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OPTICALCOMPUTER Authors B.Mallikarjuna Reddy K.Gnanendra Chekravarthy II B.Tech (CSE) II B.Tech (CSE) Roll: 07L21A0502 Roll: 07L21A0538 Email: [email protected] Email:[email protected] Cell: 9441496893 Cells: 9966131963 VAAGDEVI INSTITUTE OF TECHNOLOGY AND SCIENCES PEDDASETTIPALLI (VILL), PRODDATUR, KADAPA DT.ANDHRA PRADESH OPTICAL COMPUTER CONTENTS 1 Introduction 2 Optical Computer 3 Optical Components for binary digital computer 4 Basic components for digital computer 5 The elements of a binary digital computer 6 Advantages 7 Conclusion OPTICAL COMPUTER confined essential to two dimensions. Introduction: Now a days we are using the electronic computer, just think for a while if all the electronic components are replaced with optical one. Optical computer is the computer which performs operations ten or more times faster than Electric currents must be guided around each other, and this make three dimensional wiring necessary. Thus an optical computer besides being much faster than an electronic one, might also be smaller. the conventional electronic computers. This optical computer uses the infrared beams to manipulate store, transmit data. Optical Computer: Optical computer is a computer that uses light instead of electricity (photons instead of electrons) to manipulate, store and transmit data. It uses the IR beams to perform digital computations, which results an optical computer which perform operations ten or more faster than an electronic computer. Electrical crossovers (top) require three dimensions, but optical crossovers (bottom) require only two dimensions because light beams don’t intersect. Optical components for binary digital computer: Visible light and IR beams and unlike electric currents, pass through each other with out interacting. Several laser beams can be shone so their paths intersect, but there is not interference among the beams, even when they are The fundamental building block for mechanical, electronics, optical, whatever modern electronic computers is transistor. component is needed that controlled by To replace electronic components with this both states and, what is more optical optical important, it has to be possible to go from transistor is required. This is achieved one state go other state in a conventional using materials with a non-linear refractive way, i.e. according to some pre determined index. In particular, materials exist where non-linear function. In other words we the intensity of incoming light affects the have to be able to switch between these intensity of the light, transmitted through two stable states. the material in a similar manner to the An electronic switch: ones, voltage an response equivalent of an In electronics, switching is done by electronic transistor. This “optical transistor” effect is the transistor. used to create logic gates, which in turn The transistor consists of three are assembled into the higher level layers: the emitter, collector and base. The components of the computer CPU. base is the middle layer and is made of Basic components for digital it can acts either as an insulator between computer: In optical computer which utilizes photons as information carriers instead of electrons. An important step in building this optical semi conducting material. This means that computer has been construction of an optical alternative for the electronic transistor. Basic components: A switch o An electronic switch. o Photos carrying information o Optical bistability o Optical switch A switch: A binary digital computer needs to be able to represent two states, “1” and “0”, the true and the false. So some emitter and collector, or as a conductor. If a small current flows from base to collector, some electrons traverse the base. This changes the base from an insulator to a conductor. If there is not current from base to collector, the base acts as an insulator again. Now we have an electronic switch, because if the base acts as a conductor and we let some (large) current flow from emitter to collector, we can stop this current by stopping the (small) current base to collector. However, this switch is subject to some limitations. There is a limit to the speed by which electrons can traverse the base, and in modern VSLI design, this limit is reached with approximately a nanosecond. But there might be other media to transport the information in a computer, thus attaining a higher speed. Photons carrying information. Figure: Nonlinear refraction with hysteresis loop. Photons carrying information: The way we depicted the relation The highest speed ever attainable is the speed of light. So it seems logical to see light, or electromagnetic radiation in general, as the perfect way of pushing First of all, the electrons affect each other at distance, while photos do not. In particular, electrons repel each other because of their negative magnetic load. This property is an advantage in switching a transistor, in changing the base from an insulator to a conductor and vice versa. And this where another advantage of photos come in: two beams of light can without affecting intensity of a beam of light going through some material as described in the previous section is only partly true. It is actually so, computing to its limits. cross between the incident and the transmitted each other, that the diagram representing an increasing incident beam slightly differs from the diagram representing a decreasing incident beam. That is, the “switching-intensity” (the incident intensity needed for the steep line in the diagram) of the incident beam differs. Representing this phenomenon in one diagram results in the one depicted in figure. It has a loop called the hysteresis loop. By this hysteresis loop we again provided their angle is not less than 10. This increase the number of possible interconnections, something we come back to later. Optical bistability: To build gates and storage (the real hardware components of the conventional digital computer), taking the transphasor as a staring point, we will explain something more about a property of some materials, called optical bistability. have two stable states. If we keep the incident beam at an intensity in the domain of the hysteresis loop, the transmitted intensity remains at the same level (high or low). An optical switch: At this point we take a closer look at the conventional transistor. In the electronic transistor, the two currents of electrons do not really interact. The semi conducting material acts as an intermedium. If we want to build a switch and follow the idea of the transistor, we are going to use the latter. Waves interfere have to find a material isomorphic to the under certain circumstances. This means semi conducting material i.e. a device of that if two waves are aligned, they may which we can change the properties just by reinforce or destruct each