Dual-channel optical image authentication method based on polarization multiplexing metasurface

Abstract

The invention discloses a dual-channel optical image authentication method based on a polarization multiplexing metasurface, and the method comprises the steps: firstly, calculating an authentication phase of a dual-channel plaintext image through employing a sparse constraint-driven authentication holographic algorithm; the method comprises the following steps: firstly, obtaining a target transmission phase and a geometric phase of a polarization multiplexing metasurface according to a composite phase regulation and control principle, then carrying out parameter scanning on a basic unit of the nano-column metasurface, establishing a transmission and geometric phase database, and finally determining structural parameters of each nano-column pixel by pixel, thereby completing construction of the polarization multiplexing authentication metasurface. And an authentication step: firstly, respectively illuminating the metasurface by using left-handed circularly polarized light and right-handed circularly polarized light to obtain a far-field diffracted noise-like image, then calculating nonlinear correlation distribution of the diffracted image and a plaintext image of a corresponding channel, and judging an authentication result of each channel according to whether the signal-to-noise ratio of the nonlinear correlation distribution reaches the standard or not. The method provided by the invention has the advantages of large authentication capacity, high authentication efficiency and no plaintext information leakage.

Description

Technical Field

[0001] This invention relates to the field of information security technology, specifically to a dual-channel optical image authentication method based on a polarization multiplexing metasurface. Background Technology

[0002] Since the introduction of the dual-random phase coding method, information security technologies based on optical principles have attracted widespread attention from researchers. The core idea of ​​this type of technology lies in using various optical principles to encode and transform plaintext information to achieve information encryption. However, traditional optical information security systems generally rely on bulky and complex optical components such as lenses and spatial light modulators, severely limiting system integration and portability, making it difficult to develop towards miniaturization and portability. In recent years, the rapid rise of metasurface technology has opened up a new path for building flexible, efficient, lightweight, and convenient optical information security systems. As an artificial electromagnetic structure composed of subwavelength scale units, metasurfaces can precisely control the geometric parameters and arrangement of the unit structure to flexibly modulate the amplitude, phase, polarization, and other physical properties of incident light. Based on this characteristic, metasurfaces have been continuously introduced into the field of optical information security, playing a key role in improving encryption security, expanding information encoding capacity, and enhancing the integration of cryptographic systems. Current mainstream metasurface optical image encryption schemes generally employ a technique of encoding the plaintext image to be encrypted into the complex amplitude distribution of the metasurface structure, and then completing the encryption and decryption operations by controlling the physical properties of the incident or probe light. However, such schemes share a common technical problem: during the decryption process, the original plaintext information is completely and clearly restored, leading to a potential risk of plaintext information leakage during the decryption stage. To avoid this hidden danger, some researchers have proposed metasurface optical image authentication systems in recent years. Unlike metasurface optical image encryption schemes, metasurface optical image authentication systems do not require the restoration of plaintext information, eliminating the possibility of plaintext information leakage at the source. They also possess functions such as user identification and user permission determination, thus having extremely high application prospects and research value. For example, in 2017, Wang et al. pioneered an information authentication method based on all-dielectric metasurfaces. This method can achieve accurate authentication of image information without disclosing any plaintext information, effectively ensuring the confidentiality of secret information. However, this scheme does not introduce any information dimension reuse mechanism, resulting in a single authentication metasurface only being able to carry and authenticate the plaintext information of a single image. This not only causes a serious waste of the metasurface's information encoding capacity but also creates a rigid "single metasurface-single image" authentication mode, greatly restricting the capacity and efficiency of the authentication metasurface. To address the above bottleneck problem, in 2024, Xue et al. proposed a multi-image authentication method based on the superposition of mutually exclusive sparse matrices. By improving the sparse constraint coding algorithm, they successfully achieved simultaneous authentication of multiple images by a single metasurface, breaking through the limitations of the "single metasurface-single image" authentication mode. Building on this, in 2025, Zhou et al. proposed the concept of a holographic labeled metasurface by separating the mutually exclusive sparse matrices into different binary keys and combining the polarization multiplexing principle. This not only realized the "single metasurface-multiple image" authentication mode but also had the function of user identity discrimination.Subsequently, Zhou et al. further expanded the functional boundaries of this scheme by integrating steganography into a multi-image authentication system. This enabled the synchronous encoding of the secret image and the authentication image on a single polarization-reused metasurface, thereby achieving the information decryption function after successful user authentication and improving the integrated "authentication-decryption" process. It should be noted that although the above two schemes introduce a polarization multiplexing mechanism, the function of polarization multiplexing in the holographic-marked metasurface scheme and the "steganography-authentication" collaborative scheme is to increase the synchronous encoding of the holographic marker, the secret image, and the authentication image, respectively. It does not actually improve authentication capacity or efficiency. In other words, the core logic of existing schemes in expanding authentication capacity and improving authentication efficiency is still limited to algorithm optimization using mutually exclusive sparse matrices, and has not yet deeply explored the multiplexing mechanism within the physical properties of the authentication metasurface. Therefore, there is an urgent need to propose a metasurface optical image authentication method based on physical property multiplexing, which can construct multiple authentication channels by exploring the multiplexing potential of the metasurface's physical properties, thereby achieving a dual improvement in authentication capacity and efficiency. Based on this, the present invention proposes a dual-channel optical image authentication method based on a polarization multiplexing metasurface, which aims to add polarization characteristic channels to the authentication metasurface to improve the capacity and efficiency of the authentication metasurface. Summary of the Invention

