CN111145071B - Three-channel super-surface multiplexing method for superposing watermarks in continuous gray level images - Google Patents
Three-channel super-surface multiplexing method for superposing watermarks in continuous gray level images Download PDFInfo
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- G06T1/0078—Robust watermarking, e.g. average attack or collusion attack resistant using multiple thresholds
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Abstract
The invention relates to the technical field of micro-nano optics and optical anti-counterfeiting, and discloses a three-channel super-surface multiplexing method for superposing watermarks in continuous gray level images, which comprises the following steps: the nano brick array comprises a plurality of nano brick structure units, and at least two groups of alternative size parameters with different spectral responses of the nano brick structure units are obtained through optimization; selecting a three-channel super surface to multiplex a continuous gray image, a watermark image and a binary image; designing a nano-brick steering angle in the nano-brick array according to the continuous gray level image and the watermark anti-counterfeiting image; selecting nano brick structure units with corresponding sizes from multiple groups of candidate size parameters according to the binary image to arrange; and arranging the nano brick unit structures according to the nano brick unit structure size parameters and the nano brick steering angles to obtain the three-channel metamaterial. The invention can realize the multiplexing of three-channel information through a single super surface array structure and has the characteristics of compact structure, high information density and strong concealment.
Description
Technical Field
The invention relates to the technical field of micro-nano optics, in particular to a three-channel super-surface multiplexing method for superposing watermarks in continuous gray level images.
Background
The anti-counterfeiting of various articles has been a major concern in both production and life. The watermark anti-counterfeiting image is a common anti-counterfeiting means, but with the development of the technical level, the anti-counterfeiting is carried out only by using the watermark anti-counterfeiting image, because the concealment is not enough, the watermark anti-counterfeiting image is easy to imitate, and the security obviously cannot meet the increasing anti-counterfeiting requirement.
The super-surface material can flexibly and effectively regulate and control the amplitude, the phase, the polarization state and the like of an optical wave electromagnetic field in a sub-wavelength scale, has the advantages of small size, light weight, convenience in processing and the like, and is widely applied to various optical fields. In the process of designing the super-surface, an information multiplexing method can be adopted to improve the information density, namely, a large amount of information is stored on the same super-surface according to different wavelengths, polarization states and other parameters of incident light waves, so that the information density is obviously improved.
By utilizing the super surface multiplexing method, the safety of optical anti-counterfeiting by utilizing the super surface can be obviously improved, and the information density of the super surface can be improved by adopting a multi-channel multiplexing mode. The existing methods for performing anti-counterfeiting on the super surface still need 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 three-channel super-surface multiplexing method for superposing watermarks in continuous gray level images.
The scheme adopted by the invention for solving the technical problems is as follows:
a three-channel super-surface multiplexing method for superposing watermarks in continuous gray images comprises 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 candidate 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 candidate size nano brick structure units are different, but the peak value positions of the spectral responses of the at least two groups of candidate size nano brick structure units are different at a specific wavelength lambda0The complex reflection coefficients or the transmission coefficients of the lower parts along the long axis directions of the nano brick structure units with at least two groups of alternative sizes are correspondingly equal, and the complex reflection coefficients or the transmission coefficients along the long axis directions of the nano brick structure units with at least two groups of sizes are correspondingly equalThe complex reflection coefficient or the transmission coefficient in the element short axis direction is also correspondingly equal, and the functions of the element short axis direction are equivalent to micro-nano polarizers when linearly polarized light with working wavelength vertically enters each group of nano brick structure units with the alternative sizes;
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 polarization detection direction is alpha2The analyzer obtains the emergent light intensity and the polarization direction alpha of the linearly polarized light1Nano-brick steering angle theta of nano-brick structural unit and polarization analyzing direction alpha of polarization analyzer2Functional relationship between; designing a gray image, and calculating four selectable values of the nano-brick steering angle theta in each nano-brick structural unit in the nano-brick array according to the gray distribution required by the gray image display and the functional relation;
designing a watermark 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 the four calculated optional values of the nano-brick steering angle theta according to the gray scale requirement displayed by the watermark image and the functional relationship obtained in the step, so that the nano-brick array can respectively display a gray scale image and a gray scale image superposed with the watermark in different polarization directions of an analyzer;
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 display requirements of the bi-color image, and arranging the nano-brick steering angles in the nano-brick structure units with the sizes corresponding to each position according to the determined final values of the corresponding nano-brick steering angles in the 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 analyzer is rotated by a specific angle, the linearly polarized light is continuously incident to the metamaterial and passes through the analyzer, and then a continuous gray image superposed with a watermark image is displayed; when the metamaterial is incident with a broad spectrum light wave, a two-color image is displayed.
