Structural and nonlinear optical properties of epitaxial LiNbO3 films grown by pulsed laser deposition

Epitaxial LiNbO3 films were grown on Al2O3 substrates using pulsed laser deposition. Formation of the Li-deficient phase could be suppressed by lowering deposition temperature. With a shadow mask, surface smoothness of the film was significantly improved and its propagation loss was reduced to 3 dB cm−1. On Al2O3(0001) substrates, the films with different twin ratios could be grown by varying the growth conditions and their second harmonic generation (SHG) properties were investigated. In order to analyze the SHG patterns, the contributions of the structural twins and polarization domains were taken into account. The nonlinear optical susceptibilities and linear electro-optic (EO) coefficients of the LiNbO3(0001)/Al2O3(0001) film were found to be comparable to those of single crystals. On Al2O3(112̱0) substrates, it was possible to obtain two kinds of films with different crystal orientations and their EO behaviors were found to be quite different. LiNbO3(0001) films had negligible EO properties but LiNbO3(112̱0) films showed a very large quadratic EO behavior with an effective coefficient of 2.38×10−15 m2 V−2.