CN111210713B - Anti-counterfeiting shading and image multiplexing-based anti-counterfeiting super surface design method - Google Patents
Anti-counterfeiting shading and image multiplexing-based anti-counterfeiting super surface design method Download PDFInfo
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Abstract
The invention relates to micro-nano optics and opticsThe anti-counterfeiting technical field discloses an anti-counterfeiting super surface design method based on anti-counterfeiting shading and image multiplexing, which comprises the following steps: constructing a nano brick array, wherein the nano brick array comprises a plurality of nano brick structure units, optimally obtaining the optional size parameters of at least two groups of nano brick structure units with the functions equivalent to a micro-nano polarizer and different spectral responses, and each group of nano brick structure with the optional size is arranged at the wavelength lambda0The response characteristics are the same; determining a continuous gray image, an anti-counterfeiting shading image and a double-color image which are required to be multiplexed on the super surface; the dimensions of the nano-brick unit structures and the turning angles of the nano-bricks are arranged according to the images subjected to multiplexing to form the super-surface material. The super surface designed by the invention can display gray images or anti-counterfeiting shading images under the incidence of linearly polarized light in different polarization directions, and can display double-color images under white light illumination, and the super surface has the advantages of low algorithm complexity, high safety, strong concealment and the like.
Description
Technical Field
The invention relates to the technical field of micro-nano optics and optical anti-counterfeiting, in particular to an anti-counterfeiting super-surface design method based on anti-counterfeiting shading and image multiplexing.
Background
The anti-counterfeiting shading is anti-counterfeiting by completely using lines, can generate abundant changes, has the characteristics of anti-counterfeiting, anti-scanning and the like, and is an anti-counterfeiting technology with low cost and good anti-counterfeiting effect. However, with the improvement of science and technology, the anti-counterfeiting shading is adopted for anti-counterfeiting, so that the anti-counterfeiting mark is easily damaged by lawbreakers, even is tampered or forged, and the anti-counterfeiting security needs to be improved. By super-surface is meant an artificial layered material with a thickness less than the wavelength. The super surface can realize flexible and effective regulation and control of characteristics such as electromagnetic wave polarization, amplitude, phase, polarization mode, propagation mode and the like. In the super-surface design, the information density can be improved through a multiplexing technology; in the field of optical anti-counterfeiting, the safety of optical anti-counterfeiting can be obviously improved by multiplexing multi-channel information. The existing method for utilizing the super surface to multiplex can obviously improve the safety of utilizing the super surface to carry out optical anti-counterfeiting, and the multi-channel multiplexing mode also enables the information density of the super surface to be improved. However, the anti-counterfeiting method for the super-surface in the prior art needs to be improved in the aspects of simplicity of structure, flexibility of design, information density, anti-counterfeiting safety and the like.
Disclosure of Invention
The invention aims to provide a method for designing an anti-counterfeiting super surface based on multiplexing of anti-counterfeiting shading and images.
The scheme adopted by the invention for solving the technical problems is as follows:
a design method of an anti-counterfeiting super surface based on anti-counterfeiting shading and image multiplexing is characterized by comprising the following steps:
constructing a nano brick array, wherein the nano brick array comprises a plurality of nano brick structure units, the nano brick steering angle of each nano brick structure unit is theta, optimizing to obtain at least two groups of alternative size parameters of the nano brick structure units with different spectral responses, the peak value positions of the spectral responses of the at least two groups of nano brick structure units with the alternative sizes are different, but the peak value positions of the spectral responses of the incident electric field direction along the long axis of the nano brick at the wavelength lambda are different0Has equal reflectivity at a wavelength λ0When the linearly polarized light vertically enters each group of nano brick structure units with the alternative sizes, the functions of the linearly polarized light are equivalent to micro-nano polarizers;
with an intensity of I0Polarization direction of alpha1And the wavelength is lambda0The linearly polarized light is sequentially incident into the nano brick structure unit and the analyzer with the light transmission axis direction perpendicular to the polarization direction of the incident light to obtain the emergent light intensity and the polarization direction alpha of the linearly polarized light1And a functional relationship between the nano-brick steering angles theta of the nano-brick structural units; designing a gray image, and calculating to obtain the nano-bricks of each nano-brick structural unit in the nano-brick array according to the gray distribution required by the gray image display and the functional relationSteering angle theta is [0, pi/2 ]]Two selectable values within the range;
designing an anti-counterfeiting shading image, and determining a final value of a nano-brick steering angle corresponding to each nano-brick structural unit in the nano-brick array from two optional values of the calculated nano-brick steering angle theta according to the strength value displayed by the anti-counterfeiting shading image and the functional relationship obtained in the step;
designing a bi-color image, determining the size parameters corresponding to the nano-brick structure units at each position in the nano-brick structure array from the various optional size parameters according to the strength requirement displayed by the bi-color image, and arranging the obtained nano-brick structure units with the corresponding sizes at each position according to the final values of the steering angles of the corresponding nano-bricks determined in the above steps, so as to obtain the required super-surface material;
a certain linear polarized light is incident into the metamaterial, and a continuous gray image is displayed after the metamaterial passes through a corresponding analyzer; after the incident linearly polarized light is rotated by a specific angle, the incident linearly polarized light enters the super surface material and passes through a corresponding analyzer, and an anti-counterfeiting shading image is displayed; when the meta-surface material is incident with white light, a bi-color image is displayed.
