View source for Physics:Fiber-optic communication

{{Short description|Method of transmitting information}}

[[Image:Optical-fibre-junction-box.jpg|thumb|right|An optical fiber patching cabinet. The yellow cables are [[Engineering:Single-mode optical fiber|single mode fibers]]; the orange and blue cables are multi-mode fibers: 62.5/125&nbsp;μm OM1 and 50/125&nbsp;μm OM3 fibers, respectively.]]
[[File:Stealth Fiber Crew installing fiber cable underneath the streets of Manhattan.jpg|thumb|Stealth Communications fiber crew installing a 432-count dark fiber cable underneath the streets of Midtown Manhattan, New York City]]

'''Fiber-optic communication''' is a method of [[Data communication|transmitting information]] from one place to another by sending pulses of [[Physics:Infrared|infrared]] or [[Physics:Visible light|visible light]] through an [[Engineering:Optical fiber|optical fiber]].<ref>{{Cite web|url=https://www.thefoa.org/tech/wavelength.htm|title=Understanding Wavelengths In Fiber Optics|website=thefoa.org|access-date=2019-12-16}}</ref><ref name=":7">{{Cite book |last1=McIntosh |first1=Jane |title=History of the World in 1,000 Objects |last2=Chrisp |first2=Peter |last3=Parker |first3=Philip |last4=Gibson |first4=Carrie |last5=Grant |first5=R. G. |last6=Regan |first6=Sally |date=October 2014 |publisher=DK and the Smithsonian |isbn=978-1-4654-2289-7 |location=New York |page=382 |author-link2=Peter Chrisp}}</ref> The light is a form of [[Carrier wave|carrier wave]] that is [[Engineering:Modulation|modulated]] to carry information.<ref>{{cite book|date=July 2, 2014|title=Future Trends in Fiber Optics Communication|url=http://www.iaeng.org/publication/WCE2014/WCE2014_pp438-442.pdf|publisher=WCE, London UK|isbn=978-988-19252-7-5}}</ref> Fiber is preferred over electrical cabling when high [[Bandwidth (computing)|bandwidth]], long distance, or immunity to [[Engineering:Electromagnetic interference|electromagnetic interference]] is required.<ref>{{cite web|title=How Fiber Optics Work|url=https://computer.howstuffworks.com/fiber-optic4.htm|website=How Stuff Works|date=6 March 2001|access-date=27 May 2020}}</ref> This type of communication can transmit voice, video, and telemetry through local area networks or across long distances.<ref>{{cite web|title=What are the Basic Elements of a Fibre Optic Communication System?|url=https://www.fibreoptic.com.au/basic-elements-fibre-optic-communication-system/|website=FOS|access-date=27 May 2020}}</ref>

Optical fiber is used by many telecommunications companies to transmit telephone signals, internet communication, and cable television signals. Researchers at [[Organization:Bell Labs|Bell Labs]] have reached a record bandwidth–distance product of over {{nowrap|100 [[Petabit|petabit]] ×}} kilometers per second using fiber-optic communication.<ref>{{cite web|title=Press release: Alcatel-Lucent Bell Labs announces new optical transmission record and breaks 100 Petabit per second kilometer barrier|url=http://www.alcatel-lucent.com/wps/portal/NewsReleases/Detail?LMSG_CABINET=Docs_and_Resource_Ctr&LMSG_CONTENT_FILE=News_Releases_2009/News_Article_001797.xml&lu_lang_code=en|publisher=Alcatel-Lucent|archive-url=https://web.archive.org/web/20091018060720/http://www.alcatel-lucent.com/wps/portal/NewsReleases/Detail?LMSG_CABINET=Docs_and_Resource_Ctr&LMSG_CONTENT_FILE=News_Releases_2009%2FNews_Article_001797.xml&lu_lang_code=en|archive-date=October 18, 2009|date=September 28, 2009|url-status=dead}}</ref>{{Better source needed|date=April 2023|reason=press release}}

== Background ==
First developed in the 1970s, fiber-optics have revolutionized the telecommunications industry and have played a major role in the advent of the [[Philosophy:Information Age|Information Age]].<ref>{{cite book |last=Alwayn |first=Vivek |chapter=Fiber-Optic Technologies |date=April 23, 2004 |url=https://www.ciscopress.com/articles/article.asp?p=170740 |access-date=2020-08-08 |title=Optical Network Design and Implementation |isbn=978-1-58705-105-0 |publisher=Cisco Press}}</ref> Because of its advantages over electrical transmission, optical fibers have largely replaced copper wire communications in backbone networks in the developed world.<ref>{{cite journal |last=Jacoby |first=Mitch |title=As telecom demands grow, optical fibers will need to level up |url=https://cen.acs.org/materials/photonics/telecom-demands-grow-optical-fibers/98/i10 |journal=Chemical & Engineering News |date=March 16, 2020 |access-date=May 27, 2020}}</ref>

The process of communicating using fiber optics involves the following basic steps:
# creating the optical signal involving the use of a transmitter,<ref>{{cite web |title=Guide To Fiber Optics & Permises Cabling |url=http://www.thefoa.org/tech/ref/appln/transceiver.html |publisher=The Fiber Optics Association |access-date=December 22, 2015}}</ref> usually from an electrical signal
# relaying the signal along the fiber, ensuring that the signal does not become too distorted or weak
# receiving the optical signal
# converting it into an electrical signal

== Applications ==
[[Engineering:Optical fiber|Optical fiber]] is used by telecommunications companies to transmit telephone signals, Internet communication and cable television signals. It is also used in other industries, including medical, defense, government, industrial and commercial. In addition to serving the purposes of telecommunications, it is used as light guides, for imaging tools, lasers, hydrophones for seismic waves, SONAR, and as sensors to measure pressure and temperature.

Due to lower [[Physics:Attenuation|attenuation]] and [[Engineering:Electromagnetic interference|interference]], optical fiber has advantages over copper wire in long-distance, high-bandwidth applications. However, infrastructure development within cities is relatively difficult and time-consuming, and fiber-optic systems can be complex and expensive to install and operate. Due to these difficulties, early fiber-optic communication systems were primarily installed in long-distance applications, where they can be used to their full transmission capacity, offsetting the increased cost. The prices of fiber-optic communications have dropped considerably since 2000.<ref>{{Cite web|date=2020-11-10|title=Fiber Optics Market by Application and Region - Global Forecast to 2024 {{!}} Technavio|url=https://www.businesswire.com/news/home/20201109005774/en/Fiber-Optics-Market-by-Application-and-Region---Global-Forecast-to-2024-Technavio|access-date=2021-04-18|website=BusinessWire |language=en}}</ref>

The price for rolling out fiber to homes has currently become more cost-effective than that of rolling out a copper-based network. Prices have dropped to $850 per subscriber in the US and lower in countries like The Netherlands, where digging costs are low and housing density is high.{{citation needed|date=May 2021}}

Since 1990, when [[Physics:Optical amplifier|optical-amplification systems]] became commercially available, the telecommunications industry has laid a vast network of intercity and transoceanic fiber communication lines. By 2002, an intercontinental network of 250,000&nbsp;km of [[Engineering:Submarine communications cable|submarine communications cable]] with a capacity of 2.56 [[Terabit|Tb]]/s was completed, and although specific network capacities are privileged information, telecommunications investment reports indicate that network capacity has increased dramatically since 2004.<ref>{{Cite web |first=Trish |last=Novicio |title=15 Largest Fiber Optic Companies in the World |url=https://finance.yahoo.com/news/15-largest-fiber-optic-companies-185636794.html |access-date=2021-04-18 |website=finance.yahoo.com |date=3 December 2020 |language=en-US}}</ref> As of 2020, over 5 billion kilometers of fiber-optic cable has been deployed around the globe.<ref>{{Cite web|title=Corning Celebrates Delivering its 1 Billionth Kilometer of Optical Fiber |url=https://www.corning.com/optical-communications/worldwide/en/home/products/fiber/milestone.html |date=2017-09-28 |access-date=2021-11-23|publisher=Corning|language=en-us}}</ref>

