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Holographie adaptative pour la réalisation de capteurs à fibres optiques de très grande sensibilité : application à la détection d’ondes acoustiques sous-marines / Adaptive holographic interferometry for high sensitivity fiber optic sensors : study of underwater acoustic waves detectionPeigné, Arnaud 25 February 2016 (has links)
Ces dernières années, des avancées considérables ont été obtenues dans le domaine des capteurs à fibres optiques, principalement grâce à l’élan des applications industrielles, de plus en plus diverses et nombreuses (monitoring de structures, surveillance, environnement, applications médicales, ….). Cette thèse concerne le domaine des antennes acoustiques SONAR en technologie « tout-optique » Dans ce travail, nous nous sommes intéressés à l’étude d’un capteur de contrainte longitudinale à fibre optique. La modulation de phase optique induite par la contrainte est démodulée par un interféromètre adaptatif basé sur le principe de l’holographie dynamique. Cet interféromètre permet, par essence, (i) le filtrage des perturbations basse fréquence de l’environnement, (ii) un fonctionnement en régime linéaire (iii) la démodulation d’un front d’onde complexe, type speckle issu d’une fibre optique multimode. L’holographie dynamique repose sur l’interaction entre deux ondes optiques dans un milieu non-linéaire. Pour notre application, le milieu non-linéaire retenu est un modulateur spatial de lumière adressé optiquement (OASLM) à 1,55 μm. Nous présentons tout d’abord nos travaux de conception, réalisation et caractérisation de l’interféromètre adaptatif. Nous démontrons ensuite un capteur de contrainte à fibre optique basé sur cet interféromètre. Nous étudions également l’augmentation de sensibilité du capteur par l’utilisation d’une fibre optique multimode. Nous discutons finalement nos résultats et le potentiel de la technologie étudiée au regard de l’application visée. / Fiber optic sensors are a key technology for future developments with a large field of applications ranging from structure health monitoring to medical applications. Due to its high compactness, its electromagnetic immunity and the low transmission losses in the telecom window, optical fibers are very promising for underwater acoustic waves detection. We present a method relying on adaptive holographic interferometry based on two beam coupling in an optically addressed spatial light modulator (OASLM). This method allows filtering the slow phase perturbations coming from the environment directly on the sensing optical fiber. In this work, we will first introduce the OASLM operating at 1,55 μm that we have manufactured and the realization of an adaptive holographic interferometer based on this component. Moreover, we will show that it is possible to associate this demodulation method with a multimode optical fiber to reach a better sensitivity. Finally, we will focus on sensors architectures to evaluate the benefit of this technology compared to conventional techniques.
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Slab-Coupled Optical Fiber Sensors for Electric Field Sensing ApplicationsGibson, Richard S. 20 November 2009 (has links) (PDF)
This dissertation presents the creation of slab coupled optical sensors (SCOS) for electric field sensing applications. SCOS devices utilize the benefits of an optical fiber system for high bandwidth and low electromagnetic interference. These sensors are fabricated by means of mode coupling between a small section of D-shaped optical fiber (D-fiber) with a multi-mode electro-optic slab waveguide. Electric field detection is accomplished by monitoring the behavior of the resonances, seen as transmission dips in the D-fiber transmission, as they shift with electric fields. The novelties of SCOS devices include their small compact nature, potential for sensor multiplexing and a dielectric structure allowing low electromagnetic interference. The SCOS developed in this work been used to measure fields as low as 30 V/m with 1 kHz resolution bandwidth and a high degree of linearity. Due to their compact size they are capable of placement within devices to measure interior electric fields immeasurable by other sensors that are either too large for internal placement or disruptive of the internal fields due to metallic structure. Wavelength multiplexing allows multiple sensors to be placed on a single fiber for mapping electric fields at multiple instances. As an extension, SCOS multiplexing allows the potential for 3-d field sensing by use of multiple electro-optic crystals having orthogonal orientations of the electro-optic axis. This work performs a thorough analysis of SCOS design in order to optimize sensor efficiency for its various applications. Furthermore, the straightforward fabrication process for these sensors is outlined for the development of future uses of these sensors.
