Acousto-optic couplings in two-dimensional lithium niobate phoxonic crystal
Résumé
We investigate the acousto-optic couplings in two-dimensional infinite piezoelectric phoXonic crystal cavities. The periodic structure considered consists in a square array of air inclusions drilled in Lithium Niobate matrix. This structure allows the simultaneous confinement of acoustic and optic waves in a point defect obtained by removing one hole from the structure. Our theoretical analysis takes into account three different coupling mechanisms. In addition to the traditional effects: photo-elastic effect and opto-mechanic effect existing in non-piezoelectric materials, we consider the electro-optic effect introduced by the electric filed accompanying the phonon. Using the finite element method, we analyze the perturbation of the photonic cavity modes under the action of phononic cavity modes. We first discuss some aspects of the additional electro-optic effect. For illustration purposes, we compare the coupling strength of two analogous breathing modes, one as found in the LiNbO3 structure and another mode qualitatively comparable but evidenced in a similar silicon structure. Then, we end the discussion by an analysis of the coupling strength dependence on typical crystallographic cuts of Lithium Niobate.