Brillouin interactions with fundamental acoustic waves (Invited Paper)

Stimulated Brillouin scattering couples optical and acoustic waves with applications for signal processing, narrow-linewidth lasers, and environmental sensors. Traditional Brillouin interactions in waveguides are fixed in frequency by momentum conservation for backward scattering, and by the geometrically determined cutoff frequencies for forward scatting. Alternatively, a wide new range of frequencies become accessible with Forward InterModal coupling to the Fundamental Acoustic Modes (FIM-FAM) in waveguides with more than one optical mode. With FIM-FAM, record Brillouin coupling strengths and ultranarrow linewidths become available as well as qualitatively new behavior such as phonon self-interference. This talk will review recent investigations of FIM-FAM including ultranarrow linewidths in fiber tapers, tunable record-performance RF filters, as well as strong FIM-FAM interactions in integrated silicon nitride devices.