Photonic computing
Encyclopedia
Today's computers use the movement of electrons in-and-out of transistors to do logic. Optical or Photonic computing is intended to use photon
s or light particles, produced by lasers or diodes, in place of electrons. Compared to electrons, photons are much faster – light travels about 30 cm, or one foot, in a nanosecond
– and have a higher bandwidth.
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 electrons into photons and back. This also slows down transmission of messages. All-optical computers eliminate the need for optical-electrical-optical (OEO) conversions.
Application-specific devices have been designed which use principles of optical computing, e.g., optical correlators. Such devices can be used for detecting and tracking objects, for example.
. To replace electronic components with optical ones, an equivalent "optical transistor" is required. This is achieved using materials with a non-linear refractive index. In particular, materials exist where the intensity of incoming light affects the intensity of the light transmitted through the material in a similar manner to the voltage response of an electronic transistor. Such an "optical transistor" can be used to create optical logic gates, which in turn are assembled into the higher level components of the computer's CPU. These will be non linear crystals used to manipulate light beams into controlling others.
of an optical communication channel is greater than the thermal noise of an electrical channel which, from information theory
, means that more signal power is required to achieve the same data capacity. However, over longer distances and at greater data rates, the loss in electrical lines is sufficiently large that optical communications will comparatively use a lower amount of power. As communication data rates rise, this distance becomes longer and so the prospect of using optics in computing systems becomes more practical.
A significant challenge to optical computing is that computation is a nonlinear process in which multiple signals must interact to perform computations. Light, which is an electromagnetic wave, can only interact with another electromagnetic wave in the presence of electrons in a material, 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 results in the processing elements for an optical computer requiring more power and larger dimensions than those for a conventional electronic computer using transistors.
) in logic gate
s (NOT, AND, OR, NAND, NOR, XOR, XNOR). Switching is obtained using nonlinear optical effects
when two or more signals are combined.
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 molecular level
, using photoluminescent
chemicals. In a recent demonstration, Flood et al. performed logical operations using molecules and SERS
.
Optical Implemnetation of Bounded non Deterministic Turing Machine, Patent by Shlomi Dolev and Yuval Nir Filed May 2003 in Israel, May 2004 USA;
Solving Hamiltonian, and other NP-Complete problems.
Photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
s or light particles, produced by lasers or diodes, in place of electrons. Compared to electrons, photons are much faster – light travels about 30 cm, or one foot, in a nanosecond
Nanosecond
A nanosecond is one billionth of a second . One nanosecond is to one second as one second is to 31.7 years.The word nanosecond is formed by the prefix nano and the unit second. Its symbol is ns....
– and have a higher bandwidth.
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 electrons into photons and back. This also slows down transmission of messages. All-optical computers eliminate the need for optical-electrical-optical (OEO) conversions.
Application-specific devices have been designed which use principles of optical computing, e.g., optical correlators. Such devices can be used for detecting and tracking objects, for example.
Optical components for binary digital computer
The fundamental building block of modern electronic computers is the transistorTransistor
A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...
. To replace electronic components with optical ones, an equivalent "optical transistor" is required. This is achieved using materials with a non-linear refractive index. In particular, materials exist where the intensity of incoming light affects the intensity of the light transmitted through the material in a similar manner to the voltage response of an electronic transistor. Such an "optical transistor" can be used to create optical logic gates, which in turn are assembled into the higher level components of the computer's CPU. These will be non linear crystals used to manipulate light beams into controlling others.
Controversy
There are ongoing disagreements among researchers with regard to the future capabilities of optical computers: will they be able to compete with semiconductor-based electronic computers in terms of speed, power consumption, cost, and form factor? Opponents of the idea that optical computers can be competitive note that 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 paradigm shift in computing itself.Misconceptions, challenges and prospects
A claimed advantage of optics is that it can reduce power consumption, but an optical communication system will typically use more power over short distances than an electronic one. This is because the shot noiseShot noise
Shot noise is a type of electronic noise that may be dominant when the finite number of particles that carry energy is sufficiently small so that uncertainties due to the Poisson distribution, which describes the occurrence of independent random events, are of significance...
of an optical communication channel is greater than the thermal noise of an electrical channel which, from information theory
Information theory
Information theory is a branch of applied mathematics and electrical engineering involving the quantification of information. Information theory was developed by Claude E. Shannon to find fundamental limits on signal processing operations such as compressing data and on reliably storing and...
, means that more signal power is required to achieve the same data capacity. However, over longer distances and at greater data rates, the loss in electrical lines is sufficiently large that optical communications will comparatively use a lower amount of power. As communication data rates rise, this distance becomes longer and so the prospect of using optics in computing systems becomes more practical.
A significant challenge to optical computing is that computation is a nonlinear process in which multiple signals must interact to perform computations. Light, which is an electromagnetic wave, can only interact with another electromagnetic wave in the presence of electrons in a material, 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 results in the processing elements for an optical computer requiring more power and larger dimensions than those for a conventional electronic computer using transistors.
