Regenerated Fiber Bragg Gratings in Non-Hydrogen-Loaded Photosensitive Fibers for High-Temperature Sensor Networks

We report about a thermal regeneration of fiber Bragg gratings written in photosensitive fibers without hydrogen loading and with the use of UV nanosecond laser pulses. We observe a complex regenerative process which indicates a secondary grating growth in an optical fiber by thermal activation. This process leads to an increased temperature stability of the gratings up to 600 degrees C which differs from the commonly known Type I gratings. With the use of an interferometric writing technique it is possible to generate arrays of regenerated fiber Bragg gratings (RFBGs) for sensor networks. The writing conditions of such new type of gratings are investigated and the temperature behavior of these RFBGs is analyzed. This type of gratings is suitable for high temperature sensor networks by combining the attributes of good spectral shape and high reflectivity with high temperature stability showing no drift or hysteresis.