IBM uses silicon waveguides to advance computers using light

Researchers have had a difficult time with Moore's law in recent years as we are reaching the limits of performance for current computer technology. For the last decade and a half, IBM says the clock rate of single processor cores has stalled at a few gigahertz and pushing the boundaries of Moore's law, which has to do with the number of transistors on a chip, can no longer be pushed.

The next big breakthrough in computing will be optical circuits. Researchers have recently managed to efficiently guide visible light through silicon wire, which is an important milestone for faster, more efficient integrated circuits.IBM says the low-loss silicon waveguide could enable new photonic chip designs for applications relying on visible light. The silicon waveguide could also lead to more efficient lasers and modulators used in telecoms.

Optical circuits encode information using light rather than electronics. IBM built an ultrafast all-optical transistor in partnership with the Skolkovo Institute of Science and Technology in 2019. That transistor operated at room temperature, and IBM's latest work builds on that past research. The silicon waveguide can be used to connect that type of transistor carrying light between them with minimal losses.

The ability to wire up transistors of an optical circuit with silicon waveguides is crucial for a compact and highly integrated chip. IBM says it's also easier to integrate other components, including electrodes, if the waveguide is made of silicon, which is a cheap and abundant material that's also an excellent semiconductor.

IBM did face a challenge in that silicon can absorb visible light. To get around that issue, IBM used nanostructures called high contrast gratings that consist of nanometer-sized posts lined up to form a fence that prevents light from escaping. The posts are 150 nanometers in diameter and are spaced so light passing through them interferes destructively with light passing between them. This prevents any light leak through the grating, and most light gets reflected back inside the waveguides. IBM next plans to engineer the coupling of light out of the waveguides into other components.