Further, the nano brick structure unit comprises a working face and a nano brick arranged on the working face, the directions parallel to the two edges of the working face are respectively set as an x axis and a y axis to establish an xoy coordinate system, a long axis L and a short axis W are arranged on the surface of the nano brick parallel to the working face, and a turning angle theta of the nano brick is an included angle between the long axis L of the nano brick and the positive direction of the x axis.
Furthermore, the size parameters of the nano-brick structure units include the long axis L, the short axis W, the height H of the nano-brick and the size of the side length C of the working face, the long axis L is not equal to the short axis W, and the center distances of the nano-brick structure units are equal.
Further, the at least two groups of nano-brick structure units with alternative sizes comprise a first group of nano-brick structure units with alternative sizes and a second group of nano-brick structure units, and the optimization method of the size parameters of the at least two groups of nano-brick structure units with alternative sizes comprises the following steps: optimized to the direction of the electric fieldLinearly polarized light with long axis of nano brick at wavelength lambda under normal incidence1The dimension parameters of the first group of nano-brick structure units with the reflectivity not less than 90 percent are determined, and the linear polarized light along the long axis of the nano-brick in the direction of the electric field is in normal incidence at the wavelength lambda2The size parameter of the second group of nano-brick structure units with the reflectivity not lower than 90 percent, and when linearly polarized light along the long axis of the nano-brick in the direction of the electric field is normally incident on the nano-brick structure units with the two sizes, the two nano-brick structure units have the wavelength lambda0Has equal reflectivity of and λ0≠λ1≠λ2。
Further, the functional equivalence of the nano brick structure unit is a micro-nano polarizer, and the light intensity is I0Wavelength of λ0Polarization direction of alpha1The incident angle of the linearly polarized light to the nano-brick structure unit with the theta direction angle, reflected light passes through the analyzer with the polarization analysis direction vertical to the polarization direction of the incident linearly polarized light, and the intensity I of emergent light is obtained1And alpha1The functional relationship between θ is:
further, when the transmission axis direction of the analyzer is perpendicular to the polarization direction of the incident linearly polarized light, the wavelength λ is set to be the wavelength0Monochromatic linear polarized light with the electric field direction of pi/4 is incident to the metamaterial, and a gray image is displayed through a corresponding analyzer; when the wavelength is lambda0And the monochromatic linear polarized light with the electric field direction of pi 3/8 is incident into the super surface material and passes through a corresponding analyzer to display the anti-counterfeiting shading image.
