UCLA Engineering: UCLA Engineer Magazine

UCLA Scientists Demonstrate First Silicon Laser
Recent Breakthroughs Further Advance the Technology

Lasers made of silicon were long thought impossible by many in the field. But a string of recent breakthroughs - led by researchers in the UCLA Henry Samueli School of Engineering and Applied Science - has turned conventional thinking on its head and renewed interest in the field.

Professor Bahram Jalali in his lab.

Last October, UCLA electrical engineering professor Bahram Jalali and researcher Ozdal Boyraz demonstrated the world’s first silicon laser. The laser exploits the Raman effect, which is used in optical fibers for light generation and amplification. The UCLA breakthrough, as well as more recent work by researchers at Intel and Harvard, could significantly improve computer processing speeds.

“We were excited to be the first to demonstrate that a laser can indeed be made on a silicon chip,” said Jalali, a member of the California NanoSystems Institute. “Our approach uses the natural atomic vibrations of silicon to create or amplify light, which is significant because no special impurity or complicated device structure is needed.”

Silicon lasers could enable the integration of optical and electronic elements on the same chip, and would be relatively inexpensive to produce, as UCLA researchers are using the same type of technology as that used to mass manufacture electronic chips.

The silicon laser developed by Professor Bahram Jalali and his research team.

They can also enable optical wireless communications at wavelengths optimized for transmission through air or even fog, detection of chemicals and biological molecules, and be used in defense systems guarding against heat-seeking missiles.

Jalali and his team recently achieved another first, successfully demonstrating electronic switching of the laser, a key attribute for its use in optical interconnections and optical computing, showing that the device can be electronically controlled and able to carry data.

As early as 2001, UCLA researchers were exploring the possibility of using the Raman effect to overcome silicon’s light emission problems. In 2002, Jalali and his team devised a new way of creating light emitters and amplifiers using the Raman effect in silicon.

Dr. Ozdal Boyraz

Prior to their work, the Raman effect had not been considered for creating silicon optical devices, since several kilo meters of fiber were required to make a useful device, whereas the typical silicon chip is millimeters in size. Through their research, Jalali’s group was able to significantly reduce the fiber requirements, realizing the possibility of a silicon laser.

“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.”

Jalali’s team determined that the Raman effect - or the changes in wavelength for some light photons caused when passing through transparent material - is 10,000 times stronger in pure silicon than in glass, and can be used to amplify data considerably.

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

“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 Technol-ogy 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.”

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.

“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.”

For more about this project, please visit http://www.ee.ucla.edu/~oecs/.

- Marlys Amundson and Christopher Sutton