Analysis of Thermally Induced Loss in Fiber-Optic Ribbons

Unless special precautions are taken, fiber-optic cables installed in the outside plant could experience temperatures ranging from --45°F * Plastics Engineering Consultants, Inc., Lawrenceville, GA. 993 to +190°F. Thus, optical transmission loss resulting from this thermal history directly impacts the coating and ribbon choices for a particular system design. An understanding of the relationships among the thermally induced strains on the "ribboned" glass fibers, the resulting added transmission loss, and fiber parameters is crucial to properly evaluating candidate fiber-coating materials, ribbon structures, and/or ribbon-matrix materials. Moreover, it is desirable to be able to predict long-term behavior from short-term testing, thereby simplifying the environmental testing procedure. The added loss in environmental testing is generally thought to be associated with the microbending of the axis of the fiber. Moreover, it has been shown by other investigators that when intimate contact is forced between a fiber and a microscopically rough surface, losses due to microbending can be substantial and are a function of the fiber geometric and optical parameters as well as the elastic modulus of the rough surface.1,2 Therefore, thermally induced strains on the ribbon structure can indirectly result in added loss by increasing the contact forces between fibers. In addition, the sensitivity of a particular fiber to microbending loss is said to be associated with irregularities at the core-cladding interface, which may be due to core-diameter variations and/or refractive index variations.3 In this paper, a thermoviscoelastic analysis is used to compute the axial and transverse strains that are imparted to a fiber-optic ribbon when it is subjected to any given thermal cycle.