Research On Real-time Polarization Imaging Devices Based On Patterned Functional Liquid Crystals

Real-time polarization imaging is a technique that combines traditional imaging optics with polarization optics.It obtains the polarization information of the target as well as the two-dimensional information of the target.It has important potential in biomedical,defect detection and other military and civilian fields,and is one of the hot research and application development at home and abroad.Polarization element is the core component to realize realtime polarization imaging technology,which mainly uses traditional optics or metasurface optics.Traditional optical components such as microlenses have large system alignment errors and loss of spatial resolution.Metasurface optical components such as wire grating have high machining accuracy requirements and complex preparation technology,so it is difficult to meet the requirements of high precision polarization imaging measurement.Therefore,a new real-time polarization imaging component is needed to make up for the above shortcomings.Liquid crystal optical element has the advantages of low cost,light weight and low energy loss.It can realize polarization control through the self-assembly behavior of patterned liquid crystal molecules.However,the current mainstream patterned liquid crystal orientation technology mainly adopts mask lithography,which not only needs to solve the alignment error caused by the distributed exposure of multiple masks,but also increases the preparation cost.In order to commercialize liquid crystal real-time polarization imaging devices,an efficient and low-cost patterned liquid crystal processing technology is urgently needed.In this paper,a liquid crystal chiral lens prepared by digital holographic lithography technology is proposed,which can be combined with image sensor CMOS to extract the circular polarization information of the target object.In order to obtain the linear polarization information of the target object,a liquid crystal micropolarizer array is prepared by using unmasked laser direct writing technology,and a liquid crystal real-time polarization imaging device is constructed.At the same time,the application of this imaging device in polarization image enhancement is verified experimentally.Firstly,a chiral planar lens based on liquid crystal birefringence is proposed in this paper.Based on the principle of liquid crystal geometric phase,the liquid crystal planar chiral lens is designed and simulated to extract the circular polarization information of the object in the opposite rotation direction in real time.Digital holographic lithography,as a pattern orientation technology of liquid crystal,can realize the orientation of chiral lens.The liquid crystal domains are modulated by patterned nanogrooves in different directions,with a minimum pixel size of 10 μm.Based on Berremen’s principle,a nanochannel model was established,and the order degree of liquid crystal molecules reached 0.79 by optimizing the period and depth of the groove,and the molecular pointing vector could be controlled arbitrarily within the patternized region.The liquid crystal lens has the characteristics of large aperture,low cost and real-time polarization imaging.In addition,the real-time polarization imaging device built with the image sensor CMOS has the advantages of small size and light weight.At the same time,the circular polarization information of the target object can be obtained under the wide field of view of±20°.In order to obtain the linear polarization information of the target object,a real-time polarization imaging device based on liquid crystal micropolarizer array is proposed.Firstly,by using nematic liquid crystal polymer doped with dichroic dyes,a kind of micropolarizer array which can be cured at room temperature was prepared by photomask less laser direct writing technique.The polarization properties of the liquid crystal dye mixture were optimized,and the extinction ratio was 22,the dye sequence parameter was 0.75,the polarization efficiency was 91%and the film thickness was 1.73 μm in the visible band.The alignment errors between the sub-pixels of the micropolarizer array and the pixels of the sensor and the fitting errors during integration are studied and optimized.By photographing the object,the object with high polarization characteristics can be recognized effectively in the natural environment,and its good imaging effect and diversified application potential are verified.In the future development of real-time polarization imaging technology,it is expected to achieve high cost performance and high precision real-time polarization detection and imaging.