A triple optical encryption method based on metasurface material

Abstract

The application discloses a kind of triple optical encryption methods based on super surface material, it is with super surface polarizer as carrier, super surface is by multiple size same, corner different nano brick structure unit array in a plane, it is equivalent to a polarizer to each nano brick structure unit in array, design and construct two kinds of exit light intensity modulation function with different decryption difficulty level, encode camouflage information and real information respectively.The application introduces the concept of camouflage information in optical encryption technology, which is set at different decoding difficulty from real information, which can improve the security of encryption.The application method not only has strong originality and novelty, but also has scalability, since the design method is ingenious, the structure used is simple, so it is very easy to extend to other wave bands and optical platforms.In addition, since the super surface is small in volume, light in weight and highly integrated, the application is also very suitable for the development of future miniaturization, miniaturization and portable optical encryption technology.

Description

Technical Field

[0001] This invention belongs to the field of micro-nano optics and polarization optics technology, and particularly relates to a triple optical encryption method based on metasurface materials. Background Technology

[0002] With the continuous development of computer technology, almost everything people do is closely related to the internet. Therefore, information security and authentication remain extremely challenging, both now and in the near future. A common method to improve security is information encryption technology. Among numerous encryption technologies, optical encryption technology has gained increasing attention due to its advantages such as multi-dimensional key space, naturally fast parallel processing of large amounts of data, and multiple degrees of controllability. Metasurface materials, as artificial and powerful two-dimensional planar structural materials, provide a new approach to optical information encryption. Optical encryption technologies based on metasurface materials, such as metasurface holography and metasurface nanoprinting, have greatly enriched the research content of optical encryption. This invention proposes a new triple optical encryption technology based on metasurface materials. Summary of the Invention

[0003] The purpose of this invention is to provide a triple optical encryption method based on metasurface materials. This invention utilizes the rotation angles of multiple nano-brick structural units of the same size to simultaneously encode a uniform grayscale image, a continuous grayscale image, and a binary image on a single metasurface. The uniform grayscale image and the continuous grayscale image represent pre-defined forged information, while the binary image represents the real information. The forged and real information have different decoding difficulties, thus ensuring that even if the forged information is decrypted, the real information remains secure. A second set of pre-defined forged information is also hidden within the first forged information and requires a key for decryption. Therefore, the real information is triple-encrypted, providing high security.

[0004] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0005] A triple optical encryption method based on metasurface materials is proposed. The metasurface is composed of multiple identical nanobrick structural units arrayed on a plane. Each nanobrick structural unit in the array is equivalent to a polarizer. Using the nanobrick polarizers of the metasurface as carriers, when light is incident perpendicularly to the metasurface or a filter is introduced in the optical path, only a uniform intensity image is seen because the multiple nanobricks have the same size (i.e., the multiple nanobricks of the metasurface have the same size), which constitutes the first camouflage information. Simultaneously with introducing a filter in the incident optical path, a polarizer can also be introduced to construct a first outgoing light intensity modulation function, used to encode the second camouflage information. Then, an analyzer is introduced in the outgoing optical path to further construct a second outgoing light intensity modulation function, used to encode the real information. The two camouflage information and one real phenomenon constructed in this way have different decryption difficulty levels, and the real information is encoded in the highest decoding difficulty, thus achieving triple encryption.

[0006] Furthermore, the first camouflage information is a uniform grayscale image, the second camouflage information can be a grayscale image or a binary image, and the real information is a binary image.

[0007] The metasurface structure consists of a transparent substrate and an array of nanobricks deposited on it. When directly observing the metasurface, only a uniform grayscale is visible, devoid of any information; this constitutes the first spoofed information. By adding a filter and a polarizer to the optical path, and rotating the polarizer to a specific position, another spoofed information can be observed on the surface of the metasurface material structure using a magnification system. Even rotating the polarizer within the angular range of [0, 180°], no real information can be observed. Only by adding an analyzer to the outgoing optical path and simultaneously rotating both the polarizer and analyzer to a specific angle can the real information be observed.

