Wide-range temperature dependence of Brillouin shift in a dispersion-shifted fiber and its annealing effect

Temperature dependence of the Brillouin shift in a commercially available dispersion-shifted fiber has been experimentally investigated in the range of 20 to 820°C. When the as-fabricated fiber underwent a temperature cycle in the entire temperature rage, the Brillouin shift exhibited a noticeable hysteresis having the maximum frequency discrepancy of 48 MHz or larger between heating and cooling processes. After the fiber was annealed for 9 h at 850°C, however, the hysteresis almost disappeared and, among repeated temperature cycles in the ranges of 20-820°C and of 500-800°C, the maximum frequency discrepancy was reduced to ±12.5 MHz or less. It is thus demonstrated that a suitably annealed fiber is reliable for the Brillouin shift-based distributed sensing over the wide temperature range.