Second-harmonic green generation from two-dimensional χ(2) nonlinear photonic crystal with orthorhombic lattice structure

We report the synthesis of nonlinear photonic crystals (NPCs) with a periodical distribution of inverted χ(2) nonlinearity having an orthorhombic lattice structure on Z-cut congruent-grown lithium niobate (LiNbO3) substrate. The quasiphase-matching (QPM) mechanism of nonlinear wave interaction is examined by monitoring the far-field emission pattern of second-harmonic generation (SHG) as the NPC is pumped by a Nd:yttritium–aluminum–garnet laser beam. We observe (i) a series distribution of green SHG in a direction transverse to the fundamental beam, and (ii) an increase of phase-matching temperature in the SHG peak signal with the azimuth rotation angle in the x–y plane. These observations are ascribed to the high-order reciprocal lattice vectors assisted QPM–SHG process in a NPC that has a distribution of χ(2) nonlinearity with an orthorhombic crystal symmetry.