Further, the nano-brick structure unit comprises a working surface and a nano-brick arranged on the working surface, 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 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 and the x axis of the nano-brick.
Further, the structural parameters of the nano-brick structural unit include a major axis L, a minor axis W, a height H of the nano-brick, and a dimension of the side length C of the working face, and the major axis L is not equal to the minor axis W.
Furthermore, when the function of the nano brick structure unit is equivalent to that of a micro-nano polarizer, the emergent light intensity I and the incident light intensity I0The polarization direction of linearly polarized light alpha1The steering angle theta of the nano brick and the polarization analyzing direction of the polarization analyzer are alpha2The functional relationship between the two is as follows:
further, when the analyzer has an analyzing direction α2With the polarization direction alpha of the incident linearly polarized light1When the included angle between the two materials is pi/2, certain monochromatic linear polarized light is incident to the metamaterial and a gray image is displayed through a corresponding analyzer; when the polarization analyzing direction alpha of the polarization analyzer2With the polarization direction alpha of the incident linearly polarized light1When the included angle between the two components is pi/4, the monochromatic linear polarized light is continuously incident to the metamaterial, and the grayscale image superposed with the watermark image is displayed after passing through the analyzer.
Further, when the analyzer has an analyzing direction α2With the polarization direction alpha of the incident linearly polarized light1When the included angle between the two is pi/2, the monochromatic linear polarized light is incident on the metamaterial and emits light intensity I after passing through the analyzer2：
When the polarization analyzing direction alpha of the polarization analyzer2With the polarization direction alpha of the incident linearly polarized light1When the included angle between the two is pi/4, the monochromatic linear polarized light is incident on the metamaterial and emits light intensity I after passing through the analyzer3Comprises the following steps:
determining four optional values of the steering angle theta of the nano brick respectively corresponding to I2≈I3、I2>I3And I2＜I3Which case of (1);
comparing the pixel points at the same position corresponding to the watermark image and the gray image, and selecting I from the nano-brick corresponding to the nano-brick structural unit corresponding to the pixel point when the pixel point has no watermark image2≈I3The selectable value of the corresponding nano brick steering angle theta; when the pixel point has the watermark image, a proper gray threshold value is set to be T for the gray imagehWhen the gray value of the pixel point in the gray image is larger than ThThen, selecting I from the nano-brick structural unit corresponding to the pixel point2>I3The selectable value of the corresponding nano brick steering angle theta; when the gray value of the pixel point in the gray image is less than ThThen, selecting I from the nano-bricks corresponding to the nano-brick structural units corresponding to the pixel points2＜I3The corresponding selectable value of the nano-brick steering angle theta.
Further, the pixel values in the dual-color image are respectively 0 or 1, any pixel point on the dual-color image is selected, and when the pixel value of the pixel point is 0, one of the nano-brick structural units with the alternative size parameters is selected; and when the pixel value of the pixel point is 1, selecting the nano-brick structural unit with another alternative size parameter.
Further, the working surface is made of silicon dioxide, and the nano-brick is made of a silver material.
Another object of the present invention is to provide a metamaterial obtained by the above three-channel super-surface multiplexing method for superimposing watermarks in continuous gray scale images.
Compared with the prior art, the invention has at least the following beneficial effects:
1. the three-channel super surface designed by the invention can superpose the watermark anti-counterfeiting image in the continuous gray image and can simultaneously realize the multiplexing with an arbitrary binary image, thereby not only improving the information capacity, but also greatly improving the anti-counterfeiting safety;
2. the multiplexing method of the three-channel super surface adopts the nano brick unit structures with two size parameters to form the super surface structure, the multiplexing method has simple design process and convenient structure processing, and the multiplexed continuous gray level image, the watermark anti-counterfeiting image and the binary image can be randomly selected according to the anti-counterfeiting or display requirements, so the design process is simple and the design has great flexibility;
3. due to the size parameter of the nanometer brick unit structure with the sub-wavelength magnitude, the three-channel super-surface information multiplexing has the characteristics of compact structure, high information density and strong concealment.