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Ionizing Radiation Resistance of Random Hole Optical Fiber for Nuclear Instrumentation and Control ApplicationsAlfeeli, Bassam 03 June 2009 (has links)
Random hole optical fibers (RHOF) offer advantages over other types of microstructured optical fibers (MOFs). They are inexpensive and easy-to-make when compared to the high cost of ordered hole MOFs. They also have unique characteristics since they contain open and closed holes. The open holes contain ambient air under normal conditions and the closed holes contain residual gases from the fabrication process at certain pressure. The objective of this research work was to investigate the radiation resistance of Random Hole Optical Fibers (RHOF) for possible use as both sensing element and data transmission medium in nuclear reactor instrumentation and control applications.
This work is motivated by the demand for efficient, cost effective, and safe operation of nuclear power plants, which accounts for more than 14% of the world's electricity production.
This work has studied the effect of gamma irradiation on RHOF fibers by comparing their performance to that of standard solid telecommunication fibers and commercially available specialty solid fiber designed to be radiations hardened fiber. The fibers were evaluated at different absorbed dose levels: 12 mGy(Si), 350 mGy(Si), and 7200 Gy(Si) by measuring their radiation induced absorption (RIA) on-line. In the low dose test, the maximum RIA measured in untreated RHOF was approximately 8 dB while the RIA in the untreated MMF fibers reached a maximum at about 28 dB. In the high dose test, the maximum RIA measured in untreated RHOF was 36 dB while RIA in the methanol washed RHOF was only 9 dB. RHOF also demonstrated superior radiation damage recovery time over all of the other fibers tested. Based on the experimental evaluations, it was deduced that RHOFs used in this work are resistant to gamma radiation. and recover from radiation damage at a faster rate compared to other fibers tested. The radiation induced absorption (RIA) at the 1550 nm window in the RHOF fibers could be attributed to the OH absorption band tail. However, the existence of other mechanisms responsible for RIA is also postulated. Some of these mechanisms include bulk and surface defects which are related to the fabrication process and the influence of the gases confined within the RHOF microstructure.
Gamma radiation resistance of RHOFs can be attributed to the lack of dopants and also possibly the inherent OH and nitrogen content. The behavior of thermally annealed RHOF and their fast recovery is in favor of this hypothesis. / Master of Science
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Extrinsic Fabry-Perot Interferometer System Using Wavelength Modulated SourceMeller, Scott A. 04 December 1996 (has links)
Interferometric optical fiber sensors have proved many orders of magnitude more sensitive than their electrical counterparts, but they suffer from limitations in signal demodulation caused by phase ambiguity and complex fringe counting when the output phase difference exceeds one fringe period. Various signal demodulation methods have been developed to overcome some of the these drawbacks with limited success. This thesis proposes a new measurement system for the extrinsic Fabry-Perot interferometer (EFPI) sensor. Using a wavelength modulated source and a novel extended-gap EFPI, some of the limitations of interferometric signal demodulation are overcome. By scanning the output wavelength of a multilongitudinal mode laser diode through current modulation, the EFPI sensor signal is scanned through multiple fringes. Gap movement is then unambiguously determined by monitoring the phase of the multiple fringe pattern. / Master of Science
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Optical Fiber Sensors for Temperature and Strain MeasurementZhou, Dapeng January 2010 (has links)
Optical fiber sensors have already been developed from the experimental stage to practical applications in the past 20 years. There is no doubt that this technology can bring a wealth of applications, ranging from sensors in medical industry, aerospace and wind-energy industries, through to distributed sensors in oil and gas industry. Among a large amount of physical and chemical parameters which optical fiber sensors could measure, temperature and strain are the most widely studied. This thesis presents several low-cost optical fiber sensor configurations primarily for temperature and strain measurement.
