Very-simple metasurface-based double-wave encryption design method and metasurface device

Abstract

The invention belongs to the technical field of micro-nano optics, and discloses a double-wave encryption design method based on a very simple metasurface and a metasurface device. A basic structure for constructing the metasurface device comprises a substrate and a nano brick array, the nano brick array is composed of nano bricks of two sizes, and the geometric size of the metasurface device and the size arrangement and steering angle arrangement of a plurality of nano bricks in the nano brick array are determined based on two selected working wavelengths and encrypted images; circularly polarized light is respectively incident under two working wavelengths, and meaningless binary holographic images are obtained in a far field after the circularly polarized light is reflected by the metasurface device; only when circularly polarized light with a specific rotation direction is incident at the same time under double working wavelengths, and after being reflected by the metasurface device, the circularly polarized light is superposed in a far field to obtain an encrypted image. The dual-wavelength holographic encryption display device can realize holographic encryption display under dual wavelengths, can improve the security of information encryption, and has the advantages of simple design and easiness in processing.

Description

Technical Field

[0001] The present invention belongs to the field of micro-nano optical technology, and more specifically, relates to a dual-wave encryption design method based on a minimalist metasurface and a metasurface device. Background Art

[0002] As a new type of artificial subwavelength structure, metasurface can be designed to realize many functions, such as large numerical aperture lens, nano-printing, vortex light generator, achromatic lens, etc. Compared with traditional optical elements, metasurface has more control freedom and can be applied to the field of information encryption.

[0003] At present, most of the information encryption schemes based on metasurfaces use metasurface encoding to encrypt information under specific incident states. However, this scheme can achieve brute force decryption by scanning the wavelength and polarization state of the incident light, which leads to insufficient security. Summary of the invention

[0004] The present invention solves the problem that the security of information encryption schemes based on metasurfaces in the prior art needs to be further improved by providing a dual-wave encryption design method based on a minimalist metasurface and a metasurface device.

[0005] The present invention provides a dual-wave encryption design method based on a minimalist metasurface, comprising the following steps:

[0006] Constructing the basic structure of a metasurface device, wherein the metasurface device is a minimalist metasurface, and the basic structure of the metasurface device comprises a substrate and a nanobrick array located on a working surface of the substrate; the nanobrick array is composed of nanobricks of two sizes; the substrate is divided into a plurality of substrate unit structures of the same size, and each substrate unit structure is provided with a nanobrick;

[0007] Selecting a first working wavelength, a second working wavelength and an encrypted image; determining the geometric dimensions of the metasurface device, and the size arrangement and steering angle arrangement of a plurality of nanobricks in the nanobrick array based on the two selected working wavelengths and the encrypted image, to obtain the desired metasurface device;

[0008] After obtaining the required metasurface device, circularly polarized light is incident at the first working wavelength and the second working wavelength respectively, and after reflection by the metasurface device, a meaningless binary holographic image is obtained in the far field; only when circularly polarized light with a first rotation direction is incident on the metasurface at the first working wavelength and circularly polarized light with a second rotation direction is incident on the metasurface at the second working wavelength at the same time, after reflection by the metasurface device, the encrypted image is obtained by superposition in the far field.

[0009] Preferably, an xoy coordinate system is established with the directions of the two sides parallel to the working surface of the substrate set as the x-axis and the y-axis respectively, the nanobrick is a rectangular structure, the major axis and the minor axis of the nanobrick are parallel to the working surface of the substrate, and the lengths of the major axis and the minor axis are different; the steering angle of the nanobrick is the angle between the major axis of the nanobrick and the x-axis; the working surface of the substrate unit structure is a square; the two sizes of nanobricks have the same height, different lengths and different widths.

[0010] Preferably, when determining the geometric dimensions of the metasurface device, the height of the nanobrick and the side length of the working surface of the substrate unit structure are first determined, and then the length and width dimension parameters of the nanobrick are scanned at the first working wavelength and the second working wavelength respectively through electromagnetic simulation to obtain the transmission phase scanning results at the two working wavelengths; finally, two groups of dimensions are selected as the determined dimension parameters of the nanobrick according to the transmission phase scanning results at the two working wavelengths, and the transmission phase difference between the two sizes of nanobricks selected at the first working wavelength is π / 2, and the transmission phase difference between the two sizes of nanobricks selected at the second working wavelength is also π / 2.

