Broad multiwavelength second-harmonic generation from two-dimensional chi((2)) nonlinear photonic crystals of tetragonal lattice structure

Abstract

We investigate the effects of lattice spacing and domain-filling ratio on the wavelength dependence in second-harmonic generation (SHG) from two-dimensional chi((2)) nonlinear photonic crystals (2-D NPC) on lithium niobate. Spectral coverage of 150 and 200 nm around 1.5 and 1.9 mum in quasi-phase-matched (QPM) SHG is obtained by angular rotation of the NPC with a lattice periodicity of 20 x 20 and 29.5 x 29.5 mum(2), respectively. The SHG signals are shown to have off-axial propagation directions determined by the incident wavelength and the QPM vector. The intensity of the high-order reciprocal-lattice-vector (G(mn))-assisted SHG signal is shown to depend on the domain-filling ratio. These observations are attributed to the unique dispersion of G(mn) together with the nonzero chi((2)) (G(mn)) nonlinearity in the 2-D QPM-NPC having a tetragonal lattice structure.