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[[Image:Fibreoptic.jpg|thumb|right|Optical fibers]]
== you suck!!! =='''''
An '''optical fiber''' (or '''fibre''') is a [[glass]] or [[plastic]] fiber designed to guide [[light]] along its length. '''Fiber optics''' is the overlap of [[applied science]] and [[engineering]] concerned with the design and application of optical fibers. Optical fibers are widely used in [[fiber-optic communication]], which permits transmission over longer distances and at higher data rates than other forms of communications. Fibers are used instead of metal wires because signals travel along them with less [[Attenuation|loss]], and they are immune to [[electromagnetic interference]]. Optical fibers are also used to form [[sensor]]s, and in a variety of other applications.

Light is kept in the "core" of the optical fiber by [[total internal reflection]]. This causes the fiber to act as a [[Waveguide (optics)|waveguide]]. Fibers which support many propagation paths or [[transverse mode]]s are called [[multimode fiber]]s (MMF). Fibers which support only a single mode are called [[singlemode fiber]]s (SMF). Multimode fibers generally have a large-diameter core, and are used for short-distance communication links or for applications where high power must be transmitted. Singlemode fibers are used for most communication links longer than 200 meters.

Joining lengths of optical fiber is more complex than joining electrical wire or cable. The ends of the fibers must be carefully [[Cleave (fiber)|cleaved]], and then spliced together either [[Mechanical splice|mechanically]] or by [[Fusion splicing|fusing]] them together with an [[electric arc]]. Special [[Optical fiber connector|connectors]] are used to make removable connections.

==History==
The light-guiding principle behind optical fibers was first demonstrated by [[Jean-Daniel Colladon|Daniel Colladon]] and [[Jacques Babinet]] in Paris in the 1840s, with Irish inventor [[John Tyndall]] offering public displays using water-fountains ten years later.<ref name=regis>{{cite book
| last =Bates
| first =Regis J
| authorlink =
| coauthors =
| title =Optical Switching and Networking Handbook
| publisher =McGraw-Hill
| date= 2001
| location =New York
| pages =p10
| url =
| doi =
| id = ISBN 007137356X}}</ref> Practical applications, such as close internal illumination during dentistry, appeared early in the twentieth century. Image transmission through tubes was demonstrated independently by the radio experimenter [[Clarence Hansell]] and the television pioneer [[John Logie Baird]] in the 1920s. The principle was first used for internal medical examinations by [[Heinrich Lamm]] in the following decade. In 1952, physicist [[Narinder Singh Kapany]] conducted experiments that led to the invention of optical fiber, based on Tyndall's earlier studies; modern optical fibers, where the glass fiber is coated with a transparent cladding to offer a more suitable [[refractive index]], appeared later in the decade.<ref name=regis/> Development then focused on fiber bundles for image transmission. The first fiber optic semi-flexible gastroscope was patented by [[Basil Hirschowitz]], C. Wilbur Peters, and Lawrence E. Curtiss, researchers at the [[University of Michigan]], in 1956. In the process of developing the gastroscope, Curtiss produced the first glass-clad fibers; previous optical fibers had relied on air or impractical oils and waxes as the low-index cladding material. A variety of other image transmission applications soon followed. The advent of ultrapure silicon for semiconductor devices made low-loss silica fiber practical.

In 1965, [[Charles K. Kao]] and George A. Hockham of the British company [[Standard Telephones and Cables]] were the first to suggest that attenuation of contemporary fibers was caused by impurities, which could be removed, rather than fundamental physical effects such as scattering. They speculated that optical fiber could be a practical medium for communication, if the [[attenuation (electromagnetic radiation)|attenuation]] could be reduced below 20 [[Decibel#Optics|dB]] per kilometer.<ref name=hecht1999>{{cite book
| last= Hecht
| first= Jeff
| title= City of Light, The Story of Fiber Optics
| publisher= Oxford University Press
| location= New York
| date= 1999
| id= ISBN 0195108183
| pages = p114}}</ref> This attenuation level was first achieved in 1970, by researchers [[Robert D. Maurer]], [[Donald Keck]], [[Peter C. Schultz]], and Frank Zimar working for American glass maker Corning Glass Works, now [[Corning Inc.]] They demonstrated a fiber with 17 dB optic attenuation per kilometer by [[Doping (semiconductors)|doping]] [[silica glass]] with [[titanium]]. A few years later they produced a fiber with only 4 dB/km using [[germanium oxide]] as the core dopant. Such low attenuations ushered in optical fiber telecommunications and enabled the Internet. Nowadays, attenuations in optical cables are far less than those in electrical copper cables, leading to long-haul fiber connections with repeater distances of 500–800 km.

