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A

SEMINAR REPORT

ON

OPTICAL COMPUTINGFor the partial fulfilment of the requirement for the award of

Bachelor of TechnologyDegree in

Electronics & comm unicationFrom

GBTU, LucknowPresented By:

SUNIL KUMAR PANDEYRoll no: - 0900431080

3rd year (Electronics & communication Engg.)

Submitted to:Er. Sanjeev kr. Gupta, ECE Deptt.

Faculty of Engineering & technology, RBS College, Agra


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Certificate

It is certified that SUNIL KUMAR PANDEY roll no: 0900431080 ofElectronics & communication engg. 3rd year from FET, RBS college,

Agra presented a seminar report on OPTICAL COMPUTING.

Er. Sanjeev kr. GuptaAsst. Professor

ECE Deptt.

FET, R.B.S College, Agra


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CONTENTS

1. INTRODUCTION2. NEED FOR OPTICAL COMPUTING3. SOME KEY OPTICAL COMPONENTS FOR COMPUTING4. ROLE OF NLO IN OPTICAL COMPUTING5. ADVANCES IN PHOTONIC SWITCHES6. OPTICAL MEMORY7. APPLICATIONS

8. MERITS9. DRAW BACKS10.FUTURE TRENDS11.CONCLUSION12.REFERENCES


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ABSTRACTOptical computing means performing computations,operations, storage and transmission of data using light.Instead of silicon chips optical computer uses organicpolymers like phthalocyanine and polydiacetylene.Opticaltechnology promises massive upgrades in the efficiency andspeed of computers,as well as significant shrinkage in theirsize and cost. An optical desktop computer is capable ofprocessing data up to 1,00,000 times faster than current

models.


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1. INTRODUCTIONWith the growth of computing technology the need of highperformance computers (HPC) has significantly increased.Optics has been used in computing for a number of years butthe main emphasis has been and continues to be to linkportions of computers, for communications, or moreintrinsically in devices that have some optical application orcomponent (optical pattern recognition etc.) Opticalcomputing was a hot research area in 1980s.But the work

tapered off due to materials limitations that preventedoptochips from getting small enough and cheap enoughbeyond laboratory curiosities. Now, optical computersare back with advances in self-assembled conducting organicpolymers that promise super-tiny of all optical chips.Optical computing technology is, in general, developing in twodirections.One approach is to build computers that have the

same architecture as present day computers but using opticsthat is Electro optical hybrids. Another approachis to generate a completely new kind of computer, which canperform all functional operations in optical mode. In recentyears, a number of devices that can ultimately lead us to realoptical computers have already been manufactured.These include optical logic gates, optical switches, opticalinterconnections andoptical memory.Current trends in optical

computing emphasize communications, for example the useof free space optical interconnects as a potential solution toremove Bottlenecks experienced in electronicarchitectures.Optical technology is one of the most promising,and may eventually lead to new computing


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applications as a consequence of faster processing speed, aswell as betterconnectivity and higher bandwidth.2. NEED FOR OPTICAL COMPUTING

The pressing need for optical technology stems from the factthat todays computers are limited by the time response ofelectronic circuits. A solid transmission medium limits both thespeed and volume of signals, as well as building up heat thatdamages components. One of the theoretical limits on howfast a computer can function is given by Einsteins principlethat signal cannot propagate faster than speed of light. Soto make computers faster, their components must be smaller

and there by decrease the distance between them. This hasresulted in the development of very large scale integration(VLSI) technology, with smaller device dimensions andgreater complexity. The smallest dimensions of VLSInowadays are about 0.08mm. Despite the incredible progressin the development and refinement of the basic technologiesover the past decade, there is growing concern that these

technologies may not be capable of solving the computingproblems of even the current millennium. The speed ofcomputers was achieved by miniaturizing electroniccomponents to a very small micron-size scale, but they arelimited not only by the speed of electrons in matter but also bythe increasing density of interconnections necessary to linkthe electronic gates on microchips.The optical computercomes as a solution of miniaturizing problem.Optical data processing can perform several operations inparallel much faster and easier than electrons. Thisparallelism helps in staggering computational power. Forexample a calculation that takes a conventional electroniccomputer more than 11 years to complete could be performed


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by an optical computer in a single hour. Any way we canrealize that in an optical computer, electrons are replacedbyphotons, the subatomic bits of electromagnetic radiationthat

makeup light.

