Bsc Optical Computers Doc

8/2/2019 Bsc Optical Computers Doc

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OPTICAL COMPUTERS

CHAPTER 1

INTRODUCTION

1.1 HISTORY

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-todate dimensions of VLSI reached 0.08 urn 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

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.

Today's computers use the movement of electrons in-and-out of transistors to do

logic.The speed of the present computers has now become a pressing problem as

electronic circuits reach their miniaturization limit. The rapid growth of the Internet,

expanding at almost 15% per month, demands faster speeds and larger bandwidths than


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electronic circuits can provide. Electronic switching limits network speeds to about 50

Gigabits per second

1.2 NEED FOR OPTICAL COMPUTERSOptical technologies research group, states that Terabit speeds (1 Terabit,

abbreviated "Tb", is 1012

, or 1 trillion bits) are needed to accommodate the growth rate of

the Internet and the increasing demand for bandwidth-intensive data streams. Optical data

processing can perform several operations simultaneously (in parallel) much faster and

easier than electronics. This "parallelism" when associated with fast switching speeds

would result in staggering computational power.

An electric current flows at only about 10 percent of the speed of light. This limits

the rate at which data can be exchanged over long distances, and is one of the factors that

led to the evolution of optical fiber. 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.

1.3 LITERATURE SURVEY

In this survey we consider optical computers that encode data using images andcompute transforming such images. We give an overview of a number of such optical

computing architectures, including descriptions of the type of hardware commonly used in

optical computing,as well as some of the computational efficiencies of optical devices. We

go on to discuss opticalcomputing from the point of view of computational complexity

theory, with the aim of puttingsome old, and some very recent, results in context. Finally,

we focus on a particular opticalmodel of computation called the continuous space

machine. We describe some results for thismodel including characterisations in terms of

well-known complexity classes.

1.4 ORGANISATION OF THESIS

This thesis consists of six chapters. chapter 1 discuss about overview of seminar literature

survey , organization of thesis.,history and need for optical computer.

Chapter 2 contains construction and types of optical computer.

Chapter 3 includes the explanation for block diagram

Chapter 4 includes merits and demerits


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Chapter 5 includes applications.

Chapter 6 includes conclusion and future scope


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CHAPTER 2

CONSTRUCTION AND TYPES OF OPTICAL

COMPUTERS

2.1 CONSTRUCTION

The fundamental building block of modern electronic computers is the transistor.

To replace electronic components with optical ones, an equivalent "optical transistor" is

required. This is achieved using materials with a non-linear refractive index. In particular,materials exist where the intensity of incoming light affects the intensity of the light

transmitted through the material in a similar manner to the voltage response of an

electronic transistor. This "optical transistor" effect is used to create logic gates, which in

turn are assembled into the higher-level components of the computer's CPU.

2.2 TYPES OF OPTICAL COMPUTERS

There are two different types of optical computers.

(1)Electro-Optical Hybrid computers

(2)Pure Optical computers

2.2.1 ELECTRO-OPTICAL HYBRID COMPUTERS

Electro-optical hybrid computers are the computers which use optical fibers to read

the data and electric parts to direct data from the processor. Here instead of voltage

packets unlike electronic computers, uses light pulses to send information from one

location to other. Optical Processors in this type change the information from binary code

to light pulses using lasers. The processed Information is then detected and decoded

electronically back into binary code.

2.2.2 PURE OPTICAL COMPUTERS

Pure optical computers use multiple frequencies of light for the operations.

Information in these computers is sent throughout computer as light waves and packets.

Electrons are not involved here. Everything is done using photons so no electron based


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systems are involved. These computers dont require the conversion of data from binary to

optical. This leads to the increase in speed of transaction and finally increasing

performance of the system.


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CHAPTER 3

BLOCK DIAGRAM OF AN OPTICAL COMPUTER

Fig 3.1 Block diagram of optical computer

3.1 EXPLANATION OF EACH BLOCK

The various Optical Computer Hardware components are

1. Optical Transistor2. Optical Gate and Switch3. Holographic Memory4. Input-Output Devices5. Optical Networking6. Optical processor

3.1.1 OPTICAL TRANSISTORS

Optical transistors are based on the fabry-perot interferometer. In electronic

computers everything is done using 0s and 1s (b inary code) which forms the basic for

operations. In optical transistors this binary code is generated using the concept of


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interference of light. The constructive interference which gives high intensity output can

be used as 1 and destructive interference output as 0.

Fig 3.2 Constructive interference

Fig 3.3 Destructive interference


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3.1.2 OPTICAL LOGIC GATE

Logic gates are the basic components of a digital system. An

optical logic gate is a switch that controls one light beam with another. It is "on" when the

device transmits light, and "off" when it blocks the light. The universal gate of theelectronic system is the NAND gate by using which all other gates can be created. The

AND gate implemented using the optical system is given below

Fig 3.4 Optical logic gate

3.1.3 INPUT OUTPUT DEVICES

The optical computer hardware requires optical input and optical

output devices. Many of the input output devices of optical computer are identical or

similar to those th at we se e ev en no w. Th e va ri ou s op ti cal bas ed

electronic devices can be made optically and can do paralle l process ing

much fast er than t he curr ent electronic o r opto-electronic devices

.

