CN111008948B - Method for combining random pattern with space-frequency multiplexing super-surface image - Google Patents
Method for combining random pattern with space-frequency multiplexing super-surface image Download PDFInfo
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Abstract
The invention discloses a method for combining random patterns with space-frequency multiplexing super-surface images, which relates to the technical field of micro-nano optics, and is characterized in that a nano brick array comprising a plurality of nano brick structure units is constructed, the distribution of the steering angles of nano bricks in the nano brick array is ingeniously designed, when linearly polarized light is incident on the super surface, the light intensity and the polarization direction of the linearly polarized light are modulated and then emitted as reflected light, the reflected light displays a mixed image with high resolution in a near field through an analyzer, different image information can be extracted from the mixed image under different cut-off frequencies, a random image is designed, and the steering angles of the nano bricks in the nano brick array are properly adjusted; when the super-surface material is rotated by a specific angle, the original mixed graph is switched into a random image based on the nano printing display of polarization control, the graph distribution in the random image is difficult to repeat and has uniqueness, and the random image is acquired by three channels by combining three different information and can be applied to the anti-counterfeiting of high-end products.
Description
Technical Field
The invention relates to the technical field of micro-nano optics, in particular to a method for combining random patterns with space-frequency multiplexing super-surface images.
Background
In recent years, due to the high profit temptation, many illegal vendors have spent on counterfeiting and producing and selling fraudulent goods, and the potential hazards and risks thereof threaten consumers and brand manufacturers all the time. Conventional anti-counterfeiting methods such as holograms and the like have poor anti-counterfeiting effects because the enhancement of counterfeiting technical means is easy to copy. Researchers are constantly improving and updating anti-counterfeiting technologies in order to protect enterprise brands, protect markets and protect the legal rights and interests of consumers. Recently, anti-counterfeiting technology based on a super surface is continuously proposed, and the super surface can be embedded into various products due to the extremely small volume and the easiness in miniaturization. The super-surface has extremely superior electromagnetic characteristics, precise control on the amplitude, phase, polarization state and the like of an electromagnetic field can be realized through simple design, and the structure size of the sub-wavelength level is suitable for the development trend of miniaturization, microminiaturization, so that the super-surface has attracted extensive attention of researchers. 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. However, the current methods for performing super-surface anti-counterfeiting have yet to be improved in terms of simplicity of structure, flexibility of design, information capacity, and ease of replication.
Disclosure of Invention
The invention aims to provide a method for combining a random pattern with a space-frequency multiplexing super-surface image, which not only increases the difficulty of copying and the security of encryption, but also can hide more information in the designed random pattern, and has good application and development prospects.
The scheme adopted by the invention for solving the technical problems is as follows:
a method of combining random patterns with space-frequency multiplexed super-surface images, comprising the steps of:
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 the nano brick structure units with the functions equivalent to half-wave plates when linearly polarized light with working wavelength is vertically incident are obtained through optimization;
with an intensity of I 0 Polarization direction of alpha 1 The linearly polarized light is sequentially incident to the nano brick structure units and the polarization detection direction is alpha 2 The analyzer obtains the emergent light intensity and the polarization direction alpha of the linearly polarized light 1 Nano brick steering angle theta and polarization analyzing direction alpha of polarization analyzer 2 Functional relationship between; designing a mixed image, and calculating to obtain a nano-brick steering angle theta value in each corresponding nano-brick structural unit in the nano-brick array according to the gray scale distribution required by the display of the mixed image and the functional relationFinally, arranging each nano brick in the nano brick array according to the obtained steering angle theta value corresponding to each position, thereby obtaining the required nano brick array;
designing a random image, wherein the random image is a binary image;
checking a nano brick steering angle theta corresponding to a pixel point at any same position on a random image according to the gray value of the pixel point on the random image corresponding to the mixed image, adjusting the nano brick steering angle corresponding to the pixel point on the mixed image to pi/2-theta or pi-theta when the gray value of the pixel point on the random image is equal to 0, adjusting the nano brick steering angle corresponding to the pixel point on the mixed image to pi/2 + theta or theta when the gray value of the pixel point on the random image is equal to 255, and readjusting the corresponding nano brick steering angle in the nano brick array according to the method to obtain the target super surface material;
sequentially irradiating the linear polarized light with a specific polarization direction to the metamaterial and the corresponding analyzer, and displaying a mixed image in a near field; when the super-surface material is rotated by another specific angle, the linearly polarized light is continuously and sequentially incident to the super-surface material and the corresponding analyzer, and then a random image is displayed in a near field.
