Apparatus and method for modulating quasi-monochromatic electromagnetic radiation utilizing a controllable diffraction grating. A reflection diffraction grating is comprised of a material deformable in the presence of an applied electric field. A first electrode, comprised of a flexible radiation-reflecting material, is applied to the first surface of the deformable material, forming a reflecting surface of the diffraction grating. A second electrode is applied to a second surface of the deformable material. The electrodes are arranged to provide a periodic surface distortion on the reflecting electrode upon application of a voltage between the first and the second electrodes, thereby resulting in a blazed diffraction grating. In addition, the blaze angle of the diffraction grating can be varied as a function of applied voltage, and consequently diffracted radiation pattern can be modulated as a function of the applied voltage. The controllable diffraction grating can modulate the diffracted radiation in a digital or in an analog mode of operation.