Intel connects chips with optical fiber

It's going to take a number of years, but optical fiber is going to get inside your PC.

Intel's Components Research Lab is working on ways to replace copper wiring between motherboards and chips inside computers with faster, more energy-efficient optical fiber.

The lab has created a prototype system with chips connected to each other through eight optical channels, transferring data at more than 1 gigabit of data per second for an aggregate bandwidth of more than 8 gigabits per second. The individual channels, called waveguides, can transfer data at up to 3gbps.

That's slower than conventional optical technology--and even some standard connections in PCs today--but the entire unit is housed inside a chip package and should be cheaper than current optical parts. And eventually, it will speed up, Intel said.

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The effort is largely aimed at dodging some of the looming problems with metal interconnects and buses. Channels in PCI Express--a faster connection for shuttling data within a PC--can pass data at 2.5gbps, but metal channels will likely top out at between 10gbps and 20gbps because of signal attenuation and other problems, said Ian Young, director of advanced circuits and technology integration at Intel.

"We are going to start to have trouble (with copper interconnections) at 10 gigabits," he said. "As frequency increases, optical attenuation occurs much more slowly than electrical attenuation."

Optical-chip company Primarion is working on similar technology. Both Intel and Primarion started examining optical interconnects a few years ago.

Fiber is currently being used to connect servers, but it will likely begin to connect boards inside computers in two to seven years. Chip-to-chip optical connections will start to appear in about seven years, Young said.

Although optical fiber provides better performance, optical parts historically have been far more expensive and tricky to make.

Intel is trying to remove some of the inherent difficulties of optical technology by making as many of the components as possible on standard silicon wafers. The company recently showed off a silicon modulator that chops up laser light into 1s and 0s.

Not all components can go into silicon, though. Light can't be generated out of silicon, for instance. In addition, the chip-to-chip interconnection contains components that are made with gallium arsenide and germanium, which raises manufacturing costs. Still, enough of the technology can be integrated into standard silicon chips to make the proposition viable, Young said.

"Even though it is a hybrid package, we think we can meet the cost and performance" levels, he said.

Peter Glaskowsky, editor in chief of the Microprocessor Report, said optical technology could certainly advance overall computing performance but that it won't be easy. Microprocessors generate substantial amounts of heat, and optical equipment can malfunction if heated.

"Heat changes dimensions of everything in a chip," he said.