Fiber optic cables are made of very thin strands of glass or plastic, each of which is less than a tenth the thickness of a human hair. These threads are known as optical fibers, and each of them is capable of transmitting around 25,000 phone calls. Fiber optic cables typically range from a minimum of two to several hundred strands.
To ensure uninterrupted light transmission, the glass used in the manufacture of optical fibers must be very pure, so the core of a cable is usually made of silicon dioxide. Surrounding this core is a somewhat different layer or coating of glass, which is usually infused or "doped" with remnants of elements such as boron or germanium.
The core and cladding are covered with a plastic cladding and a Kevlar or metal fiber cladding, and the entire assembly is sealed against water and dirt by a protective outer layer.