3. SOME KEY OPTICAL COMPONENTS FORCOMPUTINGThe major breakthroughs on optical computing have beencentered on thedevelopment of micro-optic devices for datainput.

1. VCSEL (VERTICAL CAVITY SURFACE EMITTINGLACER)VCSEL (pronounced vixel) is a semiconductor vertical cavitysurface emitting laser diode that emits light in a cylindricalbeam vertically from the surface of a fabricated wafer, andoffers significant advantages when compared to the edge-emitting lasers currently used in the majority of fiber optic

communications devices. The principle involved in theoperation of a VCSEL is very similar to those of regularlasers.There are two special semiconductor materialssandwiching an active layer where all the action takes place.But rather than reflective ends, in a VCSEL there are severallayers of partially reflective mirrors above and belowthe active layer. Layers of semiconductors with differingcompositions create these mirrors, and each mirror reflects anarrow range of wavelengths back in to the cavity in order tocause light emission at just one wavelength.


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2. SLM (SPATIAL LIGHT MODULATORS)SLM play an important role in several technical areas wherethe 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 smalland cheap a device as possible.

3. SMART PIXEL TECHNOLOGYSmart pixel technology is a relatively new approach tointegrating electronic circuitry and optoelectronic devices in acommon framework. The purpose is to leverage theadvantages of each individual technology and provide

improved performance for specific applications. Here, theelectronic circuitry provides complex functionality andprogrammability while the optoelectronic devices providehigh-speed switching and compatibility with existing opticalmedia.


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4. WDM (WAVELENGTH DIVISION MULTIPLEXING)Wavelength division multiplexing is a method of sendingmany different wavelengths down the same optical fiber.

Using this technology, modern networks in which individuallasers can transmit at 10 gigabits per second through thesame fiber at the same time.

WDM can transmit up to 32 wavelengths through a singlefiber, but cannot meet the bandwidth requirements of thepresent day communication systems. So nowadays DWDM(Dense wavelength division multiplexing) is used. This cantransmit up to 1000 wavelengths through a single fiber. Thatis by using this we can improve the bandwidth efficiency.


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OPTICAL INTERCONNECTION OF CIRCUIT BOARDSUSING VCSEL AND PHOTODIODE

VCSEL

convert the electrical signal to optical signal when the light beamsare passed through a pair of lenses and micromirrors.Micromirrors are used to direct the light beams and this light


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rays is passed through a polymer waveguide which serves asthe path for transmitting data instead of copper wires inelectronic computers. Then these optical beams are again

passed through a pair of lenses and sent to a photodiode.Thisphotodiode convert the optical signal back to the electricalsignal.

SLM FOR DISPLAY PURPOSESFor display purposes the desire is to have as many pixels aspossible in as small and cheap a device as possible. For suchpurposes designing silicon chips for use as spatial light

modulators has been effective. The basic idea is to have a setof memory cells laid out on a regular grid. These cells areelectrically connected to metal mirrors, such that the voltageon the mirror depends on the value stored in the memory cell.A layer of optically active liquid crystal is sandwiched betweenthis array of mirrors and a piece of glass with a conductivecoating. The voltage between individual mirrors and the front

electrode affects the optical activity of liquid crystal in thatneighborhood. Hence by being able to individually programthe memory locations one can set up a pattern of opticalactivity in the liquid crystal


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4. ROLE OF NLO IN OPTICAL COMPUTINGThe role of nonlinear materials in optical computing hasbecome extremely significant. Non-linear materials are those,

which interact with light and modulate its properties. Severalof the optical components require efficient nonlinear materialsfor their operations. What in fact restrains the widespread useof all optical devices is the in efficiency of currently availablenonlinear materials, which require large amount of energy forresponding or switching. Organic materials have manyfeatures that make them desirable for use in optical devicessuch as

1. High nonlinearities2. Flexibility of molecular design3. Damage resistance to optical radiationsSome organic materials belonging to the classes ofphthalocyanines and polydiacetylenes are promising foroptical thin films and wave guides. These compounds exhibitstrong electronic transitions in the visible region and have

high chemical and thermal stability up to 400 degree Celsius.Polydiacetylenes are among the most widely investigatedclass of polymers for nonlinear optical applications. Theirsubpicosecond time response to laser signals makes themcandidates for high-speed optoelectronics and informationprocessing.To make thin polymer film for electro-opticapplications, NASA scientists dissolve a monomer (thebuilding block of a polymer) in an organic solvent. Thissolution is then put into a growth cell with a quartz window,shining a laser through the quartz can cause the polymer todeposit in specific pattern.