== History ==

In 1880 [[Biography:Alexander Graham Bell|Alexander Graham Bell]] and his assistant Charles Sumner Tainter created a very early precursor to fiber-optic communications, the [[Physics:Photophone|Photophone]], at Bell's newly established Volta Laboratory in [[Place:Washington, D.C.|Washington, D.C.]] Bell considered it his most important invention. The device allowed for the [[Engineering:Transmission (telecommunications)|transmission]] of sound on a beam of light. On June 3, 1880, Bell conducted the world's first wireless [[Engineering:Telephone|telephone]] transmission between two buildings, some 213 meters apart.<ref>
  {{cite book
 |author= Mary Kay Carson
 |title=Alexander Graham Bell: Giving Voice To The World |publisher=Sterling Publishing
 |location= New York
 |year=2007
 |series=Sterling Biographies
 |pages=[https://archive.org/details/alexandergrahamb0000cars/page/76 76]–78
 |isbn=978-1-4027-3230-0
 |url=https://archive.org/details/alexandergrahamb0000cars
|url-access= registration
 }}</ref><ref>
  {{cite journal
 |author= Alexander Graham Bell
 |title= On the Production and Reproduction of Sound by Light
 |journal= American Journal of Science |series=Third Series
 |volume= XX |number= 118
 |date= October 1880
 |bibcode= 1880AmJS...20..305B
 |doi= 10.2475/ajs.s3-20.118.305
 |s2cid= 130048089
 |url= https://zenodo.org/record/1450056
 }} also published as "Selenium and the Photophone" in ''Nature'', September 1880.
</ref> Due to its use of an atmospheric transmission medium, the Photophone would not prove practical until advances in laser and optical fiber technologies permitted the secure transport of light. The Photophone's first practical use came in military communication systems many decades later.<ref>{{Cite web|last=By|date=2021-02-18|title=A Brief History Of Optical Communication|url=https://hackaday.com/2021/02/18/a-brief-history-of-optical-communication/|access-date=2021-04-18|website=Hackaday|language=en-US}}</ref>

In 1954 [[Biography:Harold Hopkins (physicist)|Harold Hopkins]] and [[Biography:Narinder Singh Kapany|Narinder Singh Kapany]] showed that rolled fiber glass allowed light to be transmitted.<ref>{{cite journal |last1=Bhatt |first1=Jaimin |last2=Jones |first2=Adam |last3=Foley |first3=Stephen |last4=Shah |first4=Zaheer |last5=Malone |first5=Peter|last6=Fawcett |first6=Derek|last7=Kumar |first7=Sunil |date=27 October 2010|title=Harold Horace Hopkins: A Short Biography |journal=BJU International |volume=106 |issue=10 |pages=1425–1428 |doi=10.1111/j.1464-410X.2010.09717.x |pmid=21049584 |s2cid=36285370 |doi-access=free }}</ref> Jun-ichi Nishizawa, a Japanese scientist at Tohoku University, proposed the use of optical fibers for communications in 1963.<ref name=Bhat>{{cite book
|editor=Bhat, K. N. |editor2=DasGupta, Amitava
|title = Physics of semiconductor devices
|publisher =Narosa Publishing House
|year= 2004
|location =New Delhi, India
|chapter=Terahertz wave generation and light amplification using Raman effect
|author1=Nishizawa, Jun-ichi  |author2=Suto, Ken
|name-list-style=amp |chapter-url =https://books.google.com/books?id=2NTpSnfhResC&pg=PA27
|isbn =978-81-7319-567-9
|page =27}}</ref> Nishizawa invented the [[Physics:PIN diode|PIN diode]] and the [[Engineering:Static induction transistor|static induction transistor]], both of which contributed to the development of optical fiber communications.<ref name="Sendai New">{{cite web|work=Sendai New |title=Optical Fiber |url=http://www.city.sendai.jp/soumu/kouhou/s-new-e6/page01.html |access-date=April 5, 2009 |url-status=dead |archive-url=https://web.archive.org/web/20090929124200/http://www.city.sendai.jp/soumu/kouhou/s-new-e6/page01.html |archive-date=September 29, 2009 }}</ref><ref name=IEEE>{{cite web
 |work=Institute of Electrical and Electronics Engineers
 |title=New Medal Honors Japanese Microelectrics Industry Leader
 |url=http://www.ieee.org/portal/site/tionline/menuitem.130a3558587d56e8fb2275875bac26c8/index.jsp?&pName=institute_level1_article&TheCat=1003&article=tionline/legacy/inst2003/jun03/6w.nishizawa.xml&}}</ref>

In 1966 [[Biography:Charles K. Kao|Charles K. Kao]] and George Hockham at [[Organization:Standard Telecommunication Laboratories|Standard Telecommunication Laboratories]] showed that the losses of 1,000&nbsp;dB/km in existing glass (compared to 5–10&nbsp;dB/km in coaxial cable) were due to contaminants which could potentially be removed.

Optical fiber with attenuation low enough for communication purposes (about 20&nbsp;[[Physics:Decibel|dB]]/km) was developed in 1970 by Corning Glass Works. At the same time, GaAs [[Engineering:Laser diode|semiconductor lasers]] were developed that were compact and therefore suitable for transmitting light through fiber optic cables for long distances.

In 1973, Optelecom, Inc., co-founded by the inventor of the laser, [[Biography:Gordon Gould|Gordon Gould]], received a contract from ARPA for one of the first optical communication systems. Developed for Army Missile Command in Huntsville, Alabama, the system was intended to allow a short-range missile with video processing to communicate by laser to the ground by means of a five-kilometer long optical fiber that unspooled from the missile as it flew.<ref>{{Cite book |title=Laser: The Inventor, the Nobel Laureate, the Thirty-year Patent War |last1=Taylor |first1=Nick |publisher=Universe |year=2007 |isbn= 9780595465286 |edition=reprint |pages=169–171}}</ref> Optelecom then delivered the first commercial optical communications system to Chevron.<ref>{{Cite book|last=Taylor|first=Nick|title=Laser: The Inventor, the Nobel Laureate, and the Thirty-Year Patent War|publisher=Simon & Schuster|year=2000|pages=226}}</ref>

After a period of research starting from 1975, the first commercial fiber-optic telecommunications system was developed which operated at a wavelength around 0.8&nbsp;μm and used GaAs semiconductor lasers. This first-generation system operated at a bit rate of 45&nbsp;Mbit/s with repeater spacing of up to 10&nbsp;km. Soon on 22 April 1977, General Telephone and Electronics sent the first live telephone traffic through fiber optics at a 6&nbsp;Mbit/s throughput in Long Beach, California.{{citation needed|date=April 2021}}

In October 1973, Corning Glass signed a development contract with [[Company:CSELT|CSELT]] and Pirelli aimed to test fiber optics in an urban environment: in September 1977, the second cable in this test series, named COS-2, was experimentally deployed in two lines (9&nbsp;km) in [[Place:Turin|Turin]], for the first time in a big city, at a speed of 140&nbsp;Mbit/s.<ref>{{cite conference |author=Buzzelli, S. |display-authors=0 |url=http://www.chezbasilio.org/immagini/cos1_cos2_cos3_expts.pdf |title=Optical fibre field experiments in Italy: COS1, COS2 and COS3/FOSTER |conference=International Conference on Communications |location=Seattle |date=1980}}</ref>

The second generation of fiber-optic communication was developed for commercial use in the early 1980s, operated at 1.3&nbsp;μm and used InGaAsP semiconductor lasers. These early systems were initially limited by [[Engineering:Multi-mode optical fiber|multi-mode fiber]] dispersion, and in 1981 the [[Engineering:Single-mode optical fiber|single-mode fiber]] was revealed to greatly improve system performance, however practical connectors capable of working with single mode fiber proved difficult to develop. Canadian service provider SaskTel had completed construction of what was then the world's longest commercial fiber optic network, which covered {{cvt|3,268|km}} and linked 52 communities.<ref>{{cite web|last=Rigby|first=Pauline|date=January 22, 2014|title=Three decades of innovation|website=Lightwave|url=https://www.lightwaveonline.com/network-design/high-speed-networks/article/16649744/three-decades-of-innovation}}</ref> By 1987, these systems were operating at bit rates of up to {{val|1.7|u=Gbit/s}} with repeater spacing up to {{cvt|50|km}}.

The first transatlantic telephone cable to use optical fiber was TAT-8, based on Desurvire optimized laser amplification technology. It went into operation in 1988.

Third-generation fiber-optic systems operated at 1.55&nbsp;μm and had losses of about 0.2&nbsp;dB/km. This development was spurred by the discovery of [[Chemistry:Indium gallium arsenide|indium gallium arsenide]] and the development of the indium gallium arsenide photodiode by Pearsall. Engineers overcame earlier difficulties with [[Physics:Dispersion (optics)|pulse-spreading]] using conventional InGaAsP semiconductor lasers at that wavelength by using [[Engineering:Dispersion-shifted fiber|dispersion-shifted fiber]]s designed to have minimal dispersion at 1.55&nbsp;μm or by limiting the laser spectrum to a single [[Physics:Longitudinal mode|longitudinal mode]]. These developments eventually allowed third-generation systems to operate commercially at {{val|2.5|u=Gbit/s}} with repeater spacing in excess of {{cvt|100|km}}.

