LiNbO₃ Nonlinear Photonic Crystal with 12-Fold Rotational Symmetry

We fabricate z-cut LiNbO₃ nonlinear photonic crystal with two-dimensional dodecagonal superlattice by applying high voltage pulses. By using collinear quasi-phase matching technique, second-harmonics at five wavelengths 620 nm, 574 nm, 555 nm, 515nnm and 492 nm are observed simultaneously in one quasiperiodically poled crystal. The distributions of the reciprocal vectors and the diffraction spots in this quasiperiodic structure are theoretically and experimentally analyzed. The same results can be obtained by rotating around z-axis by intervals of 30°.