Optical computing: Difference between revisions

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{{short description|Computer that uses photons or light waves}}

'''Optical computing''' or '''photonic computing''' uses [[light wave]]s produced by [[laser]]s or incoherent sources for [[data processing]], data storage or [[data communication]] for [[computing]]. For decades, [[photon]]s have shown promise to enable a higher [[Bandwidth (signal processing)|bandwidth]] than the [[electron]]s used in conventional computers (see [[optical fiber]]s).

Most research projects focus on replacing current computer components with optical equivalents, resulting in an optical [[digital computer]] system processing [[binary data]]. This approach appears to offer the best short-term prospects for commercial optical computing, since optical components could be integrated into traditional computers to produce an optical-electronic hybrid. However, [[optoelectronic]] devices consume 30% of their energy converting electronic energy into photons and back; this conversion also slows the transmission of messages. All-optical computers eliminate the need for optical-electrical-optical (OEO) conversions, thus reducing electrical [[power consumption]].<ref>{{cite book |first=D.D. |last=Nolte |title=Mind at Light Speed: A New Kind of Intelligence |url=https://books.google.com/books?id=Q9lB-REWP5EC&pg=PA34 |date=2001 |publisher=Simon and Schuster |isbn=978-0-7432-0501-6 |page=34}}</ref>

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==Optical components for binary digital computer==

The fundamental building block of modern electronic computers is the [[transistor]]. To replace electronic components with optical ones, an equivalent [[optical transistor]] is required. This is achieved by [[crystal optics]] (using materials with a [[Refractive index#Nonlinearity|non-linear refractive index]]).<ref>{{Cite web |title=These Optical Gates Offer Electronic Access - IEEE Spectrum |url=https://spectrum.ieee.org/optical-computing-picosecond-gates |access-date=2022-12-30 |website=spectrum.ieee.org[[IEEE]] |language=en}}</ref> In particular, materials exist<ref>{{Cite webencyclopedia | url=https://www.rp-photonics.com/nonlinear_index.html | title=Encyclopedia of Laser Physics and Technology - nonlinear index, Kerr effect| encyclopedia=RP Photonics Encyclopedia| date=8 December 2006| last1=Paschotta| first1=Dr Rüdiger}}</ref> where the intensity of incoming light affects the intensity of the light transmitted through the material in a similar manner to the current response of a bipolar transistor. Such an optical transistor<ref>{{cite journal |last1=Jain |first1=K. | last2=Pratt | first2=G. W. Jr. |title=Optical transistor |journal=Appl. Phys. Lett. |volume=28 |issue=12 |pages=719 |date=1976 |doi=10.1063/1.88627 |bibcode=1976ApPhL..28..719J }}</ref><ref name=jainprattpatent>{{cite patent

| country = US

| number = 4382660

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}}</ref> can be used to create optical [[logic gate]]s,<ref name=jainprattpatent /> which in turn are assembled into the higher level components of the computer's [[central processing unit]] (CPU). These will be nonlinear optical crystals used to manipulate light beams into controlling other light beams.

Like any computing system, an optical computing system needs threefour things to function well:

# optical processor

# optical data transfer, e.g. fiber-optic cable

# [[optical storage]],<ref>{{Cite web|url=https://www.microsoft.com/en-us/research/video/project-silica-storing-data-in-glass|title=Project Silica|website=Microsoft Research|date=4 November 2019 |language=en-US|access-date=2019-11-07}}</ref>

# optical power source (light source)

Substituting electrical components will need data format conversion from photons to electrons, which will make the system slower.

