Liquid Crystal Anti-counterfeiting Device Based On Photoalignment Technology

Liquid crystal optical devices have the advantages of high integration,light weight,low power consumption,and are widely used in display,optical communication,anti-counterfeiting and other fields.The realization of the devices function is closely related to the directional distribution of liquid crystal molecules.It is of great importance to fabricate functional liquid crystal optical devices by controlling the alignment of liquid crystal molecules.Among the alignment techniques,the photoalignment technique has become a research hotspot because it is easy to generate multi-domain liquid crystal optical devices.Compared with the traditional photoalignment technology,the photoalignment technology based on DMD exposure system does not need to make a mask in advance,and the cost is lower.Moreover,it overcomes the problem of alignment error faced by most masks,and can produce relatively complex photoalignment patterns.However,the mask made by AI or Flash animation still has the problem of single graphics and low efficiency.In this paper,by using the image processing library OpenCV,a more efficient pattern generation method is introduced.The process of graph generation and import,polarization control,exposure time setting and other processes are highly integrated,so as to realize the intelligent control of the generation process of arbitrary photoalignment pattern.Furthermore,based on the nematic liquid crystal and cholesteric liquid crystal fingerprint texture,two kinds of liquid crystal optical devices with high information capacity with information hiding and display functions were fabricated,which have broad application prospects in the field of anti-counterfeiting.The main work includes:1.The exposure graphics were generated by using C++reference image processing library OpenCV.Combined with Thorlabs controls and plugins,a series of complex photoalignment processes including setting the exposure region,adjusting the polarization angle,calculating the exposure time and so on were integrated.And a preparation system with high automation and strong stability was obtained,which could realize any complex alignment of liquid crystal.2.A liquid crystal optical device for anti-counterfeiting was prepared based on nematic liquid crystal by self-made automatic photoalignment exposure system.The five circular eigenvalues of center,radius,color,number and distance and the hidden character eigenvalues generated by Moore Smith code were used for anti-counterfeiting.Through the process of color model conversion,Gaussian denoising,contour extraction,line track recognition and so on,the pattern under polarized microscope could be analyzed to identify hidden information,which is expected to be a new anti-counterfeiting material with high information capacity.3.A liquid crystal anti-counterfeiting optical device based on cholesteric liquid crystal fingerprint texture was fabricated by automatic photoalignment exposure system,in which the information storage carrier was the direction of the texture.The direction of fingerprint texture can be identified through image recognition processes such as smoothing filtering,image enhancement,edge detection and Hofton line fitting,which is expected to be a new anti-counterfeiting material with high recognition rate.