The [[erbium-doped fiber amplifier]], which reduced the cost of long-distance fiber systems by reducing or even in many cases eliminating the need for optical-electrical-optical repeaters, was co-developed by teams led by [[David Payne]] of the [[University of Southampton]], and [[Emmanuel Desurvire]] at [[Bell Laboratories]] in 1986. The more robust optical fiber commonly used today utilizes glass for both core and sheath and is therefore less prone to aging processes. It was invented by Gerhard Bernsee in 1973 by [[Schott Glass]] in Germany.[http://www.freepatentsonline.com/3966300.html]

In 1991, the emerging field of [[photonic crystal]]s led to the development of [[Photonic-crystal fiber|photonic crystal fiber]] (''Science'' (2003), vol 299, page 358), which guides light by means of diffraction from a periodic structure, rather than total internal reflection. The first photonic crystal fibers became commercially available in 1996.[http://www.crystal-fibre.com/] Photonic crystal fibers can be designed to carry higher power than conventional fiber, and their wavelength dependent properties can be manipulated to improve their performance in certain applications.

==Applications==
===Optical fiber communication===
{{main|Fiber-optic communication}}
Optical fiber can be used as a medium for telecommunication and [[Computer network|networking]] because it is flexible and can be bundled as cables. It is especially advantageous for long-distance communications, because light propagates through the fiber with little attenuation compared to electrical cables. This allows long distances to be spanned with few [[Optical communications repeater|repeaters]]. Additionally, the light signals propagating in the fiber can be modulated at rates as high as 40 [[Gigabit|Gb]]/s <ref>{{Citation | last = Ramachandran | year = 2001 | title = Higher-order-mode dispersion compensation: enabler for long distance WDM at 40 Gb/sec | periodical = Proceedings of the SPIE | volume = 4532 | pages = 220-226 }}</ref>, and each fiber can carry many independent channels, each by a different wavelength of light ([[wavelength-division multiplexing]]). Over short distances, such as networking within a building, fiber saves space in cable ducts because a single fiber can carry much more data than a single electrical cable.<!--specific numbers would be useful--> Fiber is also immune to electrical interference, which prevents cross-talk between signals in different cables and pickup of environmental noise. Also, [[wiretapping]] is more difficult compared to electrical connections, and there are concentric dual core fibers that are said to be tap-proof. Because they are non-electrical, fiber cables can bridge very high electrical potential differences and can be used in environments where explosive fumes are present, without danger of ignition.

Although fibers can be made out of transparent [[Plastic optical fiber|plastic]], [[All-silica fiber|glass]], or a [[plastic-clad silica fiber|combination of the two]], the fibers used in long-distance telecommunications applications are always glass, because of the lower optical [[attenuation]]. Both multi-mode and single-mode fibers are used in communications, with multi-mode fiber used mostly for short distances (up to 500 m), and single-mode fiber used for longer distance ''links''. Because of the tighter tolerances required to couple light into and between single-mode fibers (core diameter about 10 micrometers), single-mode transmitters, receivers, amplifiers and other components are generally more expensive than multi-mode components.

===Fiber optic sensors===
Optical fibers can be used as sensors to measure strain, temperature, pressure and other parameters. The small size and the fact that no electrical power is needed at the remote location gives the fiber optic sensor an advantage over a conventional electrical sensor in certain applications.

