Metasurface encryption device and design method thereof

Abstract

The present application belongs to the field of micro-nano optical technology, and discloses a super surface encryption device and a design method thereof. The present application firstly constructs the basic structure of the super surface encryption device, then selects an encryption image, and uses a scrambling algorithm to scramble the encryption image, taking the scrambled image as a first target image; taking the transformation parameter and the iteration number in the scrambling algorithm as a first key, and taking the image containing the first key information as a second target image; taking the observation conditions of the first target image and the second target image as a second key, and taking the image containing the second key information as a third target image; then obtaining the phase control quantity corresponding to the three target images at three wavelengths respectively, and finally determining the size selection and arrangement of a plurality of nanometer bricks in the super surface encryption device according to the three phase control quantities. The present application can realize wavelength decoupling and simple structure, and can improve the reliability and security of information encryption.

Description

Technical Field

[0001] This invention belongs to the field of micro-nano optics technology, and more specifically, relates to a metasurface encryption device and its design method. Background Technology

[0002] As informatization and digitalization deepen, the importance of information security is becoming increasingly apparent. Unlike traditional software-based information encryption methods, metasurfaces, artificial subwavelength materials, are promising candidates for new encryption devices due to their small size, ease of integration, and powerful and diverse control over light waves.

[0003] However, conventional metasurface encryption devices typically rely on multiplexing based on amplitude, angle, and polarization. Wavelength-based metasurface devices are often structurally complex, and staggered or stacked arrangements cannot achieve wavelength decoupling and are highly complex to manufacture. Furthermore, most conventional metasurface encryption devices rely solely on altering the incident conditions for encryption, resulting in low security and reliability of the encrypted information. Summary of the Invention

[0004] This invention provides a metasurface encryption device and its design method, which solves the problems of existing metasurface encryption devices based on wavelength multiplexing being unable to achieve wavelength decoupling, having complex structures, and exhibiting poor reliability and security in information encryption.

[0005] This invention provides a design method for a metasurface encryption device, comprising the following steps:

[0006] The basic structure of a metasurface encryption device is constructed, the metasurface encryption device comprising a substrate and an array of nanobricks located on the substrate, the array of nanobricks being composed of nanobricks of two sizes;

[0007] Select an encrypted image, scramble the encrypted image using a scrambling algorithm, and use the scrambled image as the first target image; use the transformation parameters and iteration number in the scrambling algorithm as the first key, and use the image containing the first key information as the second target image; use the observation conditions of the first target image and the second target image as the second key, and use the image containing the second key information as the third target image;

[0008] Acquire the first phase modulation amount corresponding to the first target image at the first wavelength, the second phase modulation amount corresponding to the second target image at the second wavelength, and the third phase modulation amount corresponding to the third target image at the third wavelength;

[0009] The size selection and arrangement of several nanobricks in the metasurface encryption device are determined based on three phase modulation quantities.

[0010] Preferably, the first target image and the second target image are encoded into the metasurface encryption device for near-field holographic display; the third target image is encoded into the metasurface encryption device for far-field holographic display.

[0011] Preferably, the observation conditions include the diffraction distance and the polarization state of the incident light.

[0012] Preferably, the substrate is divided into multiple unit structures of the same size, the working surface of the unit structure is square, one unit structure and one nanobrick located on the working surface of the unit structure constitute a nanounit structure, the size of the nanounit structure is at the subwavelength level; the two sizes of nanobricks have the same height, different lengths and different widths.

[0013] Preferably, the phase modulation amount includes the modulation amount of the transmission phase and the modulation amount of the geometric phase;

[0014] The amount of adjustment of the transmission phase is expressed as:

[0015]

[0016] The amount of adjustment of the geometric phase is expressed as:

[0017]

[0018] In the formula, This is the amount of control for the transmission phase. The equivalent refractive index of the nanobrick is... For wavelength, The height of the nano brick, This is the amount of adjustment for the geometric phase. For the corner of the nanobrick.