The method for determining the final value of the steering angle of the nano brick comprises the following steps:
when alpha is1When the light intensity is pi/4, the emergent light intensity is high
Normalizing the intensity of the gray image according to the normalized intensity distribution and I of the gray image1Calculating the function relation with theta to obtain the turning angle theta of each nano-brick structural unit in the nano-brick array in [0, pi/2 ]]Two in the rangeA selectable value theta1And theta2Theta corresponding to an arbitrary intensity1And theta2Satisfies theta1+θ2＝π/2；
When alpha is1Pi 3/8, the intensity of the emergent light is
The emergent light intensity corresponding to the two selectable values
Let I ">I′；
The anti-counterfeiting shading image is set to be a double-color image, and the pixel value corresponding to any nano brick structure unit in the anti-counterfeiting shading image is 0 or 1; defining that emergent light of a nano brick structure unit corresponding to a pixel value 1 is strong when monochromatic linear polarized light is incident, and displaying the emergent light as bright; defining that the emergent light intensity of the nano brick structure unit corresponding to the pixel value 0 is small when monochromatic linear polarized light is incident, and displaying the light intensity as dark; selecting the nano-brick structure unit at any corresponding position in the anti-counterfeiting shading image and the gray level image for comparison, and if the pixel value of the nano-brick structure unit in the anti-counterfeiting shading image is 1, selecting the nano-brick steering angle of the nano-brick structure unit as theta2(ii) a If the corresponding pixel value of the nano-brick structure unit in the anti-counterfeiting shading image is 0, selecting the nano-brick steering angle of the nano-brick structure unit as theta1。
Further, the pixel values of the bi-color image are respectively 0 or 1, any nano-brick structural unit on the bi-color image is selected, and when the pixel value corresponding to the nano-brick structure is 0, one nano-brick structural unit with one optional size parameter is selected; another nano-brick structural unit of an alternative size parameter is selected when the pixel value of the nano-brick structural unit is 1.
Further, the working surface is made of silicon dioxide, and the nano-brick is made of a silver material.
The invention also aims to provide the super surface material obtained by the method for designing the anti-counterfeiting super surface based on the anti-counterfeiting shading and image multiplexing.
Compared with the prior art, the invention has at least the following beneficial effects:
1. the super-surface design algorithm provided by the invention has low complexity, is simpler and easier to implement, realizes the multiplexing of a gray image, an anti-counterfeiting shading and a double-color image through a single super surface, can obviously improve the information density, and the multiplexed image can be selected according to the requirement, so that the design flexibility is high;
2. the invention multiplexes the anti-counterfeiting shading with the gray level image and the double-color image, can realize multiple anti-counterfeiting, has small super surface size and high concealment, and has higher anti-counterfeiting safety because the anti-counterfeiting shading only appears under specific conditions and is not easy to imitate and tamper;
3. the super-surface structure unit designed by the invention is simple and has small processing and manufacturing difficulty.
Drawings
FIG. 1 is a schematic structural diagram of a nanostructure element in an embodiment of the present invention;
FIG. 2 shows the spectral responses of two sets of dimensional parameters of the optimized design of the nano-brick structure unit according to the embodiment of the present invention;
FIG. 3 is a continuous gray scale image selected in an embodiment of the present invention;
FIG. 4 is an anti-counterfeiting shading image selected in an embodiment of the invention;
FIG. 5 is a selected bi-color image in an embodiment of the invention;
FIG. 6 is a diagram showing selectable values of the turning angle of the super-surface nano-brick determined by the gray-scale image in the range of [0, π/4] in the embodiment of the present invention;
FIG. 7 is a graph showing selectable values of the super-surface nanoblock turning angle within the range of (π/4, π/2) as determined from a grayscale image in an embodiment of the present invention;
FIG. 8 shows a super-surface nano-brick steering angle arrangement designed in an embodiment of the present invention;
FIG. 9 is a schematic diagram of a super-surface structure of the present invention, in which nano-brick structure units of two sizes and different turning angles are arranged at equal intervals in the length and width directions;
FIG. 10 is a super surface gray scale image display simulation calculation result designed in the embodiment of the present invention;
FIG. 11 is a simulation calculation result of the super-surface anti-counterfeiting shading display designed in the embodiment of the invention.
Detailed Description
The following examples are provided to further illustrate the present invention for better understanding, but the present invention is not limited to the following examples.
The invention provides a design method of an anti-counterfeiting super surface based on anti-counterfeiting shading and image multiplexing, which comprises the following steps:
first, an array of nano-bricks is constructed.
