Bragg gratings photoinduced in ZBLAN fibers by femtosecond pulses at 800 nm

Fiber Bragg gratings were written in thulium-doped and undoped single-mode ZBLAN fibers by focusing fermosecond laser pulses on the fiber core through a phase mask. Maximum index modulation of the order of 1 X 10(-3) was induced in both types of fibers. Measurements of the transverse refractive index changes across the core and cladding regions indicate that the grating formation originates from a negative index change. (c) 2007 Optical Society of America.