UCLA Scientists Demonstrate First Silicon Laser

LOS ANGELES, Oct. 26 -- Researchers at the University of California Los Angeles (UCLA) have demonstrated the first silicon laser, which could lead to more effective biochemical detection, secure communications and defense against heat-seeking missiles.

"This development shows that despite popular belief, a laser can indeed be made on a silicon chip," said Bahram Jalali, professor of electrical engineering at UCLA'a Henry Samueli School of Engineering and Applied Science, who led the research team.

"The lack of a silicon laser has been a major roadblock in the progress of silicon optoelectronics and photonics," said Jagdeep Shah, program manager of the Defense Advanced Research Projects Agency Microsystems Technology Office, which funded the research. "The demonstration of a Raman laser in silicon has the potential to lead to new military applications in communications and sensing." Shah is a fellow of the American Physical Society and the Optical Society of America.

Jalali said, "Our approach uses the natural atomic vibrations of silicon to create or amplify light. This is significant because no special impurity or complicated device structure is needed."

This approach, called the Raman effect, is used in optical fibers for light generation and amplification. Until the UCLA research began, it had not been considered for creating silicon optical devices, since several kilometers of fiber are required to make a useful device whereas the typical silicon chip is millimeters in size.

In the past, many researchers have attempted, without success, to create a silicon laser by introducing impurities in the material, or by using exotic and complex device structures. Even if successful, such processes render the device incompatible with standard silicon manufacturing technology. In addition, these techniques generate light only at fixed wavelengths, and often do not correspond to the optimum wavelength for most applications.

While silicon is the so-called "bread-and-butter" material of the electronic industry, said Jalali, conventional wisdom contends that it cannot be used to generate light.

The UCLA researchers exploited several properties of silicon in order to successfully demonstrate their silicon laser device.

"Silicon is a crystal with a well-ordered atomic arrangement, compared to glass fiber, for example, which is amorphous with a random atomic arrangement," Jalali said. "This results in a very strong Raman effect in silicon that can be exploited to create a laser on a chip."

Silicon also has a high refractive index (3.5), whereas glass has a low index (1.5), and the optical energy in silicon waveguides is tightly confined, resulting in high intensity, further enhancing the Raman effect.

According to the researchers, the silicon laser exhibits nearly ideal characteristics and is already producing pulsed radiation with a very high peak power of one watt. Pulsed operation is needed in many detection and communication systems.

"A key attribute of the new technology is that it can produce mid-infrared radiation without any cooling," Jalali said. "This is a drastic improvement over current technology, where antimonite-based material plus cryogenic conditions are required to achieve lasing."

The research team includes UCLA postdoctoral researcher Ozdal Boyraz. Jalali is a fellow of the Institute of Electrical and Electronics Engineers, a trustee of the California Science Center and the author of more than 200 technical publications. He is also a member of the California NanoSystems Institute, a joint effort of UCLA and UC Santa Barbara.

For more information, visit: ucla.edu