Streamlining the construction of optical communication networks with extremely small-diameter and lightweight optical fiber cablesExtremely high-density optical fiber cable technologyNTT Access Network Service Systems Laboratories

This is an optical fiber cable technology in which optical fibers are mounted in extremely high density and made extremely small-diameter and lightweight. Using this technology, we have developed 24- to 200-fiber self-supporting and non-self-supporting cables for aerial facilities, and 100- and 200-fiber water blocking cables for rising sections. The 200-fiber cable has achieved a 30% reduction in outer diameter and a 60% reduction in weight compared to existing optical fiber cables. When applied to aerial sections, these optical fiber cables can be installed without the use of a pulling machine, etc., by taking advantage of their light weight. By taking advantage of the small diameter, more optical fibers can be installed when applied to sections that have limited cable installation space, such as conduits.
This enables the creation of more efficient optical communication networks.

It is important to ensure that optical fiber cables have stable transmission characteristics and sufficient reliability under long-term use in a real environment. In order to satisfy these characteristics, conventional optical fiber cables were designed to be protected by slotted rods that prevent external forces such as bending and strain from being applied to the optical fiber. Therefore, there was a limit to how small the diameter of the cable could be. In addition, when constructing an optical communication network using multi-fiber cables, technology to enable the connection of multiple optical fibers at once is essential to enhancing the efficiency of optical fiber splicing. For this reason, optical fiber ribbons (Fig. 2(b)), which consist of multiple optical fibers are aligned in parallel and are coated with co-coating, have been widely used in Japan and overseas. However, conventional optical fiber ribbons are structurally difficult to flexibly deform, meaning that when they are stored in high density, the optical fibers in the optical fiber cable are subjected to excessive bending and strain, increasing the possibility of increased optical loss and breakage. For this reason, it is important to achieve both mass connectivity, as well as reductions in bending loss and strain, to reduce the diameter and increase the density of multi-fiber cables.

• Using low-bending-loss optical fibers and a new structure of partially-bonded ribbon has made the optical fiber cables extremely high-density
• Lighter weight improves the workability of optical fiber cables
• Smaller diameters enable the effective use of optical fiber cable installation space

In this technology, we have developed a new structure, "partially-bonded ribbon," in which multiple low-bending-loss optical fibers are partially bonded. The use of low-bending-loss optical fiber reduces increases in optical loss caused by high-density mounting of the optical fiber in the cables.
In addition, partially-bonded ribbon can be flexibly deformed to reduce the strain applied when optical fiber is densely mounted in the cable.
These technologies have enabled the ultimate in small-diameter, high-density optical fiber cables.

Low-bending-loss optical fiber
A typical optical fiber used for optical communication is made of two quartz glasses with different refractive indices. The center of the optical fiber is formed by a high refractive index part called the "core," and a low refractive index part called the "cladding" formed around the periphery. This structure allows light to be trapped in a core, which has a high refractive index. Low-bending-loss optical fiber is an optical fiber in which the difference in refractive index between the core and the cladding is relatively large, and is less prone to optical loss due to bending than conventional optical fiber.

NTT Access Network Service Systems Laboratories - Access Equipment Project