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High-quality Bragg gratings with refractive index modulations > 7 ?? 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??C. The Bragg resonance shift with temperature is observed to be 3-4 times higher than similar gratings in silica fiber.