[0003] The purpose of this invention is to provide a dual-channel optical image authentication method based on a polarization-multiplexed metasurface. This invention first utilizes the Sparse Constraint-Driven Authentication Holography (SCDAH) algorithm to calculate the dual-channel authentication phase of two plaintext images. Then, based on the principle of composite phase modulation, it obtains the target transmission phase and geometric phase of the polarization-multiplexed metasurface. Finally, combining the parameter scanning result library of the basic unit of the nanopillar metasurface, it determines the structural parameters of each nanopillar pixel by pixel, thereby forming the authentication metasurface. The constructed polarization-multiplexed authentication metasurface can reconstruct noise-like images that can successfully authenticate with two plaintext images under independent illumination of left-handed and right-handed circularly polarized light. This invention improves the reuse capability of traditional authentication metasurfaces from the perspective of physical properties, realizing a highly efficient "single metasurface-dual-image" authentication mode, with advantages such as large authentication capacity, high authentication efficiency, and no plaintext information leakage.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution: an optical image authentication method based on a polarization multiplexing metasurface, characterized in that it includes an encryption step:

[0005] S1: Dual-channel authentication phase calculation based on SCDASH algorithm: The SCDASH algorithm is used to calculate the dual-channel plaintext image (left-hand circular polarization channel plaintext image). Plaintext image of a right-hand circularly polarized channel The authentication phase is calculated, and the specific calculation process is as follows:

[0006] plain text images For example: First, set a... A matrix with identical pixel values ​​and all elements equal to 1 is used as the initial amplitude. Subsequently, regarding and Perform a Double Random Phase Encoding (DRPE) operation once, then extract... Amplitude after DRPE operation and Phase after DRPE operation And combine the two into a new complex amplitude. After that, regarding Perform a Double Random Phase Code-Decode (DRPD) operation, then extract... The amplitude after DRPD operation is used as the decoded image. ,Right now:

[0007] (1)

[0008] in, , , , These represent the double random phase encoding, double random phase decoding, amplitude extraction, and phase extraction operations, respectively.

[0009] Next, the decoded image is calculated. With plain text images Correlation coefficient between If the correlation coefficient The preset threshold was not reached. Then use the decoded image For the initial amplitude Update the formula and then execute formula (1) again; if the correlation coefficient... Exceeding the preset threshold Then output the values ​​in this iteration. and ,Right now Subsequently, sparse matrices were used. For the output Sparse constraint processing is performed to obtain sparse complex amplitudes, and then a DRPD operation is performed on the sparse complex amplitudes to obtain the certified amplitudes. ,Right now:

[0010] (2)

[0011] After that, As the target amplitude, the GS algorithm in the Fourier domain is used to iteratively calculate the phase hologram corresponding to the target amplitude, and the holographic reconstructed image and the target amplitude are selected. Correlation coefficient between As an evaluation function, and set The preset threshold is Ultimately, the phase distribution output of this hologram is used as the authentication phase for the left-hand circular polarization channel. .

[0012] Similarly, follow the steps described above for the plaintext image of the right-hand circular polarization channel. The certified phase is also calculated to obtain the certified phase of the right-hand circular polarization channel. Next, perform encryption step S2.

[0013] S2: Transmission and Geometric Phase Calculation Based on Composite Phase Modulation: Based on the principle of composite phase modulation, according to the dual-channel authentication phase calculated in encryption step S1 ( and The target transmission phase of the polarization multiplexing metasurface to be designed can be calculated. and geometric phase They are respectively:

[0014] (3)

[0015] Next, perform encryption step S3.

[0016] S3: Metasurface Unit Structure Design and Parameter Scanning: Set the operating wavelength and material selection of the metasurface unit, establish the three-dimensional nanopillar geometry of the metasurface unit, and use electromagnetic simulation software to perform parameter scanning on the nanopillar with a fixed height to obtain the transmission phase modulation amount under different nanopillar lengths and widths, as well as the geometric phase modulation amount under different nanopillar rotation angles, which are respectively recorded as the transmission phase database and the geometric phase database.

[0017] S4: Construction of the polarization multiplexing authentication metasurface: In the transmission phase database obtained in encryption step S3, a search algorithm is used to search for the target transmission phase obtained in encryption step S2 pixel by pixel. Corresponding nanopillar length and nanopillar width In the geometric phase database obtained in encryption step S3, a search algorithm is used to search for the target geometric phase obtained in encryption step S2 pixel by pixel. Corresponding nanopillar rotation angle After traversing all pixels, the metasurface unit structure parameters corresponding to each pixel are obtained, thereby completing the construction of the polarization multiplexing certified metasurface PMAM.

[0018] This completes the encryption process.

[0019] Authentication steps:

[0020] J1: Diffraction of the Authentication Metasurface under Polarized Illumination: The authentication metasurface PMAM is illuminated with collimated right-handed circularly polarized light. After phase modulation by the PMAM, the light wave begins to diffract forward. The background component (right-handed circularly polarized component) in the diffracted light is filtered out, and the amplitude information of the left-handed circularly polarized component is obtained at the far field, denoted as the left-handed circularly polarized channel diffraction image. The authentication metasurface PMAM is illuminated using collimated left-handed circularly polarized light. After phase modulation by the PMAM, the light wave begins to diffract forward. The background component (right-handed circularly polarized component) in the diffracted light is filtered out, and the amplitude information of the right-handed circularly polarized component is obtained at the far field, denoted as the right-handed circularly polarized channel diffraction image. Next, perform authentication step J2.

