High-safety optical information encryption method based on grafting type vector vortex light beam

Abstract

The invention discloses a high-safety optical information encryption method based on a grafting type vector vortex beam. The high-safety optical information encryption method comprises the following steps: firstly, obtaining a single-wavelength grafting type perfect vector vortex beam (GPVVB) based on spin multiplexing and a topological charge grafting method; the multi-wavelength dispersion control and spatial multiplexing technology of the metasurface is further combined, different colors and spatial positions are customized for the generated GPVVB, and the GPVVB carrying various wavelength information and topological charges at any spatial position and the ultra-capacity high-safety optical information encryption application are achieved by optimizing the metasurface size, the unit structure and the design of the GPVVB. According to the invention, control on multiple aspects of light field phase, polarization, wavelength, topological charge and the like can be realized at the same time, the number and flexibility of wavelength and topological charge control are remarkably improved, more degrees of freedom are provided for information bearing, and the method has remarkable advantages in the aspect of improving information encryption capacity and security.

Description

Technical Field

[0001] This invention belongs to the field of micro-nano optics technology, specifically relating to a high-security optical information encryption method based on grafted vector vortex beams. Background Technology

[0002] In recent years, metasurfaces composed of subwavelength structure arrays have demonstrated remarkable capabilities in modulating the phase, wavelength, polarization, and amplitude of light, showing great potential in fields such as superlenses, holographic imaging, and vortex beam generation. They provide a novel platform for multi-dimensional optical field manipulation and multi-channel information multiplexing, attracting significant attention from researchers both domestically and internationally. The information capacity of a metasurface is directly related to the number of its channels, and orbital angular momentum (OAM) is considered the final dimension of optical field manipulation. Due to its infinite number of spiral modes and the orthogonality between modes, it brings new opportunities for research in ultra-high capacity information optics. In recent years, researchers have successfully fabricated various vortex beams (VBs) carrying different OAM information using highly integrated metasurfaces, covering types such as vector vortex beams (VVBs), perfect vortex beams (PVBs), and perfect vector vortex beams (PVVBs).

[0003] Perfect vector vortex beams are special structural beams that combine the characteristics of vortex beams (carrying OAM) and vector beams (with spatially varied polarization distributions). They are typically generated by superimposing orthogonally circularly polarized perfect vortex beams with different topological charges. In recent years, they have become a hot topic in micro-nano photonics research and have shown great application potential in the field of information encryption. However, since traditional vortex beams can only carry one topological charge information, to improve information capacity and security, two or more vortex optics with different topological charges are "grafted" together. This allows multiple combinations of topological charge information to be contained in a single beam, overcoming the bottleneck of the limited number of topological charges in traditional perfect vector vortex beams and providing more flexible design freedom and more complex OAM distributions. Furthermore, by combining metasurface multi-wavelength dispersion and precise 3D position manipulation, multispectral grafted perfect vector vortex beams with different colors and different topological charges and polarization orders (polarization distribution along a circumference of the vortex beam) at arbitrary positions in 3D space can be achieved and applied to information encryption, significantly improving information capacity and security. Although the above theory is entirely feasible, no one has yet achieved a grafted perfect vector vortex beam and information encryption method that incorporates combinations of different wavelengths, initial azimuth angles, topological charges, and polarization orders. Summary of the Invention

