Optischer Computer

2018-07-16T14:18:58Z

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{{Expert needed |Physics |talk=Analog optical computing |date=November 2012 }}
'''Optical''' or '''photonic computing''' uses [[photon]]s produced by [[lasers]] or [[diode]]s for computation. For decades, photons have promised to allow a higher [[Bandwidth (signal processing)|bandwidth]] than the [[electrons]] used in conventional computers.

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 lose 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 lessening the need for electrical power.<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>

Application-specific devices, such as [[synthetic aperture radar]] (SAR) and ''[[optical correlator]]s'', have been designed to use the principles of optical computing. Correlators can be used, for example, to detect and track objects,<ref>{{cite book |title=Optical Computing: A Survey for Computer Scientists |chapter=Chapter 3: Optical Image and Signal Processing |last=Feitelson |first=Dror G. |date=1988 |publisher=MIT Press |location=Cambridge, Massachusetts |isbn=0-262-06112-0 }}</ref> and to classify serial time-domain optical data.<ref>{{cite journal |last=Kim |first=S. K. |last2=Goda |first2=K.|last3=Fard |first3=A. M. |last4=Jalali |first4=B.|title= Optical time-domain analog pattern correlator for high-speed real-time image recognition |journal=Optics Letters |volume=36 |issue=2 |pages=220 |date=2011 |doi= 10.1364/ol.36.000220|bibcode=2011OptL...36..220K }}</ref>

==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 using materials with a [[Refractive index#Nonlinearity|non-linear refractive index]]. In particular, materials exist<ref>https://www.rp-photonics.com/nonlinear_index.html</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 |last=Jain |first=K. |last2=Pratt, Jr. |first2=G. W. |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
| title = Optical transistors and logic circuits embodying the same
| pubdate = May 10, 1983
| fdate = Jun 16, 1976
| pridate = Jun 16, 1976
| invent1 = K. Jain
| invent2 = G.W. Pratt, Jr.
}}</ref> can be used to create optical [[logic gates]],<ref name=jainprattpatent /> which in turn are assembled into the higher level components of the computer's [[CPU]]. These will be nonlinear optical crystals used to manipulate light beams into controlling other light beams.

===Controversy===
There are disagreements between researchers about the future capabilities of optical computers; whether or not they may be able to compete with semiconductor-based electronic computers in terms of speed, power consumption, cost, and size is an open question. Critics note that<ref name="Tucker">{{cite journal |first=R.S. |last=Tucker |title=The role of optics in computing |journal=Nature Photonics |volume=4 |pages=405 |date=2010 |doi=10.1038/nphoton.2010.162 |url=http://www.nature.com/nphoton/journal/v4/n7/full/nphoton.2010.162.html|bibcode=2010NaPho...4..405T }}</ref> real-world logic systems require "logic-level restoration, cascadability, [[fan-out]] and input–output isolation", all of which are currently provided by electronic transistors at low cost, low power, and high speed. For optical logic to be competitive beyond a few niche applications, major breakthroughs in non-linear optical device technology would be required, or perhaps a change in the nature of computing itself.<ref>{{cite web|last1=Rajan|first1=Renju|last2=Babu|first2=Padmanabhan Ramesh|last3=Senthilnathan|first3=Krishnamoorthy|title=All-Optical Logic Gates Show Promise for Optical Computing|url=https://www.photonics.com/a63226/All-Optical_Logic_Gates_Show_Promise_for_Optical|website=Photonics|publisher=Photonics Spectra|accessdate=8 April 2018}}</ref><ref>{{cite book|last1=Rajan|first1=Renju|last2=Babu|first2=Padmanabhan Ramesh|last3=Senthilnathan|first3=Krishnamoorthy|title=The Dawn of Photonic Crystals: An Avenue for Optical Computing|publisher=Intech|isbn=978-953-51-3962-1|url=https://www.intechopen.com/books/theoretical-foundations-and-application-of-photonic-crystals/the-dawn-of-photonic-crystals-an-avenue-for-optical-computing|accessdate=4 April 2018}}</ref>

==Misconceptions, challenges, and prospects==
A significant challenge to optical computing is that computation is a [[nonlinear]] 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=0387946594 |author=Philip R. Wallace|title= Paradox Lost: Images of the Quantum|date=1996}}</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 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]]. However, in [[fiber optic communications]], practical limits such as [[dispersion (optics)|dispersion]] often constrain [[Wavelength-division multiplexing|channels]] to bandwidths of 10s 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.

