Evaluation of high-temperature absorption coefficients of optical fibers

The large absorption coefficient /spl alpha/ of single-mode optical fiber at high temperatures is closely related to the generation of the fiber fuse phenomenon. We propose a high-temperature loss-increase mechanism, which includes three factors that bring about an increase in the /spl alpha/ values: 1) point-defect (Ge E´ center) formation; 2) electronic conductivity due to the thermal ionization of a Ge-doped silica core; and 3) thermochemical SiO production in the silica glass. Ge E´-center formation and electronic conductivity in the Ge-doped silica core are dominant factors at temperatures near the critical temperature of 1323 K. However, these factors cannot explain the large /spl alpha/ values observed at high temperatures above 2273 K. By contrast, SiO gas and/or solid, which are thermochemically produced in the silica glass, exhibit large /spl alpha/ values of the order of 10⁴ m/sup -1/ at 2293 K. The /spl alpha/ value estimated at 0.5 μm is close to the experimental value reported in the fiber fuse experiments.