Light: Driving the Next Computer Revolution
by John Gagnon
Dr. Peter Moran has the best of two worlds.
An assistant professor jointly appointed in materials science and engineering and the physics department, he uses both disciplines in his work-which he loves. "I get paid to think," he says.
He and a colleague, associate professor Dr. Miguel Levy (also jointly appointed in physics and materials science/engineering), have been doing some interesting thinking lately as they investigate a man-made material with some unusual mechanical and optical properties. Moran describes their inquiry as "uncharted territory."
The two researchers work in three worlds: that of microns, nanoscale, and atomic scale.
Devices on silicon chips are in the micron world (one-tenth the diameter of a human hair, or one-millionth of a meter); a nanometer is one-thousandth of a micron-10,000 times smaller than the diameter of a human hair.
The nano-world is in kind of a limbo; scientists know more about the atomic world and the micron world than the nano-world.
Moran and Levy bridge all three as they study PZN-PT, a crystal which is comprised of the oxides of lead, zinc, niobium, and titanium.
The material has an unusually large piezoelectric property; that is, it changes dramatically in size when a voltage is applied. That characteristic is useful for making tiny mechanical devices like motors, valves, pumps, and mirrors.
Levy and Moran are studying the "massive" piezoelectric effect of this material on the atomic level in order to understand how to apply it on the micron scale. Michigan Tech is one of the handful of universities in the country with the facilities to conduct the necessary experiments, Moran says.
The material also has interesting optical characteristics. Levy and Moran, who recently demonstrated the first optical waveguide in PZN-PT, are on the "leading edge" of figuring out how this material can be used on the nanoscale to create new devices that manipulate light. (The wavelength of visible light is on the order of a few hundred nanometers.)
Levy says the immediate technological "driving force" for their work is "smaller, cheaper, and more powerful" ways for handling information in telecommunications.
Devices that manipulate light can used to "imprint" information on a light signal traveling down a waveguide or optical fiber—just as the components of an electrical computer "imprint" information on an electrical signal traveling down a wire.
Although an all-optical computer would potentially be much faster than today's fastest electrical computers, it is not an imminent prospect. Levy says that optical computers are "far-removed" from today's science. Moran agrees.
"You're not going to see an optical laptop anytime soon. We're not making optical chips."
Moran says their work is basic science: understanding how and why these materials work, how to make them, and how to process them into nanoscale optical devices.
Their initial approach is to "carve out" periodic arrays of tiny PZN-PT "pillars," spaced a few tens of nanometers apart. These arrays are called "photonic crystals."
The unusually large piezoelectric effect in PZN-PT will allow the scientists to change the spacing between the pillars in the array by applying a voltage-and thus be able to steer and modulate a light signal. (Picture a roomful of mirrors, precisely arranged, directing light around.)
"There's a fair amount of work to be done just in figuring out how to make these photonic crystals," Moran says.
They first slice off a thin film (on the order of 10 microns) of the single crystal PZN-PT, using a method pioneered by Levy. They then bond the film to another substrate.
These films are about the thickness of a human hair, which makes for delicate work. The films must be smooth and uniform-what Moran calls "a few atoms rough"—which is tantamount to plowing flat the land from New York to San Francisco.
They then bombard the film with ions to carve out the photonic crystals. At that point, Moran says, "some very exciting fundamental science" begins. It's cutting-edge stuff, literally.
One unknown: how the piezoelectric and optical properties of the nanoscale structure will differ from those of the bulk material. "No one knows how they will work in practice because nobody has made them before," Moran says.
The research is funded by the Office of Naval Research, which has provided $510,000 for three years of work.
Moran can see far beyond even that. The development of a whole new class of devices, the building of a unique nanoscale fabrication infrastructure, and the expertise that the two researchers are developing at MTU—all of it could easily add up to a decade or more of projects, he says. He is excited about where the work might lead.
"The most exciting thing about doing something completely new is that you're never sure where the results of your efforts will take you," he concludes.