflexion et la modulation se basant sur la photo-inscription de guides a été proposée et démontrée expérimentalement dans les matériaux SBN et LiTaO3. Nous avons aussi montré pour la première fois la possibilité de réaliser à l'aide de cette technique le confinement dans les deux dimensions (2D) transversales. Les études expérimentales concernant l'influence des intensités des illuminations de contrôle et du champ appliqué sur le profil du guide sont en bonne adéquation avec les prédictions théoriques concernant le mode fondamental attendu / The realization transparent achievement of optical networks that do not need electronic components for the temporary detection and regenration of signals asks for optical routing and interconnection elements which are reconfigurable in short time, in the order of milliseconds in the case telecommunications networks. The use of optical waveguides in active materials made of active materials by conventional techniques, such as ion-indiffusion, proton exchange or ion implantation is badly suitable for this goal. These techniques give rise only to static waveguides close to the material surface and they are not easily modified. The technique of light inducing waveguides by lateral illumination developed in this work allows to cross an important step towards purely optical devices in which light is used to guide and manipulate light without resorting to complex manufacturing steps. The main advantage is that this effect can be erased, giving rise to dynamic structures that do note cause a permanent damage of the material. Another advantage is the versatility with respect to the form of the waveguides, that is defined by the structure imposed to control the illumination perpendicular to the direction of propagation. The feasibility of reconfigurable 1-dimensional waveguides has been experimentally demonstrated in the electro-optic ferroelectric crystals SrxBa1xNb2O6 (SBN, x=0.61) and Sn2P2S6 (SPS). The illuminating wavelengths used were 514 nm for SBN and 633 nm for SPS. Response and reconfiguration times of the order of 1 ms are shown to be possible in the case of SPS. The dynamics of the waveguides has been studied on the basis of theoretical treatment and numerical simulations. The evolution of light induced one-dimensional waveguides when the sustaining electric field is switched off leads to a novel kind of dynamic light deflection. We have studied this effect in detail using SBN and LiTaO3 crystals. Simulations of the beam propagation in the split waveguide on the base of a simple model lead to a good agreement with the experimental observations. Light modulation by the help of this effect has been demonstrated as well. Finally, we realized for the first time, the recording of dynamically reconfigurable bulk channel waveguides confined in two dimensions using lateral illumination technique. The experimental studies of the dependence of the output probe wave profile on the intensities of two control waves and on the applied electric field were found to be in good agreement with the expectations based on a simplified step profile for the photorefractive by induced refractive index change and on mode calculations
9

Properties Of High Energy Laser Light Transmission Through Large Core Optical Cables

Kennedy, Christopher 01 January 2013 (has links)
Laser induced damage is of interest in studying the transmission of large amounts of optical energy through step-index, large core multimode fibers. Optical fibers often have to be routed around objects when laser light is being transmitted between two locations which require the fiber to bend into a curve. Depending on how tight the bend is, this can result in transmission losses or even catastrophic damage when the energy density of the laser pulse exceeds the damage threshold of silica glass. The purpose of this study is to: Establish a minimum bend radius that would allow high energy (GW/cm2 ) to be transmitted through multimode fiber. Evaluate unique fiber routing configurations including loops, 180 bends, and S-bends. Develop optical modeling simulations backed with experimental data that can serve to predict critical areas for future systems. Waveguide theory predicts that light traveling through a bend will form whispering-gallery modes that propagate through total internal reflection bounces along the inside of the outer edge of the bend. This is critical since in these locations the energy density of the light will increase significantly, raising the potential of laser damage, nonlinear effects, and transmission losses. This loss is especially problematic when two 90° bends going in opposite directions are in close proximity to each other, forming an ‘S-bend’. Light that is grouped along the outer edge going through the first bend will enter the second bend at a sharper angle which causes much high transmission losses and raises the possibility of failure. iv Models using R-Soft BeamProp and Zemax were developed to study transmission losses, investigate light interactions at critical areas, and predict under which conditions laser damage would occur. BeamProp presents a clearer view of the modal distribution of light within the core of the fiber and is used to analyze how a plane wave with a Gaussian intensity distribution excites the fiber modes. Zemax provides a tool to perform non-sequential ray tracing through the fiber cable and stray light analysis within the core and once the light exits the fiber. Intensity distributions of the cross sectional area of the fiber shows the whispering gallery modes forming as the light propagates around bends and disburses as it propagates afterwards. It was discovered using R-Soft that if the separation distance between bends in an S-bend is approximately 3 mm there exists a condition where maximum transmission occurs. For 365 µm diameter core fiber it was calculated that the difference in output power could be as high as 150%. This was initially completely unexpected; however ray tracing using Zemax was able to verify that this distance allows the light to transition so that it enters the 2nd bend at the optimal angle to enter the whispering gallery mode. Experiments were performed that validated the models’ predictions and images were captured clearly showing the spatial distribution shift of the light within the core of the fiber. Experiments were performed to verify light grouping together to form whispering gallery modes as predicted by Zemax. Microscope images were taken as a function of distance from various bends to observe the periodic nature in which the laser light fills up the fiber. Additionally, a configuration was setup to examine stimulated Brillioun scattering and determine the onset of laser damage in the fiber. Fibers were tested as a function of bend radius and number of shots v and recommendations for future systems were made. Lastly, mechanical failure tests were performed to determine the relationship between stress placed on the fiber through bending and fiber lifetime in a static environment. This allowed a minimum safe bend radius to be calculated for a 30 year lifetime that agreed with previous calculated values.
10

