Relaxation of internal stresses in optical fibers

A method for measuring the relaxation of internal stresses of optical fibers is developed. The authors discuss a few principal previous publications on the subject of annealing and relaxation of glass. The internal stress measurement setup is explained, and useful relations are given. It is pointed out that the relaxation of internal stresses of optical fibers can be represented by the equations of J. De Bast and P. Gilard (1963) σ=σ_oexp-(at) ^b (b is constant in the annealing region and a depends on temperature). It is shown that the internal stress profile change is negligible at temperatures of use after 25 years. Hence, the initial internal stress profile, i.e. the refractive index profile, of a high-tension MCVD fiber is not modified during the optical-fiber cable lifetime