CASE STUDY

ON

OPTICAL COMPUTERSBY

SHAGUFTA PERWEEN

Department of Computer Science & Engineering

Al-Falah School of Engineering and Technology Dhauj, Faridabad, Haryana. Phone No.0129-3218859, 2206223

www.afset.

CERTIFICATE

This is to certify that the project entitled “SEMINAR TITLE” has been carried out by NAME OF THE STUDENT under my guidance in partial fulfillment of the degree of Bachelor of Engineering in Computer Engineering / Information Technology of Al-Falah School of Engineering & Technology during the academic year 2004-2005. To the best of my knowledge and belief this work has not been submitted elsewhere for the award of any other degree.

Guide Examiner Head of the Department Mr. Name Mr. Name

PAGE INDEX

Topic Page No.

1. Introduction.

2. What is Optical Computer?

3. Fiber Optics.

4. Optical Mouse.

5. A Pipelined Processor.

6. An Electronic Switch.

7. Storage Elements.

8. Gates.

9. An Optical Switch.

10.CPU Design.

11.References.

Conclusion Bibliography Appendix – A. Power Point Slides

Chapter 1 Introduction

1.1 What is Optical Computer?

We describe Optical Computer that utilizes photons as information-carriers

instead of electrons. Way back in the 1990, A. Huang and his colleagues at Bell

Laboratories have actually built a computer. An important step in building this

computer has been the construction of an optical alternative for the electronic

transistor.

An optical computer (also called a Photonic Computer) is a device that uses

visible light or infrared (IR) beams, rather than electric current, to perform digital

computations. 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.

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.

Three-dimensional, full-motion video can be transmitted along a bundle of

fibers by breaking the image into voxels (see voxel). Some optical devices can be

controlled by electronic currents, even though the impulses carrying the data are

visible light or IR.

A voxel is a unit of graphic information that defines a point in three-

dimensional space. Since a pixel (picture element) defines a point in two

dimensional space with its x and y coordinates, a third z coordinate is needed. In 3-

D space, each of the coordinates is defined in terms of its position, color, and

density. Think of a cube where any point on an outer side is expressed with an x, y

coordinate and the third, z coordinate defines a location into the cube from that

side, its density, and its color. With this information and 3-D rendering software, a

two-dimensional view from various angles of an image can be obtained and

viewed at your computer.

Optical technology has made its most significant inroads in digital

communications, where fiber optic data transmission has become commonplace.

The ultimate goal is the so-called photonic network, which uses visible and IR

energy exclusively between each source and destination. Optical technology is

employed in CD-ROM drives and their relatives, laser printers, and most

photocopiers and scanners. However, none of these devices are fully optical; all

rely to some extent on conventional electronic circuits and components. It consists

of various part as:-

• A switch

• An Electronic Switch

• Photons Carrying Information

• An Optical Switch

• Optical Bi-stability

• The Elements of a Binary Digital Computer

• Gates

• Storage Elements

• Assembling the Elements

• The function/interconnection module

• A pipelined processor

Fiber Optics:

Unlike a copper cable, which sends electricity one

pulse at a time, optical fibers can transmit several pieces of data

as waves of different colors of light which can travel down a

fiber simultaneously.

Beyond the copper, electricity and silicon that make up the

bulk of today's computers, NASA scientists are looking into

super fast optical computers, which would replace electrons

zooming through metal with light waves refracting through man-

made, organic molecules. Though the technology may not

become reality for another 15 years, scientists said, the power of

optical computers will make today's machines look as slow as

abacuses.

"Optically, we can solve a problem in one hour which

would take an electronic computer 11 years to solve," said

Hossin Abduldayem, a senior research scientist at NASA's

Marshall Space Flight Center in Huntsville, Ala.

Optics — the science of light — is already used in

computing, most often in the fiber-optic glass cables that

currently transmit data down Internet lines much more quickly

than traditional copper wires.

Unlike a copper cable, which sends electricity one pulse at

a time, optical fibers can transmit several pieces of data as

waves of different colors of light which can travel down a fiber

simultaneously. That's much faster.

"When you send information electronically it has to be

done sequentially, whereas with this you can do parallel

processing," said Don Frazier, chief scientist for physical

chemistry at MSFC. "There's no limitation on how many beams

or packets of information you can send at once."

As electronic chips get denser and denser, and the tiny switches

that let computers make decisions get smaller and smaller,

eventually they're going to reach a physical limit where circuits

can't get any smaller, Frazier said.

That's where optical computers come in. Using light

moving through and refracted by thin films of man-made

organic molecules rather than electrons streaming through metal,

they would move and process data much faster. Just like the

difference between fiber-optic cables and copper wire, optical

computers will be able to do parallel computations where

electronic machines have sets of lines that move electrons one at

a time, Frazier said.

Most shorter-term research is focused on advances in

electronics which are promising vastly improved computers with

a mix of optical and electronic components

"Electronics has gotten very good at doing computing, but optics

is very good at transmitting information. Computers will be

opto-electronic computers.

