Thermodynamical behavior of the E’ center in the optical-fiber drawing process

The influence of the drawing condition on the concentration of E' centers in SiO₂-based fibers is examined using electron-spin-resonance techniques. The E'-center concentration increases with increasing maximum temperature in the drawing furnace. Moreover, with increasing drawing speed, the E'-center concentration increases in the region below 100 m/min and decreases in the region above 100 m/min. These results are analyzed on the basis of the thermodynamical theory of point defects and the following conclusions are obtained: (1) The concentration of precursors for the E' center is 7.8×{}10²² g^-1. (2) The activation energies for creation of the E' center and for its reconversion to a precursor are 11 and 7 eV, respectively. (3) The E' center is created through the evaporation of oxygen atoms from the SiO₂ glass network.