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Accueil du site > Recherche > Projets > Thème MOSAIQ > Optical fibres and radiations (OFR)

Optical fibres and radiations (OFR)

- Leader : Benabdesselam Mourad

- Collaborators within the LPMC : Mady Franck, Dussardier Bernard, Blanc Wilfried

- External Collaborators : Ollier N. (LSI, CNRS/CEA/École Polytechnique, Palaiseau), Boch J. (IES, Université Sciences et Techniques du Languedoc, Montpellier II), Peterka P. (IPEE, Prague), Caussanel M. (PROMES, Perpignan)

- PhD students/Post-doctoral fellows : Mebrouk Yasmine, Duchez Jean-Bernard

- Financial supports : Projet Hapolo Fondation EADS (Convention EADS 098-AO11-2408) ; Projet ANR Jeune chercheur, ANR 11-JS04-007, PARADYSIO ; Projet ANR DROID (ANR 11-RSNR-0008)

- Technological platforms : Specialty optical fibres manufacture

- Description :

The scope of this research includes passive and active optical fibres, fibre systems (amplifiers, lasers...) and fibre sensors involved in civilian nuclear environments, military, space or used in the storage of radioactive wastes and large scientific infrastructures. In addition to the effects associated with external radiation fields, our study includes phenomena induced by the radiations that can be guided in the fibres, and in particular by the pump photons in the case of active fibres.

Interactions between these radiations and silica optical fibres basically consist in ionizations that result in charge transfer processes and finally in the formation of optically active defects responsible for transmission losses. The appearance of such defects can be considered as harmful ("darkening" of the fibre) or, conversely, harnessed to design radiation detectors (in passive or active modes) and fiber-based dosimeters (radiation metrology). Our research is structured around these two antagonistic but complementary approaches.

As regards the "degradation" axis, the major challenge is to propose proper "hardening" routes allowing the fibres to maintain their performance in an acceptable tolerance throughout its service, i.e. after imparting a given absorbed dose of radiation defined according to the intended application. This requires a detailed understanding of the microscopic mechanisms of ionization and formation of optical centres involved in the degradation. Advances in hardening recipes face difficulties that essentially result from the extrinsic nature of these darkening mechanisms. Whereas they are determined by the fibre composition, including the nature and concentration of its dopants, they also show a strong dependency on the characteristics of the given radiation. First, it is necessary to distinguish the effects of external radiation (radio-darkening) from that due to guided radiation (sub-gap photons, photo-darkening). Second, specific effects associated with different types of external radiations (X-or gamma-rays, protons, electrons, neutrons, ions) and their dose rate (intensity of radiation) have to be elucidated. Indeed, routine laboratory tests can be conducted with the aid of flexible and available irradiation means (soft X-rays from, laboratory generators), most often at dose rates that are very different from those experienced in service conditions.

The "radiation fibre sensors" axis also benefits from the understanding of the physical mechanisms governing the radiation-fibre interactions, but with the aim of enhancing the sensitivity of the fibre to various radiations. Again, sensitization routes must be adapted with regard to the composition and the type of radiation, depending on the intended application. These sensors can be in passive form (delayed dosimeter reading) and active (real-time detector), on the basis of changes in spectroscopic or/and luminescent properties.

This activity is currently structured by three funded projects whose details are presented below. The axis "hardening" develops around two projects supported by the LPMC : PARADYSIO (ANR), and HAPoLO (EADS foundation). The axis "sensor" is particularly supported in the DROID (ANR) project, supported by the PROMES laboratory (UPR 8521), Perpignan, with the LPMC as partner. Each project is based on its own network of external collaborators (see details below and links above).

- Details of the currently developed projects :

  • PARADYSIO (ANR 11-JS04-007)

In collaboration with the « Laboratoire des Solides Irradiés », LSI, UMR 7642 CNRS-CEA-École Poly-technique, Palaiseau, France (Nadège Ollier, CEA researcher).

