Structure of the outer sheath of optical cable

The outer sheath of an optical cable is a protective layer, often armored, that shields the cable from mechanical damage, moisture, and environmental hazards.

Composition and Function

The outer sheath, also called the outer jacket, is the external layer of an optical cable that provides mechanical protection and environmental resistance. It is typically applied over the inner sheath or directly over the cable core and may include armor for additional durability. Its main functions are: Mechanical protection: Prevents crushing, bending, or stretching of the cable.

Moisture and corrosion resistance: Protects the inner fibers from water ingress and corrosion of any metallic components. Environmental shielding: Guards against rodents, UV exposure, and chemical damage.

Types of Armor and Materials

Depending on the installation environment, the outer sheath may include armoring layers: Plastic-coated steel tape or stainless steel tape for overhead or direct burial applications. Single-layer or double-layer steel wire for high-strength protection. Nylon armor for lightweight protection in specialized applications.

To prevent corrosion of the metal armor, an additional outer protective layer is applied, often made of polyethylene (PE) or high-density polyethylene (HDPE) for outdoor use. In some designs, the cable core is filled with a compound or oil to prevent moisture from spreading inside the cable, enhancing durability in harsh conditions.

Variations for Different Applications

Direct burial cables: Require robust armored sheaths to withstand soil pressure and potential rodent damage. Aerial or climbing installations: Use lighter armor with UV-resistant outer jackets. Underwater cables: May include stainless steel or specialized polymer coatings for corrosion resistance.

Summary

The outer sheath of an optical cable is a multi-functional protective layer that combines mechanical strength, environmental resistance, and sometimes armoring. Its design varies according to the installation environment, ensuring the optical fibers inside remain safe and functional over the cable's lifespan.