Physicists at Intel have created the first high-speed optical modulator made from silicon. The modulator, which is silicon-based, has a bandwidth that is greater than 1 gigahertz. This is 50 times faster than previous efforts and could threaten the role of optoelectronics made from compound semiconductors (A Liu et al.2004 Nature 427 615)
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.