The fourth generation of fiber-optic communication systems used [[Physics:Optical amplifier|optical amplification]] to reduce the need for repeaters and [[Wavelength-division multiplexing|wavelength-division multiplexing]] (WDM) to increase [[Engineering:Channel capacity|data capacity]]. The introduction of WDM was the start of [[Engineering:Optical networking|optical networking]], as WDM became the technology of choice for fiber-optic bandwidth expansion.<ref>{{Cite book|last1=Grobe|first1=Klaus|title=Wavelength Division Multiplexing: A Practical Engineering Guide (Wiley Series in Pure and Applied Optics)|last2=Eiselt|first2=Michael|publisher=Wiley|year=2013|pages=2}}</ref> The first to market with a dense WDM system was Ciena Corp., in June 1996.<ref>{{Cite news|last=Markoff|first=John|date=1997-03-03|title=Fiber-Optic Technology Draws Record Stock Value|language=en-US|work=The New York Times|url=https://www.nytimes.com/1997/03/03/business/fiber-optic-technology-draws-record-stock-value.html|access-date=2021-11-09|issn=0362-4331}}</ref> The introduction of optical amplifiers and WDM caused system capacity to double every six months from 1992 until a bit rate of {{val|10|ul=Tb/s}} was reached by 2001. In 2006 a bit-rate of {{val|14|u=Tb/s}} was reached over a single {{cvt|160|km}} line using optical amplifiers.<ref name="ntt14">{{cite news
  | title = 14 Tbit/s over a single optical fiber: successful demonstration of world's largest capacity
  | publisher = NTT |work= News release
  | date = September 29, 2006
  | url = http://www.ntt.co.jp/news/news06e/0609/060929a.html
  | access-date = June 17, 2011 }}</ref> {{As of|2021}}, Japanese scientists transmitted 319 terabits per second over 3,000 kilometers with four-core fiber cables with standard cable diameter.<ref>{{Cite web|last=Starr|first=Michelle|title=With 319 Tb/s, Japan Absolutely Smashes World Record For Data Transmission Speed|url=https://www.sciencealert.com/japan-just-absolutely-smashed-the-world-data-transmission-speed-record|access-date=2021-11-09|website=ScienceAlert|date=16 July 2021 |language=en-gb}}</ref>

The focus of development for the fifth generation of fiber-optic communications is on extending the wavelength range over which a [[Wavelength-division multiplexing|WDM]] system can operate. The conventional wavelength window, known as the C band, covers the wavelength range 1525–1565&nbsp;nm, and ''dry fiber'' has a low-loss window promising an extension of that range to 1300–1650&nbsp;nm.{{citation needed|date=November 2021}} Other developments include the concept of ''[[Physics:Soliton (optics)|optical solitons]]'', pulses that preserve their shape by counteracting the effects of dispersion with the [[Physics:Nonlinear optics|nonlinear effects]] of the fiber by using pulses of a specific shape.

In the late 1990s through 2000, industry promoters, and research companies such as KMI, and RHK predicted massive increases in demand for communications bandwidth due to increased use of the [[Internet]], and commercialization of various bandwidth-intensive consumer services, such as [[Engineering:Video on demand|video on demand]]. [[Internet Protocol]] data traffic was increasing exponentially, at a faster rate than integrated circuit complexity had increased under Moore's Law. From the bust of the [[Dot-com bubble|dot-com bubble]] through 2006, however, the main trend in the industry has been [[Finance:Consolidation (business)|consolidation]] of firms and [[Finance:Offshoring|offshoring]] of manufacturing to reduce costs. Companies such as Verizon and AT&T have taken advantage of fiber-optic communications to deliver a variety of high-throughput data and broadband services to consumers' homes.

== Technology ==
Modern fiber-optic communication systems generally include optical transmitters that convert electrical signals into optical signals, [[Engineering:Optical fiber cable|optical fiber cable]]s to carry the signal, optical amplifiers, and optical receivers to convert the signal back into an electrical signal. The information transmitted is typically digital information generated by computers or [[Engineering:Digital telephony|telephone systems]].

=== Transmitters ===
[[File:Finisar GBIC SX 2.jpg|thumb|right|A GBIC module (shown here with its cover removed), is an optical and electrical [[Transceiver|transceiver]], a device combining a transmitter and a receiver in a single housing. The electrical connector is at top right and the optical connectors are at bottom left]]

The most commonly used optical transmitters are semiconductor devices such as [[Engineering:Light-emitting diode|light-emitting diode]]s (LEDs) and [[Engineering:Laser diode|laser diode]]s. The difference between LEDs and laser diodes is that LEDs produce [[Physics:Coherence#Spectral coherence|incoherent light]], while laser diodes produce coherent light. For use in optical communications, semiconductor optical transmitters must be designed to be compact, efficient and reliable, while operating in an optimal wavelength range and directly modulated at high frequencies.

In its simplest form, an LED emits light through [[Physics:Spontaneous emission|spontaneous emission]], a phenomenon referred to as [[Physics:Electroluminescence|electroluminescence]]. The emitted light is incoherent with a relatively wide spectral width of 30–60&nbsp;nm.{{efn|Communications LEDs are most commonly made from [[Chemistry:Indium gallium arsenide phosphide|Indium gallium arsenide phosphide]] (InGaAsP) or [[Chemistry:Gallium arsenide|gallium arsenide]] (GaAs). Because InGaAsP LEDs operate at a longer wavelength than GaAs LEDs (1.3 micrometers vs. 0.81–0.87 micrometers), their output spectrum, while equivalent in energy is wider in wavelength terms by a factor of about 1.7.}} The large spectrum width of LEDs is subject to higher fiber dispersion, considerably limiting their bit rate-distance product (a common measure of usefulness). LEDs are suitable primarily for [[Engineering:Local area network|local-area-network]] applications with bit rates of 10–100 Mbit/s and transmission distances of a few kilometers.

LED light transmission is inefficient, with only about 1% of input power, or about 100 microwatts, eventually converted into launched power coupled into the optical fiber.<ref>{{Cite web|title=The FOA Reference For Fiber Optics - Fiber Optic Transmitters and Receivers -|url=https://www.thefoa.org/tech/ref/appln/transceiver.html|access-date=2021-04-18|website=thefoa.org}}</ref>

LEDs have been developed that use several [[Physics:Quantum well|quantum well]]s to emit light at different wavelengths over a broad spectrum and are currently in use for local-area [[Wavelength-division multiplexing|wavelength-division multiplexing]] (WDM) applications.

LEDs have been largely superseded by [[Engineering:Vertical-cavity surface-emitting laser|vertical-cavity surface-emitting laser]] (VCSEL) devices, which offer improved speed, power and spectral properties, at a similar cost. However, due to their relatively simple design, LEDs are very useful for very low-cost applications. Commonly used classes of semiconductor laser transmitters used in fiber optics include VCSEL, Fabry–Pérot and [[Physics:Distributed-feedback laser|distributed-feedback laser]].

A semiconductor laser emits light through [[Physics:Stimulated emission|stimulated emission]] rather than spontaneous emission, which results in high output power (~100&nbsp;mW) as well as other benefits related to the nature of coherent light. The output of a laser is relatively directional, allowing high coupling efficiency (~50%) into single-mode fiber. Common VCSEL devices also couple well to multimode fiber. The narrow spectral width also allows for high bit rates since it reduces the effect of [[Physics:Dispersion (optics)|chromatic dispersion]]. Furthermore, semiconductor lasers can be modulated directly at high frequencies because of short [[Physics:Carrier generation and recombination|recombination time]].

