Purdue News

October 14, 1991

Blue-Green Lasers Will Bring Improvements In TVs, Compact Discs

WEST LAFAYETTE, IND. — New lasers may soon beam us into a future of smaller, flat-screen televisions and computers, longer-playing compact discs, advanced submarine communications and more.

Research teams at Purdue and Brown universities as well as the 3M Company have developed semiconductor lasers that operate in the blue-green, rather than the red and infrared, area of the spectrum.

"Scientists have been after this type of laser for 30 years," says Purdue's Robert Gunshor, Thomas Duncan Distinguished Professor of Microelectronics. "It's a milestone in laser technology."

Researchers at the 3M Company, located in St. Paul, Minn., announced the development of a blue-green laser device this summer. The Purdue-Brown team presented their device in September at the Fifth International Conference on II-VI Compounds in Japan.

Because the wavelength of blue light is significantly smaller than that of current lasers, the technology can be used to increase storage capacity on compact and computer discs.

"With the blue-green laser device, manufacturers can pack up to four times the amount of information on a single disc," Purdue researcher Gunshor says, noting that the sound quality of compact discs would probably not be affected.

In addition, blue-green laser technology may be used to enhance laser imaging in medical diagnostics and also may speed the use of plastic, instead of glass, in fiber optics.

The technology also holds promise in applications such as undersea communications. Because blue-green light travels easily through seawater, researchers may develop underwater links for better submarine-to-submarine communications.

As a byproduct of their laser research, the Purdue-Brown team has also produced blue-green light-emitting diodes — LEDs — with the highest efficiency to date. LEDs are used in a variety of display applications, such as automobile dashboard panels.

The new blue-green LED devices may be used to replace the bulky, cathode ray tubes now used in TVs and computers, making way for fullcolor, flat-panel displays, Gunshor says.

Both the 3M and Purdue-Brown laser devices were developed from a class of semiconducting materials known as II-VI materials, named for their position in the periodic table. Prior to these developments, laser devices were created from elements from the third and fifth columns of the periodic table.

Gunshor says scientists have been working to develop devices from II-VI materials since the 1960s. Early research was hampered, however, because conventional methods of growing the materials produced defects that inhibited their electrical capabilities.

In the early 1980s, a new technique of manufacturing semiconductors was developed that allowed scientists to produce structures in very thin layers, one atom in thickness. With this procedure — called molecular beam epitaxy — researchers had a new tool to develop semiconducting materials.

Using this layer-by-layer method, scientists at Purdue fabricated the materials from which the Purdue-Brown blue-green laser was constructed. The 3M device was constructed in a similar fashion by a team led by Charles Walker, 3M corporate scientist in charge of the company's Photonics Research Laboratory.

The new semiconductor lasers were designed to be integrated with gallium-arsenide semiconductors, which are used in state-of-the-art electronics.

The new laser device looks like a small crystal set on a microchip. The device is patterned into several sections, each of which is capable of emitting a bright blue-green beam of pulsed laser light. Though the beam appears constant to the naked eye, the device is pulsing and is actually on less than one percent of the time.

Gunshor says further engineering developments are necessary to eliminate the pulsing and make the new lasers operate continuously at room temperatures.

"I wouldn't be surprised if in a year's time this would be a more practical device, one that could be incorporated into consumer and high-technology electronics," he says.

The milestone reached by the Purdue-Brown team drew on important basic discoveries at other collaborating institutions, including, University of Notre Dame, Harvard University, North Carolina State University, the Massachusetts Institute of Technology and Rensselaer Polytechnic Institute. The seven institutions make up a consortium directed by Arto Nurmikko, professor of engineering and physics at Brown.

The consortium is supported by funding from the Defense Advanced Research Projects Agency. In addition, the research at Purdue received support from Indiana's Business Modernization and Technology Corp. through Purdue's Optoelectronics Research Center, and the U.S. Air Force Office of Scientific Research.

Purdue News Service: (765) 494-2096; purduenews@purdue.edu