Abstract

Presently, extensive research and development efforts are under way to optimize the index profile, geometry, coating, and cable-structure of single-mode (SM) fibers^1-5. The optimization includes keeping the core diameter as large as possible for ease of splicing and connectorization, while still maintaining a high resistance against macro- and microbending (MB) losses. As in case of multimode fibers, MB losses depend on the fiber parameters, the plastic coating, and the cable structure. In contrast to MM fibers, however, MB losses in SM fibers are wavelength dependent and can be eliminated in the short-wavelength region of the SM domain as has been demonstrated previously⁷. While a truly satisfactory test regarding the MB resistance of a SM fiber can only be made with a cabled and deployed fiber, simulated tests must be used to facilitate the fiber optimization process. One such test, which has become known as the ’Basket Weave" (BW) test, consists of multi-level winding the fiber on a spool, and measuring the spectral losses for different winding tensions⁷. A high immunity against the ensuing stresses is a measure of a superior jacketed-fiber structure. In addition to possibly incurring MB’s due to the transverse pressure exerted by adjacent windings, the fiber may suffer losses due to winding crossings, and macrobends due to the curvature of the spool. Because of the relaxation of the rewind stresses of the plastic-coated fiber, the excess losses generally decrease with time, and meaningful comparisons of data can only be made if the measurements are performed a specific time after the rewind process.