Redes de Bragg para medições em altas temperaturas

Abstract

This work presents results regarding pré-treatment optical fibers and / or post-treatment of Bragg gratings in order to stabilize and ensure the operational of such gratings for long periods at temperatures form 300 °C to 800 °C. Results of the growth of fiber optic gratings in standard G-652 with nominal diameter and in fiber tapers, as well as gratings recorded in optical fibers preheated by propane-butane flame, showed increased efficiency in the recording, related to the shrinking of the fiber diameter or to the pre-heating. Strong gratings, presumably of type IIA produced in non-hydrogenated G-652 fibers, showed expected survival time of approximately 17000 hours operating at 400 ºC and 3000 hours operating at 600 °C. The regenerated Bragg gratings produced on G-652 hydrogenated fiber and on photosensitive fibers showed regeneration efficiency proportional to the length and saturation of the seed grating. Regenerated Bragg gratings presented expected survival time of about 5600 hours at 600 °C and no survival for long duration intervals when operating at temperatures equal or above the regeneration temperature. Heat treatment cycles to stabilize IIA gratings are described. Results for thermal sensitivity of the Bragg gratings showed no hysteresis in heating-cooling cycle. A solution for encapsulation of the Bragg gratings through the use of alumina ceramic tube was satisfactory tested in the regions mentioned temperature, showing no degradation in performance.