Optical computing?qsrc=3044

An optical computer (also called a photonic computer) is a device that uses the photons of visible light or infrared (IR) beams, rather than electrons in the electric current, to perform digital computations. An electric current creates heat in computer systems. As the processing speed increases, so does the amount of electricity required; this extra heat is extremely damaging to the hardware. Light, however, creates insignificant amounts of heat^{[dubious – discuss]}, regardless of how much is used. Thus, the development of more powerful processing systems becomes possible. By applying some of the advantages of visible and/or IR networks at the device and component scale, a computer might someday be developed that can perform operations significantly faster than a conventional electronic computer.

Coherent light beams, unlike metal conductors, pass through each other without interfering (at least not after the intersection). Electrons repel each other while photons do not. This is why the signal from copper wire gets poorer the further you are from the telephone exchange while Fibre optic cables do not have this problem. Several laser beams can be shone so their paths intersect, but there is no interference among the beams, even when they are confined essentially to two dimensions. Electric currents must be guided around each other, and this makes three-dimensional wiring necessary. Thus, an optical computer, besides being much faster than an electronic one, might also be smaller.

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 c.30% of their energy converting electrons into photons and back, this also slows down transmission of messages. All optical computers eliminate the need for switching.^[1] Other research projects take a non-traditional approach, attempting to develop entirely new methods of computing that are not physically possible with electronics.^{[citation needed]}^{[example needed]}

Table of Contents

1	Optical components for binary digital computer
2	Misconceptions, challenges and prospects
3	Photonic logic
4	Further reading
5	References
6	External links

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 non-linear refractive index. In particular, materials exist^{[example needed]} 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. This "optical transistor" effect is used to create 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.

There has been a large expansion in the optical interconnects for photonic based computing. Currently these interconnects are being tested and expanded by Intel.

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 noise 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.^{[citation needed]}

A significant challenge to optical computing is that computation is a nonlinear process in which multiple signals must interact to compute the answer. Light, which is an electromagnetic wave, can only interact with another electromagnetic wave in the presence of electrons in a material^{[clarification needed]}, and the strength of this interaction is much weaker for electromagnetic wave 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.^{[citation needed]} Until recently, electronics was fine for computer processing, but at speeds higher than 40 GHz, only optics can cope.^[2] Another reason optical computers aren't available is that the crystals needed would be melted by the intense light.

Photonic logic

Realization of a Photonic Controlled-NOT Gate for use in Quantum Computing

Photonic logic is the use of photons (light) in logic gates (NOT, AND, OR, NAND, NOR, XOR, XNOR). Switching is obtained using nonlinear optical effects when two or more signals are combined.

Resonators 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.

References

↑ Mind at Light Speed, David Nolte, page 34
↑ Mind at Light Speed, David Nolte, page 36
↑ http://v3.espacenet.com/publicationDetails/originalDocument?CC=US&NR=2005013531&KC=&FT=E
↑ http://www.springerlink.com/content/w614x0874x040227/

External links