INPUT DEVICES

OPTICAL MOUSE

An optical mouse uses a light-emitting diode and photodiodes to

detect movement relative to the underlying surface. Modern surface-

independent optical mice work by using an optoelectronic sensor to take successive

pictures of the surface on which the mouse operates. In optical mouse, the optoelectronic


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sensor and circuitry can be replaced with the all optical circuitry. Inside each optical

mouse is a small camera that takes more than a thousand snapshot pictures every second.

A small LED (light-emitting diode) provides light underneath the mouse, helping to

highlights light differences in the surface underneath the mouse. Those differences are

reflected back into the camera, where digi tal pr ocessin g is u sed to compare

the pictur es and determine the speed and direction of movement. The laser

mouse uses an infrared laser diode instead of an LED to illuminate the surface beneath

their sensor.

OPTICAL KEYBOARD

An optical keyboard is otherwise known as a virtual keyboard. The

virtual keyboard has a virtual display of the keyboard using lasers. It can

be projected and touched on any surface. The keyboard watches finger movements and

translates them into keystrokes in the device. A laser or beamer projects visible virtual

keyboard onto level surface. A sensor or camera in the projector picks up finger

movements. The camera associated with the detector detects co-ordinates and determine

actions or characters to be generated. A direction technology based on an

optical recognition mechanism enables the user to tap on the projected key

images ,while producing real tapping sounds .All mechanical input units can be replaced

by such virtual devices, optimized for the current application and for the user's

physiology maintaining speed, simplicity and un ambiguity of manual data input.

In this virtual keyboard also, the mechanical parts have become purely optical but

the electronic parts remain the same or has become opto-electronic circuits. In

future, this electronic circuitry will be replaced by Optical Computers

3.1.4 HOLOGRAPHIC MEMORY

Memory storage in an optical computer has been all-optical with the

invention ofHolographic memory. If there wasnt a typical optical type of memory, the

data rates of the elect ronic memor y would have caused a relat ively high

delay with the optical data rates which causes the optical computer a non worthier

device.


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HOLOGRAPHIC DATA STORAGE

HDS is a potential replacement technology in the area of high-capacity data

storage currently dominated by magnetic and conventional optical data storage. It is

essentially a 3-D memory storage device. Magnetic and optical data storage

devices rely on individual bits being stored as distinct magnetic or optical

changes on the surface of the recording medium. Holographic data storage over comes this

limitation by recording information throughout the volume of the medium and is capable

of recording multiple images in the same area utilizing l i gh t a t d i f f e r en t angles.

Additionally, whereas magnetic and optical data storage records information a b i t a t a

t i m e i n a l i n e a r f a s h i o n , h o l o g r a p h i c s t o r a g e i s c a p a b l e o f

recording and reading millions of bits in parallel, enabling data transfer

rates greater than those attained by optical storage. Holographic memory

offers the possibility of storing1terabyte (TB) of data in a sugar-cube-sized crystal

3.1.5 OPTICAL PROCESSOR

The p roces s o r i s the b ra in o f a compu te r . The de s ign o f an

e f f i c i en t and r e l i ab l e processor for optical computer requires development of

various transistors and logic gates circuits in the submicron values. The optical

transistors and logic gates have been still in developing conditions. Even

though there are no all-optical processors available commercially, there are opto-

electronic hybrid optical processors available. In t e l ha s al read y de s i gned an d

c r ea t ed a ph o to n i c p r o ce ss o r ,w h i ch i s a n op t o e l e c t r o n i c h y b r i d p r o

c e s s o r .

T h e p r o c e s s o r i s a n e n t i r e l y s o l i d s t a t e p h o t o n i c processor

assembly a chip which processes data as light waves, without the need for mic r os cop i c

ye t movab le , pa r t s . The p roces s o rs c e ramic ma te r ia l ba s ed on indium

phosphide that could produce a monochromatic wavelength of laser light when

electricity is applied to it, and could also be produced as a wafer that bonds to a

silicon substrate. That major development eliminated the need

for movable gratings that refract laser light from a multiple-wavelength source, so that

a single wavelength could emerge.


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CHAPTER 4

MERITS AND DEMERITS

4.1 MERITS

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 thanan electronic one, might also be smaller.

Another claimed advantage of optics is that it can reduce power consumption, but

an optical communication system will typically use more power over short distances than

an electronic one. This is because the shot noise of an optical communication channel is

greater than the thermal noise of an electrical channel which, from information theory,

means that we require more signal power to archive the same data capacity. However,

over longer distances and at greater data rates the loss in electrical lines is sufficiently

large that optical communications will comparatively use a lower amount of power. As

communication data rates rise, this distance becomes shorter and so the prospect of using

optics in computing systems becomes more practical. Moreover optical devices which are

made up of organic materials are much economical when compared to the electronic

devices which are made up of inorganic materials (silicon). Some of advantages of optical

computer over electrical computer are

Small size Increased speed Low heating Reconfigurable Scalable for larger or small networks More complex functions done faster Applications for Artificial Intelligence Less power consumption (500 microwatts per interconnect length vs. 10 mW for

electrical)


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4.2 DEMERITS

1. Todays materials require much high power to work in consumer products, coming up

with the right materials may take five years or more.