[0008] The nanobrick structure unit includes a transparent substrate and nanobricks. The transparent substrate is placed on the plane, and the nanobricks are deposited on the transparent substrate. The turning angle of the nanobrick structure unit is θ, and the value of θ ranges from [0, 180°]. The side of the transparent substrate where the nanobricks are deposited is a square working surface with a side length of C, and the side length C is at the subwavelength level. The length L, width W, and height H of the nanobrick are all at the subwavelength level. The values ​​of L, W, and H are obtained by electromagnetic simulation optimization based on the selected incident light wavelength. An xoy coordinate system is established with the right-angled sides of the unit structure as the x-axis and y-axis, with the long side of the nanobrick as the major axis and the short side as the minor axis. The angle between the major axis of the nanobrick and the x-axis is the turning angle θ of the nanobrick.

[0009] Based on the above technical solution, as a preferred embodiment, the transparent substrate is fused silica glass material, and the nano-bricks are materials such as gold, silver, aluminum, and silicon.

[0010] Based on the above technical solutions, through optimized design, linearly polarized light incident along the long axis of the nanobrick at a certain operating wavelength can achieve high reflectivity (or transmittance) while suppressing its transmittance (or reflectivity) to near zero. Alternatively, linearly polarized light incident along the short axis of the nanobrick can achieve high transmittance (or reflectivity) while suppressing its reflectivity (or transmittance) to near zero. This achieves the function of a transmissive, reflective, or both transmissive and reflective polarizer.

[0011] Based on the above technical solution, in order to encode the preset second forged information and real information into different decryption difficulty levels, two different intensity modulation functions need to be designed. A filter is introduced into the optical path to filter out incident light of a specific wavelength, and a polarizer is introduced into the optical path to convert the filtered incident light of the specific wavelength into linearly polarized light, the polarization direction of which is denoted as α1. After the linearly polarized light with polarization direction α1 passes through the nanostructure unit, the output light intensity I1 can be expressed as:

[0012] I1=I0[A 2 cos 2 (θ-α1)+B 2 sin 2 (θ-α1)]

[0013] Where I0 is the incident light intensity, and A and B are the complex transmission coefficients or reflection coefficients of the major and minor axes of the nanobrick, respectively; when the nanobrick is a polarizer, i.e., A = 0, B = 1 (or A = 1, B = 0), by designing the polarization direction of the incident ray and setting the value of the incident intensity I0, the intensity modulation function of the outgoing light can be achieved as I1 = sin 2 θ, this function is used to encode the second camouflage information.

[0014] Furthermore, the polarization direction of the analyzer introduced in the optical path is denoted as α2. Linearly polarized light with incident intensity I0 and polarization direction α1 is sequentially incident on the nanobrick structure unit and the analyzer with polarization direction α2. The functional relationship between the outgoing light intensity I2 and the polarization direction α1 of the linearly polarized light, the nanobrick turning angle θ, and the polarization direction α2 of the analyzer is obtained as follows:

[0015]

[0016] By setting the incident intensity I0 to 4 and the angles of the polarization direction α1 and the analysis direction α2 to specific values, the intensity modulation function of the emitted light can be achieved as I2 = cos 2 (2θ-45°) is a function used to encode real information.

[0017] By rotating the nanobrick within the range of [0, 180°] and observing the intensity changes of the two intensity modulation functions in each range, the following patterns can be obtained.

[0018] Steering angle θ range <![CDATA[I1=sin 2 θ]]> <![CDATA[I2=cos 2 (2θ-45°)]]> [0,45°] 0-0.5 0-0.5 [45°,90°] 0.5-1 0.5-1 [90°,135°] 0.5-1 0-0.5 [135°,180°] 0-0.5 0.5-1

[0019] Therefore, it can be seen that a continuous grayscale image can be encoded in the first emitted light intensity modulation function, and a binary image can be encoded in the second emitted light intensity modulation function.

[0020] Based on the above technical solution, metasurface materials can be constructed using a single type of single-size nanostructure. When light is directly shone onto the metasurface material, only a uniform grayscale area is visible, without any information; this is the first camouflage information. When a filter and a polarizer are added to the optical path, and the polarizer is rotated to a set angle, an image can be observed; this is the preset second camouflage information. Only when an analyzer is added to the optical path, and both the polarizer and analyzer are rotated to a specific angle, can the hidden true information be observed. Therefore, the method of this invention has high security.

