Fiber optic cables are primarily made of ultra-pure glass (silica) or plastic, with additional layers for cladding, coating, and protection.

Core Material

The core is the central part of the fiber where light travels. It is typically made from ultra-pure silica glass (SiO₂), which may be doped with small amounts of germanium oxide to increase the refractive index, allowing light to be guided efficiently through total internal reflection . In some short-distance or cost-sensitive applications, the core can be made from plastic optical fiber (POF), such as polymethyl methacrylate (PMMA), which is more flexible but less suitable for long-distance transmission .

Cladding

Surrounding the core is the cladding, which is also made of silica glass but with a slightly lower refractive index, sometimes achieved by adding fluorine. This difference in refractive index ensures that light remains confined within the core . In plastic fibers, the cladding is made from compatible polymer materials.

Coating and Buffer

The buffer or coating protects the fiber from physical damage and environmental factors. It is usually made from acrylate or polyimide plastics, often applied in dual layers: a soft primary coating to cushion the fiber and a hard secondary coating for mechanical protection . Additional protective layers may include strength members like aramid yarn, steel, or fiberglass, and outer jackets made from polyethylene or PVC for outdoor durability .

Additional Materials

During manufacturing, chemical additives such as phosphorus oxychloride or germanium tetrachloride may be incorporated to fine-tune optical properties . For specialized applications, fiber optic cables may include water-blocking gels, UV-curable resins, or metallic components for grounding and chemical resistance .

Summary

In essence, a fiber optic cable is a layered structure: a light-transmitting core of glass or plastic, surrounded by cladding, protective coatings, and optional strength and environmental layers. Glass fibers are preferred for long-distance, high-bandwidth applications due to low signal loss, while plastic fibers are used for flexibility and short-distance installations .