Free Spectral Range Matched Interrogation (FSRMI) technique for wavelength demodulation of fiber Bragg grating sensors. We designed and tested a new wavelength demodulation system based on free-spectral-range-matched interrogation which employs a tunable fiber Fabry-Perot interferometer (FPI) and a multi-channel bandpass filter. This technique was deployed to test fiber Bragg gratings (FBG), long period gratings (LPG) and tilted fiber Bragg gratings (TFBG). In the experimental setup, a broadband source launches light into a fiber Bragg grating under test and the reflection/transmission spectrum is fed into a tunable FPI. By tuning an external bias applied to the FPI, the transmission spectrum of FPI scans over a wavelength range. The input optical signal is therefore selectively passed through the FPI and then fed into a four-channel bandpass filter followed by four photodetectors. The optical signal is converted to electrical signal by the photodiodes and is acquired by a data acquisition system. Since a bandpass filter with four channels are used in this interrogation system it can scan four distinguished wavelength ranges simultaneously and thus the scan rate is four time faster. We used this setup for doing some temperature and strain sensitivity measurements on some fiber gratings. Strain sensitivity measurements were done on FBG, TFBG and LPG and temperature sensitivity measurements were performed on TFBG. The strain and temperature sensitivity coefficients of these fiber Bragg grating sensors were obtained from experimental data. Our results show the potential of the integration of the FSRMI system with fiber Bragg gratings for temperature and strain multiple-sensor arrays with high sampling speed and high accuracy.

Free Spectral Range Matched Interrogation (FSRMI) technique for wavelength demodulation of fiber Bragg grating sensors. We designed and tested a new wavelength demodulation system based on free-spectral-range-matched interrogation which employs a tunable fiber Fabry-Perot interferometer (FPI) and a multi-channel bandpass filter. This technique was deployed to test fiber Bragg gratings (FBG), long period gratings (LPG) and tilted fiber Bragg gratings (TFBG). In the experimental setup, a broadband source launches light into a fiber Bragg grating under test and the reflection/transmission spectrum is fed into a tunable FPI. By tuning an external bias applied to the FPI, the transmission spectrum of FPI scans over a wavelength range. The input optical signal is therefore selectively passed through the FPI and then fed into a four-channel bandpass filter followed by four photodetectors. The optical signal is converted to electrical signal by the photodiodes and is acquired by a data acquisition system. Since a bandpass filter with four channels are used in this interrogation system it can scan four distinguished wavelength ranges simultaneously and thus the scan rate is four time faster. We used this setup for doing some temperature and strain sensitivity measurements on some fiber gratings. Strain sensitivity measurements were done on FBG, TFBG and LPG and temperature sensitivity measurements were performed on TFBG. The strain and temperature sensitivity coefficients of these fiber Bragg grating sensors were obtained from experimental data. Our results show the potential of the integration of the FSRMI system with fiber Bragg gratings for temperature and strain multiple-sensor arrays with high sampling speed and high accuracy.

76 Abstract: Interrogation tactics This thesis is focused on the interrogation management tactic, ie, in brief, how interrogator should conduct an interrogation to be both legal and successful. My aim in this work was to address the basic complexity of interrogation management and describe the basic procedures and techniques by which interrogator can obtain true testimony from the majority of interrogated groups. Due to the limited scope of this work, I could not incorporate specific areas of interrogation situations (questioning of juvenile, sick, etc.), so I focused mainly on interviews with the three main groups of people interrogated, which are interviews of people who can testify and want to, who want to, but can not and who do not want to testify, though they can, especially in situations where these persons are witnesses or subjects accused. In the first chapter of this thesis I deal with questioning from a general point of view of law, psychology and criminology, wherein most of the views and theories mentioned can be related to almost all specific interrogation situations. In this chapter I provided the psychological aspect of the interrogation a little more space than I originally intended, but I think it is substantiated. The psychological side of the interrogation situation is very complicated...

[pt] Este trabalho apresenta um sistema de interrogação de sensores a rede de Bragg em fibras ópticas, baseado em reflectometria no domínio do tempo e filtros fixos a rede de Bragg. Utilizando uma fonte de luz pulsada, a posição espectral do sensor é relacionada à razão da intensidade dos pulsos, tornando a detecção independente de variações de intensidade. São abordados aspectos teóricos e experimentais referentes aos princípios de funcionamento desta técnica. Uma vez que a filtragem é feita com redes de Bragg, apenas um circuito de fotodetecção é utilizado e um número reduzido de acopladores/circuladores ópticos é necessário, o sistema possibilita reduzir consideravelmente o custo para a interrogação de um conjunto de sensores. A utilização de apenas um circuito de fotodetecção apresenta a vantagem de manter as mesmas características para todos os pulsos, minimizando influências externas neste circuito como, por exemplo, variações da temperatura ambiente. Foi montada uma bancada de testes para a interrogação de seis sensores. Comparações entre os resultados experimentais e simulados mostram boa concordância. Extrapolações indicam que seria possível interrogar sensores com uma variação espectral de 2 nanômetros, com incertezas menores que 10 picometros, o que é adequado para sensores de temperatura. Análises de interferência entre dois canais adjacentes mostram pouca influência entre eles e são apresentadas opções para diminuir essa interferência. / [en] This work presents a system for the interrogation of fiber- optic Bragg grating sensors based on time domain reflectometry and Bragg grating fixed filters. Using a pulsed light source, the spectral position of the sensor is related to the ratio of two pulses intensities, making detection independent of intensity variations. Theoretical and experimental aspects regarding the working principles of this technique are discussed. Since filtering is accomplished with Bragg grating so that only one photodetection circuit is used and a reduced number of optic couplers/circulators are needed, the system provides a considerable reduction in the cost of interrogation for a set of sensors. Using only one photodetection circuit also has the advantage of maintaining the same characteristics for all pulses, thus minimizing external influences in this circuit, such as variations in the environment temperature. A test stand was assembled for the interrogation of six sensors. Comparisons between experimental and simulated results show a good agreement. Extrapolations indicate that it would be possible to interrogate sensors with a spectral variation of 2 nanometers, with uncertainties lower than 10 pm, which is adequate for temperature sensors. Cross talk analyses between two adjacent channels show small influence between them, and approaches to reduce this interference are presented.