Light Replacing Wires in Chips

IBM scientists yesterday unveiled an ultrafast nanophotonic avalanche photodetector for converting faint optical signals into electrical ones. The device, capable of receiving 40 billion bits of information per second, represents a significant step toward energy-efficient computing and could have significant implications for the future of electronics.

The company said it has "reinvented" germanium avalanche photodetectors by demonstrating high gain while suppressing multiplication noise — a very noisy process in traditional germanium photodetectors that degrades the signals — by 50 to 70 percent.

Artist's view on nanophotonic avalanche photodetector generating avalanche of electrons and holes. (Images: IBM Research)

While conventional avalanche photodetectors are not able to detect fast optical signals because the avalanche builds slowly, IBM said its device uses nanoscale effects to obtain very fast multiplication. The device operates at 40 Gb/s while achieving tenfold multiplication and requires a voltage of only 1.5 V, 20 times smaller than previous demonstrations. That means that many of these tiny communication devices could potentially be powered by just a small AA-size battery, IBM said, while traditional avalanche photodetectors require 20-30 V power supplies.

Another significant plus to its technology, IBM said, is that the device is made of silicon and germanium, materials already widely used in production of microprocessor chips, and is fabricated using standard processes used in chip manufacturing. The result is thousands of these devices can be built side-by-side with silicon transistors for high-bandwidth optical communications.

"This invention brings the vision of on-chip optical interconnections much closer to reality," said Dr. T.C. Chen, vice president, Science and Technology, IBM Research. "With optical communications embedded into the processor chips, the prospect of building power-efficient computer systems with performance at the Exaflop level might not be a very distant future."

Optical microscope photographic image of an array of nanophotonic avalanche photodetectors on a silicon chip.

"This dramatic improvement in performance is the result of manipulating the optical and electrical properties at the scale of just a few tens of atoms to achieve performance well beyond accepted boundaries," said Dr. Solomon Assefa, lead author of a paper on the research appearing in the March 2010 issue of Nature. "These tiny devices are capable of detecting very weak pulses of light and amplifying them with unprecedented bandwidth and minimal addition of unwanted noise."

The avalanche photodetector achievement is the last piece of the puzzle that completes the development of the "nanophotonics toolbox" of devices necessary to build the on-chip interconnects, IBM said.

In March 2008, IBM scientists announced the world's tiniest nanophotonic switch for "directing traffic" in on-chip optical communications, ensuring that optical messages can be efficiently routed.

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