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Light slowed with sound in photonic chip breakthrough

George Nott | Sept. 20, 2017
Researchers turn light waves into readable sound waves and back again, advancing the development of photonic chips.

Having travelled halfway round the world down underwater fibre optic cable in an instant, by the time data in light form reaches your computer, it has to be slowed down to be processed.

Photons (the elementary particles of light) are hard to handle at the microchip level, so they are translated into electrons. This takes a fair amount of energy, creates a lot of heat and as systems become more complex and data hungry, they can become bulky and expensive, and susceptible to electromagnetic radiation.

What if the chip could work with photons? Photonic chips, or photonic integrated circuits (PICs), promise a new paradigm in information processing and are being pursued by the likes of IBM and Intel.

Their potential in telecommunications, optical fibre networks and cloud computing data centres is huge. But there’s a problem: light is just too fast.

“For this to become a commercial reality, photonic data on the chip needs to be slowed down so that they can be processed, routed, stored and accessed,” explains Moritz Merklein, from the ARC Centre of Excellence for Ultrahigh bandwidth Devices for Optical Systems (CUDOS).

Together with his colleague Dr Birgit Stiller, he has demonstrated for the first time a solution that’s making a big noise in the scientific community: delay the data in the photons by storing it as sound.

“The information in our chip in acoustic form travels at a velocity five orders of magnitude slower than in the optical domain,” said Stiller, research fellow at the University of Sydney and supervisor of the project.

“It is like the difference between thunder and lightning.”


Wired for sound

The researchers – working at the School of Physics and the Sydney Nanoscience Hub at the University of Sydney where CUDOS is headquartered – have dramatically slowed digital information carried as light waves by transferring the data into sound waves in an integrated circuit, or microchip.

“Building an acoustic buffer inside a chip improves our ability to control information by several orders of magnitude,” Merklein said.

The chip was fabricated at the Australian National University’s Laser Physics Centre, a node of CUDOS. It is the first time this has been achieved.

“Storing or delaying optical signals has been a major driving force for a wide variety of research efforts as it offers new possibilities in all-optical processing and enhanced light–matter interactions,” the authors write in their paper – A chip-integrated coherent photonic-phononic memory published yesterday in Nature Communications. “An optical buffer that is able to maintain the coherence of the optial signal … and is able to operate at multiple wavelengths would greatly enhance the capacity of photonic integrated circuits and optical interconnects.”


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