An optical fiber is a flexible, transparent fiber, made by drawing or extruding glass (silica) or plastic in a diameter slightly thicker than that of a human hair. Optical fibers are more commonly used as a means to transmit light between two points of a fiber and have a wide use in fiber optic communications, where they allow transmission at greater distances and bandwidth (data rate) than the electric wires. Fibers are used instead of metal wires because the signals travel through them with less loss; In addition, the fibers are immune to electromagnetic interference, a problem from which metal cables suffer widely. Fibers are also used for lighting and imagery, and are usually wrapped in packages to introduce or remove light from tight spaces, such as a fibroscope. Some specially designed fibers are also used for a wide variety of diverse applications, some of which are fiber optic sensors and fiber lasers.
Typically, optical fibers have a core surrounded by a transparent coating material with a lower refractive index. The light is maintained in the nucleus due to the phenomenon of total internal reflection that causes the fiber to act as a waveguide. Fibers that allow many propagation paths or transverse modes are called multimode fibers (MM), while those that allow only one mode are called single mode fibers (SM). Multimode fibers generally have a larger core diameter6 and are used for short distance communication links and for applications where high power transmission is required. Single mode fibers are used for communication links larger than 1000 meters.
Being able to join optical fibers with low loss is important in fiber optic communication. This is more complex than joining electrical cable and involves careful adhesion of the fibers, precise alignment of the fiber cores and the coupling of these aligned cores. For applications that need a permanent connection, fusion splices are made. In this technique, an electric arc is used to melt the ends and thus join them together. Another common technique is mechanical splicing, where the end of the fibers is kept in contact by means of a mechanical force. Temporary or semi-permanent connections are made through a specialized fiber optic connector.
The field of applied science and engineering responsible for the design and application of optical fibers is called fiber optics. The term was coined by the Hindu physicist Narinder Singh Kapany, who is widely recognized as the father of fiber optics.
The optical fiber is used as a means of transmission in telecommunications networks because of its flexibility the optical conductors can be grouped together forming cables. The fibers used in this field are plastic or glass and sometimes of both types. Because of the low attenuation they have, glass fibers are used in interurban environments.
SOURCE: Wikipedia
