Decrease in the contrast of the speckle of the optical field using Bragg diffraction of light by sound

To decrease the contrast of the speckle of the optical field formed at the output of a multimode optical fibre, it is proposed to use the acoustooptical Bragg diffraction providing a collinear propagation of beams having different polarisation and diffracted to the +1 and -1 orders, and to focus them at the fibre input. This regime provides the 90 % diffraction efficiency. It is shown experimentally that the properties of diffraction in a TeO₂ anisotropic crystal provide an efficient control of the speckle contrast by varying the acoustic frequency, which allows a strong suppression of the speckle.