of combining the television

and telephone into a two-way communications system seemed to make a great deal of commercial sense, people called these devices “picture-phones.””

Though a few not terribly impressive prototypes could occasionally be glimpsed at fairs or on TV, they never quite made it to the mass market. This was because the cables that carried the nation’s telephone traffic couldn’t handle the load created by high-resolution, home-to-home video signals. Laying in the required wiring would have threatened to deplete world copper resources while blocking out the skies or choking the earth with thick webs of coaxial cables.

Today, researchers at USC’s 18-month-old Center for Photonic Technology are working intensively on lightwave technologies that may lead far beyond the simple idea of cheap home video telephones, into areas such as the design of machines capable of intelligently interpreting visual images.

Or, a bit farther up the line, they envision truly functional optical computers, which will rely upon lightcarrying photons instead of the charged electrons presently used by digital machines. Such computers, they believe, could conceivably make short shrift of the ongoing Japanese bid for computing supremacy through the development of a “fifth generation” system.

Researcher Stephen R. Forrest, who left Bell Laboratories last year to join the School of Engineering faculty, is spending much of his time, lately, contemplating an assortment of unusual semiconductors: unusual because of the way in which they interact with and manipulate optical signals.

The trick is to discover a compound out of which cheap optical analogs to

/ n the 1950s when the idea

the silicon microchip can be manufactured. Neither Forrest nor his colleagues at the center are entirely sure how these components will ultimately be made. But they know that without them, the photonic technology they envision will never really take off.

This would be tragic because photons have a great deal to recommend them over electrons. Both, of course, can be used to carry information; but electrons, because of the way they interact, tend to create unwanted crosstalk and electromagnetic interference. Photons, however, do not interact with one another. Beams of light can pass through each other with no measurable effect. Light-conveying optical fibers can lie next to each other without creating adverse effects in the process.

Moreover, the speed of electronic signals is limited by both the properties of electrons and the circuits in which they travel. But optic fibers have

Graduate student Greg Kavounas eases between laser beams to adjust a deflector in an experimental optical switch. Here a blue beam is split and refused in a nonlinear optical crystal.

greater potential bandwidth, which implies greater information-carrying capacity.

Nor need photon particles be confined to a wave-guide—the optical equivalent to a wire. Unlike electrons, they can travel freely in space. And because photonic broadcast is possible from one point to many, arbitrary communications could be achieved without the usual tangle of wires inherent to an electronic network.

In the field of computing, photons promise to greatly enhance parallel processing capabilities, which are presently limited in electronic computers by their primarily sequential architectures.

Of course, the aversion photons demonstrate toward interaction makes it inordinately difficult to harness them for practical usage. Light beams cannot be used directly to modulate or switch each other, and therefore must rely on an intervening active medium for these

by Sheldon Teitelbaum

functions. Hence the search for an optical chip prototype.

Center faculty have chosen to pursue optical chip concepts based on a family of semiconductor compounds called “III- IVs" since they are comprised of elements from columns IIT and IV of the periodic table of the elements. One such compound, gallium arsenide (GaAs), and its close relatives have been the subject of intensive research and development for use in ultra-small semiconductor lasers and detectors. These components currently form the basis of the entire fiber optics industry.

GaAs may not be the most ideal substance for active photonic functions, but it seems to work reasonably well with both photons and electrons. This is important because the initial applications of photonics will likely incorporate both photonic and electrical functions.

it not necessarily ideal substance indicative of the center's underlying philosophy, which places an unusual premium upon practicality and cooperation.

Its director, Daniel Dapkus, professor of electrical engineering and materials science, is also a Bell veteran. “Too many researchers,” he explains, “use materials that they believe will best suit their immediate needs. So each one comes up with a different device, which in turn is made from a different material, which cannot be used for other devices.” This situation is analogous, he says, to what might occur if computer manufacturers decided to produce devices and software that were not compatible with any of the other systems being produced on the market.

“Our view,” he says, “is that this

[es search for a widely applicable is

by Sheldon Teitelbaum

isn’t the right approach. If it keeps up there'll never be enough time or money in the real world to develop an applicable photonics technology.”

This penchant for a bottom-line approach to photonic technology development is also shared by Armand R. Tanguay, Jr., in many ways a driving force at the center. Unlike Dapkus, Forrest or William H. Steier, the center’s previous director, Tanguay did not come out of Bell Labs. But he, like his faculty colleagues, is appalled by what he views as the wastefulness of American academic research.

