UT researchers use sound to filter light

Scientists at the University of Twente have developed a new technique to manipulate light using sound. In a photonic device, they had two finely tuned lasers generate a soundwave with frequencies 1 million times higher than the human hearing threshold and trap it in a waveguide. Light sent through the waveguide interacts with the soundwave which will reflect a very small and specific part of the light spectrum, effectively filtering the signal.

“Even though Brillouin scattering has been studied extensively in the last few years, it could never be implemented reliably on a chip suitable for use in our daily lives”, tells David Marpaung, Nonlinear Nanophotonics group leader. “Trapping the soundwave in a waveguide long enough to be effective, has proven to be very difficult. ‘Acoustic leakage’ is a big problem in traditional silicon-based platforms preventing strong Brillouin interactions.”

Marpaung’s research team used low-loss multilayer silicon nitride (Si₃N₄) nanophotonic circuits to confine both the optical and the acoustic waves. These circuits consist of 50 centimeter-long spiral waveguides. This setup traps the soundwave and prevents the acoustic leakage that occurs when using a single silicon nitride core.