Generation of Second-Harmonic Conical Waves via Nonlinear Bragg Diffraction

We report on the observation of second-harmonic conical waves generated in a novel geometry of the transverse excitation of an annular periodically poled nonlinear photonic structure by a fundamental Gaussian beam. We show that the conical beams are formed as a result of the higher-order nonlinear Bragg diffraction involving two parametric processes in which an ordinary fundamental wave is converted simultaneously into ordinary and extraordinary polarized second harmonics.