Radiation-hardened fiber bragg grating based sensors for harsh environments

Fiber Bragg Grating (FBG) based sensors are nowadays used for several applications, but, even if they present advantages for their incorporation into radiation environments, commercial-off-the-shelf devices cannot still be used in harsh conditions. We recently reported a procedure for fabricating FBGs resistant to severe constraints combining both high radiation doses up to MGy levels and operation temperatures exceeding 200°C (RadHard FBGs). Following these results, the European project HOBAN was granted by Kic InnoEnergy with the aim of developing and marketing FBG-based temperature and strain monitoring systems suitable for harsh nuclear environments (350°C temperature and MGy dose levels), with their associated instrumentation devices. In this framework, we present an accurate study about the robustness of the radiation-response of these RadHard FBGs against the main grating inscription parameters. Up to the accumulated X-ray dose of 1 MGy(SiO2), no significant radiation induced Bragg wavelength shift is observed meaning that radiations induce errors below ± 0.4°C in the temperature estimation. Moreover, a study about the dose-rate dependence (1 to 50 Gy/s) of the gratings response is also reported and confirms the high radiation hardness of our RadHard FBGs at all dose rates.