Optical fibers are used as [[hydrophone]]s for seismic or [[Sonar|SONAR]] applications. Hydrophone systems with more than 100 sensors per fiber cable have been developed. Hydrophone sensor systems are used by the oil industry as well as a few countries' navies. Both bottom mounted hydrophone arrays and towed streamer systems are in use. The German company [[Sennheiser]] developed a [[Laser microphone|microphone]] working with a [[laser]] and optical fibers<ref>{{cite web | title=TP: Der Glasfaser-Schallwandler | url=http://www.heise.de/tp/r4/artikel/19/19822/1.html | accessdate=December 4 | accessyear=2005 }}</ref>.

Optical fiber sensors for temperature and pressure have been developed for downhole measurement in oil wells. The fiber optic sensor is well suited for this environment as it is functioning at temperatures too high for semiconductor sensors ([[Distributed Temperature Sensing]]).

Another use of the optical fiber as a sensor is the [[Fibre optic gyroscope|optical gyroscope]] which is in use in the [[Boeing 767]] and in some car models (for navigation purposes) and the use in [[Hydrogen microsensor]]s.

Fiber-optic sensors have been developed to measure co-located temperature and strain simultaneously with very high accuracy<ref>{{cite web | title= Title: Dual temperature and strain sensor using a combined fiber Bragg grating and fluorescence intensity ratio technique in Er3+-doped fiber | url=http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=RSINAK000074000005002880000001&idtype=cvips&gifs=yes }}</ref>. This is particularly useful when acquiring information from small complex structures.

===Other uses of optical fibers===
[[Image:Flashflight red.jpg|thumb|300px|right|A [[frisbee]] illuminated by fiber optics]]
Fibers are widely used in illumination applications. They are used as [[light guide]]s in medical and other applications where bright light needs to be shone on a target without a clear line-of-sight path. In some buildings, optical fibers are used to route sunlight from the roof to other parts of the building (see [[non-imaging optics]]). Optical fiber illumination is also used for [[Decoration|decorative]] applications, including [[Commercial signage|sign]]s, [[art]], and artificial [[Christmas tree]]s. [[Swarovski]] boutiques use optical fibers to illuminate their crystal showcases from many different angles while only employing one light source. Optical fiber is an intrinsic part of the light-transmitting concrete building product, [[LiTraCon]].
[[Image:F-O-Xmastree.jpg|thumb|A fiber-optic Christmas Tree]]

Optical fiber is also used in imaging optics. A coherent bundle of fibers is used, sometimes along with lenses, for a long, thin imaging device called an endoscope, which is used to view objects through a small hole. Medical endoscopes are used for minimally invasive exploratory or surgical procedures ([[endoscopy]]). Industrial endoscopes (see [[fiberscope]] or [[borescope]]) are used for inspecting anything hard to reach, such as jet engine interiors.

An optical fiber [[dopant|doped]] with certain [[rare-earth element]]s such as [[erbium]] can be used as the [[gain medium]] of a [[Fiber laser|laser]] or [[optical amplifier]]. Rare-earth doped optical fibers can be used to provide signal [[amplification]] by splicing a short section of doped fiber into a regular (undoped) optical fiber line. The doped fiber is [[optical pumping|optically pumped]] with a second laser wavelength that is coupled into the line in addition to the signal wave. Both wavelengths of light are transmitted through the doped fiber, which transfers energy from the second pump wavelength to the signal wave. The process that causes the amplification is [[stimulated emission]].

Optical fibers doped with a [[wavelength shifter]] are used to collect [[scintillator|scintillation]] light in [[physics]] experiments.

Optical fiber can be used to supply a low level of power (around one watt) to electronics situated in a difficult electrical environment. Examples of this are electronics in high-powered antenna elements and measurement devices used in high voltage transmission equipment.

Optical fibers are also used in [[fiber optic gyroscope]]s, and other [[interferometry]] instruments.

