Classification of internal structure of optical cables

Optical cables consist of a core, cladding, coating, strength members, and an outer jacket, each designed to ensure efficient light transmission and mechanical protection.

Core

The core is the central part of an optical fiber where light signals travel. It is typically made of high-purity silica glass or, in some cost-sensitive applications, plastic polymer. The core has a high refractive index, which allows light to propagate through total internal reflection. Core diameters vary by fiber type: single-mode fibers have cores around 8–10 microns for long-distance transmission, while multimode fibers range from 50 to 62.5 microns for shorter distances. The purity and precision of the core are critical to minimize signal attenuation, which can be as low as 0.2 dB/km for high-quality glass fibers .

Cladding

Surrounding the core is the cladding, made of glass or plastic with a lower refractive index than the core. This difference ensures that light remains confined within the core via total internal reflection, maintaining signal integrity over long distances. The cladding also provides a protective layer that helps prevent light leakage and reduces signal loss .

Coating (Buffer Layer)

The coating, or buffer layer, is a polymer layer applied around the cladding. It provides mechanical protection, moisture resistance, and durability during handling and installation. Common materials include acrylate polymers, which cushion the fiber and prevent microbending or breakage .

Strength Members

To enhance durability, optical cables include strength members such as aramid yarn (Kevlar), fiberglass, or steel wires. These components protect the fiber from mechanical stress, bending, and stretching, especially in outdoor or harsh environments. They also help the cable withstand tension during installation or long spans .

Outer Jacket

The outer jacket encases all internal components, providing the final layer of protection against environmental hazards such as UV exposure, moisture, abrasion, and fire. Jackets are often color-coded to indicate fiber type (e.g., yellow for single-mode, orange for multimode) and are selected based on installation requirements, including indoor, outdoor, or armored applications .

Summary

The combination of core, cladding, coating, strength members, and outer jacket ensures that optical cables can transmit data at high speeds over long distances with minimal loss while remaining robust against physical and environmental stresses. Advances in materials and design continue to improve performance, enabling applications in telecommunications, data centers, medical devices, and emerging technologies like 5G and AI networks .