PREDICTED STRESSES AND STRAINS IN FUSED BICONICAL TAPER COUPLERS SUBJECTED TO TENSION

In fused biconical taper (FBT) couplers, the cores of the fibers are p ositioned close to each other. In order to bring the cores of the fibe rs in close proximity, the cladding in the fused midportion of the cou pler has to be made thin. At the same time the coupler must be suffici ently strong, both on a short- and a long-time scale, and must be able to withstand appreciable axial deformations. These can be caused by t he thermal contraction mismatch of the coupler with its substrate or c an be due to a deliberate prestressing of the coupler structure in ord er to improve its dynamic stability. In this study an easy-to-apply an alytical stress model is developed for the evaluation of stresses and strains in FBT couplers from the expected or measured total elongation . In the analysis the nonprismaticity of the coupler structure as well as the nonlinear behavior of the material was considered. The numeric al example has been carried out for a coupler that is intended for und ersea applications. The results obtained can be used in the stress-str ain analyses and physical design of light-wave FBT couplers.