[0019] Preferably, LCP light is used for incident light at the first and second wavelengths, and RCP light is used for incident light at the third wavelength; the phase modulation amounts at the three wavelengths are expressed as follows:

[0020]

[0021]

[0022]

[0023] In the formula, This is the phase modulation amount at the first wavelength. This refers to the phase modulation amount at the second wavelength. This refers to the phase modulation amount at the third wavelength. The modulation amount of the transmission phase of the first-size nanobrick at the first wavelength. This refers to the modulation amount of the transmission phase of the second-sized nanobrick at the first wavelength. The modulation amount of the transmission phase of the first-size nanobrick at the second wavelength. This refers to the modulation amount of the transmission phase of the second-sized nanobrick at the second wavelength. This represents the modulation amount of the transmission phase of the first-sized nanobrick at the third wavelength. This refers to the modulation amount of the transmission phase of the second-sized nanobrick at the third wavelength.

[0024] Preferably, the phase modulation amount at three wavelengths is obtained by using a simulated annealing algorithm.

[0025] Preferably, the scrambling algorithm is the Arnold scrambling algorithm.

[0026] On the other hand, the present invention provides a metasurface encryption device, which is obtained based on the above-described design method for metasurface encryption devices.

[0027] Preferably, a third target image is observed in the far field of the metasurface encryption device at a third wavelength; a second target image and a first target image are observed in the near field of the metasurface encryption device based on a second wavelength and the second key information contained in the third target image; and an encrypted image is obtained by inverse transformation of the first target image based on the first key information contained in the second target image.

[0028] One or more technical solutions provided in this invention have at least the following technical effects or advantages:

[0029] This invention first constructs the basic structure of a metasurface encryption device. Then, it selects an encrypted image and scrambles it using a scrambling algorithm, using the scrambled image as the first target image. The transformation parameters and iteration count in the scrambling algorithm are used as the first key, and the image containing the first key information is used as the second target image. The observation conditions of the first and second target images are used as the second key, and the image containing the second key information is used as the third target image. Next, the phase modulation values ​​corresponding to the three target images at three wavelengths are obtained. Finally, the size selection and arrangement of several nano-bricks in the metasurface encryption device are determined based on the three phase modulation values. This invention achieves near-three-wavelength decoupling through a design using only two sizes of nano-bricks, and also solves the problem of high processing complexity. This invention has the advantages of flexible design and simple structure. Simultaneously, this invention adopts a design concept combining geometric phase with transmission phase-modulated light waves, combining traditional information encryption algorithms with the indirect observation method of Fresnel holography to achieve multi-key encryption, which can improve the reliability and security of information encryption. This invention uses the wavelength information of the three wavelength channels as encryption and decryption keys, further enhancing the security of information encryption. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the nanounit structure in the design method of a metasurface encryption device provided in Embodiment 1 of the present invention;

[0031] Figure 2 The spectral response diagrams of two sizes of nanobricks selected in the design method of a metasurface encryption device provided in Embodiment 1 of the present invention are shown; wherein, Figure 2 (a) in the figure shows the change in polarization conversion efficiency with wavelength. Figure 2 (b) in the figure shows the transformation of relative phase with wavelength;

[0032] Figure 3 The encrypted image and the Arnold transformed image are used in the design method of a metasurface encryption device provided in Embodiment 1 of the present invention; wherein, Figure 3 (a) in the image is an encrypted image. Figure 3 (b) in the image is the image after the Arnold transform;

[0033] Figure 4 The target image containing key information used in the design method of a metasurface encryption device provided in Embodiment 1 of the present invention; wherein, Figure 4 Image (a) in the image is the second target image containing the first key information. Figure 4 (b) in the image is the third target image containing the second key;