[0011] Preferably, when determining the geometric dimensions of the metasurface device, it also includes: scanning the length and width dimension parameters of the nanobrick at the first working wavelength and the second working wavelength respectively through electromagnetic simulation to obtain the polarization conversion efficiency scanning results at the two working wavelengths; based on the transmission phase scanning results and the polarization conversion efficiency scanning results at the two working wavelengths, two sets of dimensions that meet the transmission phase requirements and have the highest polarization conversion efficiency are selected as the determined dimensional parameters of the nanobrick.

[0012] Preferably, after determining the geometric dimensions of the metasurface device, one of the substrate unit structures and a nanobrick located on its working surface is taken as a pixel point, and the phase of the reflected light passing through the metasurface device is modulated using the steering angle of the nanobrick and the transmission phase difference between two sizes of nanobricks, and the size and steering angle of the nanobrick on each substrate unit structure are determined based on the encrypted image.

[0013] Preferably, the Jones matrix J of the nanobrick with a steering angle of θ is expressed as: The Jones vector of circularly polarized light is expressed as: The circularly polarized light reflected by the nanobrick with a steering angle of θ is expressed as: Where A and B are coefficients related to the reflectivity in the major and minor axis directions of the nanobrick, respectively.

[0014] Preferably, when the nanobrick is designed as an equivalent half-wave plate, A=-B is satisfied, and the reflected light only contains the reverse circular polarization component.

[0015] Preferably, the sizes of the base unit structure and the nanobricks are both sub-wavelength level.

[0016] Preferably, the nanobrick is made of single crystal silicon material, and the substrate is made of single crystal silicon material as a lower layer and fused quartz glass material as an upper layer.

[0017] On the other hand, the present invention provides a metasurface device, which is obtained based on the above-mentioned dual-wave encryption design method based on a minimalist metasurface; the metasurface device includes a substrate and a nanobrick array located on the working surface of the substrate, and the nanobrick array is composed of nanobricks of two sizes; circularly polarized light is incident at a first working wavelength and a second working wavelength respectively, and after reflection by the metasurface device, a meaningless binary holographic image is obtained in the far field; only when circularly polarized light with a first rotation direction at the first working wavelength and circularly polarized light with a second rotation direction at the second working wavelength are simultaneously incident on the metasurface, after reflection by the metasurface device, an encrypted image is obtained by superimposing in the far field.

[0018] One or more technical solutions provided in the present invention have at least the following technical effects or advantages:

[0019] The present invention performs dual-wave encryption design based on a minimalist metasurface. The basic structure of the metasurface device (i.e., minimalist metasurface) constructed by the present invention includes a substrate and a nanobrick array located on the working surface of the substrate, wherein the nanobrick array is composed of nanobricks of two sizes, and the substrate is divided into a plurality of substrate unit structures of the same size, each substrate unit structure being provided with a nanobrick. The present invention determines the geometric dimensions of the metasurface device, as well as the size arrangement and steering angle arrangement of a plurality of nanobricks in the nanobrick array based on the two selected working wavelengths and the encrypted image, to obtain the desired metasurface device; after obtaining the desired metasurface device, circularly polarized light is incident at a first working wavelength, and after reflection by the metasurface device, a meaningless binary holographic image is obtained in the far field, and circularly polarized light is incident at a second working wavelength, and after reflection by the metasurface device, a meaningless binary holographic image is also obtained in the far field; only when circularly polarized light with a first hand direction is incident on the metasurface at the first working wavelength and circularly polarized light with a second hand direction is incident on the metasurface at the second working wavelength at the same time, after reflection by the metasurface device, an encrypted image is obtained by superimposing in the far field. That is, the present invention can only obtain an encrypted image in the far field under the dual-wave condition of a specific wavelength plus a specific polarization state. On the one hand, the present invention introduces the wavelength dimension to encrypt information to improve the security of information encryption. On the other hand, it further increases the variables by limiting the specific polarization state (handedness), thereby increasing the difficulty of cracking. Moreover, the present invention constructs a minimalist metasurface based on only two sizes of nanobricks. Encryption can be achieved using the minimalist metasurface, which can greatly reduce the processing and design difficulty of metasurface devices, and has the advantages of simple design and easy processing. The sizes of the substrate unit structure and the nanobricks are both sub-wavelength, so the metasurface device designed by the present invention is small in size, light in weight, and can be highly integrated, which is suitable for the development of miniaturization and micro-miniaturization. The encryption scheme proposed by the present invention can increase the security of information encryption, and can also provide a new technical solution for fields such as information anti-counterfeiting. The dual-wave encryption holographic scheme proposed by the present invention has a good application development prospect and can be applied to fields such as information encryption and anti-counterfeiting. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic diagram of a substrate unit structure and nanobricks located on its working surface in a dual-wave encryption design method based on a minimalist metasurface provided in Example 1 of the present invention;