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 method for optimizing and obtaining the nano brick structure unit comprises the following steps: when circularly polarized light with a working wavelength is perpendicularly incident on the nano brick structure unit, scanning the nano brick structure unit under the working wavelength by taking the same-direction polarization reflectivity which is the same as the incident light rotation direction in emergent light and is not higher than 15% and the cross polarization reflectivity which is opposite to the incident light rotation direction and is not lower than 60% as an optimization target, and obtaining the structure parameters of the nano brick structure unit required by the target through electromagnetic simulation optimization, wherein the structure parameters of the nano brick structure unit comprise the long axis L, the short axis W and the height H of the nano brick and the size of the side length C of the working face.
Further, the emergent light intensity and the linear polarization direction alpha 1 The steering angle theta of the nano brick and the polarization analyzing direction of the polarization analyzer are alpha 2 The functional relationship between the two is as follows: i = I 0 [cos(2θ-α 2 -α 1 )] 2 。
Further, the mixed image includes a first image of a high frequency component and a second image of a low frequency component.
Further, a high-pass filter with a specific cut-off frequency is used for extracting the mixed image to obtain a first image corresponding to the high-frequency component in the mixed image, and a low-pass filter with a specific cut-off frequency is used for extracting the mixed image to obtain a second image corresponding to the low-frequency component in the mixed image.
Furthermore, the random image comprises a first binary image and a second binary image, and the gray value of any pixel point in the first binary image is marked as I b And recording the gray value of any pixel point on the second binary image as I c And I is b And I c All 0 or 255, selecting the gray values of the pixel points at the same corresponding positions in the first binary image and the second binary image for comparison, and if I is judged c >0, then make the gray value of the pixel point equal to I b (ii) a Otherwise, making the gray value of the pixel point equal to I c After the processing, the second binary image is superposed on the first binary image to form a random image.
Further, when the analyzer has an analyzing direction α 2 With the polarization direction alpha of incident linearly polarized light 1 When the included angle between the super surface material and the optical axis is 90 degrees, a mixed image is displayed in the near field of the super surface material, and when the super surface material is rotated by 22.5 degrees by taking the optical axis as a center, the polarization analysis direction alpha of the analyzer is kept 2 With the polarization direction alpha of the incident linearly polarized light 1 At an angle of 90 deg., displaying a random image in the near field of the metamaterial.
Further, the working surface is made of silicon dioxide-silicon materials, and the nano-brick is made of silicon materials.
It is another object of the present invention to provide a meta-surface material obtained according to the above method of combining random patterns with space-frequency multiplexed meta-surface images.
Compared with the prior art, the invention has at least the following beneficial effects:
1. the method combines the nano printing display based on polarization control with the image multiplexed by spatial frequency, is different from the original independent multiplexing method, can widen the channel of information multiplexing, can realize the multiplexing of three image information, and can extract the multiplexed image information in three different modes;
2. the design method provided by the invention has encryption performance in the aspect of diversity of verification modes, adopts the random pattern, has low repeatability and large copying difficulty, greatly increases the encryption safety, and can expand the information capacity of the encrypted information to a great extent due to large information capacity of the random pattern;
3. the super-surface material adopted by the invention has the structural size of sub-wavelength level, so the super-surface material has the characteristics of small volume, light weight, high integration and the like, can be combined and processed into a plurality of miniaturized devices and products, and has great advantages no matter the super-surface material is used as an anti-counterfeiting mark or an information encryption means; in addition, the super surface is a two-dimensional plane material, so that the processing and manufacturing are simple and the cost can be saved.
Drawings
FIG. 1 is a schematic structural diagram of a nanostructure element in an embodiment of the present invention;
FIG. 2 is a reflectance scan of nanostructure elements in an embodiment of the invention;
FIG. 3 is a schematic diagram of spatial frequency multiplexing of mixed images according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of the multiplexing of random images and mixed images in an embodiment of the present invention;
fig. 5 is a schematic diagram of the operation of the metamaterial in an embodiment of the present 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:
firstly, constructing a nano brick array; 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, a long axis L and a short axis W are arranged on the surface of each nano brick parallel 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. The method is characterized in that the structural size of the nano-brick structural unit which is functionally equivalent to a half-wave plate when linearly polarized light with working wavelength is vertically incident is obtained through optimization, and the specific method comprises the following steps: when circularly polarized light with a working wavelength is vertically incident on the nano brick structure unit, scanning the nano brick structure unit under the working wavelength by taking the same-direction polarization reflectivity which is the same as the incident light rotation direction in emergent light and is not higher than 15% and the cross polarization reflectivity which is opposite to the incident light rotation direction and is not lower than 60% as an optimization target, and obtaining the structure parameters of the nano brick structure unit required by the target through electromagnetic simulation optimization, wherein the structure parameters of the nano brick structure unit comprise the major axis L, the minor axis W, the height H and the size of the side length C of a working surface of a nano brick.
