The Application Of Finite-difference Time-domain Method In Liquid Crystal

Liquid crystal is a kind of special material,which has both the fluidity of liquid and the birefringence of crystal.The arrangement of molecules can be controlled by the effect of external electric field,so liquid crystal is widely used to various constructs of optical devices.Because of the advantages of simulation which are time saving,low economic cost and the ability to avoid the difficulty of production processes and experimental mistakes,simulation by computer is usually the first thing to do during the process of designing a new construction of optical device.Then perform experiments after getting the reasonable simulation results.In this thesis,the application of an optical simulation method(FDTD: Finite-difference time-domain method)in liquid crystal display is mainly researched.In the first chapter,the development of FDTD method used in liquid crystal is introduced.Although FDTD method is widely used in many fields,the application in liquid crystal is lacked.Now,for the complex structure of liquid crystal devices,this method has great potential.Besides,the optical rotatory power of blue phase liquid crystal form experimental results and Bragg reflection of cholesteric liquid crystal is also introduced in this chapter.In the second chapter,the detailed calculate process of FDTD method in three dimensions is deduced.FDTD method directly uses difference method to calculate the Maxwell equation.Electric and magnetic fields are interleaved sampling according to Yee cell when the electromagnetic wave is propagating in medium.Electric(magnetic)field component could be calculated by two iterations of electric and magnetic field after a time step.Perfectly matched layer(PML)is introduced to absorb reflected wave and terminate computation space.In the third chapter,other two optical simultaional methods,Jones matrix method and Berreman 4×4 method,are mentioned.Compared with FDTD method,the two methods take the light’s propagation as one-dimensional conditions,light beams in the plane which is perpendicular to the direction of light propagation is regarded as no influence to each other.So the two methods are also called as one-dimensional method.For comparison,FDTD method is called as multidimensional method.The advantages,disadvantages and the application scope of these two methods are discussed.In the fourth chapter,FDTD method is used into planar state and focal conic state cholesteric liquid crystal,and blue phase liquid crystal.A model of the molecular arrangement lattice in the whole space was built to simulate the properties of cholesteric liquid crystal and blue phase liquid crystal.The light leakage,Bragg reflections and the optical rotation of these three kinds of liquid crystal states are analyzed,a new conception which is called as equivalent power of optical rotation is proposed.In the fifth chapter,the effect of refractive index changes in horizontal direction when light propagating in the liquid crystal layer is researched.FDTD method is used to simulate the optical characteristics of in-plane switching blue phase liquid crystal display.Light can be convergent to the position where the refractive index is larger as it pass through the LC layer.These phenomena are explained by equivalent refractive index.Based on this phenomenon,simple polarization direction high transmission film with LC compensation layer is designed,the transmittance can be improved by about 44%.