Editing Transmission medium (section)

==== Optical fiber ====
{{main|Optical fiber}}
[[File:fibreoptic.jpg|thumb|right|A bundle of optical fiber]]
[[File:Stealth Fiber Crew installing fiber cable underneath the streets of Manhattan.jpg|thumb|Fiber crew installing a 432-count fiber cable underneath the streets of Midtown Manhattan, New York City]]
[[File:Fiber optic illuminated.jpg|thumb|A [[TOSLINK]] fiber optic audio cable with red light being shone in one end transmits the light to the other end]]
[[File:Optical-fibre-junction-box.jpg|thumb|right|A [[19-inch rack|wall-mount cabinet]] containing optical fiber interconnects. The yellow cables are [[single-mode optical fiber|single mode fibers]]; the orange and aqua cables are [[multi-mode optical fiber|multi-mode fibers]]: 50/125&nbsp;μm OM2 and 50/125&nbsp;μm OM3 fibers respectively.]]

''Optical fiber'', which has emerged as the most commonly used transmission medium for long-distance communications, is a thin strand of glass that guides light along its length. Four major factors favor optical fiber over copper: data rates, distance, installation, and costs. Optical fiber can carry huge amounts of data compared to copper. It can be run for hundreds of miles without the need for signal repeaters, in turn, reducing maintenance costs and improving the reliability of the communication system because repeaters are a common source of network failures. Glass is lighter than copper allowing for less need for specialized heavy-lifting equipment when installing long-distance optical fiber. Optical fiber for indoor applications cost approximately a dollar a foot, the same as copper.<ref>{{cite book | last = Agrawal | first = Manish | title = Business Data Communications | publisher = John Wiley & Sons, Inc. | year = 2010 | pages = 41–43 | isbn = 978-0470483367}}</ref>

[[Multi-mode optical fiber|Multimode]] and [[Single-mode optical fiber|single mode]] are two types of commonly used optical fiber. Multimode fiber uses LEDs as the light source and can carry signals over shorter distances, about 2 kilometers. Single mode can carry signals over distances of tens of miles.

An ''optical fiber'' is a flexible, [[transparency and translucency|transparent]] fiber made by [[Drawing (manufacturing)|drawing]] [[glass]] ([[silica]]) or plastic to a diameter slightly thicker than that of a [[Hair's breadth|human hair]].<ref>{{cite web|title=Optical Fiber|url=http://www.thefoa.org/tech/ref/basic/fiber.html|website=www.thefoa.org|publisher=[[The Fiber Optic Association]]|access-date=17 April 2015|archive-date=24 January 2009|archive-url=https://web.archive.org/web/20090124144105/http://www.thefoa.org/tech/ref/basic/fiber.html|url-status=live}}</ref> 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 communication]]s, where they permit transmission over longer distances and at higher [[Bandwidth (computing)|bandwidths]] (data rates) than electrical cables. Fibers are used instead of [[metal]] wires because signals travel along them with less [[Attenuation|loss]]; in addition, fibers are immune to [[electromagnetic interference]], a problem from which metal wires suffer excessively.<ref>{{cite book|ref=Senior|last1=Senior|first1=John M.|last2=Jamro|first2=M. Yousif|title=Optical fiber communications: principles and practice|date=2009|publisher=Pearson Education|isbn=978-0130326812|pages=7–9}}</ref> Fibers are also used for [[Illumination (lighting)|illumination]] and imaging, and are often wrapped in bundles so they may be used to carry light into, or images out of confined spaces, as in the case of a [[fiberscope]].<ref>{{cite web|title=Birth of Fiberscopes|url=http://www.olympus-global.com/en/corc/history/story/endo/fiber/|website=www.olympus-global.com|publisher=Olympus Corporation|access-date=17 April 2015|archive-date=9 May 2015|archive-url=https://web.archive.org/web/20150509005616/http://www.olympus-global.com/en/corc/history/story/endo/fiber/|url-status=live}}</ref> Specially designed fibers are also used for a variety of other applications, some of them being [[fiber optic sensor]]s and [[fiber laser]]s.<ref>{{cite journal|last1=Lee|first1=Byoungho|title=Review of the present status of optical fiber sensors.|journal=Optical Fiber Technology|date=2003|volume=9|issue=2|pages=57–79 |doi=10.1016/s1068-5200(02)00527-8|bibcode=2003OptFT...9...57L}}</ref>

Optical fibers typically include a [[Core (optical fiber)|core]] surrounded by a transparent [[Cladding (fiber optics)|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]].<ref>[[#Senior|Senior]], pp. 12–14</ref> Fibers that support many propagation paths or [[transverse mode]]s are called [[multi-mode fiber]]s, while those that support a single mode are called [[single-mode fiber]]s (SMF). Multi-mode fibers generally have a wider core diameter<ref>{{Cite book|url=https://books.google.com/books?id=HFMiAQAAMAAJ&q=Multi-mode+fibers+generally+have+a+wider+core+diameter+and+are+used+for+short-distance+communication+links|title=The Optical Industry & Systems Purchasing Directory|date=1984|publisher=Optical Publishing Company|language=en}}</ref> and are used for short-distance communication links and for applications where high power must be transmitted.{{citation needed|date=April 2015}} Single-mode fibers are used for most communication links longer than {{convert|1000|sp=us|m|ft}}.{{citation needed|date=April 2015}}

Being able to join optical fibers with low loss is important in fiber optic communication.<ref>[[#Senior|Senior]], p. 218</ref> This is more complex than joining electrical wire or cable and involves careful [[Cleave (fiber)|cleaving]] of the fibers, precise alignment of the fiber cores, and the coupling of these aligned cores. For applications that demand a permanent connection a [[fusion splice]] is common. In this technique, an electric arc is used to melt the ends of the fibers together. Another common technique is a [[mechanical splice]], where the ends of the fibers are held in contact by mechanical force. Temporary or semi-permanent connections are made by means of specialized [[optical fiber connector]]s.<ref>[[#Senior|Senior]], pp. 234–235</ref>

The field of applied science and engineering concerned with the design and application of optical fibers is known as '''fiber optics'''. The term was coined by Indian physicist [[Narinder Singh Kapany]], who is widely acknowledged as the father of fiber optics.<ref name="southasia.ucsc.edu">{{cite web|url=http://southasia.ucsc.edu/endowed-chairs/narinder-singh-kapany.html|title=Narinder Singh Kapany Chair in Opto-electronics|publisher=ucsc.edu|access-date=2019-05-06|archive-date=2017-05-21|archive-url=https://web.archive.org/web/20170521222508/http://southasia.ucsc.edu/endowed-chairs/narinder-singh-kapany.html|url-status=live}}</ref>