Laser diodes are often directly [[Engineering:Modulation|modulated]], that is the light output is controlled by a current applied directly to the device. For very high data rates or very long distance links, a laser source may be operated [[Continuous wave#Laser physics|continuous wave]], and the light modulated by an external device, an [[Physics:Optical modulator|optical modulator]], such as an [[Physics:Electro-absorption modulator|electro-absorption modulator]] or [[Physics:Mach–Zehnder interferometer|Mach–Zehnder interferometer]]. External modulation increases the achievable link distance by eliminating laser [[Chirp|chirp]], which broadens the linewidth in directly modulated lasers, increasing the chromatic dispersion in the fiber. For very high bandwidth efficiency, coherent modulation can be used to vary the phase of the light in addition to the amplitude, enabling the use of QPSK, QAM, and OFDM. "Dual-polarization quadrature phase shift keying is a modulation format that effectively sends four times as much information as traditional optical transmissions of the same speed."<ref>{{Cite journal|date=March 2010|title=Ultrafast networks gear-up for deployment|journal=Nature Photonics|volume=4|issue=3|pages=144|doi=10.1038/nphoton.2010.23|issn=1749-4885|bibcode=2010NaPho...4..144.|doi-access=free}}</ref>

=== Receivers ===
The main component of an optical receiver is a [[Physics:Photodetector|photodetector]] which converts light into electricity using the [[Physics:Photoelectric effect|photoelectric effect]]. The primary photodetectors for telecommunications are made from [[Chemistry:Indium gallium arsenide|Indium gallium arsenide]]. The photodetector is typically a semiconductor-based [[Physics:Photodiode|photodiode]]. Several types of photodiodes include p-n photodiodes, p-i-n photodiodes, and avalanche photodiodes. Metal-semiconductor-metal (MSM) photodetectors are also used due to their suitability for [[Engineering:Integrated circuit|circuit integration]] in [[Signal regeneration|regenerators]] and wavelength-division multiplexers.

Since light may be attenuated and distorted while passing through the fiber, photodetectors are typically coupled with a [[Engineering:Transimpedance amplifier|transimpedance amplifier]] and a limiting [[Engineering:Amplifier|amplifier]] to produce a digital signal in the electrical domain recovered from the incoming optical signal. Further signal processing such as [[Engineering:Clock recovery|clock recovery]] from data performed by a [[Engineering:Phase-locked loop|phase-locked loop]] may also be applied before the data is passed on.

Coherent receivers use a local oscillator laser in combination with a pair of hybrid couplers and four photodetectors per polarization, followed by high-speed ADCs and digital signal processing to recover data modulated with QPSK, QAM, or OFDM.{{citation needed|date=March 2022}}

=== Digital predistortion ===
An optical communication system [[Engineering:Transmitter|transmitter]] consists of a [[Digital-to-analog converter|digital-to-analog converter]] (DAC), a [[Engineering:Amplifier|driver amplifier]] and a Mach–Zehnder modulator. The deployment of higher [[Engineering:Modulation|modulation formats]] (>4-QAM) or higher baud Rates (>{{val|32|ul=GBd}}) diminishes the system performance due to linear and non-linear transmitter effects. These effects can be categorized as linear distortions due to DAC bandwidth limitation and transmitter I/Q skew as well as non-linear effects caused by gain saturation in the driver amplifier and the Mach–Zehnder modulator. Digital [[Engineering:Predistortion|predistortion]] counteracts the degrading effects and enables Baud rates up to {{val|56|u=GBd}} and modulation formats like 64-QAM and 128-QAM with the commercially available components. The transmitter [[Engineering:Digital signal processor|digital signal processor]] performs digital predistortion on the input signals using the inverse transmitter model before sending the samples to the DAC.

Older digital predistortion methods only addressed linear effects. Recent publications also consider non-linear distortions. ''Berenguer et al'' models the Mach–Zehnder modulator as an independent [[Wiener series|Wiener system]] and the DAC and the driver amplifier are modeled by a truncated, time-invariant [[Volterra series]].<ref>{{Cite journal|last1=Berenguer|first1=P. W.|last2=Nölle|first2=M.|last3=Molle|first3=L.|last4=Raman|first4=T.|last5=Napoli|first5=A.|last6=Schubert|first6=C.|last7=Fischer|first7=J. K.|year=2016|title=Nonlinear Digital Pre-Distortion of Transmitter Components|journal=Journal of Lightwave Technology|volume=34|issue=8|pages=1739–1745|via=IEEE Xplore|bibcode=2016JLwT...34.1739B|doi=10.1109/JLT.2015.2510962|s2cid=47550517}}</ref> ''Khanna et al'' use a memory polynomial to model the transmitter components jointly.<ref>{{Cite journal|last1=Khanna|first1=G.|last2=Spinnler|first2=B.|last3=Calabro|first3=S.|last4=De Man|first4=E.|last5=Hanik|first5=N.|year=2016|title=A Robust Adaptive Pre-Distortion Method for Optical Communication Transmitters|journal=IEEE Photonics Technology Letters|volume=28|issue=7|pages=752–755|via=IEEE Xplore|bibcode=2016IPTL...28..752K|doi=10.1109/LPT.2015.2509158|s2cid=6740310}}</ref> In both approaches the Volterra series or the memory polynomial coefficients are found using indirect-learning architecture. ''Duthel et al'' records, for each branch of the Mach-Zehnder modulator, several signals at different polarity and phases. The signals are used to calculate the optical field. [[Cross-correlation|Cross-correlating]] in-phase and quadrature fields identifies the timing skew. The [[Frequency response|frequency response]] and the non-linear effects are determined by the indirect-learning architecture.<ref>{{Cite journal|last1=Duthel|first1=T.|last2=Hermann|first2=P.|last3=Schiel|first3=J.|last4=Fludger|first4=C. R. S.|last5=Bisplinghoff|first5=A.|last6=Kupfer|first6=T.|year=2016|title=Characterization and Pre-Distortion of Linear and Non-Linear Transmitter Impairments for PM-64QAM Applications|journal=42nd European Conference and Exhibition on Optical Communications (ECOC)|pages=785–787|via=IEEE Xplore|url=https://ieeexplore.ieee.org/document/7767721}}</ref>

=== Fiber cable types ===
[[File:Fiber optic3.jpg|thumb|right|A cable reel trailer with conduit that can carry optical fiber]]
[[File:Fibre-optic cable in a Telstra pit.jpg|thumb|right|Multi-mode optical fiber in an underground service pit]]

An [[Engineering:Optical fiber cable|optical fiber cable]] consists of a core, [[Engineering:Cladding (fiber optics)|cladding]], and a buffer (a protective outer coating), in which the cladding guides the light along the core by using the method of [[Total internal reflection|total internal reflection]]. The core and the cladding (which has a lower-[[Physics:Refractive index|refractive-index]]) are usually made of high-quality [[Chemistry:Silicon dioxide|silica]] glass, although they can both be made of plastic as well. Connecting two optical fibers is done by [[Engineering:Fusion splicing|fusion splicing]] or [[Engineering:Mechanical splice|mechanical splicing]] and requires special skills and interconnection technology due to the microscopic precision required to align the fiber cores.<ref>
{{cite web
  | last1 = Alwayn
  | first1 = Vivek
  | title = Splicing
  | work = Fiber-Optic Technologies
  | publisher = Cisco Systems
  | date = 2004-04-23
  | url = http://www.ciscopress.com/articles/article.asp?p=170740&seqNum=9&rl=1
  | access-date = 2006-12-31
  |quote=An optical fiber will break if it is bent too sharply}}</ref>

Two main types of optical fiber used in optic communications include [[Engineering:Multi-mode optical fiber|multi-mode optical fiber]]s and [[Engineering:Single-mode optical fiber|single-mode optical fiber]]s. A multi-mode optical fiber has a larger core (≥{{nbsp}}50 [[Micrometre|micrometer]]s), allowing less precise, cheaper transmitters and receivers to connect to it as well as cheaper connectors. However, a multi-mode fiber introduces multimode distortion, which often limits the bandwidth and length of the link. Furthermore, because of its higher [[Chemistry:Dopant|dopant]] content, multi-mode fibers are usually expensive and exhibit higher attenuation. The core of a single-mode fiber is smaller (<{{nbsp}}10 micrometers) and requires more expensive components and interconnection methods, but allows much longer and higher-performance links. Both single- and multi-mode fiber is offered in different grades.

