Η παρούσα εργασία εστιάζει στη μελέτη αισθητήρων με χρήση μικροδομημένων οπτικών ινών (ή οπτικών ίνών φωτονικών κρυστάλλων) με δύο πυρήνες, οι οποίοι αλληλεπιδρούν μεταξύ τους. Για την πληρότητα της μελέτης γίνεται αρχικά μια ανασκόπηση των βασικών χαρακτηριστικών των ινών φωτονικών κρυστάλλων όπως οι απώλειες, η διασπορά, και το φαινόμενο της περιοδικής μεταφοράς ενέργειας μεταξύ των πυρήνων σε μία διπύρηνη ίνα φωτονικών κρυστάλλων. Το τελευταίο αποτελεί βάση για τη λειτουργία της ίνας ως αισθητήρα. Στη συνέχεια, αναλύονται τα βασικά χαρακτηριστικά των αισθητήρων μικροδομημένων οπτικών ινών και μελετάται η ευαισθησία συναρτήσει του μήκος κύματος της διαδιδόμενης ακτινοβολίας και των γεωμετρικών χαρακτηριστικών της ίνας. Πιο συγκεκριμένα, μελετάται η ευαισθησία για τρία μοντέλα ινών, με μία, δύο και τρεις οπές μεταξύ των πυρήνων τους. Ως υλικό γεμίσματος των οπών θεωρήθηκε το νερό, διότι είναι ένας από τους πιο κοινούς διαλύτες, κατάλληλος και για βιολογικά δείγματα. Για κάθε ένα από τα παραπάνω μοντέλα εξετάζεται η συμπεριφορά του αισθητήρα συναρτήσει του μήκους κύματος της διαδιδόμενης ακτινοβολίας. Ακολούθως, μελετάται η συμπεριφορά των αισθητήρων όταν υποβληθούν σε μεταβολή κλίμακας (scaling), δηλαδή όταν μεταβληθούν ταυτόχρονα όλες οι γεωμετρικές παράμετροι του αισθητήρα, κρατώντας σταθερές τις αναλογίες. Ο λόγος για τον οποίο γίνεται αυτό είναι διότι αυξάνοντας την διατομή της ίνας αυξάνει παράλληλα η διάμετρος των οπών με αποτέλεσμα να διευκολύνεται το γέμισμά τους με το υπό μελέτη υλικό. Όμως, καθώς αυξάνεται η διατομή της ίνας αυξάνει παράλληλα και η απόσταση μεταξύ των πυρήνων, μειώνοντας έως εξαλείφοντας την αλληλεπίδρασή τους. Για το λόγο αυτό παρουσιάζεται μια βελτιωμένη μορφή του αισθητήρα με κεντρικές οπές στους δύο πυρήνες, με σκοπό το άπλωμα των ρυθμών και κατά συνέπεια την αύξηση της αλληλεπίδρασης μεταξύ των πυρήνων. Κατ’ αυτόν τον τρόπο η μικροδομημένη ίνα μπορεί να λειτουργήσει ως αισθητήρας για σχετικά μεγάλες τιμές της μεγέθυνσης, κάτι που δεν είναι δυνατόν απουσία κεντρικών οπών. Τέλος, παρουσιάζονται αποτελέσματα και για ένα μοντέλο αισθητήρα συμβατικής οπτικής ίνας με δύο πυρήνες και κεντρικές οπές, το οποίο στηρίζεται στην ίδια αρχή λειτουργίας και παρουσιάζει παρόμοια συμπεριφορά με τις διπύρηνες μικροδομημένες ίνες. / This MSc thesis focuses on the study of sensors using microstructured optical fibers (or photonic crystal optical fibers) with two cores, which interact with each other. For the completeness of the study, first is attempted an overview of the basic characteristics of the photonic crystal fiber such as losses, dispersion and the effect of periodic transfer of energy among the cores in a dual core photonic crystal fiber. The latter forms the base for the operation of the fiber as sensing element. Then, the basic characteristics of the sensors using microstructured optical fibers are examined and the sensitivity is studied depending on the wavelength of the propagating radiation and on the geometric characteristics of the fiber. Specifically, the sensitivity of the sensor is studied for three fiber models with one, two and three holes between their cores. Water is assumed as filling material of the holes, since it is one of the most common dissolvers, also suitable for biological samples. For each model the behaviour of the sensor depending on the wavelength of the propagating radiation is studied. Afterwards, the behaviour of the sensor under scaling of the fiber dimensions is studied. In more detail all the geometrical parameters of the sensor are changed simultaneously and proportionally. From a practical point of view increasing the fiber dimensions facilitates the filling of the holes with the material under study. However, the distance between the cores is also increased, reducing or even eliminating their interaction. Therefore, an improved form of the sensor is presented. This form has central holes in the cores in order to extend the spatial overlap of the modes increasing the interaction between the cores. This way, the microstructured fiber can operate as a sensor even for relatively large scaling, which is not possible without central holes. Finally, a conventional model of ordinary dual core optical fiber sensor is studied, having central holes in both cores. It is based on the same principle of operation and has similar behaviour with the dual core microstructured optical fibers.