[0034] Figure 5The three target images used in the design method of a metasurface encryption device provided in Embodiment 1 of the present invention are simulation images optimized by a simulated annealing algorithm; wherein, Figure 5 In the middle (a), the simulated image corresponding to the third target image is shown. Figure 5 (b) is the simulated image corresponding to the second target image. Figure 5 (c) is the simulated image corresponding to the first target image;

[0035] Figure 6 This is the encrypted image obtained after decoding in the design method of a metasurface encryption device provided in Embodiment 1 of the present invention;

[0036] Figure 7 This is a schematic diagram of a metasurface encryption device for information encoding and decoding provided in Embodiment 2 of the present invention. Detailed Implementation

[0037] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0038] Example 1:

[0039] Example 1 provides a design method for a metasurface encryption device, comprising the following steps:

[0040] Step 1: Construct the basic structure of the metasurface encryption device, which includes a substrate and an array of nanobricks located on the substrate. The array of nanobricks consists of nanobricks of two different sizes.

[0041] The substrate is divided into multiple unit structures of the same size. The working surface of each unit structure is square. One unit structure and a nanobrick located on the working surface of the unit structure constitute a nanounit structure. The size of the nanounit structure is at the subwavelength level. The nanobricks of two sizes have the same height, different lengths, and different widths.

[0042] Step 2: Select an encrypted image, scramble the encrypted image using a scrambling algorithm, and use the scrambled image as the first target image; use the transformation parameters and iteration number in the scrambling algorithm as the first key, and use the image containing the first key information as the second target image; use the observation conditions of the first target image and the second target image as the second key, and use the image containing the second key information as the third target image.

[0043] The observation conditions include the diffraction distance and the polarization state of the incident light.

[0044] The present invention encodes the first target image and the second target image into the metasurface encryption device for near-field holographic display; and encodes the third target image into the metasurface encryption device for far-field holographic display.

[0045] The scrambling algorithm may be the Arnold scrambling algorithm or other existing algorithms.

[0046] Step 3: Obtain the first phase modulation amount corresponding to the first target image at the first wavelength, the second phase modulation amount corresponding to the second target image at the second wavelength, and the third phase modulation amount corresponding to the third target image at the third wavelength.

[0047] Among them, the phase modulation amount includes the modulation amount of the transmission phase and the modulation amount of the geometric phase.

[0048] The amount of adjustment of the transmission phase is expressed as:

[0049]

[0050] The amount of adjustment of the geometric phase is expressed as:

[0051]

[0052] In the formula, This is the amount of control for the transmission phase. The equivalent refractive index of the nanobrick is... For wavelength, The height of the nano brick, This is the amount of adjustment for the geometric phase. For the corner of the nanobrick.

[0053] To increase the difference among the three wavelength channels and reduce crosstalk, left-handed circularly polarized (LCP) light is used for incident light at the first and second wavelengths, while right-handed circularly polarized (RCP) light is used at the third wavelength. Correspondingly, the phase modulation amounts at the three wavelengths are expressed as follows:

[0054]

[0055]

[0056]

[0057] In the formula, This is the phase modulation amount at the first wavelength. This refers to the phase modulation amount at the second wavelength. This refers to the phase modulation amount at the third wavelength. The modulation amount of the transmission phase of the first-size nanobrick at the first wavelength. This refers to the modulation amount of the transmission phase of the second-sized nanobrick at the first wavelength. The modulation amount of the transmission phase of the first-size nanobrick at the second wavelength. This refers to the modulation amount of the transmission phase of the second-sized nanobrick at the second wavelength. This represents the modulation amount of the transmission phase of the first-sized nanobrick at the third wavelength. This refers to the modulation amount of the transmission phase of the second-sized nanobrick at the third wavelength.

[0058] Specifically, the phase modulation amount at three wavelengths can be obtained using a simulated annealing algorithm.

[0059] Step 4: Determine the size selection and arrangement of several nano-bricks in the metasurface encryption device based on the three phase modulation values.

