Uniform component of index structure induced in Ge-SiO2 fibers by spatially modulated ultraviolet light

Experimental data are presented to show that Ge(1) and Ge(2) centers are induced by trapping photoinduced electrons from the conduction band, in agreement with our previous proposal that both are trapped electron centers. The spacing (Lambda) dependence of ultraviolet (UV) light bleaching of the pre-existing Ge E' centers illustrates that the electron diffusion length is greater than Lambda of the spatially modulated UV light used in the fabrication of fiber Bragg gratings (FBGs) with Bragg wavelengths less than or equal to 1.5 mu m (short period grating) for laser powers as low as 25 mJ/cm(2). The Ge(1) and Ge(2) centers are uniformly induced by the spatially modulated UV light and therefore contribute to the uniform component of the index structure of FBGs. [S0003-6951(98)01325-4].