Investigation of Strain- and Temperature-Dependences of Brillouin Frequency Shifts in GeO₂-Doped Optical Fibers

The dependences of Brillouin frequency shifts (BFSs) on strain and temperature inGeO ₂-doped optical fibers are investigated. Our study shows that the strain (temperature) coefficient of the BFS is linearly proportional to the decrease of theGeO₂concentration in the fiber core with a relative rate of$-$1.48% ($-$1.61%) per unit mol percentage. The coefficients of 0 mol%GeO₂-doped silica (i.e., pure silica) are extracted from the least squares fitted linear dependences of the coefficients onGeO₂concentration; the results show good agreement with simulations taking into account the changes of the refractive index, the density, and the Young's modulus induced by the applied strain and the temperature change. Furthermore, when measurement upon three fibers drawn from the same preform, but under different draw tensions are done, this provides that there exists an optimized tension during fiber fabrication that maximizes the difference between strain and temperature coefficients.