Tiny component for record-breaking bandwidth

Plasmonic modulators are tiny components that convert electrical signals into optical signals in order to transport them through optical fibres. A modulator of this kind had never managed to transmit data with a frequency of over a terahertz (over a trillion oscillations per second). Now, researchers from the group led by Jürg Leuthold, Professor of Photonics and Communications at ETH Zurich, have succeeded in doing just that. Previous modulators could only convert frequencies up to 100 or 200 gigahertz – in other words, frequencies that are five to ten times lower.

Modulators of this kind could be used wherever large volumes of data are transmitted, as a bridge between the electrical world and data transmission using light. “Data is always initially present in electrical form and nowadays, its transmission always involves optical fibres at some point,” explains Professor Leuthold.

The next generation of mobile communications (6G) will operate in the terahertz range. Its backbone – the cables between the base stations – relies on optical fibre technology. “Our modulator allows radio signals and other electrical signals to be converted into optical signals directly and therefore efficiently,” says Yannik Horst, who worked on the component during his doctoral thesis.

Also for medicine and measurement technology

Although the transfer of terahertz signals onto optical fibre is already possible from a technical perspective, it is a laborious process and currently requires several expensive components. The new modulators can convert the signals directly, reducing energy consumption and increasing measurement accuracy. Moreover, different components are currently needed for different frequency ranges. The new modulator can be used with any frequency from 10 megahertz to 1.14 terahertz. “We cover the entire frequency range with a single component. It’s therefore extremely versatile in terms of applications,” says Horst.

Other potential applications include optical fibre data transmission within and between high-performance computing centres. Last but not least, the components are also of interest for high-performance measurement technology, including imaging techniques in medicine, spectroscopic methods for material analysis, baggage scanners at airports, or radar technology. Some devices of this kind already operate in the terahertz range today.

The new modulator is a tiny nanostructure made up of various materials, including gold, and makes use of the interaction between light and free electrons within the gold. The technology was developed at ETH Zurich and the device was manufactured by Polariton Technologies, an ETH spin-off that emerged from Leuthold’s group. At present, the company is working to bring the terahertz modulator to market so that it can be widely used in future applications in data transmission and measurement technology.