Research On Key Technologies Of The Liquid Crystal Optical Phased Array

Liquid crystal optical phased array(LC-OPA),which combines the microwave phased array antennas technology and the liquid crystal electro-optical properitese is a late-model device for non-mechanical laser beam steering.LC-OPA has the advantages of low diriving voltage,low power consumption,light weight,large aperture,resisting vibration and radiation,thus it has extensive application prospects in the field of laser radar and free space optical communication and has become the research hotspot in the area of optical phased array in recent years.Howerer,for the research on the LC-OPA,the system model and beam control theories is still incomplete,and the beam-steering efficiency is relatively low.Thus,this thesis focuses on the studies of LC-OPA system modeling,system performance optimization and beam control applications.The main academic contributions of this thesis are as follow:1.A set of complete LC-OPA model,including beam propagation model,phase modulation model,beam-steering control model and influence factors model is established.A steering efficience indicator to reflect the energy utilizaiton of the LC-OPA is proposed.The relation between the liquid crystal cell thickness and the LC-OPA phaseshift characterstics is studied.The impacts of parameter design,steering mode selection,fringing effect and manufacture errors on the steering efficience and steering angle are analyzed.The theoretical support and guidnace for LC-OPA device design is provided.2.For LC-OPA beam-steering efficiency optimizaiton,a close-loop optimizaiton system is designed.By applying the proposed optimizaiton methods based on the rapid search algorithm and the stochastic parallel gradient descent algorithm,the steering performance of the LC-OPA is improved and the iteration speed of the optimizaiton procedure is increased.Through experiment,the steering efficiency of the LC-OPA is significatly impoved.3.For LC-OPA multiple beams forming,sub-aperture method is proposed.By dividing independently controlled sub-arrays,multilple steering beams with low gratinglobe are formed.Array division multiplexing method is proposed,by sharing the whole aperture resource,high-resolution multiple steering beams are achieved.Iterative Fourier transform method is proposed,by using array synthesis and iterative operation,the multi-beam phased excitations of LC-OPA are generated.Through experiment,dynamic scanning multple beams are formed.4.LC-OPA beam divergence control method is proposed.By loading the phase modulation functions of the lens with variable focus length into the LC-OPA,the beam propagation parameters are transformed.Through experiment,the divergence angle of the incident laser beam is controlled.Expanding this method to the free space optical communicaiton system,a vibration suppression system based on the LC-OPA beam divergence control is designed,the optimal divergence angle in the vibrational disturbance is computed,system power penalty in the vibration is reduced.5.A angular magnification method for LC-OPA beam-steering is proposed.By cascading a inversed telescope system,the deflection angle of the LC-OPA is enlarged.A cascaded coarse-fine steering mode is designed,and the LC-OPA wide-angle continuous scanning is achieved.