Study On The Photorefractive Spatial Solitons In LiNbO₃Crystal

Lithium niobate(LiNbO3, LN), as a contender for the role of "optical silicon", has many important properties for both research and applications, such as electro-optic, acousto-optic, thermal-optic, piezoelectric and photorefractive effects etc. Photorefractive effect is induced by the special modulation of light intensity, and the change in refractive index is proportional to the modulation extent. It was reported that photorefractive spatial soliton could be realized in LN. We study in this paper the polishing technique of LN crystal, the physical conditions of generating photorefractive bright spatial soliton, and the improved model (two-center model) for describing the photorefractive process in LN.For obtaining optical grade surface required by soliton experiment, I carefully grind and polish the Fe-doped lithium niobate. After studying the polishing effect under different polishing conditions, we find the optimal effect occurs at the polishing pressure of0.8kPa, the polishing solution pH of9-10, and the polishing disc rotational speed of40r/min.The bright spatial soliton is realized in Fe-doped LN crystal with the background light power of30μW and signal light power of4.3μW. The results show that when the ratio R of Glass constants at the background wavelength and at signal light wavelength is constant and greater than one, the spatial soliton generates in Fe-doped LN. Although the refractive index change of the lithium niobate remains negative, its optical property has changed from self-defocusing to self-focusing.The spatial soliton phenomenon is essentially induced by photorefractive effect, which is usually explained by single-center model. However, the single-center model does not consider the different sites of Fe ions in the lattice structure. Here in this thesis, we establish a two-center model on the basis of the previous model and try to use it to explain the photorefractive result in Fe-doped LN.