Components of Optical Cable Sheath

The optical cable sheath consists of an inner and outer protective layer that shields the fiber core from mechanical, environmental, and moisture damage, often including armor for additional protection.

Core and Cladding

At the center of an optical cable is the core, typically made of ultra-pure silica glass or plastic, which carries the light signals. Surrounding the core is the cladding, a layer with a slightly lower refractive index that confines light within the core through total internal reflection. The core and cladding are coated with a primary protective layer to prevent physical damage and maintain optical performance.

Strengthening Members

To withstand tensile forces and mechanical stress, optical cables include strengthening fibers or members. These can be placed centrally within the cable core or along the outer periphery of the sheath. Central strengthening is common in layer-stranded or skeleton-type cores, while peripheral reinforcement is often used in U.

S.-style designs.

Inner Sheath

The inner sheath surrounds the cable core and strengthening members. It provides mechanical protection and prevents moisture ingress. Common materials include semi-hermetic bonded layers, such as plastic-coated aluminum (PAP) or steel strips (PSP), which are longitudinally bonded around the core.

Outer Sheath (Jacket)The outer sheath, or jacket, is the external layer that further protects the cable from environmental hazards, abrasion, and chemical exposure. In some applications, the outer sheath is armored with steel tape, stainless steel, or nylon to allow direct burial, climbing, underwater installation, or rodent resistance. For additional protection, oil-filled compounds may be used inside the cable core to prevent moisture spread.

Summary

In essence, the optical cable sheath is a multi-layered structure designed to protect the delicate optical fibers while maintaining flexibility and durability. The combination of inner and outer sheaths, strengthening members, and optional armor ensures reliable performance in diverse environments, from indoor patch cords to outdoor long-distance installations.