It’s not much thicker than a postcard, and a postage stamp looks enormous in comparison. Its surface shimmers blue-black, with gold inlay. Lovingly, its creator holds it up with tweezers as if it were a precious jewel. Marc Reig Escalé has developed a chip that enables high-speed data transmission and could play an essential role in the future of 5G and similar enterprises.
The trend has been clear for years: in an increasingly connected world, in which even fridges automatically reorder supplies when the milk is running low, or office chairs adapt themselves to the backs of their users because they have access to experiential data for millions of other backs, we see huge increases in data traffic. This kind of traffic generally travels along highways of fibre-optic cable. All around the world, whether beneath our streets, strung above ground from mast to mast, or in the depths of the ocean, bundles of these cables carry pulses of light to transmit coded information.
However, just as highways alone aren’t enough to get goods from A to B, because the trucks that drive on them have to be loaded and unloaded, fibre-optic cables are only half the story in the world of data traffic. The information needs to be encoded and decoded. This means it has to be “written” into the light signals and then “read” out again at the end.
Lighting circuits in miniature
With their new chip, Marc Reig Escalé and his colleagues at the Institute for Quantum Electronics at ETH Zurich have found a way to make this “writing” of information much more efficient than was previously possible. The idea was to combine the best materials from the fields of optics and microelectronics in creating the tiny chips. First, there is silicon, the most important material in the computer industry and the element that gave Silicon Valley its name. As a semiconductor, it is exceptionally well suited for building electrical circuits, such as those on the chips in computers and mobile phones. In crystal form, silicon is also used in optical chips to transmit light waves. This has practical advantages, as manufacturing in miniature format is already well established in microelectronics.
For optical purposes, however, silicon is far from the best choice. Lithium niobate offers much more favourable characteristics: for example, it can work with a wider range of light frequencies. An important attribute for data processing is this crystalline material’s ability to alter the intensity of incident light depending on what electrical voltage is applied from the outside. This makes it possible for electrical signals to be transformed into optical signals at high speed – precisely what is needed to “load the trucks” that will be travelling on the data highways.
To date, however, these lithium niobate modulators have been so large that they consume a lot of energy. Happily, Reig Escalé was able to draw on a technology developed at ETH Zurich at the start of the decade to apply extremely thin layers of lithium niobate to the familiar silicon chips. The physicist managed to peel fine structures out of this crystal layer using various etching techniques, into which laser light can be fed. When coupled with delicate gold electrodes, it becomes possible to translate electrical signals very efficiently into optical ones. The emergent laser light contains the information that had previously been sent in an electrical form to the electrodes. “Our chips consume less energy and can process signals at least twice as fast as the commercial alternatives that currently exist,” explains Reig Escalé, who works in the laboratory of ETH Professor Rachel Grange. Metaphorically speaking, this means that an individual chip can load more trucks per unit of time and can therefore serve many more data highways simultaneously as a transshipment terminal.
