Longitudinal Section Diagram of Optical Cable

A longitudinal section of an optical cable reveals a core, cladding, protective coatings, and outer sheathing designed to guide light and protect the fiber along its length.

Core and Cladding

At the center of the optical cable is the core, typically made of high-purity silica glass or plastic, where light signals propagate. Surrounding the core is the cladding, made of similar material but with a slightly lower refractive index to ensure total internal reflection, which keeps light confined within the core along the cable's length . In single-mode fibers, the core diameter is usually around 9 µm, while multimode fibers have cores of 50 µm or 62.5 µm .

Primary Coating and Buffer

Encasing the cladding is a primary coating, usually a polymer layer, which provides mechanical protection and prevents microbending or surface damage to the fiber. This coating does not affect light propagation but is essential for durability . Around the coated fiber, a buffer layer or core tube may be added to further protect the fiber from mechanical stress, moisture, and environmental factors.

Strength Members and Outer Sheath

For cables used in outdoor or long-distance applications, strength members such as aramid yarns, fiberglass rods, or steel wires are included along the longitudinal axis to bear tension and prevent stretching during installation . The outer sheath or jacket, made of durable plastic or polymer, provides additional protection against abrasion, moisture, and chemical exposure, completing the longitudinal structure of the cable .

Additional Features

Some optical cables include ripcords for easy jacket removal, water-blocking gels or tapes to prevent moisture ingress, and light-absorbing layers to reduce crosstalk between fibers in bundles . In high-density or ribbon cables, multiple fibers are arranged in parallel within the longitudinal section, each individually coated and protected.

Summary

The longitudinal section of an optical cable illustrates a carefully engineered structure: core → cladding → primary coating → buffer → strength members → outer sheath, ensuring efficient light transmission, mechanical strength, and environmental protection over the cable's entire length . This design allows optical cables to reliably transmit data at high speeds over long distances.