In the nuclear industry, there is a need for sensors that are resistant to both high temperatures and radiation. Fiber Bragg gratings inscribed into radiation resistant fibers are a potential solution to this as the femtosecond-infrared laser can inscribe Bragg gratings into fibers without a photosensitive core. In order for these gratings to be used for sensing, they need to be characterized to determine their temperature and radiation response and sensitivity. This paper characterized three commercially available fibers for use in high heat and high radiation environments. There are six fiber variants examined in this study. Three basic fiber designs are investigated: a germanium doped core, a germanium doped core with fluorine cladding, and a fluorine doped core and cladding. For each fiber design, normal and pre-irradiated versions are investigated. The fibers were tested for thermal response by heating them to 1000C and holding for 24 hours, and for radiation resistance by irradiating with gamma radiation. The germanium core doped fibers were more resistant to thermal effects but still had a wavelength shift during the 24-hour soak. The fluorine-doped fibers either had the gratings partially or completely erased during the thermal hold at 1000°C, but showed suitability for short term excursions to this temperature. The radiation data showed significant shifts in some cases, but there was not enough data to form a definitive conclusion. It appears that radiation introduces variability in the response of the Fiber Bragg Gratings (FBG).
Since the first commercial introduction in the 1980s, optical fiber technology has undergone an almost exponential growth. Currently over 2 billion fiber kilometers are deployed globally with 2014 global optical fiber production exceeding 300 million fiber kilometers. <sup>1</sup> Along with the staggering growth in optical fiber production and deployment, an increase in optical fiber technologies and applications has also followed. Although the main use of optical fibers by far has been for traditional data transmission and communications, numerous new applications are introduced each year. Initially the practical application of optical fibers was limited by cost and sensitivity of the optical fibers to stress, radiation, and other environmental factors. Tremendous advances have taken place in optical fiber design and materials allowing optical fibers to be deployed in increasingly harsh environments with exposure to increased mechanical and environmental stresses while maintaining high reliability. With the increased reliability, lower cost, and greatly expanded range of optical fiber types now available, new optical fiber deployments in harsh and high radiation environments is seeing a tremendous increase for data, communications, and sensing applications. An overview of key optical fiber applications in data, communications, and sensing for harsh environments in industrial, energy exploration, energy generation, energy transmission, and high radiation applications will be presented. Specific recent advances in new radiation resistant optical fiber types, other specialty optical fibers, optical fiber coatings, and optical fiber cable materials will be discussed to illustrate long term reliability for deployment of optical fibers in harsh and high radiation environments.