Fiber density requirements for skeleton-type optical cables

Fiber density in skeleton-type optical cables is determined by the arrangement of optical fibers within the peripheral skeleton, the pitch of the wrapping around the central skeleton, and the design of the skeleton grooves, typically allowing high fiber packing while maintaining flexibility and mechanical protection.

Skeleton Cable Structure and Fiber Arrangement

Skeleton-type optical cables consist of a central skeleton that provides structural support and a peripheral skeleton that holds the optical fibers. The peripheral skeleton is embedded with optical fibers in a pre-wrapped or tight-buffered configuration and is continuously wrapped around the central skeleton according to a preset pitch, which typically ranges from 100 mm to 1000 mm depending on design requirements . This wrapping ensures that fibers are protected from external stress while allowing some flexibility. The fibers can be arranged in bundles or ribbon-like formations within the skeleton grooves. In full-dry skeleton tight-buffered designs, each fiber is placed in a tight sleeve within the skeleton slot, which reduces resin usage and allows for compact fiber packing without compromising mechanical performance . The skeleton groove geometry is optimized to provide excess fiber length, improving bending performance and reducing the risk of fiber breakage during installation or environmental changes.

Factors Affecting Fiber Density

1. Skeleton Groove Design: The size and shape of the skeleton grooves determine how many fibers can be accommodated. U-shaped or SZ spiral grooves are commonly used to maximize fiber count while maintaining flexibility .
2. Pitch of Peripheral Wrapping: A smaller pitch allows more layers of fibers to be wrapped around the central skeleton, increasing fiber density, but may reduce flexibility. Conversely, a larger pitch improves flexibility but reduces fiber density .
3. Fiber Type and Buffering: Tight-buffered fibers occupy less space than loose-tube fibers, allowing higher density in the same skeleton structure .
4. Cable Diameter Constraints: The outer diameter of the central skeleton is typically 5–15% of the total cable diameter, which influences how many fibers can be wrapped around it .

Practical Implications

Skeleton-type optical cables are widely used in FTTH access networks, interoffice connections, and distribution networks because they allow high fiber density in a compact, mechanically robust design. The combination of a rigid central skeleton and flexible peripheral skeleton ensures that even with high fiber counts, the cable maintains good bending performance, lateral pressure resistance, and ease of splicing . The all-dry design also prevents moisture intrusion and simplifies installation. In summary, fiber density in skeleton-type optical cables is a function of groove geometry, wrapping pitch, fiber type, and cable diameter, allowing designers to balance high fiber counts with mechanical flexibility and installation efficiency .