Largest, Fastest Array of Microscopic ‘Traffic Cops’ for Optical Communications

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Engineers at the University of California, Berkeley have built a new photonic switch that can control the direction of light passing through optical fibers faster and more efficiently than ever. This optical “traffic cop” could one day revolutionize how information travels through data centers and high-performance supercomputers that are used for artificial intelligence and other data-intensive applications.

Each individual “light switch” is constructed like a microscopic highway overpass. When the switch is off, the light passes straight through a lower channel (red lines). Turning the switch on lowers a tiny ramp, directing the light to an upper channel to make a right turn (blue lines). A second ramp lowers the light back down. (Tae Joon Seok image)

The photonic switch is built with more than 50,000 microscopic “light switches,” each of which directs one of 240 tiny beams of light to either make a right turn when the switch is on, or to pass straight through when the switch is off. The 240-by-240 array of switches is etched into a silicon wafer and covers an area only slightly larger than a postage stamp.

“For the first time in a silicon switch, we are approaching the large switches that people can only build using bulk optics,” said Ming Wu, professor of electrical engineering and computer sciences at UC Berkeley and senior author of the paper, which appeared online April 11 in the journal Optica. “Our switches are not only large, but they are 10,000 times faster, so we can switch data networks in interesting ways that not many people have thought about.”

The photonic switch is built with more than 50,000 microscopic “light switches” etched into a silicon wafer. Each light switch (small raised squares) directs one of 240 tiny beams of light to either make a right turn when the switch is on, or to pass straight through when the switch is off. (Younghee Lee graphic)

Currently, the only photonic switches that can control hundreds of light beams at once are built with mirrors or lenses that must be physically turned to switch the direction of light. Each turn takes about one-tenth of a second to complete, which is eons compared to electronic data transfer rates. The new photonic switch is built using tiny integrated silicon structures that can switch on and off in a fraction of a microsecond, approaching the speed necessary for use in high-speed data networks.

The photonic switch is manufactured using a technique called photolithography, in which each “light switch” structure is etched into a silicon wafer. Each light gray square on the wafer contains 6,400 of these switches. (Kyungmok Kwon photo)

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