LITHIUM NIOBATE SINGLE CRYSTAL AND OPTICAL FUNCTIONAL ELEMENT

摘要

PROBLEM TO BE SOLVED: To enable the inversion of ferroelectric polarization at a relatively low applied voltage in high precision without generating the pinching of the polarization inversion by specifying the molar ratio of Li2O to Nb2O5 of a grown lithium niobate single crystal, thereby controlling the indefinite ratio defect concentration. SOLUTION: A lithium niobate single crystal having an Li2O/(Nb2O5+Li2O) molar ratio of 0.49-0.52 is produced e.g. by conventional pulling method from a molten liquid having a composition containing remarkably excess Li component, i.e., having an Li2O/(Nb2O5+Li2O) molar ratio of about 0.56-0.60. The produced lithium niobate single crystal has a composition having an Li:Nb ratio of about 1:1 and scarcely contains excess Li component to form large quantity of defects in the crystal. The voltage necessary for the inversion of the dielectric polarization of the single crystal can be lowered to <=10 kV/mm by this process. The wavelength of an incident laser light can be decreased or increased by constituting an optical functional element with the single crystal and periodically inverting the polarization structure of the crystal.