==Principle of operation==
An optical fiber is a cylindrical [[dielectric]] [[waveguide (optics)|waveguide]] that transmits light along its axis, by the process of [[total internal reflection]]. The fiber consists of a ''core'' surrounded by a [[cladding]] layer. To confine the optical signal in the core, the [[refractive index]] of the core must be greater than that of the cladding. The boundary between the core and cladding may either be abrupt, in ''[[Step-index profile|step-index fiber]]'', or gradual, in ''[[graded-index fiber]]''.

===Multimode fiber===
[[Image:Optical-fibre.png|thumb|right|250px|The propagation of light through a multi-mode optical fiber.]]
Fiber with large (greater than 10&nbsp;[[micrometre|μm]]) core diameter may be analyzed by [[geometric optics]]. Such fiber is called ''[[multi-mode fiber|multimode fiber]]'', from the electromagnetic analysis (see below). In a step-index multimode fiber, [[ray (optics)|rays]] of light are guided along the fiber core by total internal reflection. Rays that meet the core-cladding boundary at a high angle (measured relative to a line [[surface normal|normal]] to the boundary), greater than the [[critical angle]] for this boundary, are completely reflected. The critical angle (minimum angle for total internal reflection) is determined by the difference in index of refraction between the core and cladding materials. Rays that meet the boundary at a low angle are refracted from the [[core]] into the cladding, and do not convey light and hence information along the fiber. The critical angle determines the [[acceptance angle]] of the fiber, often reported as a [[numerical aperture]]. A high numerical aperture allows light to propagate down the fiber in rays both close to the axis and at various angles, allowing efficient coupling of light into the fiber. However, this high numerical aperture increases the amount of [[Dispersion (optics)|dispersion]] as rays at different angles have different [[Optical path length|path lengths]] and therefore take different times to traverse the fiber. A low numerical aperture may therefore be desirable.

[[Image:Optical fiber types.svg|thumb|right|250px|Optical fiber types.]]In graded-index fiber, the index of refraction in the core decreases continuously between the axis and the cladding. This causes light rays to bend smoothly as they approach the cladding, rather than reflecting abruptly from the core-cladding boundary. The resulting curved paths reduce multi-path dispersion because high angle rays pass more through the lower-index periphery of the core, rather than the high-index center. The index profile is chosen to minimize the difference in axial propagation speeds of the various rays in the fiber. This ideal index profile is very close to a [[parabola|parabolic]] relationship between the index and the distance from the axis.

===Singlemode fiber===
[[Image:Singlemode fibre structure.png|thumb|right|250px|A typical single-mode optical fiber, showing diameters of the component layers.]]
Fiber with a core diameter less than about ten times the [[wavelength]] of the propagating light cannot be modeled using geometric optics. Instead, it must be analyzed as an [[electromagnetic]] structure, by solution of [[Maxwell's equations]] as reduced to the [[electromagnetic wave equation]]. The electromagnetic analysis may also be required to understand behaviors such as [[speckle]] that occur when [[coherence (physics)|coherent]] light propagates in multi-mode fiber. As an optical waveguide, the fiber supports one or more confined [[transverse mode]]s by which light can propagate along the fiber. Fiber supporting only one mode is called [[Single-mode optical fiber|single-mode]] or ''mono-mode'' fiber. The behavior of larger-core multimode fiber can also be modeled using the wave equation, which shows that such fiber supports more than one mode of propagation (hence the name). The results of such modeling of multi-mode fiber approximately agree with the predictions of geometric optics, if the fiber core is large enough to support more than a few modes.

The waveguide analysis shows that the light energy in the fiber is not completely confined in the core. Instead, especially in single-mode fibers, a significant fraction of the energy in the bound mode travels in the cladding as an [[evanescent wave]].

The most common type of single-mode fiber has a core diameter of 8 to 10 μm and is designed for use in the [[near infrared]]. The mode structure depends on the wavelength of the light used, so that this fiber actually supports a small number of additional modes at visible wavelengths. Multi-mode fiber, by comparison, is manufactured with core diameters as small as 50 micrometres and as large as hundreds of micrometres.

===Special-purpose fiber===
Some special-purpose optical fiber is constructed with a non-cylindrical core and/or cladding layer, usually with an elliptical or rectangular cross-section. These include [[polarization-maintaining optical fiber|polarization-maintaining fiber]] and fiber designed to suppress [[whispering gallery mode]] propagation.