With an intensity of I 0 A polarization direction of alpha 1 The linearly polarized light is sequentially incident to the nano brick structure units and the polarization detection direction is alpha 2 The analyzer obtains the emergent light intensity and the polarization direction alpha of the linearly polarized light 1 Nano brick steering angle theta and polarization analyzing direction alpha of polarization analyzer 2 Functional relationship between; designing a mixed image, wherein the mixed image comprises a first image of a high-frequency component and a second image of a low-frequency component, calculating a nano-brick steering angle theta value in each corresponding nano-brick structural unit in the nano-brick array according to the gray distribution required by the display of the mixed image and the functional relation, and finally, calculating the nano-brick arrayArranging each nano brick in the row according to the obtained steering angle theta value corresponding to each position, thereby obtaining a required nano brick array;
designing a random image, wherein the random image comprises a first binary image and a second binary image, and marking the gray value of any pixel point in the first binary image as I b And recording the gray value of any pixel point on the second binary image as I c And I is b And I c All 0 or 255, selecting the gray values of the pixel points at the same corresponding positions in the first binary image and the second binary image for comparison, and if I is judged c >0, then make the gray value of the pixel point equal to I b (ii) a Otherwise, making the gray value of the pixel point equal to I c After the processing, the second binary image is superposed on the first binary image to form a random image;
checking the nano-brick steering angle theta corresponding to the pixel point according to the gray value of the pixel point at any same position on the random image corresponding to the mixed image, adjusting the nano-brick steering angle corresponding to the pixel point on the mixed image to pi/2-theta or pi-theta when the gray value of the pixel point on the random image is equal to 0, adjusting the nano-brick steering angle corresponding to the pixel point on the mixed image to pi/2 + theta or theta when the gray value of the pixel point on the random image is equal to 255, and readjusting the corresponding nano-brick steering angle in the nano-brick array according to the method to obtain the target super-surface material;
sequentially irradiating the linearly polarized light with a specific polarization direction to the metamaterial and the corresponding analyzer, and displaying a mixed image in a near field; when the metamaterial is rotated by another specific angle, the linearly polarized light is continuously incident to the metamaterial and the corresponding analyzer in sequence, and then a random image is displayed in a near field.
On the basis of the technical scheme, by designing the azimuth angle distribution of the nano brick array on the metamaterial, the incident linear polarized light can display a continuous gray mixed image with high resolution in a near field after passing through the metamaterial and the analyzer, the mixed image is formed by superposing high-frequency components and low-frequency components from two different images into one image based on the spatial frequency multiplexing principle, and image information corresponding to the high-frequency components and the low-frequency components can be extracted and obtained again after passing through a high-pass filter and a low-pass filter with specific cut-off frequency. When the sample wafer of the super surface material is rotated by a certain angle, the original mixed image is switched into a random pattern.
The invention will be described in more detail with reference to specific embodiments, in which the nano-brick array of the embodiment of the invention includes a plurality of nano-brick structure units, and each nano-brick structure unit is composed of a transparent substrate and a nano-brick etched on the working surface of the transparent substrate. The nano-brick array used in the present invention has a structure consisting of silicon-silicon dioxide-silicon, that is, the nano-brick 1 is made of a silicon material, and the transparent substrate includes a first substrate 2 made of silicon dioxide and a second substrate 3 made of silicon. The single nanometer unit structure is shown in figure 1, a square working surface with the side length of C is arranged on the substrate of the nanometer brick structure unit, a nanometer brick is etched on the square working surface, and the nanometer brick structure unit is composed of a transparent substrate and a nanometer 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 x axis.