[0021] Figure 2 A nanobrick transmission phase scan diagram at dual wavelengths in a dual-wavelength encryption design method based on a minimalist metasurface provided in Example 1 of the present invention; wherein, Figure 2 (a) is the transmission phase scan of the nanobrick at a wavelength of 550nm. Figure 2 (b) is the transmission phase scan of the nanobrick at a wavelength of 633 nm;

[0022] Figure 3A scanning diagram of the polarization conversion efficiency of nanobricks at dual wavelengths in a dual-wavelength encryption design method based on a minimalist metasurface provided in Example 1 of the present invention; wherein, Figure 3 (a) is a scan of the polarization conversion efficiency of nanobricks at a wavelength of 550nm. Figure 3 (b) is a scan of the polarization conversion efficiency of the nanobrick at a wavelength of 633 nm;

[0023] Figure 4 Schematic diagram of the effect of achieving dual-wave encryption using metasurface devices. DETAILED DESCRIPTION

[0024] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0025] Embodiment 1:

[0026] Embodiment 1 provides a dual-wave encryption design method based on a minimalist metasurface, comprising the following steps:

[0027] Constructing the basic structure of a metasurface device, wherein the metasurface device is a minimalist metasurface, and the basic structure of the metasurface device comprises a substrate and a nanobrick array located on a working surface of the substrate; the nanobrick array is composed of nanobricks of two sizes; the substrate is divided into a plurality of substrate unit structures of the same size, and each substrate unit structure is provided with a nanobrick;

[0028] Selecting a first working wavelength, a second working wavelength and an encrypted image; determining the geometric dimensions of the metasurface device, and the size arrangement and steering angle arrangement of a plurality of nanobricks in the nanobrick array based on the two selected working wavelengths and the encrypted image, to obtain the desired metasurface device;

[0029] After obtaining the required metasurface device, circularly polarized light is incident at the first working wavelength and the second working wavelength respectively, and after reflection by the metasurface device, a meaningless binary holographic image is obtained in the far field; only when circularly polarized light with a first rotation direction is incident on the metasurface at the first working wavelength and circularly polarized light with a second rotation direction is incident on the metasurface at the second working wavelength at the same time, after reflection by the metasurface device, the encrypted image is obtained by superposition in the far field.

[0030] Among them, see Figure 1, an xoy coordinate system is established with the directions of the two sides parallel to the working surface of the substrate set as the x-axis and the y-axis respectively, the nanobrick is a rectangular parallelepiped structure, the major axis and the minor axis of the nanobrick are parallel to the working surface of the substrate, and the lengths of the major axis and the minor axis are different; the steering angle θ of the nanobrick is the angle between the major axis of the nanobrick and the x-axis; the working surface of the substrate unit structure is a square with a side length of C; the two sizes of nanobricks have the same height H, different lengths L and different widths W.

[0031] The two sizes of nanobricks are respectively recorded as the first nanobrick and the second nanobrick, the structural dimensions of the first nanobrick include: a first length L1, a first width W1 and a height H, and the structural dimensions of the second nanobrick include: a second length L2, a second width W2 and a height H. The above size parameters are obtained through electromagnetic simulation optimization according to the two selected working wavelengths.

[0032] Specifically, when determining the geometric dimensions of the metasurface device, first determine the height H of the nanobrick and the side length C of the working surface of the substrate unit structure, then scan the length and width dimension parameters of the nanobrick at the first working wavelength and the second working wavelength respectively through electromagnetic simulation to obtain the transmission phase scanning results at the two working wavelengths; finally, select two groups of dimensions as the determined dimension parameters of the nanobrick according to the transmission phase scanning results at the two working wavelengths, the transmission phase difference of the selected two sizes of nanobricks at the first working wavelength is π / 2, and the transmission phase difference of the two sizes of nanobricks at the second working wavelength is also π / 2, that is, the transmission phase difference of the two nanobricks at a single working wavelength is π / 2, and the phase shift caused by the change in wavelength to the nanobricks of the two sizes is equal; in addition, the nanobricks of the two sizes have different transmission phase characteristics, which can be seen in Figure 2 .