{{Fibre legend|Comparison of fiber grades}}

In order to package fiber into a commercially viable product, it typically is protectively coated by using ultraviolet cured acrylate polymers{{citation needed|date=August 2022}} and assembled into a cable. After that, it can be laid in the ground and then run through the walls of a building and deployed aerially in a manner similar to copper cables. These fibers require less maintenance than common twisted pair wires once they are deployed.<ref>{{cite web|url=http://observernews.com/stories/current/news/021105/fiber.shtml|title=Fiber Optic Upgrade Will Upturn Yards, Streets|work=Observer Online|url-status=dead|archive-url=https://web.archive.org/web/20070927210015/http://observernews.com/stories/current/news/021105/fiber.shtml|archive-date=2007-09-27}}</ref>

Specialized cables are used for long-distance subsea data transmission, e.g. transatlantic communications cable. New (2011–2013) cables operated by commercial enterprises (Emerald Atlantis, Hibernia Atlantic) typically have four strands of fiber and signals cross the Atlantic (NYC-London) in 60–70&nbsp;ms. The cost of each such cable was about $300M in 2011.<ref>Halifax Chronicle Herald</ref>

Another common practice is to bundle many fiber optic strands within long-distance [[Engineering:Power transmission|power transmission]] cable using, for instance, an [[Engineering:Optical ground wire|optical ground wire]]. This exploits power transmission rights of way effectively, ensures a power company can own and control the fiber required to monitor its own devices and lines, is effectively immune to tampering, and simplifies the deployment of [[Engineering:Smart grid|smart grid]] technology.

=== Amplification ===
{{main|Physics:Optical amplifier}}

The transmission distance of a fiber-optic communication system has traditionally been limited by fiber attenuation and by fiber distortion. By using optoelectronic repeaters, these problems have been eliminated. These repeaters convert the signal into an electrical signal and then use a transmitter to send the signal again at a higher intensity than was received, thus counteracting the loss incurred in the previous segment. Because of the high complexity with modern wavelength-division multiplexed signals, including the fact that they had to be installed about once every {{cvt|20|km}}, the cost of these repeaters is very high.

An alternative approach is to use [[Physics:Optical amplifier|optical amplifier]]s which amplify the optical signal directly without having to convert the signal to the electrical domain. One common type of optical amplifier is an erbium-doped fiber amplifier (EDFA). These are made by doping a length of fiber with the rare-earth mineral [[Chemistry:Erbium|erbium]] and [[Physics:Laser pumping|laser pumping]] it with light with a shorter wavelength than the communications signal (typically 980&nbsp;nm). EDFAs provide gain in the ITU C band at 1550&nbsp;nm.

Optical amplifiers have several significant advantages over electrical repeaters. First, an optical amplifier can amplify a very wide band at once which can include hundreds of [[Wavelength-division multiplexing|multiplexed]] channels, eliminating the need to demultiplex signals at each amplifier. Second, optical amplifiers operate independently of the data rate and modulation format, enabling multiple data rates and modulation formats to co-exist and enabling upgrading of the data rate of a system without having to replace all of the repeaters. Third, optical amplifiers are much simpler than a repeater with the same capabilities and are therefore significantly more reliable. Optical amplifiers have largely replaced repeaters in new installations, although electronic repeaters are still widely used when signal conditioning beyond amplification is required.

=== Wavelength-division multiplexing ===
{{main|Wavelength-division multiplexing}}

Wavelength-division multiplexing (WDM) is the technique of transmitting multiple channels of information through a single optical fiber by sending multiple light beams of different wavelengths through the fiber, each modulated with a separate information channel. This allows the available capacity of optical fibers to be multiplied. This requires a wavelength division multiplexer in the transmitting equipment and a demultiplexer (essentially a [[Physics:Spectrometer|spectrometer]]) in the receiving equipment. [[Arrayed waveguide grating]]s are commonly used for multiplexing and demultiplexing in WDM.<ref>{{Cite book |last1=Cvijetic |first=Milorad |last2=Djordjevic |first2=Ivan |url=https://www.worldcat.org/oclc/875895386|title=Advanced optical communication systems and networks |date=2013 |isbn=978-1-60807-556-0 |publisher=Artech House |location=Boston |oclc=875895386}}</ref> Using WDM technology now commercially available, the bandwidth of a fiber can be divided into as many as 160 channels<ref>{{cite web|url=http://www.infinera.com/j7/servlet/NewsItem?newsItemID=108|title=Infinera Introduces New Line System|archive-url=https://web.archive.org/web/20100115090212/http://infinera.com/j7/servlet/NewsItem?newsItemID=108|archive-date=2010-01-15|website=Infinera Corp press release|access-date=2009-08-26}}</ref> to support a combined bit rate in the range of {{val|1.6|ul=Tbit/s}}.

== Parameters ==

=== Bandwidth–distance product ===
Because the effect of dispersion increases with the length of the fiber, a fiber transmission system is often characterized by its ''bandwidth–distance product'', usually expressed in units of [[Hertz|MHz]]·km. This value is a product of bandwidth and distance because there is a trade-off between the bandwidth of the signal and the distance over which it can be carried. For example, a common multi-mode fiber with bandwidth–distance product of 500&nbsp;MHz·km could carry a 500&nbsp;MHz signal for 1&nbsp;km or a 1000&nbsp;MHz signal for 0.5&nbsp;km.

=== Record speeds ===
Using [[Wavelength-division multiplexing|wavelength-division multiplexing]], each fiber can carry many independent channels, each using a different wavelength of light. The net data rate (data rate without overhead bytes) per fiber is the per-channel data rate reduced by the [[Forward error correction|forward error correction]] (FEC) overhead, multiplied by the number of channels (usually up to eighty in commercial dense WDM systems {{As of|2008|lc=on}}).{{update inline|date=January 2023}}

==== Standard fiber cables ====
The following summarizes research using standard telecoms-grade single-mode, single-solid-core fiber cables.

{| class=wikitable
!Year
!Organization
!Aggregate speed
!Propagation modes
!WDM channels
!Per-channel speed
!Distance

|-|-
|2009
|[[Company:Alcatel-Lucent|Alcatel-Lucent]]<ref name="Alcatel-Lucent 2009" />
|15.5 Tbit/s
|
|155
|100 Gbit/s
|7000&nbsp;km
|-
|2010
|[[Company:Nippon Telegraph and Telephone|NTT]]<ref name="NTT 2010" />
|69.1 Tbit/s
|
|432
|171 Gbit/s
|240&nbsp;km
|-
|2011
|[[Company:NEC|NEC]]<ref name="Hecht" />
|101.7 Tbit/s
|
|370
|273 Gbit/s
|165&nbsp;km
|-
|2011{{efn-ua|name=single source|Used a single source to drive all channels.}}
|KIT<ref name="BBC 2011" /><ref name="Hillerkuss 2011" />
|26 Tbit/s
|
|336
|77 Gbit/s
|50&nbsp;km

|-
|2016
|[[Company:BT Group|BT]] & [[Company:Huawei|Huawei]]<ref name="ISPreview 2016-05-25" />
|5.6 Tbit/s
|
|28
|200 Gbit/s
|about 140&nbsp;km ?
|-
|2016{{efn-ua|First result that pushes close to the Shannon theoretical limit.}}
|Nokia Bell Labs, Deutsche Telekom & Technical University of Munich<ref name="ISPreview 2016-09-19" />
|1 Tbit/s
|
|1
|1 Tbit/s
|
|-
|2016
|[[Company:Nokia Networks|Nokia-Alcatel-Lucent]]<ref name="ARS Technica 2016" />
|65&nbsp;Tbit/s
|
|
|
|6600&nbsp;km
|-
|2017
|[[Company:BT Group|BT]] & [[Company:Huawei|Huawei]]<ref name="BT 2017" />
|11.2&nbsp;Tbit/s
|
|28
|400&nbsp;Gbit/s
|250&nbsp;km
|-
|2020{{efn-ua|name=single source}}
|RMIT, Monash & Swinburne Universities<ref name="rmit 2020" /><ref name="Corcoran 2020" />
| 39.0 Tbit/s
|
| 160
| 244 Gbit/s
| 76.6&nbsp;km
|-
|2020
|UCL<ref name="ISPreview 2020" />
| 178.08 Tbit/s
|
| '''660'''
| 25 Gbit/s
| 40&nbsp;km
|-
|2022
|NICT<ref name="NICT 2022-11-10" /><ref name="New Atlas 2022" /><ref name="ISPreview 2022-11-12" />
| '''1.53 Pbit/s'''
| 55 (110-MIMO multiplexer)
| 184 (C-band)
| '''1.03 Tbit/s'''
| 25.9&nbsp;km
|}

{{notelist-ua}}

==== Specialized cables ====

The following summarizes research using specialized cables that allow spatial multiplexing to occur, use specialized tri-mode fiber cables or similar specialized fiber optic cables.