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==Misconceptions, challenges, and prospects==

A significant challenge to optical computing is that computation is a [[nonlinear]]{{disambiguation needed|date=April 2024}} process in which multiple signals must interact. Light, which is an [[electromagnetic wave]], can only interact with another electromagnetic wave in the presence of electrons in a material,<ref>{{cite book|isbn=978-0387946597 |author=Philip R. Wallace|title= Paradox Lost: Images of the Quantum|date=1996|publisher=Springer }}</ref> and the strength of this interaction is much weaker for electromagnetic waves, such as light, than for the electronic signals in a conventional computer. This may result in the processing elements for an optical computer requiring more power and larger dimensions than those for a conventional electronic computer using transistors.{{Citation needed|date=December 2008}}

A further misconception{{by whom|date=May 2019}} is that since light can travel much faster than the [[drift velocity]] of electrons, and at frequencies measured in [[Terahertz (unit)|THz]], optical transistors should be capable of extremely high frequencies. However, any electromagnetic wave must obey the [[Bandwidth-limited pulse|transform limit]], and therefore the rate at which an optical transistor can respond to a signal is still limited by its [[spectral bandwidth]]. In [[fiber-optic communication]]s, practical limits such as [[dispersion (optics)|dispersion]] often constrain [[Wavelength-division multiplexing|channel]]s to bandwidths of tens of GHz, only slightly better than many silicon transistors. Obtaining dramatically faster operation than electronic transistors would therefore require practical methods of transmitting [[ultrashort pulse]]s down highly dispersive waveguides.

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[[Optical cavity|Resonator]]s are especially useful in photonic logic, since they allow a build-up of energy from [[constructive interference]], thus enhancing optical nonlinear effects.

Other approaches that have been investigated include photonic logic at a [[Nanotechnology|molecular level]], using [[Photoluminescence|photoluminescent]] chemicals. In a demonstration, Witlicki et al. performed logical operations using molecules and [[surface enhanced Raman spectroscopy|SERS]].<ref>{{cite journal | title = Molecular Logic Gates Using Surface-Enhanced Raman-Scattered Light | first9 = Amar H. | last9 = Flood | first8 = Lasse | last8 = Jensen | first7 = Eric W. | last7 = Wong | first6 = Jan O. | last6 = Jeppesen | first5 = Vincent J. | last5 = Bottomley | first4 = Daniel W. | last4 = Silverstein | first3 = Stinne W. | last3 = Hansen | journal = [[J. Am. Chem. Soc.]] | first2 = Carsten | date = 2011 | volume = 133 | issue = 19 | last2 = Johnsen | pages = 7288–91 | doi = 10.1021/ja200992x | pmid = 21510609 | first1 = Edward H. | last1 = Witlicki | bibcode = 2011JAChS.133.7288W | url = https://figshare.com/articles/Molecular_Logic_Gates_Using_Surface_Enhanced_Raman_Scattered_Light/2651761 | url-access = subscription }}</ref>

==Unconventional approaches==

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[[Yoshihisa Yamamoto (scientist)|Yoshihisa Yamamoto]]'s lab at [[Stanford University|Stanford]] pioneered building Ising machines using photons. Initially Yamamoto and his colleagues built an Ising machine using lasers, mirrors, and other optical components commonly found on an [[optical table]].<ref name="courtland" /><ref name="cartlidge">{{Cite news |first=Edwin |last=Cartlidge |url=http://physicsworld.com/cws/article/news/2016/oct/31/new-ising-machine-computers-are-taken-for-a-spin |title=New Ising-machine computers are taken for a spin |date=31 October 2016 |work=Physics World}}</ref>

Later a team at [[Hewlett Packard Labs]] developed [[photonic chip]] design tools and used them to build an Ising machine on a single chip, integrating 1,052 optical components on that single chip.<ref name="courtland">{{Cite news |first=Rachel |last=Courtland |url=https://spectrum.ieee.org/semiconductors/processors/hpes-new-chip-marks-a-milestone-in-optical-computing |title=HPE's New Chip Marks a Milestone in Optical Computing |date=2 January 2017 |work=IEEE Spectrum}}</ref>

