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Communication Dans Un Congrès Année : 2015

Lagrangian Formulation of Acousto-Optical Interaction in Nanoscale Cavities and waveguides

Résumé

Interaction of light and sound in tiny optical cavities and waveguides is a vibrant topic nowadays. Indeed, both optical and elastic fields are tightly confined to a very small volume and surface effects become significant with the size reduction. Recent progress has shown that opto-acoustic interaction benefits from the combined photoelastic and moving-interface effects. While the photoelastic effect is classical in bulk acousto-optics, the moving-interface effect is specifically driven by the vibrations of surfaces. Assuming a photonic mode and a phononic mode are known beforehand, the diffraction efficiency for the creation of new photons can be estimated by overlap integrals. Reciprocally, the confined optical field also exerts mechanical forces on the material composing the cavity. The objective of this study is to obtain a variational principle describing the full acousto-optical interaction. We construct a 3-wave Lagragian describing the interaction of the original optical wave, the Doppler-shifted optical wave, and the acoustic phonons. The three waves are further phased-matched in waveguides. The Langragian exhibits both volume and surface contributions to the interaction energy. First, electrostriction results in a volume force governed by the photoelastic tensor. Second, coupling of the electromagnetic field with the mechanical motion of the cavity further results in an effective surface force. We then solve the resulting elastodynamic equation subject to volume and surface optical forces. A finite element model is derived from the variational formulation. It is applied to acousto-optical (or optomechanical) interactions in a nanoscale photonic cavity. The simulation results show that acoustic resonances can be excited all-optically in the multi-gigahertz range for infrared light. The finite element model is also applied to tiny optical waveguides and compared to experiments performed with silica micro-fibers, revealing the generation of surface acoustic waves on the waveguide boundaries.
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Dates et versions

hal-02300690 , version 1 (29-09-2019)

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  • HAL Id : hal-02300690 , version 1

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Vincent Laude, Jean Beugnot. Lagrangian Formulation of Acousto-Optical Interaction in Nanoscale Cavities and waveguides. International Congress on Ultrasonics, May 2015, Metz, France. ⟨hal-02300690⟩
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