Bragg Gratings Made in Highly Nonlinear Bismuth Oxide Fibers With Ultrafast IR Radiation

High-quality Bragg gratings with refractive index modulations $>7\times 10^{-4}$ were induced in highly nonlinear bismuth oxide glass fibers using ultrafast infrared radiation and a phase mask. Grating reflectivities approaching 95% for a 6-mm-long grating were achieved. Annealing tests show good thermal stability of the grating structure below 220 $^{\circ}\hbox{C}$ . The Bragg resonance shift with temperature is observed to be 3–4 times higher than similar gratings in silica fiber.