| "Electro-optic effect" refers to the change of the refraction and transmission characteristics of the material when exposed to applied electric field, which makes the direction, amplitude, phase and polarization characteristics of the light wave transmitted in medium change. Material with this kind of attribute is often referred to as "electro optical material." By using the electro-optic effect, the optical transmittance and the reflection of the light can be modulated by adjusting the applied effect field. That technology has been wide applied in optical communication, optical sensing and optical display. Moreover it has alluring application prospect in high power solid laser, smart glass, and solar photo-voltaic and other technology. Yet one of the problems that can’t be avoided is the "thermal effect problem." The reason is that all hard and soft electro-optic material is affected by thermal optic effect, which means change of temperature and temperature gradient will lead to the variation of both refractive index and absorption coefficient, influencing the light transmission characteristics. The thermal optic effect of the material tends to be harmful. It has greatly limited the application of electro optic control technology, and makes the electro optic materials difficult to be suitable in the complex thermal environment. Thus, the applicable temperature range of electro optic materials is usually relatively severe. In order to reduce or eliminate the problem of temperature effect, many schemes have been put forward by researchers, such as cooling temperature control mode, compensation device mode, or using the material with low thermo-optic coeffecient to replace the original material. This paper aims to propose a new thought, which is taking advantage o f the electro-optic effect of the material to regulate its thermo-optic effect, scilicet, making use of additional electric field to regulate the optical radiation transmission characteristics of electro-optic material, thus realizing the aim of reducing or eliminating the harm of thermal effects.The paper focuses on how to use electro-optic effect to modulate thermal optic effect. The research mainly contains two aspects: one is the optical-thermal coupling mechanism and optical transmission characteristics of electro-optic materials under the action of the external electric field, the other is the fundamental mechanism and the model of thermo-optic effect controlled by electro-optic effect. According to the difference between the generation mechanism of electro-optic effect and thermo-optic effect, three kinds of typical materials are studied in this paper: dielectric type electric-optic material lithium niobate, semiconductor type electro-optic material silicon crystal and conductor type electro-optic material ionic liquid.For the dielectric type electric-optic material lithium niobate, the thermal coupling effect of Gaussian laser in the process of birefringence transmission in lithium niobate is analyzed. Some factors such as incident light intensity, incident wavelength, thermo-optic effect, environmental temperature and surface heat transfer coefficient, the thickness of the material etc, are considered during the solution process. For the wavelength of incident light in the light-transparent spectrum, the emergent light parameters are obtained by directly solving the electromagnetic field frequency equation. When the wavelength of incident light is in the absorbed spectrum region, the laser absorption thermal deposition termwhich is given by the modified empirical modelis introducedto calculate the heat source term in the energy equation. Through discussion of all the above factors on the influences of the transmission light parameters, a method of controlling the electro-optic effect by using thermal-optic effect is proposed. As the incident light intensity and crystal thickness are different, the corresponding relation between the temperature and the surface heat transfer coefficient is given to adjust the emergent light parameters to the rated operating condition without considering the influence of the applied electric field on the temperature field. The analysis shows that the relationship between the environmental temperature and the applied electric field, the surface heat transfer coefficient and the applied electric field(i.e. the so-called electric thermal modulation model) is linear when the influence of the external electric field on the temperature field is ignored. To study the influence of external electric field and multiple light refraction and reflection on the process of optical transmission and heat transfer, we conduct the research of the birefringence transmission and the electric thermal modulation of Gaussian laser in the lithium niobate by considering the electric-optic-thermal coupling effect. The effect of thermo-optic two-way-coupling and applied electric field on optical transmission and temperature field are considered. The full coupling method is used to solve both the equation composed of an electromagnetic beam envelope and the energy equation, and to simulate the propagation of multiple photorefractive/optical reflection Gauss laser in the absorption single axis crystal. The heat production due to the light absorption which is obtained by calculating the electromagnetic ene rgy dissipation density is been set in the energy equation as source term. The influence of the external electric field intensity, incidence light intensity, incident wavelength, thermo optic effect, environmental temperature, heat transfer coefficient and the thickness of the material etc. on the emergent optical characteristic parameters is obtained through coupled solution. The walk-off angles of O-ray and E-ray and the discrete angel in the cases of different conditions are discussed. The electro-thermal modulation correlation formula between the electric field and the environment temperature and the surface heat transfer coefficient is given under the full coupling condition. Meanwhile, the applicability of the electro-thermal modulation is analyzed and discussed. The analysis shows that the electro-thermal modulation correlation formula is no longer a linear rule by considering the influence of the electric field and multiple light refractions/reflections.In order to study the silicon based semiconductor’s electro-optic-thermal muti-field coupling characteristics and electric modulation problems, both the Poisson equation and the carrier continuity equation are introduced to calculate the carrier concentration distribution in the carrier transport proc ession. The Drude Lorentz and K-K relation has also been employed in this chapter to discuss the effect of the change of the carrier concentration on the refractive index and absorption coefficient. The same method dealing with lithium niobate is used to solve the electromagnetic wave equation and the energy equation. With the effect of external voltage, initial concentration of carrier and heat transfer coefficient, the change of dielectric properties, optical transmission behavior of silicon based semiconductor are also analyzed by coupling solution and analysis. The research shows that the reflective optical field mode of the semiconductor P area is increased with the increase of the applied voltage, and decreased with the increase of the heat transfer coefficient. Using this mechanism, the paper presents a scheme of electric thermal modulation for the space distribution of the reflection intensity.Due to lack of associated physical mechanism, theoretical models, basic data and testing methods of electro-optic and thermo-optic effect, the conductor type electro-optic material ionic liquid has been investigated by the method of experimental observation, and the qualitative explanation is supplemented. The main propose is to obtain the characteristics of electro optic response of ionic liquids at room temperature. To achieve this goal, an experiment apparatus has been proposed to measure the value of the visible and near infrared refractive index and absorption characteristics of ionic liquid under the action of uniform electric field. The variation of refractive index and absorption coefficient of five different kinds of imidazole type ionic liquid with different applied electric field are measured. Afterwards, the experiment results are tentatively analyzed by using the carrier transport theory coupled with electric polarization theory. In addition, the infrared micro measurement system for the transmission characteristics of the ionic liquid boundary layer is designed according to the effect of ionic liquid boundary layer in the vicinity of the electrode. Taking the methyl propyl imidazo le iodized salt as the research object, the effect of the applied electric field and the spacial position on the light transmission characteristics is measured and analyzed. The results show that the refractive index and absorption coefficient of ionic liq uid will be affected both by the external electric field and by the distribution of concentration of anion and cation, which is similar to the plasma dispersion theory in the silicon based semiconductor. |
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