Análise de dispositivos com materiais magnetoópticos para aplicações em sistemas de comunicações ópticas / not available

Gonçalves, Evandro Assis Costa 21 September 2001 (has links)
As redes ópticas de comunicação têm possibilitado, cada vez mais, o oferecimento de serviços do tipo faixa larga. A rede de comunicação totalmente óptica está se tornando a meta tecnológica mais ambiciosa. Grandes esforços têm sido concentrados no desenvolvimento e aperfeiçoamento de materiais e dispositivos não-recíprocos, como isoladores e circuladores constituem uma importante classe de dispositivos ópticos. Os isoladores são utilizados em sistemas ópticos para prevenir a reflexão de luz em lasers e amplificadores. Os circuladores são empregados em esquemas de derivação de sinais que utilizam multiplexação em comprimento de onda (WDM). O funcionamento destes dispositivos é baseado nas propriedades de materiais magnetoópticos. As metas desta dissertação são apresentar as principais características dos materiais magnetoópticos, explorando as características não-recíprocas dos modos TM. Guias planares e tridimensionais são analisados neste trabalho. Para tanto, são obtidas as expressões das componentes dos campos e as equações características dos modos de interesse em estruturas planares por meio da técnica de matriz de transferência (TMT). A análise de propagação de onda em guias planares com materiais magnetoópticos é feita por meio de simulação numérica empregando o método de propagação de feixe (BPM) baseado em diferenças finitas (FD) e o esquema de Crank-Nicholson (CN) na discretização da solução da equação de onda. A condição de fronteira transparente (TBC) é incorporada ao algoritmo FD-BPM com a finalidade de se evitar reflexões de ondas eletromagnéticas para dentro da janela computacional. O método do índice efetivo é empregado na análise de guias de onda tridimensionais do tipo rib. / Optical communication networks have allowed a continuous increase of broadband services offer. The all-optical communication networks are becoming the most ambitious technological goal. Great efforts have been concentrated on the materiaIs and devices development and improvement to make it possible. Nonreciprocal devices, such as isolators and circulators constitute an important class of optical devices. Isolators are used in optical systems to avoid reflection of light in lasers and amplifiers. Circulators are used in signal derivation schemes that use wavelength division multiplexing (WDM). The operation of these devices is based on the properties of magnetooptic materiaIs. The purposes of this dissertation are to present the main features of the magnetooptic materiaIs as well as to analyze the eletromagnetic wave propagation in magnetooptic waveguides, exploring nonreciprocal features of TM modes. Planar and three-dimensional waveguides are analysed in this present study. Therefore expressions of electromagnetic field components and characteristic equations of the modes of interest in planar structures are obtained by using transfer matrix technique (TMT). The wave propagation analysis in planar magnetooptic waveguides is realized by using the finite-difference beam propagation method (FD-BPM) and Crank-Nicholson scheme (CN) applied to wave equation solution discretization. In order to avoid electromagnetic wave reflection into computational window, the transparent boundary condition (TBC) is incorporated to the FD-BPM formalism. The effective index method (EIM) is used in the analysis of three-dimensional rib magnetooptic waveguides.

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