[0021] The triple optical encryption technology based on metasurface materials designed in this invention has the following advantages and positive effects:

[0022] 1. This invention only requires arranging the turning angles of single-size nanobrick structures, without combining multiple nanobrick structures, thus greatly reducing the difficulty of its processing and design.

[0023] 2. The working mode of this invention is also arbitrary. It can work in transmission mode or reflection mode, or it can work simultaneously in transmission and reflection modes, which is of great convenience in practical applications.

[0024] 3. The method of the present invention introduces preset forged information and designs it to have a different decryption difficulty level than the real information. Furthermore, the real information of the present invention can only be decoded under a few specific combinations of polarizers and analyzers, which further increases the security of optical information encryption.

[0025] 4. This invention not only possesses the common advantages of optical encryption technology, but also has strong originality, novelty and scalability. Due to its ingenious design method and simple structure, it is very easy to extend to other wavebands and optical platforms.

[0026] 5. Due to the small size, light weight, and high integration of metasurfaces, this invention is also very suitable for the future development of miniaturized, micro-sized, and portable optical encryption technologies. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the nanobrick unit structure in this embodiment.

[0028] Figure 2 This is a scan of the transmittance and reflectance of the nanounit structure in this embodiment.

[0029] Figure 3 This is a graph showing the relationship between the intensity modulation function and the turning angle of the nanobrick in this embodiment.

[0030] Figure 4 This is a schematic diagram illustrating the implementation of triple optical encryption in this embodiment. Detailed Implementation

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention and / or the prior art, the specific implementation methods of the present invention will be described below with reference to the accompanying drawings. Obviously, the accompanying drawings described below are merely embodiments of the present invention. For those skilled in the art, other drawings and other implementation methods can be obtained based on these drawings without any creative effort.

[0032] The present invention will be further described below with reference to specific embodiments and accompanying drawings. Figure 1 In the diagram, L is the length of the nanobrick, W is the width of the nanobrick, H is the height of the nanobrick, C is the size of the nanobrick unit, θ is the turning angle of the nanobrick, and θ is the angle between the major axis of the nanobrick and the x-axis.

[0033] Example: This example illustrates a specific implementation process of a triple optical encryption method based on metasurface materials.

[0034] In this embodiment, the nanounit structure consists of silver nanobricks and a silicon substrate. The selected design wavelength is λ = 633 nm. For this wavelength, the nanounit structure is optimized using electromagnetic simulation software CST. The optimized dimensions of the silver nanobricks are: length L = 160 nm, width W = 80 nm, height H = 70 nm, and the side length of the substrate is C = 300 nm. Under these structural parameters, the transmission and reflection efficiency of the nanobricks for linearly polarized light incident along the long and short axes of the nanobricks is as follows: Figure 2 As shown, where R l R s These represent the reflected light efficiency along the long and short axes of the nanobrick, respectively. Specifically, at the working wavelength of 633 nm, the reflectivity R along the long axis of the nanobrick is... l Transmittance T along the short axis of nanobricks s The reflectance reached 92.6% and 95.3% respectively, while the reflectance R along the short axis of the nanobrick was... s and transmittance T along the long axis of the nanobrick l The concentrations are suppressed to below 4% and 2%. Therefore, at 633 nm, the optimized nanobricks can be considered ideal polarizers in both reflection and transmission modes.

[0035] When linearly polarized light with a working wavelength of 633 nm vibrating along the y-axis is incident on the nanobrick polarizer, the relationship between the intensity of the emitted light and the turning angle of the nanobrick is shown in the figure. Figure 3 Satisfying I1 = sin 2 The θ function. When an analyzer is added to the optical path and the incident light intensity is set to 4, the relationship between the output light intensity and the nanobrick turning angle is shown in the figure. Figure 3 Satisfying I2 = cos 2 (2θ-45°), therefore, two images can be encoded based on two intensity modulation functions. As an example, this invention encodes two binary images respectively.

[0036] The expected results of this implementation are as follows: Figure 4 When key1 is used directly to decrypt the metasurface material, no information is observed; this is the first set of false information. Adding new decoding conditions to key1 yields key2, from which a binary image can be decoded. However, this is the second set of false information, used to confuse the user. To obtain the true information, further decoding conditions must be added to key2 and set to specific conditions to truly obtain the encrypted information. Therefore, this invention provides triple encryption, ensuring high security. Key1 involves direct light irradiation or the addition of a filter; key2 involves adding a filter and polarizer during light irradiation; and key3 involves adding an analyzer to key2.