Optical connections within electronic computer systems

will speed data between the parts of a computer, he said, and

optical switches will mix in with electronic processors to move

information quickly without generating the heat that comes off

copper wires.

Optical networking technologies that can move data at 160

gigabits per second. That's 16,000 times faster than today's

average Ethernet connection.

All-optical technologies may still come to pass further in

the future, he said. And even beyond that are "quantum

computers," which use the properties of quantum mechanics to

process data at incredibly high speeds. You'll probably see those

on your desk between 2030 and 2050, Abduldayem said.

Optical mouse:

An optical mouse is an advanced computer pointing device

that uses a light-emitting diode (LED), an optical sensor, and

digital signal processing (DSP) in place of the traditional mouse

ball and electromechanical transducer. Movement is detected by

sensing changes in reflected light, rather than by interpreting the

motion of a rolling sphere.

The optical mouse takes microscopic snapshots of the

working surface at a rate of more than 1,000 images per second.

If the mouse is moved, the image changes. An example of a poor

optical-mousing surface is unfrosted glass.

In practice, an optical mouse does not need cleaning,

because it has no moving parts. This all-electronic feature also

eliminates mechanical fatigue and failure. If the device is used

with the proper surface, sensing is more precise than is possible

with any pointing device using the old electromec

A pipelined Processor:

The function/interconnection modules are cascadable to

form a pipelined processor, programmable to do every wanted

computation. Synchronization is done using a clock-signal (In a

solution to the problem of clock distribution is given). The

clocksignal can control the customizing inputs of the various

function/interconnection modules. Each cycle, only one of the

modules is needed, so the other modules can simply be disabled,

by using low-level customizing inputs. If there are latches

(storage elements that preserve the signal during one clock-

cycle) between the modules, also

controlled by the clock-signal, data can flow through the

pipeline.

An Electronic Switch:

In electronics, switching is done by the transistor. The

principle is well known, but to be able to make a comparison

with its optical counterpart we recapitulate the essentials briefly.

The transistor consists of three layers: the emitter, collector

and base. The base is the middle layer and is made of semi-

conducting material. This means that it can acts either as an

insulator between 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 no 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 from 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 VLSI 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.

Storage Elements:-

In a binary computer there is a need for storage elements

able to represent two stable states. Optical bistability is applied

in order to get such a device.

If we look at figure we see that sending a laser beam with an

intensity within the domain of the hysteresis loop through a

nonlinear material results in two stable states. If the transmitted

beam was of high-level intensity, it will remain high-level. If it

was of low-level intensity, it will remain low-level.

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 while, such that the added

intensity is just enough to get a high-level transmitted intensity .

Putting a ``0'' in the device can be done by just stopping the

beam for a short while.

Nevertheless, a commercial optical computer is a long way off.

The reason that so much power can be crammed into so

little space is that laser beams do not cause short circuits when

they cross paths, thereby making it possible to process multiple

streams of data at the same time. This means that in the field of

telecommunications, for instance, a single optical chip will be

able to handle the telephone calls of all the five billion

inhabitants of the earth talking simultaneously.

Gates:

The logic performed by a conventional computer is done

with sixteen 14oolean 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 (as we already stated, we can tune it

in such a way that the domain of the hysteresis loop is zero).

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.

An Optical Switch:

In 1896 the French physicists Charles Fabry and Alfred

Perot invented their interferometer. It simply consists of two

partially reflecting mirrors, placed parallel to each other. This

might be the basis for an optical transistor. If a beam of light

strikes the first mirror, some percentage of the light is reflected,

and some goes through. The same happens at the other mirror.

But if we take two mirrors that let only 10 percent of the light go

through, only 1 percent of the light goes through both mirrors

(the transmitted beam) and some of the light stays between the

mirrors (in what is called the cavity) for a while.

Optical Computer Chip :

Researchers at the University of Toronto have developed a

hybrid plastic that can produce light at wavelengths used for

fiber-optic communication, paving the way for an optical

computer chip.

The material was developed by a joint team of engineers

and chemists. It is a plastic embedded with quantum dots that

convert electrons into photons. The findings hold promise for

directly linking high-speed computers with networks that

transmit information using light — the largest capacity carrier of

information available.

Nanocrystals of lead sulphide using a cost-effective

technique that allowed them to work at room pressure and at

temperatures of less than 150 degrees Celsius. Traditionally,

creating the crystals used in generating light for fiber-optic

communications means working in a vacuum at temperatures

approaching 600 to 800 degrees Celsius.

To stabilize the surfaces of the quantum dot nanocrystals,

the team placed a special layer of molecules around the

nanocrystals. These crystals were combined with a

semiconducting polymer material to create a thin, smooth film

of the hybrid polymer.

When electrons cross the conductive polymer, they

encounter what are essentially "canyons," with a quantum dot

located at the bottom. Electrons must fall over the edge of the

"canyon" and reach the bottom before producing light. The team

tailored the stabilizing molecules The colors of light the

researchers generated, ranging from 1.3 microns to 1.6 microns

in wavelength, spanned the full range of colors used to

communicate information using light.

so they would hold special electrical properties, ensuring a

flow of electrons into the light-producing "canyons."