Drawings
FIG. 1 is a flow chart of a design method of a three-channel metamaterial surface material in an embodiment of the present invention;
FIG. 2 is a schematic structural diagram of a nanostructure element in an embodiment of the present invention;
FIG. 3 is a graph showing the spectral responses corresponding to the dimensional parameters of the two sets of nano-brick unit structures optimally designed according to the embodiment of the present invention;
FIG. 4 is a schematic diagram of intensity modulation before and after a nano-brick unit structure with a function equivalent to a micro-nano polarizer rotates pi/4 in the transmission axis direction of an analyzer in the embodiment of the invention;
FIG. 5 is a continuous gray scale image selected in an embodiment of the present invention;
FIG. 6 is a watermark anti-counterfeiting image selected in an embodiment of the invention;
FIG. 7 is a binary image selected in an embodiment of the present invention;
FIG. 8 is a schematic diagram of an optical path for displaying a continuous gray image and a watermark anti-counterfeiting pattern on a three-channel super-surface according to an embodiment of the present invention;
FIG. 9 shows a simulation result of superimposing a watermark anti-counterfeit image on a continuous gray scale image according to an embodiment of the present invention;
fig. 10 is a schematic diagram of a nano-brick array structure formed by two nano-brick unit structures with different sizes and different direction angles arranged at equal intervals in the length and width directions 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 a high-frequency and low-frequency multiplexing super-surface anti-counterfeiting image with a watermark, which comprises the following steps as shown in figure 1:
first, an array of nano-bricks is constructed. The nano brick array comprises a plurality of nano brick structure units, each nano brick structure unit comprises a working surface and a nano brick arranged on the working surface, an x axis and a y axis are respectively set in the directions parallel to two edges of the working surface to establish an xoy coordinate system, the surface of each nano brick parallel to the working surface is provided with a long axis L and a short axis W, each nano brick is also provided with a height H vertical to the working surface, and the steering angle theta of each nano brick is the included angle between the long axis L and the x axis of each nano brick. Optimizing to obtain at least two groups of candidate size parameters with different spectral responses of the nano-brick structure units, wherein the peak positions of the spectral responses of the nano-brick structure units with the at least two groups of candidate sizes are different but the spectral responses of the nano-brick structure units with the at least two groups of candidate sizes are different at a certain specific wavelength lambda0There is a significant coincidence, i.e. at this particular wavelength λ0The complex reflection coefficient or transmission coefficient along the major axis direction of the nano-brick structure units with at least two groups of alternative sizes are correspondingly equal, and the complex reflection coefficient or transmission coefficient along the minor axis direction of the nano-brick structure units with at least two groups of sizes are also correspondingly equal, because the complex reflection coefficient or transmission coefficient at the wavelength of lambda is equal0The responses of the nano-brick unit structures of the two groups of size parameters are the same, so the wavelength lambda is considered0Under the condition of light wave incidence, the nano brick steering angle of the nano brick unit structure is designed according to the polarization modulation characteristic of the nano brick unit structure. Linearly polarized light with working wavelength vertically enters each group of nano brick structure units with alternative sizes, and the functions of the nano brick structure units 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 polarization detection direction is alpha2The analyzer obtains the emergent light intensity and the polarization direction alpha of the linearly polarized light1Nano-brick steering angle theta of nano-brick structural unit and polarization analyzing direction alpha of polarization analyzer2Functional relationship between; designing a continuous gray image, and calculating four selectable values of the nano-brick steering angle theta in each nano-brick structural unit in the nano-brick array according to the gray distribution required by gray image display and the functional relation;
designing a watermark 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 the four selectable values of the nano-brick steering angle theta according to the gray scale requirement displayed by the watermark image and the functional relationship obtained in the step, so that the nano-brick array can display both a continuous gray scale image and a gray scale image superposed with the watermark;
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 display requirements of the bi-color image, and arranging the nano-brick steering angles in the nano-brick structure units with the sizes corresponding to each position according to the determined final values of the corresponding nano-brick steering angles in the 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 analyzer is rotated by a specific angle, the linearly polarized light is continuously incident to the metamaterial and passes through the analyzer, and then a continuous gray image superposed with a watermark image is displayed; when the metamaterial is incident with a broad spectrum light wave, a two-color image is displayed.
