The refractive-index modulation of chemical composition gratings in fluorine–germanium-doped silica fibers as a function of thermal treatment during manufacturing has been studied. The final grating strength was found to depend strongly on an intermediate annealing step, with an optimum temperature near 600–700 °C, before development at a fixed temperature of 1000 °C. Low–temperature treatment, aimed at removing any remaining hydrogen from the fiber, performed at 100 °C for 20 h before the annealing step, also significantly increased the final refractive-index modulation.
© 2002 Optical Society of America
Michael Fokine, "Growth dynamics of chemical composition gratings in fluorine-doped silica optical fibers," Opt. Lett. 27, 1974-1976 (2002)