Monday, December 8, 2008

Intel breaks record with optical CMOS device

Researchers from Intel Corp. have demonstrated a photo detector built in CMOS that the company claims is the highest performance optical component of its class to date. The avalanche photodetector (APD) described in a paper in the journal Nature Photonics shows the way to designs that could increase the distance or lower power and cost of optical links, Intel said.

The research effort is one of many small steps forward in silicon photonics in recent years from Intel. The company aims to commercialize some of its work in PC platforms in as little as two to three years, said Mario Paniccia, director of Intel's photonics lab who reported the advance.

Intel's APD achieved a gain-bandwidth product of 340 GHz, higher than any previous device made in any process technology. The metric is a broad measure of the component's signal amplification capability at any given speed.

"This is the first time a silicon photonics device has a better performance than a III-V device, in this case specifically indium phosphide," said Paniccia. "We started with goal of getting [in silicon] 90 percent of the performance of [more] exotic materials with an order of magnitude less cost, but we now have a silicon devoice that is better performance than anything measured in indium phosphide," he added.

APDs are primarily used today in relatively costly modules enabling optical links at 10 Gbits/second over tens of kilometers. The Intel APD could support devices with throughput up to 40 Gbits/s at an order of magnitude less cost, Intel said.

An APD amplifies an optical signal by creating tens or hundreds of electron pairs for every photon. The Intel device is something of a hybrid. It uses silicon as an amplifying material, however it also uses a layer of germanium as a light absorption region to allow operating in infrared wavelengths.

"The goal is to put as much of the photonics in silicon as possible, and I think we can do everything except the laser which requires a tiny piece of germanium," said Paniccia. "So it will be a hybrid device in future with a little indium phosphide as a light source," he added.

Intel worked on the project with two researchers from the University of California at Santa Barbara who held the previous record for an APD. "This APD utilizes the inherently superior characteristics of silicon for high-speed amplification to create world-class optical technology," said John Bowers, one of the UCSB professors, speaking in a press statement.

The research was funded in part by the Defense Advanced Research Projects Agency. It was carried out at Numonyx, a non-volatile memory maker spun out of Intel.

Besides use in optical computer and communications links, technology based on the new device could be used to make highly sensitive infrared imaging systems and cameras. It could also be used to create more sensitive biochips or better fibre-to-the-home components.

"I think this is a core technology that has multiple applications goring forward, so it's quite exciting," said Paniccia.

The Intel lab has announced a handful of advances in silicon photonics in the last four years including work in light sources and modulators supporting data rates of 40 Gbits/s and beyond. Much work remains at the research level to create waveguides to channel photons, improve overall device sensitivity and optimize devices for commercial uses likely to initially focus on rates of 10-20 Gbit/s, said Paniccia.

Initially, optical links for PCs will appear at the board level in separate packaging from microprocessors, he added. "We are working to aggressively drive optics in our platforms, and you will see [commercial] optics in the next couple years," he predicted.

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