Radiation effects on Brillouin-based sensors: temperature and strain discrimination capability using telecom-grade optical fibers

We investigate the performances accessible in terms of strain and temperature discrimination using Brillouin Optical Time Domain Analysis combined with the LEAF fiber from Corning, AllWave fiber (AW) from Lucent and TrueWave (TW) fiber from OFS when exposed to γ rays and X-rays up to 1 MGy(SiO2). All these fibers present a multipeak Brillouin Gain Spectrum (BGS) with unique dependencies of each of its peaks over temperature (T) and strain (ε). The evolution of their T and ε discrimination capability is investigated to evaluate how radiation affects the sensing performances. High dose irradiation changes the sensor performances through two main effects. First, the Radiation Induced Attenuation (RIA) limits the BGS amplitude, the sensing range and discrimination capability techniques relying on BGS amplitude. Second, radiations modify the Brillouin scattering properties by slightly changing the refractive indices and the acoustic velocities of the silica-based leading to small changes in T and ε dependencies and also to a limited Radiation Induced Brillouin Frequency Shift (RI-BFS) that causes a direct measurement error. Results exhibit an overall decrease of T and ε uncertainties through discrimination process after 1 MGy reaching 0.9°C and 29 με for 0.1 MHz frequency uncertainty for sensors based on the LEAF fiber.