{| class=wikitable
!Year
!Organization
!Aggregate speed
!No. of propagation modes
!No. of cores
!WDM channels (per core)
!Per channel speed
!Distance

|-|-
|2011
|[[Organization:National Institute of Information and Communications Technology|NICT]]<ref name="Hecht" />
|109.2 Tbit/s
|
|7
|
|
|
|-
|2012
|[[Company:NEC|NEC]], [[Company:Corning Inc.|Corning]]<ref name="Optics 2013" />
|1.05 Pbit/s
|
|12
|
|
|52.4&nbsp;km
|-
|2013
|[[Organization:University of Southampton|University of Southampton]]<ref name="New Scientist 2013" />
|73.7 Tbit/s
|
|1 (hollow)
|3x96 (mode DM)<ref name="Anthony 2013" />
|256&nbsp;Gbit/s
|310&nbsp;m
|-
|2014
|Technical University of Denmark<ref name="ISPreview 2014" />
|43 Tbit/s
|
|7
|
|
|1045&nbsp;km
|-
|2014
|[[Organization:Eindhoven University of Technology|Eindhoven University of Technology]] (TU/e) and [[Organization:University of Central Florida|University of Central Florida]] (CREOL)<ref name="ExtremeTech 2014" />
|255 Tbit/s
|
|7
|50
|'''~728&nbsp;Gbit/s'''
|1&nbsp;km
|-
|2015
|[[Organization:National Institute of Information and Communications Technology|NICT]], Sumitomo Electric and RAM Photonics<ref name="NICT 2015" />
|2.15&nbsp;Pbit/s
|
|22
|402 (C+L bands)
|243&nbsp;Gbit/s
|31&nbsp;km
|-
|2017
|[[Company:Nippon Telegraph and Telephone|NTT]]<ref name="NTT 2017" />
|1&nbsp;Pbit/s
|single-mode
|32
|46
|680&nbsp;Gbit/s
|205.6&nbsp;km
|-
|2017
|KDDI Research and Sumitomo Electric<ref name="Global Sei 2017" />
|'''10.16&nbsp;Pbit/s'''
|'''6-mode'''
|19
|739 (C+L bands)
|120&nbsp;Gbit/s
|11.3&nbsp;km
|-
|2018{{efn-ua|New record for throughput using a single core cable, that is, not using [[Spatial multiplexing|spatial multiplexing]].}}
|[[Organization:National Institute of Information and Communications Technology|NICT]]<ref name="Fibre Systems 2018" />
|159 Tbit/s
|tri-mode
|1
|348
|414&nbsp;Gbit/s
|1045&nbsp;km
|-
|2021
|NICT<ref name="ISPreview 2021" />
| 319 Tbit/s
| single-mode
| 4
| 552 (S, C & L bands)
| 144.5 Gbit/s
| '''3001&nbsp;km (69.8&nbsp;km)'''
|-
|2022
|NICT<ref name="NICT 2022-05-30" /><ref name="ISPreview 2022-06-07" /><ref name="New Atlas 2022-06-01" />
| 1.02 Pbit/s
|
| 4
| '''801''' (S+C+L bands)
| 
| 51.7&nbsp;km
|-
|2022{{efn-ua|New record for throughput using a photonic chip.}}
|Technical University of Denmark<ref name="Nature 2022" /><ref name="Tom's Hardware 2022" />
| 1.84 Pbit/s
| 
| '''37'''
| 223
| 223 Gbit/s
| 7.9&nbsp;km
|}

{{notelist-ua}}

==== New techniques ====

Research from DTU, Fujikura and [[Company:Nippon Telegraph and Telephone|NTT]] is notable in that the team was able to reduce the power consumption of the optics to around 5% compared with more mainstream techniques, which could lead to a new generation of very power-efficient optic components.

{| class=wikitable
!Year
!Organization
!Effective speed
!No. of Propagation Modes
!No. of cores
!WDM channels (per core)
!Per channel speed
!Distance

|-|-
|2018
|Hao Hu, et al. (DTU, Fujikura & NTT)<ref name="Hu 2018" />
|768 Tbit/s (661 Tbit/s)
|Single-mode
|30
|80
|320&nbsp;Gbit/s
|
|}

Research conducted by the RMIT University, Melbourne, Australia, have developed a nanophotonic device that carries data on light waves that have been twisted into a spiral form and achieved a 100-fold increase in current attainable fiber optic speeds.<ref>{{cite web
  | title = Groundbreaking new technology could allow 100-times-faster internet by harnessing twisted light beams
  | publisher = Phys.org
  | date = 2018-10-24
  | url = https://phys.org/news/2018-10-groundbreaking-technology-times-faster-internet-harnessing.html
  | access-date = 2018-10-25}}</ref>
The technique is known as orbital angular momentum (OAM). The nanophotonic device uses ultra-thin sheets to measure a fraction of a millimeter of twisted light. Nano-electronic device is embedded within a connector smaller than the size of a USB connector and may be fitted at the end of an optical fiber cable.<ref>{{cite journal
  | title = Angular-momentum nanometrology in an ultrathin plasmonic topological insulator film
  | journal = Nature Communications
 | volume = 9
 | issue = 1
 | pages = 4413
 | publisher = Nature Communications (volume 9, Article number: 4413)
  | date = 2018-10-24
  | doi = 10.1038/s41467-018-06952-1
 | pmid = 30356063
 | pmc = 6200795
 | last1 = Yue
 | first1 = Zengji
 | last2 = Ren
 | first2 = Haoran
 | last3 = Wei
 | first3 = Shibiao
 | last4 = Lin
 | first4 = Jiao
 | last5 = Gu
 | first5 = Min
 | bibcode = 2018NatCo...9.4413Y
 }}</ref>

=== Dispersion ===
For modern glass optical fiber, the maximum transmission distance is limited not by direct material absorption but by [[Physics:Dispersion (optics)|dispersion]], the spreading of optical pulses as they travel along the fiber. Dispersion limits the bandwidth of the fiber because the spreading optical pulse limits the rate which pulses can follow one another on the fiber and still be distinguishable at the receiver. Dispersion in optical fibers is caused by a variety of factors.

Intermodal dispersion, caused by the different axial speeds of different [[Physics:Transverse mode|transverse mode]]s, limits the performance of [[Engineering:Multi-mode optical fiber|multi-mode fiber]]. Because single-mode fiber supports only one transverse mode, intermodal dispersion is eliminated.

In single-mode fiber performance is primarily limited by chromatic dispersion, which occurs because the index of the glass varies slightly depending on the wavelength of the light, and, due to modulation, light from optical transmitters necessarily occupies a (narrow) range of wavelengths. [[Physics:Polarization mode dispersion|Polarization mode dispersion]], another source of limitation, occurs because although the single-mode fiber can sustain only one transverse mode, it can carry this mode with two different polarizations, and slight imperfections or distortions in a fiber can alter the propagation velocities for the two polarizations. This phenomenon is called [[Physics:Birefringence|birefringence]] and can be counteracted by [[Engineering:Polarization-maintaining optical fiber|polarization-maintaining optical fiber]].

Some dispersion, notably chromatic dispersion, can be removed by a dispersion compensator. This works by using a specially prepared length of fiber that has the opposite dispersion to that induced by the transmission fiber, and this sharpens the pulse so that it can be correctly decoded by the electronics.

=== Attenuation ===
Fiber attenuation is caused by a combination of [[Physics:Absorption (electromagnetic radiation)|material absorption]], [[Physics:Rayleigh scattering|Rayleigh scattering]], Mie scattering, and losses in connectors. Material absorption for pure silica is only around 0.03&nbsp;dB/km. Impurities in early optical fibers caused attenuation of about 1000&nbsp;dB/km. Modern fiber has attenuation around 0.3&nbsp;dB/km. Other forms of attenuation are caused by physical stresses to the fiber, microscopic fluctuations in density, and imperfect splicing techniques.<ref>{{Cite web |url=https://user.eng.umd.edu/~davis/optfib.html |title=Fiber Optic Technology and its Role in the Information Revolution |author=Christopher C. Davis}}</ref>

=== Transmission windows {{anchor|Optical bands}}===
<!-- this section linked from redirect Optical bands via the anchor tag above the section header, please do not modify or remove the anchor tag, thanks-->
Each effect that contributes to attenuation and dispersion depends on the optical wavelength. There are wavelength bands (or windows) where these effects are weakest, and these are the most favorable for transmission. These windows have been standardized.<ref>{{Cite web|url=https://www.rp-photonics.com/optical_fiber_communications.html|title=Optical Fiber Communications|first1=Dr Rüdiger|last1=Paschotta|website=rp-photonics.com}}</ref>
{| class=wikitable
|+Standard bands for optical fiber communications
!Band
!Description
!Wavelength range
|-
!O band
|Original
|1260–1360&nbsp;nm
|-
!E band
|Extended
|1360–1460&nbsp;nm
|-
!S band
|Short wavelengths
|1460–1530&nbsp;nm
|-
!C band
|Conventional (''erbium window'')
|1530–1565&nbsp;nm
|-
!L band
|Long wavelengths
|1565–1625&nbsp;nm
|-
!U band
|Ultralong wavelengths
|1625–1675&nbsp;nm
|}

Note that this table shows that current technology has managed to bridge the E and S windows that were originally disjoint.

