BioEd Online

A silicon laser than produces a continuous beam of laser light has been unveiled. This is an important milestone in the quest to create computers that can easily switch from using electrical currents to using light.

Laser light is already used to carry information along optical fibres, but data crunching inside computers relies on electrical circuits. Turning a current into light requires expensive components that slow the computing process, so researchers want to make a silicon laser than can be included in microchips during normal manufacturing.

But silicon has always stubbornly refused to generate a steady laser beam. Semiconductor lasers have been made using relatively exotic materials such as gallium arsenide, but "these devices are expensive and incompatible with silicon-based circuits", says Haisheng Rong, who worked on the study and is a physicist at the computer-technology company Intel in Santa Clara, California.

"Our silicon laser runs continuously at room temperature for as long as the power is on," says Rong, whose results are published in this week's Nature¹.

"This is a significant advance for the development of practical silicon lasers," comments Jérôme Faist, a physicist at the University of Neuchâtel in Switzerland.

Pumped up

Rong's chip produces laser light when it is 'pumped' with another laser. Silicon tends to absorb most of the laser light as soon as it is generated, dispersing the energy as vibrations between the atoms in the crystal. So the researchers added a 1.5-micrometre-wide ridge that snakes in an S-shape through the chip. This confines the light without absorbing it. The ridge is embedded in a diode that draws away electrons that might otherwise disrupt the beam.

Much more research is needed before a commercial silicon laser could be produced, says Rong. The energy needed to create the laser beam, for example, must eventually come from an electrical signal and not an external laser.

But Rong adds that the device is an important proof of principle. It also opens up the possibility of creating low-cost infrared silicon lasers that could be useful in medical imaging.

Steady progress

The team's breakthrough follows hot on the heels of its previous paper, published in Nature last month, which showed that silicon could produce very short pulses of laser light, mere nanoseconds long².

The first report of a pulsed silicon laser (see " First silicon laser pulses with light") came just before that in October 2004, but the device required 8 metres of optical fibre cable to loop part of the laser light back into the front of the silicon crystal³.

Bahram Jalali, the physicist from the University of California, Los Angeles, who developed the first pulsed laser, says: "I think Intel's report is a significant achievement because continuous operation is a major milestone in the development of any new laser."

"Silicon-based photonics has developed rapidly in the past few years," adds Rong, who hopes that his team's achievement will give other groups working in the area a boost.