Optical cables are primarily made of ultra-pure glass (silica) or plastic fibers, surrounded by cladding, protective coatings, and additional layers for strength and environmental protection.

Core and Cladding

The core of an optical fiber is the central part through which light travels. It is typically made from ultra-pure silica glass or, in some cases, specialized plastics like PMMA (polymethyl methacrylate) for polymer optical fibers . The cladding surrounds the core and has a slightly lower refractive index, which ensures that light is reflected back into the core through total internal reflection, allowing efficient light transmission over long distances . In glass fibers, the core may be doped with small amounts of germanium oxide to increase the refractive index, while the cladding may contain fluorine to lower it .

Protective Coatings and Buffers

Around the cladding, a buffer layer is applied, usually made from acrylate polymers or polyimide, to protect the fiber from physical damage and environmental factors . This buffer can be part of a resin tube or core tube, which forms the cable core. Additional layers, such as Kevlar yarn, aramid fibers, or steel strength members, provide tensile strength and protect the fiber from stretching, crushing, or impact .

Outer Sheathing and Armor

The outermost layers of an optical cable, called the jacket or sheathing, are made from materials like PVC, polyethylene, or other plastics, chosen based on the installation environment. For outdoor or submarine cables, extra protection may include water-repellent gels, solid barriers, or armored layers to prevent damage from moisture, animals, or mechanical hazards .

Glass vs. Plastic Fibers

• Glass fibers: Made from silica, they offer low signal loss and are ideal for long-distance transmission but are more fragile and harder to handle .
• Plastic fibers: Made from polymers like acrylate or polyimide, they are more flexible and easier to install but have higher signal attenuation, making them suitable for short-distance applications .

Summary

In essence, optical cables are a layered assembly: a light-carrying core of glass or plastic, surrounded by cladding, protective coatings, strength members, and an outer jacket. Each material is selected to optimize light transmission, durability, and environmental resistance, enabling high-speed data communication across various applications .