[0004] To address the shortcomings of existing technologies, inspired by plant grafting, and combining the principles of metasurface geometric phase modulation, spin multiplexing, and phase multiplexing techniques, this invention provides a high-security optical information encryption method based on grafted vector vortex beams. Multiple topological charges are carried within the same perfect vector vortex beam to generate grafted perfect vector vortex beams (GPVVBs) with different spatial polarization rates and ellipticities. The polarization distribution of the GPVVBs can be dynamically modulated by controlling the polarization state of the incident rays.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a high-security optical information encryption method based on grafted vector vortex beams, comprising the following steps: S1. Metasurface phase profile distribution of a single-wavelength GPVVB is obtained based on spin multiplexing and topological charge grafting methods. S2. Based on metalens dispersion manipulation, spatial and phase multiplexing, the metasurface single-phase profile distribution of multiple multicolor GPVVBs is obtained. S3. Further optimize the design of parameters such as the number, location, and wavelength of the generated GPVVBs; S4. Prepare metasurface samples based on phase profiles; S5. Test the metasurface sample prepared in step S4; S6. For the metasurface obtained in step S5 that can clearly display the polarization order combination, wavelength and initial angle information on each grafted perfect vector vortex beam, information encryption encoding is performed to form a unique codebook, achieving high security and high capacity information encryption.

[0006] Furthermore, step S1 specifically includes the following processes: First, GPVVB is achieved by superimposing two grafted perfect vortex beams (GPVB) with orthogonal circular polarization states; mathematically, GPVVB is expressed as: here, In the above formula, It is the initial phase. Let be the polarization angle of the incident linearly polarized light. It is the radius. It is the width of the GPVVB ring; N, ln and 𝜓 These represent the number of GPVBs, the topological charge number carried by each vortex beam, and the azimuth angle, respectively; the polarization distribution in a specific region can be represented by the polarization order. To describe; among them l an and lbn The topological charge design parameters for grafted vortex beams GOVBa and GOVBb with orthogonal circular polarization, respectively; It should be noted that, in this invention, the topological charge designed for the grafted perfect vortex beam of two orthogonally circularly polarized states is a conjugate. Therefore m n It can be simplified to m n = l n Alternatively, any other combination of non-conjugate topological loads can be selected; Next, in order to achieve this in a geometrically phased metasurface system at any position ( x j ，y j ，f j The initial phase is generated at () ， Ellipticity is r The label is j For the GPVVB, the required metasurface phase profile is: Representing the j The wavelength of the GPVVB design; d j γ is the period of the conical lens, used to control the ring radius of the vortex beam; γ represents the ellipticity, which determines the ratio of the major axis to the minor axis of the generated PVB. The initial angle is set; , , These correspond to the phases of the grafted perfect vortex beam, the lens, and the conical lens, respectively; the phase distribution of the conical lens produces a Bessel-Gaussian beam, while the phase distribution of the lens can achieve a Fourier transform.

[0007] Furthermore, step S2 specifically includes the following processes: In order to convert linearly polarized light into Q For GPVVBs located at different positions in 3D space, carrying different combinations of color information and topological charge numbers, the required phase profile of the metasurface is as follows: (6) here, j It takes values ​​from 1 to... Q An integer, used to represent the first j Located in ( x j , yj , f j GPVVB at )

[0008] Furthermore, step S3 specifically includes the following processes: Based on the aforementioned phase profile design principle, in order to obtain the optimal design of a high-capacity, high-security optical information encryption metasurface based on a multispectral grafted perfect vector vortex beam, it is necessary to further optimize the parameters such as the number, position, and wavelength of the generated GPVVB. The specific optimization design method is as follows: The number of GPVVBs at different angular positions on a single focal plane or more focal planes in the longitudinal direction are increased. First, under a single operating wavelength, different combinations of topological charge numbers and initial angles are designed for the GPVVBs. The influence of the intensity profile sharpness on the number of GPVVBs, the focal plane position of the GPVVBs, the diameter and ellipticity of the GPVVB beams, the designed combinations of topological charge numbers, and the initial angle is further analyzed. Furthermore, by combining the metalens dispersion manipulation principle, different colors are encoded for different grafted perfect vector vortex beams. The crosstalk between multiple GPVVBs of different colors and positions is studied. The spatial position, ellipticity, different combinations of topological charge numbers, and wavelengths of the GPVVBs are continuously adjusted and optimized. The optimized metasurface single-phase profile with multiple positions in 3D space, carrying multiple wavelength information and topological charge numbers, and ultra-high capacity high-security optical information encryption is designed.

