Optical fiber systems have been developed during the past twenty-five years with primary applications in long distance, high speed digital information communication. Optical fiber sensors have also been developed over the past fifteen years for the nondestructive inspection and evaluation of materials used in the aerospace, energy, transportation, and medical industries. Optical fibers may be used as the field-sensitive elements in sensors for the measurement of environmental parameters such as displacement, strain, temperature, vibration, chemical concentrations and electromagnetic fields. Their advantages for such measurements include 1) an inherent immunity to electromagnetic interference (EMD), 2) avoidance of ground loops, 3) the capability of responding to a wide variety of measurands, 4) excellent resolution, 5) the avoidance of sparks, especially important for applications within explosive environments, and 6) operation at temperatures of approximately 800°C for silica waveguides and above 1900°C for sapphire waveguides. Phase-modulated optical fiber sensors have been shown to possess the highest sensitivities to a given measurand. This dissertation describes several novel phase-modulated optical fiber sensors. The sensors described include a strain gage, a temperature sensor for applications up to and including 1700°C, a displacement sensor with sub-Angstrom resolution, and a vibration mode filter. For each sensing concept, a description and method of operation is given, followed by fabrication methods and experimental results. / Ph. D.

Changes in heat content are almost universally associated with chemical reactions. Thermometry as an analytical tool has been extensively researched and developed. Finding solutions to problems involving thermal isolation, specificity, sensitivity, and cross-sensitivity remain as active areas of interest. Fiberoptic interferometers, which use phase phenomena associated with propagating light, are extremely sensitive to heat. This research has focused on a special "birefringent" optical fiber. Two channels of information are generated in this single-fiber interferometer which correspond to the heat evolved from a catalytic reaction isolated on the fiber surface. Because of the unique transduction mechanism associated with the "birefringent" optical fiber, this device is sensitive to heat and remarkably insensitive to pressure. Details of the characterization and development of the birefringent optical fiber into a useful analytical probe are presented. / Ph. D.

Orientador: Luiz Carlos Barbosa / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-04T20:34:50Z (GMT). No. of bitstreams: 1 GarciaRivera_VictorAnthony_M.pdf: 15268986 bytes, checksum: 03f47604e1a522457d30d9fa547a024d (MD5) Previous issue date: 2005 / Resumo: Neste trabalho de pesquisa, reporto a fabricação e caracterização de vidros germano-telurito para amplificadores ópticos curtos. Estes são fabricados em guias de onda planar e canal pela técnica de troca iônica e fibra em vidro, dopados com altas concentrações de íons de Er3+ cuja composição é: 75TeO2 ¿ 2GeO2 ¿ (10+x)Na2O ¿ (12-x)ZnO ¿ 1Er2O3 (mol%, onde x=0, 2 e 5). São preparados guias multímodos e monomodos, as profundidades dos guias podem ser controladas pela variação do tempo e da temperatura no processo da troca iônica. Com o vidro de maior índice de refração consegui fabricar fibra óptica (só nucleo) e solda com outro vidro de menor índice de refração, pela técnica de fibra em vidro. A preparação dos vidros foi feita pela técnica convencional de fusão à temperatura de 7500C. Encontrou-se grande estabilidade térmica nos sistemas vítreos. Realizou-se as medidas de espectroscopia Raman, absorção, emissão e tempo de vida, onde se mostra a maior largura de banda de emissão dos vidros germano-teluritos dopados com íons Er3+ quando comparado com amplificadores comerciais feitos à base de vidros silicatos. Os vidros já polidos passaram pelo processo de fotolitografía, durante a fabricação dos guias de ondas se empregou a técnica de troca iônica dos íons Ag+. Na+, processo tomando por base a temperatura de início de cristalização Tg; neste processo os vidros foram submergidos num banho de sais que continha 2AgNaO3 ¿ 49NaNO3 ¿ 49KNO3. Os índices efetivos dos modos foram medidos pela técnica de acoplamento por prisma com o equipamento Metricom. Foram determinados o perfil do índice de refração e os parâmetros da difusão: coeficiente de difusão efetiva De e a energia de ativação ED. Conseguiu-se fabricar guias de onda planar e canais monomodos e multímodos pela técnica de troca iônica em vidros germano-teluritos dopados com altas concentrações de íons de Er3+. Empregando a técnica de fibra em vidro, consegui fabricar um guia de onda. Método totalemente novo que consiste na solda de uma fibra óptica (núcleo) com um substrato de menor índice de refração que é a casca para esta fibra mediante esta técnica. Neste processo deve-se ter em conta a região de temperatura Tg ¿ Tx, para evitar possiveis processos de cristalização no processo de solda da fibra óptica com o substrato / Abstract: In this work the production and characterization of germane-tellurite glasses for small optical amplifiers are reported. These materials were applied in the manufacture of planar e channel waveguide using the technique of ionic exchange in glasses and fiber on glass, doped with high concentrations of ions of Er3+ whose composition is: 75TeO2 ¿ 2GeO2 ¿ (10+x)Na2O - (12-x)ZnO ¿ 1Er2 O3 (mol%, x= 0, 2 e 5). Multimode and monomode guides have been prepared, and the depths of the guide can be controlled for the time and the temperature variation in the process of the ionic exchange. With the glass of high refraction index, manufacture of the optic fiber (only nucleus), and welding this with another glass of smaller refraction index were carried out for the fiber technique on glass purpose. The preparation of glasses was made by the conventional technique of fusing at the temperature of 7500C and glasses of great thermal stability were obtained characterization Raman, optical absorption, light emission and lifetime measurements were performed. The optical absorption of glasses doped tellurite with ions Er3+ has been considerably broader than those of the amplifiers of glass base silicate glasses. The polishing of glasses was done using the photo-lithographical process during the construction of the waveguides. The technique of Ag+. Na+ ion-exchange was applied near Tg and below Tx. In this process, the glasses have been submerged in a bath of melted 2AgNaO3 ¿ 49NaNO3 ¿ 49KNO3. The effective refraction index was measured by the coupled prism technique using the Metricom equipment. The refraction index profile and the diffusion parameters as the diffusion effective coefficient De and the energy of activation ED were determined. Planar monomode and multimode waveguide channel was manufactured using the ion-exchange technique in germane-tellurite glasses doped with high concentration of Er3+ ions. A new method of glass fiber preparation is introduced and consists of the soldering of a fiber optic (nucleus) to a substrate of smaller refraction index. In this process the temperature region between Tg and Tx was avoided in order to prevent against any possible crystallization soldering process / Mestrado / Física / Mestre em Física