Constructing a nano brick array, wherein the nano brick array comprises a plurality of nano brick structure units, the nano brick steering angle of each nano brick structure unit is theta, optimizing to obtain at least two groups of alternative size parameters of the nano brick structure units with different spectral responses, the peak value positions of the spectral responses of the at least two groups of nano brick structure units with the alternative sizes are different, but the peak value positions of the spectral responses of the incident electric field direction along the long axis of the nano brick at the wavelength lambda are different0Has equal reflectivity at a wavelength λ0When the linearly polarized light vertically enters each group of nano brick structure units with the optional sizes, the functions of the linearly polarized light are equivalent to micro-nano polarizers. The nano brick structure unit comprises a working surface and a nano brick arranged on the working surface, wherein an x axis and a y axis are respectively set in directions parallel to two edges of the working surface to establish an xoy coordinate system, a long axis L and a short axis W are arranged on a surface parallel to the working surface on the nano brick, and a turning angle theta of the nano brick is an included angle between the long axis L of the nano brick and the positive direction of the x axis; the size parameters of the nano brick structure units comprise the long axis L, the short axis W, the height H of the nano brick and the size of the side length C of the working face, the long axis L is not equal to the short axis W, and the center distance of each nano brick structure unit is equal. The at least two groups of nano brick structure units with alternative sizes comprise a first group of nano brick structure units with alternative sizes and a second group of nano brick structure units, and the optimization method of the size parameters of the at least two groups of nano brick structure units with alternative sizes comprises the following steps: the linear polarized light along the long axis of the nano brick along the electric field direction at the wavelength lambda is obtained through optimization1First with reflectivity not less than 90%The dimension parameters of the nano-brick structure units with the group dimensions are determined according to the wavelength lambda of linearly polarized light which is in normal incidence along the long axis of the nano-brick in the direction of an electric field2The size parameter of the second group of nano-brick structure units with the reflectivity not lower than 90 percent, and when linearly polarized light along the long axis of the nano-brick in the direction of the electric field is normally incident on the nano-brick structure units with the two sizes, the two nano-brick structure units have the wavelength lambda0Has equal reflectivity of and λ0≠λ1≠λ2。
With an intensity of I0Polarization direction of alpha1And the wavelength is lambda0The linearly polarized light is sequentially incident into the nano brick structure unit and the analyzer with the light transmission axis direction perpendicular to the polarization direction of the incident light to obtain the emergent light intensity and the polarization direction alpha of the linearly polarized light1And a functional relationship between the nano-brick steering angles theta of the nano-brick structural units; designing a gray level image, and calculating to obtain the nano-brick steering angle theta of each nano-brick structural unit in the nano-brick array in [0, pi/2 ] according to the gray level distribution required by the gray level image display and the functional relation]Two selectable values within the range;
designing an anti-counterfeiting shading image, and determining a final value of a nano-brick steering angle corresponding to each nano-brick structural unit in the nano-brick array from two optional values of the calculated nano-brick steering angle theta according to the strength value displayed by the anti-counterfeiting shading image and the functional relationship obtained in the step;
designing a bi-color image, determining the size parameters corresponding to the nano-brick structure units at each position in the nano-brick structure array from the various optional size parameters according to the strength requirement displayed by the bi-color image, and arranging the obtained nano-brick structure units with the corresponding sizes at each position according to the final values of the steering angles of the corresponding nano-bricks determined in the above steps, so as to obtain the required super-surface material;
when the polarization direction of the analyzer is perpendicular to the polarization direction of the incident linearly polarized light, the wavelength is lambda0Monochromatic linear polarized light with the electric field direction of pi/4 is incident to the metamaterial, and a gray image is displayed through a corresponding analyzer; when the wavelength is lambda0Monochromatic line with electric field direction pi 3/8And the polarized light is incident to the metamaterial, and the anti-counterfeiting shading image is displayed after passing through a corresponding analyzer. The principle involved in the invention is as follows:
1) principle of realizing gray image display:
due to the wavelength of lambda0The response characteristics of the nano-brick structural units of the two groups of size parameters are the same, so that the wavelength is lambda0At least two sets of nano-brick structural units of alternative dimensional parameters may be described by the same jones matrix. The Jones matrix of the nano brick structural unit which is optimally designed and functionally equivalent to a micro-nano polarizer can be expressed as follows when the steering angle is theta:
wherein R (theta) is a rotation matrix, and theta is the direction angle of the nano-brick structural unit.
When the light intensity is I0The included angle alpha between the polarization direction and the x-axis1After the reflected light passes through the analyzer with the light transmission axis direction vertical to the incident linearly polarized light direction, the emergent light intensity is as follows:
when taking alpha1And pi/4, the emergent light intensity is:
as shown in the formula (3), the emergent light intensity can be changed by changing the steering angle of the nano brick structure unit; and because the steering angle of the nano brick structure unit can be continuously changed, the continuous adjustment of emergent light intensity can be realized, namely the display of continuous gray level images is realized.