In the present embodiment, taking λ =633nm as an example of the operating wavelength, creating a model through electromagnetic simulation software and simulating and optimizing parameters and performance of the nano-cell structure, as an embodiment, circularly polarized light incidence is taken as an example for simplifying the model, and left-handed circularly polarized light incidence is taken as an example here as an example. The structural parameters of the scanning nano-unit structure under the working wavelength include L, W, H and C, as shown in FIG. 2, the optimization aims at the lowest codirectional polarization reflectivity which is the same as the incident light rotation direction in emergent light and the highest cross polarization reflectivity which is opposite to the incident light rotation direction. The scanning result is shown in fig. 2, and at the working wavelength of 633nm, the structural parameters of the nano unit are as follows: when C =300nm, L =200nm, W =100nm, and H =220nm, the reflectance of cross polarization in the outgoing light is the highest, exceeding 65% or more, and at this time, the function of the simulated nano-cell structure is equivalent to an ideal half-wave plate.
Each nano-structure unit in the super-surface material works as a half-wave plate, and taking a single nano-structure unit as an example, when a beam of linearly polarized light is incident to the nano-structure unit and the analyzer, the Jones matrix of emergent light can be expressed as follows:
combining with the Malus theorem, the light intensity of emergent light is:
I＝I 0 [cos(2θ-α 2 -α 1 )] 2 (2)
wherein, I 0 Is the intensity of incident linearly polarized light, theta is the steering angle of the nano brick, alpha 1 Is the polarization direction of incident linearly polarized light, alpha 2 Is the polarization analyzing direction of the analyzer.
As can be seen from equation (2), if the polarization direction of the incident linearly polarized light and the polarization analysis direction of the analyzer are both kept unchanged, arbitrary local gray scale modulation can be realized by changing the azimuth angle θ. When the super-surface sample wafer is rotated around the optical axis
In time, the light intensity of the outgoing light changes as follows:
as an example, the polarization direction α of incident linearly polarized light is set 1 And the direction of polarization analysis alpha of the analyzer 2 Included angle therebetween is
Then, the equations (2) and (3) can be simplified as follows:
I 1 ＝I 0 cos 2 2θ (4)
and
as can be seen from the formulas (4) and (5), when the polarization direction of the incident linearly polarized light and the polarization analysis direction of the analyzer are kept unchanged, the sample wafer with the super-surface material is in the original state and rotates
After the angle of (D), the intensity of the emergent light is I 1 And I 2 And continuously changes with the difference of the azimuth angle theta of the nano brick.
In this embodiment, as shown in fig. 3, we select a target mixed image as in fig. 3 (f), which includes two images "cat" (fig. 3 (e)) and "dog" (fig. 3 (d)), each having a pixel size of 500 × 500. By using the principle of spatial frequency multiplexing, the cut-off frequency of the low frequency is set to 25c/i (cycle/image), the cut-off frequency of the high frequency is set to 30c/i, and in other embodiments, the cut-off frequency of the high frequency and the cut-off frequency of the low frequency are determined according to actual needs, so as to extract the low frequency component of the image "dog" and the high frequency part of the image "cat", the low frequency component of the image contains more contour information of the original image, and the high frequency component contains more detail information of the image, and in fig. 3, (d) and (e) are spatial domain images extracted after the images "dog" and "cat" pass through the low frequency filtering and the high frequency filtering, respectively. Superimposing the extracted high-frequency component image and low-frequency component image on the same image constitutes a mixed image as shown in fig. 3 (f), which contains both the low-frequency information of the image "dog" and the high-frequency information of the image "cat". Because the human eye vision system has different degrees of sensitivity to information in different frequency domains at different distances, the image information of the dog and the cat contained in the mixed image can be observed respectively when the observation distance is adjusted.
The target mixed image in the figure 3 (f) is used as a continuous gray image to be displayed by utilizing the nano printing based on the super surface, and the gray value of each pixel point required by the display of the mixed image is combined with the functional relation obtained by the formula (2) because of the formula(2) Middle alpha 1 And alpha 2 As is known, the steering angle θ of each nano-brick of each nano-structure unit in the nano-brick array can be calculated according to the formula and the gray value displayed by each pixel point, and finally, each nano-brick in the nano-brick array is arranged according to the obtained steering angle θ corresponding to each position, so as to obtain the required nano-brick array. In order to simplify the calculation, the present embodiment limits all angles of the turning angle θ of the nano-brick to [0, π/4 ]]In between.
