School of Electrical & Computer Engineering OPTICAL COMPUTERS
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SCHOOL OF ELECTRICAL & COMPUTER
ENGINEERING
OPTICAL COMPUTERS
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Introduction to Optical Computers, Schemes and Mind Maps of Computer Engineering and Programming
Introduction to optical computers
Typology: Schemes and Mind Maps
2018/2019
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SCHOOL OF ELECTRICAL & COMPUTER
ENGINEERING
OPTICAL COMPUTERS
Contents
Overview of Optical computers
1 Components of Optical computers...................... 12
1.1 Hard Disk 1.2 CPU 1.3 Memory 1.4 Cache Memory 1.5 Main Memory 1.6 Screen 1.7 Power Supply
2 Need of Optical Computers......................... 18
3 Optical Components for Computing.................. 23
3.1 VCSEL
3.2 SLM
3.3 WDM
3.4 Optical Memory
4 Fibre Optics...................................... 32
4.1 Use of Fibre Optics in Computing
4.2 Why use Fibre Optics
5 An Optical Computer Powered by Germanium Laser.... 43
6 Concept of Picosecond (By NASA).................... 47
7 Optical computer Bus............................... 52
Application
Merits
Drawback
Some current research
Future Trends
References
AN OVERVIEW OF OPTICAL COMPUTING
Computers have become an indispensable part of life. We need computers everywhere, be it for work, research or in any such field. As the use of computers in our day-to-day life increases, the computing resources that we need also go up. For companies like Google and Microsoft, harnessing the resources as and when they need it is not a problem. But when it comes to smaller enterprises, affordability becomes a huge factor. With the huge infrastructure come problems like machines failure, hard drive crashes, software bugs, etc. This might be a big headache for such a community. Optical Computing offers a solution to this situation. An Optical Computer is a hypothetical device that uses visible light or infrared beams, rather than electric current, to perform digital computations. An electric current flows at only about 10 percent of speed of light. By applying some of the advantages of visible and/or IR networks at the device and component scale, a computer can be developed that can perform operations very much times faster than a conventional electronic computer.
Optical computing describes a new technological approach for constructing computer’s processors and other components. Instead of the current approach of electrically transmitting data along tiny wires etched onto silicon. Optical computing employs a technology called silicon photonics that uses laser light instead.
This use of optical lasers overcomes the constraints associated with heat dissipation in today’s components and allows much more information to be stored and transmitted in the same amount of space. Optical computing means performing computations, operations, storage and transmission of data using light. Optical technology promises massive upgrades in the efficiency and speed of computers, as well as significant shrinkage in their size and cost. An optical desktop computer is capable of processing data up to 1,00,000 times faster than current models.
An optical computer (also called a photonic computer) is a device that uses the photons of visible light or infrared (IR) beams, rather than 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.
F or decades, silicon, with its talent for carrying electrons, has been the mainstay of computing. But for a variety of reasons (see "The Coming Light Years"), we're rapidly approaching the day when electrons will no longer cut it. Within 10 years, in fact, silicon will fall to the computer scientist's triple curse: "It's bulky, it's slow, and it runs too hot." At this point, computers will need a new architecture, one that depends less on electrons and more on... well...what else?
Computer of 2010
Standard, electrical-based, computers rapidly approach fundamental limitation. Alternative principles should be explored in order to keep computing developments at the current pace or even faster. Optical computing has major potential in providing a solution through its use of photons to perform computations instead of electrons. This workshop will be an opportunity to bring people together from optics and computer science who are interested in establishing important principles and in developing optical computers. This will also be an opportunity to meet with pioneering figures and to discuss the future of optical supercomputing.
