Generation of conical second harmonic waves by nonlinear Bragg diffraction in two-dimensional nonlinear photonic structures

We generate conical second-harmonic waves through the parametric frequency conversion in a two-dimensional annular, periodically poled nonlinear photonic structure under the transverse excitation with a fundamental Gaussian beam. We explain the effects observed experimentally by applying the concept of nonlinear Bragg diffraction to the case of the conical frequency generation. We study the polarization properties of the conical emission at the second-harmonic frequency and demonstrate that each of the parametrically generated waves represents a superposition of the Bessel beams.