“T'm not too long out of school myself,” he says, “but I've already become tired of the kind of research we typically end up doing.”

Most scientists, he says, work themselves raw “chasing the best, most profound idea they can come up with,” never worrying if that idea can ever really mean something.

“For example,” he says, “we've been doing intensive research on a particular kind of spatial light modulator at my lab ever since I was a graduate student. That's 13 years that I've devoted to trying to understand this one device. Although we’ve learned a tremendous amount from these investigations, we've also discovered that this device may never become incorporated in operational systems, primarily because it has not proved to be manufacturable.

“What we're trying to say here is that there are lots of best ideas. So why not choose the ones that can have an impact on the systems that are going to come into being over the next 15 to 20 years?”

he Center for Photonic Technology was established a year and a half ago when, says Forrest, “‘it became apparent that we have an anomalously large group of people at USC who are involved in photonics.”” “There's been an underlying feeling for a couple of years,” adds Dapkus, “that although we had people like Alexander Sawchuk, Elsa Garmire and Anupam Madhukar, each of them very well known in the field, we just weren't having the impact, as a school, that we thought we could have.”” These faculty members, each of them independently funded, subsequently set out to create a center

dedicated to intensive, crossdisciplinary research. Its goal was nothing less than the rapid realization of a generic, photonic technology with wide applicability to problems such as local area network switching, communication system sources and detectors, signal processing and conditioning, silicon microchip enhancement, optical informational processing and, of course, advanced computational systems.

Today, the center has a core group of some 10 researchers from the departments of materials science, physics and electrical engineering.

Tanguay believes that the center will be able to ensure rapid progress in these areas only by promoting cooperation and coordination among faculty members and graduate students whenever possible.

“The degree of faculty collaboration

Tanguay, Forrest, Dapkus and (seated) Steier: A group of faculty set out to create a center dedicated to intensive, cross-disciplinary research, with the rapid realization of a generic photonic technology as their goal.

Ph.D. candidate Julia G. Johnson, a photonic technology center fellow, loads a thermocouple into one of the lab’s liquid phase epitaxial crystal growth systems. The materials grown here are used to construct integrated optical receivers, which change light signals into electricity.

here at USC is unique,” he says. “For example, I’ve published about an equal number of papers with other faculty members as I have by myself, purely as a result of this.”

Steier adds that the center’s future ability to solicit government block grants will depend, in great part, upon the mechanisms for cooperation now being thrashed out.

“When you're funded by such grants, you're expected to interact,” he says. “They evaluate you on how well you do it. So this way, in marked contrast to the loner, entrepreneurial spirit that has governed most American research to date, the encouragement to coordinate will be coming from both above and below.””

Of course, common sense will also play a role in governing the discourse prevailing at the new center. Few of the researchers who work there, whether from the systems, materials or device end of photonics, can escape the very real physical limits to what they can accomplish. Tanguay, for instance, has proved a theorem which demonstrates that the achievement of high resolution, high sensitivity, high frame rate and high dynamic range in spatial light modulators “‘is absolutely impossible.”

Determining these limits is probably one of the more important tasks the center has taken on. It helps detour researchers from entering blind alleys while encouraging them to find clever ways to avoid encountering the limits altogether.

orative efforts with private companies. The idea is to develop an “industrial partners” scheme geared toward encouraging private funding for generic research over the broad base of photonic technology,

They are also eager to engage corporate researchers in cooperative endeavors. Dapkus envisions an ideal relationship coming out of this: ‘We'll provide the more far-out research directions,” he quips, “and they'll provide the damper—the real world insight.”

So far, verbal commitments have been received from five companies. The target is 15. But Dapkus, who has been on the industrial as well as the academic side of the table, senses an enthusiasm for the center and its approach which he thinks answers the critics within the scientific community who argue that a genuine photonic technology, comparable with presentday electronics, is basically unrealizable.

Adds Forrest, ‘When you see these deep divisions among scientists before a system has even materialized, this means that there are still fundamental issues to be determined. It gives you a sense of the distance that has to be covered before you can get a practical system going.

“The fact that we're receiving encouragement from industry means that most people recognize the potential for progress in this field.” 0

E he center is also pursuing collab-