Durabilité des capteurs à fibres optiques sous environnement radiatif

Nous avons étudié le comportement de capteurs répartis par rétrodiffusion Brillouin dans des fibres optiques soumises à des environnements radiatifs pour la mesure de contraintes thermomécaniques. Le premier chapitre présente le besoin de mesure répartie par fibre optique pour le stockage sur site géologique des déchets radioactifs de moyennes et hautes activités vie longue (MA-VL et HA-VL) envisagé par l Andra. Le second chapitre précise la méthodologie utilisée durant la thèse. Le choix de fibres optiques utilisées ainsi que les moyens de caractérisation exploités pour étudier l évolution de la réponse des fibres optiques y sont présentés. Dans la troisième partie, nous montrerons l influence de l exposition aux rayonnements UV sur le spectre Brillouin de certaines fibres optiques. La réponse de la fibre optique fortement dopées au Germanium montre une grande sensibilité de l atténuation et des changements sur la fréquence Brillouin induits par des rayonnements UV. Dans la quatrième partie, nous montrerons les résultats de la méthodologie appliquée pour la caractérisation de la réponse capteurs répartis par rétrodiffusion Brillouin dans diverses fibres optiques au cours des irradiations gamma. Ces études ont permis de converger vers la conception d une fibre optique spéciale dopée au Fluor qui est adaptée l application de surveillance d alvéole de stockage de déchets radioactifs de type HA-VL et MA-VL pendant une échelle séculaireWe studied the behavior distributed Brillouin sensor in optical fibers under radiative environments for strain and temperature measurements. The first chapter presents the need for distributed measurement by using optical fiber for the storage of radioactive waste geological site of medium and high long-lived activities (MA- VL and HA-VL) proposed by Andra. The second chapter outlines the methodology used in the thesis. The choice of fiber used and the characterization means operated to study the evolution of the response of the optical fibers are presented. In the third part, we show the influence of exposure to UV radiation on the Brillouin spectrum of several optical fibers. The response of the optical fiber highly doped with Germanium shows high sensitivity on the attenuation and the Brillouin frequency induced by UV radiation. In the fourth section, we show results from our methodology for the characterization of the response Brillouin sensors in various optical fibers during differents gamma irradiation conditions. These studies converge towards the design of a special fluorine -doped optical fiber which is suitable for the application of monitoring of the future site for the storage of radioactive waste type HA- MA- VL and VL for a century scaleST ETIENNE-Bib. électronique (422189901) / SudocSudocFranceF

Discriminated measures of strain and temperature in metallic specimen with embedded superimposed long and short fibre Bragg Gratings

International audienceWe propose a superimposed fibre Bragg gratings device to measure, localize and discriminate strain and temperature effects simultaneously for structural health monitoring purpose. Long period grating (LPG) and fibre Bragg grating (FBG) exhibit different responses to an applied solicitation, thus, strain and temperature influences can be determined separately by measuring the corresponding wavelength shifts. In this paper we present a configuration based on the use of these two gratings types: a LPG and a FBG written in the same fibre section which allows us to discriminate the contributions of these two main solicitations. The sensor is calibrated in a temperature range from 22°C to 120°C, and in a strain range from 0 to 1400 µε. The reported errors are estimated to be within ± 0.4°C and ±5µε respectively. Our sensor is compared to the ones suggested in literature for the discrimination between strain and temperature with Bragg gratings. We propose a parameter E which allows to compare the relative uncoupling efficiency of those techniques. These sensors were embedded and tested in metallic material plates for a validation purpose of structural health monitoring

Sol-gel derived ionic copper-doped microstructured optical fiber: a potential selective ultraviolet radiation dosimeter

