Ever since ancient times, people had a principal need to communicate with one another. This need created interests in devising communication systems for sending messages from one distant place to another. Optical communication methods were of special interest among the many systems that people tried to use. One of the earliest known optical transmission links was a fire-signal method used by the Greeks in the eighth century BC for sending alarms, calls for help, or announcements of certain events. Improvements of these optical transmission systems were not pursued very actively because of technology limitations at the time. For example, the speed of sending information over the communication link was limited since the transmission rate depended on how fast the senders could move their hands, the optical signal receiver was the error-phone human eye, line-of-sight transmission paths were required, and atmospheric effects such as fog and rain made the transmission path unreliable. Thus it turned out to be faster, more efficient, and more dependable to send messages by a courier over the road network. Optical fiber is a term for any sort of plastic or glass conduit meant to transport light. The principles behind it are actually quite old, but in recent years it has become an incredibly important technology, as communications infrastructure has begun to use this fiber to transmit data at extremely high rates. Aside from fiber optic communications, however, it has a number of applications in medicine, consumer products, and physics. This sort of fiber offers a number of advantages over traditional metal wire, the most important being that there is considerably less signal degradation. Additionally, it is immune to electromagnetic interference, which can seriously impede the transmission of data along normal metal wires. This adds an added security measure, as well, since optical fiber can survive an electromagnetic pulse that would destroy metal cables.