Optical fibers by a hybrid process using sol–gel silica overcladding tubes

Abstract We have successfully developed a sol–gel process to produce large silica glass bodies to be used as optical fiber preform overcladding tubes which meet the demands of optical fiber. We have made and tested tubes weighing approximately 4.5 kg, which comprise about 90% of the eventual fiber's mass. This sol–gel process uses colloidal silica dispersed in high pH water. The sol is cast, gelled by reducing the pH and dried to a porous tube. The dried body is heat treated to remove organics, to dehydrate and to purify by removing both refractory oxide particles and transition metal ions to the parts/billion range and then sintered to transparency in He. These tubes are competitive with vapor deposited synthetic silica tubes and produce fiber meeting current commercial standards. Net shape formation of large precision glass bodies by gel casting is demonstrated.