Optical Computing Adwait R. Pande & S. M. Gulhane Dept. of Electronics & Telecommunication Engineering, J.D.I.E.T. Yavatmal, India E-mail : [email protected], [email protected] Abstract – Today's computers use the movement of improved computing capabilities is desirable. Optical electrons in-and-out of transistors to do logic. Optical or computing includes the optical calculation of transforms Photonic computing is intended to use photons or light and optical pattern matching. Emerging technologies particles, produced by lasers or diodes, in place of also make the optical storage of data a reality. electrons. Compare to electrons, photons are much faster – light travels about 30 cm, or one foot, in a nanosecond – The speed of computers was achieved by and have a higher bandwidth. miniaturizing electronic components to a very small Most research projects focus on replacing current micron-size scale, but they are limited not only by the computer components with optical equivalents, resulting in speed of electrons in matter (Einstein‟s principle that an optical digital computer system processing binary data. signals cannot propagate faster than the speed of light) This approach appears to offer best short-term prospects but also by the increasing density of interconnections for commercial optical computing, since optical necessary to link the electronic gates on microchips. The components could be integrated into traditional computers optical computer comes as a solution of miniaturization to produce an optical (or) electronic hybrid. However, problem. In an optical computer, electrons are replaced optoelectronic devices lose 30% of their energy converting by photons, the subatomic bits of electromagnetic electrons into photons and back. This also slows down transmission of messages. All-optical computers eliminate radiation that make up light. Optics, which is the science the need for optical-electrical-optical (OEO) conversions. of light, is already used in computing, most often in the fibre-optic glass cables that currently transmit data on I. INTRODUCTION communication networks much faster than via traditional copper wires. Thus, optical signals might be With today‟s growing dependence on computing the ticket for the fastest supercomputers ever. Compared technology, the need for high performance computers to light, electronic signals in chips travel at snail speed. (HPC) has significantly increased. Many performance Moreover, there is no such thing as a short circuit with improvements in conventional computers are achieved light, so beams could cross with no problem after being by miniaturizing electronic components to very small redirected by pinpoint-size mirrors in a switchboard. In micron-size scale so that electrons need to travel only a pursuit to probe into cutting-edge research areas, short distances within a very short time. This approach optical technology (optoelectronic, photonic devices)is relies on the steadily shrinking trace size on microchips one of the most promising, and may eventually lead to (i.e. the size of elements that can be „drawn‟ onto each new computing applications as a consequence of faster chip). This has resulted in the development of Very processor speeds, as well as better connectivity and Large Scale Integration (VLSI) technology with smaller higher bandwidth. device dimensions and greater complexity. The smallest dimensions of VLSI nowadays are about 0.08 mm. II. LITERATURE REVIEW Despite the incredible progress in the development and refinement of the basic technologies over the past The “ancient” history of optical computing is linked decade, there is growing concern that these technologies to that of radar systems. Optical computing system may not be capable of solving the computing problems received a great push from the invention of laser in of even the current millennium. Applications of HPC 1960.In 1960s the first schemes for all-optical digital and visualization technologies lead to breakthroughs in computers were proposed. In 1990s emphasis has engineering and manufacturing in a wide range of shifted to optical interconnection of arrays of industries. With the help of virtual product design and semiconductor smart pixels. development, costs can be reduced; hence looking for ISSN (Print) : 2278-8948, Volume-2, Issue-4, 2013 147 International Journal of Advanced Electrical and Electronics Engineering, (IJAEEE) In most modern computers, electrons travel was achieved by miniaturizing electronic components to between transistor switches on metal wires or traces to a very small micron-size scale, but they are limited not gather process and store information. The optical only by the speed of electrons in matter but also by the computers of the future will instead use photons increasing density of interconnections necessary to link traveling on optical fibers or thin films to perform these the electronic gates on microchips. functions. But entirely optical computer systems are still The optical computer comes as a solution of far into the future. Right now scientists are focusing on miniaturizing problem. Optical data processing can developing hybrids by combining electronics with perform several operations in parallel much faster and photonics. Electro-optic hybrids were first made easier than electrons. This parallelism helps in possible around 1978, when researchers realized that staggering computational power. For example a photons could respond to electrons through certain calculation that takes a conventional electronic media such as lithium niobate (LiNbO3). computer more than 11 years to complete could be Extreme miniaturization of tiny electronic performed by an optical computer in a single hour. Any components leads to „cross-talk‟ – signal errors that way we can realize that in an optical computer, electrons affect the system‟s reliability. Light does not have the are replaced by photons, the subatomic bits of time response limitations of electronics, does not need electromagnetic radiation that make up light. insulators, and can even send dozens or hundreds of SOME KEY OPTICAL COMPONENTS FOR photon signal streams simultaneously using different COMPUTING colour frequencies. Those are immune to electromagnetic interference, and free from electrical The major breakthroughs on optical computing short circuits. They have low-loss transmission and have been centered on the development of micro-optic provide large bandwidth; i.e. multiplexing capability, devices for data input. capable of communicating several channels in parallel 1. VCSEL (VERTICAL CAVITY SURFACE without interference. They are capable of propagating EMITTING LASER) signals within the same or adjacent fibres with essentially no interference or cross talk. They are VCSEL (pronounced „vixel‟) is a semiconductor compact, lightweight, and inexpensive to manufacture, vertical cavity surface emitting laser diode that emits as well as more facile with stored information than light in a cylindrical beam vertically from the surface of magnetic materials. By replacing electrons and wires a fabricated wafer, and offers significant advantages with photons, fibre optics, crystals, thin films and when compared to the edge-emitting lasers currently mirrors, researchers are hoping to build a new used in the majority of fiber optic communications generation of computers that work 100million times devices. The principle involved in the operation of a faster than today‟s machines. VCSEL is very similar to those of regular lasers. III. NEED FOR OPTICAL COMPUTING There are two special semiconductor materials sandwiching an active layer where all the action takes The need for optical technology stems from the fact place. But rather than reflective ends, in a VCSEL there that today‟s computers are limited by the time response are several layers of partially reflective mirrors above of electronic circuits. A solid transmission medium and below the active layer. Layers of semiconductors limits both the speed and volume of signals, as well as with differing compositions create these mirrors, and building up heat that damages components. each mirror reflects a narrow range of wavelengths back in to the cavity in order to cause light emission at just One of the theoretical limits on how fast a computer one wavelength. can function is given by Einstein‟s principle that signal cannot propagate faster than speed of light. So to make computers faster, their components must be smaller and there by decrease the distance between them. This has resulted in the development of very large scale integration (VLSI) technology, with smaller device dimensions and greater complexity. The smallest dimensions of VLSI nowadays are about 0.08mm. Despite the incredible progress in the development and refinement of the basic technologies over the past decade, there is growing concern that these technologies may not be capable of solving the computing problems Fig. (a) VCSEL (Vertical Cavity Surface Emitting LASER) of even the current millennium. The speed of computers (b) VCSEL Wafer ISSN (Print) : 2278-8948, Volume-2, Issue-4, 2013 148 International Journal of Advanced Electrical and Electronics Engineering, (IJAEEE) 2. SLM (SPATIAL LIGHT MODULATORS) again passed through a pair of lenses and sent to a photodiode. This photodiode convert the optical signal SLM play an important role in several technical back to the electrical signal. areas where the control of light on a pixel-by-pixel basis is a key element, such as optical processing and displays.