Photonic logic
Photonic logic is the use of photons (lightLight
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
) in logic gate
Logic gate
A logic gate is an idealized or physical device implementing a Boolean function, that is, it performs a logical operation on one or more logic inputs and produces a single logic output. Depending on the context, the term may refer to an ideal logic gate, one that has for instance zero rise time and...
s (NOT, AND, OR, NAND, NOR, XOR, XNOR). Switching is obtained using nonlinear optical effects
Nonlinear optics
Nonlinear optics is the branch of optics that describes the behavior of light in nonlinear media, that is, media in which the dielectric polarization P responds nonlinearly to the electric field E of the light...
when two or more signals are combined.
Resonator
Resonator
A resonator is a device or system that exhibits resonance or resonant behavior, that is, it naturally oscillates at some frequencies, called its resonant frequencies, with greater amplitude than at others. The oscillations in a resonator can be either electromagnetic or mechanical...
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 molecular level
Nanotechnology
Nanotechnology is the study of manipulating matter on an atomic and molecular scale. Generally, nanotechnology deals with developing materials, devices, or other structures possessing at least one dimension sized from 1 to 100 nanometres...
, using photoluminescent
Photoluminescence
Photoluminescence is a process in which a substance absorbs photons and then re-radiates photons. Quantum mechanically, this can be described as an excitation to a higher energy state and then a return to a lower energy state accompanied by the emission of a photon...
chemicals. In a recent demonstration, Flood et al. performed logical operations using molecules and SERS
Surface Enhanced Raman Spectroscopy
Surface enhanced Raman spectroscopy or surface enhanced Raman scattering is a surface-sensitive technique that enhances Raman scattering by molecules adsorbed on rough metal surfaces...
.
Further reading
- Ibrahim TA, Amarnath K, Kuo LC, Grover R, Van V, Ho PT. Photonic logic NOR gate based on two symmetric microring resonators. Opt Lett. 2004 Dec 1;29(23):2779-81.
- Biancardo M et al. A potential and ion switched molecular photonic logic gate, Chem. Commun., 2005, (31), 3918-3920
- J. Jahns and S. H. Lee, eds., "Optical Computing Hardware", Academic Press, Boston (1994).
- BARROS S., GUAN S. & ALUKAIDEY T., "An MPP reconfigurable architecture using free-space optical interconnects and Petri net configuring" in Journal of System Architecture (The EUROMICRO Journal) Special Double Issue on Massively Parallel Computing Systems vol. 43, no. 6 & 7, pp. 391–402, April 1997
- D. GoswamiDebabrata GoswamiDebabrata Goswami is an Indian spectroscopist, winner of the Wellcome Trust Senior Research Fellow Award , Swarnajayanti Award , presently Professor of the Department of Chemistry at the Indian Institute of Technology Kanpur.-Career:...
, "Optical Computing", Resonance, June 2003; ibid July 2003. Web Archive of www.iisc.ernet.in/academy/resonance/July2003/July2003p8-21.html - Todd Main, Robert J. Feuerstein, Harry F. Jordan, Vincent P. Heuring, John Feehrer, and Carl E. Love, "Implementation of a general-purpose stored-program digital optical computer," Applied Optics, Vol. 33, pp. 1619–1628 (1994) (http://www.opticsinfobase.org/abstract.cfm?URI=ao-33-8-1619)
- T.S. Guan & S.P.V. Barros, "Reconfigurable Multi-Behavioural Architecture using Free-Space Optical Communication" in Proceedings of the IEEE International Workshop on Massively Parallel Processing using Optical Interconnections. , April 1994
- T.S. Guan & S.P.V. Barros, "Parallel Processor Communications through Free-Space Optics" in IEEE Region 10's Ninth Annual International Conference on Frontiers of Computer Technology , August 1994
- Architectural issues in designing symbolic processors in optics
- K.-H. Brenner, Alan Huang: "Logic and architectures for digital optical computers (A)", J. Opt. Soc. Am., A 3, 62, (1986)
- K.-H. Brenner: "A programmable optical processor based on symbolic substitution", Appl. Opt. 27, No. 9, 1687–1691, (1988)
- N. Streibl, K.-H. Brenner, A. Huang, J. Jahns, J. L. Jewell, A. W. Lohmann, D.A.B. Miller, M. J. Murdocca, M. E. Prise, and T. Sizer II, Digital Optics, Proc. IEEE 77, 1954-1969 (1989)
- NASA scientists working to improve optical computing technology
- Optical solutions for NP-complete problems
- International Workshop on Optical SuperComputing 2008
- International Workshop on Optical SuperComputing 2009
- International Workshop on Optical SuperComputing 2010
- Speed-of-light computing comes a step closer New Scientist
Optical Implemnetation of Bounded non Deterministic Turing Machine, Patent by Shlomi Dolev and Yuval Nir Filed May 2003 in Israel, May 2004 USA;
Solving Hamiltonian, and other NP-Complete problems.