Sol-gel fabrication and properties of silica cores of optical fibers dopedwith Yb3+, Er3+, Al2O3 or TiO2

Optical cores of preforms for drawing optical fibers doped with Er3+ and Yb 3+ were fabricated by the sol-gel method with the aim of increasing the thi ckness of glass layers coated in a single coating cycle and to determine th e relation between the preparation conditions and optical properties of the fibers. Al2O3-P2O5-SiO2 and TiO2-P2O5-SiO2 glasses have been studied as ma trices for entrapping the rare-earth elements. Input sols have been prepare d from silicon and titanium alkoxides, AlCl3, ErCl3, YbCl3, POCl3, water an d a modifier under acidic catalysis of HCl. The sols were coated on the inn er wall of a silica substrate tube and the gel layers were sintered at high temperatures up to 2000 degrees C after which the tube was collapsed into the preform. Continuous and homogenous glass films with the maximum thickne ss of about 8 mu m were fabricated. The influence of high-temperature heat treatment of the layers on their composition and optical attenuation was ob served. The amplified stimulated emission of Er3+ around 1.55 mu m was meas ured under the excitation of the fibers by an Nd :YAG laser at 1.064 mu m.