Orientador: Hugo Enrique Hernández Figueroa / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-22T14:17:05Z (GMT). No. of bitstreams: 1 RamosGonzales_RoddyElky_D.pdf: 101751842 bytes, checksum: 8dc15b7e91881cfef8e1c24fa619f3ca (MD5) Previous issue date: 2013 / Resumo: Propor uma técnica eficiente para controlar o Comprimento de Onda da Dispersão Zero (ZDW - Zero Dispersion Wavelength) de uma Fibra Óptica Microestruturada (MOF - Microstructured Optical Fiber). Esta técnica baseia-se na variação do índice de refração linear e na variação da espessura de um filme fino que cobre as superfícies interiores dos buracos da MOF. Foi utilizado um código potente e preciso baseado na formulação do Método dos Elementos Finitos (FEM - Finite Element Method) totalmente vetorial em conjunto com Camadas Perfeitamente Casadas (PMLs - Perfectly Matched Layers). E demonstrado um deslocamento Maximo do ZDW de 570 nm. Este filme fino pode ser incluído durante ou apos a fabricação da MOF, isso significa que a Dispersão Zero (ZD - Zero Dispersion) da fibra pode ser adaptada conforme a necessidade / Abstract: An efficient technique to control the zero-dispersion wavelength (ZDW) of a microstructured optical fiber (MOF) is proposed and numerically demonstrated in this work. This technique is based on the variation of the linear refractive index and the thickness of a thin film covering the microstructured optical fiber holes' inner surfaces. A powerful and accurate code based on a full-vector finite-element method formulation in conjunction with perfectly matched layers was used. A maximum of 570-nm zero-dispersion wavelength displacement is demonstrated. This thin film can be included after the microstructured optical fiber has been fabricated, and that means the zero dispersion of such fiber can be tailored as needed / Doutorado / Telecomunicações e Telemática / Doutor em Engenharia Elétrica

