Ghent University and imec demonstrate interaction between light and sound in nanoscale waveguide

Scientists from Ghent University and imec announce today that they demonstrated interaction between light and sound in a nanoscale area. Their findings elucidate the physics of light-matter coupling at these scales – and pave the way for enhanced signal processing on mass-producible silicon photonic chips.

In the last decade, the field of silicon photonics has gained increasing attention as a key driver of lab-on-a-chip biosensors and of faster-than-electronics communication between computer chips. The technology builds on tiny structures known as silicon photonic wires, which are roughly a hundred times narrower than a typical human hair. These nanowires carry optical signals from one point to another at the speed of light. They are fabricated with the same technological toolset as electronic circuitry.

Fundamentally, the wires work only because light moves slower in the silicon core than in the surrounding air and glass. Thus, the light is trapped inside the wire by the phenomenon of total internal reflection. Simply confining light is one thing, but manipulating it is another. The issue is that one light beam cannot easily change the properties of another. This is where light-matter interaction comes into the picture: it allows some photons to control other photons.

Publishing in Nature Photonics [1], researchers from the Photonics Research Group of Ghent University and imec report on a peculiar type of light-matter interaction. They managed to confine not only light but also sound to the silicon nanowires. The sound oscillates ten billion times per second: far more rapid than human ears can hear. They realized that the sound cannot be trapped in the wire by total internal reflection. Unlike light, sound moves faster in the silicon core than in the surrounding air and glass. Thus, the scientists sculpted the environment of the core to make sure any vibrational wave trying to escape it would actually bounce back. Doing so, they confined both light and sound to the same nanoscale waveguide core – a world’s first observation.

Both light (left) and sound (right) are trapped in a nanoscale silicon core.

Trapped in that incredibly small area, the light and vibrations strongly influence each other: light generates sound and sound shifts the color of light, a process known as stimulated Brillouin scattering. The scientists exploited this interaction to amplify specific colors of light. They anticipate this demonstration to open up new ways to manipulate optical information. For instance, light pulses could be converted into sonic pulses and back into light – thereby implementing much-needed delay lines. Further, the researchers expect that similar techniques can be applied to even smaller entities such as viruses and DNA. These particles have unique acoustic vibrations that may be used to probe their global structure.

[1] R. Van Laer, B. Kuyken, D. Van Thourhout and R. Baets. Interaction between light and highly confined hypersound in a silicon photonic nanowire. Nature Photonics (2015)
About the Photonics Research Group
The Photonics Research Group in the Department of Information Technology of Ghent University is active in the field of photonic integration – more specifically silicon photonics – and its applications in information and communication technology, in sensing and in life sciences.
The group puts its research focus on new concepts for photonic integrated devices and circuits and on the associated technologies and design methodologies. This includes passive and active waveguide-based photonic components, based on CMOS-compatible materials and processes as well as hybrid approaches combining silicon with other functional materials. The activities center around the telecom wavelength of 1.55 micrometer but are expanding both to longer wavelengths (mid-IR) and shorter wavelengths (visible). The infrastructure of the group includes cleanroom facilities for in-house fabrication of components as well as a variety of CAD-tools and measurement labs. The group is associated with the nano-electronics research center imec in Leuven and uses the CMOS-oriented research facilities of imec for research on silicon photonics.

About Ghent University
Ghent University (UGent) consists of 117 departments across 11 faculties and offers high-quality research-based educational programs in virtually every scientific discipline. UGent distinguishes itself as a socially committed and pluralistic university in a broad international perspective. The motto of the university is ‘Dare to Think’. The university’s appeal is growing every year, with about 41,000 students in 2014, of whom 11% (students) and 35% (PhD students) are international. Numerous research groups, centres and institutes have been founded over the years, becoming world-renowned in disciplines such as biotechnology, aquaculture and photonics.
Ghent University is the only Belgian university in the top 100 of both the Shanghai (70) and Times ranking (85). The University has participated in more than 200 research projects in the EU’s Sixth Framework Programme (2002-2006) and in 260 projects in the Seventh Framework Programme, of which 26 ERC grants and 26 Marie Curie Fellowships. Ghent University coordinated 42 collaborative projects in FP7. The university provides excellent training opportunities to both young and experienced researchers, and is one of the fastest growing European universities in terms of research capacity and productivity.

About imec
Imec performs world-leading research in nano-electronics. Imec leverages its scientific knowledge with the innovative power of its global partnerships in ICT, healthcare and energy. Imec delivers industry-relevant technology solutions. In a unique high-tech environment, its international top talent is committed to providing the building blocks for a better life in a sustainable society. Imec is headquartered in Leuven, Belgium, and has offices in the Netherlands, Taiwan, US, China, India and Japan. Its staff of over 2,080 people includes more than 670 industrial residents and guest researchers. In 2013, imec’s revenue (P&L) totaled 332 million euro. Further information on imec can be found at
Imec is a registered trademark for the activities of IMEC International (a legal entity set up under Belgian law as a “stichting van openbaar nut”), imec Belgium (IMEC vzw supported by the Flemish Government), imec the Netherlands (Stichting IMEC Nederland, part of Holst Centre which is supported by the Dutch Government), imec Taiwan (IMEC Taiwan Co.) and imec China (IMEC Microelectronics (Shanghai) Co. Ltd.) and imec India (Imec India Private Limited).