Optical computing: As per Wikipedia
Optical computing or photonic
computing uses photons produced by lasers or diodes for computation. For
decades, photons have shown promise to enable a higher bandwidth than
the electrons used in
conventional computers (see optical fibers).
Most research projects focus on replacing current
computer components with optical equivalents, resulting in an optical digital computer system
processing binary data.
This approach appears to offer the best short-term prospects for commercial
optical computing, since optical components could be integrated into
traditional computers to produce an optical-electronic hybrid. However, optoelectronic devices
consume 30% of their energy converting electronic energy into photons and back;
this conversion also slows the transmission of messages. All-optical computers
eliminate the need for optical-electrical-optical (OEO) conversions, thus
reducing electrical power consumption.
Application-specific devices, such as synthetic aperture radar (SAR) and optical correlators, have been designed to use the principles of optical computing. Correlators can be used, for example, to detect and track objects, and to classify serial time-domain optical data.
Optical components for binary digital computer
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 current response of a bipolar transistor.
Such an optical transistor[5][6] can
be used to create optical logic
gates,[6] which
in turn are assembled into the higher level components of the computer's central
processing unit (CPU). These will be nonlinear optical crystals used
to manipulate light beams into controlling other light beams.
Like any computing system, an optical computing system needs
three things to function well:
· optical
processor
· optical
data transfer, e.g. fiber optic cable
Substituting electrical components will need data format
conversion from photons to electrons, which will make the system slower.
Controversy
There are some disagreements between researchers about the
future capabilities of optical computers; whether or not they may be able to
compete with semiconductor-based electronic computers in terms of speed, power
consumption, cost, and size is an open question. Critics note
that real-world logic systems require "logic-level restoration,
cascadability, fan-out and
input–output isolation", all of which are currently provided by electronic
transistors at low cost, low power, and high speed. For optical logic to be
competitive beyond a few niche applications, major breakthroughs in non-linear
optical device technology would be required, or perhaps a change in the nature
of computing itself.
Misconceptions, challenges, and prospects
A significant challenge to optical computing is that
computation is a nonlinear process
in which multiple signals must interact. Light, which is an electromagnetic
wave, can only interact with another electromagnetic wave in the presence
of electrons in a material,[10] and
the strength of this interaction is much weaker for electromagnetic waves, such
as light, than for the electronic signals in a conventional computer. This may
result in the processing elements for an optical computer requiring more power
and larger dimensions than those for a conventional electronic computer using
transistors.
A further misconception is that since light can travel
much faster than the drift
velocity of electrons, and at frequencies measured in THz,
optical transistors should be capable of extremely high frequencies. However,
any electromagnetic wave must obey the transform
limit, and therefore the rate at which an optical transistor can respond to
a signal is still limited by its spectral
bandwidth. However, in fiber
optic communications, practical limits such as dispersion often
constrain channels to
bandwidths of 10s of GHz, only slightly better than many silicon transistors.
Obtaining dramatically faster operation than electronic transistors would
therefore require practical methods of transmitting ultrashort
pulses down highly dispersive waveguides.
Photonic logic
Realization of a photonic controlled-NOT gate for use in quantum computing
Photonic logic is the use
of photons (light)
in logic
gates (NOT, AND, OR, NAND, NOR, XOR, XNOR). Switching is obtained
using nonlinear
optical effects when two or more signals are combined.
Resonators are
especially useful in photonic logic, since they allow a build-up of energy
from constructive
interference, thus enhancing optical nonlinear effects.
Other approaches that have been
investigated include photonic logic at a molecular
level, using photoluminescent chemicals.
In a demonstration, Witlicki et al. performed logical operations using
molecules and SERS.
From
<https://en.wikipedia.org/wiki/Optical_computing>
What is Optical Computer?
An optical computer (also called
a photonic computer) is a device that uses the photons in 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.
Some engineers think optical
computing will someday be common, but most agree that transitions will occur in
specialized areas one at a time. Some optical integrated circuits have been
designed and manufactured. (At least one complete, although rather large,
computer has been built using optical circuits.) Three-dimensional, full-motion
video can be transmitted along a bundle of fibers by breaking the image into
voxels. Some optical devices can be controlled by electronic currents, even
though the impulses carrying the data are visible light or IR. 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 andIR 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.
