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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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