Computers have enhanced human life to a great extent. The speed of conventional computers is achieved by miniaturizing electronic components to a very small micron-size scale so that those electrons need to travel only very short distances within a very short time. The goal of improving on computer speed has resulted in the development of the Very Large Scale Integration (VLSI) technology with smaller device dimensions and greater complexity. Last year, the smallest-to date dimensions of VLSI reached 0.08 m by researchers at Lucent Technology. Whereas VLSI technology has revolutionized the electronics industry and established the 20th^ century as the computer age, increasing usage of the Internet demands better accommodation of a 10 to 15 percent per month growth rate. Additionally, our daily lives demand solutions to increasingly sophisticated and complex problems, which requires more speed and better performance of computers. For these reasons, it is unfortunate that VLSI technology is approaching its fundamental limits in the sub-micron miniaturization process. It is now possible to fit up to 300 million transistors on a single silicon chip. It is also estimated that the number of transistor switches that can be put onto a chip doubles every 18 months. Further miniaturization of lithography introduces several problems such as dielectric breakdown, hot carriers, and short channel effects. All of these 2 factors combine to seriously degrade device reliability. Even if developing technology succeeded in temporarily overcoming these physical problems, we will continue to face them as long as increasing demands for higher integration continues. Therefore, a dramatic solution to the problem is needed, and unless we gear our thoughts toward a totally different pathway, we will not be able to further improve our computer performance for the future. Optical interconnections and optical integrated circuits will provide a way out of these limitations to computational speed and complexity inherent in conventional electronics. Optical computers will use photons traveling on optical fibers or thin films instead of electrons to perform the appropriate functions. In the optical computer of the future, electronic circuits and wires will be replaced by a
few optical fibers and films, making the systems more efficient with no interference, more cost effective, lighter and more compact. Optical components would not need to have insulators as those needed between electronic components because they donot experience cross talk. Indeed, multiple frequencies (or different colors) of light can travel through optical components without interfacing with each others, allowing photonic devices to process multiple streams of data simultaneously.
SECURITY
The PC will be protected from theft, thanks to an advanced biometric scanner that can recognize your fingerprint. INTERFACE
You'll communicate with the PC primarily with your voice, putting it truly at your beck and call.
The Desktop as Desk Top
In 2010, a "desktop" will be a desk top...in other words, by plugging our computer into an office desk, its top becomes a gigantic computer screen--an interactive photonic display. You won't need a keyboard because files can be opened and closed simply by touching and dragging with your finger. And for those throwbacks who must have a keyboard, we've supplied that as well. A virtual keyboard can be momentarily created on the table top, only to disappear when no longer needed. Now you see it, now you don't. Your Digital Butler
What do we do with our 2010 computer when we arrive home after a long day's work? The computer becomes the operating system for our house, and our house, in turn, knows our habits and responds to our needs. ("Brew coffee at 7, play Beethoven the moment the front door opens, and tell me when I'm low on milk.")
Your Home
The PC of 2010 plugs into your home so your house becomes a smart operating system.
An optical computer (also called a photonic computer) is a device that uses the photons of visible light or infrared (IR) beams, rather than 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, 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 10 or more times faster than a conventional electronic computer.
Visible-light and IR beams, unlike electric currents, pass through each other without interacting. Several (or many) 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 photonic 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. Other research projects take a non-traditional approach, attempting to develop entirely new methods of computing that are not physically possible with electronics.
Optical computing where the processing of electrical energy is replaced by light quanta is very attractive for future technologies. The replacement of wires by optical pathways is of special interest because light can cross without interference and thus, the complex wiring of modern computers may be appreciably simplified. Moreover, optical computers can operate at very high rates because there are not the problems of electrical computers such as inductivities of wires and loading of parasitic capacitors. Chemical structures are required for the handling of light and this has to be done by suitable chromophores. Organic materials are preferred because of their chemical variability and uncritical recycling for mass production. There are mainly three obstacles for the development of optical computers: firstly the preservation of the optical energy, secondly the low light-fastness of many active optical components and thirdly the comparably long wavelengths of light of about 0.5 m. The former two problems can be solved by the application of highly light-fast fluorescence dyes
where the fluorescence quantum yield is a measure of the preservation of light- energy; light fast fluorescent dyes with 100% fluorescence quantum yield are known. The third problem sets a lower limit to the size of conventional optical components and hinders the construction of an optical computer on a molecular scale. However, the development of molecular optics would reduce the size of such components by a factor of 500. The limitation of resolution by the wavelengths of light may be overcome by the transport of the energy of light instead of the emission and absorption of light quanta. This corresponds to the use of the alternating current (50 Hz) with a problematic wavelength of some 6000 km where the electrical energy is handled on a human scale or even lower. In analogy to such a transport of electrical energy an energy transfer between chromophores can replace the absorption and emission of light quanta in optical signal processing components. The transfer will proceed rapidly if the distance between the two chromophores lies within the F¨orster radius, that means between 2 and 3 nm for most combinations of similarly absorbing chromophores. On the other hand, this F¨orster radius would be the natural lower limit for the size of complex arrangements of switching components for handling energy transfer because going below this limit would spread energy over many chromophores without control; a solution of this limiting problem would be the prerequisite for the development of optical computers with very high densities of integration.
