By J.R. Wilson
The question of whether the future may see an all-optical or photonic computing environment elicits a wide — and often negative — response, as commercial and military systems designers move to incorporate fiber optic networks into current and next-generation systems.
Jay Betker, director of business development and engineering at ITT Industries Cannon in Santa Ana, Calif., says only engineers at Lucent Labs have been seriously investigating 100 percent photonic computing — "and that is a long ways out there."
Meanwhile, Dave Einstein, technology manager for the optical networking group at Lucent Technologies Integrated Network Solutions in Holmdel, N.J., places it "in the realm of science fiction."
Then again, David Eastley, parallel optics product manager for Agilent Fiber Optic Products Division in San Jose, Calif., says he believes "the prospects for all-optical computing are good, but the timeframe is the $64,000 question."
The military interest in optical computing is simple: speed. Logic operations in today's computers are measured in nanoseconds, but the promise of photonic computing is speeds of 100,000 times faster. And with the possibility of optical networking systems capable of moving data at 600 gigabits per second, such computer speeds — well beyond the capabilities of silicon — will be necessary.
What actually constitutes an optical computer?
"Optical computers will use photons traveling on optical fibers or thin films instead of electrons to perform the appropriate functions," says Dr. Hossin Abdeldayem, a NASA physicist working on the problem at the Marshall Space Flight Center's Space Sciences Laboratory in Huntsville, Ala.
In the optical computer of the future, electronic circuits and wires will give way to a few optical fibers and films, making the systems more efficient with no interference, more cost effective, lighter, and more compact, he says.
Optical components would not need insulators between electronic components because they do not experience crosstalk. Several different frequencies (or different colors) of light can travel through optical components without interfacing with each other, allowing photonic devices to process multiple streams of data simultaneously.
The speed of such a system would be incredible, capable of performing in less than one hour a computation that might take a state-of-the-art electronic computer more than 11 years to complete.
Dr. Donald Frazier, head of the NASA research team at Marshall, says interest in optical computers waned in the 1990s due to a lack of materials that would make them practical.
Still, he says, optical computing is enjoying a resurgence today because new types of conducting polymers are enabling smaller transistor-like switches that are 1,000 times faster than silicon. In addition, research in Germany has demonstrated, contrary to previous belief, that data can be stored in the form of photons. Even so, he does not expect an actual working desktop computer for another 15 years.
"We're taking baby steps," Betker agrees. "Mercury Computers [of Chelmsford, Mass.] is the cutting edge of military-grade processing and is wildly successful with massively paralleled RACE technology computers. They are discrete semiconductor-based architectures put into parallel, but if you get inside their computers, they pick up optics on board-to-board at the backplane. No one has backplane interconnects that can operate above 10 gigabits per second, so when you get to those Mercury is producing for the Joint Strike Fighter, they have to move to optics to move data from board to board.
"All optical switching and routing can be almost as important as computing when you look at network architectures of the future" Betker continues. "When you look at terabit or petabit routers, those are being done in all-optical architectures that never convert it to an electrical signal. I would think all-optical switching and routing is five years away, but I wouldn't want to conjecture about all-optical computing."
Despite the German research, Einstein says the basic problem remains the lack of a reliable optical memory mechanism — or how to store a computational result photonically.
"It always has to be put on some form of physical media. Until you have optical memory, it is difficult to do fully optical computing," he says. "There are people working those issues, but it is nowhere close to commercialization."
Eastley may be among the most optimistic prognosticators, saying he would not expect to see all-optical computing before 2008.
"We will have one additional generation between now and then where this interconnect technology will move closer to the processor," Eastley says. "The generation beyond that will potentially start to have microprocessors with integrated technology for optical interconnect. The real unknowns between now and then are how to form this type of interconnect — how would you arrive at a mix of materials, some silicon, some exotic," he says.
"Other considerations are actual deployment," Eastley continues. "If you look at the architecture of a PC today, with a motherboard and traditional bus, will the future be embedded waveguides in a printed circuit board or some type of freespace interconnect or are we still going to see traditional receptors and connectors? A lot of that will be up to companies like Intel and AMD that drive the next-generation microprocessors."
There is one other key question facing computer designers, especially for the U.S. military, Eastley says: will photonic computing follow the same developmental path as did the computers and components are manufactured today?
"A key fundamental step is to determine how those new architectures will migrate with the current model," he says. "The PC market is really served today by Taiwanese contract manufacturers — which may be moving to mainland China. That may leave Taiwan as the next generation high-end PC community, with the older technology making the move to the PRC."
