Tatsuo Kawaguchi

Efficient 340-nm light generation by a ridge-type waveguide in a first-order periodically poled MgO :LiNbO3

Quasi-phase-matched (QPM) UV second-harmonic generation (SHG) in a periodically poled MgO:LiNbO3 waveguide is presented. A ridge-type waveguide with high nonlinearity and strong resistance to photorefractive damage was achieved by use of an ultraprecision machining technique. By use of this waveguide in 1.4-microm periodically poled MgO:LiNbO3, a first-order QPM SHG device for 340-nm UV radiation was demonstrated. In a single-pass configuration, continuous-wave 22.4-mW UV light was generated for a fundamental power of 81 mW, corresponding to a normalized conversion efficiency of 340%/W.

Growth of high crystalline quality LiNbO3 thin films by a new liquid phase epitaxial technique from a solid-liquid coexisting melt

Abstract LiNbO3 films of higher crystalline quality than underlying LiNbO3 substrates have been successfully grown from a solid-liquid coexisting melt using a new liquid phase epitaxial technique. The dependence of crystallinity and lattice mismatch on film thickness and growth temperature has been investigated in detail through X-ray rocking curve analysis.

Liquid-phase epitaxial growth of Zn-doped LiNbO3 thin films and optical damage resistance for second-harmonic generation

ZnO-doped LiNbO3 (LN) liquid-phase epitaxial thin films grown on LN substrates were investigated as modified LN substrates for optical waveguide devices. The potential for optical use as substrates compatible with conventional ones was examined in quasi-phase-matched second-harmonic generation (SHG) devices from the viewpoint of the domain inversion process and optical damage properties. The formation of a periodically inverted-domain structure and the increased optical damage resistance in SHG were demonstrated.

Liquid phase epitaxial growth and characterization of LiNbO3 single crystal films

Abstract LiNbO3 (LN) thin film crystals are prepared on LN substrates by a liquid phase epitaxial method. An X-ray double crystal diffraction technique is used to characterize misfit strain in LN films. Analysis of lattice parameter differences along the c-axis shows that LN films of almost stoichiometric composition can be grown on an LN substrate prepared by the Czochralski method. X-ray topography reveals that the LN films have a lower dislocation density than the substrate crystals. Surface morphology is changed with increasing film thickness; thicker films do not show a mirror surface, rather hillocks with a three-fold symmetry appear.

Growth-temperature dependence of the LiNb ratio in LPE-grown LiNbO3 films estimated by second-harmonic generation

The relationship between the Li/Nb ratio of liquid-phase epitaxial (LPE) grown LiNbO 3 films and the growth temperature is investigated by means of second-harmonic generation measurements. Uniform 3-inch-wafer-size epitaxial films, which are available in conventional device fabrication processes, were successfully grown.

Crystal structure of LPE-grown LiNb1-xTaxO3 epitaxial films

Abstract LiNb 1− x Ta x O 3 epitaxial films, which were grown on LiNbO 3 substrates at various growth temperatures by the liquid-phase epitaxial method, were characterized using X-ray rocking curves, diffraction-space maps and absolute lattice constants. The films had relaxed structures regardless of the growth temperature, and the density of the dislocations due to the lattice mismatch between the films and the substrates increased with increasing growth temperature. Therefore, the crystallinity of the films became poor with increasing growth temperature.

Stoichiometry of liquid-phase epitaxial grown LiNb1−xTaxO3 films on LiNbO3 substrates

The tantalum composition (x) in LiNb1−xTaxO3 solid-solution films grown on LiNbO3 by liquid-phase epitaxy can be precisely controlled by changing the growth temperature. The composition of the film was found to be nearly stoichiometric (Li(Nb + Ta) = 1) based on electron probe microanalysis and X-ray rocking curve analysis. The second-harmonic generation phase-matching wavelength becomes longer by substituting Ta for Nb in LiNbO3.

Domain-inverted growth of LiNbO3 films by liquid-phase epitaxy

Abstract The ferroelectric domain structures of various liquid-phase epitaxially grown thin films, such as MgO-doped LiNb1 − xTaxO3 grown from the Li2OV2O5 flux system, were investigated using unique LiNbO3 substrates such as a rectangular bar and cylindrical fiber. Domain-inverted films were grown only on the surface of LiNbO3 oriented toward the + Z direction, except in the case of homoepitaxial growth. Unexpected domain structure was observed in the case of the LiNb1 − xTaxO3 film grown on the LiNbO3 substrate, that is, complex multi-domain structured LiNb1 − xTaxO3 films were grown on X surfaces, even though single-poled films were obtained on Z surfaces.

Crystal structure of LPE-grown LiNbO3 epitaxial films

Abstract LPE (liquid-phase epitaxial)-grown LiNbO 3 films with various thicknesses on LiNbO 3 substrates were characterized using diffraction-space maps and absolute lattice constants. The Li content in the films was estimated from the absolute lattice constants. The films had strained structures regardless of the film thickness. The Li content increased as the film thickness increased to about 15-μm, and it was constant at film thicknesses thicker than about 15-μm. It was found that the crystallinity of the films with thicknesses ranging from about 15-μm to about 25-μm was better than that of the substrates, because the composition was nearly stoichiometric and the films had a small composition gradient, few dislocations and little thermal stress.

Growth of LiNbO3LiNb1 − xTaxO3 multilayered waveguides on LiNbO3 by liquid phase epitaxy

LiNbO 3 /LiNb 1-x Ta x O 3 multilayered films, which form an optical waveguide structure, were grown on a LiNbO 3 substrate by the liquid phase epitaxial method.