In the invention, the size parameters of the nano brick unit structure are optimized through electromagnetic simulation software, the optimally designed nano brick unit structure has the function equivalent to a micro-nano polarizer, and the multiplexing of three-channel information is realized according to the modulation characteristic of the nano brick unit structure on the linear polarization light wave intensity and the spectral response characteristic of the nano brick unit structure. The three-channel super surface can superpose the watermark anti-counterfeiting image in the continuous gray image and can simultaneously realize multiplexing with an arbitrary binary image, so that the information capacity is improved, and the anti-counterfeiting safety is also greatly improved.
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-brick array adopted in the invention is of a structure formed by silver-silicon dioxide, namely, the nano-bricks 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 and the x axis of the nano brick, namely the value range of the nano brick steering angle theta is 0-pi.
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 unit structure can have anisotropy and has different responses to light waves in different polarization states. In addition, the response of the nano-brick unit structure is related to the size and wavelength of the nano-brick 2, so that the nano-brick 2 with the same size parameter has different responses to light waves with different wavelengths. The size parameters of the two groups of nano brick unit structures, including the height H, the length L, the width W and the side length C of the base working surface of the nano brick 2, are optimized through electromagnetic simulation software, so that the peak values of the spectral responses of the two groups of nano brick unit structures with the sizes are different, but the peak values are different at a specific wavelength lambda0Along the long axis and the short axis of the nano brickRespectively, are correspondingly equal. The two nano brick unit structures can display different colors under the incidence of white light, and have the same modulation characteristics on light waves at the wavelength positions with equal spectral response, namely the size parameters of the optimized nano brick unit structures.
In this embodiment, two sets of candidate size parameters of the nano-brick unit structure with the function equivalent to that of a micro-nano polarizer are obtained through the optimized design by using the CST electromagnetic simulation software, and respectively: l is1＝160nm，W1＝60nm，H1＝70nm，C1300nm and L2＝120nm，W2＝80nm，H2＝70nm，C2300 nm. The spectral response of the nano-brick unit structures for the two sets of alternative dimensional parameters is shown in fig. 3. As can be seen from FIG. 3, the light wave response of the nano-brick unit structures of the two sets of size parameters is the same at 604 nm. Therefore, the steering angle of the nanoblock array may be designed for the case where a linearly polarized light wave having a wavelength of 604nm is incident.
The spectral response of the nano-brick unit structures of different size parameters is different. See fig. 3, the spectral response at wavelength 604nm for the two sets of nano-brick structural units of alternative dimensional parameters is the same. Therefore, the nano-brick unit structures of two sets of alternative size parameters at a wavelength of 604nm can be described by the same Jones matrix.
The jones matrix of the optimally designed anisotropic nano brick unit structure can be expressed as follows when the steering angle is theta:
where R (θ) is the rotation matrix, θ is the nano-tile steering angle, and A and B are the complex reflection (or transmission) coefficients along the nano-tile major and minor axes, respectively.
When linearly polarized light with unit amplitude passes through an anisotropic nano brick unit structure and then passes through an analyzer, the Jones vector of transmitted light wave is expressed as:
in the formula, alpha1Is the angle between the vibration direction of incident linearly polarized light and the x axis, alpha2Is the angle between the transmission axis direction of the analyzer and the x-axis.
When the intensity of incident linearly polarized light is I0Then, the intensity of the emergent light of the linearly polarized light passing through the anisotropic nano brick unit structure and then passing through the analyzer is as follows:
when the included angle between the transmission axis of the polarizer and the x axis is set to be pi/2, the transmission axis of the analyzer is along the x axis, namely alpha1＝π/2，α2When 0, then equation (3) can be simplified as:
when the included angle between the transmission axis of the polarizer and the x axis is pi/2, the included angle between the transmission axis of the analyzer and the x axis is pi/4, namely alpha1＝π/2，α2Pi/4, then equation (3) can be simplified as:
if the function of the nano brick unit structure is equivalent to a micro-nano polarizer, a is 1, B is 0, and the incident light wave is the unit light intensity, then the equations (4) and (5) can be simplified as follows:
thus before and after the analyzer rotates pi/4, the ratio of intensity changes is:
designing a continuous gray image, and calculating to obtain four optional values theta of the nano-brick steering angle in each nano-brick structure unit within the range of 0-pi according to the gray value of each pixel point of the continuous gray image and the simplified formula (6)1、θ2、θ3、θ4。
From the formulas (6) and (7), in conjunction with fig. 4, it can be seen that there are clearly 3 different regions when the nano-brick turning angle of the nano-brick unit structure is varied within the range of 0 to pi: i is2≈I3，I2>I3，I2＜I33 intervals of (a). As shown in FIG. 4, four optional values θ of the turning angle of the nano-brick can be correspondingly determined1、θ2、θ3、θ4Respectively correspond to I2≈I3、I2>I3And I2＜I3Which case in (1).
