Departments
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Week of 23 January 1998 |
Vol. I, No. 17 |
Feature
Article
BU researchers create new, blue laser
by Eric McHenry
Although a unique laser developed recently at the BU Photonics Center is blue, its creators are anything but. Their achievement is already causing a stir in the scientific community, and they couldn't be more pleased.
"I would say without any doubt that other universities would be happy to be in our position," says E. Fred Schubert, an ENG professor of electrical and computer engineering who oversaw the research effort that yielded the new laser. When Dean Stocker, a GRS doctoral candidate in physics and Schubert's associate on the laser project, presented a poster with their results at a Materials Research Society conference in early December, it generated so much interest that he was unable to leave on time.
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E. Fred Schubert (left), ENG
professor of electrical and computer engineering,
and Dean Stocker, a GRS doctoral candidate in
physics, study one of the blue lasers they've
created. Photo by Kalman
Zabarsky
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In late 1997, after more than two years of work on the project, Schubert and Stocker felt ready to disclose their conclusions.
"There was a hot period of about four months -- I'd say August to November -- during which we knew we were getting closer and closer," Schubert recalls, "but we had to make sure everything was correct and in its place."
"We had basically no laser results before we moved into the new Photonics Center facility, and then from the time we moved in, everything worked!" Stocker adds with a laugh.
The MRS conference proceedings reported the new laser, and the scientists have since submitted a paper documenting their results to three of the field's top scholarly journals. They anticipate approval of a patent application within about six months, which will enable licensing of the new technology. Such interaction with the private sector is among the Photonics Center's governing objectives, Schubert says, because it rewards successful research with continuing support.
"That's one of the Center's main agenda points -- to license patents and get into commercial enterprises," he says. "Provided that we license this patent, which I think is likely, there will be a revenue flow back to the Photonics Center, which will allow us to do more research."
In support of this particular project, however, cooperation with the private sector has been under way since long before there was a laser to license. A Connecticut-based company called Advanced Technology Materials, Inc., has furnished materials for the project from the outset and will now share in its success.
"They're very excited about it," Schubert says. "They see this as a big step forward, and they will definitely benefit from it. They may even increase their revenue, because there are other companies asking them for the laser samples we've developed."
Schubert's and Stocker's is the first laser fabricated at BU, and the first gallium indium nitride/gallium nitride double-hetero structure laser fabricated anywhere. Composed of extremely small pieces of polished sapphire under even smaller layers of semiconducting crystal, the laser has several distinctive properties that make it a significant discovery.
Lasers generally convert electricity to light with little energy loss, Schubert says. His blue laser, however, is particularly efficient in this regard.
"Doubling the amount of current you're pumping into the laser increases the amount of light it produces by a factor of 35," says Stocker, "and by a factor of 200 at the peak wavelength."
The laser materials also cleave very cleanly, producing the extremely smooth facets that are necessary to control the trajectories of photons, which are what constitute the laser's light beam. Stocker scratches the sapphire and gallium nitride with a diamond, one of the only substances hard enough to make such a cut, then breaks them to create mirror surfaces, off which the photons can bounce, with a roughness of approximately 20 nanometers. That's 20 billionths of a meter, or about 1/4000 the thickness of a human hair. Such successful cleaving is one of the project's definitive discoveries, Schubert says.
"The behavior of this material, sapphire, was really not well documented. There was contradictory information in books. Some said it cleaved, some said it parted, which is another sort of cleaving, and some said it wouldn't cleave at all," he explains. "We've demonstrated not only that the sapphire cleaves well, but that the active material on the sapphire, gallium nitride, produces a minimal roughness."
Schubert calls this cleaving "a very manufacturable technique" and foresees the blue laser itself having many practical and commercial applications.
"We now have the complete optical spectrum -- red, yellow, green, and blue lasers," he says. "Therefore, I think that one application will be color displays. Another will be the next generation CD or DVD [digital video disk]. The CD has been around for 15 years, and the current generation is DVD. But with out doubt, there will be a next generation."
"CDs use infrared lasers," says Stocker. "The DVD uses red, and changing from infrared to red allows you to pack in about four times as much information. So if you switch to blue or violet, you can increase it again by about four times."