[0037] The above embodiments are used to explain and illustrate the present invention, but not to limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A triple optical encryption method based on metasurface materials, characterized in that... The metasurface is composed of multiple nanobrick structural units arrayed on a plane. Each nanobrick structural unit in the array is equivalent to a polarizer. Using the nanobrick polarizer of the metasurface as a carrier, when light is incident perpendicularly on the metasurface or when a filter is introduced in the optical path, only a uniform intensity image can be seen because the multiple nanobricks have the same size. This constitutes the first camouflage information. At the same time as introducing a filter in the incident optical path, a polarizer is also introduced to construct the first outgoing light intensity modulation function, which is used to encode the second code camouflage information. Then, an analyzer is introduced in the outgoing optical path to further construct the second outgoing light intensity modulation function, which is used to encode the real information. The two types of disguised information and one real phenomenon constructed in this way have different levels of decryption difficulty, and the real information is encoded in the highest level of decryption difficulty, thus achieving triple encryption. The nanobrick structure unit includes a transparent substrate and nanobricks, with the transparent substrate placed on the plane and the nanobricks deposited on the transparent substrate; The orientation angle of the nanobrick structural unit is θ, and the value of θ ranges from [0, π]. The transparent substrate is made of fused silica glass, and the material of the nanobrick includes gold, silver, aluminum, or silicon. The filter introduced in the optical path is used to filter out incident light of a specific wavelength. The polarizer introduced in the optical path is used to convert the incident light of the specific wavelength obtained by filtering into linearly polarized light. The polarization direction of the linearly polarized light is denoted as α1. Linearly polarized light with polarization direction α1, after passing through a nanostructure unit, can have its emitted light intensity I1 expressed as: I1=I0[A 2 cos 2 (θ-α1)+B 2 sin 2 (θ-α1)] Where I0 is the incident light intensity, and A and B are the complex transmission coefficients or reflection coefficients of the major and minor axes of the nanobrick, respectively; when the nanobrick is a polarizer, i.e., A = 0, B = 1 or A = 1, B = 0, by designing the polarization direction of the incident linearly polarized light and setting the value of the incident intensity I0, the intensity modulation function of the outgoing light can be achieved as I1 = sin 2 θ, this function is used to encode the second camouflage information; The polarization direction of the analyzer introduced in the optical path is denoted as α2. Linearly polarized light with incident intensity I0 and polarization direction α1 is sequentially incident on the nanobrick structure unit and the analyzer with polarization direction α2. The functional relationship between the outgoing light intensity I2 and the polarization direction α1 of the linearly polarized light, the nanobrick turning angle θ, and the polarization direction α2 of the analyzer is obtained as follows: By setting the incident intensity I0 to 4 and the angles of the polarization direction α1 and the analysis direction α2 to specific values, the intensity modulation function of the emitted light can be achieved as I2 = cos 2 (2θ-45°) is a function used to encode real information.

2. The triple optical encryption method based on metasurface materials as described in claim 1, characterized in that... The transparent substrate has a square working surface with a side length C on one side where nanobricks are deposited. The side length C is at the subwavelength level. The length L, width W, and height H of the nanobricks are all at the subwavelength level. The L, W, and H are obtained by electromagnetic simulation optimization based on the selected incident light wavelength. An xoy coordinate system is established with the right-angled sides of the unit structure as the x-axis and y-axis, the long side of the nanobrick as the major axis, the short side as the minor axis, and the angle between the major axis of the nanobrick and the x-axis as the turning angle θ of the nanobrick.

3. The triple optical encryption method based on metasurface materials as described in claim 1, characterized in that... Through optimized design, nanobricks can be made to have polarization-splitting properties. That is, when the incident light wave passes through the nanobrick at the working wavelength, linearly polarized light with polarization direction along the long axis of the nanobrick is reflected or transmitted, or linearly polarized light with polarization direction along the short axis of the nanobrick is reflected or transmitted.

4. The triple optical encryption method based on metasurface materials as described in claim 1, characterized in that... The first camouflage information is a uniform intensity image, the second camouflage information is a grayscale image or a binary image, and the real information is a binary image.

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