Improved Properties of Stoichiometric LiNbO3 for Electro-Optic Applications

High quality stoichiometric LiNbO ₃ single crystals, 40 mm in diameter and 80-100 mm in length, have been successfully grown by the double crucible Czochralski method equipped with automatic powder supply system using radio-frequency heating and automatic diameter control system. Although some difficulties still exist in growing 3 inch size single crystals from offcongruent composition melts, our results demonstrate that stoichiometric LiNbO ₃ crystals containing much less nonstoichiometric defects than congruent LiNbO ₃ exhibit some advantageous properties for holographic data storage applications. This was confirmed by the results of two-beam coupling experiment and digital hologram test. In digital holographic data storage, we have demonstrated that stoichiometric LiNbO ₃ shows more than 10 times larger photorefractive sensitivity than congruent LiNbO ₃ In order to interpret the high performance of stoichiometric LiNbO ₃ , we compared several relevant parameters such as electro-optic constants, photoconductivity, and photogalvanic constants between stoichiometric and congruent LiNbO ₃ crystals. We report that material parameters are strongly dependent on the density of nonstoichiometric defects and control of these defects is of key importance in improving and tailoring those properties.