Fabrication Of LiNbO₃ Grating By Photosensitive Sol-gel Method And Investigation Of Diffraction Property

Diffraction grating is a kind of optical element with good optical beam spectrum. It has broad application prospects in light beam splitter, wavelength division multiplexer, sensor and spectrum measurement, and has been widely studied in the field of integrated optics. LiNbO3 with good light transmission and low optical loss was used for the preparation of the waveguide and the diffraction grating. However, due to the low light damage threshold of the LiNbO3 material, The preparation of gratings by general physical method is easy to cause material defects, while pure chemical processing can avoid the occurrence of material defects and show strong processing advantages. In this paper, LiNbO3 grating with high density and high groove depth was prepared by the photosensitive sol-gel method, and the effect of its morphology on the diffraction efficiency of grating was studied. This laid the foundation for production of lithium niobate waveguide and micro integrated device. The main contents and results were as follows:(1) In the paper, Nb source (Niobium chloride and Niobium Ethoxide) and Li source(Lithium acetate dihydrate ) were used to prepare LiNbO3 sol respectively. The results showed that the LiNbO3 sol could be synthesized by using niobium ethoxide as Nb source and the metal ion ratio of Li: Nb=1.06:1. The LiNbO3 thin films was prepared on the Si substrate by dip-coating method. The results manifested that the high refractive index and good transparency of LiNbO3 optical thin film were fabricated by pre-treatment at 350℃ and end-processing at 650 ℃.(2) The LiNbO3 gel film were researched by the ultraviolet spectrum and the infrared spectrum. The results indicated that the LiNbO3 gel film sensitive to ultraviolet light near 350nm.(3) The micro-machining processability of photosensitive LiNbO3 gel film was proved after preparing different shapes of fine graphics by ultraviolet mask. The parameters of LiNbO3 grating preparing by laser interference process were studied. The results showed that LiNbO3 grating could be prepared by which the gel film was dried at 70℃ for 10min, exposured 6～10min, and was ded in mixed solution consists of isopropyl alcohol and ethanol. Finally, the different depths and different types of LiNbO3 gratings were prepared by laser interferometry and the diffraction efficiency was studied. The results show that the LiNbO3 sgrating depth increasing, the diffraction efficiency increases.