(2) THE CENTRAL PROCESSING UNIT (CPU)
Our 2010 CPU will operate on the same principle as today's PCs. But instead of electronic microprocessors providing the brains and brawn, our future CPU will have optoelectronic integrated circuits (chips that use silicon to switch but optics to communicate). This will give us huge increases in speed and efficiency. Why? Because the CPU of today spends far too much time waiting around for data to process. Instantaneous on-chip optical communication, and memory running as fast as the processor, will guarantee a continuous stream of data processing within the CPU. With communication between components no longer bottlenecked by electronic transmission, we can probably push the clock rate to 100 gigahertz. Our universal appliance of tomorrow also has a hexagonal optoelectronic processor surrounded by a ring of fast cache, so that data for any part of the chip can be fetched from the closest part of the cache. The result will be computer performance- -or, at any rate, delivery of computational results--comparable to today'ssupercomputers.
WHERE ARE WE? Optoelectronic integrated circuits do exist today, on a small scale and for specialized purposes. Getting from the current state of the art to a complete and superfast optoelectronic CPU will require tremendous effort and the accumulation of an entirely new body of intellectual property.
WHO'S WORKING ON IT? Scientific-Atlanta, Lucent, and Nortel. Advanced work in optical interconnection is now being done at Stanford. Intel, through its purchase of Danish optoelectronics company GIGA, intends to have the fast track outofthegate.
TIME OF COMPLETION? 2010, If we're really lucky.
(3) MEMORY(RAM)
When we stir optical communication into the old-fashioned electronic computer, some of the greatest potential gains will involve your computer's short-term memory. In the long-gone days (1980) of the 80286, computers enjoyed a design advantage that we've never had since. The memory bus speed--that is, the speed at which data flowed between CPU and memory--was the same as the CPU's clock rate, or how fast it operates. (Of course, they were both 8 megahertz , but we said this was a long time ago.) Data reached the CPU as fast as the chip could process it, which kept the CPU from waiting around being bored. We've never reached that pinnacle again, and since then, the situation has gotten steadily worse. A reasonably fast computer today has a CPU clock of 600 megahertz and a memory bus speed of 133 megahertz. Despite various clever technical feats, the CPU still spends half to two-thirds of its time just waiting around for data from memory. Optoelectronics will knock this problem out of the park. With a properly designed optical memory bus, speed of fetch from memory can once again equal CPU clock rate. Of course, this also will require that processing in RAM be very quick, so we'll need a faster RAM architecture, which luckily is--or will be--available. A large cache (see below) made of superfast, nonvolatile magnetic RAM will hold information that the CPU needs quickly and repeatedly. It will be backed up by a much larger area of holographic (pure optical) main RAM that will hold programs, files, images, etc., while you work with them.
(4) FAST MEMORY (CACHE)
To build our new fast cache, we'll need to get rid of the inefficiencies of today's product, which requires the computer to constantly refresh it, just like short-term memory in humans needs to be constantly refreshed or it's forgotten. The inefficiencies in cache are so bad, in fact, that once you know the speed of your cache you can assume that its real-world performance will be about a third of that--the missing two-thirds being sacrificed to refresh cycles.
TIME OF COMPLETION? 2009, or maybe a tad earlier.
(6) POWER SUPPLY
One of the biggest advantages of photonic circuitry is an extremely low power requirement. A long, sticklike lithium battery, bent into a doughnut and installed in the periphery of the computer, will run it for a couple of weeks. But fresh power is as close as the charging cradle on the nearest wall, which resembles the one for today's cordless or cellular phones.
WHERE ARE WE? Pretty close. We've come a long way in battery development in the past few years.
WHO'S WORKING ON IT? Hewlett-Packard.
TIME OF COMPLETION? 2007.
(7) THE SCREEN
Size does matter in our 2010 computer screen. It will either be very large, literally the desk top of your desktop, or very small, a monocle you hold up to your eye. For the bigger version, our computer screen will depend on some kind of photonically excited liquid crystal, with power requirements significantly lower than today's monitors. Colors will be vivid and images precise (think plasma displays). In fact, today's concept of "resolution" will be largely obsolete. Get ready for pay-per-view Webcasts.
