Acousto-optical coupling of the side surface acoustic and optical waves in a two-dimensional phoxonic crystal slab hetero-structure cavity

Abstract

Phoxonic crystal is a kind of artificial periodic structure which can manipulate light and sound in the same time and space domain. It has good application prospect in optical communication system and opto-mechnical sensor. In this paper, a two-dimensional silicon phoxonic crystal slab structure is proposed, which can exhibit large phononic and photonic bandgaps simultaneously. Then a periodic cylindrical structure is introduced on the side surface of the slab. The effects of the height and radius of the cylinder on the side surface wave modes are analyzed. On this basis, a phoxonic crystal hetero-structure cavity composed of cylinders with different radii and heights is constructed, which can simultaneously confine the acoustic and optical modes because of mode gap effect. Seven phononic cavity modes and two photonic cavity modes are obtained. The two photonic cavity modes are called dielectric mode and air mode respectively. Further, the acousto-optical coupling rates between the seven phononic cavity modes and dielectric mode are calculated. Finally, a gap is etched on each cylinder in hetero-structure cavity, which can increase the surface area of the cavity by 23%. Then two phononic cavity modes and photonic dielectric mode with higher coupling rates are considered. The results show that etching the z-direction gap in the center of the cylinder can effectively increase the acousto-optical coupling rates.