An acousto-optic (AO) frequency shifter includes an anisotropic crystal having an optical axis and an input face, and an acoustic transducer having electrodes affixed to the face for receiving an electrical signal and projecting an acoustic wave into the crystal. The anisotropic crystal is cut relative to the face so that the transducer is at an acoustic angle (θa) corresponding to a predetermined angle of incidence (θi) of an optical beam to be directed relative to the optic axis of the anisotropic crystal to substantially satisfy the parallel tangents phase matching condition.