Optical fibers are primarily made of highly pure glass (silica) or plastic, with a core, cladding, and protective coating designed to guide light efficiently.

Core Material

The core is the central part of the fiber where light travels. It is made of highly purified silica glass (SiO₂) or, in some cases, specialized plastics such as acrylate or polyimide . The purity of the core material is critical because impurities can cause signal loss, known as attenuation. In glass fibers, additional chemicals like germanium tetrachloride (GeCl₄) or phosphorus oxychloride (POCl₃) may be added to adjust the refractive index and improve optical properties .

Cladding

Surrounding the core is the cladding, which is also made of glass or plastic but has a lower refractive index than the core. This difference in refractive index enables total internal reflection, keeping light confined within the core and allowing it to travel long distances with minimal loss . In glass fibers, the cladding is often fluoride-doped silica, while in plastic fibers, it is made from compatible polymers .

Protective Coating

The coating or buffer surrounds the cladding to protect the fiber from physical damage, moisture, and environmental stress. This layer is typically made of plastic materials such as acrylate, polyethylene, or Kevlar-reinforced layers for added strength . In fiber optic cables, multiple fibers are bundled together around a central support, which may be a steel wire or high-strength plastic, and then covered with additional protective layers.

Types of Fibers

• Single-mode fibers have a very small core (around 9 micrometers) and are ideal for long-distance communication because they allow only one light mode to propagate .
• Multi-mode fibers have a larger core (typically 50–125 micrometers) and can carry multiple light modes, making them suitable for shorter distances and high-power applications .

Summary

In essence, optical fibers are sophisticated waveguides made of glass or plastic cores, surrounded by cladding with a lower refractive index, and protected by plastic coatings. The choice of materials and chemical additives directly affects the fiber's signal transmission efficiency, flexibility, and durability, making them essential for high-speed data communication, medical imaging, and other optical applications .