An optical fiber or optical fibre is a flexible, transparent fiber made by drawing glass (silica) or plastic to a diameter slightly thicker than that of a human hair.Optical fibers are used most often as a means to transmit light between the two ends of the fiber and find wide usage in fiber-optic communications, where they permit transmission over longer distances and at higher bandwidths (data rates) than wire cables. Fibers are used instead of metal wires because signals travel along them with less loss, in addition, fibers are immune to electromagnetic interference, a problem from which metal wires suffer excessively.
Optical fibers typically include a core surrounded by a transparent cladding material with a lower index of refraction. Light is kept in the core by the phenomenon of total internal reflection which causes the fiber to act as a waveguide.Fibers that support a single mode are called single mode fibers(SMF) while those many propagation paths or transverse modes are called multi-mode fibers (MMF)
Single mode fibers have a smaller diameter core (9μm) that only allows for one mode of light to propagate. As a result, the amount of light leakage decreases and minimizes the attenuation, allowing the signal to travel longer distances. Typically, single mode fiber is used for distances beyond several hundred meters by telecom and CATV service providers, government agencies, and major enterprises and universities with large campuses and networks.
Multimode fibers have a larger diameter core (50μm or 62.5μm) than single mode fibers, which allows for the propagation of multiple modes of light. The amount of light that passes through the core is increased, thus enabling a higher amount of information to pass through at any one time. Because of the higher rates of dispersion and attenuation, the signal quality is significantly reduced over longer distances, so multimode fibers are typically deployed for short distance applications within data centers, Local Area Networks (LAN) and other similar networks. Similar to single mode and other communication fibers, subsets of mutimode fiber types exist on the basis of construction/makeup (step-index, graded-index, etc) and for varying bandwidth rates over specific distances (OM2, OM3, OM4).