[[Photonic crystal fiber]] is made with a regular pattern of index variation (often in the form of cylindrical holes that run along the length of the fiber). Such fiber uses [[diffraction]] effects instead of or in addition to total internal reflection, to confine light to the fiber's core. The properties of the fiber can be tailored to a wide variety of applications.

==Manufacturing==
===Materials===
Glass optical fibers are almost always made from [[silica]], but some other materials, such as [[fluorozirconate glass|fluorozirconate]], [[fluoroaluminate glass|fluoroaluminate]], and [[Chalcogenide glass|chalcogenide]] glasses, are used for longer-wavelength infrared applications. Like other glasses, these glasses have a refractive index of about 1.5. Typically the difference between core and cladding is less than one percent.

[[Plastic optical fiber]]s (POF) are commonly step-index multimode fibers with a core diameter of 0.5&nbsp;mm or larger. POF typically have higher attenuation co-efficients than glass fibers, 1&nbsp;dB/m or higher, and this high attenuation limits the range of POF-based systems.

===Process===
Standard optical fibers are made by first constructing a large-diameter ''preform'', with a carefully controlled refractive index profile, and then ''pulling'' the preform to form the long, thin optical fiber. The preform is commonly made by three [[chemical vapor deposition]] methods: ''inside vapor deposition'', ''outside vapor deposition'', and ''vapor axial deposition''.<ref name=gowar1993>{{cite book
| last= Gowar
| first= John
| title= Optical Communication Systems
| edition= 2d ed.
| publisher= Prentice-Hall
| location= Hempstead, UK
| date= 1993
| id= ISBN 0136387276
| pages= p209}}</ref>

With ''inside vapor deposition'', a hollow glass tube approximately 40 cm in length known as a "preform" is placed horizontally and rotated slowly on a lathe, and gases such as [[silicon tetrachloride]] (SiCl<sub>4</sub>) or [[germanium tetrachloride]] (GeCl<sub>4</sub>) are injected with [[oxygen]] in the end of the tube. The gases are then heated by means of an external hydrogen burner, bringing the temperature of the gas up to 1900 [[kelvin]]s, where the tetrachlorides react with oxygen to produce [[silica]] or germania ([[germanium oxide]]) particles. When the reaction conditions are chosen to allow this reaction to occur in the gas phase throughout the tube volume, in contrast to earlier techniques where the reaction occurred only on the glass surface, this technique is called ''modified chemical vapor deposition''.

The oxide particles then agglomerate to form large particle chains, which subsequently deposit on the walls of the tube as soot. The deposition is due to the large difference in temperature between the gas core and the wall causing the gas to push the particles outwards (this is known as [[thermophoresis]]). The torch is then traversed up and down the length of the tube to deposit the material evenly. After the torch has reached the end of the tube, it is then brought back to the beginning of the tube and the deposited particles are then melted to form a solid layer. This process is repeated until a sufficient amount of material has been deposited. For each layer the composition can be modified by varying the gas composition, resulting in precise control of the finished fiber's optical properties.

In outside vapor deposition or vapor axial deposition, the glass is formed by ''flame hydrolysis'', a reaction in which silicon tetrachloride and germanium tetrachloride are oxidized by reaction with water (H<sub>2</sub>O) in an [[oxyhydrogen flame]]. In outside vapor deposition the glass is deposited onto a solid rod, which is removed before further processing. In vapor axial deposition, a short ''seed rod'' is used, and a porous preform, whose length is not limited by the size of the source rod, is built up on its end. The porous preform is consolidated into a transparent, solid preform by heating to about 1800 kelvins.

The preform, however constructed, is then placed in a device known as a [[drawing tower]], where the preform tip is heated and the optic fiber is pulled out as a string. By measuring the resultant fiber width, the tension on the fiber can be controlled to maintain the fiber thickness.

