Este trabalho apresenta a gravação e caracterização de redes de Bragg em fibras óticas (FBGs), com comprimentos de onda otimizados para a banda do visível, a partir de pulsos de laser femtossegundo em UV ajustados por um oscilador paramétrico ótico (OPO – optical parametric oscillator). Para tal propósito foi usado o método de inscrição direta sob máscara de fase, tendo como base diferentes fibras óticas previamente hidrogenadas com vista a incrementar a sua fotossensibilidade. Durante o processo de gravação dos sensores a fibra ótica, as FBGs foram monitoradas espectralmente em reflexão e posteriormente caracterizados em temperatura e deformação longitudinal, para a análise dos seus coeficientes de sensibilidades; seus principais parâmetros pós-gravação foram analisados comparativamente em relação às redes de Bragg funcionais na faixa espectral do infravermelho. / In this work, a visible wavelength fiber Bragg gratings (FBGs) were produced using ultrafast laser pulses adjusted with an OPO (optical parametric oscillator) to 248 nm UV femtosecond laser source. For that purpose it was employed the normal phase-mask method and different fibers loaded with hydrogen previously, in order to increase its photosensitivity. During de process the spectral characteristics were analyzed in terms of reflection as well as temperature and longitudinal deformations were made to analyze the post inscription main parameters of sensitivity comparing with IR spectral range produced FBGs.

Este trabalho apresenta a implementação do sistema de gravação de redes de período longo, através da técnica de incidência lateral de radiação ultravioleta ponto-a-ponto, no Laboratório de Laser da UTFPR. Foram escritas redes em fibras óticas com o uso de um laser de Nd:YAG operando em 266 nm. A evolução espectral das redes foi analisada tanto durante o processo de escrita quanto após o seu término, ao longo de intervalos que variaram de 1 a 595 horas. Essas redes foram submetidas a várias caracterizações com vistas à sua aplicação no sensoriamento de parâmetros físico-químicos. Na avaliação da sensibilidade ao índice de refração do meio externo às redes, foram utilizados fluidos com índices de refração entre 1,0000 e 1,4315. Registraram-se alterações na sensibilidade térmica de valores negativos para positivos, para variações de temperatura de até 24°C, com mudanças de comportamentos lineares para não lineares, dependendo do índice de refração do meio. No ensaio para caracterização da resposta às deformações longitudinais a rede analisada demonstrou-se pouco sensível, com um valor obtido de sensibilidade de -0,19 ± 0,15 pm/µe na faixa de 0 a 125 µe. Foram feitos testes da caracterização térmica desses dispositivos, utilizando um elemento Peltier e um forno de laboratório. Com o uso do elemento Peltier as redes de período longo passaram por ciclos de aquecimento e resfriamento compreendidos entre -1,5°C e 61,1°C. Já no forno de laboratório, as redes chegaram a ser submetidas a temperaturas que variaram de 25°C a 1200°C sem serem completamente apagadas. Uma das questões experimentais mais determinantes foi a investigação da estabilização térmica das redes. Para tanto foram testados e comparados dois diferentes processos de estabilização. O primeiro consistiu em submeter a rede a ciclos de recozimento seguidos de resfriamento lento e o segundo a ciclos de recozimento seguidos de resfriamento brusco, nos quais a máxima temperatura atingida pelas redes foi de 425°C. O segundo método demonstrou-se mais eficaz para o propósito de estabilização térmica. A rede estabilizada mostrou uma sensibilizada térmica não linear que variou de -0,044 nm/°C quando aquecida de 20°C a 300°C. Em função das características assimétricas inerentes ao processo empregado para escrita das redes, foram realizados ensaios para verificar a viabilidade da utilização desses dispositivos como transdutores para medição de curvatura em diferentes direções, com emprego de redes neurais artificiais para análise desses dados. / This work shows the implementation of a writing system for long-period gratings production, by using a side point-by-point ilumination with ultraviolet light, at Laser Laboratory in UTFPR. Gratings were written in optical fibers with a Nd: YAG laser operating at 266 nm. The spectral evolution of gratings was analyzed both during and after the writing process, along time intervals from 1 to 595 hours. The gratings were submitted to several characterizations aiming its application in physicochemical parameters sensing. For the assessment of gratings sensitivity to the external medium refractive index, fluid samples with refractice indices ranging from 1,0000 to 1.4315 were used. Changes of thermal sensitivity from negative do positive values were quantified, for temperature variations up to 24°C, with behaviours transitioning from linear to nonlinear, depending on the refractive index of external medium. For the studies of sensitivities of longitudinal strain, the analyzed grating showed a low sensitivity value of -0,19±0,15 pm/µe in the range between 0 to 125 µe. A thermal characterization of the produced devices was carried out with a thermo element Peltier and with a laboratory furnace. For the Peltier the gratings were submitted to thermal cycles from -1,5°C to 61.1°C. For the furnace the gratings were exposed to temperatures between 25°C a 1200°C without completely erased. An experimental issue was the investigation about the thermal stabilization of gratings. Two different processes to reach the thermal stabilization were studied: annealing and quenching. The former consisted of annealing cycles with slow cooling whereas the later comprised of thermal cycles with sudden cooling from a maximum temperature of 425°C, the second one revealing to be more efficient to reach the thermal stabilization. The stabilized grating showed a non-linear thermal sensitivity ranging from -0,044 nm/°C within the temperature range from 20°C to 300°C. Owing to the inherent asymmetric characteristics of the process employed to record the gratings, the viability of using such devices as transducers for curvature sensing in different directions was studied, employing artificial neural networks to analyze the data.

