OPTICAL COMPUTER

INTRODUCTION TO OPTICAL COMPUTER

Watches tick in seconds. Basketball games are timed in 10ths of a second, and drag racers in 100ths. Computers used to work in milliseconds (1,000ths), then moved up to micr oseconds (millionths), and now are approaching nanoseconds(billionths) for logic operation and picoseconds (trillionths!) for the switches and gates in chips.

Since the dawn of the silicon age, computer processors have worked in essentially the same way bits of data travel through the circuits of our computer in the form of electrons.


It works well; it’s fast, and cheap. But chipmakers are beginning to run up against absolute physical limits to make microprocessors even faster. The next significant advance

in computer technology will require new materials or new ways of transporting data. One promising new pathway: ELECTRO - OPTICS . Nothing travels faster than photons, the subatomic bits of electromagnetic radiation that make up light. Harnessing photons to transmit data could make computers exponentially faster than they are today.

OPTICAL COMPUTER is not the so called general purpose supercomputer by any means. It will be reasonable to assume that the optical computer and the general-purpose computers will have niches of their own in the future. With electronics, conversion of data from one - dimension to two-dimension is very time-consuming work, and information input, also, takes time. Consequently, such I/O bottlenecks are bound to slow down the process.

Silicon and other inorganics are often used in electronic computer hardware, the all optical computers of the future will probably use mostly organic parts. Optical computer will someday eliminate the need for the enormous tangle of wires used in electronic computer today. Optical computers will be more compact and yet will have faster speeds, larger B.W. and more capabilities than modern electronic computers.

Most components now in demand are electro-optical (EO) hybrids, limited by the speed of their electronic parts. All-optical components will have the advantage of speed over EO devices, but there is a lack of efficient nonlinear optical (NLO) materials that can respond at low power levels. Almost all current all-optical components require a high level of laser power to function as required

Companies, universities and government labs are reporting more all-optical and organic technology developments almost weekly. Stay tuned for more hot future news in this bright new realm of science!

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Optical computer-1 Introduction

Optical Development Boom

Photonics development is booming worldwide in optics and optical components for computing and other applications. Estimates of global photonic technology sales in 1999 were as high as $100 billion and rising with the ever-increasing demands of data traffic. KMI Corp. reports data traffic growing at 100% per year worldwide, while London's Phillips Group estimates that U.S. data traffic will increase by 300% annually.

Right: Blue and red lasers reflecting off mirrors -- a glimpse of things to come in computing technology? Photo Credit: Department of Energy/Coherent Inc Laser Group.
Most components now in demand are electro-optical (EO) hybrids, which are limited by the speed of their electronic part.All optical components will have the advantage of speed over EO devices, but there is a lack of efficient nonlinear optical (NLO) materials that can respond at low power levels. Almost all current all-optical components require a high level of laser power to function as required.

Researchers from the University of Southern California working with a team from the University of California at Los Angeles have jointly developed an organic polymer with switching frequency of 60 GHz -- three times faster than the current industry-standard lithium niobate crystal-based devices. Commercial development of such a device could revolutionize the "information superhighway" and speed data processing for optical computing.

Another group at Brown University and IBM Corporation's Almaden Research Center in San Jose, CA, have used ultra fast laser pulses to build ultra fast data-storage Services, achieving switching down to 100ps -- results that are almost ten times faster than currently available "speed limits".

A European collaborative effort has demonstrated high-speed optical data input and output in free-space between IC chips in computers at a rate of more than 1 TB/sec. Astro Terra, in collaboration with Jet Propulsion Laboratory (Pasadena, CA) has built a 32-channel 1-Gigabit per second earth-to-satellite link with a 2000 km range.

In Japan, NEC Corporation has developed a method for interconnecting circuit boards optically using Vertical Cavity Surface Emitting Laser arrays (VCSEL). Researchers at Osaka City University reported a method for automatic alignment of a set of optical beams in space with a set of optical fibers. Researchers at NTT in Tokyo have designed an optical back plane with free-space optical interconnects using tunable beam deflectors and a mirror. Their project achieved 1000 interconnections per printed-circuit board, with throughput ranging from 1 to 10 Terabits/sec.

------Optical Computer -2 Worldwide Boom

STORED PROGRAM OPTICAL COMPUTER (SPOC)

The Stored Program Optical Computer is the world's first general purpose optical computer. The computer was built using fibers and lithium niobate directional couplers. The computer does not contain any flip-flops, and instead the latch less architecture uses time of flight design. The computer has a memory, an ALU, an accumulator, a PC, and the ability to do conditional jumps and simple mathematical and boolean function. The clock rate is of 50 MHz and it has a word size of 16 bits. The current work is to time multiplex two machines on the same hardware by increasing the clock rate to 100 MHz. The computer was designed, using the XHatch computer aided design tool for time-of-flight synchronized circuits.

XHATCH INFORMATION :

XHatch is an X Windows CAD program used for the design of time-of-flight synchronized opto-electronic circuits. The program includes schematic capture, logic simulation, delay distribution, and power loss or cross-talk analysis.

