Residual stresses of fibers in tape-type optical cable and their reduction

When the tape-type optical fibers are twisted or cabled, longitudinal stress is generated in the fibers. This stress has been discussed solely as a practical problem on the stress generation among the tape-type fibers. In this paper, a practical model is set up and calculation is conducted for the stress generated in the fibers of a tape-type optical cable. Under the practical condition of normal tape cabling, the main stresses generated on the fiber surfaces are governed by the twists appearing on the individual fibers. The direction of the main stress caused by the twist is different from the stress direction by the conventionally applied screening strength test. Accordingly, it is needed to apply screening to the fiber elements in a tape-type cable under more intense tensile stress. To reduce the fiber stresses generated by the fiber tape cabling, we propose a “pre-twisting method” where the fibers are pretwisted in the opposite direction to that of tape cabling, thereby cancelling the cabling stresses. Its effectiveness has been made clear by the experiment.