[0033] In a preferred scheme, when determining the geometric dimensions of the metasurface device, the length and width dimension parameters of the nanobrick are scanned at the first working wavelength and the second working wavelength respectively through electromagnetic simulation to obtain the polarization conversion efficiency scanning results at the two working wavelengths; based on the transmission phase scanning results and the polarization conversion efficiency scanning results at the two working wavelengths, two sets of dimensions that meet the transmission phase requirements and have the highest polarization conversion efficiency are selected as the determined dimensional parameters of the nanobrick.

[0034] After determining the geometric size of the metasurface device, one of the substrate unit structures and one nanobrick located on its working surface is taken as a pixel point, and the phase of the reflected light from the metasurface device is modulated using the steering angle of the nanobrick and the transmission phase difference between the two sizes of nanobricks, and the size and steering angle of the nanobrick on each substrate unit structure are determined according to the encrypted image. That is, it is determined which size of the two sizes each nanobrick in the nanobrick array adopts, and the size of the steering angle of each nanobrick is determined.

[0035] The Jones matrix J of the nanobrick with a steering angle of θ is expressed as: The Jones vector of circularly polarized light is expressed as: The circularly polarized light reflected by the nanobrick with a steering angle of θ is expressed as: Where A and B are coefficients related to the reflectivity in the major and minor axis directions of the nanobrick, respectively.

[0036] It can be seen that the reflected light consists of a co-directional circular polarization component and a reverse circular polarization component, wherein the phase of the reverse circular polarization component can be regulated by the steering angle θ of the nanobrick. At the same time, when the nanobrick is designed as an equivalent half-wave plate, A=-B is satisfied. At this time, the reflected light only contains the reverse circular polarization component, and the corresponding polarization conversion efficiency reaches the highest.

[0037] The sizes of the base unit structure and the nanobricks are both sub-wavelength level.

[0038] In terms of materials, the nanobricks can be made of single crystal silicon material, and the substrate can be made of single crystal silicon material as the lower layer and fused quartz glass material as the upper layer. Since the metasurface device designed by the present invention works in a reflection mode, and single crystal silicon + fused quartz + single crystal silicon material has a higher efficiency when working in the reflection mode, the above preparation scheme is preferably used.

[0039] A dual-wave encryption design method based on a minimalist metasurface provided in Example 1 can realize holographic encryption display at dual wavelengths by using only a minimalist metasurface (i.e., a metasurface device) containing two nanobricks of different sizes.

[0040] The present invention is further described below.

[0041] When light of any polarization state is incident and passes through the minimalist metasurface, the phase of the reflected light is modulated. By optimizing the arrangement of two sizes of nanobricks and the steering angle θ of the minimalist metasurface, at the first working wavelength λ1, when left-handed circularly polarized light passes through the minimalist metasurface, the phase of the reflected light is modulated, and a meaningless binary image is obtained in the far field; at the second working wavelength λ2, when right-handed circularly polarized light passes through the minimalist metasurface, the phase of the reflected light is modulated, and another meaningless binary image is obtained in the far field. Only when left-handed circularly polarized light at the first working wavelength λ1 and right-handed circularly polarized light at the second working wavelength λ2 are incident on the minimalist metasurface at the same time, an encrypted image is obtained by superposition in the far field, that is, the design method of the present invention can realize dual-wave encrypted display.

[0042] It should be noted that the above description takes left-handed circularly polarized light incident at the first working wavelength and right-handed circularly polarized light incident at the second working wavelength as examples, but is not limited to the above options.

[0043] Taking the first working wavelength λ1 = 550nm and the second working wavelength λ2 = 633nm as an example, electromagnetic simulation software is used for modeling and simulation. Left-handed circularly polarized light is incident vertically, and the structural parameters of the nano-unit are scanned at the working wavelength, including the structural dimensions of the first nano-brick: L1, W1, H, the structural dimensions of the second nano-brick: L2, W2, H, and the working surface dimension C of the substrate unit structure. The scanning results of the transmission phase are shown in Figure 2 As shown, Figure 2 (a) is the transmission phase scan of the nanobrick at a wavelength of 550nm. It represents the transmission phase result of scanning at 550nm wavelength. Figure 2 (b) is the transmission phase scan of the nanobrick at a wavelength of 633nm. It shows the transmission phase result of scanning at 633nm wavelength.

