Nature of bulk periodic poled lithium niobate formation

The bulk growth of periodic poled lithium niobate (PPLN) is made by the off-centered Czochralski technique adding an impurity to the melt. The periodic domain structures are obtained with different impurities such as Er, Yb, Nd, Cr, Fe and Y. The impurity distribution along the bulk PPLN crystals has been studied to understand the formation mechanism of the periodic domain structure. The distribution coefficient of the impurities, the temperature fields and the shape of the solid-liquid interface have been found to play a key role in the PPLN formation. The cooling rate and other growth conditions control the size of the areas where the periodic domain structure appears. It has been found that independently of the impurity added to the melt the dopant concentration is constant along the periodical domain structure, while it has been observed that exists a periodical variation of the Nb concentration which is related one to one with the periodical domain structure.