Acousto-optical devices, such as deflectors, modulators or filters, provide an effective way of light control and signal processing techniques. However, their operation range is limited to visible and near-infrared wavelengths due to quadratic law of efficiency decrease of acousto-optical interaction with the wavelength increase. Besides, high-quality acousto-optic materials such as TeO2 are non-transparent at wavelengths larger than 5 µm, while the infrared optical materials provide significantly lower acousto-optic quality. Here we demonstrate how these limitations could be overcome by applying of specifically designed multilayered structures with electromagnetic modes strongly coupled to the incident light using Otto configuration of prism coupling. Such approach could be used for a novel acousto-optical device operating at 8-14 μm wavelengths. Acoustic wave is excited via a piezoelectric transducer in the prism provides modulation of the coupling intensity which results in up to 100% modulation of the transmitted light at the spatial scale less than the ultrasound wavelength. Therefore, it provides the possibility to achieve efficient acousto-optical modulation at frequencies over several gigahertz.