Packaged Optical Sensors Based on Regenerated Fiber Bragg Gratings for High Temperature Applications

We report on temperature sensors based on regenerated fiber Bragg gratings (RFBGs) for measurements up to 1100 degrees C. The annealing process required to regenerate such gratings makes the optical fiber too delicate, thus making an adequate packaging necessary. Prior to the grating regeneration the optical fiber is protected with a ceramic tube which in turn is shielded with a thick metal casing. We have performed a thorough characterization of the thermo-optical response of both packaged and unpackaged RFBG sensors placing especial attention on possible residual hysteresis after several temperature cycling tests. The response and recovery times of packaged sensors were found to be, respectively, similar to 9 s and similar to 22 s.