In order to increase the difficulty of copying and expand the information capacity of the encrypted information, as shown in fig. 4, a random image is designed by using Matlab software, and the pixel size of the random image is 500 × 500, which is a binary image. A plurality of random numbers are generated using the Matlab function and applied to determine the pattern size and coordinate position of the random image. In this embodiment, the random image is formed by superimposing the first binary image and the second binary image, the pattern used in the first binary image is a triangle, and a triangle having a random size and a center position is arbitrarily superimposed within a frame of 500 × 500 so as to fill the entire space, as shown in fig. 4 (b). On this basis, we superimpose a second binary image (500 × 500 as shown in c in fig. 4) on the first binary image, assuming that the gray value of any pixel in the first binary image (e.g. fig. 4 (b)) is I b The gray value of any pixel in the second binary image (as shown in fig. 4 (c)) is I c And I is b And I c Both 0 and 255. Selecting pixels at the same position in the first binary image and the second binary image for gray value comparison, and if I is judged c >0, then make the gray value of the pixel point equal to I b (ii) a Otherwise, making the gray value of the pixel point equal to I c Thereby obtaining a random image in which the two binary images are superimposed, as shown in (d) of fig. 4.
In order to multiplex the random pattern and the designed mixed image onto the same super surface, checking a nano brick steering angle theta corresponding to a pixel point at any same position on the random image and corresponding to the mixed image according to the gray value of the pixel point, and if the gray value of the random image at the pixel point is 0, checking the nano brick steering angle theta corresponding to the pixel pointReadjusting the steering angle of the meter bricks, and adjusting the steering angle theta of the nanometer bricks new = π/2- θ or θ new = π - θ; if the gray value of the random image is 255, the steering angle of the nano-brick corresponding to the pixel point is readjusted to be theta new = π/2+ θ or θ new And (= theta), and readjusting the steering angle of the corresponding nano-bricks in the nano-brick array according to the method to obtain the target super-surface material. The super surface designed by the design method can display the mixed image and the random pattern based on space-frequency multiplexing in a near field switching mode by rotating the super surface.
As shown in fig. 5, laser with a working wavelength of 633nm passes through a polarizer to generate linearly polarized light with a polarization direction of 45 ° with an X axis, the linearly polarized light is incident on the metamaterial sample wafer and then reflected, the reflected light passes through an analyzer, and the polarization direction of the analyzer forms-45 ° with the X axis, and then a designed mixed image is observed; the super surface sample is rotated by 22.5 degrees (pi/8) by taking the optical axis as a center, and the mixed image disappears and is switched into a random pattern.
The random pattern and the space-frequency multiplexing super-surface image are multiplexed by using a super-surface nano-printing display mode, and three image information generated by the method can be extracted by three different modes: when the super surface material sample wafer displays a gray level mixed image multiplexed by space frequency at a certain angle, the super surface material sample wafer is switched into a random pattern when being rotated to another specific angle. For a mixed image, different image information is extracted when a high-frequency filter and a low-frequency filter of a specific cutoff frequency are used, and different spatial domain images can be observed at different distances. Based on the design method, the multiplexed image information can be extracted in three different modes while the multiplexing of the three image information is realized, and the adoption of the random pattern not only increases the difficulty of copying and the security of encryption, but also can hide more information in the designed random pattern, so that the method can obtain good development prospects in the fields of information encryption, information multiplexing, anti-counterfeiting and the like.
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 method of combining a random pattern with a space-frequency multiplexed super-surface image, comprising the steps of:
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 the nano brick structure units are optimized to obtain the nano brick structure units with the function equivalent of a half-wave plate when linearly polarized light with working wavelength is vertically incident;
with an intensity of I 0 Polarization direction of alpha 1 The linearly polarized light is sequentially incident to the nano brick structure units and the polarization detection direction is alpha 2 The analyzer obtains the emergent light intensity and the polarization direction alpha of the linearly polarized light 1 Nano brick steering angle theta and polarization analyzing direction alpha of polarization analyzer 2 Functional relationship between; designing a mixed image, calculating to obtain a steering angle theta value of the nano bricks in each corresponding nano brick structure unit in the nano brick array according to gray level distribution required by the display of the mixed image and the functional relation, and finally arranging each nano brick in the nano brick array according to the obtained steering angle theta value corresponding to each position, thereby obtaining the required nano brick array;
designing a random image, wherein the random image is a binary image;
checking the nano-brick steering angle theta corresponding to the pixel point according to the gray value of the pixel point at any same position on the random image corresponding to the mixed image, adjusting the nano-brick steering angle corresponding to the pixel point on the mixed image to pi/2-theta or pi-theta when the gray value of the pixel point on the random image is equal to 0, adjusting the nano-brick steering angle corresponding to the pixel point on the mixed image to pi/2 + theta or theta when the gray value of the pixel point on the random image is equal to 255, and readjusting the corresponding nano-brick steering angle in the nano-brick array according to the method to obtain the target super-surface material;
sequentially irradiating the linear polarized light with a specific polarization direction to the metamaterial and the corresponding analyzer, and displaying a mixed image in a near field; when the metamaterial is rotated by another specific angle, the linearly polarized light is continuously incident to the metamaterial and the corresponding analyzer in sequence, and then a random image is displayed in a near field.