Designing a watermark image, wherein in order to ensure that the nano-brick array can display both a continuous gray image and a watermark image superposed in the continuous gray image, four optional values theta are provided from the nano-brick steering angle according to a gray value combination formula (3) required by the watermark image display1、θ2、θ3、θ4And determining the final value of the steering angle of the nano-brick corresponding to each nano-brick structural unit in the nano-brick array. Specifically, pixel points at the same position corresponding to the watermark image and the gray image at will are compared, and when the pixel point has no watermark image, the nano-brick of the nano-brick structural unit corresponding to the pixel point selects I2≈I3The corresponding selectable values of the steering angles of the nano bricks are arranged. When the pixel point has the watermark image, a proper gray threshold value is set to be T for the gray imagehWhen the gray value of the pixel point in the gray image is larger than ThThen the nano brick structure unit corresponding to the pixel pointNano brick selection I2>I3Arranging the corresponding selectable values of the steering angles of the nano bricks; when the gray value of the pixel point in the gray image is less than ThThen, selecting I from the nano-bricks of the nano-brick structural unit corresponding to the pixel point2＜I3And arranging the corresponding selectable values of the nano-brick steering angles, so as to obtain the nano-brick steering angle arrangement condition of each nano-brick structural unit on the whole nano-brick array.
And designing a binary image, and determining the size parameters of each nano-brick structure unit according to the pixel values of the binary image. The specific method comprises the following steps: and respectively selecting two groups of alternative size parameters corresponding to the nano brick unit structure with optimized design at positions corresponding to pixel values 0 and 1 of the binary image, wherein the position of the value 0 corresponds to one group of alternative size parameters of the nano brick unit structure, and the position of the value 1 corresponds to the other group of alternative size parameters. Under the condition of white light incidence, due to the fact that the spectral responses of the nano-brick unit structures corresponding to the two sets of size parameters are different, a double-color image can be presented. Therefore, the turning angle and the size parameters of the nano-bricks of the nano-brick unit structure can be determined according to the multiplexed continuous gray level image, the watermark anti-counterfeiting image and the binary image, the nano-brick unit structures are arranged at equal intervals, and the super-surface material is obtained.
The present embodiment will be further described with reference to a specific design pattern. The continuous gray scale image and the watermark anti-counterfeiting image selected in the embodiment are respectively shown in fig. 5 and fig. 6. For the gray value of each pixel point in the continuous gray image of fig. 5, according to equation (6), four selectable values θ of the nano-brick steering angle of each nano-brick structural unit in the nano-brick array can be calculated and obtained1、θ2、θ3、θ4And the four selectable values of the turning angle of the nano-brick structural unit corresponding to a certain pixel point correspond to A, B, C and D points in FIG. 4. And (3) selecting a corresponding nano brick steering angle in the corresponding interval shown in the figure 4 according to the gray value condition displayed by the watermark anti-counterfeiting pattern in combination with the watermark anti-counterfeiting pattern shown in the figure 6. The specific method comprises the following steps: comparing the pixel points at the same position corresponding to the watermark anti-counterfeiting image and the continuous gray level image at will, if the pixel points are in the waterIn the anti-counterfeiting image, the pixel point has no anti-counterfeiting watermark, that is, no 'super-surface anti-counterfeiting' character watermark in fig. 6, and the nano-brick steering angle of the nano-brick structural unit corresponding to the pixel point is selected within the range of R1 in fig. 4, that is, the nano-brick steering angle corresponding to the point a is selected. If the watermark anti-counterfeiting image is provided with the anti-counterfeiting watermark at the point, namely the watermark of the character of 'super-surface anti-counterfeiting' in the figure 6, a proper gray threshold value is set for the continuous gray image, so that the value of the turning angle of the nano brick is selected within the range of R2 or R3. In this embodiment, the grayscale threshold is 0.5, when the relative grayscale value of the pixel point in the continuous grayscale image is less than 0.5, the angle within the range of R2 in fig. 4 is selected as the nano-brick steering angle of the nano-brick structural unit corresponding to the pixel point, and the nano-brick steering angle corresponding to the B point or the C point in fig. 4 can be selected, but since the light intensity change before and after the B point polarization detector rotates is larger, the contrast ratio is higher, and therefore, it is more appropriate to select the nano-brick steering angle corresponding to the B point. When the relative gray value of the pixel point position in the continuous gray image is greater than 0.5, the nano-brick steering angle of the nano-brick structural unit corresponding to the pixel point is selected within the range of the R3 interval in fig. 4, that is, the nano-brick steering angle corresponding to the D point is selected.