Several basic optical fiber components which are good candidates as optical fiber sensors are used in our experiments, such as fiber Bragg gratings (FBGs), multimode fibers (MMFs), small-core dispersion compensation fibers (SCDCFs), high-birefringence fiber loop mirrors (HBFLMs), and polarization-maintaining photonic crystal fibers (PMPCFs). Temperature and strain cross sensitivity is a crucial issue when designing high performance optical fiber sensors, since most of the sensing components are both sensitive to temperature and strain. This would introduce an error when measuring each of them independently. We developed several schemes to overcome this problem by cascading an FBG and a section of MMF, inserting an FBG into an HBFLM, and space division multiplexing two HBFLMs. By measuring the wavelength shifts of the two independent components' spectra in each scheme, simultaneous measurement of temperature and strain could be achieved. However, all the above schemes need optical spectrum analyzers to monitor the spectral information, which increases the cost of the system and limits the operation speed. In order to avoid using optical spectrum analyzers, we use an intensity-based interrogation method with MMFs and HBFLMs as edge filters. By measuring power ratio changes, instead of monitoring spectra shifts, simultaneous measurement of temperature and strain could be realized with a low cost and high speed. The resolutions of the above five configurations are between 0.26 - 1.2 ^oC in temperature and 9.21 - 29.5 με in strain, which are sufficient for certain applications.
We also investigate the sensing applications with the SCDCF. Since the cutoff wavelength of this kind of fiber is around 1663 nm, which makes it naturally an MMF in the wavelength range of 1550 nm. By slightly offsetting the core of the SCDCF with respect to that of the standard single-mode fiber (SMF), a high extinction ratio could be achieved with almost 9 dB. When a lateral force (lateral strain) applied on the SCDCF, extinction ratio will decrease. The change of the extinction ratio is almost independent of temperature variation. The measured extinction ratio change has a good quadratic relationship with respect to applied lateral force. This feature could be used to measure lateral force (lateral strain). In addition, we also use this feature to realize simultaneous measurement of both the longitudinal strain and lateral strain, since the applied longitudinal strain results in the whole spectrum shift. Moreover, a miniature high temperature sensor could also be made using the SCDCF. One end of a 4-mm long SCDCF is spliced directly to SMF with the other end cleaved. By monitoring the reflection spectrum of the SCDCF, temperature information could be obtained. This sensing head is very compact and could realize high temperature measurement up to 600 ^oC.
Recently, a kind of PMPCF has been found to have very small responses to temperature change. This offers an opportunity to measure other parameters without considering temperature influence. We construct a compact 7-mm long transmission-type sensor with this kind of PMPCF. The interference spectrum generated by the coupling of cladding modes and core mode is obtained by slightly offsetting the PMPCF core to SMF core. The experiment shows that the interference spectrum is almost unchanged within the temperature range of 25-60 ^oC. The presented sensor has the potential to be used to measure strain and refractive index in the normal environment without temperature discrimination for practical applications.
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Optical Fiber Sensors for Temperature and Strain MeasurementZhou, Dapeng January 2010 (has links)
Optical fiber sensors have already been developed from the experimental stage to practical applications in the past 20 years. There is no doubt that this technology can bring a wealth of applications, ranging from sensors in medical industry, aerospace and wind-energy industries, through to distributed sensors in oil and gas industry. Among a large amount of physical and chemical parameters which optical fiber sensors could measure, temperature and strain are the most widely studied. This thesis presents several low-cost optical fiber sensor configurations primarily for temperature and strain measurement.
Several basic optical fiber components which are good candidates as optical fiber sensors are used in our experiments, such as fiber Bragg gratings (FBGs), multimode fibers (MMFs), small-core dispersion compensation fibers (SCDCFs), high-birefringence fiber loop mirrors (HBFLMs), and polarization-maintaining photonic crystal fibers (PMPCFs). Temperature and strain cross sensitivity is a crucial issue when designing high performance optical fiber sensors, since most of the sensing components are both sensitive to temperature and strain. This would introduce an error when measuring each of them independently. We developed several schemes to overcome this problem by cascading an FBG and a section of MMF, inserting an FBG into an HBFLM, and space division multiplexing two HBFLMs. By measuring the wavelength shifts of the two independent components' spectra in each scheme, simultaneous measurement of temperature and strain could be achieved. However, all the above schemes need optical spectrum analyzers to monitor the spectral information, which increases the cost of the system and limits the operation speed. In order to avoid using optical spectrum analyzers, we use an intensity-based interrogation method with MMFs and HBFLMs as edge filters. By measuring power ratio changes, instead of monitoring spectra shifts, simultaneous measurement of temperature and strain could be realized with a low cost and high speed. The resolutions of the above five configurations are between 0.26 - 1.2 ^oC in temperature and 9.21 - 29.5 με in strain, which are sufficient for certain applications.