[0021] J2: Nonlinear Correlation Authentication of Polarization Channel-Dependent Diffraction Images: Calculating Left-Handed Circular Polarization Channel Diffraction Images Using a Nonlinear Correlation Algorithm Plaintext images of left-hand circular polarization channels Nonlinear correlation distribution And calculate its signal-to-noise ratio. The diffraction image of the right-hand circular polarization channel was calculated using a nonlinear correlation algorithm. Plaintext image of right-hand circular polarization channel Nonlinear correlation distribution And calculate its signal-to-noise ratio. .when Greater than the preset threshold When the signal is 1, it indicates successful authentication of the left-hand circular polarization channel; otherwise, it indicates failed authentication. Greater than the preset threshold When the signal is 1, it indicates successful authentication of the right-hand circular polarization channel; otherwise, it indicates failed authentication of the left-hand circular polarization channel. and Each greater than a preset threshold and When this time is reached, it indicates that dual-channel authentication has been successfully completed.

[0022] This completes the authentication process.

[0023] In the above-mentioned dual-channel optical image authentication method based on polarization multiplexing metasurface, in the encryption step S1, the DRPE operation can select any one of the Fourier domain, Fresnel domain, or fractional Fourier domain as the operation domain.

[0024] In the above-mentioned dual-channel optical image authentication method based on polarization multiplexing metasurface, in the encryption step S1, the built-in parameters used in the DRPD operation are exactly the same as those used in the DRPE operation, and the random phase used in the DRPD operation is conjugate to the random phase used in the DRPE operation.

[0025] The aforementioned dual-channel optical image authentication method based on a polarization-multiplexed metasurface, wherein the authentication step J1 can be completed either digitally or optically, and when completed optically, the accompanying device is a metasurface diffraction imaging device based on polarization illumination, including a laser 1, and a half-wave plate 2, a quarter-wave plate 3, a converging lens 4, a pinhole 5, a microscope objective 6, an authentication metasurface 7, a quarter-wave plate 8, a polarizer 9, a Fourier transform lens 10, and an image sensor 11 arranged sequentially along the optical axis. The characteristic feature is that the metasurface diffraction imaging device operates under two independent illumination modes: left-handed circularly polarized light and right-handed circularly polarized light; the half-wave plate 2 and... The polarization modulation module composed of quarter-wave plate 3 is used to adjust the polarization state of the illumination light; the beam-shrinking collimation module composed of convex lens 4, pinhole 5 and microscope objective 6 is used to reduce, filter and collimate the illumination light, wherein pinhole 5 is placed on the image-side focal point of converging lens 4 and the image-side focal point of converging lens 4 coincides with the focal point of microscope objective 6; the polarization filtering module composed of quarter-wave plate 8 and polarizer 9 is used to filter out the background component in the diffracted light; the focal length of Fourier transform lens 10 is the same as the distance from Fourier transform lens 10 to image sensor 11; the image sensor 11 is a charge-coupled device (CCD) or complementary metal-oxide-semiconductor (CMOS).

[0026] The beneficial effects of this invention are as follows: (1) This invention constructs a dual-channel authentication system through polarization multiplexing mechanism, and embeds two plaintext images into the left-hand circular polarization channel and the right-hand circular polarization channel respectively, breaking through the rigid authentication limitation of the traditional "single metasurface-single image", and significantly improving the information encoding capacity of the metasurface and the overall efficiency of image authentication; (2) This invention effectively realizes the dual-channel optical image authentication technology driven by polarization multiplexing. By exploring the reuse potential of the physical properties of the metasurface, it forms a complementary and synergistic technical path with traditional algorithm optimization (such as mutually exclusive sparse matrices). The two are not substitutes, but form a dual gain mechanism of "physical multiplexing-algorithm optimization" to further break through the upper limit of authentication capacity and efficiency; (3) This invention relies on the logic of independent encoding of dual-channel polarization states. The plaintext information of different polarization channels is isolated from each other. Even if an attacker obtains the reconstructed image under a single polarization state, he still cannot crack the plaintext information across channels. It constructs a dual protection barrier and significantly improves the anti-attack capability of the authentication system; (4) The authentication process of this invention is simple and efficient, and can be easily implemented through digital or optical methods. Moreover, the entire authentication process does not require the restoration of any information from the original plaintext image, thus eliminating the risk of plaintext leakage at the source. It has both high information confidentiality and concealment, and can adapt to information security authentication needs in multiple scenarios. Attached Figure Description

[0027] Figure 1 This is a flowchart of the encryption steps in a dual-channel optical image authentication method based on a polarization multiplexing metasurface.

[0028] Figure 2 To aid in describing the encryption steps, a flowchart is provided, where DRPE, DRPD, AU, and CAS represent double random phase encoding, double random phase decoding, amplitude update, and complex amplitude synthesis, respectively; GS represents the GS algorithm in the Fourier domain; CPM represents composite phase modulation; and PMMU and PMAM represent polarization multiplexing metasurface unit and polarization multiplexing authentication metasurface, respectively.

[0029] Figure 3 This is a flowchart of the authentication steps in a dual-channel optical image authentication method based on a polarization multiplexing metasurface.