other, dependent sending a beam of light through it. Perhaps on whether they are in equal or opposite we can find a device that sometimes phase. If the mirrors are placed at a (dependent on another beam) is opaque, distance equal to halfway an integral and sometimes transparent. In 1896 the number of half wavelengths, the beams of French physicist Charles Fabry and Alfred light that are in the cavity interfere Petor invented their interferometer. It is constructively. simply consists of two partially reflecting transmitted beam is far more that 1 mirrors, placed parallel to each other. This percent, it might even be a 100 percent. On might be the basis for an optical transistor. the other hand, if the mirrors are placed at If a beam of light strikes the first mirror, an integral number of half wavelengths, some percentage of the light is reflected, the waves interfere destructively. The and some goes through. The same happens transmitted beam is even less than 1 at the other mirror. But if we take two percent. Thus, we have some sort of a mirrors that let only 10 percent of the light switch. But so far it only switches by go through, only 1 percent of the light goes placing the mirrors at another distance. This means that the through both mirrors (the transmitted Now we come back to the major beam) and some of the light stays between problem of how to switch without moving the mirrors (in what is called the cavity) parts. It would be nice to be able to change for a while. the wavelength of a beam. The development of lasers, sources of very powerful coherent radiation, it was discovered that the refractive index of some materials changes if the intensity of incoming the beam of light exceeds a certain boundary. This is called nonlinear refraction, because we get a nonlinear diagram if the incident intensity is plotted A property of light is that we may against the transmitted intensity. This look at it in two different ways: as results in two levels: a low level and a high particles (photons) and as waves. Now we level. The elements of a binary digital than the switching intensity of the computer: transphasor, but higher than half the Optical bistability and switching provide us with the means of building a binary digital computer. Gates and storage elements are useful transform a transphasor in to a logic gate and how to build a storage elements using optical switching-intensity. Both incident beams are aimed at the same spot on the first mirror. Only if both incident beams have an intensity. If both incident beams, or one of them, has an intensity below its highlevel, the transmitted beam will be of lowlevel intensity. This is exactly like an bistability. AND gate in electronics. Gates: The logic performed by a conventional computer is done with sixteen Boolean functions, but two of them (AND, OR and NOT) are sufficient, because we can combine these to perform one of the other fourteen. We now show that it is very easy to transform a transphasor in either an AND or an OR gate. Because there is no need for optical bistability, a transphasor without hysteresis is needed. To make an OR gate we only have to make sure that the high-level intensities of the incident beams are equal to the switching-intensity of the transphasor. If one or both incident beams have high-level intensities, the transmitted beam has a high-level intensity. Otherwise, both incident beams must have a low-level intensity. Again the working of the optical OR gate is very analogous to the working of the electronic one. The optical NOT gate is constructed by taking the reflected beam as the output. As the reflected beam is the inverse of the transmitted beam, an increase of incident intensity produces low output while decreasing the incident beam provides high output. Storage elements: An AND gate is formed by taking two incident beams acting as the two inputs of the gate. The high level intensities of both beams must be lower In a binary computer there is a need for storage elements able to represent two stable states. If the high-level intensity represents a “1” and the low-level a “0”, putting a “1” in the device can be done by just by adding some other beam for a short module usable both to perform logic while, such that the added intensity is just operations as to interconnect various logic enough to get a high-level transmitted functions. intensity. Putting a “0” in the device can A pipelined processor: be done by just stopping the beam for a The function/interconnection module are short while. cascadable to form a pipelined processor, programmable do every wanted computation. Synchronization is done Assembling the elements: In order to communicate between all the elements interconnection is needed. A reliable outcome signals need to be synchronized by some sort of clock signals. It uses function/interconnection using a clock signal. The clock signal can control the customizing inputs of the various function/interconnection modules. Latches (storage elements that preserve the signal during one clock cycle) between the modules, also controlled by clock signal, module and a pipelined processor. The function/interconnection module: The base of the design are the data can flow through the pipeline. Advantages: function/interconnection modules that are 1. One of the major advantages of optical programmable with 16 customizing inputs. computing is to increase the speed of The idea is to combine signal-pairs computation, light travels at 186,000 (a signal pair consists of a signal and its miles per second i.e. in one nano inverse, say A and A or B and B) using second photos of light travels just a bit four tri-input AND gates. This is called less than a foot. It is enough to do functional logic block. things Two functional logic blocks very quickly in micro miniaturized computer chips. (having two signal-pairs as input and one 2. Optical computer is immune to electro signal-pair as output) can be combined magnetic interference and free from yielding a functional logical cell. It is clear electrical short circuits. that the output of such a cell can be used as one of the input pairs of another cell. 3. They have low loss of transmission and provide large bandwidth capable Grouping two functional logic cells of propagating signals within the same (having a total of two input pairs, two or adjacent fibers with essential no output pairs and sixteen customizing interference or cross talk. inputs) gives a function/interconnection 4. Another major advantage of optical methods over computing is electronic the ones optical is data processing can be done much easier and less expensive in parallel than can be done in electronics. Conclusion: Researches are working to replace all electronic components with optical ones. Soon we can see computers which have the capability of computing more than ten or more times faster than now present conventional electronic computers.