Editing Optical communication (section)

==Electronic forms==
In the present day a variety of electronic systems optically transmit and receive information carried by pulses of light. [[Fiber-optic communication]] cables are employed to carry electronic data and telephone traffic.  [[Free-space optical communication]]s are also used every day in various applications.

=== Optical fiber ===
{{Main|Fiber-optic communication}}
Optical fiber is the most common type of channel for optical communications. The transmitters in optical fiber links are generally [[light-emitting diode]]s (LEDs) or [[laser diode]]s.  [[Infrared]] light is used more commonly than [[visible light]], because optical fibers transmit infrared wavelengths with less [[attenuation (electromagnetic radiation)|attenuation]] and [[Dispersion (optics)|dispersion]]. The signal encoding is typically simple [[intensity modulation]], although historically optical phase and [[frequency modulation]] have been demonstrated in the lab. The need for periodic [[signal regeneration]] was largely superseded by the introduction of the [[erbium-doped fiber amplifier]], which extended link distances at significantly lower cost. The commercial introduction of dense [[wavelength-division multiplexing]] (WDM) in 1996 by [[Ciena|Ciena Corp]] was the real start of optical networking.<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=2021-11-08|issn=0362-4331}}</ref><ref>{{Cite book|last=Cvijetic|first=Milorad|title=Advanced optical communication systems and networks|date=2013|others=Ivan Djordjevic|isbn=978-1-60807-556-0|location=Boston|oclc=875895386}}</ref> WDM is now the common basis of nearly every high-capacity optical system in the world.<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; 1st edition|year=2013|page=2}}</ref>

The first optical communication systems were designed and delivered to the U.S. Army and Chevron by Optelecom, Inc.,<ref>{{Cite book|last=Nick|first=Taylor|title=Laser: The Inventor the Nobel Laureate and the Thirty-Year Patent War|publisher=Jonas Street Books|year=2019|page=226}}</ref> the venture co-founded by Gordon Gould, the inventor of the optical amplifier<ref>{{Cite book|last=Nick|first=Taylor|title=Laser: The Inventor the Nobel Laureate and the Thirty-Year Patent War|publisher=Jones Street Books|year=2019|page=212}}</ref> and the laser.<ref>{{Cite book|last=Nick|first=Taylor|title=Laser: The Inventor the Nobel Laureate and the Thirty-Year Patent War|publisher=Jones Street Books|year=2019|page=283}}</ref>

=== Photophone ===
{{Main|Photophone}}
The photophone (originally given an alternate name, [[radiophone]]) is a communication device which allowed for the [[transmission (telecommunications)|transmission]] of speech on a beam of [[light]]. It was invented jointly by [[Alexander Graham Bell]] and his assistant [[Charles Sumner Tainter]] on February 19, 1880, at Bell's 1325 'L' Street laboratory in Washington, D.C.<ref>Bruce 1990, pg. 336</ref><ref name="SDU">Jones, Newell. [http://history.sandiego.edu/gen/recording/ar304.html First 'Radio' Built by San Diego Resident Partner of Inventor of Telephone: Keeps Notebook of Experiences With Bell] {{webarchive|url=https://archive.today/20060904235846/http://history.sandiego.edu/gen/recording/ar304.html |date=2006-09-04 }}, San Diego Evening Tribune, July 31, 1937. Retrieved from the University of San Diego History Department website, November 26, 2009.</ref> Both were later to become full associates in the [[Volta Laboratory and Bureau#Laboratory projects|Volta Laboratory Association]], created and financed by Bell.

On June 21, 1880, Bell's assistant transmitted a wireless voice telephone message of considerable distance, from the roof of the [[Franklin School (Washington, D.C.)|Franklin School]] to the window of Bell's laboratory, some 213 meters (about 700&nbsp;ft) away.<ref>Bruce 1990, pg. 338</ref><ref name="Carson-2007-gvttw">Carson 2007, pg. 76-78</ref><ref name="Groth">Groth, Mike. [http://www.bluehaze.com.au/modlight/GrothArticle1.htm Photophones Revisted], 'Amateur Radio' magazine, [[Wireless Institute of Australia]], Melbourne, April 1987 pp. 12–17 and May 1987 pp. 13–17.</ref><ref name="Mims 1982, p. 11">Mims 1982, p. 11.</ref>

Bell believed the photophone was his most important [[invention]]. Of the 18 [[patent]]s granted in Bell's name alone, and the 12 he shared with his collaborators, four were for the photophone, which Bell referred to as his "greatest achievement", telling a reporter shortly before his death that the photophone was "the greatest invention [I have] ever made, greater than the telephone".<ref name="Mims 1982, p. 14">Mims 1982, p. 14.</ref>

The photophone was a precursor to the [[fiber-optic communication]] systems which achieved popular worldwide usage starting in the 1980s.<ref name="Morgan">Morgan, Tim J. "The Fiber Optic Backbone", [[University of North Texas]], 2011.</ref><ref name="AmericanScientist-1984.V72.No1">Miller, Stewart E. "Lightwaves and Telecommunication", ''[[American Scientist]]'', Sigma Xi, The Scientific Research Society, January–February 1984, Vol. 72, No. 1, pp. 66-71, [https://www.jstor.org/stable/i27852430 Issue Stable URL].</ref><ref name="Gallardo+Mims">Gallardo, Arturo; [[Forrest Mims|Mims III, Forrest M.]] [http://www.mysanantonio.com/default/article/Fiber-optic-communication-began-130-years-ago-783469.php Fiber-optic Communication Began 130 Years Ago], ''[[San Antonio Express-News]]'', June 21, 2010. Accessed January 1, 2013.</ref> The master patent for the photophone ({{US patent|235199}} ''Apparatus for Signalling and Communicating, called Photophone''), was issued in December 1880,<ref name="Groth" /> many decades before its principles came to have practical applications.

=== Free-space optical communication ===
{{Main|Free-space optical communication |Optical wireless communications}}
Free-space optics (FSO) systems are employed for '[[Last mile (telecommunications)|last mile]]' [[telecommunications]] and can function over distances of several kilometers as long as there is a clear [[Line-of-sight propagation|line of sight]] between the source and the destination, and the optical receiver can reliably decode the transmitted information.<ref>{{cite web |title= A 173-mile 2-way all-electronic optical contact |url= http://www.modulatedlight.org/optical_comms/optical_qso_173mile.html |work= Modulated light web site |author= Clint Turner |date= October 3, 2007 |access-date= June 28, 2011 }}</ref> Other free-space systems can provide high-data-rate, long-range links using small, low-mass, low-power-consumption subsystems which make them suitable for communications in space.<ref>{{cite report |last=Wilson|first=K.|title=Recent Development in High-Data Rate Optical Communications at JPL |website=Jet Propulsion Laboratory |hdl=2014/18156 |hdl-access=free |date=2000-01-04}}</ref> Various planned [[satellite constellation]]s intended to provide global broadband coverage take advantage of these benefits and employ [[laser communication in space|laser communication]] for inter-satellite links between the several hundred to thousand satellites effectively creating a space-based [[optical mesh network]].

More generally, transmission of unguided optical signals is known as [[optical wireless communications]] (OWC). Examples include medium-range [[visible light communication]] and short-distance [[Infrared Data Association|IrDA]], using infrared LEDs.