High-Reflectivity Thermally Stable Ultrafast Induced Fiber Bragg Gratings in H$_{2}$ -Loaded SMF-28 Fiber

High-temperature stable high-reflectivity gratings are fabricated in hydrogen-loaded single-mode fiber (SMF-28) using ultrafast 800-nm radiation. An index modulation of ~ 9 x 10
^-4
and a loss of >15 dB at the Bragg resonance is present after isochronal annealing up to 1000degC followed by 96 h of isothermal annealing.