2. 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. Incoherent processing on the other

hand cannot store phase information.


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CHAPTER 5

APPLICATIONS

5.1 APPLICATIONS

Lasers, fibers, and optical components have already proven their reliability and

high levels of performance in many applications such as CD-ROM drives, laser printers,

photocopiers and scanners, Storage Area Networks (SANs), optical switches, all-optical

data networks, holographic storage devices, and biometric devices at airports to track

weapons and drugs. At the same time, the promise of optical computing comes from the

many advantages that optical interconnections and optical integrated circuits have over

their electronic counterparts. Optical computing is immune to electromagnetic interference

and free from electrical short circuits and proves to be handier when compared to the

electronic computing machines in the given circumstances.

Moreover photons of different colors can travel together in the same fiber or cross each

other in free space without interference or cross-talk. Since photons have low-loss

transmission and provide large bandwidth, they offer multiplexing capacity forcommunicating several channels in parallel without interference.

Optical materials are compact, lightweight, inexpensive to manufacture, more

facile with stored information than magnetic materials, and possess superior storage

density and accessibility compared to magnetic materials. Progress in holographic storage

devices can enable storage of the entire U.S. Library of Congress onto a sugar-cube-size

hologram. Furthermore, optical parallel data processing is easier and less expensive than

electronic. In addition, optical computing systems offer computational speeds more than

107 times faster than the currently fastest electronic systems. This means a computation

that takes a conventional computer more than 11 years to solve would take an optical

computer less than one hour.


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CHAPTER 6

CONCLUSION AND FUTURE SCOPE

6.1 CONCLUSION

The building blocks, such as all-optical logic gates, optical switches, optical

memory, and optical interconnections are all available, but we still dont have an optical

computing system. There are several factors impeding the technology, the most important

of which are cascadability, material development, and funding. Cascadability to integrate a

large number of all-optical gates is a highly complex problem and a major obstacle in the

way of building a complete optical computing system. Binary half adders data processors,

which combine several optical logic gates, are the basic building blocks of binary

operations. Nonlinear optical mechanisms play important roles in ultra-fast, all-optical

logic gates and optical switches. Most of the nonlinear mechanisms in these switches

require pumping high optical power into the system for these devices to function.

However, the high optical power in the system has the disadvantage of generating

undesirable signals such as stimulated Brillouin scattering (SBS) and self-phase

modulations (SPM), which might affect the system's reliability. Material scientists and

chemists, therefore, have the challenging problem of finding materials with adequate

response at low power and at the same time demonstrate reliability, speed, and optical

efficiency.

Furthermore, development of an optical computer is an interdisciplinary enterprise

requiring coordination and funding of optical engineers, material scientists, chemists,

physicists, computer architects, and representatives of other disciplines. Government

funding incentives, to fill a gap created by industry's return-on-investment requirements

can encourage formation of such teams and expedite development of optical computer

systems. It is projected that the development of a bulky prototype optical within the next

1015 years. With the current level of progress in the area of optical computing research,

it may easily take up to 1520 years before optical computers commonly appear on our

desktops.


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6.2 FUTURE SCOPE

The Ministry of Information Technology has initiated a photonic development

program. Under this program some funded projects are continuing in fiber optic high-

speed network systems. Research is going on for developing new laser diodes, photo

detectors, and nonlinear material studies for faster switches. Research efforts on nano

particle thin film or layer studies for display devices are also in progress. At the Indian

Institute of Technology (IIT), Mumbai, efforts are in progress to generate a white light

source from a diode-case based fiber amplifier system in order to provide WDM

communication channel

Fig 6.1 Future trends of optical computer


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REFERENCES

MA: MIT Press. ISBN 0262061120.

McAulay,Alastair D. (1991). New York, NY: John Wiley &Sons. ISBN 0471632422.

Ibrahim TA, Amarnath K, Kuo LC, Grover R, Van V, Ho PT. Photonic logic NORgate based on two symmetric microring resonators. Opt Lett. 2004 Dec

1;29(23):2779-81.

Biancardo M et al. A potential and ion switched molecular photonic logic gate,Chem. Commun., 2005, (31), 3918-3920

J. Jahns Feitelson, Dror G. (1988).. Cambridge, and S. H. Lee, eds., "OpticalComputing Hardware", Academic Press, Boston (1994).

BARROS S., GUAN S. & ALUKAIDEY T., "An MPP reconfigurable architectureusing free-space optical interconnects and Petri net configuring" in Journal of

System Architecture (The EUROMICRO Journal) Special Double Issue on

Massively Parallel Computing Systems vol. 43, no. 6 & 7, pp. 391402, April

1997

D. Goswami, "Optical Computing", Resonance, June 2003; ibid July 2003. WebArchive of www.iisc.ernet.in/academy/resonance/July2003/July2003p8-21.html
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