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This Chip for AI Works Using Light, Not Electrons

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As demand for artificial intelligence grows, so does hunger for the computer power needed to keep AI running.

Lightmatter, a startup born at MIT, is betting that AI’s voracious hunger will spawn demand for a fundamentally different kind of computer chip—one that uses light to perform key calculations.

“Either we invent new kinds of computers to continue,” says Lightmatter CEO Nick Harris, “or AI slows down.”

Conventional computer chips work by using transistors to control the flow of electrons through a semiconductor. By reducing information to a series of 1s and 0s, these chips can perform a wide array of logical operations, and power complex software. Lightmatter’s chip, by contrast, is designed to perform only a specific kind of mathematical calculation that is critical to running powerful AI programs.

Harris showed WIRED the new chip at the company’s headquarters in Boston recently. It looked like a regular computer chip with several fiber optic wires snaking out of it. But it performed calculations by splitting and mixing beams of light within tiny channels, measuring just nanometers. An underlying silicon chip orchestrates the functioning of the photonic part, and also provides temporary memory storage.

Lightmatter plans to start shipping its first light-based AI chip, called Envise, later this year. It will ship server blades containing 16 chips that fit into conventional data centers. The company has raised $22 million from GV (formerly Google Ventures), Spark Capital, and Matrix Partners.

The company says its chip runs 1.5 to 10 times faster than a top-of-the-line Nvidia A100 AI chip, depending on the task. Running a natural language model called BERT, for example, Lightmatter says Envise is five times faster than the Nvidia chip; it also consumes one-sixth of the power. Nvidia declined to comment.

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The technology has technical limits, and it may prove difficult to persuade companies to shift to an unproven design. But Rich Wawrzyniak, an analyst with Semico who has been briefed on the technology, says he believes it has a decent chance of gaining traction. “What they showed me—I think it's pretty good,” he says.

Wawrzyniak expects big tech companies to at least test the technology because demand for AI—and the cost of using it—are growing so fast. “This is a pressing issue from a lot of different points of view,” he says. The power needs of data centers are “climbing like a rocket.”

Lightmatter’s chip is faster and more efficient for certain AI calculations because information can be encoded more efficiently in different wavelengths of light, and because controlling light requires less power than controlling the flow of electrons with transistors.

A key limitation of the Lightmatter chip is that its calculations are analog rather than digital. This makes it inherently less accurate than digital silicon chips, but the company has come up with techniques for improving the precision of calculations. Lightmatter will market its chips initially for running pre-trained AI models rather than for training models, since this requires less precision, but Harris says in principle they can do both.

The chip will be most useful for a type of AI known as deep learning, based on training very large or “deep” neural networks to make sense of data and make useful decisions. The approach has given computers new capabilities in image and video processing, natural language understanding, robotics, and for making sense of business data. But it requires large amounts of data and computer power.

Training and running deep neural networks means performing many parallel calculations, a task well suited to high-end graphics chips. The rise of deep learning has already inspired a flourishing of new chip designs, from specialized ones for data centers to highly efficient designs for mobile gadgets and wearable devices.

Aydogan Ozcan, a professor at UCLA who works on photonic computing, believes the rise of AI could bring technology like Lightmatter’s to the fore. He suggests that a shift toward new forms of photonic computing might even unlock new ways of doing AI. “We might see major advances in computing speed, power and parallelism, which will further feed into and accelerate the success of AI,” he says.


The idea of using light for computation is far from new, dating back to the 1950s. But electronic computing proved more practical to develop and commercialize. In the 1980s, Bell Labs tried to create a general purpose light-based chip, but it failed due to the difficulty of building a working optical transistor.

Lightmatter says its chips can be dropped into an existing data center and work with most major AI software. Later this year the company plans to launch a new technology for connecting chips, including those made by other companies, using its photonic technology. Light is widely used to shuttle information between computers, using fiber-optic cables.

Harris argues that AI will hit a wall in the next few years because of rising costs and energy use, and because of engineering constraints on the horizon. As engineers try to cram more transistors into a chip to speed up performance, chips may get too hot to manage.

Even if chipmakers continue to wring more computation out of their designs using clever engineering and manufacturing, the field of AI appears to be on an almost unsustainable trajectory. Recent data from OpenAI shows that the amount of computer power needed to do landmark AI research has doubled roughly every 3.4 months—increasing 300,000 times between 2012 and 2018.

But some AI experts warn that progress in AI could start to slow because of the cost of continually scaling up computer power. Others are concerned about the potential environmental impact of widespread use of power-hungry AI algorithms.

Updated, 3-10-21, 11:30am ET: An earlier version of this article incorrectly said Lightmatter's server blades would contain 14 Envise chips.

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