Distributed temperature and strain fiber-based sensing in radiation environment

We investigate the radiation effects on a Brillouin based optical fiber sensor (OFS). This OFS exploits a single-mode optical fiber (SMF) having a Brillouin signature presenting multiple peaks. This specificity allows performing distributed and discriminated measurements of the temperature and strain time evolutions along the fiber. The particular structure (composition and refractive-index profile) of the investigated SMF was first conceived and optimized thanks to a home-made simulation tool to assess its capability to discriminate between the two environmental parameters. At the same time, it should also present a good radiation tolerance in order that the sensor could operate in radiation-rich environments (up to MGy levels). The modeled germanosilicate SMF has then been manufactured by the modified chemical vapor deposition process by iXblue and its sensing performances have been experimentally demonstrated. Samples of the SMF have been irradiated under steady state X-rays at a dose rate of 2.3 Gy(SiO2)/s up to 180 kGy at room temperature. The radiation tests showed that the Brillouin sensor can be implemented in such severe environments. At these dose levels, radiation induced errors are limited to ~3°C and ~0.15 με in the worst conditions. Finally, we discuss perspectives about possible new fiber structures to target even more challenging applications in terms of radiations and sensing requirements.