Este trabalho tem por objetivo a modelagem numérica das fibras microestruturadas e a proposição de dispositivos inovadores com base nos modelos numéricos construídos. Primeiramente, são implementados dois formalismos distintos: o FDTD (do inglês Finite Diference Time Domain) para a geração dos diagramas de bandas dos cristais fotônicos e o SOR (do inglês Successive Over Relaxation) para a análise modal das fibras. A partir destes modelos, são propostas três aplicações distintas que utilizam as propriedades inovadoras das fibras microestruturadas, a saber: compensador de dispersão a fibra com capacidade de compensar um enlace óptico com cerca de vinte vezes seu comprimento, amplificador Raman com alto ganho óptico e isolador óptico a fibra microestruturada. / The goal of this work is the numerical modeling of microstructured optical fibers and the proposition of novel applications using the model developed. First, two distinct formalisms are implemented, the Finite Difference Time Domain Method (FDTD) to generate the photonic crystal band diagrams and the Successive Over Relaxation method (SOR) to carry out modal analysis on the microstructured optical fibers. By means of these models, three applications are investigated: high performance dispersion compensation fiber, high gain Raman amplifier and microstructured optical fiber isolator.

De nombreuses applications militaires ou civiles, telles que la spectroscopie dans les bandes de transmission de l’atmosphère (bandes 3-5µm et 8-12µm), nécessitent de disposer de sources émettant dans le moyen infrarouge (IR). Les travaux de cette thèse portent sur la génération de rayonnement dans la bande 3-5µm par amplification paramétrique (mélange à quatre ondes) dans les fibres optiques en verres fluorés et en verres de chalcogénures. La première partie de ce travail a été consacrée à l’étude théorique et à la modélisation des conditions d’accord de phase et du gain paramétrique dans des fibres à saut d’indice monomodes en verres fluorés ZBLAN et verres de chalcogénures As2S3 et As2Se3. La nature des résultats obtenus nous a conduit à étudier théoriquement le potentiel de l’accord de phase multimode dans les fibres en verres de chalcogénures. La deuxième partie de ce travail a porté sur la modélisation de l’amplification paramétrique dans des fibres en verres de chalcogénures microstructurées à géométrie hexagonale. Pour ce faire, un modèle simplifié de la propagation dans les fibres microstructurées hexagonales a été développé : le modèle de l’indice effectif de gaine (EIM). Il a ensuite été comparé à une méthode de résolution aux éléments finis. Grâce à cette comparaison, nous avons pu améliorer la précision du modèle EIM en déterminant la valeur de plusieurs paramètres empiriques. Ce modèle nous a alors permis de prédire l’efficacité du processus d’amplification paramétrique dans les fibres microstructurées. L’ensemble de ces études théoriques a permis d’identifier les fibres les plus adaptées à la conversion de fréquence vers la bande 3-5µm. Enfin, nous avons réalisé un banc de mesure de la dispersion chromatique des fibres, ainsi que le dimensionnement d’un convertisseur de fréquence utilisant les fibres identifiées dans l’étude théorique. / Various civil or military applications, such as spectroscopy in the atmospheric transparency windows (3 – 5 µm and 8 – 12 µm ranges), require the use of mid-infrared emitting laser sources.The work presented in this thesis is about light generation in the 3 – 5 µm range by parametric amplification (four-wave mixing) in fluoride and chalcogenide fibers. The first part of the study is devoted to modelizations of phase-matching condition and parametric gain in monomode step-index ZBLAN fluoride fibers as well as As2S3 and As2Se3 chalcogenide fibers. The results obtained in this modelization led to the theoretical study of multimode phase-matching conditions in chalcogenide fibers.The second part of the study presents the modelization of parametric amplification in hexagonal microstructured chalcogenide fibers. A simplified model, called the effective index method (EIM), has been developed and compared to the finite element method. Thanks to this comparison, the accuracy of the EIM model was improved through the determination of several empirical parameters. Using the improved EIM model, we have been able to predict the parametric amplification efficiency in microstructured fibers. Thus, all those theoretical studies allowed us to identify the most adapted fibers for frequency conversion in the 3 – 5 µm range. Eventually, we realized an experimental bench to measure the chromatic dispersion of optical fibers, and we suggested an experimental architecture using the fibers we had indentified in the theoretical study.