We also investigate the sensing applications with the SCDCF. Since the cutoff wavelength of this kind of fiber is around 1663 nm, which makes it naturally an MMF in the wavelength range of 1550 nm. By slightly offsetting the core of the SCDCF with respect to that of the standard single-mode fiber (SMF), a high extinction ratio could be achieved with almost 9 dB. When a lateral force (lateral strain) applied on the SCDCF, extinction ratio will decrease. The change of the extinction ratio is almost independent of temperature variation. The measured extinction ratio change has a good quadratic relationship with respect to applied lateral force. This feature could be used to measure lateral force (lateral strain). In addition, we also use this feature to realize simultaneous measurement of both the longitudinal strain and lateral strain, since the applied longitudinal strain results in the whole spectrum shift. Moreover, a miniature high temperature sensor could also be made using the SCDCF. One end of a 4-mm long SCDCF is spliced directly to SMF with the other end cleaved. By monitoring the reflection spectrum of the SCDCF, temperature information could be obtained. This sensing head is very compact and could realize high temperature measurement up to 600 ^oC.
Recently, a kind of PMPCF has been found to have very small responses to temperature change. This offers an opportunity to measure other parameters without considering temperature influence. We construct a compact 7-mm long transmission-type sensor with this kind of PMPCF. The interference spectrum generated by the coupling of cladding modes and core mode is obtained by slightly offsetting the PMPCF core to SMF core. The experiment shows that the interference spectrum is almost unchanged within the temperature range of 25-60 ^oC. The presented sensor has the potential to be used to measure strain and refractive index in the normal environment without temperature discrimination for practical applications.
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Design et développement d'un capteur à fibre optique pour la détection d'hydrogène / Design and development of an optical fiber sensor for hydrogen detectionPerrotton, Cédric 13 January 2012 (has links)
La détection de l'hydrogène est une priorité environnementale. De nombreux capteurs à hydrogène ont déjà été développés, mais aucun d’eux ne répond aux exigences de l'industrie. Les capteurs à fibres optiques, électriquement isolés, sont d’excellents candidats pour fonctionner dans des environnements explosifs. Notre objectif est de développer un capteur à fibres optiques intrinsèque par Résonance de Plasmon de Surface pour la détection d’hydrogène. Dans cette thèse, nous étudions deux designs de capteurs à hydrogène. Le premier, basé sur la modulation d'amplitude, se compose d'une couche mince de Pd déposé sur le cœur de la fibre multimode, après avoir enlevé la gaine optique. Dans le second, basé sur la modulation de longueur d'onde, nous remplaçons la couche de Pd par un empilement de couches (Au / SiO 2 / Pd). Dans cette thèse, nous démontrons que les capteurs plasmoniques peuvent être une solution pour développer des capteurs à hydrogène fiables et rapides. Enfin, nous étudions des alliages de Mg comme matériaux sensibles à l’hydrogène afin d’optimiser la plage de détection des capteurs à hydrogène. / Hydrogen detection is an environmental priority. Numerous hydrogen sensors have been developed, but none of them meet the industry requirements. Optical fiber sensors, electrically isolated, are excellent candidates for operating in explosive environments. Our goal is to develop an intrinsic optical fiber sensor based on Surface Plasmon Resonance. In this thesis, we study two optical fiber hydrogen sensors. The first sensor, based on amplitude modulation, consists of a thin Pd layer deposited on the multimode fiber core, after removing the optical cladding. The second design, based on wavelength modulation, consists of replacing the single Pd layer by a Au/ SiO2/ Pd multilayer stack. We demonstrate in this thesis that plasmonic sensors may be a solution to develop fast and reliable fiber hydrogen sensors. Finally, we study Mg alloys as hydrogen sensitive material in order to improve the detection range of hydrogen sensors.
