Stress Relaxations at Elevated Temperatures in Optical Fibers Based on Silica Glass

Stress relaxations in a bent optical fiber were measured at temperatures well below the glass transition temperature. Experimental data were analyzed using the "stretched exponential" equation or the Kohlrausch-Williams-Watts (KWW) function. It is found that the relaxation time increases with decreasing temperature and is described well by the Arrhenius equation-type dependence. The activation energy of relaxation for glass with a low content of hydroxyl groups turned out to be noticeably higher than for glass with a high content of hydroxyl groups (322.3 +/- 13.6 and 259.5 +/- 10.3 kJ/mol, respectively). The obtained parameters make it possible to estimate the degree of relaxation of stressed optical fibers based on silica glass on time when used at high temperatures.