Research On Liquid Crystal Optical Phased Array Devices And Beam-Forming Method

Liquid Crystal Optical Phased Array(LCOPA)is a kind of electroniccally programmable optical phased array device using liquid crystals as the phase modulation material,which can provide accurate,stable,fast and agile beam steering and beam forming.The laser beam control system based on LCOPA can reduce the size,weight and power consumption(SWaP),and it is expected to bring great application prospects and values in the future space laser communication,LiDAR,high-energy laser and other fields.Although the LCOPA has realized the principle or engineering application in certain fields,there are still some shortcomings in terms of its practical performance,so we need to make further research on the LCOPA.On the other hand,domestic research on LCOPAs started late and is not comprehensive enough,so more research work is needed to achieve significan progress.Therefore,this dissertation focuses on the practical applications of LCOPA,and studies the physics of device as well as related beam steering methods,including device principle and system modeling,device fabrication and characterization,phased access characteristics,beam forming method,etc.In terms of device principle and system modeling,based on the electronically controlled phase shifting mechanism and the beam propagation principle,combined with two typical beam steering models,the LCOPA was systematically modeled including simulations of liquid crystal director,and calculations of near-field phase and far-field intensity pattern.Meanwhile,the near-field phase distribution and far-field grating lobes were numerically analyzed.A formula of deflection efficiency was proposed which takes into account both the flyback effects and the steering angle,then the influencing factors of the deflection efficiency and optimization methods were described.The results provide an important basis for numerical analysis,parameter optimization,and device design of LCOPAs.In terms of device fabrication and characterization,the comprehensive factors that needed to be considered when designing LCOPA devices are analyzed,which provides references for device structure design and liquid crystal material selection.The manufacturing process of LCOPA were explored,and a one-dimensional transmissive LCOPA device was developed.Several experimental platforms to test the steering performance of LCOPA were built,and the voltage-phase characteristic curve,response time,steering precision and accuracy were characterized and analyzed.The results provide a material basis for future research and experimental verification of beam forming methods.In terms of phase controlled access characteristics,we mainly focused on dynamic linking in phase controlled laser communication or other application scenarios,then the phase controlled access mechanism of LCOPA was elaborated in detail,and the angular relationship problem within the process of phase controlled access was reealed.A beam vector propagation method was proposed,a numerical calculation model was also built,so that the phase modulation and steering performance of LCOPA were studied when a backward-oblique arriving beam propagating through the LCOPA.Based on simulations and experiments,a linear relationship between angle-of-arrival,steering angle and acceptance angle during phased access was verified.The results provide a basis for LCOPA to realize accurate phase controlled access.In terms of beam forming methods,three key technical issues of LCOPA were studied: the angular range,multi-beam forming,and polarization dependence.First,an improved high-order grating method(i-HOG)was proposed to increase the angular range of LCOPA by increasing the phase reset order of the near-field phase modulation.And a wide-angle LCOPA with more than 4? phase retardation was fabricated.The simulation and experimental results showed that the angular range of modulo-2k? approach is k times larger than that of traditional modulo-2? approach.Furthermore,the i-HOG method also showed a higher deflection efficiency than the mode-2? approach.Secondly,a cascaded amplitude and phase method(CAP)and a multi-beam forming system based on 4-f imaging were proposed.Two cascaded liquid crystal optical phased arrays(LC-OPAs)controllably modulate the amplitude and phase of an incident laser beam to realize the near-field wavefronts of multiple simultaneous beams with arbitrary directions.Simulation results showed the characteristics of amplitude and phase modulation profiles,as well as the far-field intensity patterns.An experimental multi-beam forming system was biult to show that the CAP method can generate multiple beams with arbitrary number and direction.Finally,a polarization-independent and two-dimensional laser beam steering system was proposed.Based on the polarization division and bidirectional loop structure,two LCOPAs were aligned orthogonally to modulate the orthogonal components of unpolarized incident beam.Properties of polarization-independence as well as two-dimensional beam steering were mathematically and experimentally verified with a good agreement.And an experimental platform was established to show that the proposed system can realize continuous two-dimensional beam steering of incident light with arbitrary polarization.