2) The principle of multiplexing the gray level image and the anti-counterfeiting shading is realized.
As can be seen from the formula (3), for any outputIntensity of emitted light IGo out 1Theta is in [0, pi/2 ]]Within range of two selectable values theta1And theta2And satisfies the following conditions:
θ1+θ2＝π/2#(4)
by the formula (2), take alpha1Pi 3/8, the exit light intensity is:
for theta satisfying the formula (4)1And theta2In other words, the intensity of the emitted light is alpha1Pi/4 is the same, but the intensity of the emitted light is alpha1Pi 3/8, so that for a single nanoblock unit with a defined turning angle, the intensity of the emitted light is dependent on the polarization direction of the linearly polarized light in the case of an incident linearly polarized light. Therefore, multiplexing of different images can be achieved on a single meta-surface by changing the polarization direction of linearly polarized light.
3) Principle for realizing double-color image display
Two groups of nano brick structure units with optimized sizes are arranged at the design wavelength lambda1And λ2The function of the micro-nano polarizer can be realized respectively, but the spectral response is different. Under the condition of adopting white light incidence, the two nano brick structure units can present different colors.
According to the 0 value and 1 value distribution of the bi-color image, two kinds of nano-brick structure units are respectively arranged at the positions corresponding to 0 and 1, and under the incidence of white light, the positions of 0 value and 1 value can display different colors, so that the bi-color image with certain contrast can be displayed.
To illustrate the present invention more clearly, the invention is described in more detail below with reference to specific examples, in which the nano-brick array of the present invention includes a plurality of nano-brick structure units, and the nano-brick structure units are composed of a transparent substrate and nano-bricks etched on the working surface thereof. The nano-bricks in the nano-brick array adopted in the invention are made of silver materials, and the transparent substrate is made of silicon dioxide. A single nano brick structure unit is shown in figure 2, a square working surface with the side length of C is arranged on the substrate of the nano brick structure unit, a nano brick is etched on the square working surface, and the nano brick structure unit is composed of a 1-substrate and a 2-nano brick. And the directions of the two edges parallel to the working surface are respectively set as an x axis and a y axis to establish an xoy coordinate system, the surface of the nano brick parallel to the working surface is provided with a long axis L and a short axis W, the nano brick is also provided with a height H vertical to the working surface, and the long axis L, the short axis W and the height H are all sub-wavelength levels. The nano brick steering angle theta in the nano brick structure unit is the included angle between the long axis L of the nano brick and the positive direction of the x axis.
In the invention, the long and short axis sizes of the nano-brick are different, and the electromagnetic responses along the two directions are different, so that the nano-brick structural unit can have anisotropy and has different responses to light waves in different polarization states. In addition, the response of the nano-brick structural unit is related to the size and the wavelength of the nano-brick 1, so that the nano-brick 1 with the same size parameter has different responses to light waves with different wavelengths. The size parameters of the two groups of nano-brick structure units, including the height H, the length L, the width W and the side length C of the working surface of the substrate of the nano-brick 1, are optimized through electromagnetic simulation software, so that the peak values of the spectral responses of the two groups of nano-brick structure units with the sizes are different, but the peak values are different at a specific wavelength lambda0And then, the reflectivity of the two groups of nano brick structure units to the linearly polarized light along the long axis of the nano brick structure units in the electric field direction is equal. And optimizing to obtain the size parameters of the micro-nano polarizer, wherein the functions of the nano-brick structural units are equivalent to the size parameters of the micro-nano polarizer when linearly polarized light with the working wavelength vertically enters each group of nano-brick structural units with the optional sizes.