Thesis (MSc (Physics))--University of Stellenbosch, 2009. / The role fulfilled by theoretical models is rapidly increasing due to lasers becoming appli- cation driven to satisfy certain criteria and demands. Construction of high precision lasers requires good theoretical models and consequently good approximations of the parameters that such models are based upon. Despite the di erent model formalisms, most share a com- mon set of input parameters, including fibre waveguiding properties, input powers, transition cross-sections and overlaps between guided modes and the dopand distribution. Experimental and numerical work which was aimed at obtaining the wide-band emission and absorption cross-sections of fibre indirectly by means of the Giles parameters was done. The Giles parameters were used rather than the well known ionic cross-sections primarily because of the convenient encapsulation of the cumbersome overlap factors and the ionic cross-sections within the Giles parameters. The wide band spectral characteristics of the Giles parameters are indispensable in the design of fibre lasers and amplifiers, as they form the key parameters for laser models. These parameters are normally obtained utilizing absorption spectroscopy to obtain the absorption cross-sections and models such as the Fuchtbauer Ladenberg relation, the Mc- Cumber relation or uorescence spectroscopy to obtain the emission cross-sections. Recent research however indicates that these methods are inaccurate in certain spectral regions. An investigation was launched to extract the Giles parameters from measurements of the ampli- fied spontaneous emission (ASE) and pump absorption in ytterbium-doped fibre for several lengths of fibre and subsequent computer simulations, utilizing an ampli fier model. The Giles parameters are extracted with a fitting algorithm that adjusts the relevant numerical values to minimize the least square difference between the numerical data obtained from the amplifier model and the measured data. Using the model devised in this project on literature data, the Giles parameters were extracted and compared to the Giles parameters extracted in literature on the same data. This comparison conforms the extraction of the Giles parameters, utilizing the model devised in this project, as successful. Subsequently the model devised in this project was applied to extract the Giles parameters from experimental data measured at Stellenbosch, using a double cladding ytterbium-doped fibre. Finally a fibre laser was built utilizing the double cladding ytterbium-doped fibre and the output was measured. The Giles parameters extracted were then used in a fibre laser model to calculate the output and compare it to the measurements taken. This served as suffcient verification that the Giles parameters extracted can be used to model a fibre laser effciently.

Thesis (MSc)--University of Stellenbosch, 2011. / Please refer to full text to view abstract.