[0060] The following section uses the Arnold scrambling algorithm as an example to further explain the main steps of this invention, taking into account the parameters.

[0061] (1) Construct the basic structure of the metasurface encryption device.

[0062] The metasurface encryption device consists of a substrate and two carefully arranged nanobricks of different sizes etched onto the substrate. Based on the height of the selected structural material and a roughly determined operating wavelength, electromagnetic simulation software was used to scan the length and width of the nanobricks, selecting two types of nanobricks whose transmission phases at three specific wavelengths meet the design conditions and approximate half-wave plates. To improve the three-wavelength decoupling effect, the difference in transmission phase difference between the two types of nanobricks at the three specific wavelengths should be significant. See also... Figure 1 The selected nanoscale unit structure's dimensional parameters include the nanobrick's length L, width W, and height H, as well as the side length (i.e., period CS) of the unit structure's working surface. The rotation angle of the nanobrick is denoted as... .

[0063] (2) Obtain three target images.

[0064] Select an encrypted image and scramble it using the Arnold scrambling algorithm. Arnold scrambling is a cropping transformation. Let the pixel coordinates of an N×N image be (…). , ), The Arnold transform is:

[0065]

[0066] The extended generalized Arnold transform is:

[0067]

[0068] The Arnold matrix is ​​invertible, and the inverse Arnold transform is:

[0069]

[0070] in,( , ) represents the transformed pixel coordinates, a and b are transformation parameters less than N, and N is the image size.

[0071] The Arnold transform, performed K times, can scramble the relationships between pixels in an original image, transforming it into an image indistinguishable to the human eye. Only when the parameters a and b, and the number of iterations K, are known can the transformed image be inversely transformed back to the original. Therefore, the parameters a and b, and the number of iterations K, can be used as keys to further enhance the security of information encryption.

[0072] The parameters a and b of the Arnold transform, along with the iteration number K, are used as the first key and encoded into the metasurface, then displayed using Fresnel holography. When the diffraction distance z is sufficiently larger than the size of the diffraction screen, the complex amplitude of the Fresnel diffracted light wave can be approximated by the following formula:

[0073]

[0074] in, Let z be the complex amplitude distribution of the incident field, and z be the diffraction distance.

[0075] Clearly, both the incident wavelength and the diffraction distance will cause changes in the Fresnel diffraction pattern. Furthermore, changes in the polarization state of the incident light wave will lead to changes in the incident light field, thereby altering the diffraction pattern. Therefore, the diffraction distance and the polarization state of the incident light can be used as a second key to encrypt the first key and the information after the Arnold transform.

[0076] (3) Obtain three phase control values.

[0077] A phase modulation method combining geometric phase and transmission phase is used to design three wavelength channels ( , , Phase modulation amount () , , ).

[0078] The amount of geometric phase modulation depends only on the rotation angle of the nanobrick and is independent of the wavelength and geometric parameters of the nanostructure. The phase modulation amount is: In the above formula, "+" represents the phase modulation amount when LCP light is incident, and "-" represents the phase modulation amount when RCP light is incident.

[0079] The phase modulation amount of the transmission phase is:

[0080]

[0081] in, The equivalent refractive index of the nanobrick is... Let H be the wavelength and H be the height of the nanobrick. Typically, altering the geometry or shape of a nanostructure changes its equivalent refractive index with the surrounding medium, resulting in different phase retardations. This invention changes the equivalent refractive index by varying the length and width of the nanobrick.

[0082] Based on the above equation, it can be seen that the modulation amount of the transmission phase is closely related to the size and wavelength of the nanobrick. Changing the size and operating wavelength of the nanobrick can achieve different transmission phases at different wavelengths. Based on the above theory, the phase modulation amounts of two sizes of nanobricks at three wavelengths can be designed as follows:

[0083]

[0084]

[0085]

[0086] Since the two structures need to have different transmission phase differences at the three wavelengths, this invention sets the first two wavelength channels to LCP light incident, and sets the third wavelength channel to RCP light incident to increase the difference between the three wavelength channels and thus reduce crosstalk. It should be noted that other polarization state settings can also be used in this invention; the above settings are merely illustrative.