Historically, there was a window of wavelengths shorter than O band, called the first window, at 800–900&nbsp;nm; however, losses are high in this region so this window is used primarily for short-distance communications. The current lower windows (O and E) around 1300&nbsp;nm have much lower losses. This region has zero dispersion. The middle windows (S and C) around 1500&nbsp;nm are the most widely used. This region has the lowest attenuation losses and achieves the longest range. It does have some dispersion, so dispersion compensator devices are used to address this.

=== Regeneration ===
When a communications link must span a larger distance than existing fiber-optic technology is capable of, the signal must be ''regenerated'' at intermediate points in the link by [[Engineering:Optical communications repeater|optical communications repeater]]s. Repeaters add substantial cost to a communication system, and so system designers attempt to minimize their use.

Recent advances in fiber and optical communications technology have reduced signal degradation to the point that ''regeneration'' of the optical signal is only needed over distances of hundreds of kilometers. This has greatly reduced the cost of optical networking, particularly over undersea spans where the cost and reliability of repeaters is one of the key factors determining the performance of the whole cable system. The main advances contributing to these performance improvements are dispersion management, which seeks to balance the effects of dispersion against non-linearity; and [[Physics:Soliton (optics)|soliton]]s, which use nonlinear effects in the fiber to enable dispersion-free propagation over long distances.<!--User:Kvng/RTH-->

=== Last mile ===
Although fiber-optic systems excel in high-bandwidth applications, optical fiber has been slow to achieve its goal of fiber to the premises or to solve the [[Engineering:Last mile (telecommunications)|last mile]] problem. However, FTTH deployment has increased significantly over the last decade and is projected to serve millions more subscribers in the near future. In Japan, for instance [[Passive optical network|EPON]] has largely replaced DSL as a broadband Internet source. South Korea's KT also provides a service called FTTH (Fiber To The Home), which provides fiber-optic connections to the subscriber's home. The largest FTTH deployments are in Japan, South Korea, and China. Singapore started implementation of their all-fiber Next Generation Nationwide Broadband Network (Next Gen NBN), which is slated for completion in 2012 and is being installed by OpenNet. Since they began rolling out services in September 2010, network coverage in Singapore has reached 85% nationwide.

In the US, Verizon Communications provides a FTTH service called FiOS to select high-ARPU (Average Revenue Per User) markets within its existing territory. The other major surviving ILEC (or Incumbent Local Exchange Carrier), AT&T, uses a FTTN (Fiber To The Node) service called U-verse with twisted-pair to the home. Their MSO competitors employ FTTN with coax using [[Engineering:Hybrid fibre-coaxial|HFC]]. All of the major access networks use fiber for the bulk of the distance from the service provider's network to the customer.

The globally dominant access network technology is EPON (Ethernet Passive Optical Network). In Europe, and among telcos in the United States, BPON (ATM-based Broadband PON) and GPON (Gigabit PON) had roots in the FSAN (Full Service Access Network) and ITU-T standards organizations under their control.

== Comparison with electrical transmission ==
[[File:Fiber Splice Lab.jpg|thumb|A mobile fiber [[Engineering:Fusion splicing|optic splice]] lab used to access and splice underground cables]]
[[File:Fiber Splice.jpg|thumb|An underground fiber optic splice enclosure opened up]]

The choice between optical fiber and electrical (or [[Chemistry:Copper|copper]]) transmission for a particular system is made based on a number of trade-offs. Optical fiber is generally chosen for systems requiring higher [[Bandwidth (computing)|bandwidth]] or spanning longer distances than electrical cabling can accommodate.

The main benefits of fiber are its exceptionally low loss (allowing long distances between amplifiers/repeaters), its absence of ground currents and other [[Parasitic oscillation|parasite signal]] and power issues common to long parallel electric conductor runs (due to its reliance on light rather than electricity for transmission, and the dielectric nature of fiber optic), and its inherently high data-carrying capacity. Thousands of electrical links would be required to replace a single high-bandwidth fiber cable. Another benefit of fibers is that even when run alongside each other for long distances, fiber cables experience effectively no [[Crosstalk|crosstalk]], in contrast to some types of electrical [[Engineering:Transmission line|transmission line]]s. Fiber can be installed in areas with high [[Engineering:Electromagnetic interference|electromagnetic interference]] (EMI), such as alongside utility lines, power lines, and railroad tracks. Nonmetallic all-dielectric cables are also ideal for areas of high lightning-strike incidence.

For comparison, while single-line, voice-grade copper systems longer than a couple of kilometers require in-line signal repeaters for satisfactory performance, it is not unusual for optical systems to go over {{convert|100|km|mi|sp=us}}, with no active or passive processing. Single-mode fiber cables are commonly available in {{cvt|12|km}} lengths, minimizing the number of splices required over a long cable run. Multi-mode fiber is available in lengths up to 4&nbsp;km, although industrial standards only mandate 2&nbsp;km unbroken runs.

In short-distance and relatively low-bandwidth applications, electrical transmission is often preferred because of its
* Lower material cost, where large quantities are not required
* Lower cost of transmitters and receivers
* Capability to carry [[Physics:Electric power|electrical power]] as well as signals (in appropriately designed cables)
* Ease of operating transducers in [[Linearity#Electronics|linear]] mode.

Optical fibers are more difficult and expensive to splice than electrical conductors. And at higher powers, optical fibers are susceptible to [[Engineering:Optical fiber#Fiber fuse|fiber fuse]], resulting in catastrophic destruction of the fiber core and damage to transmission components.<ref>{{cite journal|last1=Lee |first1=M. M. |author2=J. M. Roth |author3=T. G. Ulmer |author4=C. V. Cryan |year=2006 |title=The Fiber Fuse Phenomenon in Polarization-Maintaining Fibers at 1.55&nbsp;μm |journal=Conference on Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference and Photonic Applications Systems Technologies |version=paper JWB66 |publisher=Optical Society of America |url=http://www.toddulmer.com/work/lee_ulmerCLEO2006.pdf |access-date=March 14, 2010 |url-status=dead |archive-url=https://web.archive.org/web/20110717065456/http://www.toddulmer.com/work/lee_ulmerCLEO2006.pdf |archive-date=July 17, 2011 }}</ref>

Because of these benefits of electrical transmission, optical communication is not common in short box-to-box, [[Engineering:Backplane|backplane]], or chip-to-chip applications; however, optical systems on those scales have been demonstrated in the laboratory.

In certain situations, fiber may be used even for short-distance or low-bandwidth applications, due to other important features:
* Immunity to electromagnetic interference, including nuclear [[Physics:Electromagnetic pulse|electromagnetic pulse]]s.
* High [[Physics:Electrical resistance|electrical resistance]], making it safe to use near high-voltage equipment or between areas with different [[Engineering:Earth potential rise|earth potentials]].
* Lighter weight—important, for example, in aircraft.
* No sparks—important in flammable or explosive gas environments.<ref>{{cite book |title=Military Laser Technology for Defense: Technology for Revolutionizing 21st Century Warfare |first1=Alastair D. |last1=McAulay |publisher=John Wiley & Sons |date=2011 |isbn=9781118019542 |quote=Optical sensors are advantageous in hazardous environments because there are no sparks when a fiber breaks or its cover is worn.}}</ref>
* Not electromagnetically radiating, and difficult to tap without disrupting the signal—important in high-security environments.
* Much smaller cable size—important where the pathway is limited, such as networking an existing building, where smaller channels can be drilled and space can be saved in existing cable ducts and trays.
* Resistance to corrosion due to non-metallic transmission medium

Optical fiber cables can be installed in buildings with the same equipment that is used to install copper and coaxial cables, with some modifications due to the small size and limited pull tension and bend radius of optical cables. Optical cables can typically be installed in duct systems in spans of 6000 meters or more depending on the duct's condition, layout of the duct system, and installation technique. Longer cables can be coiled at an intermediate point and pulled farther into the duct system as necessary.

