Germanium Laser Breakthrough Brings Optical Computing Closer

Researchers at MIT have demonstrated the first laser that uses the element germanium.

The laser, which operates at room temperature, could prove to be an important step toward computer chips that move data using light instead of electricity, say the researchers.

“This is a very important breakthrough, one I would say that has the highest possible significance in the field,” says Eli Yablonovitch, a professor in the electrical engineering and computer science department of the University of California, Berkeley who was not involved in the research told Wired.com. “It will greatly reduce the cost of� communications and make for faster chips.”

Even as processors become more powerful, they’re running into a communications barrier: Just moving data between different parts of the chip takes too long. Also, higher bandwidth connections are needed to send data to memory. Traditional copper connections are becoming impractical because they consume too much power to transport data at the increasingly higher rates needed by next-generation chips. Copper also generates excessive heat, and that imposes other design limits because engineers need to find ways of dissipating the heat.

Transmitting data with lasers, which can concentrate light into a narrow, powerful beam, could be a cheaper and more power efficient alternative. The idea, known as photonic computing, has become one of the hottest areas of computer research.

“The laser is just totally new physics,” says Lionel Kimerling, an MIT professor whose Electronic Materials Research Group developed the germanium laser.

While lasers are attractive, the materials that are used in lasers currently — such as gallium arsenide — can be difficult to integrate into fabs.

That’s given birth to “external lasers,” says Yablonovitch. Lasers have to be constructed separately and grafted on to the chips, instead of directly building them on the same silicon that holds the chips’ circuits. This reduces the efficiency and increases the cost.

A germanium laser solves that problem, because it could in principle be built alongside the rest of the chip, using similar processes and in the same factory.

“It’s going to take a few years to learn how to integrate this type of laser into a standard silicon process,” says Yablonovitch. “But once we know that we can have silicon communication chips that have internal lasers.”

Eventually, MIT researchers believe germanium lasers could be used not just for communications, but for the logic elements of the chips too — helping to build�computers that perform calculations using light instead of electricity.

But University of California, Berkeley’s Yablonovitch says it is unlikely that light will replace electricity entirely. “I think we will be using light in conjunction with electronic logic circuits,” he says. “Light allows internal communications much more efficiently, but the logic elements themselves are likely to remain driven by electricity.”

Graphic:Christine Daniloff/MIT