Wednesday, June 25, 2008

A Record-Breaking Optical Chip

Intel researchers have built a superfast silicon chip for optical networking.

By Kate Greene

Light it up: The silver-colored rectangular chip in the middle of the copper-colored holder is Intel’s latest advance in silicon photonics. The chip contains eight modulators that encode data onto light that enters and exits from the side via optical fibers (not pictured). This chip can process 200 gigabits of data per second and is used to test designs that could ultimately process a terabit of data per second. Credit: Intel

The road to a faster Internet, data center, and personal computer is paved with silicon. Or so believe researchers at Intel who have unveiled a test chip--made entirely from silicon--that can encode 200 gigabits of data per second on a beam of light. In contrast, the most advanced chips used in today's fastest optical networks operate at speeds of 100 gigabits per second. And these 100-gigabit chips, which are made from nonsilicon materials, have limitations that Intel's chip doesn't: they can't scale to faster speeds as inexpensively as can those made from silicon.

While silicon is the material of choice in the electronics industry, it has been overlooked in the photonics industry because its optical properties are inferior to those of other semiconductors. Silicon doesn't produce, detect, and manipulate photons as well as materials such as indium phosphide and gallium arsenide. But within the past few years, optical engineers have been giving silicon a second look and cleverly engineering around some of its natural limitations.

The new Intel test chip splits an incoming beam of light into eight channels. Within each channel is a modulator, a device that encodes data onto light. After the beams are encoded with data, they are recombined. In the tests, each modulator ran at a rate of 25 gigabits per second, and each performed nearly identically, says Mario Paniccia, director of the company's silicon-photonics lab. He notes that only one modulator was tested at a time but says that in a future paper his team will publish the results from running multiple channels simultaneously. The multiple channels could produce cross talk, electrical or optical activity that could hinder performance. However, preliminary results, Paniccia says, show that due to the design, cross talk is limited.

In 2004, Intel researchers, led by Paniccia, proved that silicon could be used to build a one-gigabit-per-second modulator; in 2005, the team boosted the speed to 10 gigabits per second. Also in 2005, the researchers built a remarkably good all-silicon laser, and in 2006, they introduced a hybrid laser that combines indium phosphide with silicon, allowing a practical telecom laser to be fabricated on a silicon wafer. Most recently, they have sped up the modulator to 40 gigabits and built a silicon detector.