IBM slows down light signals in chips

Researchers at Big Blue have published a paper demonstrating how optical signals--photons that represent data--traveling within a microprocessor can be delayed, a key element in developing chips that can relay signals with optical fiber.

Intel, IBM and relative newcomers such as Primarion and Luxtera are trying to devise ways to replace the metal cables that connect chips inside computers, as well as wire connections inside chips, with optical components. Optical technology consumes much less energy. Plus, it doesn't generate heat, and it can transfer signals faster than metal wires.

Designers often refer to optical component design as a black art that defies easy mastery. Currently, optical components are typically made out of "exotic" materials such as gallium or indium compounds.

Ideally, companies experimenting in this arena want to make these chip-size optical components out of silicon wafers to keep the cost low. Among other parts, Intel and others have produced silicon lasers and waveguides--structures that guide waves, whether electromagnetic, light or sound. But these companies have not yet integrated the lasers and waveguides into commercial products.

IBM's latest contribution is slightly different than many of the earlier breakthroughs. It seeks to slow down the flow of signals so the transfer of information remains controlled and synchronized.

To delay the signals, the light passes through a "microring resonator," which is a waveguide looped into several circles rather than a straight line. Because the light has to travel much farther than it would if the waveguide directly connected two points, the data traffic can be buffered.

The circular design also means that the waveguide is small enough to integrate into a chip. Because of all of the traffic loops, roughly 10 bits of optical information can travel simultaneously within a space, taking up 0.03 square millimeters.