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Electric Field Sensing in a Railgun Using Slab Coupled Optical Fiber SensorsNoren, Jonathan Robert 27 March 2012 (has links) (PDF)
This thesis discusses the application of Slab Coupled Optical Fiber Sensors (SCOS) in a railgun. The specific goal of these sensors is to create an electric field profile at a specific point in the gun as the armature passes. The thesis explores the theory that powers the railgun as well as the principles of the SCOS sensors. It also elaborates on the various noise sources found throughout the detection system and concludes with a summary of the various field tests that were performed throughout this project. There are many benefits to using a railgun over traditional weapons in the field. These benefits not only include both safety and cost, but also greater overall defense capabilities. Unfortunately, the velocity skin effect (VSE) causes the current railgun designs to have limited life span through wear on the rails. In order to develop superior railguns and railgun armatures, the accurate detection of the VSE through measuring the electric field is of great interest. We used a SCOS, a small directionally precise dielectric sensor, as a small sensing area is required to be able to measure the electric fields inside of the rail gun. The actual usage of the SCOS within the railgun produced an additional set of problems that are not commonly encountered in the lab. The chief amongst these was noise from strain, RF pickup, and phase noise. This thesis also reports various methods used to reduce each of these noise sources.
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[en] EFFECTS AND APPLICATIONS OF NON-HOMOGENEOUS STRAINS IN BRAGG GRATINGS / [pt] EFEITOS E APLICAÇÕES DE DEFORMAÇÕES NÃO HOMOGÊNEAS EM REDES DE BRAGGADRIANO FERNANDES PINHO 21 September 2005 (has links)
[pt] Redes de Bragg em fibras ópticas (RBF) são formadas por
modulações periódicas
introduzidas no índice de refração do núcleo de fibras
ópticas. Estes componentes
comportam-se como filtros espectrais de banda passante, ou
seja, quando iluminados por
um sinal óptico de banda larga, refletem apenas uma fina
fatia espectral de luz, cujo
centro, o comprimento de onda de Bragg, é proporcional ao
período espacial da
modulação no índice de refração. As RBF têm encontrado
aplicações importantes no
sensoriamento das mais diversas grandezas, sendo hoje
utilizadas em sistemas de
monitoramento para vários segmentos industriais, tais como
os setores de petróleo e gás,
construção civil e aeroespacial, que, estima-se, respondem
em conjunto por cerca de 70%
destas aplicações. Em diversas situações o sensoriamento
com RBF baseia-se em
medidas indiretas da grandeza de interesse, sendo
empregados mecanismos de
transdução que transformam variações do mensurando em
deformações na fibra óptica.
Nestes casos, um problema que deve ser tratado com atenção
é o acoplamento entre
temperatura e deformação, uma vez que as RBF são sensíveis
a estas duas variáveis. Não
raro, a alternativa é utilizar simultaneamente duas RBF
para obter-se a compensação de
temperatura na medida de deformação.
Este trabalho apresenta um estudo sobre deformações não
homogêneas em redes de
Bragg e discute aplicações de duas técnicas que podem ser
utilizadas como alternativas
para eliminar o efeito da temperatura no sensoriamento de
deformação com apenas uma
RBF. A primeira delas explora a birrefringência óptica
induzida na RBF por
carregamentos transversais à fibra óptica. A segunda
baseia-se nos efeitos sobre o
espectro refletido pela rede de Bragg quando submetida a
um campo de deformações
longitudinais não uniformes ao longo da direção axial da
fibra óptica. No trabalho são
apresentados protótipos e dispositivos que exploram tais
técnicas para a medida simultânea de pressão e
temperatura. Esses protótipos foram projetados com auxílio
de
ferramentas CAD e modelados utilizando-se o método de
elementos finitos em conjunto
com a teoria de modos acoplados da Rede de Bragg. As
previsões obtidas utilizando-se
estes modelos mostraram-se bastante próximas dos
resultados das implementações
experimentais dos protótipos, indicando que a metodologia
de modelagem desenvolvida
pode ser aplicada nos projetos de transdutores baseados
nas duas técnicas estudadas. / [en] Fiber Bragg gratings (FBG) are modulations in the
effective refractive index of
optical fibers, introduced in a small length along the
fiber core. Such components operate
as narrow band reflective filters, that is, when
illuminated by a broad-band light source,
they reflect a narrow spectral band centered at a specific
wavelength, the Bragg
wavelength. This wavelength is proportional to the spatial
period of the refractive index
modulation. Fiber Bragg gratings have find an increasing
number of applications as
sensors for different quantities, and today are being
employed as part of permanent, real
time monitoring systems in various industrial segments.
