Radiation and High Temperature Effects on Regenerated Fiber Bragg Grating

Fiber Bragg gratings (FBGs) are promising sensors for operation in harsh environments mixing temperature and radiation constraints. Regenerated FBGs (RFBGs) are suited to perform measurements at very high temperatures (up to 1295 degrees C) as those encountered in nuclear reactor cores. However, only a few studies have been done regarding combined effects of radiations and temperature on RFBGs. We studied the response of such gratings under X-rays at several irradiation temperatures from 25 degrees C to 250 degrees C. Tested RFBGs have been inscribed on a pre-hydrogenated Ge-doped fiber with UV laser (KrF) using a phase mask and the regeneration has been done at 750 degrees C. Our results show that RFBGs are relatively radiation tolerant at 25 degrees C with a Bragg wavelength shift (BWS) of less than 50 pm (similar to 5 degrees C error) for a total dose of 100 kGy(SiO2). However, at increased irradiation temperatures (>150 degrees C), the BWS is limited, remaining below 10 pm (<1 degrees C error). We also studied the influence of a pre-thermal treatment (300 degrees C for 5 h) on the RFBGs response as well as the influence of other irradiation parameters, such as the close rate (1-20 Gy/s), the pre-irradiation (100 kGy) and the total dose (2 MGy) at 25 degrees C. Radiation induced-BWS increases with dose rate, whereas the prethermal treatment has no influence.