[0030] Figure 4 The flowchart used to illustrate the authentication process is as follows: 1 represents the laser, 2 represents the half-wave plate, 3 represents the quarter-wave plate, 4 represents the converging lens, 5 represents the pinhole, 6 represents the microscope objective, 7 represents the authentication metasurface, 8 represents the quarter-wave plate, 9 represents the polarizer, 10 represents the Fourier transform lens, and 11 represents the image sensor; NCC represents the nonlinear correlation algorithm.

[0031] Figure 5 (a) is a plaintext image of the left-hand circular polarization channel. (b) is a plaintext image of the right-hand circular polarization channel (“Surveillance”). ("Aerial"); (c) is a sparse matrix , (d) is a sparse matrix (e) represents the sparse amplitude. (f) represents the sparse amplitude. (g) is the certified phase of the left-hand circular polarization channel. (h) represents the certified phase of the right-hand circular polarization channel. (i) represents the target transmission phase of the polarization multiplexing metasurface. , (j) represents the target geometric phase of the polarization multiplexing metasurface. .

[0032] Figure 6 (a) is the metasurface unit model; (b) is the transport phase database; (c) is the geometric phase database; (d) is the nanopillar length distribution of the certified metasurface; (e) is the nanopillar width distribution of the certified metasurface; (f) is the nanopillar rotation angle distribution of the certified metasurface; (g) is the polarization multiplexing certified metasurface PMAM.

[0033] Figure 7 (a) is the diffraction image of the left-hand circular polarization channel. (b) is the diffraction image of the right-hand circular polarization channel. (c) represents the nonlinear correlation distribution. (d) represents the nonlinear correlation distribution. (e) is the certified phase of the left-hand circular polarization channel. The test phase, (f) is the authentication phase of the right-hand circular polarization channel. The test phase, (g) is the polarization multiplexing certified metasurface PMAMR, and (h) is the diffraction image of the left-hand circular polarization channel. (i) is the diffraction image of the right-hand circular polarization channel. , (j) is a nonlinear correlation distribution ,(k) is a nonlinear correlation distribution (l) is a grayscale image ("Mandrill") that differs from the dual-channel plaintext image ("Surveillance", "Aerial"), and (m) is a nonlinear correlation distribution. , (n) is a nonlinear correlation distribution . Detailed Implementation

[0034] The present invention will be further described below with reference to the embodiments and accompanying drawings, but this should not be construed as limiting the present invention.

[0035] Example: An optical image authentication method based on a polarization multiplexing metasurface, including as follows Figure 1 The encryption steps shown are appended to aid in the description of the encryption steps. Figure 2 (Flowchart shown)

[0036] S1: Dual-channel authentication phase calculation based on SCDASH algorithm: The SCDASH algorithm is used to calculate the dual-channel plaintext image (left-hand circular polarization channel plaintext image). Plaintext image of a right-hand circularly polarized channel The authentication phase is calculated, and the specific calculation process is as follows:

[0037] plain text images For example: First, set a... A matrix with identical pixel values ​​and all elements equal to 1 is used as the initial amplitude. Subsequently, regarding and Perform the DRPE operation once each, then extract. Amplitude after DRPE operation and Phase after DRPE operation And combine the two into a new complex amplitude. After that, regarding Perform a DRPD operation once, then extract. The amplitude after DRPD operation is used as the decoded image. ,Right now:

[0038] (1)

[0039] in, , , , These represent the double random phase encoding, double random phase decoding, amplitude extraction, and phase extraction operations, respectively.

[0040] Next, the decoded image is calculated. With plain text images Correlation coefficient between If the correlation coefficient The preset threshold was not reached. Then use the decoded image For the initial amplitude Update the formula and then execute formula (1) again; if the correlation coefficient... Exceeding the preset threshold Then output the values ​​in this iteration. and ,Right now Subsequently, sparse matrices were used. For the output Sparse constraint processing is performed to obtain sparse complex amplitudes, and then a DRPD operation is performed on the sparse complex amplitudes to obtain the certified amplitudes. ,Right now:

[0041] (2)

[0042] After that, As the target amplitude, the GS algorithm in the Fourier domain is used to iteratively calculate the phase hologram corresponding to the target amplitude, and the holographic reconstructed image and the target amplitude are selected. Correlation coefficient between As an evaluation function, and set The preset threshold is Ultimately, the phase distribution output of this hologram is used as the authentication phase for the left-hand circular polarization channel. .

[0043] Similarly, follow the steps described above for the plaintext image of the right-hand circular polarization channel. The certified phase is also calculated to obtain the certified phase of the right-hand circular polarization channel. Next, perform encryption step S2.

[0044] S2: Transmission and Geometric Phase Calculation Based on Composite Phase Modulation: Based on the principle of composite phase modulation, according to the dual-channel authentication phase calculated in encryption step S1 ( and The target transmission phase of the polarization multiplexing metasurface to be designed can be calculated. and geometric phase They are respectively:

[0045] (3)

[0046] Next, perform encryption step S3.

[0047] S3: Metasurface Unit Structure Design and Parameter Scanning: Set the operating wavelength and material selection of the metasurface unit, establish the three-dimensional nanopillar geometry of the metasurface unit, and use electromagnetic simulation software to perform parameter scanning on the nanopillar with a fixed height to obtain the transmission phase modulation amount under different nanopillar lengths and widths, as well as the geometric phase modulation amount under different nanopillar rotation angles, which are respectively recorded as the transmission phase database and the geometric phase database.