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5. ADVANCES IN PHOTONIC SWITCHESLogic gates are the building blocks of any digital system. Anoptical logic gate is a switch that controls one light beam by

another; it is ON when the device transmits light and it is OFFwhen it blocks the light. To demonstrate the AND gate in thephthalocyanine film, two focused collinear laser beams arewave guided through a thin film of phthalocyanine.Nanosecond green pulsed Nd:YAG laser was used togetherwith a red continuous wave (cw) He-Ne beam. At the output anarrow band filter was set to block the green beam and allowonly the He-Ne beam. Then the transmitted beam was

detected on an oscilloscope. It was found that the transmittedHe-Ne cw beamwas pulsating with a nanosecond durationand in synchronous with the inputNd:YAG nanosecond pulse.This demonstrated the characteristic table


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EXPLANATION OF COMPONENTS USED IN OPTICALANDGATE

1. He-Ne laserThis is the most widely used laser with continuous poweroutput (cw laser) in the fraction of 1mW to 100mW. It isrelatively easy to construct and isreliable in operation.z

This was the first gas laser consists of a fused quartz tube

with a diameter of about 1cm and length about 80cm. Thetube is filled with a mixture of helium and neon gases in theratio 10:1. The ends of the tube have Brewster windows.There are two reflectors and pumping takes place due to theelectron impact.

WORKINGA few energy levels of He&Ne atoms which correspond to theimportant laser transitions are shown in figure.


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When the RF discharge at about 30MHz is passed through

He-Ne gas mixture, the He atoms colliding with the electronsreceive the energy and they are excited to levels F2 and F3from F1. The energy levels F2&F3 are metastable. Ne atomsalso have energy levels E4&E6 which have nearly the sameenergy as F2&F3. Unexcited Ne atoms colliding with theexcited He atoms are excited and taken to the metastablestates E4&E6. Population density in E4&E6 increases at thisstage and appropriate photons can initiate laser emission.Stimulated emission takes place from E6 to E5, E6 to E3, andE4 to E3. From the level E3 by spontaneous emission theatoms come to the level E2 and there after by colliding withthe walls, de-excitation takes place and the atoms come totheground state. The emitted photons move two and fro withinthe gas between theend mirrors. Through the partially

reflecting surface laser output is obtained.


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2. Nd:YAG laserNeodymium:Yttrium Aluminium Garnet is a solid state fourlevel laser system

The optically excited Neodymium ions from the bands E1&E2quicklydecay to the metastable upper laser level. The

difference in energy is transferredto the crystal lattice. Theupper lifetime is about 230micro second. It is quite long, sopopulation can be accumulated over a relatively long timeduring the pumping cycle. In this level (upper laser level), theions are stimulated byphotons due to spontaneous emission,to emit on the main 1.064micrometer laser.The ions aredropped to a lower laser level. They quickly leave again

bytransferring the energy to the crystal lattice.3. CONVEX LENSThese are used to converge the light after passing throughthe phthalocyanine film.4. FILTER


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Narrow band filter was set to block the Nd:YAG laser beamand pass only He-Ne laser beam.

5. DETECTORThe purpose of the detector is to convert the optical laser (He-Ne laser) signal into electrical signal.6. OSCILLOSCOPEOscilloscope is used to view the AND gate properties of thetwo laserbeams, after it was passed through a phthalocyaninefilm.

OPTICAL NAND GATEIn an optical NAND gate the phthalocyanine film is replacedby a hollow fiber filled with polydiacetylene. Nd:YAG greenpicosecond laser pulse was sent collinearly with red cw He-Ne laser onto one end of the fiber. At the other end ofthe fiber a lens was focusing the output on to the narrow slit ofa monochrometer with its grating set for the red He-Ne laser.

