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January 24, 2002

PHOTONICS: At the speed of light

In his newly renovated lab in Old Engineering Hall, David W. Snoke of Pitt's physics department is running a "time arrival" experiment. He's measuring how long it takes photons (electromagnetic particles having zero mass, no electrical charge and indefinitely long lifetimes) from a laser pulse to reach an assigned destination.

The wait isn't long.

"The whole experiment is over in a few trillionths of a second," the assistant professor explains. "But then we repeat it many millions of times."

It only seems that photonics itself — the technology for generating and controlling light — is moving ahead equally fast, both scientifically and commercially.

Photonics includes such diverse, high-tech specializations as optical imaging (spy and weather satellites, night vision, holography), optical detectors (supermarket scanners, medical optics, nondestructive evaluation of materials), lasers (laser surgery, welding lasers, etc.) spectroscopy (chemical analysis and detection, optical fingerprinting) and one of the areas relevant to Snoke's research, optical communications (including fiber-optics and infrared links).

Among its other applications, photonics offers the best hope for building ultra-fast personal computers and unclogging Internet traffic, which has been doubling in volume every year.

As Snoke points out, today's high-speed telecommunications networks are electro-optic hybrids. "The state of the art right now still relies on electronics to send ultrafast light signals over fiber-optic cables, and then convert those light signals back into electrical signals on the receiving end," he says.

"One of the holy grails of photonics is to develop all-optical networks, speeding up the communication process by eliminating the need to convert light signals into electronic ones."

Speed in the telecommunications business is "a bit of a misnomer," Snoke adds. "Electrical signals travel at about two-thirds the speed of light, so it's not the speed of going from here to there that matters so much, it's the bandwidth: how fast you can modulate or change a signal's frequency."

The bandwidth of a telephone signal is about 25 kilohertz, or 25,000 cycles per second. Radio communications are measured in megahertz. State-of-the-art computer processors such as the Pentium, which are still based on electronics, max out at about a gigahertz, or 1 billion cycles per second. "You'll notice, if your computer has one of the newest Pentiums, that there's a huge fan blowing heat out of the back of your computer," Snoke says. "The electronics are generating a huge amount of heat."

All-optical computers — which may be a decade or two from reality, Snoke believes — might have peak bandwidths of a terahertz, or one trillion cycles per second, and would generate much less heat.

In fall 2000, Pitt became one of a handful of universities to launch an academic program in photonics (in Pitt's case, an undergraduate certificate program), with Snoke as director. "Since that time," he says, "I've found that there is a lot of research on optics and photonics going on around campus that I wasn't aware of before, because we're scattered in so many departments — physics, chemistry, electrical engineering and others."

Among Pitt's other photonics researchers is physics professor Hrvoje Petek, who hopes by this summer to create a unique microscope that employs a laser emitting pulses lasting just 1 billionth of a second. "The laser will act as an extremely fast strobe to excite the electrons in metals or semi-conductors," Petek says. "The microscope will then record images of the dynamics of these electrons."

Studying the movements of electrons through solid materials should lead to the production of better microprocessors and microelectric circuits, says Petek, who plans to teach several topics in Pitt photonics program courses.

Arts and sciences Dean N. John Cooper called photonics "one of those interesting interdisciplinary areas that combines really deep basic research in physics and chemistry with technological applications. It's a natural way to think about what otherwise might be seen as disconnected [faculty] hires in several departments and to also bring those research resources into the undergraduate photonics program and the doctoral programs in chemistry and physics, by showing how the bits go together to form a really very exciting whole.

"I think photonics is a natural future focus for both physics and chemistry. It gives us a focus and puts us ahead of the curve in solid state chemistry and condensed matter physics."

— Bruce Steele

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