In this embodiment, two sets of candidate size parameters of the nano-brick structure unit with the function equivalent to that of the micro-nano polarizer obtained by optimization design through the CST electromagnetic simulation software are respectively: l is1＝120hm、W180nm and H170nm and L2＝160nm、W260nm and H2The center-to-center spacing C of the nano brick structural units is 300hm, 70 nm. The spectral responses of the two sets of nano-brick structural units of the candidate dimensional parameters are shown in FIG. 2, where the peak response wavelength of the nano-brick structural units of the first set of dimensions is λ1568nm, the peak response wavelength of the second set of nano-brick structural units is λ2670nm, and both at wavelength λ0The response characteristics were the same at 605 nm. The reflectivity of the nano-brick structural unit under the structural parameters is shown in figure 2, wherein R1lAnd R2lRespectively, the reflectance of the nanoblock structure units of the first and second sets of dimensions upon which linearly polarized light vibrating in the long axis direction is normally incident. As can be seen from FIG. 2, R1lAt a wavelength of λ1At (568nm) and R2lAt a wavelength of λ2(670nm) is higher than 90%, and R is1lAnd R2lAt a wavelength of λ0The positions at (605nm) are equal, and the design requirements are met. Therefore, the nano-brick steering angle of the nano-brick array can be designed for the case where a linearly polarized light wave with a wavelength of 605nm is incident.
The present embodiment will be further described with reference to a specific design pattern. The continuous gray scale image and the anti-counterfeiting shading image selected in the embodiment are respectively shown in fig. 3 and 4, and the number of pixels of the continuous gray scale image and the number of pixels of the anti-counterfeiting shading image are 829 × 1171. Aiming at the gray value corresponding to any one nano-brick structure unit in the continuous gray image of FIG. 3, the steering angle of each nano-structure unit is [0, 2] according to the formula (3)]Within range of two selectable values theta1And theta2(ii) a Let theta1＜θ2Then each position corresponds to theta1And theta2The distributions are shown in fig. 6 and 7, respectively.
An anti-counterfeiting shading image is designed, see fig. 4, the anti-counterfeiting shading image is set to be a double-color image, the pixel value corresponding to any nano brick structure unit in the anti-counterfeiting shading image is 0 or 1, emergent light of the nano brick structure unit corresponding to the pixel value 1 is strong when monochromatic linear polarized light is incident and is displayed to be bright, and emergent light of the nano brick structure unit corresponding to the pixel value 0 is small when the monochromatic linear polarized light is incident and is displayed to be dark. From equation (5), two selectable values of the steering angle θ for each nano-brick structural unit can be derived1And theta2，θ1And theta2Corresponding emergent light intensity
Assume I "> I'. SelectingComparing any corresponding nano-brick structure unit in the anti-counterfeiting shading image with any corresponding nano-brick structure unit in the continuous gray level image, and if the pixel value of the nano-brick structure unit in the anti-counterfeiting shading image is 1, selecting the nano-brick steering angle of the nano-brick structure unit as theta2(ii) a If the pixel value of the nano-brick structure unit in the anti-counterfeiting shading image is 0, selecting the nano-brick steering angle of the nano-brick structure unit as theta1。
Designing a dual-color image which is multiplexed as shown in fig. 5, wherein the dual-color image is also a binary image, the pixel value corresponding to any nano-brick structural unit in the dual-color image is 0 or 1, and the size parameter of the nano-brick structural unit corresponding to 0 can be selected to be L1＝120nm、W180nm and H170 nm; 1 the size parameter of the corresponding nano brick structural unit is L2＝160nm、W260nm and H270nm, and the center-to-center spacing C of the nano-brick structural units is 300 nm. Of course, the size parameters of the nano-brick structure units corresponding to pixel values 0 and 1 can be interchanged. Thus, the dimensional parameters of the nano-brick structural units at each location in the nano-brick array can be uniquely determined. And then, the final values of the turning angles of the nano-bricks of the nano-brick structural units in the nano-brick array obtained in fig. 8 are combined for arrangement, the nano-brick structural units are arranged at equal intervals in the length and width directions, and a schematic diagram of the structure of the super-surface material designed according to the embodiment of the invention is shown in fig. 9.
When linearly polarized light with the wavelength of 605nm and the polarization direction of pi/4 is vertically incident to the metamaterial and passes through the analyzer with the light transmission axis direction vertical to the incident linearly polarized light direction, a continuous gray image can be clearly seen, and the continuous gray image is shown in figure 10; when the incident linearly polarized light is rotated by pi/8, the linearly polarized light with the wavelength of 605nm and the polarization direction of 3 pi/8 vertically enters the metamaterial, and an anti-counterfeiting shading image shown in figure 11 is displayed after passing through a corresponding analyzer; when white light incident on the meta-surface material is used, a two-color image can be seen, see FIG. 5; the invention realizes the multiplexing of the gray image, the anti-counterfeiting shading and the dual-color image. The super-surface structure unit is in a sub-wavelength order, so that the optical display resolution based on the super-surface is extremely high; the multiplexing of the gray level image, the anti-counterfeiting shading and the double-color image is realized through a single super surface, the information density is improved, and the anti-counterfeiting safety is also greatly improved.
