RF Over Fiber: A New Era in Data Center Efficiency

How fast you can train gigantic new AI models boils down to two words: up and out.

In data-center terms, scaling out means increasing how many AI computers you can link together to tackle a big problem in chunks. Scaling up, on the other hand, means jamming as many GPUs as possible into each of those computers, linking them so that they act like a single gigantic GPU, and allowing them to do bigger pieces of a problem faster.

The two domains rely on two different physical connections. Scaling out mostly relies on photonic chips and optical fiber, which together can sling data hundreds or thousands of meters. Scaling up, which results in networks that are roughly 10 times as dense, is the domain of much simpler and less costly technology—copper cables that often span no more than a meter or two.

But the increasingly high GPU-to-GPU data rates needed to make more powerful computers work are coming up against the physical limits of copper. As the bandwidth demands on copper cables approach the terabit-per-second realm, physics demands that they be made shorter and thicker, says David Kuo, vice president of product marketing and business development at the data-center-interconnect startup Point2 Technology. That’s a big problem, given the congestion inside computer racks today and the fact that Nvidia, the leading AI hardware company, plans an eightfold increase in the maximum number of GPUs per system, from 72 to 576 by 2027.

“We call it the copper cliff,” says Kuo.

The industry is working on ways to unclog data centers by extending copper’s reach and bringing slim, long-reaching optical fiber closer to the GPUs themselves. But Point2 and another startup, AttoTude, advocate for a solution that’s simultaneously in between the two technologies and completely different from them. They claim the tech will deliver the low cost and reliability of copper as well as some of the narrow gauge and distance of optical—a combination that will handily meet the needs of future AI systems.

Their answer? Radio.

Later this year, Point2 will begin manufacturing the chips behind a 1.6-terabit-per-second cable consisting of eight slender polymer waveguides, each capable of carrying 448 gigabits per second using two frequencies, 90 gigahertz and 225 GHz. At each end of the waveguide are plug-in modules that turn electronic bits into modulated radio waves and back again. AttoTude is planning essentially the same thing, but at terahertz frequencies and with a different kind of svelte, flexible cable.

Both companies say their technologies can easily outdo copper in reach—spanning 10 to 20 meters without significant loss, which is certainly long enough to handle Nvidia’s announced scale-up plans. And in Point2’s case, the system consumes one-third of optical’s power, costs one-third as much, and offers as little as one-thousandth the latency.

According to its proponents, radio’s reliability and ease of manufacturing compared with those of optics mean that…