| With the rapid development of modern optical communication,higher requirements are put forward for optical communication technology and devices,and even the vision of implementation of all-optical system in optical communication in the future.The optical switching devices are the most critical devices in all-optical systems,but the mechanical optical switching devices which rely on high-speed electronic components for switching or routing have few ports,slow response speed and low integration.The traditional electro-optic materials(such as lithium niobate)with small electro-optic coefficients and high half-wave voltage can not meet the application requirements of optical communication in the future.In order to solve this problem,this study is based on the lanthanum doped lead zirconate titanate(PZLT)dielectric material which exhbits huge quadratic electro-optic coefficient and fast response speed.Through regulating the composition ratio and the preparation process of PLZT dielectric material,the mechanism of producing electro-optic effect was clarified,and finally the PLZT thin film dielectric material with excellent quadratic electro-optic effect was obtained.The PLZT dielectric materials not only have huge quadratic electro-optic coefficient,good optical properties,but also possess excellent dielectric property.By combine PLZT with polyvinylidene fluoride(PVDF),dielectric composite films with good flexibility and high energy storage density can be obtained which may meet the requirements of lightweight and miniaturization of electronic components.The PLZT fillers of di Fferent dimensions(0D,1D and 2D)were synthesized in this study.Then the PLZT/PVDF composite thin films with different dimensions of PLZT were prepared by solution casting method,and the effects of different dimensions of PLZT fillers on the dielectric properties of composite films are clarified by theoretical models.The main research and conclusions of this study are as follows:(1)Based on PLZT(9/65/35)system,the microwave sintering method can realize the rapid sintering of PLZT ceramics at a lower temperature,which reduce the sintering temperature by 200°C and the sintering time from 3 h to 20 min compared with the traditional sintering method.The PLZT ceramics prepared by microwave sintering are more compact and uniform,with small grain size,obvious grain boundary and small porosity.In order to solve the low diffusion problem of Zr4+and Ti4+,which is difficult to mix uniformly at the molecular level,the PLZT powders were prepared by partial coprecipitation method which improves the sintering activity of raw material powder.The relative density of PLZT ceramics is 96.5%,the dielectric constant is 3895,dielectric loss is 0.029 and the highest transmittance is 53.8%.(2)In order to further improve the transmittance of PLZT dielectric materials,the smooth and crack-free PLZT thin films were prepared by plasma annealing method.The highest transmittance is 89.2%.After La doping,the influence mechanism of the oxygen vacancy which was introduced by La doping on the properties of PLZT(x/65/35)thin films was investigated.And when the content of La is 9%,the hysteresis loop of PLZT(9/65/35)thin film shows a typical quadratic type,which is a slimmer hysteresis loop and a lower intensity of remanent polarization(18.2?C/cm2).The optical properties of the film are excellent,the absorption coefficient is nearly zero and the forbidden band width is large(?3.6 e V).At last,we designed PLZT thin film waveguide,and the insertion loss of the PLZT optical waveguide is less than 5 d B.(3)For promoting the optical and quadratic electro-optic properties of the PLZT thin films,high quality PLZT(x/65/35)thin films were prepared on ITO/Si O2 conductive glass substrates by improved sol-gel process,multi-layer spin coating and layer upon layer plasma annealing.Through improved preparation process,the internal thermal stress between layers is eliminated and the defects between layers will be reduced.The structure of the thin films shows typically(110)preferred orientation,with the highest transmittance of 93.8%,and the surface root mean square(RMS)roughness of the PLZT thin films is around 1 nm.In this study,the test system for quadratic electro-optic effect was improved,and the optical path was simplified.The maximum quadratic electro-optic coefficient of the PLZT thin films is 3.54×10-15 m2/V2 by the above system.And the PLZT electro-optic modulators are manufactured based on the PLZT thin films.The 3 d B bandwidth is about 65 GHz,and the half wave voltage V?L is 7.4 V·cm,which are expected to be widely used in all-optical communication in the future to realize fast voltage switching optical signal or modulation of optical signal.The process of internal ferroelectric domain changing with applied electric field was studied by piezoelectric response force microscope(PFM)technology.The results show that the motion and switching of 90°domain affect the piezoelectric response of the PLZT thin film,and determine the value of quadratic electro-optic coefficient.The more 90°domain regions,the stronger piezoelectric and quadratic electro-optic effects.(4)The PLZT/PVDF composite films were obtained by solution casting method.The dielectric constant of the thin films was increased by adding PLZT fillers,which enhanced from 8.0(no fillers)to 12.03(2 vol%PLZT fillers),and the energy density was 7.18 J/cm3.The PLZT fillers with different dimensions were prepared,and the compatibility of PLZT fillers with polymer was ameliorated by dopamine surface modification.Based on Maxwell-Garnet dielectric model,new dielectric models for composites with different dimensional fillers were derived.The dielectric constant of composites with different dimensional PLZT fillers are calculated by the new model.With the increase of PLZT fillers dimension,the composite thin films exhibit better dielectric and energy storage properties.The maximum dielectric constant(19.76)of PLZT/PVDF composite thin films was obtained by 2D PLZT filler and the energy storage density is 13.86 J/cm3. |
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