In the conventional method of delivering FTTH (Fiber-To-The-Home) fiber optic networks services, ribbon slotted-core cables (Fig.1) are generally used as underground cables. The slotted core-type cables contain in their slots multiple layers of optical fiber ribbons, each of which is made of four 0.25-mm diameter optical fibers assembled together side by side in a jacket (coating). To connect a fiber optic cable to equipment in a subscriber's premises, a fiber ribbon is pulled out from one of the slots and the ribbon jacket needs to be removed to take out a single-core fiber.
To eliminate the removal of cable jackets and enhance handling properties, we have developed a new underground cable solution using bundled cable units (Fig.3), which contain multiple 0.5-mm single-core fibers (Fig.2). The new underground optical cables are now available in three types of products: "slotless-type 40-fiber cable" (Fig.4) with reduced fiber diameter and weight for improved workability; "slot-type 40-fiber cable" (Fig.5) for use in difficult installation conditions, such as frozen ducts; and "slot-type 100-fiber cable" that meets the need for multi-core cables. Individual units of 0.5-mm optical fiber cables are bound with a broad and shiny color-code binding tape for easy identification of a specific cable unit in dark conditions underground.