Designing a binary image which is multiplexed as shown in fig. 7, wherein the pixel value of any pixel point in the binary image is 0 or 1, and the size parameter of the nano-brick unit structure corresponding to 0 is selected to be L1＝160nm，W1＝60nm，H1＝70nm，C1The dimension parameter of the nano brick unit structure corresponding to 1 is L (300 nm)2＝120nm，W2＝80nm，H2＝70nm，C2300 nm. Of course, the dimensional parameters of the nano-brick structural units corresponding to 0 and 1 can be interchanged. Therefore, the dimension parameter of the nano-brick unit structure at each position 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 structure units in the obtained nano brick array are combined for arrangement, the nano brick unit structures are arranged at equal intervals along 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. 10.
When the incident light 3 with the wavelength of 604nm is vertically incident on the polarizer 4 to generate linearly polarized light wave vertical to the x axis and is incident on the metamaterial 5, a continuous gray image can be clearly seen by combining the analyzer 6 along the x axis in the direction of the light transmission axis, as shown in fig. 5; if the light transmission axis direction of the analyzer 6 is rotated to the included angle pi/4 with the x axis, the watermark anti-counterfeiting image superimposed in the continuous gray level image can be seen, as shown in fig. 9; when the broadband white light is adopted to be incident into the super-surface material, a double-color image can be seen, as shown in figure 7, namely, three-channel super-surface multiplexing of superposing the watermark anti-counterfeiting image in a continuous gray image is realized.
In summary, the invention optimizes two groups of nano brick unit structures with different sizes, and makes a single nano brick unit structure function as a micro-nano polarizer, the two groups of nano brick unit structures with different sizes have different spectral response peak positions, but the spectral responses of the two groups of nano brick unit structures are obviously overlapped at a certain specific wavelength; according to the modulation characteristic of the nano brick unit structure on the polarized light wave and the spectral response characteristic of the nano brick unit structure, the watermark anti-counterfeiting pattern can be superposed into a continuous gray image, the multiplexing of three channels of information in a single super surface is realized by combining a binary image, and the multiplexed image information in three channels can be displayed by changing the direction of a light transmission axis of an analyzer or changing incident light waves.
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 (9)
1. A three-channel super-surface multiplexing method for superposing watermarks in continuous gray images 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, and optimizing to obtain at least two groups of nano brick structure units with different spectral responsesCandidate dimension parameter, the peak positions of the spectral responses of at least two groups of nano-brick structure units with candidate dimensions are different, but at a specific wavelength lambda0The complex reflection coefficients or the transmission coefficients along the long axis direction of at least two groups of nano brick structure units with the alternative sizes are correspondingly equal, the complex reflection coefficients or the transmission coefficients along the short axis direction of at least two groups of nano brick structure units with the alternative sizes are also correspondingly equal, and the functions of the nano brick structure units are equivalent to micro-nano polarizers when linearly polarized light with working wavelength vertically enters each group of nano brick structure units with the alternative sizes;
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 polarization detection direction is alpha2The analyzer obtains the emergent light intensity and the polarization direction alpha of the linearly polarized light1Nano-brick steering angle theta of nano-brick structural unit and polarization analyzing direction alpha of polarization analyzer2Functional relationship between; designing a gray image, and calculating four selectable values of the nano-brick steering angle theta in each nano-brick structural unit in the nano-brick array according to the gray distribution required by the gray image display and the functional relation;
designing a watermark image, and determining a final value of a nano-brick steering angle corresponding to each nano-brick structure unit in the nano-brick array from the four calculated optional values of the nano-brick steering angle theta according to the gray scale requirement displayed by the watermark image and the functional relationship obtained in the step, so that the nano-brick array can respectively display a gray scale image and watermarks superposed in the gray scale image in different polarization directions of an analyzer;
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 display requirements of the bi-color image, and arranging the nano-brick steering angles in the nano-brick structure units with the sizes corresponding to each position according to the determined final values of the corresponding nano-brick steering angles in the steps, so as to obtain the required super-surface material;
at a wavelength λ0Is incident on the metamaterial surface material and passes through the correspondingDisplaying a continuous gray image after the analyzer; when the analyzer is rotated by pi/4, the linearly polarized light is continuously incident to the metamaterial and passes through the analyzer, and then a continuous gray image superposed with a watermark image is displayed; when the metamaterial is incident with a broad spectrum light wave, a two-color image is displayed.