Este trabalho tem por objetivo a modelagem numérica das fibras microestruturadas e a proposição de dispositivos inovadores com base nos modelos numéricos construídos. Primeiramente, são implementados dois formalismos distintos: o FDTD (do inglês Finite Diference Time Domain) para a geração dos diagramas de bandas dos cristais fotônicos e o SOR (do inglês Successive Over Relaxation) para a análise modal das fibras. A partir destes modelos, são propostas três aplicações distintas que utilizam as propriedades inovadoras das fibras microestruturadas, a saber: compensador de dispersão a fibra com capacidade de compensar um enlace óptico com cerca de vinte vezes seu comprimento, amplificador Raman com alto ganho óptico e isolador óptico a fibra microestruturada. / The goal of this work is the numerical modeling of microstructured optical fibers and the proposition of novel applications using the model developed. First, two distinct formalisms are implemented, the Finite Difference Time Domain Method (FDTD) to generate the photonic crystal band diagrams and the Successive Over Relaxation method (SOR) to carry out modal analysis on the microstructured optical fibers. By means of these models, three applications are investigated: high performance dispersion compensation fiber, high gain Raman amplifier and microstructured optical fiber isolator.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / Neste trabalho sÃo apresentados estudos de simulaÃÃo numÃrica de propagaÃÃo/chaveamento de pulsos ultracurtos em acopladores de cristais fotÃnicos e de Acesso MÃltiplo por DivisÃo de CÃdigo Ãptico (OCDMA) utilizando Fibras de Grade de Bragg (FBG). Para a codificaÃÃo foram obtidos analiticamente cÃdigos de Gold. Na anÃlise de acopladores de cristais fotÃnicos (microestruturados) foram investigadas as propriedades da propagaÃÃo de pulsos de luz na forma de sÃlitons. Foram utilizados pulsos ultracurtos, de duraÃÃo mÃnima de 100 femtossegundos (fs). Para este tipo de propagaÃÃo em acopladores deve ser resolvida numericamente a EquaÃÃo NÃo linear de SchrÃdinger Generalizada (ENLSG) dos modos acoplados com o acrÃscimo de termos de dispersÃo de terceira ordem, espalhamento Raman intrapulso, auto inclinaÃÃo e dispersÃo do coeficiente de acoplamento. Um acoplador com comprimento de acoplamento de 1,8 centÃmetros e comprimento de 33 centÃmetros foi simulado. Utilizando este comprimento de dispositivo os efeitos de alta ordem (dispersÃes, auto inclinaÃÃo, Raman, dispersÃo do acoplamento) foram fatores importantes a serem considerados. PorÃm, para dispositivos pequenos, com atà 2 comprimentos de acoplamento, estes efeitos podem ser desconsiderados. Na segunda anÃlise, foi estudada a codificaÃÃo em amplitude de 5 cÃdigos de Gold utilizando uma FBG codificadora/decodificadora de comprimento 41,58 milÃmetros. Para a grade utilizada, a codificaÃÃo em amplitude e a interferÃncia entre usuÃrios neste dispositivo foram investigadas. Houve um aumento da interferÃncia ao se acrescentar usuÃrios partindo de valores de 6 decibÃis atà cerca de 10,5 decibÃis para este dispositivo. Utilizando acopladores fotÃnicos com a FBG linear, o chaveamento de pulsos entre os canais do acoplador pÃde ser visualizado para ganhos altos (a partir de 50 decibÃis). / This paper presents numerical simulation studies of propagation/switching of ultra-short pulses in photonic crystal couplers and Optical Code Division Multiple Access (OCDMA) using