Advances in Brillouin based distributed optical fiber temperature sensing

This paper demonstrates the recent achievements in the field of Brillouin based distributed optical fiber temperature sensing. When a dispersion-shifted fiber was subjected to a temperature cycle between 20 and 820 degrees C, the Brillouin shift exhibited an undesired hysteresis with a maximum frequency discrepancy of larger than 48 MHz between heating and cooling processes. After the fiber was annealed for 9 h at 850 degrees C, however, the hysteresis almost disappeared for repeated temperature cycles in the ranges of 20-820 degrees C and of 500-800 degrees C with deviations of the measurements from the best-fit curve of less than +/- 12.5MHz. The temperature dependence of Brillouin shift in the range of 20-820 degrees C in the annealed fiber was well expressed by a second order function of temperature. A sensing scheme that utilizes both output signals of the fiber Mach-Zehnder interferometer used as an optical frequency discriminator has been proposed. The scheme that has the advantages of less system adjustment and fast measurement, combined with a suitably annealed fiber, offers a reliable means for the Brillouin shift-based distributed sensing over the wide temperature range.