Pressure-independent Brillouin Fiber Optic Sensors for temperature measurements

Abstract Fiber Optic Sensors (FOSs) based on Brillouin scattering are widely used in large infrastructures to detect modifications over large distances. In doped silica fibers the Brillouin Frequency Shift (BFS) is proportional both to temperature and strains. In this work we establish that the sensitivity of FOSs to hydrostatic pressure can be forecast from the behavior of the glass under hydrostatic compressions in a diamond anvil cell. It is shown that the BFS under a hydrostatic pressure is a manifestation of the elastic anomaly observed in silica glass. This anomaly vanishes in GeO 2 glass and accounts for the decrease of the sensor sensitivity when the GeO 2 doping concentration increases in a silica fiber. The progressive vanishing of the anomaly in sodium aluminosilicate glasses which contain the same amount of silicon dioxide (75%) but differ in the Na 2 O and Al 2 O 3 ratio allows to determine the composition of a glass with a BFS independent of the pressure. Such a glass composition will provide a pressure-independent temperature FOSs.