Thesis (PhD)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: The concept of broadband coherent supercontinuum (SC) generation in all-normal dispersion (ANDi) fibers in the near-infrared, visible and ultraviolet (UV) spectral regions is introduced and investigated in detail. In numerical studies, explicit design criteria are established for ANDi photonic crystal fiber (PCF) designs that allow the generation of flat and smooth ultrabroad spectral profiles without significant fine structure and with excellent stability and coherence properties. The key benefit of SC generation in ANDi fibers is the conservation of a single ultrashort pulse in the time domain with smooth and recompressible phase distribution. In the numerical investigation of the SC generation dynamics self-phase modulation and optical wave breaking are identified as the dominant nonlinear effects responsible for the nonlinear spectral broadening. It is further demonstrated that coherence properties, spectral bandwidth and temporal compressibility are independent of input pulse duration for constant peak power. The numerical predictions are in excellent agreement with experimental results obtained in two realizations of ANDi PCF optimized for the near-infrared and visible spectral region. In these experiments, the broadest SC spectrum generated in the normal dispersion regime of an optical fiber to date is achieved. The exceptional temporal properties of the generated SC pulses are verified experimentally and their applicability for the time-resolved study of molecular dynamics in ultrafast transient absorption spectroscopy is demonstrated. In an additional nonlinear pulse compression experiment, the SC pulses obtained in a short piece of ANDi PCF could be temporally recompressed to sub-two cycle durations by linear chirp compensation. Numerical simulations show that even shorter pulse durations with excellent quality can be achieved by full phase compensation. The concept is further extended into the UV spectral regime by considering tapered optical fibers with submicron waist diameter. It is shown that coherent SC spectra with considerable spectral power densities in the usually hard to reach wavelength region below 300 nm can be generated using these freestanding photonic nanowires. Although technological difficulties currently prevent the fabrication of adequate nanofibers, the concept could be experimentally verified by coherent visible octave-spanning SC generation in tapered suspended core fibers with ANDi profile. The work contained in this thesis therefore makes important contributions to the availability and applicability of fiber-based broadband coherent SC sources with numerous high-impact applications in fundamental science and modern technology. / AFRIKAANSE OPSOMMING: Die konsep van breëband koherente superkontinuum (SK) in alles-normaal dispersiewe (ANDi) vesels in die naby-infrarooi, sigbare en ultraviolet (UV) spektrale gebiede word voorgestel en in detail ondersoek. In numeriese studies word eksplisiete ontwerpskriteria vasgestel vir ANDi fotoniese kristal vesel (FKV) ontwerpe wat dit moontlik maak om plat en gladde ultra-breë spektrale profiele te genereer sonder noemenswaardige fynstruktuur en met uitstekende stabiliteit en koherensie eienskappe. Die sleutel voordeel van SK genering in ANDi vesels is die behoud van ’n enkele ultrakort puls in tyd met ’n gladde en saamdrukbare fase distribusie. In die numeriese ondersoek van die SK generering is die dinamika van fase selfmodulering geïdentifiseer as die dominante nie-lineêre effek wat verantwoordelik is vir die nie-lineêre spektrale verbreding. Daar word voorts aangetoon dat die koherensie eienskappe, spektrale bandwydte en saamdrukbaarheid in tyd onafhanklik is van die inset pulsduur vir konstante drywing. Die numeriese voorspellings stem uitstekend ooreen met die eksperimentele resultate wat verkry is met twee ANDi FKVÕs wat optimeer is vir die naby-infrarooi en sigbare spektrale gebied. In hierdie eksperimente is die breedste SK spektrum gegenereer wat tot hede in die normaal dispersiewe regime met ’n optiese vesel behaal is. Die besondere eienskappe van die genereerde SK pulse is eksperimenteel bevestig en die toepasbaarheid vir tyd opgelosde studie van molekulêre dinamika is gedemonstreer. In ’n addisionele nie-lineêre puls kompressie eksperiment is SK pulse verkry in ’n kort stuk ANDi FKV wat in tyd saamgedruk kon word tot sub-twee siklus tydsduur deur liniêre tjirp kompensering. Numeriese simulasies toon aan dat selfs korter pulse met uitstekende kwaliteit behaalbaar is met volledige fase kompensasie. Die konsep is verder uitgebrei na die UV spektrale gebied deur ’n koniese vesel te beskou met sub-mikron diameter. Daar is aangetoon dat koherente SK spektra met noemenswaardige spektrale drywing in die golflengte gebied onder 300 nm, wat gewoonlik as moeilik toeganklik beskou word, bereik kan word deur hierdie vrystaande fotoniese nano-vesels aan te wend. Alhoewel tegnologiese probleme die vervaardiging van voldoende nano-vesels verhinder, kon die konsep eksperimenteel bewys word deur koherente sigbare oktaafspannende SK te genereer in koniese gesuspendeerde kern vesels met ’n ANDi profiel aan te wend. Die werk wat in die tesis vervat is, maak dus belangrike bydraes tot die beskikbaarheid en toepasbaarheid van vesel gebaseerde breëband koherente SK bronne met verskeie hoë impak toepassings in fundamentele wetenskap en moderne tegnologie.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2009. / The PBMR has called for research into the possibility of distributed in-core temperature measurement. In this thesis, several methods for distributed temperature measurement in high-pressure, -radiation and -temperature environments have been investigated by means of a literature study. The literature study has revealed FBG temperature sensors as the most feasible solution to the temperature measurement challenge. Various parameters affecting the propagation of light in optical fibres and consequently the FBG reflection profile was researched. The differential equations describing FBG structures were solved and implemented in Matlab in order to simulate WDM of a distributed FBG sensing system. Distributed sensing with apodized FBGs written in sapphire optical fibre show the most promise of becoming a solution to the measurement challenge. However, practical testing of sapphire FBGs exposed to the environment in the PBMR core is required. With this long-term goal in mind, a general test platform for FBG temperature sensors was assembled. A heater controller was built for a specialized fibre heating element capable of controlling the temperature of a single FBG up to 1600 C. Temperature measurement using wavelength division multiplexing of apodized FBGs written in silica optical fibre were demonstrated in the test platform with great success. The measured results corresponded very well with the theory. Finally, the implementation of FBGs in the PBMR is discussed and recommendations are made for future work

published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

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