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1. INTRODUCTION
With the growth of computing technology the need of high performance
computers (HPC) has significantly increased. Optics has been used in computing
for a number of years but the main emphasis has been and continues to be to link
portions of computers, for communications, or more intrinsically in devices that
have some optical application or component (optical pattern recognition etc.)
Optical computing was a hot research area in 1980’s.But the work tapered
off due to materials limitations that prevented optochips from getting small
enough and cheap enough beyond laboratory curiosities. Now, optical computers
are back with advances in self-assembled conducting organic polymers that
promise super-tiny of all optical chips.
Optical computing technology is, in general, developing in two directions.
One approach is to build computers that have the same architecture as present
day computers but using optics that is Electro optical hybrids. Another approach
is to generate a completely new kind of computer, which can perform all
functional operations in optical mode. In recent years, a number of devices that
can ultimately lead us to real optical computers have already been manufactured.
These include optical logic gates, optical switches, optical interconnections and
optical memory.
Current trends in optical computing emphasize communications, for
example the use of free space optical interconnects as a potential solution to
remove ‘Bottlenecks’ experienced in electronic architectures. Optical technology
is one of the most promising, and may eventually lead to new computing
applications as a consequence of faster processing speed, as well as better
connectivity and higher bandwidth.
NEED FOR OPTICAL COMPUTING
The pressing need for optical technology stems from the fact that today’s
computers are limited by the time response of electronic circuits. A solid
transmission medium limits both the speed and volume of signals, as well as
building up heat that damages components.
One of the theoretical limits on how fast a computer can function is given
by Einstein’s principle that signal cannot propagate faster than speed of light. So
to make computers faster, their components must be smaller and there by
decrease the distance between them. This has resulted in the development of very
large scale integration (VLSI) technology, with smaller device dimensions and
greater complexity. The smallest dimensions of VLSI nowadays are about
0.08mm. Despite the incredible progress in the development and refinement of
the basic technologies over the past decade, there is growing concern that these
technologies may not be capable of solving the computing problems of even the
current millennium. The speed of computers was achieved by miniaturizing
electronic components to a very small micron-size scale, but they are limited not
only by the speed of electrons in matter but also by the increasing density of
interconnections necessary to link the electronic gates on microchips.
The optical computer comes as a solution of miniaturizing problem.
Optical data processing can perform several operations in parallel much faster
and easier than electrons. This parallelism helps in staggering computational
power. For example a calculation that takes a conventional electronic computer
more than 11 years to complete could be performed by an optical computer in a
single hour. Any way we can realize that in an optical computer, electrons are
replaced by photons, the subatomic bits of electromagnetic radiation that make
up light.
SOME KEY OPTICAL COMPONENTS FOR
COMPUTING
The major breakthroughs on optical computing have been centered on the
development of micro-optic devices for data input.
1. VCSEL (VERTICAL CAVITY SURFACE EMITTING
LACER)
VCSEL (pronounced ‘vixel’) is a semiconductor vertical cavity surface
emitting laser diode that emits light in a cylindrical beam vertically from the
surface of a fabricated wafer, and offers significant advantages when compared
to the edge-emitting lasers currently used in the majority of fiber optic
communications devices. The principle involved in the operation of a VCSEL is
very similar to those of regular lasers.
There are two special semiconductor materials sandwiching an active
layer where all the action takes place. But rather than reflective ends, in a
VCSEL there are several layers of partially reflective mirrors above and below
the active layer. Layers of semiconductors with differing compositions create
these mirrors, and each mirror reflects a narrow range of wavelengths back in to
the cavity in order to cause light emission at just one wavelength.
2. SLM (SPATIAL LIGHT MODULATORS)
SLM play an important role in several technical areas where the control of
light on a pixel-by-pixel basis is a key element, such as optical processing and
displays. For display purposes the desire is to have as many pixels as possible in
assmall and cheap a device as possible.
3. SMART PIXEL TECHNOLOGY
Smart pixel technology is a relatively new approach to integrating
electronic circuitry and optoelectronic devices in a common framework. The
purpose is to leverage the advantages of each individual technology and provide
improved performance for specific applications. Here, the electronic circuitry
provides complex functionality and programmability while the optoelectronic
devices provide high-speed switching and compatibility with existing optical
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