------Optical Computer-3 SPOC

Pushing the Limits of Computer Technology

Using Light and Organic Molecules to Form Materials in Space

By using light and organic molecules to form materials in space, NASA scientists may improve both the speed and capabilities of computers

Led by “Donald Frazier” of the Space Sciences Laboratory at the Marshal Space Flight Center, NASA is working with Optron Systems, Inc. in Bedford, Mass., to do development in thin-film materials for devices using both electrons and photons to transmit data. These film could be used in electronic/optical hybrids such as electro-optic computers.

In most modern computers, electrons travel between the switches of transistors 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 on thin films to perform these functions. But entirely Optical Computer systems are still far into the future. Right now scientists are focusing on developing hybrid by combining electronics with photons. Electro-optic hybrid was first made possible around 1978, when researchers realized that photons could respond to electrons through certain media such as lithium niobate (LiNbO3).

To make the thin polymer films for electro-optic applications, NASA scientists dissolve a monomer (the building block of a polymer) in an organic solvent. This solution is then put into a growth cell with a quartz window. An ultraviolet lamp shining through this window creates a chemical reaction, causing a thin polymer film to deposit on the quartz.

Left: A polymer film "painted on" with an ultraviolet laser next to a film created with a broad-spectrum ultraviolet lamp. Blocking the UV rays with a piece of paper (shaped like the Space Shuttle) prevents the film from adhering to the quartz..

NASA scientists are making these organic thin films on the Space Shuttle to overcome problems caused by convection. Convection is a circular motion in air or in a liquid created from uneven heating. On the surface of earth, when a gas or liquid is heated it expands, becoming lighter and less dense. This lighter material rises, mixing with cooler and denser material from above. Such turbulence occurs in the world's weather patterns or even in a pot of water boiling on the stove.

In the optical computer of the future," says Frazier, "electronic circuits and wires will be replaced by a few optical fibers and films, making the systems more efficient with no interference, more cost effective, lighter and more compact."

------Optical Computer-4 NASA & Electro-Optonics

Further…

Convection is actually caused both by heating and the Earth's gravity. The microgravity conditions of space reduce the effects of convection because there is no "up" direction for the heated material to head towards. Any aggregates in space-produced films can only reach the quartz through the slower process of diffusion. Because microgravity reduces convection, films made in space have fewer polymer aggregates than those made on Earth.

Convection causes other problems for the production of optical films. Convection can affect the distribution of molecules in a fluid, so films created on Earth can have regions that are rich or poor in certain molecules rather than evenly dispersed throughout. Films made in microgravity often have more highly-aligned and densely-packed molecules than Earth-formed films. Because there is little convection in a microgravity environment, scientists can produce smoother and more uniform films in space.
Below: Example of microgravity films versus films formed on Earth, magnified 30,000x. These films were developed by the 3M Corporation using physical vapor transport. Left: Top view of films; Right:side view.

"Space allows us to study in more detail how film defects form," says Mark Paley of NASA/Marshall. "That will show us how to do things differently on the ground. The ultimate goal is to be able to produce uniform thin-films here on Earth."

All-optical computer components and thin-films developed by NASA are essential to the current worldwide work in electro-optical hybrid computers - and will help to make possible the astounding organic optical computers that will be the standard of future terrestrial and space information, operating and communication systems.

------Optical Computer-5 Research & Development

Photons Carrying Information

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 computing to its limits. However, there are some fundamental differences between electrons and photons that hold us back.

First of all, electrons affect each other at distance, while photons 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. On the other hand it is a drawback when communication is concerned, because it leads to phenomena like induction. But it also yields a more important problem: two currents of electrons may not cross.

And this is where another advantage of photons comes in: two beams of light can cross without affecting each other, provided their angle is not less than 10 degrees. This increases the number of possible interconnections, something we come back to later.

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 semiconducting material acts as an intermedium. If we want to build a switch and follow the idea of the transistor, we have to find a material isomorphic to the semiconducting material, i.e. a device of which we can change the properties just by sending a beam of light through it. Perhaps we can find a device that sometimes (dependent on another beam) is opaque, and sometimes transparent.

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-6 Advanced Features

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.

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 than the switching-intensity of the transphasor, but higher than half the switching-intensity. Both incident beams are aimed at the same spot on the first mirror. Only if both incident beams have an intensity equal to their high-level, enough power is fed into the cavity to get a high-level transmitted intensity. If both incident beams, or one of them, has an intensity below its high-level, the transmitted beam will be of low-level intensity. This is exactly like an AND gate in electronics.

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.

The function/interconnection module

The base of the design are the function/interconnection modules that are programmable with 16 customizing inputs. The idea is to combine two signal-pairs (a signal pair consists of a signal and its inverse, say A and A’, or B and B’ ) using four tri-input AND gates. Each combination is fed into an AND gate along with some customizing input . The outputs of the gates are combined. Huang calls this a functional logic block.