==Industry==

Some additional companies involved with optical computing development include [[IBM]],<ref>{{Cite web |first= Daphne |last=Leprince-Ringuet |date=2021-01-08 |title=IBM is using light, instead of electricity, to create ultra-fast computing |url=https://www.zdnet.com/article/ibm-is-using-light-instead-of-electricity-to-create-ultra-fast-computing/ |access-date=2023-07-02 |website=ZDNET |language=en}}</ref> [[Microsoft]],<ref>{{Cite news |last=Wickens |first=Katie |date=2023-06-30 |title=Microsoft's light-based computer marks 'the unravelling of Moore's Law' |language=en |work=PC Gamer |url=https://www.pcgamer.com/microsofts-light-based-computer-marks-the-unravelling-of-moores-law/ |access-date=2023-07-02}}</ref> Procyon Photonics,<ref>{{Cite arXiv |last=Redrouthu |first=Sathvik|date=2022-08-13 |title=Tensor Algebra on an Optoelectronic Microchip|class=cs.PL |eprint=2208.06749 }}</ref> [[Lightelligence]],<ref>{{Cite web |date=2021-06-02 |first=Daniel |last=de Wolff |title=Accelerating AI at the speed of light |url=https://news.mit.edu/2021/lightelligence-accelerating-ai-speed-light-0602 |access-date=2023-07-02 |website=MIT News |language=en}}</ref> [[Lightmatter]],<ref>{{cite news |last1=Metz |first1=Rachel |title=Photonic Computing Startup Lightmatter Hits $1.2 Billion Valuation |url=https://www.bloomberg.com/news/articles/2023-12-19/gv-co-leads-funding-round-for-photonic-computing-startup-lightmatter?srnd=premium&sref=CIpmV6x8 |access-date=19 December 2023 |work=Bloomberg.com |date=19 December 2023 |language=en}}</ref> [[Optalysys]],<ref>{{Cite web |date=2019-03-07 |title=Optalysys launches FT:X 2000 - The world's first commercial optical processing system |url=https://insidehpc.com/2019/03/optalysys-launches-ftx-2000-the-worlds-first-commercial-optical-processing-system/ |access-date=2023-07-02 |website=insideHPC.com |language=en-US}}</ref> [[Xanadu Quantum Technologies]], [[QuiX Quantum]], [[ORCA Computing]], [[PsiQuantum]], {{interlanguage link|Quandela|fr}}, and [[TundraSystems Global]].<ref>{{Cite web |first=Kerem |last=Gülen |date=2022-12-15 |title=What Is Optical Computing: How Does It Work, Companies And More |url=https://dataconomy.com/2022/12/15/optical-computing-photonic/ |website=Dataconomy.com |access-date=2023-07-02 |language=en-US}}</ref>

==See also==

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* {{cite book |first1=S. |last1=Dolev |first2=M. |last2=Oltean |title=Optical Supercomputing: 4th International Workshop, OSC 2012, in Memory of H. John Caulfield, Bertinoro, Italy, July 19–21, 2012. Revised Selected Papers |url=https://books.google.com/books?id=Sy-7BQAAQBAJ |date=2013 |publisher=Springer |isbn=978-3-642-38250-5}}

* [https://web.archive.org/web/20090913002603/http://www.newscientist.com/article/mg19526136.400-speedoflight-computing-comes-a-step-closer.html Speed-of-light computing comes a step closer] ''New Scientist''

* {{cite journal |author= Caulfield H.|author2= Dolev S.|title= Why future supercomputing requires optics| journal= Nature Photonics| volume=4 |issue= 5|pages=261–263 |date=2010 |doi=10.1038/nphoton.2010.94|bibcode= 2010NaPho...4..261C}}

* {{cite journal |author= Cohen E.|author2= Dolev S.|author3=Rosenblit M.| title= All-optical design for inherently energy-conserving reversible gates and circuits| journal= Nature Communications| volume=7 |pages=11424 |date=2016 |doi=10.1038/ncomms11424 | pmid=27113510 | pmc=4853429|bibcode=2016NatCo...711424C}}

* {{cite book |first1=Yevgeny B.|last1=Karasik |title=Optical Computational Geometry |url=https://www.amazon.com/Optical-Computational-Geometry-computational-constructions-dp-B095MQJ8NJ/dp/B095MQJ8NJ |date=2019 |isbn=979-8511243344}}