In the early 1980s fiber-optic cables connected most of the major cities in North America. Today fiber-optic cables circle the globe caring voice, video and data signals over these glass fibers. There are many different types of fiber-optic cables dedicated to many different applications, but they all share the same common configuration.
The very center of the fiber-optic cable is a thin piece of glass that provides the path that the light signals follow. This part of a fiber-optic cable is called the core. The core is very small in diameter. Both single-mode and multimode fibers (cores) are 125 microns outside diameter. To put this in perspective, a micron is one 1 millionth of a meter, or 125 microns, and is equal to 0.005 inch.
The core is covered or surrounded by optical material. This part of the fiber-optic cable is called the "cladding." Typically the cladding is also made of extremely pure glass just like the core, although there are variations that use plastic. The cladding's job is to surround the core and reflect light signals back into the core. As light signals travel through the core they do not always travel in the direct line but may angle off in many different directions.
Surrounding the cladding (which in turn surrounds the core) is the next part of the fiber-optic cable and it is called the buffer coating. The buffer coating does not perform any electrical functions. Its job is to protect the cladding covered core from damage or moisture. Typically the buffer coating is composed of plastic.
The outer jacket is the last part of the fiber-optic cable. Sometimes called the outer sheath, this jacket is composed of very tough polyurethane and protects the interior components of the fiber-optic cable. Some fiber-optic cables have an additional part or layer between the outer jacket and the buffer called the Aramid (Kevlar) strength member.