The PARADYSIO project should provide a clear, comprehensive understanding of the darkening mechanisms at play in ytterbium-doped silica optical fibres (YDF). It is expected to allow the identification of the radiation-induced colour centres responsible for excess attenuation (darkening), and then to highlight possible radiation hardening routes (by composition and possibly design). The latter will be checked against tests in various amplifying conditions under radiation exposure. Compared with erbium-doped fibres, YDF are not only damaged by external ionizing radiations (radio-darkening), but also due to pump photons themselves (photo-darkening). Tackling the darkening processes in YDF is therefore a exciting challenge. Although processes of energy absorption are obviously different for ionizing particles or photons in the NIR range, it seems that both radiation types activate the same defects. Therefore a detailed examination and comparison of the build-up of both darkening types in YDF, and of the effects related to their superimposition, must be conducted. Radiation-induced defects are efficiently characterized by coupling thermoluminescence, ESR and photo-spectrometry measurements. Darkening kinetics are approached through pump-probe-like techniques. Radiation hardening routes are sought based on a simulation tool including the basic physics and mechanisms hypothesized from characterization data. This tool should eventually account for composition, dose and dose rate effects on the tolerence of YDF against photo- and radio-darkening.

  • Hapolo (Fondation EADS 098-AO11-2408)

In collaboration with the « Institut d’Electronique du Sud », IES, CNRS UMR 5214, Université Montpellier 2 (Jérôme BOCH), and IPE Prague (Pavel Peterka).

L’intégration des fibres optiques amplificatrices (FOAs) dans les technologies aérospatiales embarquées (gyroscopes, communications inter-satellites, LiDAR,…) se heurte à la dégradation des performances des FOAs sous l’effet des radiations spatiales (protons et électrons essentiellement). Comme pour les composants électroniques, le lancement de FOAs ne devrait se faire qu’au terme d’une procédure de « qualification spatiale », consistant à vérifier sur Terre que la fibre franchit un test standardisé de tenue au rayonnement. Pourtant ces tests souffrent d’un double défaut. Tout d’abord, ils utilisent le plus souvent des rayonnements X ou gammas, facilement accessible et peu coûteux en routine bien que différents des radiations spatiales. Ensuite, le débit de dose utilisé lors des tests est supérieur de plusieurs ordres de grandeurs au débit spatial (ce dernier est très faible : 10-4 à 10-2 Gy h-1). Les tests sur terre sont donc accélérés : la dose typique reçue par un composant sur les 15 années d’une mission spatiale (500 Gy au plus) peut être délivrée en quelques minutes. Or, il est très probable que le niveau de dégradation soit largement sous estimé à fort débit. Malgré ces failles, des protocoles de tests standardisés existent depuis de nombreuses années pour les composants électroniques. Heureusement, ce terrain demeure vierge d’exploration concernant les fibres optiques. L’étude de la tenue des FOAs aux radiations s’est développée au cours des 10 dernières années, principalement autour des fibres en silice dopées erbium, sans considérer les deux limitations citées. L’ambition du projet HAPoLO est de contribuer significativement au comblement du manque en comparant les effets des irradiations protoniques à ceux d’irradiations de routine (rayons X), en proposant ensuite une caractérisation expérimentale poussée et une modélisation des effets de débit de dose, en recherchant enfin sur une base physique solide des modalités de tests accélérés équivalents à une mission. Ce travail s’appuie sur le développement d’un banc de test permettant de suivre la dégradation d’une source laser fibrée de puissance (configuration MOPA) sous irradiation à débit variable. Les FOAs considérées sont en premier lieu des fibres dopées erbium, même si l’étude de fibres dopées ytterbium permettra de tirer un profit majeur des mécanismes de dégradations identifiés et modélisés par le projet HAPoLO mené parallèlement par l’équipe. Cela doit permettre de tester les voies de durcissement vis à vis des radiations spatiales d’après un protocole validé.

  • DROID (ANR 11-RSNR-0008)

Led by the PROMES Laboratory, University of Perpignan (Matthieu Caussanel).

The Droid project aims to contribute to the safety of nuclear facilities and radiation protection staff in developing a method of dosimetric monitoring that allows for real-time monitoring of the sensitivity of specialty optical fibres to radiations. This original distributed fiber dosimeter reads the Radio-Induced Attenuation (RIA) by spatially resolved optical reflectometry. The dose mapping may be performed to 1, 2 or 3 dimensions. This new technique will benefit from the optical fibre composition and geometry versatility to adapt the resolution in terms of dose and space (from cm to km). Such a dosimeter system has numerous applications in a nuclear power plant for the production of energy.

Mots-clés

MOSAIQ, Fibres Optiques