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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. 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.
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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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. |
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.
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. 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. "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." |
magnification
than films formed in microgravity. Photo credit: David N. Donovan.
Corporation using physical
vapor transport. Left: Top view of films; Right:side view. Photo
copyright: 3M Corporation.
"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." 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. |
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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 a "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
by electronics." 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 recogni 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. |
bout 50 gigabits per second (1 gigabit
(Gb) is 109,
or 1 billion bits).
tion 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.|
More Space Science Headlines - NASA research on the web Life and Microgravity Sciences and Applications information from NASA HQ on science in space Microgravity Research Programs Office headquartered at Marshall Space Flight Center Microgravity News online version of NASA's latest in Microgravity advancements, published quarterly. |
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