Pushing the Limits of Computer Technology
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Pushing the Limits of Computer Technology Using Light and Organic Molecules
to Form Materials in Space
May 18, 1999: By using light and organic molecules
to form materials in space, NASA scientists may improve both
the speed and capabilities of computers.
Right: Dr. Donald Frazier monitors a blue laser light used with thin-film materials.
Led by Dr. Donald Frazier of the Space Sciences Laboratory at the Marshall Space Flight Center, NASA is working with Optron Systems, Inc. in Bedford, Mass., to develop thin-film materials for devices that use both electrons and photons to transmit data. These films could be used in electronic/optical hybrids such as electro-optic computers.
Left: Dr. Steve Paley discusses the the goals of optical computing. Click on the image for a brief RealVideo. The clip is also available in QuickTime format. Free players for QuickTime or RealVideo content are available from the vendors.
In most modern computers, electrons travel between transistor switches 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 thin films to perform these functions. But entirely optical computer systems are still far into the future. Right now scientists are focusing on developing hybrids by combining electronics with photonics. Electro-optic hybrids were first made possible around 1978, when researchers realized that photons could respond to electrons through certain media such as lithium niobate (LiNbO3).
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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. Photo credit: David N. Donovan.
An ultraviolet lamp causes the entire quartz surface to become coated, but shining a laser through the quartz can cause the polymer to deposit in specific patterns. Because a laser is a thin beam of focused light, it can be used to draw exact lines. A laser beam's focus can be as small as a micron-sized spot (1 micron is 1-millionth of a meter, or 1/25,000 of an inch), so scientists can deposit the organic materials on the quartz in very sophisticated patterns. By "painting with light," scientists can create optical circuits that may one day replace the electronics currently used in computers.
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Convection creates difficulties when trying to create a uniform
film. A UV lamp or laser light will raise the temperature of
the film solution, causing the hotter solution to rise. Aggregates
of solid polymers often form in the solution, and convective
flows that develop in the solution can carry these aggregates
to the surface of the quartz. Because aggregates on optical films
can cause light to scatter, the goal is to make the films as
smooth and uniform as possible.
Right: Earth-formed films (above) show more polymer aggregates under 1,000x magnification than films formed in microgravity. Photo credit: David N. Donovan.
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. Photo copyright: 3M Corporation.
"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."
NASA Space Product Development - provided the funding for the program to develop thin films in space.
Alliance for Nonlinear Optics - College students from 5 universities work with NASA to identify new materials for nonlinear optical devices.
Microgravity News - Winter 1995 report about the Alliance for Nonlinear Optics.
"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."
Smaller, more compact computers are often faster because computation time depends on shorter connections between components. In the search for speed, computer chips have grown ever smaller: it is estimated that the number of transistor switches that can be put onto a chip doubles every 18 months. It is now possible to fit 300 million transistors on a single silicon chip, and some scientists have predicted that in the next few decades computer technology will have reached the atomic level.
Left: Magnification of an Intel i4004 microprocessor chip. Photo copyright: National High Magnetic Field Laboratory, Florida State University.
But more transistors mean the signals have to travel a greater distance on thinner wires. As the switches and connecting wires are squeezed closer together, the resulting crosstalk can inadvertently cause a digital signal to change from a 1 to a 0. Scientists are working on developing newer, better insulators to combat this problem. But optical computers wouldn't need better insulators because they don't experience crosstalk. The thin-films used in electro-optic computers would eliminate many such problems plaguing electronics today.
"The thin-films allow us to transmit information using
light. And because we're working with light, we're working with
the speed of light without generating as much heat as electrons,"
says Frazier. "We can move information faster than electronic
circuits, and without the need to remove damaging heat."
Right: Blue and red lasers reflecting off mirrors. Photo Credit: Department of Energy/Coherent Inc Laser Group.
Multiple frequencies (or different colors) of light can travel through optical components without interference, allowing photonic devices to process multiple streams of data simultaneously. And the optical components permit a much higher data rate for any one of these streams than electrical conductors. Complex programs that take 100 to 1,000 hours to process on modern electronic computers could eventually take an hour or less on photonic computers.
The speed of computers becomes a pressing problem as electronic circuits reach their maximum limit in network communications. The growth of the Internet demands faster speeds and larger bandwidths than electronic circuits can provide. Electronic switching limits network speeds to about 50 gigabits per second (1 gigabit (Gb) is 109, or 1 billion bits).
"Terabit speeds are already needed to accommodate the
10 to 15 percent per month growth rate of the Internet, and the
increasing demand for bandwidth-intensive data such as digital
video," says Dr. David Smith of NASA/Marshall (1 Tb is 1012, or 1 trillion
bits). "All-optical switching using optical materials can
relieve the escalating problem of bandwidth limitations imposed
Left: The all-optical computers of the future will have more capabilities than today's electronic computers. Photo credit: NASA.
Last year Lucent Technologies' Bell Laboratory introduced technology with the capacity to carry the entire world's Internet traffic simultaneously over a single optical cable. Optical computers will someday eliminate the need for the enormous tangle of wires used in electronic computers today. Optical computers will be more compact and yet will have faster speeds, larger bandwidths and more capabilities than modern electronic computers.
Frazier and his group have designed and built all-optical
circuits for data processing and are working on a system for
pattern recognition. Currently, electro-optic pattern recognition systems are used for automated
fingerprint and photograph scanning, as well as for rapid identification
of moving objects such as military aircraft and vehicles. And
other scientists are using the non-linear pattern-recognition
capabilities of optical computers to develop artificial intelligence
systems that can learn and evolve.
Right: Dr. Hossin Abdeldayem of NASA/Marshall works with lasers to develop a system for pattern recognition.
Optical components like the thin-films developed by NASA are essential for the development of these advanced computers. By developing components for electro-optic hybrids in the present, NASA scientists are helping to make possible the amazing optical computers that will someday dominate the future.
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