The Field-induced Enhancement Of Voltage-controlled Diffractive Of Paraelectric Potassium Tantalat Niobate

As the rapidly development of the network communications, the demand ofbandwidth and transmission speed is growing sharply. Developing the all-opticalnetwork has become a tendency. Optical switch and optical switch arrays are thecore devices for realizing all-optical switching network, which can be used in routerswitching, wavelength switching, OXC and network protection on optical level.Therefore, optical switch becomes the hotspot in research of opticalcommunications. In this thesis, the systematical investigations have been made onthe electro-optic properties and the field induced enhancement of voltage-controlleddiffractive of paraelectric potassium tantalant niobate (KTN).Firstly, the basic physical properties of the KTN crystals were studied. Theconstituent fluctuations theory suggests that KTN crystals have weak dispersionphase transition properties. The dielectric abnormal phenomenon near the Curietemperature was studied combining the evolution of spontaneous polarization in theprocess of phase change. The frequency dependence of the dielectric constantindicates that the crystals have frequency dispersion. It is explained that the relativedielectric constant of the [001] direction is significantly greater than the [110]direction at the temperature a little higher than the Curie temperature. The opticaltransmission spectrums and the dispersions of the refractive index from400nm to900nm were measured by the optical spectrometer and the spectroscopicellipsometry. The red shift phenomenon was explained by using the KTN crystaldoped placeholder mechanism. From the perspective of energy band structure, it isexplained that why KTN crystals have similar optical properties of ABO3perovskitestructure compounds.Then the quadric electro-optic properties of the KTN crystals were studiedsystematically. Firstly, according to the theory of coordinate rotation, the refractiveindex ellipsoid equation was deduced in any direction of the applied voltage. TheQEO coefficients component s11and s12were measured by the dynamicMach-Zehnder interferometer and s44was measured by the automated scanningSenarmont compensator method. The QEO coefficients at different temperaturewere also investigated. The difference of s44of the cooling and heating process wasalso discussed.Finally, the field induced enhancement of voltage-controlled diffractive ofparaelectric potassium tantalant niobate was investigated. The voltage controlledphotorefractive properties were analyzed by the band transport model. When the gratings were recorded under no voltage and voltage process, the energy transferduring the process and voltage-controlled diffractive in the reading process werediscussed. By comparing the diffraction efficiency and Grating recorded time ofthese two cases, it is explained the gratings recorded under voltage process canrealize the field induced enhancement of voltage-controlled diffractive. The energytransfer in the gratings recording process was studied. By changing the angle of therecording light, the relationship between electric field enhancement and gratingvector size was discussed. The crystal has good electric field enhancement effect inlarger range of the grating vector, indicating that this research will help to optimizethe performance of the holographic optical switch control.