WHERE ARE WE? This design, if fully realized, depends on a technology that doesn't exist today. Optical excitement of a liquid crystal is the stuff of research papers. More likely is that our computer will end up with a less ambitious display, one like our
current PCs possess but much, much better. We've got 10 fruitful years to develop it, after all.
WHO'S WORKING ON IT? Sharp Electronics, a world leader in color LCD technology, which is also investing heavily in optoelectronics. Sony, Toshiba, and IBM are the current leaders in flat-panel displays.
TIME OF COMPLETION? 2010, if we're lucky.
replaced by photons, the subatomic bits of electromagnetic radiation that make up light. Optics, which is the science of light, is already used in computing, most often in the fiber-optic glass cables that currently transmit data on communication networks much faster than via traditional copper wires. Thus, optical signals might be the ticket for the fastest supercomputers ever. Compared to light, electronic signals in chips travel at snail speed. Moreover, there is no such thing as a short circuit with light, so beams could cross with no problem after being redirected by pinpoint-size mirrors in a switchboard. In a pursuit to probe into cutting-edge research areas, optical technology (optoelectronic, photonic devices) is one of the most promising, and may eventually lead to new computing applications as a consequence of faster processor speeds, as well as better connectivity and higher bandwidth. The pressing need for optical technology stems from the fact that today’s computers are limited by the time response of electronic circuits. A solid transmission medium limits both the speed and volume of signals, as well as building up heat that damages components. For example, a one-foot length of wire produces approximately one nanosecond (billionth of a second) of time delay. Extreme miniaturization of tiny electronic com- Optical computing includes the optical calculation of transforms and optical pattern matching. Emerging technologies also make the optical storage of data.
These and other obstacles have led scientists to seek answers in light itself. Light does not have the time response limitations of electronics, does not need insulators, and can even send dozens or hundreds of photon signal streams simultaneously using different color frequencies. Those are immune to electromagnetic interference, and free from electrical short circuits. They have low-loss transmission and provide large bandwidth; i.e. multiplexing capability, capable of communicating several channels in parallel without interference. They are capable of propagating signals within the same or adjacent fibers with essentially no interference or cross talk. They are compact, lightweight, and inexpensive to manufacture, as well as more facile with stored information than magnetic materials. By replacing electrons and wires with photons, fiber optics, crystals, thin films and mirrors, researchers are hoping to build a new generation of computers that work 100 million times faster than today’s machines.
The fundamental issues associated with optical computing, its advantages over conventional (electronics-based) computing, current applications of optics in computers are discussed in this part. In the second part of this article the problems that remain to be overcome and current research will be discussed.
Optical computing was a hot research area in the 1980s. But the work tapered off because of materials limitations that seemed to prevent optochips from getting small enough and cheap enough to be more than laboratory curiosities. Now, optical computers are back with advances in self-assembled conducting organic polymers that promise super-tiny all-optical chips.
[1]. Advances in optical storage device have generated the promise of efficient, compact and large-scale storage devices
[2]. Another advantage of optical methods over electronic ones for computing is that parallel data processing can frequently be done much more easily and less expensively in optics than in electronics
[3]. Light does not have the time response limitations of electronics, does not need insulators, and can even send dozens or hundreds of photon signal streams simultaneously using different color frequencies. Parallelism, the capability to execute more than one operation simultaneously, is now common in electronic computer architectures. But, most electronic computers still execute instructions sequentially; parallelism with electronics remains sparsely used. Its first widespread appearance was in Cray supercomputers in the early 1980’s when two processors were used in conjunction with one shared memory. Today, large supercomputers may utilize thousands of processors but communication overhead frequently results in reduced overall efficiency
[4]. On the other hand for some applications in input-output (I/O), such as image processing, by using a simple optical design an array of pixels can be transferred simultaneously in parallel from one point to another. Optical technology promises massive upgrades in the efficiency and speed of computers, as well as significant shrinkage in their size and cost. An optical desktop computer could be capable of processing data up to 100,000 times faster than current models because multiple operations can be performed simultaneously. Other advantages of optics include low manufacturing costs, immunity to electromagnetic interference, a tolerance for lowloss transmissions, freedom from short electrical circuits and the capability to supply large bandwidth and propagate signals within the same or adjacent fibers without interference. One oversimplified example may help to appreciate the difference between optical and electronic parallelism. Consider an imaging system with 1000 1000 independent points per mm2 in the object plane which are connected optically by a lens to a corresponding number of points per mm2 in