Fiber Bragg Grating (FBG). For coding were obtained analytically Gold codes. In the analysis of photonic crystal couplers (microstructured) investigated the properties of the propagation of light pulses as SÃlitons. Ultra-short pulses of minimum duration of 100 femtoseconds (fs) were used. For this type of propagation in couplers, must be solved numerically the Equation nonlinear SchrÃdinger Generalized (ENLSG) of the coupled modes in accordance with the addition of third order dispersion, intrapulse Raman scattering, self-steepening and the dispersion of coupling coefficient. A coupler with coupling length of 1.8 cm and length 33 cm was simulated. Using this device length, the high-order effects (dispersion, self-steepening, raman, dispersion of the coupling) were important factors to consider. But, for small devices, with up to two coupling lengths, these effects may be ignored. In the second analysis, we studied the coding range of 5 Gold codes using an FBG encoder/decoder of length 41.58 mm. For the grid used, the encoding amplitude and interference between users of this device have been investigated. There was an increase of interference by adding values of users starting from 6 dB to about 10.5 dB for this device. Using photonic couplers with the FBG linear switching pulses between the channels of the coupler could be visualized to high gains (from 50 decibels).

Made available in DSpace on 2016-03-15T19:38:07Z (GMT). No. of bitstreams: 1 Alfredo Almeida Araujo.pdf: 1307305 bytes, checksum: fd5b49227c52b28ef3a5392983927234 (MD5) Previous issue date: 2008-02-13 / This dissertation aims to describe the basic characteristics of microstructured fibers, their concept and performance, and to investigate the application of a low loss microstructured fiber to the development of Raman amplifiers. An analysis of the use of these amplifiers in Telecommunication applications is described. To this end, simulations were carried out with these waveguides with the data of a real fiber described in the literature. Simulations were also carried out to determine the amplifier s net gain and noise figure and to establish the advantages of its use in a complete optical fiber span, including the compensation dispersion in the O band (1260-1360 nm). As a result, it was demonstrated that the microstructured fiber presents, in some aspects, a performance that is higher than that of conventional Raman amplifiers, and complementary to that of a commercial amplifiers, such as those based on Erbium doped fiber. / Esta dissertação tem como objetivo descrever as características básicas das fibras microestruturadas, seu conceito e desempenho, e investigar a aplicação de uma fibra microestruturada de baixa perda para o desenvolvimento de amplificadores Raman. Uma análise do uso destes em aplicações de Telecomunicações é descrita. Para isso, foram realizadas simulações destes guias de onda com dados de uma fibra real descrita na literatura. Também foram realizadas simulações para verificação do ganho líquido e figura de ruído de um amplificador baseado nesta fibra e das vantagens de seu uso em um enlace óptico completo, incluindo compensação de dispersão para sinais da banda O (1260-1360 nm). Como resultado, demonstrou-se um desempenho superior em alguns aspectos aos amplificadores Raman convencionais, e complementar aos amplificadores disponíveis atualmente no mercado, como os baseados em fibra dopada com Érbio.

