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(degree)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(degree)C, however, the hysteresis almost disappeared and, among repeated temperature cycles in the ranges of 20-820(degree)C and of 500-800(degree)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.