Research On Technology Of Liquid Crystal Phased Array Beam Deflection

With the continuous development of lidar and space optical communication,higher requirements are put forward for the beam deflection accuracy and scanning speed.The traditional mechanical beam deflection is unable to meet the needs of rapid and high precision.Therefore,it is of great research significance and value to explore the rapid and high precision beam deflection technique.Liquid crystal optical phased array uses the electro-optic effect of liquid crystal material to realize the dynamic direction of light beam in a certain space,which possesses no mechanical scanning,random pointing,and programmable control.By these characteristics,it provides new ideas for solving the problems of traditional mechanical beam deflection.However,it is difficult for a single liquid crystal optical phased array device to have large angle,high resolution and high diffraction efficiency at the same time.Therefore,researching how to improve the diffraction efficiency,angular resolution,and scanning field of view is the key to realizing liquid crystal optical phased array beam deflection.This thesis,the modulation mechanism of liquid crystal spatial light modulator and liquid crystal polarization grating beam is discussed.We have studied the director dynamic distribution of liquid crystal molecules,mechanism of electro-optic modulation,adaptive iterative liquid crystal spatial light modulator polarization beam correction and optimization,multi-layer grating cascade beam control system design and coarse fine two-stage liquid crystal optical phased array beam modulation system design and implementation of the content such as research.The specific content is as follows:1.The electro-optic modulation mechanism of liquid crystal spatial light modulator is studied,and the dynamic distribution law of liquid crystal director under the action of external electric field is investigated.Liquid crystal spatial light modulator is composed of the orientation,conductive layer,liquid crystal layer,etc.Affected by the dielectric partial voltage of the alignment layer and the ripple voltage,the deflection angle of the outgoing beam at the theoretical voltage deviates from the theoretical deflection angle.in order to get the actual load voltage code required,based on the establishment of an electrical model of the multilayer physical structure of the liquid crystal spatial light modulator,a quantitative calculating model for the mapping relationship between the actual deflection angle and the driving voltage is proposed.The wave control method of the periodic and aperiodic blazed grating is further used to achieve precise control of the beam deflection.2.In order to improve the deflection efficiency of light beam,the spatial light propagation model of the liquid crystal spatial light modulator is established,the analysis of structural characteristics of liquid crystal spatial light modulator,the Gaussian of the incident light and the manufacturing process errors on the deflection efficiency of the light beam of the liquid crystal spatial light modulator.An adaptive wave control voltage correction system of the liquid crystal spatial light modulator is designed.Beam deflection performance optimization algorithms based on Rosenbrock rotating coordinate method and the stochastic parallel gradient descent method of is proposed.The effectiveness of the proposed method is verified by simulation and experiment,and the beam deflection efficiency of the liquid crystal spatial light modulator is improved.3.In order to obtain a large field of view and high-resolution beam deflection,based on the optical transmission matrix and diffraction theory,the mechanism of the liquid crystal polarization grating beam modulation is studied,the influence of the shape defect,the thickness error of the liquid crystal layer and the Fresnel reflection on the beam modulation characteristics is analyzed.Aiming at the problem that a single liquid crystal polarization grating has only three diffraction orders,which results in the limited angular resolution,a multi-layer liquid crystal polarization grating cascaded beam deflection system architecture is constructed,a multi-channel liquid crystal polarization grating driving circuit for a multilayer liquid crystal polarization grating cascaded beam deflection system is designed,and the effectiveness of the cascaded system is verified by experiments.4.Aiming at the requirements of high speed,high resolution,high precision and large field of view,a two-stage cascade beam deflection system of liquid crystal spatial light modulator and liquid crystal polarization grating is proposed and designed,which combines the characteristics of liquid crystal spatial light modulator high resolution and liquid crystal polarization grating large field of view.The mapping law between the incident angle of laser beam and the effective refractive index of liquid crystal molecule is studied,and a phase modulation method of liquid crystal optical phased array with oblique incident beam is proposed,which not only simplifies the optical path of the system,but also greatly reduces the loss of optical energy.The two-stage cascade beam deflection system is simulated by ZEMAX software,and the experimental platform of the liquid crystal optical phased array composite beam deflection system is built.Through simulation and experiment,the effectiveness of the proposed method is verified,which provides theoretical basis and technical guidance for the needs of large field of view and high resolution beam deflection,such as lidar,space optical communication and laser weapons.