Made available in DSpace on 2016-03-15T19:38:17Z (GMT). No. of bitstreams: 1 Rafael Euzebio Pereira de Oliveira.pdf: 3969043 bytes, checksum: cfa66f3e9f3a18e9e86b364cd01a2c0a (MD5) Previous issue date: 2010-05-13 / In this dissertation the transmission properties of photonic crystal fibers are assessed under the influence of pressure and temperature for sensing applications. A review is given of the light propagation in conventional optical fibers and the effects of pressure and temperature on the refractive index of silica are studied. Photonic crystals in 1 and 2 dimensions are also studied. Then, microstructured fibers and photonic crystal fibers are addressed and their guidance properties and general applications are shown. A review is made of temperature and pressure sensors based on conventional fibers, Bragg gratings and microstructured and photonic crystal fibers described in the literature. Finally, results are shown and discussed of the experiments with the application of pressure on a hollow-core photonic crystal fiber, for which high-order bandgaps, in the visible spectral region, were identified and characterized for the first time. These bandgaps are shown to be pressure sensitive. Applying external hydrostatic pressure over the fiber, optical transmission variations of a few dB were observed for pressures of hundreds of kgf/cm², while when the fiber holes were internally pressurized a similar variation was achieved for units of kgf/cm². The response of light polarization, and hence of the fiber birefringence, to internal pressure was also analyzed.. In the other part of the experimental work, the temperature-induced bandgap spectral shift of photonic bandgap fibers was characterized. The response of a hollow-core fiber, a hybrid fiber and an all-solid fiber was characterized with bandgap shifts of up to 36 pm/°C in straight fibers. For the all-solid fiber the influence of bending over the bandgaps was characterized, as well as temperature-induced bandgaps shifts under these conditions. For a straight fiber, a simple model for the bandgap shift calculation is presented and showed good agreement with the experimental results. Closing the work, the conclusions are presented. / Nessa dissertação são avaliadas as propriedades de transmissão em fibras de cristal fotônico sob influência da pressão e da temperatura visando aplicações em sensoriamento. Antes é feita uma revisão da propagação da luz em fibras ópticas convencionais e os efeitos da pressão e temperatura sobre o índice de refração da sílica. Também são estudados os cristais fotônicos em 1 e 2 dimensões. Em seguida são estudadas as fibras microestruturadas e de cristal fotônico e são mostradas suas propriedades de guiamento e aplicações gerais. Em seguida é mostrada uma revisão sobre sensores de temperatura e pressão utilizando fibras convencionais, redes de Bragg e fibras de cristal fotônico. Finalmente são mostrados e discutidos os resultados dos experimentos com pressão em uma fibra de cristal fotônico de núcleo oco, para a qual foram identificados, caracterizados e reportados pela primeira vez bandgaps de ordem superior localizados na região visível do espectro, que são sensíveis à pressão. Aplicando-se pressão hidrostática na parte externa da fibra obteve-se variação de alguns dB na transmissão óptica para pressões de centenas de kgf/cm², enquanto que quando a pressão era aplicada no interior dos buracos da fibra obteve-se variação semelhante para unidades de kgf/cm². Também foi analisada a resposta da polarização da luz guiada, e portanto da birrefringência da fibra, à pressão interna. Em outra parte do trabalho experimental foi caracterizada a resposta à temperatura do deslocamento espectral dos bandgaps em fibras de bandgap fotônico. Foram caracterizadas as respostas de uma fibra de núcleo oco, uma fibra híbrida e uma fibra totalmente sólida com deslocamentos de até 36 pm/°C para fibras esticadas. Para a fibra totalmente sólida foi também caracterizada a influência da curvatura da fibra sobre os bandgaps e como o deslocamento devido à temperatura é afetado nessas condições. Para uma fibra esticada é apresentado um modelo para o cálculo aproximado do deslocamento dos bandgaps em função da temperatura obtendo-se resultados satisfatórios com o experimento. Na ultima parte do trabalho são apresentadas as conclusões finais.

Ce travail concerne le développement d’une fibre optique à structure originale permettant la montée en puissance moyenne et crête dans les systèmes lasers à 2μm. La gestion des effets thermiques est devenue aujourd’hui un enjeu primordial notamment pour essayer de repousser le seuil d’apparition des instabilités modales transverses. Le principe mis en avant ici est basé sur la rupture de symétrie de la gaine microstructurée de la fibre afin d’améliorer la délocalisation des modes d’ordre supérieur vers l’extérieur du milieu à gain. Ainsi une propagation quasi-monomode est obtenue dans une fibre apériodique passive avec un coeur de 140μm à 2μm. Un travail de modélisation a été mené de manière à proposer d’autres structures basées sur une modulation contrôlée de l’indice de réfraction dans le milieu à gain afin de repousser