Temperature Effects Of Electro-optic Crystal Materials

Lithium niobate crystal is one of the most comprehensive used electro-optic materials. The striking characteristic of lithium niobate crystal is electro-optic effect. Under the action of electric field, its refractive index principle axis and the refractive index in all directions will be changed. This is the electro-optic effect. The lithium niobate crystal also has many other quality characteristic for its comprehensive use. First, it's wide spectral range made it a good transmission which ranged from infrared, visible and ultraviolet band, especially the transmission are better than 95% ranged from 400-500nm. Second, the half-wave voltage can be changed by the crystal's size. The half-wave voltage can be reduced by enhancing length-thickness ratio. With the advancing of technology, the crystal with length-thickness ratio 100:1 has been made and its half-wave voltage can be reduced to very small value. Third, lithium niobate crystal have better diffraction ratio, fast photorefractive response and intensive anti-scattering etc, low cost, simple and utility. But lithium niobate crystal is affected by temperature as other electro-optic materials and the stability of device's performance will change. So it's necessary to make profound study on lithium niobate crystal's electro-optic effect with temperature changes. And here, based on the experiments, it's expounded in detail that the effect to chief properties and various parameters which temperature imposed on lithium niobate crystal.The paper includes five chapters. In the first chapter exordium, the development history and study existing state of lithium niobate crystal are introduced. The content, purpose and significance of this paper are also recited.In the second chapter, the basic knowledge of electro-optic crystal isintroduced. First, the general character of electro-optic crystal------ "electro-opticeffect" is introduced , chiefly includes the basic principle and expression method of electro-optic effect, and the expression method of refractive index and linear electro-optic coefficient are recommended as well. After that, the electro-optic effect of two typical electro-optic crystal ------KDP & LiNbO₃ are recited indetail. At last, the electro-optic crystal phase retardation of lithium niobate crystal is discussed. Different electro-optic effect will generate when the voltage imposed on various directions. Generally the cross direction and the longitudinal direction mode are applied. The principle and characteristic of them are introduced and the advantage and disadvantage of them are compared as well.In the third chapter, the chief applications of electro-optic crystal are introduced. The output light intensity will be changed regularly as the voltage changes when appropriate voltage and operating spot are selected. This is the electro-optic intensity modulation. After that, the phase modulation, the input light will be modulated by the phase modulation rate and will be modulated by the voltage actually. Applying the principle of electro-optic intensity modulation, an electro-optic Q switch can be made-up by applying voltage or not, i.e, impulse electrical signal to control the light path's on-off. That achieves good application on electro-optic Q modulation laser. Light deflection can also be realized applying lithium niobate crystal's electro-optic effect. The beam will be discrete on special space positions or move continuously according to preset rule in space. It's chiefly applied to optics information process and memory technology and various display technology.In the forth chapter, the effect of the temperature imposed on lithium niobate crystal is expounded. The change trend of refractive index is analyzed as the temperature grows. At the same time the method of removing the nature birefringence effect is introduced. Generally electro-optic coefficient is the function of temperature. And here the factors which affect the electro-optic coefficient are analyzed theoretically and the major methods of electro-optic coefficient measurement are introduced. Then the effect that temperature imposed on lithium niobate crystal phase retardation is analyzed. At last the effect that temperature imposed on lithium niobate crystal's transmission is introduced.In the fifth chapter, Experimental study is made on lithium niobate crystal's electro-optic effect. Profound research on lithium niobate crystal's electro-opticeffect is proceeded applying the system composed of semiconductor laser, polarized prism, temperature controlled device and photoelectric detector. The chief accomplished work is as follows:(1) At 650nm wavelength, the change state of lithium niobate crystal's transmission is measured and analyzed as the temperature grows.(2) Based on the measurement of (1), the change state of lithium niobate crystal's absorption coefficient is obtained as the temperature grows.(3) Different half-wave voltage is measured at different temperature and the change state of lithium niobate crystal's electro-optic coefficient is obtained as the temperature grows.(4) Based on the measurement of (1), the change state of lithium niobate crystal's phase retardation is analyzed as the temperature grows.(5) The change state of lithium niobate crystal's phase retardation is analyzed as the input light azimuth angle changes.At last, the existing questions and improvement methods of experiments are discussed.The innovation of this work is that theory connects with practice, the change states of lithium niobate crystal's parameter are measured as the temperature grows in experiment successfully and the difference between theory and experiment is explained. In the experimental technology, the temperature control device is made successfully and excellent control result is obtained. The change rules of absorption coefficient and absorption coefficient are obtained as the temperature grows. The change state of lithium niobate crystal's phase retardation is explained as the input light azimuth angle changes and also the feasibility of applying the change of input light azimuth angle to compensate the effect of temperature imposed on lithium niobate crystal's phase retardation is advanced.