The oil and gas sector, together
with civil infrastructure and aeronautics and aerospace,
account for almost 70% of this
applications. In a number of situations, FBG sensing is
based on indirect measurements
of the quantity being monitored, and a transduction
mechanism is employed to transform
changes in the measured quantity in strain sensed by the
optical fiber. Since the FBG is
sensitive to strain and temperature, proper temperature
compensation is always
necessary. Usually, a second grating is employed to
simultaneously measure temperature
and strain, performing the required compensation.
This thesis presents a study on effects due to non-
homogeneous strains in the
Bragg grating and discusses application of two different
techniques, based on these
effects, to allow temperature compensated strain
measurement using a single FBG. The
first technique explores strain induced optical
birefringence when the fiber is loaded
transversely. The second technique is based on changes in
the spectral shape of the light
signal reflected by the grating when subjected to non
homogeneous axial strain fields.
Prototypes of pressure and temperature transducers based
on these techniques have been
developed. These prototypes have been designed by
employing CAD techniques and
modeled using the finite element method in conjunction
with the theory of coupled
modes for fiber Bragg gratings. Comparisons between
results provided by theoretical models and experimental
realizations of the prototypes are very close,
demonstrating that
the developed approach can be applied to design
transducers based on the discussed
techniques. Results obtained with the proposed pressure
and temperature sensors are also
encouraging indicating that the two techniques are
suitable for industrial applications.
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Advantages and limitations of distributed optical-frequency-domain-reflectometry for optical fiber-based sensors in harsh environments / Avantages et limites des capteurs à fibre optique distribuée basés sur la réflectométrie optique dans le domaine fréquentiel en milieux radiatifs / Vantaggi e limiti dei sensori a fibra ottica distribuiti basati sulla riflettometria ottica nel dominio delle frequenze in ambienti radiativiRizzolo, Serena 04 April 2016 (has links)
L’accident de Fukushima-Daiichi du 11 Mars 2011 a fortement marqué l'industrie nucléaire en mettant en évidence plusieurs faiblesses dans le contrôle des systèmes critiques qui assurent la sécurité des centrales nucléaires, en particulier, lors de conditions accidentelles. Cette thèse a été réalisée en collaboration avec AREVA, groupe industriel français actif dans le domaine de l'énergie, avec l’objectif de réaliser des capteurs à fibres optiques résistants aux contraintes sévères d'une centrale nucléaire et, en particulier, de surveiller la température et le niveau de l'eau à l'intérieur d’une piscine de stockage de combustible. La thèse est composée de deux parties organisées en 7 chapitres. Dans la première partie, le chapitre 1 traite des phénomènes contribuant à l'atténuation de la lumière au cours de sa propagation dans la fibre et donne un aperçu des effets des radiations sur les fibres optiques. Pour identifier la technique la plus prometteuse adaptée aux applications visées par AREVA, le chapitre 2 propose un état de l’art sur les capteurs distribués à fibres optiques existants avec une attention particulière à leur emploi dans des environnements radiatifs. La dernière partie de ce chapitre est consacrée à la description détaillée de l’OFDR qui est la technique retenue pour cette application. La deuxième partie est consacrée à la présentation des résultats obtenus et leur analyse. Le chapitre 3 présente le détail des irradiations et des traitements thermiques, les échantillons retenus et les bancs de mesure utilisés. Afin de déterminer la meilleure combinaison fibre/technique par rapport à l’application visée, une étude systématique des capteurs distribués de température et de contrainte a été réalisée. Les effets permanents des rayonnements (niveaux de dose du MGy) sont étudiés dans le chapitre 4. Le chapitre 5 illustre des mesures in situ sur les fibres résistantes aux radiations pour comprendre les effets combinés de la température et des radiations (rayons X), effets représentatifs des conditions nominales et accidentelles des piscines de stockage. Enfin, nous avons développé un prototype de capteur de niveau d’eau pour les piscines de combustible qui est décrit dans le chapitre 6. Ensuite, les