Study Of Growth And Improvement Of Optical Properties Of Indium-Doped Lithium Niobate

In:Zn:LiNbO₃, In:Zn:Fe:LiNbO₃, In:Mn:Fe:LiNbO₃ crystals with different In2O₃ concentration and In:LiNbO₃ crystals with different [Li]/[Nb] ratios were grown by Czochralski technique using the intermediate frequency furnace as the heater. By selecting appropriate growth technical parameters, crystals with good optical homogeneity and no macroscopic defects have been grown. After the annealing and polarization progress, a series of samples were prepared for measuring the properties. The reasons for the cracking of the LiNbO₃ were discussed and several effective methods were found to conquer it.The structure of the In-doped LiNbO₃ crystals has been measured by X-ray powder diffraction technique. The results indicated that the doped crystals kept the same lattice structure as that of pure LiNbO₃ crystal. But the lattice constants of doped-LiNbO₃ crystals changed compared with pure LiNbO₃ crystal. The Curie temperature of the crystals was measured by differential thermal analysis. The results showed that the Curie temperature increased with the In-doped concentration and [Li]/[Nb] ratio firstly, and then decreased.The infrared absorption spectra and ultraviolet-visible absorption spectra of In-doped LiNbO₃ crystals were measured. The OH- absorption peak of infrared absorption spectra and the absorption edge of ultraviolet-visible absorption spectra shifted with the In-doped concentration and [Li]/[Nb] ratio. The occupy mechanism of the dopants were investingated. The analysis showed that In³⁺ firstly replaced the anti-site Nb ( Nb_Li⁴⁺), which located at Li site. When the In-doped concentration reached the threshold, all the anti-site Nb ( Nb_Li⁴⁺) ions were replaced and In³⁺ began to occupy the ordinary Li and Nb sites.The photo-refractive resistant property was measured by transmitted facula- distoration method. The influence of the In-doped concentration and [Li]/[Nb] ratio on the photo-refractive resistant properties was investigated systematically. The results indicated that the photo-refractive resistant properties improved with the increasing of the In-doped concentration and [Li]/[Nb] ratio. When the In-doped concentration reached the threshold, the photo-refractive resistant ability was two orders of magnitude higher than that of those crystals without In-doped.The second harmonic generation (SHG) propertiesof In:Zn:LiNbO₃ and In:LiNbO₃ with different [Li]/[Nb] ratio were measured and the results indicated that the SHG properties were improved with the In-doped and the increasing of [Li]/[Nb] ratio. The SHG conversation efficiencies of In(2mol%):Zn(2mol%):LiNbO₃ and In(1mol%):LiNbO₃ ([Li]/[Nb]=1.0) were the highest, which were 42% and 50%, respectively. In:Zn:LiNbO₃ optical waveguide substrate were prepared by annealing proton exchange method and the optical damage property of the optical waveguide substrate was investigated by the m-line technique. The optical damage resistant ability was two orders of magnitude higher than that of pure LiNbO₃, when the In-doped concentration reached the threshold.The photo-refractive properties of the In-doped LiNbO₃ crystals were measured. The two-beam coupling exponential gain coefficient, the diffraction efficiency and the dynamic range decreased, while the response time shortened and the photo- refractive sensitivity improved followed by the increasing of the In-doped concentration. The analysis showed that the reduction of the efficient charge carrier density leads to the decreasing of the photo-refractive properties, while the improvement of the photoconduction cause the shortening of the response time.The holographic storage experiment was carried out by using In:Mn:Fe:LiNbO₃ crystal as the storage medium. The results showed that, for the In-doped, the distoration of the coherent peak facula decreased, the establishing time of the optical grating shorted and the quality of the output pictures optimized. The storage properties improved.The research showed that the optical properties of the LiNbO₃ crystal could be improved by doping In ions and changing [Li]/[Nb] ratio. It was helpful for the development of the application of LiNbO₃ crystal.