The threshold for the fabrication of fiber Bragg gratings with ultrafast 800-nm radiation and a phase mask was studied in SMF-28 and all-silica core fiber by use of 125-fs pulses. High-pressure molecular hydrogen loading (H<sub>2</sub> loading) was observed to significantly lower the grating writing threshold in standard Ge-doped telecommunication fiber. No reduction was observed with all-silica core fiber. The index change appeared to be confined to the Ge-doped core region of the fiber. Gratings in H<sub>2</sub>-loaded SMF-28 had thermal annealing behavior similar to UV-induced gratings. Unlike UV-induced H<sub>2</sub>-loaded gratings, no absorption associated with Ge–OH defect formation was observed.
© 2004 Optical Society of America
(230.1480) Optical devices : Bragg reflectors
(320.2250) Ultrafast optics : Femtosecond phenomena
(320.7140) Ultrafast optics : Ultrafast processes in fibers
(350.3390) Other areas of optics : Laser materials processing
Christopher W. Smelser, Stephen J. Mihailov, and Dan Grobnic, "Hydrogen loading for fiber grating writing with a femtosecond laser and a phase mask," Opt. Lett. 29, 2127-2129 (2004)