[0048] S4: Construction of the polarization multiplexing authentication metasurface: In the transmission phase database obtained in encryption step S3, a search algorithm is used to search for the target transmission phase obtained in encryption step S2 pixel by pixel. Corresponding nanopillar length and nanopillar width In the geometric phase database obtained in encryption step S3, a search algorithm is used to search for the target geometric phase obtained in encryption step S2 pixel by pixel. Corresponding nanopillar rotation angle After traversing all pixels, the metasurface unit structure parameters corresponding to each pixel are obtained, thereby completing the construction of the polarization multiplexing certified metasurface PMAM.

[0049] This completes the encryption process.

[0050] like Figure 3 The authentication steps shown are as follows:

[0051] J1: Diffraction of the Authentication Metasurface under Polarized Illumination: The authentication metasurface PMAM is illuminated with collimated right-handed circularly polarized light. After phase modulation by the PMAM, the light wave begins to diffract forward. The background component (right-handed circularly polarized component) in the diffracted light is filtered out, and the amplitude information of the left-handed circularly polarized component is obtained at the far field, denoted as the left-handed circularly polarized channel diffraction image. The authentication metasurface PMAM is illuminated using collimated left-handed circularly polarized light. After phase modulation by the PMAM, the light wave begins to diffract forward. The background component (right-handed circularly polarized component) in the diffracted light is filtered out, and the amplitude information of the right-handed circularly polarized component is obtained at the far field, denoted as the right-handed circularly polarized channel diffraction image. Next, perform authentication step J2.

[0052] J2: Nonlinear Correlation Authentication of Polarization Channel-Dependent Diffraction Images: Calculating Left-Handed Circular Polarization Channel Diffraction Images Using a Nonlinear Correlation Algorithm Plaintext images of left-hand circular polarization channels Nonlinear correlation distribution And calculate its signal-to-noise ratio. The diffraction image of the right-hand circular polarization channel was calculated using a nonlinear correlation algorithm. Plaintext image of right-hand circular polarization channel Nonlinear correlation distribution And calculate its signal-to-noise ratio. .when Greater than the preset threshold When the signal is 1, it indicates successful authentication of the left-hand circular polarization channel; otherwise, it indicates failed authentication. Greater than the preset threshold When the signal is 1, it indicates successful authentication of the right-hand circular polarization channel; otherwise, it indicates failed authentication of the left-hand circular polarization channel. and Each greater than a preset threshold and When this time is reached, it indicates that dual-channel authentication has been successfully completed.

[0053] This completes the authentication process. Authentication step J1 can be performed digitally or optically. The optical method that can be used for authentication step J1 is described below, requiring the use of the polarized illumination-based metasurface diffraction imaging device provided in this invention, such as... Figure 4 As shown, the device includes a laser 1, and a half-wave plate 2, a quarter-wave plate 3, a converging lens 4, a pinhole 5, a microscope objective 6, a metasurface 7, a quarter-wave plate 8, a polarizer 9, a Fourier transform lens 10, and an image sensor 11 arranged sequentially along the optical axis. Its features include: the metasurface diffraction imaging device operates under two independent illumination modes: left-handed circularly polarized light and right-handed circularly polarized light; the polarization modulation module composed of the half-wave plate 2 and the quarter-wave plate 3 is used to adjust the polarization state of the illumination light; and the convex lens 4, the pinhole 5, and the microscope objective... The beam-shrinking and collimating module consisting of 6 is used to reduce, filter, and collimate the illumination light. The pinhole 5 is placed on the image-side focal point of the converging lens 4, and the image-side focal point of the converging lens 4 coincides with the focal point of the microscope objective 6. The polarization filtering module consisting of the quarter-wave plate 8 and the polarizer 9 is used to filter out the background component in the diffracted light. The focal length of the Fourier transform lens 10 is the same as the distance from the Fourier transform lens 10 to the image sensor 11. The image sensor 11 is a charge-coupled device (CCD) or a complementary metal-oxide-semiconductor (CMOS).

[0054] The specific diffraction imaging process is as follows: (1) Left-hand circularly polarized light illumination mode: The linearly polarized light emitted from the laser 1 is incident perpendicularly onto the half-wave plate 2 and the quarter-wave plate 3 in sequence. By rotating the half-wave plate 2, the angle between the linear polarization direction emitted from the half-wave plate 2 and the slow axis direction of the quarter-wave plate 3 is 45°. At this time, the light emitted from the quarter-wave plate 3 is left-hand circularly polarized light. After passing through the beam-shrinking collimation system composed of the convex lens 4, the pinhole 5 and the microscope objective 6, it forms collimated left-hand circularly polarized light and is incident perpendicularly onto the authentication metasurface 7. After that, it passes through the beam-shrinking collimation system composed of the convex lens 4, the pinhole 5 and the microscope objective 6. The light wave, after being phase-modulated by the certified metasurface 7, begins to diffract forward, passing sequentially through a quarter-wave plate 8 and a polarizer 9. By rotating the polarizer 2, the angle between the linear polarization direction of the polarizer 2 and the fast axis direction of the quarter-wave plate 8 is 45°. At this point, the background component (left-hand circularly polarized component) in the diffracted light is filtered out. The diffracted light then passes through the Fourier transform lens 10 and reaches the image sensor 11. This completes the certified metasurface diffraction under left-hand circularly polarized light illumination. The image recorded on the image sensor 11 at this point is the right-hand circularly polarized channel. Diffraction image; (2) Right-hand circularly polarized illumination mode: Linearly polarized light emitted from laser 1 is incident perpendicularly onto half-wave plate 2 and quarter-wave plate 3 in sequence. By rotating half-wave plate 2, the angle between the linear polarization direction emitted from half-wave plate 2 and the fast axis direction of quarter-wave plate 3 is 45°. At this time, the light emitted from quarter-wave plate 3 is right-hand circularly polarized light. After passing through the beam-shrinking collimation system composed of convex lens 4, pinhole 5 and microscope objective 6, it forms collimated right-hand circularly polarized light and is incident perpendicularly onto the certification metasurface 7. After passing through the certification metasurface... The phase-modulated light wave from surface 7 begins to diffract forward, passing sequentially through a quarter-wave plate 8 and a polarizer 9. By rotating polarizer 2, the angle between the linear polarization direction of polarizer 2 and the slow axis direction of quarter-wave plate 8 is 45°. At this point, the background component (left-hand circular polarization component) in the diffracted light is filtered out. Then, the diffracted light passes through Fourier transform lens 10 and reaches image sensor 11. This completes the authentication metasurface diffraction under right-hand circular polarization illumination. The image recorded on image sensor 11 at this point is the diffraction image of the left-hand circular polarization channel.

