New Devices Could Realize Optical Microprocessing

The development of two new devices — a modulator and a tunable filter — that are energy efficient and were built using a standard IBM advanced CMOS process represents a major milestone in optical microprocessing, researchers say.

As part of DARPA’s Photonically Optimized Embedded Microprocessors (POEM) project, researchers from the University of Colorado, Boulder, MIT and the University of California, Berkeley are working to demonstrate that low-power photonic devices can be fabricated using standard chip-making processes.

Microscope image of the full chip fabricated in IBM’s CMOS process. Courtesy of MIT.

These two devices are key components for the communication link between a computer’s central processing unit and its memory. The modulator converts electrical signals into optical signals, while the tunable filter can pick out light signals of particular frequencies, allowing it to select a signal from multiple frequencies, each of which carries data. Used in conjunction with a photodetector, the filter converts optical signals to electrical signals.

“This is a really nice first step for silicon photonics to take over some areas of technology where electronics has really dominated and to start building complex electronic/photonic systems that require dense integration,” said researcher Mark Wade of the UC-Boulder.

Chip-to-chip communication links using these photonic devices could have at least 10 times higher bandwidth density. This allows for the transmission of more information using a smaller amount of space, as different optical signals can share the same optical wire. Contrarily, sending multiple electrical signals either requires multiple electronic wires or schemes that require more chip space and energy, limiting computational power, Wade said.

The researchers anticipate that photonics will be at least 10 times more energy efficient than electronics.

For more information, visit www.darpa.mil.