Abstract: Lithium niobate film on insulator (LNOI) is increasingly applied in the field of key devices in the new generation of information technology. With the development of the techniques of lithium niobate single crystal thin film and photonic integrated circuits, low cost, high integration is the eternal development direction. Therefore, it is urgently needed the large-scale lithium niobate crystal. In this paper, the variation of natural convection of melt in large-sized crucible as the liquid level decrease was discussed, and the growth characteristics of Z- and X-axis lithium niobate crystal were discussed. The 8-inch Z- and X-axis lithium niobate crystals with the size of larger than ϕ210 mm×50 mm were obtained. The transmission of the spectral range of 380~3 300 nm is more than 70% for 1 mm thick X-axis lithium niobate wafers. The chip moire pattern images show the presence of refractive index ripple defects in the crystal, indicating that the quality of the crystal still needs improvement.

Key words: lithium niobate, 8-inch, natural convection, Czochralski method, refractive index ripple