[0087] Based on three target images, a simulated annealing algorithm can be used to optimize the normalized intensity of the three wavelength channels, thereby revealing the geometric phase distribution and transmission phase distribution of the nanobrick.

[0088] (4) Determine the size selection and arrangement of several nano-bricks in the metasurface encryption device based on the three phase control quantities.

[0089] Based on the geometric phase distribution and transmission phase distribution of the nanobricks obtained in the previous steps, the nanobricks are arranged. The rotational distribution of the nanobricks can be obtained based on the formula for the geometric phase modulation and the optimized geometric phase. The transmission phase at each wavelength is composed of the selective transmission phases of the two sizes of nanobricks at the corresponding wavelength. By correlating the transmission phase distributions of the two sizes of nanobricks at a specific wavelength, a selective array composed of the two sizes of nanobricks can be obtained.

[0090] The encryption and decryption processes for the metasurface encryption device obtained based on the above design method are as follows.

[0091] Encryption: First, the encrypted image is scrambled using Arnold gradient scrambling. Then, the Arnold transform parameters a and b, along with the iteration number K, are used as the first key. The encrypted image after the Arnold transform and the first key are encoded into a metasurface for a Fresnel near-field holographic display that cannot be directly observed. The observation conditions of the encrypted image and the first key are then encoded into the metasurface as the second key for a Fourier far-field holographic display that can be directly observed. Through this layered encryption, the security and reliability of the three-wavelength multi-key encryption device are greatly improved.

[0092] Decryption: The decryption process is the reverse of the encryption process. After obtaining the wavelength information, the observation method of the first key and the encrypted image can be directly observed, thus allowing direct observation of the second key. Based on the second key and the wavelength information, the first key and the encrypted information after Arnold transformation can be decoded. Then, an inverse Arnold transformation can be performed based on the first key to finally obtain the encrypted image.

[0093] For example, the substrate material is silicon dioxide ( The nanobricks are made of phosphosilicate ( ).

[0094] Select two nanobricks of different sizes that meet the requirements. The polarization conversion efficiency of the two nanobricks at the same wavelength should be as consistent as possible, and the transmission phase difference at the three wavelengths should be different.

[0095] like Figure 1 As shown, establish an xyz rectangular coordinate system, with the long side of the nano-rotor as the major axis direction, parallel to the x-axis; and the short side direction as the minor axis direction, parallel to the y-axis. θ To determine the angle between the period CS and the long axis of the nanobrick (ranging from 0 to 180°), the period CS is initially determined to be 400 nm, and the height H of the nanobrick is determined to be 380 nm.

[0096] The length and width of the nanobricks were optimized using electromagnetic simulation software. Nanobricks with a length range of 150 nm to 300 nm and a width range of 50 nm to 150 nm were scanned with a step size of 10 nm. Finally, three wavelengths, 470 nm, 560 nm and 650 nm, were selected. The length L of the first size of nanobrick was 170 nm and the width was 80 nm; the length L of the second size of nanobrick was 230 nm and the width was 120 nm.

[0097] The transmission phases of the two sizes of nanobricks at three corresponding wavelengths are as follows: , , , , .

[0098] That is, two sizes of nanobricks (i.e. Figure 2 The transmission phase differences of structures 1 and 2 at the three wavelengths are 0, 0, 0. The polarization conversion efficiencies of π and π are close, such as Figure 2 As shown, where, Figure 2 (a) shows the polarization conversion efficiency of nanobricks of two sizes as a function of wavelength. Figure 2 (b) in the figure shows the relative phase of nanobricks of two sizes as a function of wavelength.