While the foregoing is directed to the preferred embodiment of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
Claims (10)
1. A design method of an anti-counterfeiting super surface based on anti-counterfeiting shading and image multiplexing is characterized by comprising the following steps:
constructing a nano brick array, wherein the nano brick array comprises a plurality of nano brick structure units, the nano brick steering angle of each nano brick structure unit is theta, optimizing to obtain at least two groups of alternative size parameters of the nano brick structure units with different spectral responses, the peak value positions of the spectral responses of the at least two groups of nano brick structure units with the alternative sizes are different, but the peak value positions of the spectral responses of the incident electric field direction along the long axis of the nano brick at the wavelength lambda are different0Has equal reflectivity at a wavelength λ0When the linearly polarized light vertically enters each group of nano brick structure units with the alternative sizes, the functions of the linearly polarized light are equivalent to micro-nano polarizers;
with an intensity of I0Polarization direction of alpha1And the wavelength is lambda0The linearly polarized light is sequentially incident into the nano brick structure unit and the analyzer with the light transmission axis direction perpendicular to the polarization direction of the incident light to obtain the emergent light intensity and the polarization direction alpha of the linearly polarized light1And a functional relationship between the nano-brick steering angles theta of the nano-brick structural units; designing a gray level image, and calculating to obtain the nano-brick steering angle theta of each nano-brick structural unit in the nano-brick array in [0, pi/2 ] according to the gray level distribution required by the gray level image display and the functional relation]Two selectable values within the range;
designing an anti-counterfeiting shading image, and determining a final value of a nano-brick steering angle corresponding to each nano-brick structural unit in the nano-brick array from two optional values of the calculated nano-brick steering angle theta according to the strength value displayed by the anti-counterfeiting shading image and the functional relationship obtained in the step;
designing a bi-color image, determining the size parameters corresponding to the nano-brick structure units at each position in the nano-brick structure array from the various optional size parameters according to the strength requirement displayed by the bi-color image, and arranging the obtained nano-brick structure units with the corresponding sizes at each position according to the final values of the steering angles of the corresponding nano-bricks determined in the above steps, so as to obtain the required super-surface material;
a certain linear polarized light is incident into the metamaterial, and a continuous gray image is displayed after the metamaterial passes through a corresponding analyzer; when the incident linearly polarized light is rotated by n pi/8 and then enters the super surface material and passes through a corresponding analyzer, an anti-counterfeiting shading image is displayed; when the meta-surface material is incident with white light, a bi-color image is displayed.
2. The method for designing an anti-counterfeiting super surface based on the anti-counterfeiting shading and image multiplexing of claim 1, wherein the nano-brick structure unit comprises a working surface and a nano-brick arranged on the working surface, a xoy coordinate system is established by respectively setting directions parallel to two edges of the working surface as an x axis and a y axis, a long axis L and a short axis W are arranged on the surface of the nano-brick parallel to the working surface, and a turning angle theta of the nano-brick is an included angle between the long axis L of the nano-brick and the positive direction of the x axis.
3. The method according to claim 2, wherein the dimension parameters of the nano-brick structure units include a major axis L, a minor axis W, and a height H of the nano-brick and a dimension of the side length C of the working surface, and the major axis L is not equal to the minor axis W, and the distances between centers of the nano-brick structure units are equal.
