Research On Liquid Crystal Optical Phased Array Beam Pointing Control Technology

Liquid crystal optical phased array(LCOPA)is a new type of programmable phase modulation device.It implements far-field beam pointing control by modulating the wave-front phase of the incident laser with an applied voltage,and has the advantages of small size,light weight,low power consumption,strong radiation resistance,etc.Therefore,it has broad application prospects in the military field of laser communications,laser radar,and laser directed energy weapons.At present,LCOPA devices are limited by manufacturing processes,temperature,and atmospheric interference,resulting in beam deflection performance far below the theoretical level.Based on the basic theory of LCOPA,this paper conducts in-depth research on the optimization of diffraction efficiency and deflection accuracy of LCOPA.The main research contents are as follows:The basic theory of the LCOPA and its electro-optic effect are introduced firstly.On this basis,the director distribution,voltage-phase shift characteristics and beam deflection principle of the LCOPA are studied: The liquid crystal director distribution is solved based on differential iterative algorithm.The relationship between phase delay and voltage is deduced.The beam deflection control model is established.The deflection error model is built from two aspects: diffraction efficiency and deflection accuracy.the factors affecting beam deflection performance are studied in depth.This provides theoretical basis and guidance for the next performance optimization.For the problem of low beam diffraction efficiency,a beam performance optimization system was designed.LCOPA diffraction model is established based on the traditional optical diffraction model,Which provided theoretical support for analyzing far-field light intensity distribution.LCOPA beam performance is optimized based on stochastic parallel gradient descent(SPGD)method.Corresponding optimization evaluation indicator is established,The optimization effect based on the SPGD method was verified by simulation experiments.The results show that the diffraction efficiency can reach 80% on the basis of increasing the optimization iteration speed.For the problem of low beam deflection accuracy,a closed-loop control system for beam deflection was established.The LCOPA mathematical model is qualitatively analyzed from the perspective of device material characteristics and kinetic principles,and the exact transfer function is established through experimental test data.Fractional order controller based on vector gain robustness is designed.The simulation results show: for a sinusoidal disturbance signal with amplitude of 1,frequency of 0.16 HZ,the system disturbance rejection ratio is-21.09 dB.Which verified the closed-loop control system of LCOPA beam deflection based on fractional-order controller has good dynamic performance and robustness.