The core of optical fiber cables

The core of an optical fiber cable is typically made of ultra-pure glass (silicon dioxide) or, in some cases, specialized plastic, and it serves as the medium through which light signals travel.

Material Composition

The core is usually composed of high-purity silica glass (SiO2), which is exceptionally transparent and allows light to travel long distances with minimal signal loss. For certain short-distance applications, plastic cores are used, which are easier to manufacture and handle but have higher attenuation compared to glass cores . To modify the optical properties, trace elements like germanium dioxide may be added to increase the refractive index of the core relative to the surrounding cladding .

Core Structure and Function

The core is a cylindrical strand at the center of the fiber, surrounded by a cladding layer with a slightly lower refractive index. This difference enables total internal reflection, which confines light within the core and allows it to propagate over long distances without escaping . The core's diameter varies depending on the fiber type:

• Single-mode fiber: Core diameter is typically 8–10 microns, usually 9 microns, allowing light to travel in a single path for long-distance, high-bandwidth applications .
• Multimode fiber: Core diameter is larger, typically 50–62.5 microns, allowing multiple light paths, suitable for shorter distances like campus networks or indoor installations .

Summary

The core is the functional heart of the optical fiber, responsible for transmitting light signals efficiently. Its material (glass or plastic), diameter, and refractive index are carefully engineered to optimize signal transmission for specific applications, from high-speed internet backbones to short-range data links .