(Image courtesy of Massachusetts Institute of Technology).

Researchers Test An Optical Chip For Deep Learning

The computer chip learned to recognize four basic vowel sounds, and it guessed correctly three out of every four times when tested. Other processors are more accurate - correct around 90% of the time - but few are as unique.

On Monday, researchers at the Massachusetts Institute of Technology revealed that new chip, called a nanophotonic processor, which uses light instead of electricity to solve the unforgiving math at the heart of machine learning. Using microscopic lenses instead of transistors, it could vastly improve algorithms that learn to make decisions in smartphones to sensors.

The ten researchers, writing in the journal Nature Photonics, said that the experimental chip could be carefully tuned to control light and solve so-called matrix multiplications much faster and more efficiently than traditional computers and graphics chips. The idea is that light moves much faster than the electrons cascading through transistors. 

These calculations are vital to deep learning algorithms, which mimic how the brain learns from an accumulation of examples to improve voice recognition, image classification, or autonomous driving software. But these multiplication tables not only take the most time but also consume the most power.

The optical chip contains multiple waveguides that shoot beams of light at each other simultaneously, creating interference patterns that correspond to mathematical results. The proof-of-concept performs matrix calculations with a thousandth of the power used by traditional chips, the researchers said

"The chip, once you tune it, can carry out matrix multiplication with, in principle, zero energy, instantly," said Marin Soljacic, an electrical engineering professor at MIT, in a statement. The accuracy leaves something to be desired for making out vowels, but the nanophotonic chip is still a work-in-progress.

Years from now, it could be useful "whenever you need to do a lot of computation but you don't have a lot of power or time," said Nicholas Harris, an author of the paper, in a statement. It could also improve signal processing because light, which is analog, would not have to be converted into a digital signal.

The nanophotonic chip is still not a complete system, and Soljacic said that further advances would only be possible with more time and investment. "We've demonstrated the crucial building blocks but not yet the full system," he said in a statement.

Other platforms have targeted matrix multiplications, which help strengthen links between the virtual neurons in deep learning software. The Volta graphics chip released by Nvidia last month, for instance, contain specialized "tensor cores" that solve matrix multiplication for training and inferencing faster and more efficiently than other chips.

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