Design And Research Of New Optical Anti-counterfeiting Device Based On Metasurfaces Technology

At present,the sub-wavelength structure dichroic optical anti-counterfeiting technology is widely used in the field of holographic anti-counterfeiting,such as passports,identity cards,etc.However,the effectiveness of anti-counterfeiting has been seriously challenged,and it is urgent to further improve the anti-counterfeiting performance.Metasurfaces technology based on binary optics,which can control wavefront polarization,phase and amplitude and obtain phase functional devices such as Fresnel lens,vortex light and hologram,may be a solution.In order to solve the problem of inadequate optical anti-counterfeiting performance of two-color optical converter,a new type of optical anti-counterfeiting device based on the sub-wavelength structure of three-color optical converter proposed by the laboratory is proposed,which integrates three-color optical converter and polarization multiplexing metasurfaces technology.When natural light is incident,the red,green and blue three-color optical output with high derivative efficiency can be observed in different azimuth directions.When X and Y polarized light is incident,different character displays are obtained on the same observation plane,which breaks through the limitations of the current two-color optical variable technology.The main contents of this paper are as follows:1.A three-color light converter based on simple-period sub-wavelength structure is designed to achieve high-efficiency red,green and blue light output in different azimuth directions when natural light is incident.Based on the rigorous coupled-wave theory,a scientific evaluation function is established for TE polarized light incident on simple-period subwavelength structure.The period,groove depth and duty cycle of sub-wavelength grating are optimized by self-programming.When the azimuth angle of reflection is 12 degrees,67 degrees and 90 degrees,the zero-order reflectivities of blue,green and red three-color output with high diffraction efficiency reach 85%,86% and 99%,respectively.Finally,the commercial software Rsoft is used to verify the design results.The results show that the design results obtained by the self-programming optimization in this paper are the same as those obtained by Rsoft,which verifies the correctness of the design results in this paper.2.A polarization multiplexing metasurfaces device based on ZnS rectangular cylinder element is designed,which achieves high derivative character output of different shapes on the Same observation plane under X and Y linear polarization incidence.The mechanism of phase difference of metasurfaces micro-elements is analyzed by using equivalent medium theory.The influence of height,length and width of ZnS rectangular column on phase difference of microelements is simulated and analyzed.Finally,the micro-column with height of 600 nm is obtained.In order to obtain the character image output on the output surface,the continuous phase plane of the metasurfaces is obtained by improving Fresnel's phase recovery algorithm,then the evaluation function is set to optimize the phase value and transmission efficiency of the element,and the phase of the metasurfaces is realized by using different size of the element.Finally,the simulation is carried out by using FDTD method.The simulation results show that the character of "SZU" can be observed on the output plane when X-ray polarized light is incident,and the character of "CET" can be obtained on the same output plane when Y-ray polarized light is incident on the same metasurfaces.The simulation results are consistent with the theoretical results,which proves the feasibility of the design in this paper.3.The experimental optical system of X and Y linear polarized light multiplexing metasurfaces is built,and the polarized multiplexing character display function of the metasurfaces is verified experimentally.The display optical path is designed,and the ideal phase plane calculated by the phase recovery algorithm and the phase plane arranged by the elements selected by different evaluation functions are loaded separately.Through the display of CCD,the characters of "SZU" output from X-polarized phase plane and "CET" output from Y-polarized phase plane are clearly observed,which is consistent with the design results.4.A new optical anti-counterfeiting device based on embedded grating structure and polarization multiplexing multi-character display metasurfaces technology is designed,which realizes multi-color light change display and polarization multiplexing multi-character display.The design results of this paper can obtain high derivative anti-counterfeiting devices with polarization multiplexing character display and tricolor photo-change function,greatly improve the performance of optical anti-counterfeiting,break through the limitations of DICOLOR photo-change anti-counterfeiting technology,and can be applied in the field of holographic photo-change image anti-counterfeiting.