INTRODUCTIONWith the growth of computing technology the need of high performance computers has significantly increased.Optical computing was a hot research area in 1980’s.But the work tapered off due to materials limitations i.e. Using light, instead of electric power, for performing computations. This choice is motivated by several features that light has: •It is very fast. •It can be easily manipulated •It is very well suited for parallelization
Why we Use Optics for Computing? One of the theoretical limits on how fast a computer can function is given by Einstein’s principle that “signal cannot propagate faster than speed of light”. To make computers faster, their components must be smaller and there by decrease the distance between them. Optical computing can solve miniaturization problem. Optical data processing can be performed in parallel. In optical computing, the electrons are replaced by photons
Why We Use OpTICs fOR COmpUTINg?What’s wrong with What’s right with Optics? electronics? Light doesn’t suffer Miniaturisation can lead to cross talk. from the electronic time Speed of electrons in response. matter. No need for insulators. Solid medium limits Optical communication: both speed and magnitude. • Multiplexing and different Build up to heat. wavelengths with no 30 cm length of wire interference. produces ~ 1 ns delay. • Low signal loss, large Low bandwidth bandwidth. interconnections. • Compact, lightweight, inexpensive
OPTICAL COMPUTER An optical computer (also called a photonic computer) is a device that uses the PHOTONS in visible light or infrared beams, rather than electric current to perform digital computations. An optical computer, besides being much faster than an electronic one, might also be smaller. Unlike transistors, transphasors can be built to handle several incoming signals at once.
OPTICAL COMPUTER Bright flashes of laser light can be sent hundreds of miles along fine strands of specially made glass or plastic called OPTICAL FIBERS.
Optic Fiber cables made of glass or plasticGlass optic fiber Plastic optic fiber
OPTICAL COMPUTER Instead of transistors, such a computer will have TRANSPHASORS.
OPTICAL COMPUTER• Beams of light can crisscross and overlap without becoming mixed up, whereas crossed electric currents would get hopelessly confused.
OPTICAL COMPUTER• The arrangement of connections and switches would not have to be flat, as in an electronic computer. It could be placed in any direction in space, allowing totally new designs in information processing.
SOME KEY OPTICAL COMPONENTS FOR COMPUTING VCSEL SMART PIXEL TECHNOLOGY WDM SLM
1. VCSEL (VERTICAL CAVITY SURFACE EMITTING LASER) VCSEL(pronounced‘vixel’)is a semiconductor vertical cavity surface emitting laser diode that emits light in a cylindrical beam vertically from the surface of a fabricated wafer. But rather than reflective ends, in a VCSEL there are several layers of partially reflective mirrors above and below the active layer. Layers of semiconductors with differing compositions create these mirrors, and each mirror reflects a narrow range of wavelengths back in to the cavity in order to cause light emission at just one wavelength.
Optical interconnection of circuit boards using VCSEL and PHOTODIODE
2. SMART PIXEL TECHNOLOGY Smart pixel technology is a relatively new approach to integrating electronic circuitry and optoelectronic devices in a common framework. Here, the electronic circuitry provides complex functionality and programmability. While the optoelectronic devices provide high- speed switching and compatibility with existing optical media. Arrays of these smart pixels leverage the parallelism of optics for interconnections as well as computation..
3. WDM (WAVELENGTH DIVISION MULTIPLEXING) Wavelength division multiplexing is a method of sending many different wavelengths down the same optical fiber. WDM can transmit up to 32 wavelengths through a single fiber, but cannot meet the bandwidth requirements of the present day communication systems. Nowadays DWDM (Dense wavelength division multiplexing) is used. This can transmit up to 1000 wavelengths through a single fiber. That is by using this we can improve the bandwidth efficiency.
4. SLM (SPATIAL LIGHT MODULATORS)• SLM play an important role in several technical areas where the control of light on a pixel-by-pixel basis is a key element, such as optical processing and displays.• For display purposes the desire is to have as many pixels as possible in as small and cheap a device as possible.
MERITS Optical computing is at least 1000 to 100000 times faster than today’s silicon machines. Optical storage will provide an extremely optimized way to store data, with space requirements far lesser than today’s silicon chips. No short circuits, light beam can cross each other without interfering with each other’s data. Higher performance. Higher parallelism. Less heat is released. Less noise. Less loss in communication.
DRAWBACKS Today’s materials require much high power to work in consumer products, coming up with the right materials may take five years or more. Optical computing using a coherent source is simple to compute and understand, but it has many drawbacks like any imperfections or dust on the optical components will create unwanted interference pattern due to scattering effects. Optical components and their production is still expensive. New expensive high-tech factories have to be built .
APPLICATION High Speed CommunicationOptical Cross Bar Inter ConnectProcess Sattelite Data
Progress in Optical ComputingRecent optical devices created: Optical logic gates optical switches Optical interconnections optical memorySwitching device performance Speeds of 10 -15 seconds Power requirements one millionth of a watt
FUTURE TRENDSThe Ministry of Information Technology has initiated aphotonic development program.Under this program some funded projects are continuing infiber optic high-speed network systems. Research is going on for developing New laser diodes Photo detectors Nonlinear material studies for faster switches.
CONCLUSION Research in optical computing has opened up newpossibilities in several fields related to high performancecomputing, high-speed communications. To designalgorithms that execute applications faster ,the specificproperties of optics must be considered, such as theirability to exploit massive parallelism, and globalinterconnections. As optoelectronic and smart pixeldevices mature, software development will have a majorimpact in the future and the ground rules for thecomputing may have to be rewritten.