Intel Engineers Use Light Waves to Carry Data

Intel researchers have developed a method of generating a continuous laser with a silicon device, one of the first steps toward introducing optical interconnects in future processors, servers, and PCs, the company said today.

Exploiting a principle called the Raman effect and using standard chip-manufacturing techniques, Intel built a transistor-like device that can produce a continuous beam of light. Those light waves can carry data at faster speeds than copper, the current standard for chip interconnects, said Mario Paniccia, director of Intel's Photonics Technology Lab. Intel's findings were published today on the Web site of the scientific journal Nature.

"These building blocks are still a research project, but we hope to transfer the technology by the end of the decade," Paniccia said during a conference call Wednesday.

The Shrinking Transistor

Intel's research in this area is part of the chip industry's search for alternative techniques and materials to enable it to continue reducing the size of transistors well into the future. Companies such as Intel and IBM are working on ways to boost chip performance as chip components shrink to the size of individual atoms, a point at which the decades-long practice of diminishing the size of transistors becomes exceedingly difficult.

One way to improve the performance of chips, servers, and networking devices is by replacing the electrical charges that carry data today with light particles (also known as photons). This discipline, called photonics, is well under way in the networking industry, where fiber-optic materials are replacing older copper wire as the preferred means of transmitting signals over long-haul communications networks, Paniccia said.

Unfortunately, fiber-optic materials are expensive and complex. Using silicon materials to generate light waves would solve many of the cost issues, but silicon does not naturally emit light. On the other hand, existing silicon devices can be used as channels for laser beams capable of carrying data signals, Paniccia said.

The Raman Effect

In building a silicon photonics device, Intel researchers drew on the properties of the Raman effect. When a technician pumps a strong beam of photons into a chamber alongside a weaker stream of data, the Raman effect causes vibrating atoms within the chamber to transfer energy from the data stream to the photons. This effect is amplified as the technician allows a second light source to reflect back and forth across the chamber, producing a stronger data beam at the other end of the fiber.

The Raman effect is extremely pronounced in silicon, though it isn't in fiber materials, Paniccia said. One-kilometer lengths of fiber are needed to produce a laser beam of the same strength that mere centimeters of silicon can generate, he said.

Intel has been working with the Raman effect and silicon photonics for over a year, but it has now figured out how to bypass a key roadblock that was sapping the strength of the laser beam.

Silicon is naturally transparent to infrared light waves, so photons passing through it usually have no effect. But on occasion, two photons may strike the same silicon atom at the same time and knock electrons out of that atom. This decreases the strength of the laser as electrons build up and start to absorb photons from the amplified laser beam.

To get around this problem, Intel built what it calls a PIN device, consisting of a sandwich of positively charged silicon, intrinsic or neutrally charged silicon, and negatively charged silicon.

The electrical field generated by the opposing charges sweeps the loose electrons out of the waveguide, or the intrinsic silicon layer, Paniccia said. This produces a steady laser beam at the other end that doesn't lose its strength.

The new laser technology could be used in everything from chip components to portable medical devices, Paniccia said. The silicon laser presented Wednesday is one of many optical components that researchers must test and further develop before it can be used in chip-to-chip or motherboard-to-motherboard connections, he said.

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