Tiny Device Stores Light

Continued from page 1

By Prachi Patel

Friday, December 22, 2006

By connecting many rings, the researchers can build up the delay. With 56 rings connected to a common silicon wire, they get the longest delay: about half a nanosecond--which amounts to storing 10 optical bits--at a data speed of 20 gigabits per second.

Other researchers have made resonators on silicon before. But the smallest resonators so far have been about 100 micrometers wide, and cascading tens of them yields a device that is a few millimeters long--too big to be integrated into an electronic circuit. The IBM researchers make rings that are 12 micrometers in diameter, and they can fit up to 100 ring resonators into an area that is less than one-tenth of a square millimeter.

The size of the device is a major advance, Bergman says: "It is very close to the kinds of densities you would like to have on chip for optical interconnects." Achieving a delay of 10 bits at gigabits-per-second speeds, which would be typical of the data speed that optical interconnects of the future would be handling, is a breakthrough, she says. "This is a major step towards making optical interconnects a reality."

The device loses more light than would be acceptable in practical circuits, and Vlasov says that he and his team are working to reduce these losses. Once they do that, he says, they could put thousands of resonators together to store even more optical bits. For practical optical interconnects, you would need to store hundreds and thousands of bits.

It might take another 10 years before we see optical interconnects in computers, but the IBM research shows that the technology is viable, says Risto Puhakka, president of market-research firm VLSI Research, in Santa Clara, CA. "There are legs on this technology, and it could eventually be integrated with current circuits into chips."