UC Berkeley research clears path to use light energy in microchips

Experimental evidence of adiabatic elimination in ultra-dense nano photonic circuitry
Michael Mrejen/Courtesy
Experimental evidence of adiabatic elimination in ultra-dense nano photonic circuitry

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UC Berkeley researchers are one step closer to implementing light energy for chip-scale quantum computing.

Researchers with the Lawrence Berkeley National Laboratory and UC Berkeley have conducted a study involving light-based, or photonic, circuitry and have developed a technique that allows scientists to control light-pulse signals in closely packed waveguides, or wires, which would lead to faster data transitions and could be the solution to an impending computer energy limit.

Photonics, an area of study that involves the use of radiant energy, such as light, uses light pulses transmitted over optic fiber in lieu of electrical signals over copper wires. Light pulses not only can reduce the amount of heat dissipated and consume less power, but they also transmit a larger amount of data in a shorter amount of time.

According to Michael Mrejen, a campus graduate student researcher and lead author, “everything is based on electronics. Energy needs in the computer industry have been doubling every two years.”

To keep up with the demand, processing designers have managed to squeeze more, smaller transistors onto a silicon chip. This acceleration trend is reaching its limits, however, according to Mrejen. The increasing power levels needed are too high to function efficiently and can lead to overheating. Electronic chips will likely reach their limits within 10 years, Mrejen said.

Researchers want to use photonics to replace the silicon chips. But a problem of “crosstalk” occurs when two waveguides are placed too closely together, causing light pulses to mix and the two separate signals to interfere with each other. This research may allow photonics to replace electrical energy — a feat previously unattainable on micro scales because of crosstalk.

According to Xiang Zhang — corresponding author and Berkeley lab director of the material sciences division — crosstalk places a restriction on how close the waveguides can be put together. Using a process known as adiabatic elimination, the team placed a third “dark” waveguide between the original two. The third wire not only effectively cuts off the crosstalk, or “leakage of light” between the original waveguides, but also allows for more control over them.

“Although the three are completely isolated, we can tune the two original wires by controlling the third,” Mrejen said. “Adiabatic elimination is not a new concept — it just has never been applied to light.”

Large companies, such as Intel and IBM, have been investing in photonics for the last decade, Mrejen said. Co-lead author Haim Suchowski said that the team issued a patent provision about a year ago and that in a couple of weeks, it will continue the patent application.

“We are just bringing this technology to the people’s desktop,” Mrejen said.

Contact Cindy Yang at cyang@dailycal.org.

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