Finite Element Analysis of Ribbon Stack Coupling in Dry Single Tube Fiber Optic Cables

The recent trend in the fiber optic cable industry from grease filled cables to dry (grease-free) cables led to research indicating that sufficient levels of coupling between the ribbon stack and the remainder of the cable are necessary to control excess ribbon length (ERL) or slack in the cable. Under certain loading conditions, inadequate levels of coupling can lead to local accumulation of ERL and excessive signal attenuation. Water blocking greases used in the industry provided a high level of coupling; however, the cable industry desires to move toward the dry cable technology. This paper describes an application of finite element analysis (FEA) used to evaluate the structural interaction between cable ribbon and cable jacket for duct and aerial installation during multiple load cycles. The nonlinear behavior of the friction interfaces and the significant stiffness difference of the ribbons in tension and compression are considered in the evaluation. Finite element results compare closely with the measured ribbon displacements achieved in practical ribbon coupling tests for a variety of cables.

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