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ABSTRACT: The use of distributed strain and temperature in optical fiber sensors based on Brillouin scattering for the monitoring of nuclear waste repository requires investigation of their performance changes under irradiation. For this purpose, we irradiated various fiber types at high gamma doses which represented the harsh environment constraints associated with the considered application. Radiation leads to two phenomena impacting the Brillouin scattering: 1) decreasing in the fiber linear transmission through the radiation-induced attenuation (RIA) phenomenon which impacts distance range and 2) modifying the Brillouin scattering properties, both intrinsic frequency position of Brillouin loss and its dependence on strain and temperature. We then examined the dose dependence of these radiation-induced changes in the 1 to 10 MGy dose range, showing that the responses strongly depend on the fiber composition. We characterized the radiation effects on strain and temperature coefficients, dependencies of the Brillouin frequency, providing evidence for a strong robustness of these intrinsic properties against radiations. From our results, Fluorine-doped fibers appear to be very promising candidates for temperature and strain sensing through Brillouin-based sensors in high gamma-ray dose radiative environments.
Optics Express 11/2012; 20(24):26978-85. · 3.59 Impact Factor
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ABSTRACT: We investigated the efficiencies of two different approaches to increase the radiation hardness of optical amplifiers through development of improved rare-earth (RE) doped optical fibers. We demonstrated the efficiency of codoping with Cerium the core of Erbium/Ytterbium doped optical fibers to improve their radiation tolerance. We compared the γ-rays induced degradation of two amplifiers with comparable pre-irradiation characteristics (~19 dB gain for an input power of ~10 dBm): first one is made with the standard core composition whereas the second one is Ce codoped. The radiation tolerance of the Ce-codoped fiber based amplifier is strongly enhanced. Its output gain decrease is limited to ~1.5 dB after a dose of ~900 Gy, independently of the pump power used, which authorizes the use of such fiber-based systems for challenging space missions associated with high total doses. We also showed that the responses of the two amplifiers with or without Ce-codoping can be further improved by another technique: the pre-loading of these fibers with hydrogen. In this case, the gain degradation is limited to 0.4 dB for the amplifier designed with the standard composition fiber whereas 0.2 dB are reported for the one made with Ce-codoped fiber after a cumulated dose of ~900 Gy. The mechanisms explaining the positive influences of these two treatments are discussed.
Optics Express 04/2012; 20(8):8457-65. · 3.59 Impact Factor
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ABSTRACT: The luminescence properties of the Yb/Er-doped
phosphosilicate preforms used for the design of active optical
fibers were investigated under a tunable laser excitation from
ultraviolet to infrared domain. We demonstrated that codoping
the glass matrix with Ce3+ ions strongly influences the infrared
emission associated with Er3+ ions, it enhances the energy
transfer from Yb3+ to Er3+ ions, and it provides an additional
ultraviolet excitation channel for the emission of both Yb3+ and
Er3+ ions. The excitation/emission pathways are discussed on the
basis of models proposed in literature for other systems.
IEEE Photonics Technology Letters 03/2012; 24(6):509. · 2.19 Impact Factor
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ABSTRACT: We investigated the laser-energy-density dependence of absorption changes and paramagnetic centers induced by a cw Ar(+)laser operating at 5.1 eV, in both unloaded and H(2)-loaded singlemode Ge-doped optical fibers. The induced absorption is measured in the blue and near ultraviolet spectral range by using the 3.1 eV photoluminescence, ascribed to Ge lone pair center (GLPC), as an in situ probe source. We find that the Ge(1) center (GeO-(4) ) is induced upon UV exposure by electron trapping on GeO(4) precursors, where the free electrons are most likely produced by ionization of GLPC. Ge(1) is responsible of optical transmission loss of the fiber in the investigated range. Hydrogen loading strongly influences the generation efficiency of the several observed paramagnetic defects, leading in particular to passivation of radiation-induced Ge(2) centers.
Optics Express 07/2006; 14(13):5885-94. · 3.59 Impact Factor
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ABSTRACT: Abstract—We compare the visible and infrared luminescence spectra obtained by a green (514.5 nm) and infrared (830 nm) excitation of an erbium-doped fiber before and after irradiation with 105 MeV protons to an equivalent dose of 0.6 kGy(Si). For the irradiated fiber, we measured an increase of the luminescence intensity in this wavelength range due to the generation of additional color centers. Radiation defects such as Ge-NBOHC, Si-NBOHC are generated in both the fiber core and the cladding by the 105 MeV protons. They contribute through their luminescence bands at 1.84 eV (FWHM = 0 2 eV) and 2 eV (0.2 eV) to the fiber emission spectra. Two other pre-existing luminescence bands at 1.75 eV (0.32 eV) and 2.1 eV (0.37 eV), associated to host-matrix-point-defects, are enhanced by proton-irradiation. The Er3+ ions luminescence in both visible and infrared spectral ranges is also affected by the irradiation.
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ABSTRACT: Near UV-visible absorption coefficients of an erbium-doped optical fiber were investigated through an original technique based on a transverse cw UV-laser irradiation operating at 244 nm. Such irradiation leads to the generation of a quite intense guided luminescence signal in near UV spectral range. This photoluminescence probe source combined with a longitudinal translation of the fiber sample (at a constant velocity) along the UV-laser irradiation, presents several major advantages: (i) we bypass and avoid the procedures classically used to study the radiation induced attenuation which are not adapted to our case mainly because the samples present a very strong absorption with significant difficulties due to the injection of adequate UV-light levels in a small fiber diameter; (ii) the influence of the laser irradiation on the host matrix of the optical fiber is directly correlated to the evolution of the generated photoluminescence signal and (iii) in our experimental conditions, short fiber sample lengths (typically 20–30 cm) suffice to determine the associated absorption coefficients over the entire studied spectral domain. The generated photoluminescence signal is also used to characterize the absorption of the erbium ions in the same wavelength range with no cut-back method needed.