2. The method of combining random patterns with space-frequency multiplexed super-surface images according to claim 1, wherein the nano-tile structural units comprise a working surface and nano-tiles disposed on the working surface, a xoy coordinate system is established with directions parallel to two sides of the working surface being set as an x-axis and a y-axis, respectively, the nano-tiles having a major axis L and a minor axis W on a plane parallel to the working surface, and the nano-tile steering angle θ is an angle between the major axis L of the nano-tiles and the x-axis.
3. The method of combining random patterns with space-frequency multiplexed super-surface images according to claim 2, wherein the method of optimizing the resulting nano-tile building blocks is: when circularly polarized light with a working wavelength is perpendicularly incident on the nano brick structure unit, scanning the nano brick structure unit under the working wavelength by taking the same-direction polarization reflectivity which is the same as the incident light rotation direction in emergent light and is not higher than 15% and the cross polarization reflectivity which is opposite to the incident light rotation direction and is not lower than 60% as an optimization target, and obtaining the structure parameters of the nano brick structure unit required by the target through electromagnetic simulation optimization, wherein the structure parameters of the nano brick structure unit comprise the long axis L, the short axis W and the height H of the nano brick and the size of the side length C of the working face.
4. The method of combining random patterns with space-frequency multiplexed super-surface images according to claim 1, wherein the intensity of the emergent light and the polarization direction of the linearly polarized light α 1 The steering angle theta of the nano brick and the polarization analyzing direction of the polarization analyzer are alpha 2 The functional relationship between the two is as follows: i = I 0 [cos(2θ-α 2 -α 1 )] 2 。
5. The method of combining a random pattern with a space-frequency multiplexed super-surface image according to claim 1, wherein the blended image comprises a first image of a high frequency component and a second image of a low frequency component.
6. The method of claim 1, wherein the hybrid image is extracted using a high pass filter with a specific cut-off frequency to obtain a first image corresponding to the high frequency components in the hybrid image, and the hybrid image is extracted using a low pass filter with a specific cut-off frequency to obtain a second image corresponding to the low frequency components in the hybrid image.
7. The method of claim 1, wherein the random image comprises a first binary image and a second binary image, and the gray level of any pixel in the first binary image is denoted as I b And recording the gray value of any pixel point on the second binary image as I c And I is b And I c All 0 or 255, selecting the gray values of the pixel points at the same corresponding positions in the first binary image and the second binary image for comparison, and if I is judged c >0, then let the gray value of the pixel point equal to I b (ii) a Otherwise, making the gray value of the pixel point equal to I c After the processing, the second binary image is superposed on the first binary image to form a random image.
8. The method for combining a random pattern with a space-frequency multiplexed super-surface image according to claim 1, wherein the direction of polarization analysis α of the analyzer is the direction of polarization analysis α 2 With the polarization direction alpha of incident linearly polarized light 1 When the included angle between the super surface material and the optical axis is 90 degrees, a mixed image is displayed in the near field of the super surface material, and when the super surface material is rotated by 22.5 degrees by taking the optical axis as a center, the polarization analysis direction alpha of the analyzer is kept 2 With the direction of polarization of incident linearly polarized lightα 1 At an angle of 90 deg., displaying a random image in the near field of the metamaterial.
9. The method for combining random patterns with space-frequency multiplexed super-surface images according to claim 2, wherein the working surface is made of a silica-silica material and the nano-bricks are made of a silica material.
10. A meta-surface material obtained by a method of combining a random pattern with a space-frequency multiplexed meta-surface image according to any of claims 1 to 9.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
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| CN201911308250.0A CN111008948B (en) | 2019-12-18 | 2019-12-18 | Method for combining random pattern with space-frequency multiplexing super-surface image |
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