An acousto-optic device, comprising: a core layer having two materials (11a, 11b) of different dielectric constants arranged in a two-dimensional hexagonal periodic structure thereby forming a periodic photonic crystal structure in which unit cells corresponding to the first Brillouin zone of a hexagonal pattern are regularly repeated in the wavevector space, which results in an anisotropic hexagonal angular distribution of the refractive index at the boundary of the respective unit cell; a first clad layer on a first surface of the core layer, the first clad layer having a refractive index that is different from the refractive index of the core layer; a second clad layer on a second surface of the core layer, the second surface being opposite to the first surface, the second clad layer having a refractive index that is different from the refractive index of the core layer; and a sound wave generator (14-16, 131a, 132a) configured to apply surface acoustic waves, SAW, to the core layer, the first clad layer, the second clad layer, or any combination thereof in a direction (y) parallel to the first and second surfaces; wherein the core layer, the first clad layer, the second clad layer, or any combination thereof to which the SAW are applied includes an acousto-optic material; characterised in that the sound wave generator is arranged to apply the SAW with a wave vector extending from a first vertex of the unit cell to a neighboring second vertex of the unit cell in the wavevector space, and by means configured to direct light to the core layer with a wave vector extending from the center of the unit cell to the first vertex of the unit cell in the wavevector space. a core layer having two materials (11a, 11b) of different dielectric constants arranged in a two-dimensional hexagonal periodic structure thereby forming a periodic photonic crystal structure in which unit cells corresponding to the first Brillouin zone of a hexagonal pattern are regularly repeated in the wavevector space, which results in an anisotropic hexagonal angular distribution of the refractive index at the boundary of the respective unit cell; a first clad layer on a first surface of the core layer, the first clad layer having a refractive index that is different from the refractive index of the core layer; a second clad layer on a second surface of the core layer, the second surface being opposite to the first surface, the second clad layer having a refractive index that is different from the refractive index of the core layer; and a sound wave generator (14-16, 131a, 132a) configured to apply surface acoustic waves, SAW, to the core layer, the first clad layer, the second clad layer, or any combination thereof in a direction (y) parallel to the first and second surfaces; wherein the core layer, the first clad layer, the second clad layer, or any combination thereof to which the SAW are applied includes an acousto-optic material; characterised in that the sound wave generator is arranged to apply the SAW with a wave vector extending from a first vertex of the unit cell to a neighboring second vertex of the unit cell in the wavevector space, and by means configured to direct light to the core layer with a wave vector extending from the center of the unit cell to the first vertex of the unit cell in the wavevector space.