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Optoelectronic microprocessors promise lower power usage

Posted: 04 Jan 2016 ?? ?Print Version ?Bookmark and Share

Keywords:MIT? microprocessor? University of Colorado? optical communication? transistor?

A team of researchers at MIT, the University of California at Berkeley and the University of Colorado has developed a working optoelectronic microprocessor that computes electronically but uses light to move information. They were able to create the device using only processes found in existing microchip fabrication facilities.

Optical communication could dramatically reduce chips' power consumption, which is not only desirable in its own right but essential to maintaining the steady increases in computing power that we've come to expect.

Demonstrating that optical chips can be built with no alteration to existing semiconductor manufacturing processes should make optical communication more attractive to the computer industry. But it also makes an already daunting engineering challenge even more difficult.

"You have to use new physics and new designs to figure out how you take ingredients and process recipes that are used to make transistors, and use those to make photodetectors, light modulators, waveguides, optical filters and optical interfaces," noted MIT professor of electrical engineering Rajeev Ram, referring to the optical components necessary to encode data onto different wavelengths of light, transmit it across a chip, and then decode it. "How do you build all the optics using only the layers out of a transistor? It felt a bit like an episode of 'MacGyver' where he has to build an optical network using only old computer parts."

Optoelectronic chip

Researchers have produced a working optoelectronic chip that computes electronically but uses light to move information. The chip has 850 optical components and 70 million transistors, which, while significantly less than the billion-odd transistors of a typical microprocessor, is enough to demonstrate all the functionality that a commercial optical chip would require. Image: Glenn J. Asakawa

The project began as a collaboration between Ram, Vladimir Stojanovic, and Krste Asanovic, who were then on the MIT department of electrical engineering and computer science faculty. Stojanovic and Asanovic have since moved to Berkeley, and they, Ram, and Milos A. Popovic, who was a graduate student and postdoc at MIT before becoming an assistant professor of electrical engineering at Colorado, are the senior authors on a paper in Nature that describes the new chip.

They're joined by 19 co-authors, eight of whom were at MIT when the work was done, including two of the four first authors: graduate students Chen Sun and Jason Orcutt, who has since joined IBM's T. J. Watson Research Centre.

Powering down

The chip has 850 optical components and 70 million transistors, which, while significantly less than the billion-odd transistors of a typical microprocessor, is enough to demonstrate all the functionality that a commercial optical chip would require. In tests, the researchers found that the performance of their transistors was virtually indistinguishable from that of all-electronic computing devices built in the same facility.

Computer chips are constantly shipping data back and forth between logic circuits and memory, and today's chips cannot keep the logic circuits supplied with enough data to take advantage of their ever-increasing speed. Boosting the bandwidth of the electrical connections between logic and memory would require more power, and that would raise the chips' operating temperatures to unsustainable levels.

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