Research On Submillisecond Beam Control Method Of Liquid Crystal Phase Shifting System

Liquid crystal optical phased array has become the mainstream technology of laser beam control due to its advantages of flexible pointing,small weight,and so on,and has been widely used in space optical communication and other fields.However,with the continuous development of communication networks,the laser beam control system has been put forward by many application fields,such as space optics,space optical communication,laser radar,missile interception and other representative application fields.Therefore,it is important to study the submillisecond beam control method of laser beam control system.Based on the theory of liquid crystal phase shifter,liquid crystal material,and response time,two sub-millisecond beam control schemes for liquid crystal phase shifter are proposed in this thesis.The first method is based on ferroelectric nematic liquid crystal material to realize submillisecond beam control of the phase shifter.The second method is constructing a stackable liquid crystal device based on reducing the cell thickness to achieve the submillisecond beam control.The main contents of this thesis include the following:(1)A submillisecond beam control method for liquid crystal phase shifting is proposed based on ferroelectric nematic liquid crystal materials.The vector distribution of ferroelectric nematic liquid crystal molecules is numerically calculated,and the vector changes sharply on the up and down sides of cell and changes slowly in the middle under the control of applied electric field.By analyzing the simulation results,the orientation methods of ferroelectric nematic liquid crystal phase shifters are proposed,including light-controlled orientation,polarity-induced vertical orientation,and field-induced orientation.(2)Ferroelectric nematic liquid crystal phase shifters with different orientations were prepared.Under the control of polarity-induced vertical orientation and electricfield-induced orientation,the liquid crystal ferroelectric nematic molecules are arranged in order.The response time and phase modulation depth of the prepared device are measured.The test results show that the ferroelectric nematic liquid crystal phase shifter has 0.91π phase modulation depth and submillisecond response time.(3)Based on the core idea of reducing the thickness of liquid crystal cells,a liquid crystal pahsed array device with stackable structure is proposed.The stackable liquid crystal pahsed array device structure comprises three layers of unit devices from top to bottom.The feasibility of the design of the stackable liquid crystal phased array device is numerically verified by the distribution of the near-field phase and far-field diffracted light intensity.(4)The preparation and experimental test of the stackable liquid crystal phased array device were carried out.The stackable liquid crystal phased array device was prepared according to the four processes of mask plate rendering,unit device substrate pretreatment,unit device assembly,and stackable liquid crystal phased array device assembly.The voltage-phase relationship,beam steering angle,and dynamic response time of the prepared device were tested.The final experimental results show that the stackable liquid crystal phased array device is a two-dimensional liquid crystal laser deflector with high precision,precise angle,and sub-millisecond response.The minimum resolution angle is 2 μrad,the maximum deflection angle is 40 μrad,and the fastest beam switching time is 300 μs.