Photo-acoustic conversion based sound emitter device

A photo-acoustic conversion based sound emitter device, comprising:

• a sound output surface for transmitting sound wave vibrations to a medium outside the device;
• an optical waveguide, configured to transmit light through an optical path within the device, the optical waveguide being integrated on or in a substrate and extending in parallel with the sound output surface, and an optical coupling structure optically coupled to the optical waveguide and configured to redirect the light from the optical waveguide along said optical path in a direction having a component normal to the sound output surface;
• first and second photo-acoustic conversion volumes, at different distances from the sound output surface, for transmitting sound generated in the first and second volumes to the medium via the sound output surface, the first and second photo-acoustic conversion volumes being solid-state layers stacked one above the other between the optical waveguide and the sound output surface, the optical path being redirected by the optical coupling structure to extend successively through the first and second photo-acoustic conversion volume along said direction having a component normal to the sound output surface, wherein
• the device comprises an intermediate volume separating the first and second photo-acoustic conversion volumes along the optical path, the intermediate volume having a lower light absorption coefficient than the first and second photo-acoustic conversion volumes, the intermediate volume being an optically less absorbing layer;
• and/or
• the first and second photo-acoustic conversion volume have a different cross-section area size and/or shape with virtual planes perpendicular to the optical path;
• and/or
• the first and second photo-acoustic conversion volumes have different optical absorption coefficients, or a different optical wavelength dependence of these optical absorption coefficients.