Radiation effects on Brillouin-based Sensors: Feasibility of temperature and strain discrimination using LEAF Single-Mode optical fiber

Abstract

In this paper, we investigate the accessible performances in terms of strain and temperature discrimination using Brillouin Optical Time Domain Analysis (BOTDA) combined with the LEAF fiber (from Corning) when exposed to γ-rays up to doses of 1MGy(SiO2). This optical fiber offers a multipeak Brillouin Gain Spectrum (BGS) with unique dependencies of each of its peaks over temperature and strain. The discrimination capability evolution of LEAF is investigated at high γ doses and dose rates to evaluate the radiation effects on the sensing performances. Gamma irradiation leads to modifications of the LEAF BGS signature through two main effects. First, the Radiation Induced Attenuation (RIA) of this germanosilicate optical fiber limits the BGS amplitude, sensing range and capability for discrimination over BGS amplitude. Second, radiations modify the Brillouin scattering properties by slightly changing the refractive indices and the acoustic velocities of the fiber core and cladding leading to a small change in temperature and strain dependences as well as a limited Radiation Induced Brillouin Frequency Shift (RI-BFS) causing a direct error on the measured parameters. Results exhibit an overall decrease of temperature and strain uncertainties through discrimination process after 1MGy irradiation reaching 0.9°C and 29με for 0.1 MHz frequency uncertainty.