Effect of high-temperature treatment on optical properties of silica filmsdoped with Al2O3, P2O5 and rare-earth elements

The paper reports effects of high-temperature treatment of silica layers do ped with Al2O3, P2O5, Yb and Er ions, which are coated inside silica substr ate tubes and transformed through viscous flow into the core of a preform, on properties of these cores. The gel layers are applied inside the silica substrate tubes from sols based on tetraethoxysilane and corresponding chlo rides in isopropanol by controlled lowering the column of the sol. The laye rs are thermally treated at 500 degreesC and subject to high-temperature tr eatment from 1000 to 1300 degreesC. The tube with the layers is collapsed i nto a preform from which fibers are drawn at about 1950 degreesC. The resul ts of concentration measurements show that during the high-temperature trea tment the content of silica in the layer increases at least five times in c omparison with that of the sol composition. This effect depends on the sol composition and the number of the coated gel layers. Measurements show that in the prepared fibers there is some remaining unsaturated absorption of e rbium ions at 1535 nm, which is related to quenching of the erbium ions.