Higher order quasi-phase matched harmonics in two-dimensional quasiperiodic superlattice

Two-dimensional LiNbO3 nonlinear photonic crystal with octagonal quasilattice was fabricated by applying the external electric field. The higher order collinear quasi-phase matched second harmonics, in the red, orange and blue–green areas, along the midline of the two adjacent basic reciprocal vectors were obtained, in which the efficiency of red harmonics reached 17%. And the higher order non-collinear second-harmonic generations with the input beams parallel to the basic reciprocal vectors were studied systematically, in which the related highest-order reciprocal vector pair was (2 2 1 0) and (−2 0 1 2). All the same results can be obtained when the crystal is rotated by the integral multiples of π/4.