[0009] Furthermore, the sample in step S4 includes a glass substrate and a metasurface composed of TiO2-NPC nanorods with different in-plane orientations on the glass substrate. Based on the Pancharatnam-Berry phase (geometric phase) realization principle, the required phase profile is achieved by rotating the TiO2-NPC nanorods counterclockwise by half of the required phase profile. The geometric dimensions of the TiO2-NPC nanorod unit structure are optimized using the finite element method. The TiO2-NPC nanorod metasurface was prepared using a single-step nanoimprinting technique. The specific preparation process is as follows: S4-1. A Si template that meets the requirements for metasurface patterning is fabricated using the traditional electron beam lithography method; S4-2. After preparing the Si template, rigid polydimethylsiloxane (h-PDMS) and flexible PDMS are spin-coated and cured onto the Si template in sequence to generate a composite soft template, which is then peeled off from the Si template. S4-3, Further spin-coat TiO2-NPC, which consists of TiO2 particles with a diameter of 30 nm and UV-curable resin (before curing), onto the soft template, and press it onto the glass substrate; S4-4. Irradiate TiO2-NPC with ultraviolet light to solidify it into a Si template pattern (metasurface pattern). Then peel off the soft template to obtain the desired TiO2-NPC metasurface sample. Furthermore, the metasurface prepared in step S4 is subjected to detection using a multispectral grafted perfect vector vortex beam. The specific operation process of step S5 is as follows: The intensity distribution of grafted perfect vector vortex beams carrying different combinations of topological charge, initial angle, and wavelength information generated at different positions on multiple longitudinal planes is examined. If the polarization order combination, wavelength, and initial angle information of each grafted perfect vector vortex beam generated by the metasurface can be clearly displayed, it proves that the metasurface can be further applied to information encryption. If these information cannot be clearly displayed, the metasurface design is further optimized according to the optimization method in step S3 until the polarization order combination, wavelength, and initial angle information of each grafted perfect vector vortex beam can be clearly measured. The specific testing method is as follows: A tunable supercontinuum laser (SuperK EXTREME, NKT Photonics) is used as the incident light source; a polarizer and a quarter-wave plate are placed in front of the sample to control the polarization state of the incident light; the angle between the transmission axis of the polarizer and the fast axis of the quarter-wave plate is adjusted to 45° to achieve right-hand circularly polarized light incident; on the transmission side, an achromatic objective with a magnification of ×40 is used to observe the light field distribution on the focal plane of the superlens; another set of quarter-wave plates and analyzers are placed behind the objective, with their fast axes and transmission axes parallel to the fast axes and transmission axes of the quarter-wave plate and polarizer in front of the sample, respectively, to completely filter the light. In addition to circularly polarized light that has not undergone polarization conversion, a color CCD is used to collect the light field of the part that has undergone circular polarization conversion. When RCP polarized light is incident, all the grafted vector vortex beams we designed will be fully displayed, and the light intensity distribution on the entire vortex beam will be uniform. When measuring the polarization distribution on the grafted vector vortex beam, it is necessary to remove the two quarter-wave plates in the experimental setup at the same time, adjust the polarizer transmission axis to the horizontal direction and the analyzer transmission axis to the vertical direction, which can also completely filter out the light field that has not undergone circular polarization conversion.

[0010] Compared with related technologies, the present invention has the following beneficial effects by adopting the above technical solution: This invention relates to a high-capacity, high-security optical information encryption metasurface design method based on multispectral grafted perfect vector vortex beams. Through multi-degree-of-freedom joint control of the metasurface, grafted perfect vector vortex beams with different ellipticities are generated, and the 3D coordinates and wavelengths of the vortex beams are customized. By changing different incident wavelengths, grafted perfect vector vortex beams with different colors can be observed at different positions, and their spatially variable polarization distribution can be indirectly verified by the modulation intensity after analysis. Furthermore, by continuously adjusting the incident polarization direction, dynamic control of the grafted perfect vector vortex beams can be achieved. Simultaneously achieving controllable adjustment of grafted perfect vector vortex beams with different ellipticities, colors, and topological charges in 3D space provides more design freedom for information carrying, thereby increasing the complexity and security of the encryption space.

