Fig. 1. Evolution of regenerated grating at 900 ℃

Fig. 2. Grating reflectivity evolutions of FBGs for rapid regeneration written in (a) hydrogenated highly Ge-doped fibers and (b) hydrogenated photosensitive Ge/B-doped fibers annealed at constant temperatures

Fig. 3. Evolution of reflectivity regulation of both gratings G1 and G2 during the regeneration experiment (The inset shows the separated spectra of the fast axis and slow axis of G2)

Fig. 4. Evolutions of first-order and third-order gratings'normalized indexes during (a) isochronal and (b) isothermal annealing

Fig. 5. Photograph of Ti-Ag-Ni coated RFBG sensor

Fig. 6. Photograph of ceramic tube packaged RFBG sensor

Fig. 7. Photograph of ceramic and metal tube packaged RFBG sensor

Fig. 8. Steel tube packaged RFBG. (a) Mechanistic model; (b) photograph of sensor