Diffusion of phosphorus doped silica for active optical fibers

The diffusion of phosphorus in P 2 O 5 -SiO 2 glass has been investigated by annealing of doped layers on the inner surface of quartz glass tubes between 1700°C and 2000°C and measuring radial phosphorus profiles by X-ray microprobe analysis and refractive index profiling, respectively, subsequent to the tube collapse. By comparison with calculated profiles, diffusion coefficients could be determined, which are fitted by an Arrhenius function, where the preexponential D 0 = 10 -0.18 cm 2 s -1 is constant but the activation energy decreases with increasing concentration as E = (454-56c 0.32 )kJmol -1 K -1 , valid for a concentration range, c, between 0.04 and 10mol% P 2 O 5 . The diffusion resembles that earlier determined for aluminium in SiO 2 glass, but with smaller diffusivities and activation energies.