[0099] When selectively arranging nanobricks of two sizes, one nanobrick corresponds to one pixel. Based on the transmission phase corresponding to a pixel obtained by the simulated annealing algorithm, one size of nanobrick is selected and arranged at the position corresponding to that pixel. For example, the transmission phase at a certain wavelength is... If so, then the first size of nanobrick is selected for this position.

[0100] The parameters for the Arnold transform of the encrypted image are a=b=20, the number of iterations is 1, and the Fresnel holographic observation conditions are LCP light incident and a diffraction distance z of 100um.

[0101] Select a pixel size of 100×100 Figure 3 (a) is the encrypted image, and the image after Arnold transformation is as follows: Figure 3 As shown in (b), the transformation parameters are a=b=20, and the number of iterations is 1. Figure 4 (a) is used as the first key. Figure 4 (b) in the code serves as the second key. That is... Figure 4 Image (a) in the image is the second target image containing the first key information. Figure 4 (b) in the image is the third target image containing the second key.

[0102] Figure 3 (b) Figure 4 (a) Figure 4 (b) in the image corresponds to the three wavelength channels of 470nm, 560nm, and 650nm, respectively. The phase modulation amount for the images of the three wavelength channels is:

[0103]

[0104]

[0105]

[0106] Will Figure 3 (b) Figure 4 (a) and Figure 4In (b), three target images are used, and the phase at three wavelengths is optimized using a simulated annealing algorithm. Figure 3 (b) and Figure 4 (a) in the figure is used for approximate numerical calculations of Fresnel diffraction. Figure 4 In (b), a Fourier transform numerical simulation is performed, namely:

[0107]

[0108]

[0109]

[0110] In the formula, For the first i Wavelength channels The corresponding light intensity of the emitted light, For the first i Wavelength channels The corresponding phase, i =1, 2, 3; Represents the Fresnel transform. This represents the Fast Fourier Transform.

[0111] The final result is a three-channel simulation image, which is the simulation image after the three target images have been optimized by the simulated annealing algorithm, such as... Figure 5 As shown. Among them, Figure 5 (a) in the image is the simulation image obtained after optimization of wavelength channel λ3, which is the simulation image corresponding to the third target image and contains the second key information. Figure 5 (b) is the simulation image obtained after wavelength channel λ2 optimization, which is the simulation image corresponding to the second target image and contains the first key information; Figure 5 In the diagram, (c) represents the simulated image obtained after optimization of wavelength channel λ1, which is the simulated image corresponding to the first target image, and also the ciphertext image after Arnold transform. Figure 5 The encrypted information can be obtained by performing the inverse Arnold transform on (c) in the middle, such as... Figure 6 As shown, that is Figure 6 This is the encrypted image obtained after decoding.

[0112] Example 2:

[0113] Example 2 provides a metasurface encryption device, which is obtained based on the design method of the metasurface encryption device as described in Example 1.

[0114] Example 2 provides a schematic diagram of a metasurface encryption device for information encoding and decoding, as shown below. Figure 7As shown, a third target image is observed in the far field of the metasurface encryption device at the third wavelength; a second target image and a first target image are observed in the near field of the metasurface encryption device based on the second wavelength and the second key information contained in the third target image; the first target image is inversely transformed based on the first key information contained in the second target image to obtain an encrypted image.

[0115] For example, the encrypted image after Arnold transformation and the first key are first encoded into the metasurface according to the optimized phase and displayed as Fresnel near-field holography. Then, the second key is encoded into the metasurface according to the optimized phase formula and displayed as Fourier far-field holography. Decoding the information is the reverse process of encoding, and finally the encrypted image is obtained.

[0116] Since the metasurface encryption device provided in Example 2 is based on the design method of the metasurface encryption device provided in Example 1, Example 2 can be understood by referring to the description of Example 1, and will not be repeated here.

