Fiber Optics, also called optical fibers, are microscopic strands of very pure glass with about the same diameter of a human hair. Thousands of these optical fibers are arranged in bundles in optical cables and are used to transmit light signals over long distances. The bundles are protected by a jacket, which is the cable's outer covering.
The single optical fiber consists of the core which is the thin glass center of the fiber where the light travels, the outer optical material that surrounds the core and reflects the light back into it is the cladding, and the plastic coating that protects the fiber from moisture and damage is the buffer coating.
Single-mode and multi-mode are the two types of optical fibers. The single-mode, used for long distances, has small cores and transmits infrared laser light. The multi-mode, normally used for short distances, has large cores and transmits infrared light.