[0044] Under the premise of ensuring that the transmission phase difference of the two sizes of nanobricks at a single working wavelength is π / 2, the left-handed circularly polarized light is incident vertically, and the proportion of the right-handed circularly polarized light component in the reflected light field is optimized by the nanobricks to maximize the polarization conversion efficiency (that is, in the preferred solution, several groups of structures are selected under the premise of ensuring the phase difference, and the two structures with the highest polarization conversion efficiency are selected as the final selected structures). The scanning results are as follows Figure 3 As shown, Figure 3 (a) is a scanning diagram of the polarization conversion efficiency of nanobricks at a wavelength of 550nm. f1 It represents the polarization conversion efficiency result scanned at 550nm wavelength. Figure 3 (b) is a scan of the polarization conversion efficiency of nanobricks at a wavelength of 633 nm. f2It shows the polarization conversion efficiency results scanned at 633nm wavelength.

[0045] In this example, the final structural parameters include: L1 = 250nm, W1 = 105nm, H = 220nm; L2 = 295nm, W2 = 125nm, C = 400nm.

[0046] It should be noted that there is no difference in the calculation results when left-handed circularly polarized light or right-handed circularly polarized light is incident during simulation. When left-handed circularly polarized light is incident, the right-handed circularly polarized light component can be extracted, and when right-handed circularly polarized light is incident, the left-handed circularly polarized light component can be extracted. The above simulation example is explained by taking left-handed circularly polarized light as an example.

[0047] When circularly polarized light is incident on the minimalist metasurface, the phase of the reflected light is modulated. When left-handed circularly polarized light at 633nm is incident on the minimalist metasurface, a meaningless binary image is obtained in the far field; when right-handed circularly polarized light at 550nm is incident on the minimalist metasurface, another meaningless binary image is obtained in the far field. When two light beams are incident at the same time, the two binary images in the far field are superimposed to obtain an encrypted image. That is, the design method of the present invention can realize dual-wave encryption based on the minimalist metasurface, and the effect is as follows: Figure 4 shown.

[0048] Embodiment 2:

[0049] Embodiment 2 provides a metasurface device, and the metasurface device is obtained based on the dual-wave encryption design method based on the minimalist metasurface as described in Embodiment 1. The metasurface device provided in Embodiment 2 includes a substrate and a nanobrick array located on the working surface of the substrate, and the nanobrick array is composed of nanobricks of two sizes; circularly polarized light is incident at a first working wavelength and a second working wavelength respectively, and after reflection by the metasurface device, a meaningless binary holographic image is obtained in the far field; only when circularly polarized light with a first hand direction is incident on the metasurface at the first working wavelength and circularly polarized light with a second hand direction is incident on the metasurface at the same time, after reflection by the metasurface device, an encrypted image is obtained by superposition in the far field.

[0050] Since Embodiment 2 provides a device corresponding to the design method provided in Embodiment 1, Embodiment 2 can be understood by referring to the description of Embodiment 1, which will not be described in detail here.

[0051] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A dual-wave encryption design method based on a minimalist metasurface, characterized in that: The following steps are involved: Constructing the basic structure of a metasurface device, wherein the metasurface device is a minimalist metasurface, and the basic structure of the metasurface device comprises a substrate and a nanobrick array located on a working surface of the substrate; the nanobrick array is composed of nanobricks of two sizes; the substrate is divided into a plurality of substrate unit structures of the same size, and each substrate unit structure is provided with a nanobrick; Selecting a first working wavelength, a second working wavelength and an encrypted image; determining the geometric dimensions of the metasurface device, and the size arrangement and steering angle arrangement of a plurality of nanobricks in the nanobrick array based on the two selected working wavelengths and the encrypted image, to obtain the desired metasurface device; After obtaining the required metasurface device, circularly polarized light is incident at the first working wavelength and the second working wavelength respectively, and after reflection by the metasurface device, a meaningless binary holographic image is obtained in the far field; only when circularly polarized light with a first rotation direction is incident on the metasurface at the first working wavelength and circularly polarized light with a second rotation direction is incident on the metasurface at the second working wavelength at the same time, after reflection by the metasurface device, the encrypted image is obtained by superposition in the far field.