2. The three-channel super-surface multiplexing method for superimposing watermarks in continuous gray scale images as claimed in claim 1, wherein said nano-brick structure unit comprises a working surface and a nano-brick arranged on said working surface, a xoy coordinate system is established by setting directions parallel to two sides of said working surface as x-axis and y-axis respectively, said nano-brick has a major axis L and a minor axis W on a plane parallel to said working surface, and said nano-brick steering angle θ is an included angle between said major axis L of said nano-brick and said x-axis.
3. The three-channel super-surface multiplexing method for superimposing watermarks in continuous gray-scale images as claimed in claim 2, wherein the structural parameters of the nano-brick structural units include the major axis L, the minor axis W and the height H of the nano-brick and the size of the working face side length C, and the major axis L is not equal to the minor axis W.
4. The three-channel super-surface multiplexing method for superimposing watermarks in continuous gray-scale images according to claim 1, wherein when the nano-brick structural unit is functionally equivalent to a micro-nano polarizer, the emergent light intensity I and the incident light intensity I are0The polarization direction of linearly polarized light alpha1The steering angle theta of the nano brick and the polarization analyzing direction of the polarization analyzer are alpha2The functional relationship between the two is as follows:
5. the method of claim 1, wherein the analyzer is configured to analyze the gray scale image to determine the watermark embedded in the gray scale imageDirection alpha2With the polarization direction alpha of the incident linearly polarized light1At an angle of pi/2, at a wavelength of lambda0The monochromatic linear polarized light is incident to the metamaterial, and a gray image is displayed through a corresponding analyzer; when the polarization analyzing direction alpha of the polarization analyzer2With the polarization direction alpha of the incident linearly polarized light1When the included angle between the two components is pi/4, the monochromatic linear polarized light is continuously incident to the metamaterial, and the grayscale image superposed with the watermark image is displayed after passing through the analyzer.
6. The three-channel super-surface multiplexing method for superimposing watermarks in continuous gray-scale images as claimed in claim 5, wherein when the analyzer has its polarization direction α2With the polarization direction alpha of the incident linearly polarized light1When the included angle between the two is pi/2, the monochromatic linear polarized light is incident on the metamaterial and emits light intensity I after passing through the analyzer2：
When the polarization analyzing direction alpha of the polarization analyzer2With the polarization direction alpha of the incident linearly polarized light1When the included angle between the two is pi/4, the monochromatic linear polarized light is incident on the metamaterial and emits light intensity I after passing through the analyzer3Comprises the following steps:
determining four optional values of the steering angle theta of the nano brick respectively corresponding to I2≈I3、I2>I3And I2＜I3Which case of (1);
comparing the pixel points at the same position corresponding to the watermark image and the gray image, and selecting I from the nano-brick corresponding to the nano-brick structural unit corresponding to the pixel point when the pixel point has no watermark image2≈I3The selectable value of the corresponding nano brick steering angle theta; when the pixel isIf the watermark image is dotted, setting a proper gray threshold value to be T for the gray imagehWhen the gray value of the pixel point in the gray image is larger than ThThen, selecting I from the nano-brick structural unit corresponding to the pixel point2>I3The selectable value of the corresponding nano brick steering angle theta; when the gray value of the pixel point in the gray image is less than ThThen, selecting I from the nano-bricks corresponding to the nano-brick structural units corresponding to the pixel points2＜I3The corresponding selectable value of the nano-brick steering angle theta.
7. The three-channel super-surface multiplexing method for superimposing a watermark on a continuous gray image according to claim 1, wherein the pixel values in the bi-color image are 0 or 1, respectively, and any one pixel point on the bi-color image is selected, and when the pixel value of the pixel point is 0, one of the nano-brick structural units with the alternative size parameter is selected; and when the pixel value of the pixel point is 1, selecting the nano-brick structural unit with another alternative size parameter.
8. The three-channel super-surface multiplexing method for superimposing watermarks in continuous gray-scale images as claimed in claim 1, wherein said working surface is made of silicon dioxide and said nano-bricks are made of silver material.
