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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.