Hydrogen concentration dependence of Bragg wavelength of UV-written fiber grating

Hydrogen loading provides highly enhanced photosensitivity in Ge-doped fibe r. But the Bragg wavelength of W-written fiber grating will shift from its initial value as the remaining hydrogen diffuses out of such fiber. A simpl e model to calculate the index change of hydrogenated fibers is presented. The theoretical model is in good agreement with experimental results and it can well predict the final wavelength position of UV-written weak fiber gr ating.