Light fantastic.
In addition to between-chip communication, painted lasers could connect components on the same chip, as depicted in this artist's rendering.

Trevor Johnston / University of Toronto

Paint-On Lasers

To most people, a laser means eyeball-scorching rays of light shooting out of a bulky box or a pointer pen. But a new type of laser can literally be painted onto any surface, including silicon chips. The development could help save the multibillion-dollar computer chip industry from a looming crisis: the point when microchips can't get any faster.

The chips that make up a computer keep getting speedier, but actual performance of the whole unit lags behind. That's because the system is only as fast as its slowest part, and the copper wires currently used to connect silicon computer chips can't keep up. The gap between chip speed and performance continues to grow, and by 2010, copper wires could reach their limit. Lasers are a logical replacement because the pure light they produce travels so quickly. Many research groups are working to create a laser on a chip (ScienceNOW, 18 April 2005), but success has been limited. The trick is to make one that emits the right type of light, is compatible with silicon, and runs on electricity.

Now, a team at the University of Toronto in Canada has demonstrated the first laser to come close to meeting these conditions. The researchers suspended quantum dots--nanometer-sized particles of semiconductors--in a liquid and painted the suspension on the inside of a tiny glass tube. "It's just a goop that you splash on," says Ted Sargent, a nanotechnology researcher and the lead author of the study published 17 April in Optics Express. The substance can be applied to anything, including silicon, and the particles are the perfect size to emit infrared light, the wavelength needed in telecommunications.

One drawback is that the new laser must be powered by an external laser, which makes it too expensive to be integrated into computer systems at the moment. But it's made with a type of semiconductor that has the potential to be driven electrically, says Sargent, and it may be possible to use the electronics already found on microchips to run this laser in the future. "With the leaps and bounds people have made in improving the flow of electricity through paint-on films similar to ours, I have optimism that it's feasible," he says.

The development is indeed cause for optimism, says Philippe Fauchet, a silicon optics researcher at the University of Rochester in New York, but at this stage it's just a proof-of-concept. "It's going to be hard work to make it practical, but it's not impossible," he says. What Fauchet finds most striking about the new laser is that the wavelength, or color, of the light doesn't change with temperature. "This is a very encouraging result," he says, especially if you want your computer to work just as well in Canada as in the Arizona desert.

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