[0011] This invention demonstrates a high-capacity perfect vector vortex beam (GPVVB) with at least 8 channels in three-dimensional space (including dimensions such as different wavelengths, topological charge grafting, polarization azimuth, and ellipticity), achieving an information capacity of up to 2. 8 If the metasurface area is further increased, 2 can also be achieved. 16 Information capacity: This method has great potential to increase key space and coding space, and can achieve high security and large capacity characteristics.

[0012] This invention further combines metasurface multi-wavelength dispersion manipulation and spatial multiplexing technology to customize different colors and spatial positions for the generated GPVVB. By optimizing the metasurface size, unit structure, and GPVVB design, it enables GPVVBs carrying multiple wavelength information and topological charge at arbitrary spatial positions, as well as high-capacity, high-security optical information encryption applications. The multispectral GPVVB and metasurface design method proposed in this invention allows for simultaneous control of multiple aspects of the optical field, including phase, polarization, wavelength, and topological charge. Compared to traditional single-wavelength perfect vector vortex beams that only contain a single wavelength and topological charge information, this invention significantly increases the quantity and flexibility of wavelength and topological charge manipulation, providing more degrees of freedom for information carrying, and thus offering significant advantages in improving information encryption capacity and security. Attached Figure Description

[0013] Figure 1 This is a schematic diagram illustrating the information encryption method based on metasurface grafting vector vortex beam of the present invention; When a beam of four-wavelength, linearly polarized light shines on a metasurface, eight GPVVBs of different colors, initial angles, and ellipticities can be generated at different locations in 3D space (along a spiral curve). These GPVVBs are composed of different combinations of topological charges (polarization orders) and can achieve an information capacity of up to 2. 8 .

[0014] Each perfect vortex vector beam is grafted with a different combination of topological charges. Under linearly polarized light illumination at four working wavelengths, eight perfect vector vortex beams carrying different combinations of topological charges (polarization orders) and color information are observed on eight different observation planes. z 1. z 2. z 3. z 4. z 5. z 6. z 7. z 8. The initial polarization distribution of the grafted perfect vortex vector beam is indicated by a white arrow. By selecting appropriate operating wavelength, incident light polarization direction, analyzer transmission axis direction, and observation position, the pre-designed grafted perfect vortex beam can be displayed on different observation planes (upper right).

[0015] Figure 2 This is a design diagram of a metasurface unit structure for information encryption based on the metasurface method of this invention; Figure 2 (a) is a schematic diagram of the TiO2-NPC nanorod unit structure; (b) is the simulation result of the cross-polarization transmission spectrum of the TiO2-NPC nanorod array. This invention uses a composite material (TiO2-NPC) nanorods composed of TiO2 nanoparticles and UV-curable resin to form a dielectric metasurface to generate a geometric phase to realize the designed metasurface. The TiO2-NPC nanostructure was optimized using the finite element method. In the simulation calculation, (the refractive index of the TiO2-NPC nanorods is from the experimental measurement parameters reported in the literature Advanced Materials, 2023, 35(17): 2208520). The length, width and height of the nanorods were systematically optimized. Finally, it was found that the length is 400 nm, the width is 120 nm, the height is 910 nm, and the period of the nanorods is 450 nm. When placed on a glass substrate with a refractive index of 1.46, the calculated circular polarization cross-polarization conversion efficiency is as follows. Figure 2 As shown in (b), the conversion efficiency was found to be almost 70% or higher in the visible light range of 450 nm to 650 nm, and light that did not undergo polarization conversion could be filtered out using a specific experimental setup.