International audienceWe report the fabrication and characterization of a photonic crystal fiber (PCF) having a sol-gel core doped with ionic copper. Optical measurements demonstrate that the ionic copper is preserved in the silica glass all along the preparation steps up to fiber drawing. The photoluminescence results clearly show that such an ionic copper-doped fiber constitutes a potential candidate for UV-C (200-280 nm) radiation dosimetry. Indeed, the Cu+-related visible photoluminescence of the fiber shows a linear response to 244 nm light excitation measured for an irradiation power up to 2.7 mW at least on the Cu-doped PCF core. Moreover, this response was found to be fully reversible within the measurement accuracy of this study ( ± 1%), underlying the remarkable stability of copper in the Cu+ oxidation state within the pure silica core prepared by a sol-gel route. This reversibility offers possibilities for the achievement of reusable real-time optical fiber UV-C dosimeters

Coupled experiment/simulation approach for the design of radiation-hardened rare-earth doped optical fibers and amplifiers

We developed an approach to design radiation-hardened rare earth -doped fibers and amplifiers. This methodology combines testing experiments on these devices with particle swarm optimization (PSO) calculations. The composition of Er/Yb-doped phosphosilicate fibers was improved by introducing Cerium inside their cores. Such composition strongly reduces the amplifier radiation sensitivity, limiting its degradation: we observed a gain decreasing from 19 dB to 18 dB after 50 krad whereas previous studies reported higher degradations up to 0°dB at such doses. PSO calculations, taking only into account the radiation effects on the absorption efficiency around the pump and emission wavelengths, correctly reproduce the general trends of experimental results. This calculation tool has been used to study the influence of the amplifier design on its radiation response. The fiber length used to ensure the optimal amplification before irradiation may be rather defined and adjusted to optimize the amplifier performance over the whole space mission profile rather than before integration in the harsh environments. Both forward and backward pumping schemes lead to the same kind of degradation with our active fibers. By using this promising coupled approach, radiation-hardened amplifiers nearly insensitive to radiations may be designed in the future

Design of Radiation-Hardened Rare-Earth Doped Amplifiers Through a Coupled Experiment/Simulation Approach

We present an approach coupling a limited experimental number of tests with numerical simulations regarding the design of radiation-hardened (RH) rare earth (RE)-doped fiber amplifiers. Radiation tests are done on RE-doped fiber samples in order to measure and assess the values of the principal input parameters requested by the simulation tool based on particle swarm optimization (PSO) approach. The proposed simulation procedure is validated by comparing the calculation results with the measured degradations of two amplifiers made with standard and RH RE-doped optical fibers, respectively. After validation, the numerical code is used to theoretically investigate the influence of some amplifier design parameters on its sensitivity to radiations. Simulations show that the RE-doped fiber length used in the amplifier needs to be adjusted to optimize the amplifier performance over the whole space mission profile rather than to obtain the maximal amplification efficiency before its integration in the harsh environment. By combining this coupled approach with the newly-developed RH RE-doped fibers, fiber-based amplifiers nearly insensitive to space environment may be designed in the future

Large and Versatile Plasmonic Enhancement of Photoluminescence Using Colloidal Metallic Nanocubes

Improving phosphor photoluminescence efficiency is a key parameter to boost the performances of many optical devices. In this work, colloidal silver nanocubes, homogeneously spread on a luminescent surface, have proved to help both injecting and extracting light in and out of the photoluminescent layer and hence contributed significantly to the enhancement of the fluorescence. This approach has been applied to two materials: the well-known Y$_3$Al$_5$O$_{12}$:Ce yellow phosphor and an optical quartz. The emission efficiency, for sol-gel derived YAG:Ce layers, has increased of 80\% in the presence of an optimal nanoparticle density -- whereas for quartz, a weakly fluorescent material, the photoluminescence signal can be enhanced by a 200-fold factor. A physical analysis based on simulations shows that the disorder is an important factor and that the surface density of Ag nanoparticles is a crucial parameter

Distributed detection of hydrogen and deuterium diffusion into a single-mode optical fiber with chirped-pulse phase-sensitive optical time-domain reflectometry

