Fibers coated with copper, aluminum, gold, and steel can survive in a wide temperature range. Gold-coated FBG sensors are sure to be the most effective in extreme environments. They provide mechanical protection, hermetic sealing, high corrosion resistance, and high sensitivity. The development of. This paper details the development of temperature-resistant wavelength-multiplexed fiber Bragg gratings for temperature and strain measurements and their characterization for on-line monitoring into the liquid sodium used as a coolant for the next generation of fast reactors. Reports of completed research or a.