| Lithium niobate crystal (LiNbO3) is a widely used artificial ferroelectric crystal, which has good characteristics of photorefractive, electro-optic, acousto-optic, pyroelectric and nonlinear optical effect. And the domain engineering in LiNbO3is widely exploited for quasi-phase-matched techniques, light deflector, optical scanners, optical switches. Currently electric field polarizing is the most commonly used method of domain inversion. The domain structure of crystal is modulated by applying external electric field poling with structured electrodes and realizing the periodically polarizing of LiNbO3. But there are some problems of electric field polarizing method that the location of new domain nucleation is random, domain structure tends to deviate from the electrode area and difficult to precisely control the growth of domain structure. In recent years, laser-induced domain inversion becomes a new research direction. But there is also a disadvantage of limited depth of domain structure. Therefore, it is very important to study the characteristics of domain inversion under external electric field and optimization of domain inversion method in LiNbO3, and expand the application of domain structure. In this thesis, we study the characteristics of domain walls growing and polarization current in differently doped LiNbO3under electric field polarizing and compare the characteristics of the external electric field polarization and laser-induced domain inversion in MgO-doped LiNbO3with experimental methods. The optimization of combination of external electric field and laser-induced polarization method is explored. Finally, semicircular domain structures are fabricated in LiNbO3, and electro-optic effect of the domains structure and electro-optical diffraction effect of PPLN are studied. The main contents of this thesis include the following five aspects:(l)This thesis begins with a brief introduction of the structure and ferroelectric properties of LiNbO3. Then we introduce the domain fabrication technique and the observation methods of domain structure in LiNbO3, and introduce electro-optic effect of domain structure with opposite polarization direction of LiNbO3.(2) We study the domain inversion process of different concentrations MgO-doped LiNbO3under external electric field and find the characteristics of domain walls motion and polarization current in forward and reverse inversion process. The relation curves between domain wall motion and polarization current is given and the phenomenon is explained in the light of pinning theory.(3) The characteristics and domain inversion process are compared between external electric field polarization and laser-induced domain inversion in7mol%MgO-doped LiNbO3with experimental methods. The study show that laser-induced can control the position of new domain nucleation, and we can effectively control the growing of domain structure by the optimized combination of external electric field, light field and duration of action.(4) The non-synchronization under electric field polarizing and the synchronization under laser-induced inversion of LiNbO3are studied in multi-domain inversion process. Then semicircular domain structures are fabricated in LiNbO3, electro-optical focusing properties of the domain structure is studied, the dynamic focusing effect of the domain structure is simulated, and the impact of various geometric parameters on the dynamic focusing properties is analyzed.(5) Using the grating rigorous coupled-wave theory, the electro-optic diffraction effect of PPLN crystal is analyzed numerically. Experiments are used to study the properties of electro-optic diffraction of PPLN crystal by incident light with different polarization directions. |
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