Study And Application Of Residual Birefringence Of Lithium Niobate Crystal

Lithium Niobate is a widely used artificial crystal.It is rich in raw materials,easy to grow into large-sized crystal blocks,easy to process,and low in price.The grown crystal has the advantages of stable mechanical properties,corrosion resistance and high temperature resistance.Lithium niobate crystals also have good physical properties such as pyroelectricity,electro-optical,piezoelectric,acousto-optic,photorefractive,and elasto-optical.And differently doped lithium niobate crystals also exhibit some special properties,making it one of the most promising crystals at present.A large number of applications have been obtained in piezoelectric filters,high-speed electro-optic switches,electro-optic deflectors,holographic storage,optical amplification,frequency converters,In order to explore the electro-optic effect of LN crystals deeply,this paper first studied its residual birefringence.Using the rotating crystal method,the trajectory of the output polarization state on the Poincare sphere after the linearly polarized light passes through the LN crystal is measured.The study found that the theoretical motion trajectory without considering the residual birefringence is far from the measured trajectory,which is caused by the residual birefringence due to defects and inhomogeneities of the crystal itself.Therefore,the quaternion method is adopted in this paper to derive the relationship between the other three elements ?₄,?₅,?₆ and the output polarization state trajectory except for the three elements of the main diagonal in the dielectric constant tensor matrix of different LN crystals.Although there are some differences among different individuals,the three elements ?₄,?₅,?₆ all variation in the magnitude of 10^-3,10^-4,10^-6 respectively,which is far from the principal axis refractive index magnitude?about 2 points?.Although they are very small relatively,the effect on the polarization state cannot be ignored.This leads to LN crystals with residual birefringence,not only linear birefringence,but also circular birefringence and mode coupling.It is also found that the size of ?₄ determines the proportion of the motion track relative to the left and right distribution of the longitude line ?₂ = 0,?₅ determines the span of the motion track as a whole,and ?₆ determines the absolute size of the left and right distribution.Then,the temperature experiment of LN crystal birefringence was carried out,and the temperature characteristics between different deflection angles were measured.The results show that the residual birefringence of LN crystal does not correspond to the change of temperature.On this basis,the electro-optic effect of LN crystals considering residual birefringence is studied,and some ideas for voltage mutual inductance are proposed.Using ordinary light o direction linearly polarized light,using a paraxial oblique incidence,a voltage is applied in the direction of polarization,and a curve perpendicular to the equatorial plane and substantially parallel to the equatorial plane is found at-1°and +3.5° off the crystal axis,respectively.And can measure voltages from 0 to 5kv.Of course,the measurement accuracy can be improved by increasing the crystal length and reducing the thickness.The research results of this paper provide a feasible method for the design of new LN crystal voltage transformers.