[0055] The invention will be further explained below with reference to specific embodiments and accompanying drawings.

[0056] First, two grayscale images (“Surveillance” and “Aerial”) are selected as plaintext images for the left-hand circular polarization channel. Plaintext image of right-hand circular polarization channel , respectively Figure 5 As shown in (a) and (b). Subsequently, two sparse matrices with a sparsity of 20% are randomly generated and used as... and , respectively Figure 5 As shown in (c) and (d). Furthermore, the wavelength of the light wave used for encryption is set. for , preset threshold and preset threshold All , preset threshold and preset threshold All After the encryption step S1, two authentication amplitudes are obtained. and , respectively Figure 5 As shown in (e) and (f); and the certified phase of the left-hand circular polarization channel. And the certified phase of the right-hand circular polarization channel , respectively Figure 5 As shown in (g) and (h). Subsequently, based on the principle of composite phase modulation, the target transmission phase of the polarization multiplexing metasurface to be designed was calculated. and geometric phase , respectively Figure 5 As shown in (i) and (j).

[0057] Subsequently, a metasurface unit model of a silica (SiO2) substrate combined with rectangular silicon (Si) nanopillars was designed, and a model was established as follows: Figure 6 (a) shows the three-dimensional geometric structure, and the period of the metasurface unit is set. for The height of Si nanopillars for Subsequently, electromagnetic simulation software was used to determine the length of the Si nanopillars. and width Perform parameter scanning to obtain different nanopillar lengths and nanopillar width The transmission phase modulation amount under the following conditions, where the length and width The scanning ranges are respectively set to and The final transmission phase database is as follows Figure 6 As shown in (b); the rotation angle of the Si nanopillars was determined using electromagnetic simulation software. Perform parameter scanning to obtain different rotation angles of the nanopillars. The geometric phase modulation amount, where the rotation angle is below The scan range is set to The final geometric phase database is as follows: Figure 6 As shown in (c). Then, a search algorithm is used in... Figure 6 (b) shows a pixel-by-pixel search in the transmission phase database. Figure 5 The target transmission phase shown in (i) Corresponding nanopillar length and nanopillar width After traversing all pixels, the length distribution and width distribution of the nanopillars of the certified metasurface are obtained, as shown below. Figure 6 As shown in (d) and (e); using search algorithms in, as Figure 6 (c) shows a pixel-by-pixel search in the geometric phase database. Figure 5 The target geometric phase shown in (j) Corresponding nanopillar rotation angle After traversing all pixels, the rotation angle distribution of the nanopillars of the certified metasurface is obtained, such as... Figure 6 As shown in (f). According to... Figure 6 The data distributions shown in (d)-(f) can determine the metasurface unit structure parameters corresponding to each pixel, thereby completing the construction of the polarization multiplexing certified metasurface PMAM, as follows. Figure 6 As shown in (g). This completes the encryption process.

[0058] Next, use as follows Figure 6 (g) shows the initial certification steps for the polarization-multiplexed certified metasurface PMAM. First, a left-handed circular polarization channel diffraction image is generated after certification step J1. and right-hand circular polarization channel diffraction image , respectively Figure 7 As shown in (a) and (b). Subsequently, a nonlinear correlation algorithm was used to calculate... and Nonlinear correlation distribution as well as and Nonlinear correlation distribution , respectively Figure 7 As shown in (c) and (d). Then, calculate... signal-to-noise ratio The value is 5.76, which is greater than the preset threshold. =3, signal-to-noise ratio The value is 6.05, which is greater than the preset threshold. =3 indicates that the polarization multiplexing metasurface PMAM can successfully authenticate with a plaintext image under two different polarization illuminations, representing successful dual-channel authentication. Additionally, two randomly generated phases are used as authentication phases for the left-hand circular polarization channel. And the certified phase of the right-hand circular polarization channel The test phases are as follows: Figure 7 As shown in (e) and (f), another polarization-multiplexed certified metasurface, PMAMR, is constructed after encryption steps S2-S4, as follows. Figure 7As shown in (g). After authentication step J1, the left-hand circular polarization channel diffraction image corresponding to PMAMR is generated. and right-hand circular polarization channel diffraction image , respectively Figure 7 As shown in (h) and (i). Subsequently, a nonlinear correlation algorithm is used to calculate... and Nonlinear correlation distribution as well as and Nonlinear correlation distribution , respectively Figure 7 As shown in (j) and (k). Then, calculate... signal-to-noise ratio and signal-to-noise ratio The values ​​are 1.35 and 1.57 respectively, both less than the preset thresholds. and This indicates that the polarization-multiplexed metasurface PMAMR cannot be successfully authenticated with any plaintext image, thus proving the authentication validity of the polarization-multiplexed metasurface PMAM. Next, an arbitrary grayscale image ("Mandrill") different from the dual-channel plaintext image ("Surveillance", "Aerial") is selected, such as... Figure 7 As shown in (l). Subsequently, a nonlinear correlation algorithm was used to calculate... Nonlinear correlation distribution with grayscale image (“Mandrill”) as well as Nonlinear correlation distribution with grayscale image (“Mandrill”) , respectively Figure 7 As shown in (m) and (n). Then, calculate... signal-to-noise ratio and The signal-to-noise ratios were 1.43 and 1.75, respectively, both less than the preset threshold. and The fact that the polarization multiplexed metasurface PMAM, which was successfully authenticated with the dual-channel plaintext image (“Surveillance”, “Aerial”), failed to be authenticated with other grayscale images (“Mandrill”) demonstrates the accuracy of the authentication of the polarization multiplexed metasurface PMAM.