== Governing standards ==
In order for various manufacturers to be able to develop components that function compatibly in fiber optic communication systems, a number of standards have been developed. The [[Organization:International Telecommunication Union|International Telecommunication Union]] publishes several standards related to the characteristics and performance of fibers themselves, including
* ITU-T G.651, "Characteristics of a 50/125&nbsp;μm multimode graded index optical fibre cable"
* ITU-T G.652, "Characteristics of a single-mode optical fibre cable"

Other standards specify performance criteria for fiber, transmitters, and receivers to be used together in conforming systems. Some of these standards are:
* [[100 Gigabit Ethernet|100 Gigabit Ethernet]]
* [[10 Gigabit Ethernet|10 Gigabit Ethernet]]
* [[Engineering:Fibre Channel|Fibre Channel]]
* [[Gigabit Ethernet]]
* [[Engineering:HIPPI|HIPPI]]
* Synchronous Digital Hierarchy
* Synchronous Optical Networking
* Optical transport network (OTN)

[[TOSLINK]] is the most common format for [[Digital audio|digital audio]] cable using [[Chemistry:Plastic optical fiber|plastic optical fiber]] to connect digital sources to digital receivers.

== See also ==
* Dark fiber
* [[Fiber to the x]]
* [[Engineering:Free-space optical communication|Free-space optical communication]]

== Notes ==
{{Notelist}}

== References ==
{{reflist|refs=
<ref name="Alcatel-Lucent 2009">{{cite press release
 |title       = Alcatel-Lucent Bell Labs announces new optical transmission record and breaks 100 Petabit-per-second-kilometer barrier
 |publisher   = Alcatel-Lucent
 |date        = 2009-10-28
 |url         = http://www.alcatel-lucent.com/wps/portal/newsreleases/detail?LMSG_CABINET=Docs_and_Resource_Ctr&LMSG_CONTENT_FILE=News_Releases_2009/News_Article_001797.xml
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20130718194943/http://www3.alcatel-lucent.com/wps/portal/newsreleases/detail?LMSG_CABINET=Docs_and_Resource_Ctr&LMSG_CONTENT_FILE=News_Releases_2009%2FNews_Article_001797.xml
 |archive-date = 2013-07-18
}}</ref>
<ref name="NTT 2010">{{cite press release
  | title = World Record 69-Terabit Capacity for Optical Transmission over a Single Optical Fiber
  | publisher = NTT
  | date = 2010-03-25
  | url = http://www.ntt.co.jp/news2010/1003e/100325a.html
  | access-date = 2010-04-03}}</ref>
<ref name="Hecht">{{cite journal
  | title = Ultrafast fibre optics set new speed record
  | journal=New Scientist
  | volume=210
 | issue=2809
 | pages=24
 | date = 2011-04-29
  | url = https://www.newscientist.com/article/mg21028095.500-ultrafast-fibre-optics-set-new-speed-record.html
  | access-date = 2012-02-26| bibcode=2011NewSc.210R..24H
 | last1=Hecht
 | first1=Jeff
 | doi=10.1016/S0262-4079(11)60912-3
 }}</ref>
<ref name="BBC 2011">{{cite web
  | title = Laser puts record data rate through fibre
  | publisher = BBC
  | date = 2011-05-22
  | url = https://www.bbc.co.uk/news/science-environment-13469924}}</ref>
<ref name="Hillerkuss 2011">{{cite journal
  | title=26 Tbit s<sup>−1</sup> line-rate super-channel transmission utilizing all-optical fast Fourier transform processing
  | first1=D. |last1=Hillerkuss
  | last2=Schmogrow |first2=R.
  | last3=Schellinger |first3=T.
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  | journal=Nature Photonics |volume=5 |page=364 |year= 2011
  | issue=6 | doi=10.1038/NPHOTON.2011.74
  | bibcode=2011NaPho...5..364H }}</ref>
<ref name="ISPreview 2016-05-25">{{cite web
  | title = BT Trial 5.6Tbps on a Single Optical Fibre and 2Tbps on a Live Core Link
  | publisher = ISPreview
  | date = 2016-05-25
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  | archive-url = https://web.archive.org/web/20230408193304/https://www.ispreview.co.uk/index.php/2016/05/bt-trials-2tbps-and-5-6tbps-speeds-on-fibre-optic-link.html
  | archive-date = 2023-04-08
  | access-date = 2018-06-30}}</ref>
<ref name="ISPreview 2016-09-19">{{cite web
  | title = Scientists Successfully Push Fibre Optic Transmissions Close to the Shannon Limit
  | publisher = ISPreview
  | date = 2016-09-19
  | url = https://www.ispreview.co.uk/index.php/2016/09/scientists-successfully-push-fibre-optic-data-speeds-close-limit.html
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  | archive-date = 2023-03-29
  | access-date = 2018-06-30}}</ref>
<ref name="ARS Technica 2016">{{cite web
  | title = 65Tbps over a single fibre: Nokia sets new submarine cable speed record
  | publisher = ARS Technica
  | date = 2016-12-10
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  | access-date = 2018-06-30}}</ref>
<ref name="BT 2017">{{cite web
  | title = BT Labs delivers ultra-efficient terabit 'superchannel'
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  | access-date = 2018-08-03
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  | url-status = dead
  }}</ref>
<ref name="rmit 2020">{{cite web
  | title = Researchers just recorded world's fastest internet speed using a single optical chip
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  | date = 2020-05-22
  | url = https://www.rmit.edu.au/news/all-news/2020/may/Fastest-internet-speed
  | access-date = 2020-05-23}}{{dead link|date=April 2023}}</ref>
<ref name="Corcoran 2020">{{cite journal
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  | publisher = Nature
  | date = 2020-05-22
  |  pmid=32444605| doi = 10.1038/s41467-020-16265-x|arxiv=2003.11893 
 | last1 = Corcoran
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<ref name="ISPreview 2020">{{cite web
  | title = London UK Team Achieves Record 178Tbps Single Fibre Speed
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  | archive-date = 2022-09-28
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<ref name="NICT 2022-11-10">{{cite web
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  | access-date = 2022-11-11}}</ref>
<ref name="New Atlas 2022">{{cite web
  | title = Speed record shattered for data transmission over standard optical fiber
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  | url = https://newatlas.com/telecommunications/data-transmission-fiber-optics-speed-record/
  | access-date = 2022-11-11}}</ref>
<ref name="ISPreview 2022-11-12">{{cite web
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<ref name="Optics 2013">{{cite web
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<ref name="New Scientist 2013">{{cite web
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<ref name="Anthony 2013">{{Cite news|url=https://www.extremetech.com/computing/151498-researchers-create-fiber-network-that-operates-at-99-7-speed-of-light-smashes-speed-and-latency-records|title=Researchers create fiber network that operates at 99.7% speed of light, smashes speed and latency records - ExtremeTech|newspaper=Extremetech|date=March 25, 2013 |first=Sebastian |last=Anthony}}</ref>
<ref name="ISPreview 2014">{{cite web
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<ref name="ExtremeTech 2014">{{cite news
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<ref name="NTT 2017">{{cite web
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<ref name="Global Sei 2017">{{cite web
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<ref name="Fibre Systems 2018">{{cite web
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{{refbegin}}
* [http://www.rp-photonics.com/optical_fiber_communications.html Encyclopedia of Laser Physics and Technology]
* [http://www.ciscopress.com/articles/article.asp?p=170740&seqNum=1&rl=1 Fiber-Optic Technologies] by Vivek Alwayn
* {{cite book |last1=Agrawal |first1=Govind P. |title=Fiber-optic communication systems |publisher={{wipe|John Wiley & Sons}} |year=2002 |location=New York |isbn=978-0-471-21571-4}}
{{refend}}

== Further reading ==
* Keiser, Gerd. (2011). ''Optical fiber communications'', 4th ed. New York: McGraw-Hill, {{ISBN|9780073380711}}
* Senior, John. (2008). ''Optical Fiber Communications: Principles and Practice'', 3rd ed. Prentice Hall. {{ISBN|978-0130326812}}

==External links==
* [https://web.archive.org/web/20061230102529/http://www.redbooks.ibm.com/pubs/pdfs/redbooks/sg245230.pdf "Understanding Optical Communications"] An IBM redbook
* [https://sites.google.com/site/fiberopticsuncovered/ Fiber Optics - Internet, Cable and Telephone Communication]

{{Optical communication}}
{{Telecommunications}}

{{DEFAULTSORT:Fiber-Optic Communication}}
[[Category:Fiber-optic communications| ]]
[[Category:Photonics]]

{{Sourceattribution|Fiber-optic communication}}