==Photonic logic==
[[File:optical-NOT-gate.png|thumb|right|Realization of a photonic controlled-NOT gate for use in quantum computing]]

Photonic logic is the use of photons ([[light]]) in [[logic gate]]s (NOT, AND, OR, NAND, NOR, XOR, XNOR). Switching is obtained using [[nonlinear optics|nonlinear optical effects]] when two or more signals are combined.<ref name=jainprattpatent />

[[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 currently being investigated include photonic logic at a [[Nanotechnology|molecular level]], using [[Photoluminescence|photoluminescent]] chemicals. In a recent 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 | first = Edward H. | last = Witlicki }}</ref>

==Unconventional approaches==

===Time delays optical computing===

The basic idea is to delay light (or any other signal) in order to perform useful computations.<ref name="oltean_hamiltonian">{{cite conference|author=Mihai Oltean|title= A light-based device for solving the Hamiltonian path problem |conference=Unconventional Computing| pages= 217–227| publisher= Springer LNCS 4135|doi=10.1007/11839132_18|date=2006|arxiv=0708.1496}}</ref> Of interest would be to solve [[NP-completeness|NP-complete problems]] as those are difficult problems for the conventional computers.

There are 2 basic properties of light that are actually used in this approach:

* The light can be delayed by passing it through an optical fiber of a certain length.
* The light can be split into multiple (sub)rays. This property is also essential because we can evaluate multiple solutions in the same time.

When solving a problem with time-delays the following steps must be followed:

* The first step is to create a graph-like structure made from optical cables and splitters. Each graph has a start node and a destination node.
* The light enters through the start node and traverses the graph until it reaches the destination. It is delayed when passing through arcs and divided inside nodes.
* The light is marked when passing through an arc or through an node so that we can easily identify that fact at the destination node.
* At the destination node we will wait for a signal (fluctuation in the intensity of the signal) which arrives at a particular moment(s) in time. If there is no signal arriving at that moment, it means that we have no solution for our problem. Otherwise the problem has a solution. Fluctuations can be read with an [[photodetector]] and an [[oscilloscope]].

The first problem attacked in this way was the [[Hamiltonian path problem]].<ref name="oltean_hamiltonian"/> Later, [http://www.tcreate.org/optical other problems have been tackled in this way].

The simplest one is the [[subset sum problem]].<ref>{{cite journal|author=Mihai Oltean, Oana Muntean| title = Solving the subset-sum problem with a light-based device|journal= Natural Computing|publisher= Springer-Verlag| volume= 8| issue= 2|pages =321–331| doi=10.1007/s11047-007-9059-3| date=2009 |arxiv=0708.1964}}</ref> An optical device solving an instance with 4 numbers {a1, a2, a3, a4} is depicted below:

[[File:Optical device for solving the Subset sum problem.png|Optical device for solving the Subset sum problem]]

The light will enter in Start node. It will be divided into 2 (sub)rays of smaller intensity. These 2 rays will arrive into the second node at moments a1 and 0. Each of them will be divided into 2 subrays which
will arrive in the 3rd node at moments 0, a1, a2 and a1 + a2. These represents the all subsets of the set {a1, a2}. We expect fluctuations in the intensity of the signal at no more than 4 different moments. In the destination node we expect fluctuations at no more than 16 different moments (which are all the subsets of the given. If we have a fluctuation in the target moment B, it means that we have a solution of the problem, otherwise there is no subset whose sum of elements equals B. For the practical implementation we cannot have zero-length cables, thus all cables are increased with a small (fixed for all) value k. In this case the solution is expected at moment B+n*k.

