Research On The Expansion Method Of Beam Pointing Range Of Liquid Crystal Optical Phased Array

Space laser beam control system needs light,flexible and miniaturized actuator,and also needs to meet the technical requirements of many constraints in application scenarios.The beam deflection technology based on phase control system has the technical advantages of small-sized,light weight and low power consumption,but there is still room for improvement in beam pointing range,spatial pointing resolution,wave position switching time and deflection accuracy.Among them,the beam pointing range is one of the important indexes restricting the application of liquid crystal optical phased array antenna.Compared with the beam pointing range of microwave phased array,optical phased array is still far away.Aiming at this technical problem,this paper carries out the following research contents,including:(1)The method of expanding the beam pointing range of conformal antenna scheme is studied.The arc-shaped optical waveguide device is used to expand the direction range of the beam.Using the Bragg reflection effect and field induced nematic transmission effect of cholesteric liquid crystal,cholesteric liquid crystal is used as an optical switch for region selection,which cooperates with optical waveguide devices to realize the function of dynamic region selection.A cholesteric liquid crystal cell made of flexible PET material was developed,and five control areas that can be powered on independently were designed.The module realizes four optional areas of beam dispersion,and the angle is expanded to 5.1°.Experiments verify the feasibility of this method.However,the scheme is limited by the flexible transparent material PET with various anisotropy,resulting in the uncontrollable polarization state of the beam.(2)The method of expanding the beam pointing range of digital cascade scheme is studied.The cascaded liquid crystal polarization grating,that is large angle discrete deflection device,is used to expand the direction range of the beam and form a discrete spot lattice.Liquid crystal phased array realizes small angle continuous deflection between discrete spots.Liquid crystal polarization grating,liquid crystal half and quarter wave plates and liquid crystal optical phased array devices are developed.The large angle discrete deflection device is composed of four-stage polarization gratings to realize sixteen discrete light speckle arrays of ±11.25°.The coverage angle of liquid crystal optical phased array is ±0.75°,and the beam deflection accuracy is not less than 20°?rad.The digital cascade scheme realizes the beam deflection in the two-dimensional 24°field of view.(3)A polarization self-coherence method is proposed to prepare liquid crystal polarization gratings.According to the polarization characteristics of the liquid crystal polarization grating modulated laser,the ±1-order beam recoherence of the outgoing liquid crystal polarization grating can be used to prepare new devices,and the experimental optical path is designed.The relationship between the diffraction efficiency and the polarization state and phase delay of the transmitted beam when linearly polarized light is incident on the liquid crystal polarization grating is analyzed.The preparation optical path of this method is designed.The optical path design adopts 4f system,and the zero-order spot affecting ±1-order coherence is removed by baffle in the frequency domain of the system.The advantage of the prepared optical path is that the template device does not need to be a strict half wave condition for the phase delay of the oriented light source,and the phase delay only affects the utilization of the oriented light source.The closer to the half wave condition,the higher the utilization of the light source.The correctness of polarization autocorrelation theory is verified by experiments.