==Practical issues==
===Optical fiber cables===
{{main|Optical fiber cable}}
In practical fibers, the cladding is usually coated with a tough [[resin]] [[Buffer (optical fiber)|''buffer'']] layer, which may be further surrounded by a ''jacket'' layer, usually plastic. These layers add strength to the fiber but do not contribute to its optical wave guide properties. Rigid fiber assemblies sometimes put light-absorbing ("dark") glass between the fibers, to prevent light that leaks out of one fiber from entering another. This reduces [[cross-talk]] between the fibers, or reduces [[Lens flare|flare]] in fiber bundle imaging applications.<ref>{{cite web| url=http://zone.ni.com/devzone/cda/ph/p/id/129#toc2| title=Light collection and propagation| work=National Instruments' Developer Zone| accessdate=2007-03-19}}</ref><ref name=hecht2002>
{{cite book| first=Jeff| last=Hecht| title=Understanding Fiber Optics| year=2002| edition=4th ed.| isbn=0-13-027828-9 | publisher= Prentice Hall }}</ref>

Modern cables come in a wide variety of sheathings and armor, designed for applications such as direct burial in trenches, dual use as power lines [http://www.dced.state.ak.us/dca/AEIS/PDF_Files/AIDEA_Energy_Screening.pdf ], installation in conduit, lashing to aerial telephone poles, submarine installation, or insertion in paved streets. In recent years the cost of small fiber-count pole-mounted cables has greatly decreased due to the high Japanese and South Korean demand for [[fiber to the home]] (FTTH) installations.

Traditional fiber's loss increases greatly if the fiber is bent with a radius smaller than around 30&nbsp;mm. "Bendable fibers", targeted towards easier installation in home environments, have been standardised as ITU-T G.657. This type of fiber can be bent with a radius as low as 7.5&nbsp;mm without adverse impact. Even more bendable fibers have been developed.<ref>{{cite press release
| title = Corning announces breakthrough optical fiber technology
| publisher = [[Corning, Inc.]]
| date = [[2007-07-23]]
| url = http://www.corning.com/media_center/press_releases/2007/2007072301.aspx
| accessdate = 2007-12-09 }}</ref>
Bendable fiber may also be resistant to fiber hacking, in which the signal in a fiber is surreptitiously monitored by bending the fiber and detecting the leakage.<ref>{{cite web |url=http://blogs.techrepublic.com.com/security/?p=222 |title=Protect your network against fiber hacks |accessdate=2007-12-10 |last=Olzak |first=Tom |date=2007-05-03 |work=Techrepublic|publisher=CNET}}</ref>

===Termination and splicing===
[[Image:ST connector.jpg|thumb|right|ST fiber connector on multimode fiber]]
Optical fibers are connected to terminal equipment by [[optical fiber connector]]s. These connectors are usually of a standard type such as ''FC'', ''SC'', ''ST'', ''LC'', or ''MTRJ''.

Optical fibers may be connected to each other by connectors or by ''splicing'', that is, joining two fibers together to form a continuous optical waveguide. The generally accepted splicing method is arc fusion splicing, which melts the fiber ends together with an [[electric arc]]. For quicker fastening jobs, a "mechanical splice" is used.

Fusion splicing is done with a specialized instrument that typically operates as follows: The two cable ends are fastened inside a splice enclosure that will protect the splices, and the fiber ends are stripped of their protective polymer coating (as well as the more sturdy outer jacket, if present). The ends are ''cleaved'' (cut) with a precision cleaver to make them perpendicular, and are placed into special holders in the splicer. The splice is usually inspected via a magnified viewing screen to check the cleaves before and after the splice. The splicer uses small motors to align the end faces together, and emits a small spark between electrodes at the gap to burn off dust and moisture. Then the splicer generates a larger spark that raises the temperature above the [[melting point]] of the glass, fusing the ends together permanently. The location and energy of the spark is carefully controlled so that the molten core and cladding don't mix, and this minimizes optical loss. A splice loss estimate is measured by the splicer, by directing light through the cladding on one side and measuring the light leaking from the cladding on the other side. A splice loss under 0.1&nbsp;dB is typical. The complexity of this process makes fiber splicing much more difficult than splicing copper wire.