===Wavelength-based computing===

Wavelength-based computing<ref>{{cite conference|author=Sama Goliaei, Saeed Jalili|title= An Optical Wavelength-Based Solution to the 3-SAT Problem|conference=Optical SuperComputing Workshop|date=2009|doi=10.1007/978-3-642-10442-8_10| pages=77–85|bibcode=2009LNCS.5882...77G}}</ref> can be used to solve the [[Boolean satisfiability problem#3-satisfiability|3-SAT]] problem with n variables, m clause and with no more than 3 variables per clause. Each wavelength, contained in a light ray, is considered as possible value-assignments to n variables. The optical device contains prisms and mirrors are used to discriminate proper wavelengths which satisfy the formula.

===Computing by xeroxing on transparencies===

This approach uses a Xerox machine and transparent sheets for performing computations.<ref>{{cite conference|author=Tom Head|title= Parallel Computing by Xeroxing on Transparencies|conference= Algorithmic Bioprocesses|date= 2009|pages=631–637|publisher=Springer|doi=10.1007/978-3-540-88869-7_31}}</ref> [[Boolean satisfiability problem#3-satisfiability|k-SAT problem]] with n variables, m clauses and at most k variables per clause has been solved in 3 steps:

* Firstly all 2^n possible assignments of n variables have been generated by performing n xerox copies.
* Using at most 2k copies of the truth table, each clause is evaluated at every row of the truth table simultaneously.
* The solution is obtained by making a single copy operation of the overlapped transparencies of all m clauses.

===Masking optical beams===

[[The travelling salesman problem]] has been solved in<ref>{{cite journal| author= NT Shaked, S Messika, S Dolev, J Rosen |title=Optical solution for bounded NP-complete problems|journal= Applied Optics| publisher=OSA|pages=711–724|volume=46|issue=5|date=2007|doi=10.1364/AO.46.000711|bibcode=2007ApOpt..46..711S}}</ref> by using an optical approach. All possible TSP paths have been generated and stored in a binary matrix which was multiplied with another gray-scale vector containing the distances between cities. The multiplication is performed optically by using an optical correlator.

===Optical Fourier co-processors===

Many computations, particularly in scientific applications, require frequent use of the 2D [[discrete Fourier transform]] (DFT) – for example in solving differential equations describing propagation of waves or transfer of heat. Though modern GPU technologies typically enable high-speed computation of large 2D DFTs, recently techniques have been developed that can perform DFTs optically by utilising the natural [[Fourier optics#Fourier transforming property of lenses|Fourier transforming property of lenses]]. The input is encoded using a [[liquid crystal]] [[spatial light modulator]] and the result is measured using a conventional CMOS or CCD image sensor. Such optical architectures can offer superior scaling of computational complexity due to the inherently highly interconnected nature of optical propagation, and have been used to solve 2D heat equations.<ref>{{cite journal| author= A. J. Macfaden, G. S. D. Gordon, T. D. Wilkinson |title=An optical Fourier transform coprocessor with direct phase determination|journal= Scientific Reports | publisher= Nature Publishing Group | volume = 7 |date=2017|doi=10.1038/s41598-017-13733-1|bibcode=2017NatSR...713667M}}</ref>

=== Ising machines ===

Physical computers whose design was inspired by the theoretical [[Ising model]] are called Ising machines.<ref name="courtland" /><ref name="cartlidge" /><ref>
Adrian Cho.
[http://www.sciencemag.org/news/2016/10/odd-computer-zips-through-knotty-tasks "Odd computer zips through knotty tasks"].
</ref>

[[Yoshihisa Yamamoto (scientist)|Yoshihisa Yamamoto]] 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">
Edwin Cartlidge.
[http://physicsworld.com/cws/article/news/2016/oct/31/new-ising-machine-computers-are-taken-for-a-spin "New Ising-machine computers are taken for a spin"].
</ref>

Later a team at [[Hewlett Packard Labs]] including Dave Kielpinski 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">
Rachel Courtland.
[https://spectrum.ieee.org/semiconductors/processors/hpes-new-chip-marks-a-milestone-in-optical-computing "HPE's New Chip Marks a Milestone in Optical Computing"].
</ref>

==See also==
*[[Linear optical quantum computing]]
*[[Optical neural network]]
*[[Photonic molecule]]

