Optically functional device, single crystal substrate for the device and method for its use

An optically functional device comprising a ferroelectric single crystal substrate and polarization-inverted structures formed at portions of the substrate at a temperature of not higher than the Curie temperature by an electron beam scanning irradiation method or a voltage application method and designed to control light passed through the polarization-inverted portions, wherein a LiNbO3 crystal having a molar ratio of Li/Nb within a range of from 0.95 to 1.01, is used as the substrate, so that the change in the refractive index of the polarization-inverted boundaries is not more than 1×10−4 without a heating step to remove an optical distortion at the polarization-inverted boundaries due to the directional inversion of spontaneous polarization in the ferroelectric crystal, wherein the ferroelectric single crystal substrate is made of a LiNbO3 crystal having a molar ratio of Li/Nb within a range of from 0.95 to 1.00 and containing from 0.1 to 4.8 mol % of at least one element selected from the group consisting of Mg, Zn, Sc and In, as doped.

A method for improving the driving efficiency of an optically functional device, wherein a LiNbO3 crystal having a molar ratio of Li/Nb within a range of from 0.95 to 1.01, is used as a substrate for the optically functional device to control polarization or condensing of a laser beam entered into a single crystal having polarization structures inverted in a prism or lens shape by means of an electro-optical effect.

A method for improving the frequency conversion efficiency of an optically functional device, wherein a LiNbO3 crystal having a molar ratio of Li/Nb within a range of from 0.95 to 1.01, is used as a substrate for the optically functional device to carry out the frequency conversion of a laser entered into a single crystal having periodically inverted polarization structures by means of a nonlinear optical effect, wherein the LiNbO3 crystal has a molar ratio of Li/Nb within a range of from 0.95 to 1.00 and contains from 0.to 4.8 mol % of at least one element selected from the group consisting of Mg, Zn, Sc and In, as doped.