2. The dual-wave encryption design method based on a minimalist metasurface according to claim 1 is characterized in that: An xoy coordinate system is established by setting the directions of the two sides parallel to the working surface of the substrate as the x-axis and the y-axis respectively. The nanobrick is a rectangular structure. The major axis and the minor axis of the nanobrick are parallel to the working surface of the substrate, and the lengths of the major axis and the minor axis are different. The steering angle of the nanobrick is the angle between the major axis of the nanobrick and the x-axis. The working surface of the substrate unit structure is a square. The two sizes of nanobricks have the same height, different lengths and different widths.

3. The dual-wave encryption design method based on a minimalist metasurface according to claim 2 is characterized in that: When determining the geometric dimensions of the metasurface device, first determine the height of the nanobrick and the side length of the working surface of the substrate unit structure, and then scan the length and width dimension parameters of the nanobrick at the first working wavelength and the second working wavelength respectively through electromagnetic simulation to obtain the transmission phase scanning results at the two working wavelengths; finally, select two groups of dimensions as the determined dimension parameters of the nanobrick according to the transmission phase scanning results at the two working wavelengths, and the transmission phase difference between the two sizes of nanobricks selected at the first working wavelength is π / 2, and the transmission phase difference between the two sizes of nanobricks selected at the second working wavelength is also π / 2.

4. The dual-wave encryption design method based on a minimalist metasurface according to claim 3 is characterized in that: When determining the geometric dimensions of the metasurface device, it also includes: scanning the length and width dimension parameters of the nanobrick at the first working wavelength and the second working wavelength respectively through electromagnetic simulation to obtain the polarization conversion efficiency scanning results at the two working wavelengths; based on the transmission phase scanning results and the polarization conversion efficiency scanning results at the two working wavelengths, two sets of dimensions that meet the transmission phase requirements and have the highest polarization conversion efficiency are selected as the determined dimension parameters of the nanobrick.

5. The dual-wave encryption design method based on a minimalist metasurface according to claim 3 is characterized in that: After determining the geometric dimensions of the metasurface device, one of the substrate unit structures and a nanobrick located on its working surface is taken as a pixel point, and the phase of the reflected light from the metasurface device is modulated using the steering angle of the nanobrick and the transmission phase difference between two sizes of nanobricks. The size and steering angle of the nanobrick on each substrate unit structure are determined based on the encrypted image.

6. The dual-wave encryption design method based on a minimalist metasurface according to claim 5 is characterized in that: The Jones matrix J of the nanobrick with a steering angle of θ is expressed as: The Jones vector of circularly polarized light is expressed as: The circularly polarized light reflected by the nanobrick with a steering angle of θ is expressed as: Where A and B are coefficients related to the reflectivity in the major and minor axis directions of the nanobrick, respectively.

7. The dual-wave encryption design method based on a minimalist metasurface according to claim 6 is characterized in that: When the nanobrick is designed as an equivalent half-wave plate, A=-B is satisfied, and the reflected light only contains the reverse circular polarization component.

8. The dual-wave encryption design method based on a minimalist metasurface according to claim 1 is characterized in that: The sizes of the base unit structure and the nanobricks are both sub-wavelength level.

9. The dual-wave encryption design method based on a minimalist metasurface according to claim 1 is characterized in that: The nano bricks are made of single crystal silicon material, and the substrate is made of single crystal silicon material as a lower layer and fused quartz glass material as an upper layer.

10. A metasurface device, characterized in that: The metasurface device is obtained based on the dual-wave encryption design method based on a minimalist metasurface as described in any one of claims 1 to 9; the metasurface device includes a substrate and a nanobrick array located on the working surface of the substrate, and the nanobrick array is composed of nanobricks of two sizes; circularly polarized light is incident at a first working wavelength and a second working wavelength respectively, and after reflection by the metasurface device, a meaningless binary holographic image is obtained in the far field; only when circularly polarized light with a first rotation direction at the first working wavelength and circularly polarized light with a second rotation direction at the second working wavelength are simultaneously incident on the metasurface, after reflection by the metasurface device, an encrypted image is obtained by superimposing in the far field.

Images