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Interferómetros modais em fibra óptica para aplicações sensoras
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Abstract(s)
Os sensores em fibra óptica têm vindo a ganhar uma importância crescente na área dos sensores, devido à sua imunidade a interferências electromagnéticas, elevada sensibilidade, peso reduzido, baixas perdas e grande largura de banda. Estes sensores tornam-se importantes porque permitem a medição de um grande número de mensurandos, como por exemplo: estiramento, temperatura, índice de refracção externo e torção. Neste trabalho implementaram-se dois sensores intermodais em fibra óptica e efectuouse a sua caracterização em termos de resposta à temperatura e a variações de índice de refracção, utilizando um analisador de espectros ópticos (OSA). Desenvolveu-se também um programa de simulação, em LabVIEW, que permite analisar diferentes tipos de interferómetros com cavidades ressonantes simples ou múltiplas. Foram avaliadas três configurações distintas: a primeira utilizando uma rede de Bragg (FBG) e a reflexão de Fresnel na extremidade da fibra; a segunda utilizando duas FBGs com características espectrais idênticas, e a terceira utilizando as duas FBGs idênticas combinadas com a reflexão de Fresnel na extremidade da fibra. O programa permite observar o espectro resultante dos interferómetros com cavidades de diferentes comprimentos e aplicar as técnicas de detecção de sinal pseudo-heteródina e três técnicas heteródinas. Simulando incrementos de estiramento, de temperatura ou de alteração do índice de refracção externo aplicados aos interferómetros é ainda possível observar e prever o comportamento do espectro dos sensores e efectuar uma análise da fase e da amplitude dos diversos harmónicos. Implementou-se um sistema que emprega um laser DFB (Distributed FeedBack) e que recorre à instrumentação virtual, em LabVIEW, para registar a resposta dos sensores interferométricos, empregando as técnicas de detecção de sinal utilizadas na simulação. Por último, estudou-se interferómetros com cavidades formadas por CFBGs (Chirped Fiber Bragg Gratings) com intuito de explorar a sua sensibilidade em termos de temperatura e estiramento, e efectuar uma comparação com as cavidades formadas por FBGs normais.
Optical fiber sensors have been gaining a growing importance in the area of sensors, due to their immunity to electromagnetic interference, high sensitivity, low weight, low loss and high bandwidth. These sensors have become important because they allow the measurement of a large number of measurands, such as strain, temperature and external refractive index. In this work two optical fiber intermodal interferometers were implemented to be used as sensors and their characterization was performed by changing temperature and refractive index and registering their spectral response with an optical spectrum analyzer (OSA). We have developed a simulation program that allows LabVIEW to analyze different types of interferometers with simple or multiple resonant cavities. Three different fiber optic interferometric configurations were tested: the first, using a single fiber Bragg grating (FBG) and the Fresnel reflection at the end of the fiber; the second using two consecutive spectrally identical FBGs; and the third combining the two identical FBGs with the Fresnel reflection at the end of the fiber. The simulation program enables the visualization of the resulting spectrum of each interferometer considering different cavity lengths and simulating the acquisition performed with a laser, using the pseudo-heterodyne and heterodyne signal detection techniques. Simulating increments of strain, temperature and changes in external refractive index it is possible to observe and predict the behavior of the sensor spectral response and perform an analysis of the phase and amplitude of the different harmonics. We have implemented a system that employs a DFB (Distributed FeedBack) laser and uses LabVIEW virtual instrumentation to record the interferometric sensors response, employing the techniques of signal detection used in the simulation. Finally, we have studied interferometers with cavities formed by CFBGs (Chirped Fiber Bragg Grating) in order to explore its sensitivity in terms of temperature and strain, and do a comparison with cavities formed by normal FBGs.
Optical fiber sensors have been gaining a growing importance in the area of sensors, due to their immunity to electromagnetic interference, high sensitivity, low weight, low loss and high bandwidth. These sensors have become important because they allow the measurement of a large number of measurands, such as strain, temperature and external refractive index. In this work two optical fiber intermodal interferometers were implemented to be used as sensors and their characterization was performed by changing temperature and refractive index and registering their spectral response with an optical spectrum analyzer (OSA). We have developed a simulation program that allows LabVIEW to analyze different types of interferometers with simple or multiple resonant cavities. Three different fiber optic interferometric configurations were tested: the first, using a single fiber Bragg grating (FBG) and the Fresnel reflection at the end of the fiber; the second using two consecutive spectrally identical FBGs; and the third combining the two identical FBGs with the Fresnel reflection at the end of the fiber. The simulation program enables the visualization of the resulting spectrum of each interferometer considering different cavity lengths and simulating the acquisition performed with a laser, using the pseudo-heterodyne and heterodyne signal detection techniques. Simulating increments of strain, temperature and changes in external refractive index it is possible to observe and predict the behavior of the sensor spectral response and perform an analysis of the phase and amplitude of the different harmonics. We have implemented a system that employs a DFB (Distributed FeedBack) laser and uses LabVIEW virtual instrumentation to record the interferometric sensors response, employing the techniques of signal detection used in the simulation. Finally, we have studied interferometers with cavities formed by CFBGs (Chirped Fiber Bragg Grating) in order to explore its sensitivity in terms of temperature and strain, and do a comparison with cavities formed by normal FBGs.
Description
Keywords
Interferometria Instrumentação virtual Sensores em fibra óptica LabView Técnicas de detecção de sinal Interferometry Virtual instrumentation Fiber optic sensors Signal detection schemes Engenharia de Telecomunicações e Redes . Faculdade de Ciências Exatas e da Engenharia