Thermo- and Photo-sensitive GeO2–B2O3–SiO2Thin Glass Films

GeO 2 –B 2 O 3 –SiO 2 thin films having excellent thermo- and photo-sensitivity were fabricated by the plasma enhanced chemical vapor deposition method. Bragg gratings with high diffraction efficiency were formed in the films by irradiation with a KrF excimer laser through the phase mask without H 2 loading. The diffraction efficiency decreased rapidly by the annealing up to 500°C, but increased significantly at 600°C. Such an increase was closely related to the formation of intense absorption bands in the ultraviolet wavelength region. The growth of the thermo-induced index change was suppressed by the laser irradiation prior to the annealing. Thus the origin of the marked increase in diffraction efficiency was considered to be the formation of another type of grating with the reverse index pattern. This thermally stabilized grating was never erased by the repeated heat treatment between room temperature and 600°C.