[0059] In summary, this invention discloses a dual-channel optical image authentication method based on a polarization-multiplexed metasurface. In this invention, the encryption process first uses the SCDAH algorithm to calculate the authentication phase of the dual-channel plaintext image. Then, based on the principle of composite phase modulation, the target transmission phase and geometric phase of the polarization-multiplexed metasurface are obtained. Next, combined with the transmission and geometric phase database obtained by scanning the basic unit parameters of the nanopillar metasurface, the structural parameters of each nanopillar are determined pixel-by-pixel to form the authentication metasurface. The authentication process first obtains a noise-like image generated by far-field diffraction of this metasurface under independent illumination of left-handed and right-handed circularly polarized light. Then, nonlinear correlation authentication is performed on the dual-channel diffraction image, achieving a highly efficient "single metasurface-dual image" authentication mode. This invention constructs a dual-channel authentication system through polarization multiplexing, breaking through the rigid authentication limitations of the traditional "single metasurface-single image" approach. It improves the capacity and efficiency limits of the authentication metasurface from the perspective of physical properties, forming a high-capacity authentication mechanism that complements and synergizes with algorithm optimization. In addition, the dual-channel information is isolated from each other, forming a double protection barrier. At the same time, the authentication process eliminates the risk of plaintext leakage, thus possessing both high confidentiality and concealment to adapt to information security authentication needs in multiple scenarios.

Claims

1. A dual-channel optical image authentication method based on a polarization multiplexing metasurface, characterized in that: Including encryption steps: S1: Dual-channel authentication phase calculation based on SCDASH algorithm: The SCDASH algorithm is used to calculate the dual-channel plaintext image (left-hand circular polarization channel plaintext image). Plaintext image of a right-hand circularly polarized channel The authentication phase is calculated, and the specific calculation process is as follows: plain text images For example: First, set a... A matrix with identical pixel values ​​and all elements equal to 1 is used as the initial amplitude. Subsequently, regarding and Perform a Double Random Phase Encoding (DRPE) operation once, then extract... Amplitude after DRPE operation and Phase after DRPE operation And combine the two into a new complex amplitude. After that, regarding Perform a Double Random Phase Code-Decode (DRPD) operation, then extract... The amplitude after DRPD operation is used as the decoded image. ,Right now: (1) in, , , , These represent the double random phase encoding, double random phase decoding, amplitude extraction, and phase extraction operations, respectively. Next, the decoded image is calculated. With plain text images Correlation coefficient between If the correlation coefficient The preset threshold was not reached. Then use the decoded image For the initial amplitude Update the formula and then execute formula (1) again; if the correlation coefficient... Exceeding the preset threshold Then output the values ​​in this iteration. and ,Right now Subsequently, sparse matrices were used. For the output Sparse constraint processing is performed to obtain sparse complex amplitudes, and then a DRPD operation is performed on the sparse complex amplitudes to obtain the certified amplitudes. ,Right now: (2) After that, As the target amplitude, the GS algorithm in the Fourier domain is used to iteratively calculate the phase hologram corresponding to the target amplitude, and the holographic reconstructed image and the target amplitude are selected. Correlation coefficient between As an evaluation function, and set The preset threshold is Ultimately, the phase distribution output of this hologram is used as the authentication phase for the left-hand circular polarization channel. ; Similarly, follow the steps described above for the plaintext image of the right-hand circular polarization channel. The certified phase is also calculated to obtain the certified phase of the right-hand circular polarization channel. Then, perform encryption step S2; S2: Transmission and Geometric Phase Calculation Based on Composite Phase Modulation: Based on the principle of composite phase modulation, according to the dual-channel authentication phase calculated in encryption step S1 ( and The target transmission phase of the polarization multiplexing metasurface to be designed can be calculated. and geometric phase They are respectively: (3) Next, perform encryption step S3; S3: Metasurface Unit Structure Design and Parameter Scanning: Set the working wavelength and material selection of the metasurface unit, establish the three-dimensional nanopillar geometry of the metasurface unit, and use electromagnetic simulation software to perform parameter scanning on the nanopillar with a fixed height to obtain the transmission phase modulation amount under different nanopillar lengths and widths and the geometric phase modulation amount under different nanopillar rotation angles, which are respectively recorded as the transmission phase database and the geometric phase database. S4: Construction of the polarization multiplexing authentication metasurface: In the transmission phase database obtained in encryption step S3, a search algorithm is used to search for the target transmission phase obtained in encryption step S2 pixel by pixel. Corresponding nanopillar length and nanopillar width In the geometric phase database obtained in encryption step S3, a search algorithm is used to search for the target geometric phase obtained in encryption step S2 pixel by pixel. Corresponding nanopillar rotation angle After traversing all pixels, the metasurface unit structure parameters corresponding to each pixel are obtained, thereby completing the construction of the polarization multiplexing certified metasurface PMAM. This completes the encryption process; Authentication steps: J1: Diffraction of the Authentication Metasurface under Polarized Illumination: The authentication metasurface PMAM is illuminated with collimated right-handed circularly polarized light. After phase modulation by the PMAM, the light wave begins to diffract forward. The background component (right-handed circularly polarized component) in the diffracted light is filtered out, and the amplitude information of the left-handed circularly polarized component is obtained at the far field, denoted as the left-handed circularly polarized channel diffraction image. The authentication metasurface PMAM is illuminated using collimated left-handed circularly polarized light. After phase modulation by the PMAM, the light wave begins to diffract forward. The background component (right-handed circularly polarized component) in the diffracted light is filtered out, and the amplitude information of the right-handed circularly polarized component is obtained at the far field, denoted as the right-handed circularly polarized channel diffraction image. Next, perform authentication step J2; J2: Nonlinear Correlation Authentication of Polarization Channel-Dependent Diffraction Images: Calculating Left-Handed Circular Polarization Channel Diffraction Images Using a Nonlinear Correlation Algorithm Plaintext images of left-hand circular polarization channels Nonlinear correlation distribution And calculate its signal-to-noise ratio. The diffraction image of the right-hand circular polarization channel was calculated using a nonlinear correlation algorithm. Plaintext image of right-hand circular polarization channel Nonlinear correlation distribution And calculate its signal-to-noise ratio. .when Greater than the preset threshold When the signal is 1, it indicates successful authentication of the left-hand circular polarization channel; otherwise, it indicates failed authentication. Greater than the preset threshold When the signal is 1, it indicates successful authentication of the right-hand circular polarization channel; otherwise, it indicates failed authentication of the left-hand circular polarization channel. and All are greater than the preset threshold and When this time is reached, it indicates that dual-channel authentication has been successfully completed; This completes the authentication process.

