Thermally stabilized PCF-based sensor for temperature measurements up to 1000ºC

We report on the development of a stable Photonic Crystal Fiber (PCF) based two-mode interferometric sensor for ultra-high temperature measurements (up to 1000 degrees C). The device consists of a stub of PCF spliced to standard optical fiber. In the splice regions, the voids of the PCF are fully collapsed, thus allowing the excitation and recombination of two core modes. The device spectrum exhibits sinusoidal interference pattern which shifts with temperature. We show that, despite being compact and robust, the proposed sensor head needs a quite long burn in (thermal annealing) to achieve an adequate and stable functionality level. The burn in process eliminates the residual stress in the fiber structure, which had been accumulated during the drawing phase, and changes the glass fictive temperature.