Optical Computer – Components, Working Principle and Why We Need It
Optical Computer is indeed the computer technology of future
which uses light particles called Photons. This post will discuss Optical
Computer, Optical Components required for computation, why we need it, its
working principle, advantages and disadvantages.
What is an Optical Computer?
A device that uses Photons or Infrared beams, instead of
electric current, for its digital computations is termed as an Photonic or
Optical Computer.
The flow of electric current is only 10 percent of the speed of
light. This poses severe restrictions on long distance data transmission. Such
restrictions resulted in the evolution of optical fiber. By applying the
advantages of IR networks and/or visible light at the component and device
scale, a computer (Optical Computer) can be developed that has 10 times more
processing power than conventional systems.
Fig. 3 – Prototype of Optical Computer
Unlike electric current, IR beams and visible light can pass
through each other without interaction. Several laser beams can be projected so
as to intersect their path, but the beams will have no interference even when
they are confined to two dimensions.
From <https://electricalfundablog.com/optical-computer/>
With electric currents, three
dimensional wiring becomes necessary since they have to be guided around each
other. Thus an Optical Computer, apart from being faster, can also be smaller.
Figure 2 below shows an 8 bit or Bit-Serial Optical Computer.
Fig. 4 – Bit-Serial Optical
Computer
Main Optical Components in Optical Computer
The main Optical components
required for computing in an Optical Computer are:
· VCSEL
(Vertical Cavity Surface Emitting Micro Laser)
· Spatial
Light Modulators
· Optical
Logical Gates
· Smart
Pixels
VCSEL (Vertical Cavity Surface Emitting Micro Laser)
VCSEL is a semiconductor Micro
Laser Diode that emits light vertically from the surface. It basically converts
the Electrical Signal to Optical Signal. It is the best example of one
dimensional Photonic Crystal.
Spatial Light Modulators
Spatial Light Modulators are
responsible for modulating the intensity and the phase of the Optical beam.
They are used in Holographic Data Storage systems as they encode the
information into a laser beam.
Optical Logic Gates
An Optical Logic Gate is nothing
but an Optical Switch that controls the light beams. It is said to be “ON” when
the device transmits light and “OFF” when the device blocks the light.
Smart Pixels
Smart Pixels help Optical Systems
with high levels of Electronic Signal Processing.
Why do we need Optical Computer?
The need for Optical Computer (s) emerged from the fact that the conventional computers are limited by the time response of electronic circuits and also the building up of heat damages the electronic components. For example: Microprocessors contain billions of transistors and sometimes they operate at clock speeds in excess of 3 billion cycles per second which implies that the transistors are exposed to lots of heat, which accelerates their chances of damage.
The other factors which adds to
this need of developing a better alternate are:
· The
End of Electron Based Computing as Moore’s Law is Failing
· A
plateau in Computer Processing Chips
The End of Electron Based Computing as Moore’s Law is Failing
Computers work with zeros and
ones. Little switches called transistors make this possible and there are
billions of them found on current Integrated Circuits and Processor Chips. In
1965, the founder of Intel, Gordon Moore, predicted that there would be a
doubling in the number of transistors on every chip, every two years. This came
to be popular as Moore’s law.
This prediction was accurate up
to the beginning of the 21st century. While the predicted exponential growth
has not completely stopped, it has certainly slowed down. Transistors are
now being manufactured in atomic sizes. This implies that there will soon be
bottlenecks in the quantum mechanical effects.
Current or electrons can
disappear randomly from these minute electrical components, thereby resulting
in incorrect calculations. Also, the latest technology where transistors
measure only five nano meters has become very complex and too expensive to
advance.
A Plateau in Computer Processing Chips
A closer inspection reveals that there has been a decline in the performance of transistors. Looking back, we realize that faster computers were bombarding the market every few years. Today, however, computers are stuck at 4 GHz speed. Yet, it is possible to improve performance with smart chips and parallel processing. However, this increase in speed is attributed not only to transistors but also to various other circuitry.
Fig. 5 – Optical Transistors in Optical
Computer
All these benefits incur a cost.
Processor cores need to constantly maintain communication which consumes
energy. It is so high that communication between the chips is known to consume
more than half of the total computing power. Since computers are in our smart
phones, laptops, internet and data centers, this energy consumption leaves
behind a substantial amount of carbon footprint.
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