When both He-Ne laser and Nd:YAG laser are present therewill be no output at the oscilloscope. If either one or noneof the laser beams are present we get the output at theoscilloscope showing NAND function.6. OPTICAL MEMORYIn optical computing two types of memory are discussed. Oneconsists of arrays of one-bit-store elements and other is massstorage, which is implemented by optical disks or byholographic storage systems. This type of memorypromises very high capacity and storage density. The primarybenefits offered by holographic optical data storage overcurrent storage technologies include significantly higherstorage capacities and faster read-out rates. This research is


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expected to lead to compact, high capacity, rapid-andrandom-access, and low power and low cost data storagedevices necessary for future intelligent spacecraft. The SLMs

are used in optical data storage applications. These devicesare used to write data into the optical storage medium at highspeed. More conventional approaches to holographic storageuse ion doped lithium niobate crystals to store pages of data.

7. APPLICATIONS1. High speed communicationsThe rapid growth of internet, expanding at almost 15% per

month,demands faster speeds and larger bandwidth thanelectronic circuits can provide. Terabits speeds are needed toaccommodate the growth rate of internet since inopticalcomputers data is transmitted at the speed of light which is of

the order of310*8 m/sec hence terabit speeds areattainable.2. Optical crossbar interconnects are used in asynchronous

ransfer modes and shared memory multiprocessor systems.3. Process satellite data.

OPTICAL DISKS


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WORKINGThe 780nm light emitted from AlGaAs/GaAs laser diodes iscollimated by a lens and focused to a diameter of about


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1micrometer on the disk. If there is no pit where the light isincident, it is reflected at the Al mirror of the disk andreturns to the lens, the depth of the pit is set at a value such

that the difference between the path of the light reflected at apit and the path of light reflected at amirror is an integral multiple of half-wavelength consequently,if there is a pit where light is incident, the amount of reflectedlight decreases tremendouslybecause the reflected lights are almost cancelled byinterference. The incident and reflected beams pass throughthe quarter wave plate and all reflected light is

introduced to the photodiode by the beam splitter because ofthe polarization rotation due to the quarter wave plate. By thephotodiode the reflected light,which has a signal whether, apit is on the disk or not is changed into an electrical signal.8. MERITS1. Optical computing is at least 1000 to 100000 times fasterthan todays silicon machines.

2. Optical storage will provide an extremely optimized way tostore data,with space requirements far lesser than todayssilicon chips.3. Super fast searches through databases.4. No short circuits, light beam can cross each other withoutinterfering with each others data.5. Light beams can travel in parallel and no limit to number ofpackets that can travel in the photonic circuits.

9. DRAWBACKS


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1. Todays materials require much high power to work inconsumer products, coming up with the right materials maytake five years or more.

2. Optical computing using a coherent source is simple tocompute and understand, but it has many drawbacks like anyimperfections or dust onthe optical components will createunwanted interference pattern due to scattering effects.Incoherent processing on the other hand cannot store phaseinformation.10. FUTURE TRENDSThe Ministry of Information Technology has initiated a

photonic development program. Under this program somefunded projects are continuing in fiber optic high-speednetwork systems. Research is going on for developingnew laser diodes, photodetectors, and nonlinear materialstudies for faster switches. Research efforts on nanoparticlethin film or layer studies for display devices are also inprogress. At the Indian Institute of Technology (IIT),

Mumbai, efforts are in progress to generate a white lightsource from a diodecase based fiber amplifier system in orderto provide WDM communication channels.


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11. CONCLUSIONResearch in optical computing has opened up newpossibilities in several fields related to high performance

computing, high-speed communications. As opto electronicand smart pixel devices mature, softwaredevelopment will have a major impact in future


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12. REFERENCES1. RESONANCE-A Journal Of Science EducationJuly 2003

2. OPTIC FIBER COMMUNICATION PRINCIPLE ANDPRACTISE John.M.Senior3. OPTOELECTRONICSWilson.J , J.F.B.Hankes4. www.msfc.nasa.gov5. www.sciam.com

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