Laser Landmark: Silicon device spans technology gap

In technologies ranging from compact disc players to the Internet, circuits that manipulate electrons operate alongside those that manipulate photons. In their quest for faster and less-expensive devices, engineers have wanted to integrate both types of circuits onto single silicon chips. However, silicon’s optical properties make such a feat difficult.

Now, researchers in California have made a laser from silicon, achieving an important step toward optoelectronic or even purely photonic chips of silicon (SN: 3/6/04, p. 157: Available to subscribers at Silicon goes optical).

“This is the first time that lasing in silicon has been achieved,” says Bahram Jalali of the University of California, Los Angeles (UCLA). “It’s something the textbooks tell you can’t be done.” He and his colleagues describe the new laser in the Oct. 18 Optics Express and the Oct. 25 IEICE Electronics Express.

Microchip-laser specialist Claire F. Gmachl of Princeton University welcomes those reports as “very good news.” The new device “is a big step forward,” she says.

Richard A. Soref of the Air Force Research Laboratory at Hanscom Air Force Base near Boston says that the advance is “significant because lasing has been demonstrated in crystalline silicon . . . at room temperature.”

In a typical laser, electricity or light pumps energy into electrons in the atoms of the lasing material, which can range from gases such as carbon dioxide to crystals such as ruby. Those electrons then shed the energy as light in a coordinated manner to create an intense, 1-wavelength beam of radiation.

In silicon atoms, however, excited electrons generally lose their energy as heat rather than as light. That tendency has defeated efforts to create lasers from the material.

To get around this drawback, Jalali and his colleagues tapped a different atomic response in the celebrity semiconductor. In a process known as Raman emission, incoming energy stimulates atomic vibrations, which then decay, in part, into photons.

To build its laser, the UCLA team applied microfabrication techniques to a silicon chip to create a wire 2 centimeters long and only micrometers across. By pumping light from another laser into the wire, the researchers made the silicon lase at infrared wavelengths. When 8 meters of optical fiber linked the wire’s ends, the light recirculated through the wire, stimulating the emission of more light. Jalali and his coworkers expect to soon replace the clumsy bundle of fiber with a disk-shaped microcomponent that will shrink the laser to a size that will fit on a chip, Jalali says.

The new laser will be the first that fits on a chip and can emit certain infrared wavelengths, Jalali says. Potential uses for such a laser range from detecting chemical and biological agents to transmitting wireless Internet data at ultrahigh rates.

With its present requirement of another laser, the new device falls short of an ultimate goal for a silicon laser—conversion of a microchip’s electric power directly into laser light. Getting there, say Soref and others, will take some time.

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