4. The method of claim 2, wherein the at least two sets of candidate sizes of the anti-counterfeiting shading and image multiplexing-based anti-counterfeiting super surface design methodThe nano brick structure units comprise a first group of nano brick structure units with the size and a second group of nano brick structure units, and the optimization method of the size parameters of the at least two groups of nano brick structure units with the alternative sizes comprises the following steps: the linear polarized light along the long axis of the nano brick along the electric field direction at the wavelength lambda is obtained through optimization1The dimension parameters of the first group of nano-brick structure units with the reflectivity not less than 90 percent are determined, and the linear polarized light along the long axis of the nano-brick in the direction of the electric field is in normal incidence at the wavelength lambda2The size parameter of the second group of nano-brick structure units with the reflectivity not lower than 90 percent, and when linearly polarized light along the long axis of the nano-brick in the direction of the electric field is normally incident on the nano-brick structure units with the two sizes, the two nano-brick structure units have the wavelength lambda0Has equal reflectivity of and λ0≠λ1≠λ2。
5. The method for designing the anti-counterfeiting super surface based on the anti-counterfeiting shading and image multiplexing of claim 1, wherein the functional equivalence of the nano brick structural unit is a micro-nano polarizer, and the light intensity is I0Wavelength of λ0Polarization direction of alpha1The incident angle of the linearly polarized light to the nano-brick structure unit with the theta direction angle, reflected light passes through the analyzer with the polarization analysis direction vertical to the polarization direction of the incident linearly polarized light, and the intensity I of emergent light is obtained1And alpha1The functional relationship between θ is:
6. the method for designing an anti-counterfeiting super surface based on the anti-counterfeiting shading and image multiplexing as claimed in claim 1, wherein when the polarization analyzing direction of the analyzer is perpendicular to the polarization direction of incident linearly polarized light, the wavelength λ is0Monochromatic linear polarized light with the electric field direction of pi/4 is incident to the metamaterial, and a gray image is displayed through a corresponding analyzer; when the wavelength is lambda0And the monochromatic linear polarized light with the electric field direction of pi 3/8 is incident to the metamaterial, and the anti-counterfeiting shading image is displayed after the monochromatic linear polarized light passes through the corresponding analyzer.
7. The method for designing an anti-counterfeiting super surface based on the anti-counterfeiting shading and image multiplexing as claimed in claim 6, wherein the method for determining the final value of the turning angle of the nano brick comprises the following steps:
when alpha is1When the light intensity is pi/4, the emergent light intensity is high
Normalizing the intensity of the gray image according to the normalized intensity distribution and I of the gray image1Calculating the function relation with theta to obtain the turning angle theta of each nano-brick structural unit in the nano-brick array in [0, pi/2 ]]Two selectable values of theta within the range1And theta2Theta corresponding to an arbitrary intensity1And theta2Satisfies theta1+θ2＝π/2；
When alpha is1Pi 3/8, the intensity of the emergent light is
The emergent light intensity corresponding to the two selectable values
Let I ">I′；
The anti-counterfeiting shading image is set to be a double-color image, and the pixel value corresponding to any nano brick structure unit in the anti-counterfeiting shading image is 0 or 1; defining that emergent light of a nano brick structure unit corresponding to a pixel value 1 is strong when monochromatic linear polarized light is incident, and displaying the emergent light as bright; defining that the emergent light intensity of the nano brick structure unit corresponding to the pixel value 0 is small when monochromatic linear polarized light is incident, and displaying the light intensity as dark; selecting the nano-brick structure unit at any corresponding position in the anti-counterfeiting shading image and the gray level image for comparison, and if the pixel value of the nano-brick structure unit in the anti-counterfeiting shading image is 1, selecting the nano-brick steering angle of the nano-brick structure unit as theta2(ii) a If it isIf the pixel value of the nano-brick structural unit in the anti-counterfeiting shading image is 0, selecting the nano-brick steering angle of the nano-brick structural unit as theta1。
8. The method for designing the anti-counterfeiting super surface based on the anti-counterfeiting shading and image multiplexing as claimed in claim 1, wherein the pixel value of the bi-color image is 0 or 1, respectively, any one nano-brick structural unit on the bi-color image is selected, and when the pixel value corresponding to the nano-brick structure is 0, one of the nano-brick structural units with the alternative size parameters is selected; another nano-brick structural unit of an alternative size parameter is selected when the pixel value of the nano-brick structural unit is 1.
9. The method for designing an anti-counterfeiting super surface based on the anti-counterfeiting shading and image multiplexing of claim 2, wherein the working surface is made of silicon dioxide, and the nano brick is made of silver material.
10. A super surface material obtained by the method for designing an anti-counterfeiting super surface based on the multiplexing of the anti-counterfeiting shading and the image according to any one of claims 1 to 9.
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