Science & Technology

Scientists Created A Computer Chip That Stores Light As Sound

When it comes to futuristic breakthroughs, optical computers are right up there with neural networks in their potential to change the computing game forever. Instead of using electrons, optical computers move information in particles of light called photons. The benefit is that data can move at literally the speed of light. The drawback is that microchips aren't fast enough to keep up. We need to find a way to slow down the signal just enough, and in 2017, researchers did that in a surprising way: they turned the light into sound.

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Quicker Than A Ray Of Light

Photonic, or light-based, signals aren't just faster than electronic ones. They also solve some nagging problems that have cropped up as computers have gotten smaller and faster. Electronic resistance gobbles up energy and produces loads of heat. Electrons also fall prey to interference from electromagnetic radiation. The smaller and faster the circuits, the worse things get, and at some point, physics just says "stop."

But light isn't perfect, either. The very speed that makes it so intriguing also makes it impractical. It's too fast for existing microchips to read, so right now, photons that reach their destination have to be turned into electrons before a chip can read their signal. That means many of the same problems with electronic computing are liable to crop up in optical computing.

Good Vibrations

To solve this, Dr. Birgit Stiller and Moritz Merklein at the University of Sydney created a microchip that briefly stores optical signals as sound waves. In a paper published in the journal Nature Communications in 2017, the researchers explained how they achieved this using something called Brillouin scattering — basically, the phenomenon where several photons can interact to produce a "phonon", or particle of sound energy. Sound is much, much slower than light. "It is like the difference between thunder and lightning," Dr. Stiller said in a press release.

Here's how it works: two types of light pulses — one containing data, one containing "write" instructions — enter the chip from opposite directions. The two pulses interact to produce a sound wave that stores the data for just a few extra nanoseconds, just enough for the chip to retrieve it and process it before another light pulse comes back in and transmits the data as light again. The light itself passes through the chip in two to three nanoseconds, but the sound wave stores the data for an extra 10 nanoseconds. That's hardly anything in the human scale, but it's perfect for what current microchips need.

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This isn't the first time light has been converted to sound for a purpose like this, but it is the most practical. The researchers' technique makes it possible to use multiple wavelengths of light at the same time, making optical computing even faster and more efficient. This technique also sharpens the chip's accuracy, according to Merkelein. "Building an acoustic buffer inside a chip improves our ability to control information by several orders of magnitude," he said.

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