Bragg Gratings Made With a Femtosecond Laser in Heavily Doped Er–Yb Phosphate Glass Fiber

Bragg gratings made in heavily doped phosphate glass fibers using ultrafast infrared radiation and a phase mask are reported. Refractive indexes >1.5times10
^-3
were induced in Er-Yb-doped phosphate fiber in a few seconds of exposure corresponding to reflectivity above 99.99% for a 6-mm-long grating. Annealing test up to 400 degC shows good thermal stability of the grating structure