PREPARATION OF OPTICAL CORES OF SILICA OPTICAL FIBERS BY THE SOL-GEL METHOD

Preforms for drawing silica optical fibers have been fabricated by usi ng the MCVD method for the preparation of the optical claddings and th e sol-gel method for the preparation of the optical cores consisting o f TiO2-SiO2 or RE(3+)-Al2O3-P2O5-SiO2 (RE = Er, Yb) glasses. A novel m ethod has been developed for depositing thin gel layers on the inner s ilica tube wall, under rotation of the tube inclined at a small angle to the horizontal. The gel layers have been deposited from sols prepar ed by mixing Si(OC2H5)(4), POCl3, Ti(n-OC4H9)(4), AlCl3, ErCl3, YbCl3, H2O, C2H5OH and HCl. The gel layers deposited using these sols on the inner tube wall were heat-treated in a flow of CCl4 or POCl3 with O-2 at temperatures of from 800 degrees to 1400 degrees C. After collapsi ng the composite tube into a preform, an optical fiber has been drawn. The refractive-index profiles of the preforms and the attenuation spe ctra of the drawn fibers are shown, as well as some results on the las ing characteristics of Yb3+ sensitized, Er3+ doped fibers.