Every second that passes, untold trillions of light pulses carry voice and data traffic through the worldwide telecommunications network, yet the telephones, computers and other devices at the end of the line are, for the most part, electronic. Newly appointed faculty member Joe C. Campbell was instrumental in devising the critical component, called a high-speed avalanche photodiode, that changes photonic signals into electronic signals extremely quickly, reliably and with very little noise or distortion. For this achievement, Campbell was named to the National Academy of Engineering.

This year, Campbell joined the University as the Lucien Carr III Professor of Engineering and Applied Science at the University of Virginia in the Charles L. Brown Department of Electrical and Computer Engineering. His appointment is the first in a Board of Visitors’ initiative to raise the standing of science and engineering at the University by bringing 10 researchers of National Academy caliber to Grounds. “We are seeking researchers who have the capacity to transform reality—to vastly improve the quality of life at all levels of society with their inventions and discoveries,” comments Ariel Gomez, vice president for research and graduate studies. “Joe Campbell is a researcher of this caliber.”

Better Detectors, More Wavelengths
Campbell brings with him an extensive research agenda—and a team of graduate students and postdoctoral fellows to push it forward. “Essentially, everything we do involves converting light into large electrical signals,” he says. Campbell has projects under way that span the light spectrum, from ultraviolet to infrared. For instance, he is working with the Defense Advanced Research Projects Agency to create highly sensitive detectors that can pick out the characteristic ultraviolet signature of a missile plume in the midst of the radiation that pours from the sun. Such detectors might also be adapted to pinpoint airborne biological agents. Certain biological compounds fluoresce when excited by an ultraviolet laser. “If you could look at

“The hiring of Joe Campbell is the first step in a strategy to transform scientific research here and to position the University of Virginia as a preeminent research institution in science and engineering.”

—John T. Casteen III
President of the University of Virginia

emissions at two or three wavelengths and evaluate the ratio of signals, you could get a sense of the type of biological agent that is in the air,” Campbell says. These detectors could be used in buildings and public spaces, as well as on the battlefield.

Campbell is also exploring the possibility of developing a communications system that turns a drawback of ultraviolet light—its tendency to scatter—into a virtue. Because it scatters, ultraviolet light could carry signals around a corner, but receivers would have to be extremely sensitive to pick them up. Campbell and his students are working to achieve that level of sensitivity, setting the stage for short-distance, non-line-of-sight communications.

On the other side of the spectrum, Campbell is involved in a collaborative effort to create a new way of detecting infrared radiation. Current systems used for night-vision goggles and military tracking devices have detectors based on mercury cadmium telluride, an excellent detector but a difficult compound to work with. Campbell’s approach is to use quantum dots: minute pyramid-shaped collections of semiconductors that allow electrons to be uniquely trapped and measured. “We are hopeful that this technology will ultimately displace mercury cadmium telluride,” Campbell says. “We can now detect pretty easily in the 8- to 12- micron range. In the meantime, we are learning a lot of science—and that in itself is exciting.”

Improving the Signal-to-Noise Ratio
The critical challenge in developing faster, more sensitive avalanche photodiodes is managing the signal-to-noise ratio. Depending on the application, Campbell feels free to work on both elements of the ratio. Much of the noise produced by current photodiodes is created by the random nature of the amplification process. The number of electrons produced by a single photon is variable. To reduce noise, Campbell and his students are developing detectors that provide more consistency in amplification.

Another approach to increasing the signal-to-noise ratio is to increase the power of the signal, but this approach causes the bandwidth to degrade. Two of Campbell’s graduate students developed new photodetector structures that can accommodate the additional power. Such detectors could be used to link the remotely phased array antennas used in satellite communications.

Looking for the Next Big Challenge
These are but a sampling of the projects that Campbell is orchestrating. Their sheer breadth and number underscore the energy and creativity that underlie his success. Campbell’s decision to come to U.Va. after 17 years at the University of Texas is yet another reflection of a lifelong affinity for new challenges. “Things had gone well for me at Texas,” he says. “I was very comfortable there. I thought I could use the disruption of coming to U.Va. to

form new collaborations and move in new directions.”

And make no mistake about it, it was a disruption. In December 2005, Campbell and his students disassembled a $3 million laboratory weighing more than 44,000 pounds and reassembled it in Charlottesville. It was up and running by mid-February, and the first publishable results from research conducted at U.Va. have just been gathered.

The determining factor in Campbell’s decision to come to U.Va. was the commitment that the University has demonstrated to building world-class programs in science and engineering. “I’ve long known of U.Va. as a special place and a first-rate university,” Campbell said of his reasons for coming to Virginia. “What particularly impressed me was the University’s vision for the future in research and the energetic initiatives in place to move up in the rankings. I want to be a part of that.”

Campbell’s decision marks the beginning of a new era at U.Va. As University President John T. Casteen III notes, “The hiring of Joe Campbell is the first step in a strategy to transform scientific research here and to position the University of Virginia as a preeminent research institution in science and engineering.”