A basic optical fiber cable consists of a core, cladding, protective coatings, strength members, and an outer jacket, each serving a critical role in transmitting light signals safely and efficiently.

Core

The core is the central part of the fiber that carries light signals. It is typically made of high-purity silica glass or, in some cases, plastic. The core's refractive index is higher than the surrounding cladding, enabling total internal reflection, which confines light within the core for long-distance transmission with minimal loss. Core diameters vary: single-mode fibers usually have cores around 8–10 microns, while multimode fibers range from 50 to 100 microns, depending on the application .

Cladding

Surrounding the core is the cladding, made of glass with a slightly lower refractive index than the core. This difference in refractive index ensures that light reflects back into the core rather than escaping, maintaining signal integrity. Standard cladding diameters are typically 125 microns, with larger sizes like 140 microns used for specific multimode fibers. The cladding also provides mechanical protection to the fragile core .

Coating and Buffer Layers

The primary and secondary coatings or buffer layers are applied over the cladding to protect the fiber from mechanical stress, abrasion, and moisture. These coatings are usually made of polymer materials and help cushion the fiber during handling, installation, and environmental exposure. They also prevent microbending and macrobending losses that can degrade signal quality .

Strength Members

Strength members are reinforcing elements embedded within the cable to provide tensile strength and prevent stretching or breaking. Materials such as Kevlar yarns, fiberglass rods, or steel wires are commonly used. These members are crucial for outdoor or long-distance installations where the cable may be subjected to pulling forces or environmental stress .

Outer Jacket

The cable jacket is the outermost protective layer, made from durable materials like PVC, LSZH (Low Smoke Zero Halogen), or PVDF. It shields the internal components from environmental hazards, including moisture, chemicals, and physical impact. LSZH jackets are preferred in indoor environments for fire safety, as they emit minimal smoke and no toxic halogens when burned .

Additional Features

Some optical cables include ripcords beneath the jacket to facilitate easy removal during splicing or termination. In high-density or specialized applications, fibers may be arranged in ribbons or bundles, sometimes with light-absorbing materials between fibers to reduce crosstalk .

Summary

In essence, an optical fiber cable is a carefully engineered assembly where each layer—from the core to the outer jacket—ensures efficient light transmission, mechanical protection, and environmental resilience. Understanding these components is essential for selecting the right fiber type for specific telecommunications, data center, or industrial applications .