Radiation tolerant fiber Bragg gratings for high temperature monitoring at MGy dose levels

Abstract : We report a method for fabricating fiber Bragg gratings (FBG) resistant to very severe environments mixing high radiation doses (up to 3 MGy) and high temperatures (up to 230 degrees C). Such FBGs have been written in two types of radiation resistant optical fibers (pure-silica and fluorine-doped cores) by exposures to a 800 nm femtosecond IR laser at power exceeding 500 mW and then subjected to a thermal annealing treatment of 15 min at 750 degrees C. Under radiation, our study reveals that the radiation induced Bragg wavelength shift (BWS) at a 3 MGy dose is strongly reduced compared to responses of FBGs written with nonoptimized conditions. The BWS remains lower than 10 pm for temperatures of irradiation ranging from 25 degrees C to 230 degrees C without noticeable decrease of the FBG peak amplitude. For an applicative point of view, this radiation induced BWS corresponds to an additional error on the temperature measurements lower than 1.5 degrees C, opening the way to the development of radiation-tolerant multi-point temperature sensors for nuclear industry.