Steady-State Radiation-Induced Effects on the Performances of BOTDA and BOTDR Optical Fiber Sensors

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Abstract
Distributed optical-fiber sensors (OFSs) based on scattering phenomena are nowadays used for several applications such as temperature or strain monitoring. Whereas very promising results have already been reported for the applications of Rayleighand Raman-based OFSs in harsh environments, only few studies concern the Brillouin-based ones. Two phenomena influence the Brillouin-based OFS when the sensing fiber is exposed to radiations: the radiation-induced attenuation (RIA), which reduces the sensing range by decreasing the signal-tonoise ratio, and a frequency shift of the Brillouin peak, which entails an error on the temperature or strain measurements. We report here an in situ study on the effects of γ-rays on Brillouin optical time-domain analysis (BOTDA) OFS up to the accumulated dose of 10 MGy(SiO 2 ) and those of X-rays on Brillouin optical time-domain reflectometer sensor up to 1 MGy. We compare the vulnerability levels for fiber composition, fiber packaging, as well as the influence of a preirradiation on the sensing performances. Whereas the Ge-doped fibers present a too high RIA that limits drastically the sensing range at high doses, especially with the BOTDA technique; the F-doped ones appear suitable for integration in high dose levels environments. Indeed the error induced by the Brillouin frequency shift on temperature measurements is smaller than 5 °C after a 10-MGy dose.

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