GHz acousto-optical tunable filter configurations in uniaxial crystals

A novel type of wide angular aperture noncollinear acoustooptical tunable filter (AOTF) configuration in uniaxial crystals is described. These AOTF configurations have a very high figure of merit and operate at a few GHz. They are very attractive because of the recent advent of efficient GHz multilayer ZnO transducers. A formulation is presented which allows an analytical solution for the dependence of the Bragg angles with respect to both the refractive indices and the acoustic wave propagation direction. As a consequence it is shown that, provided the figure of merit is nonzero, these configurations are obtained for any acoustic wave propagation direction. This is in contrast to previously reported noncollinear AOTF configurations which are only obtained when the acoustic-wave propagation direction is constrained to lie within an angular range depending only on the refractive indices of the medium. AOTFs based on the proposed configurations are analyzed in TeO₂ , LiTaO₃, quartz, Al₂O₃ and Te and illustrative calculations related to the tuning curves, the figure of merit and the resolution in these materials are given