[0016] Figure 3 This is a flowchart illustrating the preparation process of TiO2-NPC nanorods for information encryption based on the metasurface method of this invention. like Figure 3As shown: First, a Si master mode that meets the metasurface pattern requirements is fabricated using traditional electron beam lithography. After preparing the Si master mode, hard polydimethylsiloxane (h-PDMS) and flexible PDMS are spin-coated and cured sequentially onto the Si master mode to generate a composite soft master mode, which is then peeled off from the Si master mode. Next, TiO2-NPC, composed of TiO2 particles with a diameter of 30 nm and UV-curable resin (before curing), is spin-coated onto the soft master mode and pressed onto a glass substrate. UV irradiation is used to cure the TiO2-NPC according to the Si master mode pattern (metasurface pattern). Then, the soft master mode is peeled off to obtain the desired TiO2-NPC metasurface sample.

[0017] Figure 4 This is a schematic diagram of a testing apparatus for testing metasurface samples; The testing setup uses a tunable supercontinuum laser (SuperK EXTREME, NKT Photonics) as the incident light source. A polarizer and a quarter-wave plate are placed in front of the sample to control the polarization state of the incident light. Adjusting the angle between the transmission axis of the polarizer and the fast axis of the quarter-wave plate to 45° allows for right-hand circularly polarized light to be incident. On the transmission side, an achromatic objective with a magnification of ×40 is used to observe the light field distribution on the focal plane of the superlens. Behind the objective, another set of quarter-wave plates and analyzers are placed, with their fast and transmission axes parallel to the fast and transmission axes of the quarter-wave plate and polarizer in front of the sample, respectively. This completely filters out circularly polarized light that has not undergone polarization conversion, and a color CCD is used to collect the portion of the light field where circular polarization conversion has occurred. Figure 4 As shown, when RCP-polarized light is incident, all the grafted vector vortex beams designed in this invention will be fully displayed, and the light intensity distribution across the entire vortex beam will be uniform. When measuring the polarization distribution on the grafted vector vortex beam, it is necessary to remove both quarter-wave plates from the experimental setup simultaneously, adjust the polarizer transmission axis to a horizontal direction and the analyzer transmission axis to a vertical direction, which will also completely filter out the light field that has not undergone circular polarization conversion.

[0018] Figure 5 The invention demonstrates the realization of multiple single-wavelength grafted perfect vector vortex beams for information encryption based on metasurface methods in different spaces. The results show grafted perfect vector vortex beams with different wavelength encodings, different ellipticities, and different topological charge combinations, realized through four different metasurfaces on different observation planes. Here, wavelengths of λ = 480 nm, 530 nm, 580 nm, and 620 nm are used to encode grafted perfect vortex beams on observation surfaces z = 1800 μm, 520 μm, 1200 μm, and 2200 μm, respectively, with ellipticity designed as follows: =1,0.8,1,1, with topological loads of respectively l an = (3, -1), (1, -1), (3, -1), (1, -1), lbn = (-3, 1), (-1, 1), (-3, 1), (-1, 1), and the initial angles are all designed as follows: = 0°. Figure 5 (a) The intensity distribution of the vortex beam observed on the corresponding focal plane under RCP incident at different wavelengths shows that the intensity distribution across the entire beam is uniform. However, when the incident light becomes horizontally linearly polarized (as shown by the red double arrows in the figure), and the transmission axis of the analyzer is vertical (as shown by the green double arrows in the figure), the vortex beam detected on the corresponding observation plane has gaps. The number of gaps is equal to the polarization order, N=mn. Figure 5 As shown in b. This example demonstrates that by designing metasurfaces, grafted perfect vortex beams with different wavelength information and polarization distributions and varying ellipticity can be realized at different focal planes. Compared to traditional perfect vector vortex beams, which can only carry one topological charge, the grafted perfect vortex beam proposed in this invention improves both information carrying capacity and security.