==References==
{{Reflist|30em}}

==Further reading==
* {{cite book |title=Optical Computing: A Survey for Computer Scientists |last=Feitelson |first=Dror G. |date=1988 |publisher=MIT Press |location=Cambridge, Massachusetts |isbn=0-262-06112-0}}
* {{cite book |title=Optical Computer Architectures: The Application of Optical Concepts to Next Generation Computers |last=McAulay |first=Alastair D. |date=1991 |publisher=John Wiley & Sons |location=New York, NY |isbn=0-471-63242-2}}
* {{cite journal |author=Ibrahim TA|author2=Amarnath K|author3=Kuo LC|author4=Grover R|author5=Van V|author6=Ho PT |title=Photonic logic NOR gate based on two symmetric microring resonators |journal=Opt Lett |volume=29 |issue=23 |pages=2779–81 |date=2004 |doi=10.1364/OL.29.002779 |pmid=15605503|bibcode=2004OptL...29.2779I}}
* {{cite journal |author=Biancardo M|author2=Bignozzi C|author3=Doyle H|author4=Redmond G |title=A potential and ion switched molecular photonic logic gate |journal=Chem. Commun. |issue=31 |pages=3918–20 |date=2005 |doi=10.1039/B507021J |url=http://pubs.rsc.org/en/content/articlelanding/2005/cc/b507021j}}
* {{cite book |editor-first=J. |editor-last=Jahns |editor2-first=S.H. |editor2-last=Lee |title=Optical Computing Hardware: Optical Computing |url=https://books.google.com/books?id=SqCjBQAAQBAJ |date=1993 |publisher=Elsevier Science |isbn=978-1-4832-1844-1}}
* {{cite journal |author=Barros S|author2=Guan S|author3=Alukaidey T |title=An MPP reconfigurable architecture using free-space optical interconnects and Petri net configuring |journal=Journal of System Architecture |volume=43 |issue=6–7 |pages=391–402 |date=1997 |doi=10.1016/S1383-7621(96)00053-7 |url=http://www.sciencedirect.com/science/article/pii/S1383762196000537}}
* [[Debabrata Goswami|D. Goswami]], "Optical Computing", Resonance, June 2003; ibid July 2003. [https://web.archive.org/web/20071215005609/http://www.iisc.ernet.in/academy/resonance/June2003/June2003p56-71.html Web Archive of www.iisc.ernet.in/academy/resonance/July2003/July2003p8-21.html]
* {{cite journal |author=Main T|author2=Feuerstein RJ|author3=Jordan HF|author4=Heuring VP|author5=Feehrer J|author6=Love CE |title=Implementation of a general-purpose stored-program digital optical computer |journal=Applied Optics |volume=33 |pages=1619–28 |date=1994 |doi=10.1364/AO.33.001619 |url=http://www.opticsinfobase.org/ao/abstract.cfm?uri=ao-33-8-1619 |pmid=20862187|bibcode=1994ApOpt..33.1619M}}
* {{cite book |first=T.S. |last=Guan |first2=S.P.V. |last2=Barros |chapter=Reconfigurable Multi-Behavioural Architecture using Free-Space Optical Communication |chapterurl=http://ieeexplore.ieee.org/xpl/articleDetails.jsp?tp=&arnumber=336615 |title=Proceedings of the IEEE International Workshop on Massively Parallel Processing using Optical Interconnections |publisher=IEEE |date=April 1994 |isbn=0-8186-5832-0 |pages=293–305 |doi=10.1109/MPPOI.1994.336615}}
* {{cite book |first=T.S. |last=Guan |first2=S.P.V. |last2=Barros |chapter=Parallel Processor Communications through Free-Space Optics |chapterurl=http://ieeexplore.ieee.org/xpl/articleDetails.jsp?tp=&arnumber=369219 |title=TENCON '94. IEEE Region 10's Ninth Annual International Conference. Theme: Frontiers of Computer Technology |publisher=IEEE |date=August 1994 |isbn=0-7803-1862-5 |pages=677–681 |volume=2 |doi=10.1109/TENCON.1994.369219}}