For some infrastructures like oil and gas extraction boreholes or radioactive waste repositories, where distributed optical fiber sensors are employed to grant the safety of the facilities, the presence of gas species such as hydrogen or deuterium is one more relevant parameter to monitor. The possibility of employing the same kind of sensors for this purpose is of special interest, reducing the cost by employing a single interrogator, able to measure more than one parameter by simply employing an adequate sensing fiber. To meet this goal, we present here a sensor based on Chirped Pulse Phase sensitive Optical Time Domain Reflectometry, which is able to detect these species while they diffuse into the silica fiber core. Its ability to measure the induced change of its refractive index with a sensitivity around 10 8 has allowed determining hydrogen concentration in the silica core with precision in the order of 10 3 mol/m3 and spatial resolution ~6 m, while also providing an indirect measurement of the solubility of deuterium in a standard telecom-grade optical fiber.Commission of the European Communities JointMinisterio de Economía y CompetitividadMinisterio de Ciencia, Innovación y UniversidadesComunidad de Madri

Real time monitoring of water level and temperature in storage fuel pools through optical fibre sensors

We present an innovative architecture of a Rayleigh-based optical fibre sensor for the monitoring of water level and temperature inside storage nuclear fuel pools. This sensor, able to withstand the harsh constraints encountered under accidental conditions such as those pointed-out during the Fukushima-Daiichi event (temperature up to 100 °C and radiation dose level up to ~20 kGy), exploits the Optical Frequency Domain Reflectometry technique to remotely monitor a radiation resistant silica-based optical fibre i.e. its sensing probe. We validate the efficiency and the robustness of water level measurements, which are extrapolated from the temperature profile along the fibre length, in a dedicated test bench allowing the simulation of the environmental operating and accidental conditions. The conceived prototype ensures an easy, practical and no invasive integration into existing nuclear facilities. The obtained results represent a significant breakthrough and comfort the ability of the developed system to overcome both operating and accidental constraints providing the distributed profiles of the water level (0–to–5 m) and temperature (20–to–100 °C) with a resolution that in accidental condition is better than 3 cm and of ~0.5 °C respectively. These new sensors will be able, as safeguards, to contribute and reinforce the safety in existing and future nuclear power plants

Recent advances in radiation-hardened fiber-based technologies for space applications

International audience; In this topical review, the recent progress on radiation-hardened fiber-based technologies is detailed, focusing on examples for space applications. In the first part of the review, we introduce the operational principles of the various fiber-based technologies considered for use in radiation environments: passive optical fibers for data links, diagnostics, active optical fibers for amplifiers and laser sources as well as the different classes of point and distributed fiber sensors: gyroscopes, Bragg gratings, Rayleigh, Raman or Brillouin-based distributed sensors. Second, we describe the state of the art regarding our knowledge of radiation effects on the performance of these devices, from the microscopic effects observed in the amorphous silica glass used to design fiber cores and cladding, to the macroscopic response of fiber-based devices and systems. Third, we present the recent advances regarding the hardening (improvement of the radiation tolerance) of these technologies acting on the material, device or system levels. From the review, the potential of fiber-based technologies for operation in radiation environments is demonstrated and the future challenges to be overcome in the coming years are presented

Vulnerability of OFDR-based distributed sensors to high γ-ray doses

Vulnerability of Optical Frequency Domain Reflectometry (OFDR) based sensors to high γ-ray doses (up to 10 MGy) is evaluated with a specific issue of a radiation-hardened temperature and strain monitoring system for nuclear industry. For this, we characterize the main radiation effects that are expected to degrade the sensor performances in such applicative domain: the radiation-induced attenuation (RIA), the possible evolution with the dose of the Rayleigh scattering phenomenon as well as its dependence on temperature and strain. This preliminary investigation is done after the irradiation and for five different optical fiber types covering the range from radiation-hardened fibers to highly radiation sensitive ones. Our results show that at these high dose levels the scattering mechanism at the basis of the used technique for the monitoring is unaffected (changes below 5%), authorizing acceptable precision on th