encore plus le seuil du régime multimode. En outre, la fabrication de la première fibre dopée thulium à large aire modale (Dcoeur = 18μm) par la méthode REPUSIL a montré une efficacité de 50%. Ensuite, la fabrication de la première fibre rigide complètement apériodique à gaine réduite dopée thulium a été réalisée. Une fibre avec un coeur de 29μm et un diamètre extérieur de 769μm et une longueur de 86cm a été caractérisée en configuration laser et a permis d’obtenir une émission laser à 2μm de 3,8W (puissance limitée par la puissance de la diode de pompe disponible) avec un rendement de 20% et une qualité de faisceau quasi-monomode. De plus, une fibre passive complètement apériodique à polarisation unique avec un coeur de 140μm a également été réalisée et a permis d’obtenir un ratio d’extinction de polarisation de 16,5dB à 2μm. / This work deals with the development of an original leaky structure of optical fiber aiming at generating a high power laser radiation at 2μm in CW and pulsed regimes. The management of thermal effects in high power/energy regime became a major issue, in particular to push further the transverse modal instabilities threshold. Our approach consists in breaking the symmetry of the microstructured fiber cladding for to improve the delocalization of the high order modes outside of the gain medium. Thus, an effective single-mode propagation at a 2μm operating wavelength was first demonstrated into a passive aperiodic fibers whose the core diameter reaches up to 140 μm. After implementing some Stress Applying Parts over our aperiodic design, a PER of 16.5dB was achieved at 2μm using a single polarization passive FA-LPF with a core of 140 μm. Thence, a numerical study on the tailoring the active core refractive index has been carried out so as to fend off the threshold of multimodedness. Additionally, the first LMA Tm-doped fiber (Dcoeur = 18μm) fabricated by the REPUSIL method and showing an efficiency of 50% is demonstrated. Thereafter, the fabrication of the first rod-type Tm-doped FA-LPF with reduced cladding is shown. A 29 μm core FA-LPF was characterized in laser configuration, leading to an effective single-mode emission of 3.8W of average power at 2μm strictly restricted by the available pump power and an efficiency of 20%.

Made available in DSpace on 2016-03-15T19:37:31Z (GMT). No. of bitstreams: 1 Rodrigo Cesar Ribeiro Miraglia.pdf: 2147088 bytes, checksum: 67087392fe4b03bb24d9a164fd92ceed (MD5) Previous issue date: 2010-08-20 / Fundo Mackenzie de Pesquisa / Sensors based on optical fibers are being increasingly used in hostile environments for measuring pressure, temperature, stress, chemical and biological parameters, etc. These sensors have the advantage of having reduced size and weight, immunity to electromagnetic interference, of being chemically inert, and also allowing the distributed measurement of the respective parameter along the fiber. Microstructured optical fibers have characteristics that are relevant to sensing applications, such as freedom of design of their internal structure obtained by varying the diameter of the holes and the distances between them, among other parameters, which is not applicable in conventional optical fibers. The present work aims to use a microstructured optical fiber as a distributed sensor for hydrostatic pressure, using the POTDR (Polarization Optical Time-Domain Reflectometry) and the OFDR (Optical Frequency-Domain Reflectometry) measurement techniques. The application of hydrostatic pressure on the fiber changes its birefringence and, consequently, the evolution of the states of polarization, which is the parameter monitored by the techniques. By monitoring the changes of these states, it is possible to infer the changes in applied pressure. The study is undertaken via simulations and analysis, both performed in the software MatLab. / Sensores baseados em fibras ópticas vêm sendo cada vez mais utilizados em ambientes hostis para medição de pressão, temperatura, stress, análise química e biológica, etc. Esses sensores têm a vantagem de possuírem tamanho e peso reduzidos, imunidade à interferência eletromagnética, de serem quimicamente inertes, e também permitirem a medição distribuída do parâmetro a ser analisado ao longo da fibra. As fibras ópticas microestruturadas possuem características relevantes na aplicação de sensoriamento, tal como a liberdade de construção de sua estrutura interna variando o diâmetro dos buracos e a distância entre eles, entre outros parâmetros, que não são aplicáveis em fibras ópticas convencionais. Este trabalho tem como objetivo estudar uma fibra óptica microestruturada como sensor distribuído de pressão hidrostática, utilizando as técnicas de medição POTDR (Polarization Optical Time-Domain Reflectometry) e OFDR (Optical Frequency-Domain Reflectometry). A aplicação de pressão hidrostática sobre a fibra altera sua birrefringência e, consequentemente, a evolução do seu estado de polarização, sendo este último o parâmetro monitorado pelas técnicas. Analisando-se a mudança deste estado, pode-se inferir a mudança de pressão aplicada. O estudo é realizado através de simulações e análises efetuadas no software MatLab.