Thermal stress in a polymer-coated optical glass fiber with a low-modulus coating at the ends

A polymer-coated glass fiber with a low-modulus coating at the ends is considered. The objective of the analysis is to find out if there is sufficient incentive to use such a dual coating system for lower interfacial thermally induced stresses. These are due to the different coefficients of thermal expansion (contraction) of the dissimilar materials in the trimaterial structure. The study is restricted to the evaluation of the shearing stresses only and is based on a simplified strength-of-materials model, rather than on a rigorous theory-of-elasticity method. Such a approach seems to be justified, since the most accurate predictions of the magnitude and the distribution of the induced stresses are beyond the scope of this analysis. On the basis of the calculated data, we conclude that there is a definite incentive for employing a bimaterial coating system, in which ``conventional{''} (high modulus) polymeric material is used in the midportion of the fiber, while a low-modulus material (typically, with a higher coefficient of expansion) is applied at its ends. Such a system could be recommended, when there is a need to bring down the interfacial stresses, and the possible increase in the manufacturing cost is not viewed as an obstacle.