Apr 27, 2000

Now Just a Blinkin' Picosecond!

Dr. Donald Frazier monitors a blue laser light
April 28, 2000 -- 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 microseconds (millionths), and now are approaching nanoseconds (billionths) for logic operations - and picoseconds (trillionths!) for the switches and gates in chips.

"That's great in theory," says Dr. Donald Frazier of NASA's Marshall Space Flight Center. "Except that electronic signals, even with Very Large Scale Integration (VLSI) and maximum miniaturization, are bogged down by many aspects of the solid materials they travel through. So we've had to find a faster medium for the signals - and the answer seems to be light itself!"

Above: Dr. Donald Frazier monitors a blue laser light used with electro-optical materials.

Light travels at 186,000 miles per second. That's 982,080,000 feet per second -- or 11,784,960,000 inches. In a billionth of a second, one nanosecond, photons of light travel just a bit less than a foot, not considering resistance in air or of an optical fiber strand or thin film. Just right for doing things very quickly in microminiaturized computer chips.

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"Entirely optical computers are still some time in the future," says Dr. Frazier, "but electro-optical hybrids have been possible since 1978, when it was learned that photons can respond to electrons through media such as lithium niobate. Newer advances have produced a variety of thin films and optical fibers that make optical interconnections and devices practical. We are focusing on thin films made of organic molecules, which are more light sensitive than inorganics. Organics can perform functions such as switching, signal processing and frequency doubling using less power than inorganics. Inorganics such as silicon used with organic materials let us use both photons and electrons in current hybrid systems, which will eventually lead to all-optical computer systems."

"What we are accomplishing in the lab today will result in development of super-fast, super-miniaturized, super-lightweight and lower cost optical computing and optical communication devices and systems," Frazier explained.

The speed of computers has now become a pressing problem as electronic circuits reach their miniaturization limit. The rapid growth of the Internet, expanding at almost 15% per month, 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).

Dr. Hossin Abdeldayem, a member of Frazier's optical technologies research group, states that Terabit speeds (1 Terabit, abbreviated "Tb", is 1012, or 1 trillion bits) are needed to accommodate the growth rate of the Internet and the increasing demand for bandwidth-intensive data streams. Optical data processing can perform several operations simultaneously (in parallel) much faster and easier than electronics. This "parallelism" when associated with fast switching speeds would result in staggering computational power. For example, a calculation that might take a conventional electronic computer more than eleven years to complete could be performed by an optical computer in a single hour.

Dr. Hossin Abdeldayem
"All-optical switching using optical materials can relieve the escalating problem of bandwidth limitations imposed by electronics," says Dr. Abdeldayem. "In 1998, Lucent Technologies introduced a lithographic submicron technology to further miniaturize electronic circuits and enhance computer speed. Additional miniaturization of electronic components only provides a short-term solution to the problem. There are also physical problems accompanied by miniaturization that might affect the computer's reliability. "

Drs. Frazier and Abdeldayem and their group in Huntsville, AL, have designed and built all-optical logic gate circuits for data processing at Gigabit and Terabit rates, and they are also working on a system for pattern recognition.

Left: Dr. Hossin Abdeldayem of NASA/Marshall works with lasers to develop a system for pattern recognition.

"We have also developed and tested nanosecond optical switches, which can act as computer logic gates," says Dr. Abdeldayem, who recently presented the group's research paper entitled "All-Optical Logic Gates for Optical Computing" at The Pittsburgh Conference in New Orleans, LA.

"Picosecond and nanosecond all-optical switches, which act as AND and partial NAND logic gates were demonstrated in our laboratory," explains Dr. Abdeldayem. "Such logic gates are members of a large family of gates in computers that perform logic operations such as addition, subtraction and multiplication. They are vital for the development of optical computing and optical communication. Our all-optical logic gates were made using a thin film of metal-free phthalocyanine compound and a polydiacetylene polymer in a hollow fiber"


Optical Development Boom is Worldwide

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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 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.

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 a 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 ultrafast laser pulses to build ultrafast data-storage devices, achieving switching down to 100ps -- results that are almost ten times faster than currently available "speed limits".

Left: Dr. Steve Paley (NASA/Marshall) discusses the goals of optical computing. Click on the image for a brief RealVideo. The clip is also available in . Free players for QuickTime or RealVideo content are available from the vendors.

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.

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!

Logic gates are the building blocks of any digital system," he continues. "An optical logic gate is a switch that controls one light beam with another. It is "on" when the device transmits light, and "off" when it blocks the light."

"Our phthalocyanine switch operates in the nanosecond regime (i.e., Gigabits per second), functioning as an all-optical AND logic gate. To demonstrate it, we waveguided a continuous (cw) laser beam co-linearly with a nanosecond pump beam through a thin film of metal-free phthalocyanine. The output was sent to a fast photo-detector and to an oscilloscope. The cw beam was found to pulsate synchronously with the pump beam, showing the characteristic table of an AND logic gate."

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Right: A schematic of the nanosecond all-optical AND logic gate setup. More schematics and illustrations are available in "Recent Advances in Photonic Devices for Optical Computing" by NASA/Marshall's Hossin Abdeldayem, Donald O. Frazier, Mark S. Paley, and William K. Witherow.

"Our setup for the picosecond switch was similar, except that the phthalocyanine film was replaced with a hollow fiber coated from inside with a thin polydiacetylene film. Both collinear laser beams were focused on one end of the tube, and a lens at the other end focused the output onto a monochrometer with a fast detector attached. The product of the two beams demonstrates three of the four characteristics of a NAND logic gate."

"Optical bistable devices and logic gates such as these are the equivalent of electronic transistors," concludes Dr. Abdeldayem. "They operate as very high speed on-off switches and are also useful as optical cells for information storage."

According to Dr. Frazier, these 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.

Web Links

"Recent Advances in Photonic Devices for Optical Computing" by NASA/Marshall's Hossin Abdeldayem, Donald O. Frazier, Mark S. Paley, and William K. Witherow. 700kb in Microsoft Word format.

Pushing the Limits of Computer Technology -- Science@NASA headline story from May 1999.

Microgravity News - Winter 1995 report about the Alliance for Nonlinear Optics.