Diffraction-induced polarization effects in optical pattern formation

We show theoretically that patterns with concentric rings of bright or dark spots made up by modes with coprime azimuthal indexes may arise in codimen sion one bifurcations in optical systems with a metallic diffractor, a pola rizer, and a nonlinear medium. These patterns are a consequence of diffract ion-induced polarization in systems without polarization dynamics. As an ex ample of this type of system, we investigate numerically the symmetry-break ing bifurcations of a ring laser with a metallic duct and a polarizer insid e the optical cavity.