Light could replace electricity to carry computer data

Stanford engineers want to change the way data is sent back and forth between chips in computing by using light instead of electricity in a bid to replace wires.

Traditionally data is pushed through wires as a stream of electrons, but that usually takes up a lot of power – which is why laptops get so warm.

Stanford engineer Jelena Vuckovic and her team came up with a process that could make it practical to use light instead of electricity to carry data.

“Several years ago, my colleague David Miller carefully analysed power consumption in computers, and the results were striking,” said Vuckovic. “Up to 80 per cent of the microprocessor power is consumed by sending data over the wires – so called interconnects.”

The engineers are hoping to replicate at a micro scale the proven technology of the internet, which moves data by beams of photons of light through fibre optic threads. 

“Optical transport uses far less energy than sending electrons through wires,” said lead author and Stanford graduate student Alexander Piggott. “For chip-scale links, light can carry more than 20 times as much data.”

This could be doable, researchers said, because silicon is transparent to infrared light, in the same way the glass is transparent to visible light, and wires could be replaced by optical interconnects such as silicon structures designed to carry infrared light.

So far, engineers had to design optical interconnects one at a time, which made optical data transport impractical since thousands of such linkages are needed for each electronic system.

But they now invented what they call an inverse design algorithm in which the engineers specify what they want the optical circuit to do and the software provides the details of how to fabricate a silicon structure to perform the task.

“We used the algorithm to design a working optical circuit and made several copies in our lab,” Vuckovic said.

The algorithm designs silicon structures so slender that more than 20 of them could sit side-by-side inside the diameter of a human hair. These silicon interconnects can direct a specific frequency of infrared light to a specific location to replace a wire.

By loading data onto these frequencies, the algorithm can create switches or conduits or whatever else is required for the task and makes optical interconnects practical by describing how to create what amount to silicon prisms to bend infrared light.

Once the algorithm has calculated the proper shape for the task, engineers can use standard industrial processes to transfer that pattern onto a slice of silicon.

As reported in Nature Photonics, the team of engineers said the devices functioned flawlessly despite tiny imperfections.

“Our manufacturing processes are not nearly as precise as those at commercial fabrication plants,” Piggott said, but “the fact that we could build devices this robust on our equipment tells us that this technology will be easy to mass-produce at state-of-the-art facilities.”

They said the inverse design algorithm could have other applications like high bandwidth optical communications, compact microscopy systems and ultra-secure quantum communications.

By automating the process of designing optical interconnects, they feel that they have set the stage for the next generation of even faster and far more energy-efficient computers that use light rather than electricity for internal data transport.

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