Long-term reliability of layer-type tight structure cable

The long-term reliability of the optical-fiber strength in the tight structure cable is discussed from the viewpoint of residual fiber strain and prooftesting condition. The maximum fiber strain in the installed tight structure cable was evaluated as 0.05 percent experimentally as the summation of: 1) compressive strain induced by nylon jacketing; 2) added strain during cable; 3) residual strain by cable installation; and 4) thermal strain in the installed condition. Based on these measured residual strains on the typical 12-fiber cable with silicone resin and nylon-coated fiber, the required prooftest level was found to be 0.19 percent in order to guarantee the 10 000-km fiber for 25 years with failure probability less than 10^-3.