Surface Acoustic Waves Stimulated Brillouin Scattering

Stimulated interactions between light and hypersonic elastic waves, known as stimulated Brillouin scattering (SBS), provide opportunities far beyond what is possible using light alone: From basic research of light-matter interactions and quantum mechanics, to ultra-narrow laser sources, spectroscopy, communication, signal processing and sensors.

The realization of SBS in photonic integrated platforms provides large freedom of design, and would support mass production.

The objectives of the proposed research program are to reveal, investigate and employ SBS processes on the most technologically-significant integration platform: silicon-on-insulator (SOI). Such interactions are largely considered out of reach. The silicon device layer of SOI does not guide acoustic modes, which leak away to the underlying bulk.

Previous studies of SBS in silicon relied on suspended membranes and waveguides, in which the underlying silicon dioxide layer has been etched away. Suspended devices become fragile, and their subsequent processing is difficult. In addition, SBS in silicon has been restricted to the forward direction only.

Forward scattering interactions are inherently difficult to localize.To overcome this challenge, I propose to rely on surface acoustic waves (SAWs) that are guided by the upper interface between the solid substrate and the air above. The propagation of SAWs is supported by SOI, however they were not yet considered towards SBS in this platform before.

Backwards SBS will be realised between guided light in a standard SOI waveguide, with an underlying oxide layer, and a surface acoustic mode.

Analysis shows that the effect should be strong enough to be observed, and also employed in signal processing and sensing applications. Additional objectives include SAW-photonic chips with tuneable acoustic frequency and SAW spectroscopy on-chip. The program outcomes could add another dimension to standard silicon-photonics, that of acoustics.