Orientador: Hugo Henrique Hernandez Figueroa / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-12T14:40:13Z (GMT). No. of bitstreams: 1 Calixto_GustavoMoreira_M.pdf: 3030225 bytes, checksum: 2cce1022194aa1eebe73e869b225e650 (MD5) Previous issue date: 2008 / Resumo: Este trabalho tem por objetivo apresentar o desenvolvimento de um posicionador eletrônico para estruturas micrométricas e controlado através da porta paralela de um computador. O equipamento desenvolvido é controlado por um software, onde o usuário pode posicionar objetos com passos tridimensionais e micrométricos. Os resultados obtidos foram satisfatórios, visto que o equipamento pode ser aplicado em experimentos onde o posicionamento fino é necessário. / Abstract: This work has the goal to present the development of an electronic positioned for micrometric structures, controlled with a parallel port. The developed equipment is controlled by a software who the user can adjust objects with tridimensional and micrometric steps. The obtained results have been satisfactory, where the equipment might be applied in precise positioning experiments. / Mestrado / Telecomunicações e Telemática / Mestre em Engenharia Elétrica

Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

A novel detection technique to estimate the amount of chirp in fiber Bragg gratings (FBGs) is proposed. This method is based on the fact that reflectivity at central wavelength of FBG reflection changes with strain/temperature gradient (linear chirp) applied to the same. Transfer matrix approach was used to vary different grating parameters (length, strength and apodization) to optimize variation of reflectivity with linear chirp. Analysis is done for different sets of ‘FBG length-refractive index strength’ combinations for which reflectivity vary linearly with linear chirp over a decent measurement range. This work acts as a guideline to choose appropriate grating parameters in designing sensing apparatus based on change in reflectivity at central wavelength of FBG reflection. A novel high sensitive FBG strain sensing technique using lasers locked to relative frequency reference is proposed and analyzed theoretically. Static strain on FBG independent of temperature can be measured by locking frequency of diode laser to the mid reflection frequency of matched reference FBG, which responds to temperature similar to that of the sensor FBG, but is immune to strain applied to the same. Difference between light intensities reflected from the sensor and reference FBGs (proportional to the difference between respective pass band gains at the diode laser frequency) is not only proportional to the relative strain between the sensor and reference FBGs but also independent of servo residual frequency errors. Usage of relative frequency reference avoids all complexities involved in the usage of absolute frequency reference, hence, making the system simple and economical. Theoretical limit for dynamic and static strain sensitivities considering all major noise contributions are respectively of the order of 25 pε/ Hz and 1.2nε /

The demonstration of efficient single-mode fiber (SMF) coupling is a key requirement for the development of a compact, ultra-precise radial velocity (RV) spectrograph. iLocater is a next generation instrument for the Large Binocular Telescope (LBT) that uses adaptive optics (AO) to inject starlight into a SMF. In preparation for commissioning iLocater, a prototype SMF injection system was installed and tested at the LBT in the Y-band (0.970-1.065 mu m). This system was designed to verify the capability of the LBT AO system as well as characterize on-sky SMF coupling efficiencies. SMF coupling was measured on stars with variable airmasses, apparent magnitudes, and seeing conditions for six half-nights using the Large Binocular Telescope Interferometer. We present the overall optical and mechanical performance of the SMF injection system, including details of the installation and alignment procedure. A particular emphasis is placed on analyzing the instrument's performance as a function of telescope elevation to inform the final design of the fiber injection system for iLocater.

No description available.

The purpose of this research was to determine the effect of diameter fluctuations on the sensitivity of sapphire multimode optical fibers used as evanescent wave fluorescence sensors. It was predicted that fluctuations in the diameter of the fiber would act as a series of bi-tapers converting lower order modes to higher order modes increasing the evanescent wave penetration depth thereby increasing the excitation of a cladding of fluorescent fluid. Induced fluorescence from the fluid cladding would then couple back into the fiber more efficiently increasing the sensitivity of the sensor. The effect of coiling the fiber on the sensitivity of the sensor was also explored. Coiling the fiber converts lower order modes into higher order modes and increases the sensing length while maintaining a small probe size. However, coiling experiments produced unexpected results and in the course of studying these results a layer of material was discovered coating the surface of the sapphire fibers.

This work encompasses a study of fibre optic devices and micro-resonator cavities and their use as strain sensors, interferometers, and eventually as light sources. We demonstrate the use of a pi-shifted fibre Bragg grating as a strain sensor and quantify its performance through several metrics relevant to its operation in a frequency-locked system. We then discuss the use of waveguide devices as refractive index sensors in a detailed and critical analysis of most of the literature on fibre optic-based interferometry where we define new metrics of assessment that are aimed to be device-independent. We then categorize and study the performance of the literature on fiber-optic refractive index sensors and highlight few key devices of each category based on their performance or design. We relate the performance of these interferometers to various design parameters to outline a way for future researchers to create high-performance devices. Finally, we study light emission in dye-loaded droplet micro-resonators, which are a promising new platform to generate low-threshold lasing action excited by lasers coupled to the whispering gallery modes of the resonator. We characterize multiple types of emissions in these cavities and pave the way for future microdroplet-based lasers. / Graduate / 2022-08-10

Ph. D.