Entry and Termination of Central Core Optical Cables Containing Flexible Unit Tubes

Several vendors have introduced a new cable design that combines the compactness and efficiency of central core cables with the filter identification of loose tube cables. The new cable design contains flexible 12-fiber unit tubes in a dry central tube. The flexible unit tubes are significantly smaller than traditional loose tubes, with a diameter of 1.7 mm. The minimum bend radius of the flexible unit tubes is limited solely by the fiber requirements. The new cable design has advantages in termination over both traditional fiber bundle central core cables and loose tube cables. This paper compares the termination of central core cables containing flexible unit tubes with the termination of loose tube cable designs. The flexible unit tubes have a 15-mm minimum bend radius and little memory, allowing them to be easily inserted into a splice closure. Loose tubes typically maintain the helix that was imparted to them during cable construction and are stiff, complicating the routing and storage of the tubes within a splice closure. Flexible unit tubes are much easier to store within a closure. Besides the difference in cable entry and closure installation, the method of opening the flexible unit tubes is significantly different from opening loose tubes. Results from a study measuring the impact on transmission in live fibers during mid-span opening of the flexible unit tubes are presented indicate that mid-span entry of the unit tubes can be accomplished without significantly affecting transmission in live fibers.