principales conclusions et les perspectives de ce travail de thèse sont discutées / Fukushima-Daiichi event on March 11th, 2011, signed a turning point in nuclear industry by highlighting several weaknesses in the control of critical systems that ensure the safety in nuclear power plant (NPP) operating, particularly, in accidentals conditions. This PhD thesis has been carried out in collaboration with AREVA, the French industrial group active in the energy domain, with the aim of realizing optical fiber sensors resistant to the harsh environment constraints of a NPP and, in particular, to monitor temperature and water level several parameters inside the spent fuel pools (SFPs). It consists of two parts organized in 7 chapters. In the first part, chapter 1 deals with the phenomena contributing to the light attenuation during its propagation along the fiber and gives an overview on the radiation effects on optical fibers. To identify the most promising technique suitable for AREVA needs, in chapter 2 is reported the state-of-the-art on the distributed OFSs with particular attention to their employment in radiation environments. The last part of this chapter is devoted to the detailed description of the OFDR that is the selected sensor technique for this application. The second part is devoted to present and discuss the obtained results. Chapter 3 gives the experimental details on radiation and thermal treatments, investigated samples and used setups. In order to determine the best fiber/setup combination, a systematic study on temperature and strain distributed sensors was carried out in relation to the harsh constraints demanded from the application. The permanent radiation (MGy dose levels) effects on different fiber classes are investigated in Chapter 4. Chapter 5 illustrates in situ measurements on radiation resistant fibers to understand the combined temperature and radiation (X-rays) effects representative of the SFP nominal and accidental conditions. Simultaneously, we have developed the OFS design for its integration at SFP facility. The prototype is described and its performance is evaluated in chapter 6. Then, the main conclusion and perspective are discussed / L'incidente di Fukushima-Daiichi dell’11 marzo 2011 ha segnato un punto di svolta per l’industria nucleare, mettendo in evidenza diversi punti deboli nel controllo di sistemi critici che garantiscono la sicurezza nelle centrali, in particolare in condizioni di incidente. Questa tesi è stata condotta in collaborazione con AREVA, il gruppo industriale francese attivo nel settore dell'energia, con l'obiettivo di produrre sensori a fibra ottica resistenti alle condizioni estreme di una centrale nucleare e, in particolare, per controllare diversi parametri all'interno di una piscina di stoccaggio di combustibile nucleare, quali la temperatura e il livello dell'acqua. La tesi si compone di due parti organizzate in 7 capitoli. Nella prima parte, il capitolo 1 riguarda i fenomeni che contribuiscono all'attenuazione della luce durante la sua propagazione nella fibra e permette di comprendere gli effetti della radiazione sulle fibre ottiche. Per identificare la tecnologia più promettente per le esigenze di AREVA, nel capitolo 2 é discusso lo stato dell’arte sui sensori distribuiti con particolare attenzione alle loro performance in ambienti radiativi. L'ultima parte di questo capitolo è dedicato ad una descrizione dettagliata della tecnica OFDR che è la tecnologia scelta per questa applicazione. La seconda parte è dedicata a presentare e discutere i risultati. Il capitolo 3 fornisce i dettagli sui campioni studiati e i trattamenti effettuati su di essi e descrive il setup utilizzato. Per determinare la migliore combinazione fibra/tecnica per l’applicazione prevista, è stato eseguito uno studio sistematico sulla risposta alla radiazione dei sensori distribuiti di temperatura e strain. Glieffetti permanenti della radiazione (dosi dell’ordine del MGy) su diverse classi di fibre, resistenti e sensibili alle radiazioni, sono discussi nel capitolo 4. Il capitolo 5 riporta le misure in situ sulle fibre resistenti alla radiazione per investigare gli effetti combinati di temperatura e radiazioni (raggi X) rappresentativi delle condizioni operative e accidentali nelle piscine di stoccaggio. Infine, abbiamo sviluppato un prototipo di sensore del livello dell’acqua nelle piscine di stoccaggio che è descritto nel capitolo 6. In seguito, le principali conclusioni e le prospettive sono discusse
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