Dynamical generation of sound in photonic cavities and waveguides

International audienceWe describe the dynamical generation of sound, or acoustic phonons, inside dielectrics that arises from the beat note of two detuned optical frequencies. This generation is in principle noticeable whenever optical waves can be strongly confined, e.g. inside photonic cavities and waveguides, and when in addition acoustic phonons can be trapped as well. Bulk generation of acoustic phonons fromdetuned optical waves is explained by electrostriction, which is the reciprocal effect to the photoelastic effect governing inelastic scattering of light by phonons. This principle was shown to explain faithfully Brillouin light scattering in microstructured optical fibers and nanoscale optical waveguides.In case light strongly feels the interfaces between different dielectric materials or between a dielectric material and air, the beat note can induce vibrations in the interfaces themselves. This surface contribution to generation of acoustic phonons is the reciprocal effect to the moving interface effect in inelastic light scattering. A Lagrangian functional can be constructed to describe all those effects atonce. From this Lagrangian, a variational formulation is obtained that is solved to obtain the dynamics of the generated acoustic phonons from a finite element analysis. Various examples of this theory will be given, for both cavities and waveguides