Hybrid plastic can convert electric current into light, with

promising efficiency and with a defined path towards further

improvement. With this light source combined with fast

electronic transistors, light modulators, light guides and

detectors, the optical chip is in view."

Optics is entering all phases of computer technology. By

providing new research and ideas, it brings the reader up to date

on how and why optics is likely to be used in next generation

computers and at the same time explains the unique advantage

optics enjoys over conventional electronics and why this trend

will continue. Covered are basic optical concepts such as

mathematical derivations, optical devices for optical computing,

optical associative memories, optical interconnections, and

optical logic. Also suggested are a number of research activities

that are reinforcing the trend toward optics in computing,

including neural networks, the software crisis, highly parallel

computation, progress in new semiconductors, the decreasing

cost of laser diodes, communication industry investments in

fiber optics, and advances in optical devices.

Regular PC computers are constantly improving.

Every year they seem to become faster and hold more memory.

But research teams are running into specific limits to the speed

and storage capacities for the standard architecture. One possible

solution to these is the optical computer.

The information in an optical computer would be stored in

volume holograms. A laser would be split so it could read and

write information, placing a page of data in one of the beams

and crossing it with the other to create an interference pattern in

the recording medium. By varying the angles of the lasers many

different holograms can be recorded or accessed from the same

material. This is called angle multiplexing. The image could

then be read by an array of photo-detectors.

With holographic memory can process pages of data at

very high rates- billions of bits per second. The surface data

density exceeds 100 bits per square micron, 10 billion bits per

square centimeter. This kind of data storage is particularly well

suited for digital images such as movies, medical images,

maps…..

Unfortunately, the materials used to store holograms doe

not stand up to repeated use. In order to be able to record a

holographic image the medium needs to be light sensitive.

Unfortunately this means that with repeated exposure to lasers

the image will decay. Work is currently being made on both

fronts of this problem. New kinds of recording material like

polymers and crystals are being developed. Also, low powered

lasers that will do less damage are being worked on.

Multiple frequencies (or different colors) of light can travel

through optical components without interference, allowing

photonic devices to process multiple streams of data

simultaneously. And the optical components permit a much

higher data rate for any one of these streams than electrical

conductors. Complex programs that take 100 to 1,000 hours to

process on modern electronic computers could eventually take

an hour or less on photonic computers.

The speed of computers becomes a pressing problem as

electronic circuits reach their maximum limit in network

communications. The growth of the Internet demands faster

speeds and larger bandwidths than electronic circuits can

provide .

In most modern computers, electrons travel between

transistor switches on metal wires or traces to gather, process

and store information. The optical computers of the future will

instead use photons traveling on optical fibers or thin films to

perform these functions. But entirely optical computer systems

are still far into the future. Right now scientists are focusing on

developing hybrids by combining electronics with photonics.

Electro-optic hybrids were first made possible around 1978,

when researchers realized that photons could respond to

electrons through certain media such as lithium niobate

(LiNbO3).

CPU design:

To a large extent, the design of a CPU, or central

processing unit, is the design of its control unit. The modern (i.e.

1965 to 1985) way to design control logic is to write a

microprogram

CPU design was originally an ad-hoc process. Just getting a

CPU to work was a substantial governmental and technical

event.

Key design innovations include cache, virtual memory,

instruction pipelining, superscalar, CISC, RISC, virtual

machine, emulators, microprogram, and stack.

Light travels at 186,000 miles per second. That's

982,080,000 feet per second -- or 11,784,960,000 inches. In a

billionth of a second, one nanosecond, photons of light travel

just a bit less than a foot, not considering resistance in air or of

an optical fiber strand or thin film. Just right for doing things

very quickly in microminiaturized computer chips.

NASA scientists are working to solve the need for computer

speed using light itself to accelerate calculations and increase

data bandwidth.

"Entirely optical computers are still some time in the

future," says Dr. Frazier, "but electro-optical hybrids have been

possible since 1978, when it was learned that photons can

respond to electrons through media such as lithium niobate.

Newer advances have produced a variety of thin films and

optical fibers that make optical interconnections and devices

practical. We are focusing on thin films made of organic

molecules, which are more light sensitive than inorganics.

Organics can perform functions such as switching, signal

processing and frequency doubling using less power than

inorganics. Inorganics such as silicon used with organic

materials let us use both photons and electrons in current hybrid

systems, which will eventually lead to all-optical computer

systems."

What we are accomplishing in the lab today will result in

development of super-fast, super-miniaturized, super-

lightweight and lower cost optical computing and optical

communication devices and systems," Frazier explained.

The speed of 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

electronic circuits can provide. Electronic switching limits

network speeds to about 50 Gigabits per second (1 Gigabyte

(Gb) is 109, or 1 billion bits).

Dr. Hossin Abdeldayem, a member of Frazier's optical

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. For example, a

calculation that might take a conventional electronic computer

more than eleven years to complete could be performed by an

optical computer in a single hour.

References:

www.howstuffworks.com

www.thinkdigit.com

www.google.com

www.lowrycomputer.com

www.ncsconline.org