Although the prototype device’s performance is still far below that of commercial products based on materials such as lithium niobate (an alloy made of lithium, niobium and oxygen) and III-V semiconductors, the news is important. It suggests that silicon, the basis of cheap yet powerful computer chips, could also make high-speed optical switches. In future, the hope is that both optical and electronic functions could be combined on cost-effective silicon super-chips made at high-volume microelectronics factories.

“Breakthrough developments such as this fast silicon modulator suggest that a low-cost silicon optical superchip could soon be a reality,” said Graham Reed, a semiconductor scientist from the University of Surrey, UK, in an accompanying review of the breakthrough in Nature. “It [silicon] is already the world’s favourite electronic material and could yet come to dominate the photonics industry as well.”

The silicon-waveguide modulator is based on a so-called Mach-Zehnder interferometer design where a silicon waveguide is split into two arms that recombine a short distance later. Applying a voltage to one of the arms causes a small change in the refractive index of the silicon and, through optical interference, controls the amount of light leaving the device.

Intel’s prototype operates at the all-important telecommunications wavelength of 1.5 microns and requires a drive voltage of about 8 volts to work. Although it is currently inferior to commercial lithium niobate modulators, the Intel team is confident that it can significantly improve device performance by tweaking the design.