Thermal stresses in hermetically double-coated optical fibers

The thermal stresses in hermetically double-coated optical fibers are analy zed. Several thermal stresses and forces are important in a hermetically do uble-coated optical fiber. First, the shear stress at the interface of the glass fiber and primary coating will make hermetical coatings be delaminate d from the glass fiber. Second, the compressive radial stress at the interf ace of the glass fiber and primary coating would produce microbending loss. Third, the compressive axial force in the glass fiber would induce the buc kling of the fiber and also results in an increase of bending loss. Finally , the normal stresses in the hermetical coatings will make the hermetical c oatings be broken. To minimize these thermal stresses and forces, the therm al expansion coefficient of the primary coating and the Poisson's ratios of the primary coating and secondary coating should be decreased. The thermal stresses in the hermetically double-coated optical fibers are compared to those in the hermetically single-coated optical fibers. It was found that t he hermetical coatings of double-coated optical fibers are more easy to be delaminated from the glass fiber than that of single-coated optical fibers, and double-coated optical fibers will induce larger microbending loss than single-coated optical fibers. Based on the strength consideration, a best selection of hermetical coatings to minimize the thermal stresses is also d iscussed. (C) 1999 American Institute of Physics. [S0021-8979(99)00806-3].