Research On Electro-Optic Modulation Characteristics Based On The Secondary Electro-Optic Effect Of Potassium Tantalum Niobate

Potassium Tantalum Niobate(KTa_1-XNb _XO₃)crystal is a functional crystal with the largest secondary electro-optic coefficient.Under the action of an external electric field,it can exhibit excellent electro-optic performance,especially as the core device of an electro-optic modulator,which can greatly reduce the drive Voltage,improving modulation efficiency,has become a key material in many application fields,and has great application potential in optical fiber communication systems,medical fast scanning systems,and radar display systems.The theoretical and experimental research on the electro-optic modulation process of KTN crystals also helps to understand more functional characteristics appearing in other electro-optic functional crystals.Therefore,on the basis of summarizing the research progress and theories related to KTN crystal electro-optical modulation at home and abroad,this article has done further work.The main contents are as follows:KTN is difficult to grow due to the characteristics of its solid solution.In this paper,through precise temperature and growth conditions control,a 40 mm×40 mm×40 mm pure KTa_0.65Nb_0.35O₃ single crystal with a large size of 40 mm×40 mm×40 mm was grown by the top seed crystal melt growth method.The Curie temperature is 4?,and it is in the cubic phase at room temperature.The crystal is colorless and transparent and has no obvious macroscopic defects.Ion-doped KTN crystals were grown,and Fe:KTa_0.65Nb_0.35O₃crystals with a size of 40 mm×10 mm×20 mm were grown.The Curie temperature was 4?,cubic phase at room temperature,and the crystal color is normally transparent and light yellow.In addition,pure KTa_0.59Nb_0.41O₃ and Fe:KTa_0.59Nb_0.41O₃crystals with tetragonal phase were grown.After simple manual polishing of several KTN crystals,metal Au was selected as the electrode material,and Au was plated on the upper and lower surfaces of the KTN crystal as electrodes by magnetron sputtering coating method,and the film on the crystal surface after the coating was performed A rapid annealing treatment is used to improve its electrical properties.Dielectric temperature spectroscopy experiments show that Fe ion doping can significantly increase the maximum relative permittivity and secondary electro-optical coefficient of KTN crystals,which is an important means to improve the properties of KTN crystals.The effect of the cooling process on the dielectric properties of Fe:KTa_0.59Nb_0.41O₃crystal was studied.The Fr?ohlich entropy theory is introduced.According to the relationship between the Fr?ohlich entropy and the order and disorder of the crystal nano-microstructure,the Fr?ohlich entropy value in the mesothermal spectrum test and the change of the internal microstructure of the KTN crystal with temperature are analyzed.The structure of pure KTa_0.59Nb_0.41O₃ and Fe:KTa_0.59Nb_0.41O₃ crystals were analyzed by XRD diffraction test.And the focus is on the changes in the dielectric properties of the pure KTa_0.59Nb_0.41O₃ and Fe:KTa_0.59Nb_0.41O₃ crystals during the temperature rise and fall.Dielectric spectroscopy experiments on pure KTa_0.59Nb_0.41O₃ and Fe:KTa_0.59Nb_0.41O₃crystals with different cooling rates show that the change of cooling rate will not cause great changes to the dielectric properties of pure KTa_0.59Nb_0.41O₃ crystals.Only a slight lateral displacement of the dielectric peak will occur;for Fe:KTa_0.59Nb_0.41O₃ crystals,when the dielectric peak is displaced laterally,the faster the temperature drop,the greater the increase in the maximum relative permittivity of the crystal.As the cooling rate increases quantitatively,the growth of relative permittivity is gradually slowing down.The index ellipsoid model of the secondary electro-optic effect of KTN crystal is introduced and the modulation waveform of KTN crystal is simulated.By comparing the data obtained by the electro-optical experiment of the KTN crystal with the data image derived from the theory,the accuracy of the experimental measurement is proved;secondly,the influence of the temperature rise and fall process on the dielectric properties of the KTN crystal is discussed;The influence of external conditions such as the step-down process,multi-cycle repetitive voltage and incident light intensity of different powers on the secondary electro-optical coefficient of KTN crystal.In the step-up and step-down experiments,the electro-optic modulation curve is inconsistent;the greater the applied voltage,the faster the amplitude of the modulated light intensity decays;the multi-cycle voltage cycle will cause the electro-optic modulation ability of the crystal to attenuate or even disappear;with the initial optical power with increasing,the attenuation rate of the modulation depth will also increase.These phenomena all indicate that there are polar nano-domains in the Fe:KTa_0.65Nb_0.35O₃ crystal,which has an important influence on the crystal during the entire electro-optical modulation process.