Mechanical fiber splices are designed to be quicker and easier to install, but there is still the need for stripping, careful cleaning and precision cleaving. The fiber ends are aligned and held together by a precision-made sleeve, often using a clear [[index-matching gel]] that enhances the transmission of light across the joint. Such joints typically have higher optical loss and are less robust than fusion splices, especially if the gel is used. All splicing techniques involve the use of an enclosure into which the splice is placed for protection afterward.

Fibers are terminated in connectors so that the fiber end is held at the end face precisely and securely. A fiber-optic connector is basically a rigid cylindrical barrel surrounded by a sleeve that holds the barrel in its mating socket. It can be push and click, turn and latch, or threaded. A typical connector is installed by preparing the fiber end and inserting it into the rear of the connector body. Quick-set adhesive is usually used so the fiber is held securely, and a [[strain relief]] is secured to the rear. Once the adhesive has set, the fiber's end is polished to a mirror finish. Various polish profiles are used, depending on the type of fiber and the application. For singlemode fiber, the fiber ends are typically polished with a slight curvature, such that when the connectors are mated the fibers touch only at their cores. This is known as a "physical contact" (PC) polish. The curved surface may be polished at an angle, to make an "angled physical contact" (APC) connection. Such connections have higher loss than PC connections, but greatly reduced back reflection, because light that reflects from the angled surface leaks out of the fiber core; the resulting loss in signal strength is known as [[gap loss]]. APC fiber ends have low back reflection even when disconnected.

===Free-space coupling===
It often becomes necessary to align an optical fiber with another optical fiber or an optical device such as a [[light-emitting diode]], a [[laser diode]], or an [[optoelectronic device]] such as a [[modulator]]. This can involve either carefully aligning the fiber and placing it in contact with the device to which it is to couple, or can use a [[lens (optics)|lens]] to allow coupling over an air gap. In some cases the end of the fiber is polished into a curved form that is designed to allow it to act as a lens.

In a laboratory environment, the fiber end is usually aligned to the device or other fiber with a fiber launch system that uses a [[microscope objective lens]] to focus the light down to a fine point. A precision [[translation stage]] (micro-positioning table) is used to move the lens, fiber, or device to allow the coupling efficiency to be optimized.

===Fiber fuse===
At high optical intensities, above 2 [[watt|megawatts]] per square centimetre, when a fiber is subjected to a shock or is otherwise suddenly damaged, a ''fiber fuse'' can occur. The reflection from the damage vaporizes the fiber immediately before the break, and this new defect remains reflective so that the damage propagates back toward the transmitter at 1–3 meters per second.<ref>{{cite web | title=The Risks Digest Volume 12: Issue 44 | url=http://catless.ncl.ac.uk/Risks/12.44.html | accessdate=December 4 | accessyear=2005 }}</ref><sup>,</sup><ref>{{cite web | title=Optics Letters | url=http://ol.osa.org/abstract.cfm?id=72607 | accessdate=December 4 | accessyear=2005 }}</ref><sup>,</sup><ref>{{cite web | title=Photonics Spectra | url=http://www.photonics.com/spectra/tech/XQ/ASP/techid.1576/QX/read.htm | accessdate=December 4 | accessyear=2005}}</ref> The [[open fiber control]] system, which ensures [[Laser safety|laser eye safety]] in the event of a broken fiber, can also effectively halt propagation of the fiber fuse.<ref>{{cite web | title=Evaluation of High-power Endurance in Optical Fiber Links | url=http://www.furukawa.co.jp/review/fr024/fr24_04.pdf | accessdate=December 4 | accessyear=2005 }}</ref> In situations, such as undersea cables, where high power levels might be used without the need for open fiber control, a "fiber fuse" protection device at the transmitter can break the circuit to prevent any damage.