9. A three-channel super-surface multiplexing method for superimposing watermarks in continuous gray-scale images according to any of claims 1 to 8, resulting in a super-surface material.
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Citations (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105807598A (en) * | 2016-05-27 | 2016-07-27 | 武汉大学 | Silicon nano brick array structure for Fourier color holography and design method thereof |
| CN107065491A (en) * | 2017-06-20 | 2017-08-18 | 武汉大学 | Nano brick array hologram sheet and its design method applied to holographic false proof |
| WO2019088929A1 (en) * | 2017-11-03 | 2019-05-09 | Agency For Science, Technology And Research | Holographic security element and method of forming thereof |
| CN109814195A (en) * | 2019-03-29 | 2019-05-28 | 武汉邮电科学研究院有限公司 | Multi-functional super surface texture, super surface element and encryption method based on polarization |
| CN110376672A (en) * | 2019-06-27 | 2019-10-25 | 武汉大学 | A kind of super surface array structure and its application in image display multiplexing |
| CN110426758A (en) * | 2019-06-27 | 2019-11-08 | 武汉大学 | Optical film materials, construction method and its application based on super surface |
| CN110456439A (en) * | 2019-08-01 | 2019-11-15 | 武汉大学 | The super surfacing and its design method of color nano printing and the holography of colour pase type are realized simultaneously |
| CN110568540A (en) * | 2019-08-13 | 2019-12-13 | 武汉大学 | micro-nano wave plate array with double-image display function and construction method thereof |
| CN110568528A (en) * | 2019-08-29 | 2019-12-13 | 武汉大学 | Double-mode super surface based on SOI material and double-mode display application thereof |
| CN110568525A (en) * | 2019-08-08 | 2019-12-13 | 武汉大学 | Color nano printing device based on micro-nano polarizer and F-P cavity structure |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20140085693A1 (en) * | 2012-09-26 | 2014-03-27 | Northeastern University | Metasurface nanoantennas for light processing |
| US9524416B1 (en) * | 2015-07-03 | 2016-12-20 | Fingerprint Cards Ab | Fingerprint sensing device comprising three-dimensional pattern |
-
2019
- 2019-12-23 CN CN201911338062.2A patent/CN111145071B/en active Active
Patent Citations (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105807598A (en) * | 2016-05-27 | 2016-07-27 | 武汉大学 | Silicon nano brick array structure for Fourier color holography and design method thereof |
| CN107065491A (en) * | 2017-06-20 | 2017-08-18 | 武汉大学 | Nano brick array hologram sheet and its design method applied to holographic false proof |
| WO2019088929A1 (en) * | 2017-11-03 | 2019-05-09 | Agency For Science, Technology And Research | Holographic security element and method of forming thereof |
| CN109814195A (en) * | 2019-03-29 | 2019-05-28 | 武汉邮电科学研究院有限公司 | Multi-functional super surface texture, super surface element and encryption method based on polarization |
| CN110376672A (en) * | 2019-06-27 | 2019-10-25 | 武汉大学 | A kind of super surface array structure and its application in image display multiplexing |
| CN110426758A (en) * | 2019-06-27 | 2019-11-08 | 武汉大学 | Optical film materials, construction method and its application based on super surface |
| CN110456439A (en) * | 2019-08-01 | 2019-11-15 | 武汉大学 | The super surfacing and its design method of color nano printing and the holography of colour pase type are realized simultaneously |
| CN110568525A (en) * | 2019-08-08 | 2019-12-13 | 武汉大学 | Color nano printing device based on micro-nano polarizer and F-P cavity structure |
| CN110568540A (en) * | 2019-08-13 | 2019-12-13 | 武汉大学 | micro-nano wave plate array with double-image display function and construction method thereof |
| CN110568528A (en) * | 2019-08-29 | 2019-12-13 | 武汉大学 | Double-mode super surface based on SOI material and double-mode display application thereof |
Non-Patent Citations (3)
| Title |
|---|
| Ultracompact high-efficiency polarising beam splitter based on silicon nanobrick arrays;Guoxing Zheng et.al;《OPTICS EXPRESS》;20160321;第24卷(第6期);全文 * |
| 基于超表面材料的光波相位精密操控新技术;郑国兴等;《应用光学》;20170331;第38卷(第2期);第153-158页 * |
| 超表面图像显示技术研究;戴琦等;《应用光学》;20191130;第40卷(第6期);第1045-1049页 * |
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