2. The dual-channel optical image authentication method based on a polarization multiplexing metasurface according to claim 1, characterized in that: In the encryption step S1, the DRPE operation can select any one of the transform domains—Fourier domain, Fresnel domain, or fractional Fourier domain—as the operation domain.

3. The dual-channel optical image authentication method based on a polarization multiplexing metasurface according to claim 1, characterized in that: In the encryption step S1, the built-in parameters used in the DRPD operation are exactly the same as those used in the DRPE operation, and the random phase used in the DRPD operation is conjugate to the random phase used in the DRPE operation.

4. The dual-channel optical image authentication method based on a polarization multiplexing metasurface according to claim 1, characterized in that: The authentication step J1 can be completed either digitally or optically. When the optical method is used, the device used is a metasurface diffraction imaging device based on polarized illumination, including a laser 1, and a half-wave plate 2, a quarter-wave plate 3, a converging lens 4, a pinhole 5, a microscope objective 6, an authentication metasurface 7, a quarter-wave plate 8, a polarizer 9, a Fourier transform lens 10, and an image sensor 11 arranged sequentially along the optical axis.

5. A dual-channel optical image authentication method based on a polarization multiplexing metasurface according to claims 1 and 4, characterized in that: The metasurface diffraction imaging device operates under two independent illumination modes: left-handed circularly polarized light and right-handed circularly polarized light.

6. A dual-channel optical image authentication method based on a polarization multiplexing metasurface according to claims 1 and 4, characterized in that: In the metasurface diffraction imaging device, the polarization modulation module composed of half-wave plate 2 and quarter-wave plate 3 is used to adjust the polarization state of the illumination light.

7. A dual-channel optical image authentication method based on a polarization multiplexing metasurface according to claims 1 and 4, characterized in that: In the metasurface diffraction imaging device, the beam-shrinking collimation module composed of the convex lens 4, the pinhole 5, and the microscope objective 6 is used to reduce, filter, and collimate the illumination light. The pinhole 5 is placed on the image-side focal point of the converging lens 4, and the image-side focal point of the converging lens 4 coincides with the focal point of the microscope objective 6.

8. A dual-channel optical image authentication method based on a polarization multiplexing metasurface according to claims 1 and 4, characterized in that: In the metasurface diffraction imaging device, the polarization filtering module, composed of a quarter-wave plate 8 and a polarizer 9, is used to filter out the background component in the diffracted light.

9. A dual-channel optical image authentication method based on a polarization multiplexing metasurface according to claims 1 and 4, characterized in that: In the metasurface diffraction imaging device, the focal length of the Fourier transform lens 10 is the same as the distance from the Fourier transform lens 10 to the image sensor 11.

10. A dual-channel optical image authentication method based on a polarization multiplexing metasurface according to claims 1 and 4, characterized in that: In the metasurface diffraction imaging device, the image sensor 11 is a charge-coupled device (CCD) or a complementary metal-oxide-semiconductor (CMOS).

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