Fabrication of periodically poled lithium niobate crystal and poling-quality evaluation by diffraction measurement

Periodically poled lithium niobate (PPLN) is the most widely used crystal for practical implementation of quasi-phase matching (QPM). We periodically poled LiNbO3 single crystals by using an electric-field poling method. A series of PPLN samples with varying duty cycle was fabricated, and one of the faces was etched out to reveal a surface relief pattern. We measured the far-field pattern diffracted from the surface grating, and successfully evaluated the quality of the QPM grating, such as period stability and duty cycle. We could establish a quantitative relation between duty cycle information obtained from the diffraction measurement and the charge provided during the poling stake.