==See also==
{{portalpar|Electronics|Nuvola_apps_ksim.png}}
<div style="-moz-column-count:2; column-count:2;">
* [[Gradient index optics]]
* [[Optical communication]]
* [[Optical fiber connector]]: [[ST connector|ST]], [[SC connector|SC]] and [[MTRJ]]
* [[Submarine communications cable]]s
* [[Cable jetting]]
* [[Fiber Bragg grating]]
* [[Leaky mode]]
* [[SFP transceiver]]
* [[XENPAK]]
</div>

==Notes==
{{reflist}}

==References==
<div class="references-small">
* Gambling, W. A., "The Rise and Rise of Optical Fibers", ''IEEE Journal on Selected Topics in Quantum Electronics'', Vol. 6, No. 6, pp. 1084-1093, Nov./Dec. 2000.
* Hecht, Jeff, ''Understanding Fiber Optics'', 4th ed., Prentice-Hall, Upper Saddle River, NJ, USA 2002 (ISBN 0-13-027828-9).
* Mirabito, Michael M.A; and Morgenstern, Barbara L., ''The New Communications Technologies: Applications, Policy, and Impact'', 5th. Edition. Focal Press, 2004. (ISBN 0-24-080586-0).
* Nagel S. R., MacChesney J. B., Walker K. L., "An Overview of the Modified Chemical Vapor Deposition (MCVD) Process and Performance", ''IEEE Journal of Quantum Electronics'', Vol. QE-18, No. 4, p. 459, April 1982.
* Ramaswami, R., Sivarajan, K. N., ''Optical Networks: A Practical Perspective'', Morgan Kaufmann Publishers, San Francisco, 1998 (ISBN 1-55860-445-6).
</div>

==External links==
{{Commonscat|Optical fibers}}
* [http://www.thefoa.org/ The Fiber Optic Association]
* [http://www.thefoa.org/tech/connID.htm FOA color code for connectors]
* [http://www.jimhayes.com/lennielw/ Lennie Lightwave's Guide To Fiber Optics]
* "[http://www.rp-photonics.com/fibers.html Fibers]", article in RP Photonics' ''Encyclopedia of Laser Physics and Technology''
* [http://www.fabila.com/proyectos/ftth/tecnologia.asp How Fiber Optics are made] In video
* "[http://www.gare.co.uk/technology_watch/fibre.htm Fibre optic technologies]", Mercury Communications Ltd, August 1992.
* "[http://www.gare.co.uk/technology_watch/photo.htm Photonics & the future of fibre]", Mercury Communications Ltd, March 1993.
* "[http://www.arcelect.com/fibercable.htm The basics of fiber optic cable]"



{{Glass science}}

[[Category:Optical fiber| ]]
[[Category:Fiber optics| ]]
[[Category:Telecommunications equipment]]
[[Category:Glass forming]]
[[Category:Glass types]]

[[ar:الياف بصرية]]
[[bn:অপটিক্যাল ফাইবার]]
[[bs:Optičko vlakno]]
[[bg:Оптично влакно]]
[[ca:Fibra òptica]]
[[cs:Optické vlákno]]
[[da:Lysleder]]
[[de:Lichtwellenleiter]]
[[es:Cable de fibra óptica]]
[[eo:Optika fibro]]
[[fa:فیبر نوری]]
[[fr:Fibre optique]]
[[ko:광섬유]]
[[id:Serat optik]]
[[it:Fibra ottica]]
[[he:סיב אופטי]]
[[hu:Optikai szál]]
[[ka:ოპტიკური ბოჭკო]]
[[mk:Оптички влакна]]
[[nl:Glasvezel]]
[[ja:光ファイバー]]
[[no:Fiberoptikk]]
[[pl:Światłowód]]
[[pt:Fibra óptica]]
[[ro:Fibră optică]]
[[ru:Оптоволокно]]
[[simple:Optical fiber]]
[[sk:Optické vlákno]]
[[sr:Оптички кабл]]
[[fi:Valokuitu]]
[[sv:Fiberoptik]]
[[tr:Fiberoptik]]
[[uk:Оптоволокно]]
[[zh:光導纖維]]

Revision as of 22:32, 30 March 2008

== you suck!!! ==

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