Relaxation of the axial strain induced stresses in double-coated optical fibers

The axial strain induced stresses in double-seated optical fibers are analy zed by the viscoelastic theory. A closed form solution of the axial strain induced viscoelastic stresses is obtained. The viscoelastic stresses are a function of the radii, Young's moduli, relaxation times and Poisson's ratio s of the polymeric coatings. If the applied axial strain linearly increases , the induced stresses increase with the time. On the other hand. if the ax ial strain is fixed, besides the axial stress in the glass fiber, the stres ses exponentially decrease with the Lime. The relaxation of stresses is str ongly dependent on the relaxation times of the polymeric coatings. If the r elaxation time of the polymeric coating is very long, the viscous behavior of the polymeric coatings will not appear, and the axial strain induced str esses solved by the viscoelastic theory are the same as those solved by the elastic theory. On the other hand, if the relaxation time of the polymeric coating is very short, the relaxation of stresses is very apparent, A comp ressive radial stress at the interface of the glass fiber and primary coati ng will result in an increase of the transmission losses, and a tensile int erfacial radial stress will possibly produce debonding at the interface of the glass fiber and primary coating, To minimize this interfacial radial st ress, the radius, Youngs modulus and Poisson's ratio of the polymeric coati ngs should be appropriately selected, and the relaxation time of the primar y coating should be shortened. Finally the stresses in single-coated and do uble-coated optical fibers are discussed.