* {{cite book |author=Guha A.|author2=Ramnarayan R.|author3=Derstine M. |chapter=Architectural issues in designing symbolic processors in optics |chapterurl=http://dl.acm.org/citation.cfm?id=30367 |title=Proceedings of the 14th annual international symposium on Computer architecture (ISCA '87) |publisher=ACM |date=1987 |isbn=0-8186-0776-9 |pages=145–151 |doi=10.1145/30350.30367}}
* K.-H. Brenner, Alan Huang: "Logic and architectures for digital optical computers (A)", J. Opt. Soc. Am., A 3, 62, (1986)
* {{cite journal |last=Brenner |first=K.-H. |title=A programmable optical processor based on symbolic substitution |journal=Appl. Opt. |volume=27 |issue=9 |pages=1687–91 |date=1988 |doi=10.1364/AO.27.001687 |url=http://www.opticsinfobase.org/ao/abstract.cfm?uri=ao-27-9-1687 |pmid=20531637|bibcode=1988ApOpt..27.1687B }}
* {{cite journal |author=Streibl N.|author2=Brenner K.-H.|author3=Huang A.|author4=Jahns J.|author5=Jewell J.L.|author6=Lohmann A.W.|author7=Miller D.A.B.|author8=Murdocca M.J.|author9=Prise M.E.|author10=Sizer II T. |title=Digital Optics |journal=Proc. IEEE |volume=77 |issue=12 |pages=1954–69 |date=1989 |doi=10.1109/5.48834 |url=http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=48834}}
* ''[https://science.nasa.gov/headlines/y2000/ast28apr_1m.htm NASA scientists working to improve optical computing technology]'', 2000
* ''[http://www.tcreate.org/optical Optical solutions for NP-complete problems]''
* {{cite book |first=S. |last=Dolev |first2=T. |last2=Haist |first3=M.|last3= Oltean |title=Optical SuperComputing: First International Workshop, OSC 2008, Vienna, Austria, August 26, 2008, Proceedings |url=https://books.google.com/books?id=G6ZYwjKh_QcC |date=2008 |publisher=Springer |isbn=978-3-540-85672-6}}
* {{cite book |first=S. |last=Dolev |first2=M. |last2=Oltean |title=Optical Supercomputing: Second International Workshop, OSC 2009, Bertinoro, Italy, November 18–20, 2009, Proceedings |url=https://books.google.com/books?id=sl44EkMjcIkC |date=2009 |publisher=Springer |isbn=978-3-642-10441-1}}
* {{cite book |first=S. |last=Dolev |first2=M. |last2=Oltean |title=Optical Supercomputing: Third International Workshop, OSC 2010, Bertinoro, Italy, November 17–19, 2010, Revised Selected Papers |url=https://books.google.com/books?id=uf65jCXgFvwC |date=2011 |publisher=Springer |isbn=978-3-642-22493-5}}
* {{cite book |first=S. |last=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 |pages=261–263 |date=2010 |url=http://www.nature.com/nphoton/journal/v4/n5/abs/nphoton.2010.94.html |doi=10.1038/nphoton.2010.94}}
* {{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 |url=http://www.nature.com/articles/ncomms11424 |doi=10.1038/ncomms11424 | pmid=27113510 | pmc=4853429|bibcode=2016NatCo...711424C}}

==External links==
* [https://www.wired.com/news/technology/0,1282,69033,00.html?tw=newsletter_topstories_html This Laser Trick's a Quantum Leap]
* [http://www.extremetech.com/article2/0,1558,1779951,00.asp Photonics Startup Pegs Q2'06 Production Date]
* [http://www.physorg.com/news6123.html Stopping light in quantum leap]
* [http://www.physorg.com/news199470370.html High Bandwidth Optical Interconnects]
* [https://www.youtube.com/watch?v=4DeXPB3RU8Y https://www.youtube.com/watch?v=4DeXPB3RU8Y] (Movie: Computing by xeroxing on transparencies)

{{Emerging technologies}}

[[Category:Photonics]]
[[Category:Classes of computers]]
[[Category:Emerging technologies]]

Wikipedia - Benutzerbeiträge [de]

Optischer Computer