Data Centres Bet on Photonics to Cut Copper and Power Bills

A typical 100MW data centre consumes around 400 tonnes of copper, and the industry now wants to cut that number by replacing wiring with light.

"I think we're at the end of copper," says Chris Sharp, chief technology officer at data centre operator Digital Realty. He does not mean the metal is running out. He means data centres will use far less of it.

Most of that copper goes into the electrical infrastructure that powers the facility and its cooling systems. Up to 70 tonnes sits inside the computer servers doing the processing work in a 100MW facility. Another 20 tonnes goes into the network wiring that connects those servers.

It is that spaghetti-like cabling, snaking between racks, where copper is now targeted for replacement.

"The wires between these GPUs, CPUs, and all this compute are what's slowing us down," says Sharp.

Today, data moves through data centres as electrons travelling along copper. Many in the industry want to move it as photons instead. Fibre optic cable has carried long-distance telecommunications for decades. Researchers and companies now want to extend fibre's reach inside the data centre itself. The approach, called photonics, connects optical components directly to electrical ones — sometimes on the chips themselves.

The commercial logic is thermal. Light does not produce the heating effects of electricity, and less heat means less energy spent on cooling — one of a data centre's biggest operating costs.

"You can save so much energy," says Callum Littlejohns, deputy director of silicon photonics foundry Cornerstone Labs. He also notes that multiple data streams can travel down a single channel, creating more capacity from the same physical infrastructure.

Photonics will not make data centres more popular with the public. But it could make them measurably less energy-hungry.

From lab to fab

Peter O'Brien, head of research for photonics packaging and systems integration at Ireland's Tyndall Research Institute, says academics and commercial companies have worked with photonics for years, but the technology faced multiple manufacturing challenges. That has changed. The technology is now ready to make the leap from the lab into widespread application.

"What's happening now with optics and photonics is there's kind of a reset," says O'Brien.

Nvidia, the AI chip giant, has thrown its weight behind the technology — a significant endorsement given the company's grip on AI compute.

The transition is far from a straightforward swap. Photonics merges different engineering traditions and different supply chains, and cost remains the central problem.

"We've really gotten good at bringing the cost down on that electrical side, how to design it, how to manufacture it, how to test it, how to deploy it," says Andrew Wheeler, senior vice president at Hewlett Packard Labs. The industry, he says, is still working out how to do the same for photonics.

Part of the problem is geographic. Different elements of the manufacturing process are spread across the globe, with final assembly concentrated in so-called packaging houses clustered in Taiwan.

Engineering hurdles persist. Optical networking devices generate far less heat, but other components in a data centre still make the local environment hot. Optical components are very sensitive to heat, Wheeler explains. That raises reliability concerns unless operators and equipment manufacturers stay within strict thermal limits.

And while optical networks can carry data at — almost — the speed of light, installing and maintaining them will proceed at human speed. Network designers, field support engineers and installers all need new skills. With fibre, says Sharp, "You can't take tight turns. There are little nuances on how to structure that."

Keeping data in the optical domain

The full payoff arrives only when light processes data as well as carries it, says Ofer Shapiro, CEO of optical company Resolight.ai. His company proposes replacing the traditional electronic network switches that control communications between servers with all-optical devices.

Constantly converting data from photons to electrons and back to photons makes no sense, Shapiro argues. Optical interconnects between chips and network elements would keep data in the optical domain end to end, saving even more energy.

That vision sits in the future. The more immediate task is scaling up photonics manufacturing, and here the industry has an unlikely asset: old chipmaking equipment.

Photonics components are generally larger than the silicon components used in computer chips. Counterintuitively, that means organisations like Cornerstone can repurpose older silicon manufacturing tools from earlier processor generations. One of Cornerstone's manufacturing tools comes from a former Intel production line used to make the Pentium 4 chips released at the turn of the century.

Littlejohns says this ability to reuse knowledge gained through electronics manufacturing will ultimately help lower the cost of photonics.

"We know we can make it at a huge scale, so that's why it's such an interesting technology, because it can underpin many applications."

For now, the industry's bet is clear: swap electrons for photons between the chips, cut the cooling bill, and lean on decades of silicon manufacturing know-how to get there.