Investigation of the structure of preform materials and fiber-optical waveguides utilizing quartz glass doped with germanium and boron

An investigation was made of the distribution of dopants, OH impurities, and the refractive index n in preforms and glass fiber-optical waveguides (GFOW's) fabricated by the chemical vapor deposition method. It was found that diffusive redistribution of Ge and B dopants occurs during the drawing process. This was manifested by equalization of the dopant concentration and blurring of the boundaries of the waveguide structure over the effective length ~0.08α (α is the core radius). This effect should be taken into account in the development of GFOW's for wide-band fiber-optical communication lines. In addition to x-ray microanalysis, the absorption method was used for the first time to investigate the radial distribution of the GeO₂ concentration in preforms. This method was used to measure the GeO₂ distribution in an xGeO₂+(1–x)SiO₂ binary system at λ = 0.269 μ [the extinction coefficient was (1.02±0.05)cm^–1/mole %]. With an appropriate choice of spatial resolution, this method could be used to simulate diffusive redistribution of the dopant in GFOW's. The refraction method was used to investigate the dispersion of n in a step-profile preform. Considerable inhomogeneity of n₂ was observed in the quartz cladding (~5x10^–4) and Δn = n₁–n₂ was ~1x10^–4 (mole % GeO₂)^–1 lower than the value of Δn for homogeneous materials of the same composition. These values exceeded the calculated effects of mechanical stresses.