[0117] In summary, this invention provides a three-wavelength, multi-key encryption scheme based on a minimalist metasurface. The constructed metasurface encryption device consists of only two nanostructures of different sizes, enabling flexible design, simple structure, and low fabrication complexity for three-wavelength decoupling. The multi-key encryption device with layer-by-layer encryption provided by this invention can greatly improve the reliability and security of information encryption. This invention also essentially provides a multi-channel multiplexed metasurface, which is beneficial for improving the information storage capacity and density of metasurfaces and provides a new approach to multi-channel multiplexing of metasurfaces.

[0118] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method of designing a metasurface encryption device, characterized in that, The method comprises the following steps: Constructing a basic structure of a super surface encryption device, the super surface encryption device comprising a substrate and an array of nano bricks on the substrate, the array of nano bricks being composed of two sizes of nano bricks; the substrate is divided into a plurality of unit structures with consistent sizes, a working surface of the unit structure being a square, one unit structure and one nano brick on the working surface of the unit structure constituting a nano unit structure, the nano unit structure having a size of a subwavelength level; the two sizes of nano bricks have the same height and different lengths and widths; Selecting an encrypted image, performing scrambling on the encrypted image by using a scrambling algorithm, and taking the obtained scrambled image as a first target image; Taking transformation parameters and iteration numbers in the scrambling algorithm as a first key, taking an image containing first key information as a second target image, taking observation conditions of the first target image and the second target image as a second key, and taking an image containing second key information as a third target image; the observation conditions include a diffraction distance and a polarization state of incident light; Obtaining a first phase control quantity corresponding to the first target image at a first wavelength, a second phase control quantity corresponding to the second target image at a second wavelength, and a third phase control quantity corresponding to the third target image at a third wavelength; Determining size selection and arrangement of a plurality of nano bricks in the super surface encryption device according to the three phase control quantities.

2. The design method of a metasurface encryption device according to claim 1, wherein, Encoding the first target image and the second target image into the super surface encryption device for near-field holographic display, and encoding the third target image into the super surface encryption device for far-field holographic display.

3. The design method of a metasurface encryption device according to claim 1, wherein, The phase control quantity includes a transmission phase control quantity and a geometric phase control quantity; The transmission phase control quantity is represented as: The geometric phase control quantity is represented as: wherein is a governing quantity of the transmission phase, is the equivalent refractive index of the nano brick, is the wavelength, is the height of the nano brick, is a governing quantity of the geometric phase, is the turn angle of the nano brick.

4. The design method of a metasurface encryption device according to claim 3, wherein, LCP light is used for incidence at the first wavelength and the second wavelength, and RCP light is used for incidence at the third wavelength; the phase control quantities at the three wavelengths are represented as: wherein is the phase control at the first wavelength, is the phase control at the second wavelength, is the phase control at the third wavelength, is the control of the transmission phase of the first size nanobrick at the first wavelength, is the control of the transmission phase of the second size nanobrick at the first wavelength, is the control of the transmission phase of the first size nanobrick at the second wavelength, is the control of the transmission phase of the second size nanobrick at the second wavelength, is the control of the transmission phase of the first size nanobrick at the third wavelength, is the control of the transmission phase of the second size nanobrick at the third wavelength.

5. The design method of a metasurface encryption device according to claim 1, wherein, Analog annealing algorithm is used to obtain the phase control quantities at the three wavelengths.

6. The design method of a metasurface encryption device according to claim 1, wherein, The scrambling algorithm uses Arnold scrambling algorithm.

7. A metasurface encryption device, characterized in that, The super surface encryption device is obtained based on the design method of the super surface encryption device according to any one of claims 1-6.

8. The metasurface encryption device of claim 7, wherein, At the third wavelength, the third target image is observed in the far field of the super surface encryption device; according to the second wavelength and the second key information contained in the third target image, the second target image and the first target image are observed in the near field of the super surface encryption device; the first target image is inversely transformed according to the first key information contained in the second target image, and an encrypted image is obtained.

Images