Abstract: A retromodulator in the form of a triple mirror with electromechanical transducer elements for planar deformation by which incident light radiation is retroflected in modulated form. At least one face of the retromodulator is formed as an oscillatory diaphragm which is excited to natural oscillations by the transducer elements. In a preferred form of realization, the oscillatory diaphragm comprises a piezoelectric foil, on whose inner side a reflecting layer is applied and on whose outer side electrodes are applied to which the modulation signal is applied.