[0019] Figure 6 This refers to the grafted perfect vector vortex beam situation where multiple wavelength codes are achieved at different positions on the observation surface of the same metasurface; Figure 6 This further demonstrates a metasurface design with greater information capacity, enabling the creation of multiple grafted perfect vector vortex beams with different wavelength encodings, ellipticity, and topological charge combinations at different azimuth angles on the same observation plane. Here, wavelengths of λ = 480 nm, 530 nm, 580 nm, and 620 nm are used to encode the grafted perfect vortex beam on the observation plane at z = 900 μm, with ellipticity designed as follows: =1,0.8,1,1, with topological loads of respectively l an = (1, -1), (1, -1), (1, -1), (3, -1), lbn = (-1, 1), (-1, 1), (-1, 1), (-3, 1), the initial angles of (a) and (b) are designed as follows: =0°, the initial angle of (c) is designed as = 45°. Figure 6(a) shows the intensity distribution of the vortex beam observed on the same focal plane under RCP incident at different wavelengths. It is found that the intensity distribution on the entire beam is uniform. As shown in Figure (6)b. This example shows that by designing a metasurface, grafted perfect vortex beams with different wavelength information and polarization distributions and different ellipticity can be realized on different focal planes. Through the dispersion effect of the metasurface, multiple multispectral grafted perfect vector vortex beams can be realized on one focal plane at the same time, further improving information capacity and security. As shown in Figure (6)c, this example shows that when the initial angle is changed to 45°, the grafted perfect vortex beam will exhibit a new amount of information change. At this time, the amount of encrypted information will be further increased, thereby improving the information encryption capacity and security.

[0020] Figure 7 It is the information encryption status of multiple wavelengths in different spaces and positions of a grafted perfect vector vortex beam; After realizing GPVVBs that can carry multiple wavelength information and topological charge numbers at arbitrary spatial locations, and achieving ultra-high capacity and high-security optical information encryption. Figure 7 This invention encrypts and encodes the topological charge, initial angle, ellipticity, and wavelength information of a grafted perfect vortex beam. Using the international ASCII encoding for comparison, the wavelength, ellipticity, incident light rotation, and topological charge number are compared accordingly, as shown in Table 1. Based on this encoding, this invention demonstrates an example of encrypting the capitalized initials "Z", "H", "Y", "C", "I", "X", and "Y" of the School of Materials Science and Engineering at Zhengzhou University of Aeronautics and Astronautics. Figure 7 As shown, the example used in this invention is as follows. According to the encoding table, "Z" represents a wavelength of 580nm, an ellipticity of 1, an incident light rotation angle of 90°, and a topological charge combination of +4 and -2. Only when all the above information is completely correct will a grafted perfect vortex beam representing "Z" appear.

[0021] Table 1. ASCII Codes for Different Parameters of Grafted Perfect Vector Vortex Beams Detailed Implementation

[0022] A high-security optical information encryption method based on grafted vector vortex beams includes the following steps: S1. Metasurface phase profile distribution of a single-wavelength GPVVB is obtained based on spin multiplexing and topological charge grafting methods. S2. Based on metalens dispersion manipulation, spatial and phase multiplexing, the metasurface single-phase profile distribution of multiple multicolor GPVVBs is obtained. S3. Further optimize the design of parameters such as the number, location, and wavelength of the generated GPVVBs; S4. Prepare metasurface samples based on phase profiles; S5. Test the metasurface sample prepared in step S4; S6. For the metasurface obtained in step S5 that can clearly display the polarization order combination, wavelength and initial angle information on each grafted perfect vector vortex beam, information encryption encoding is performed to form a unique codebook, achieving high security and high capacity information encryption.

[0023] By implementing the above six steps, this invention achieves a high-capacity GPVVB with at least eight channels in three-dimensional space (including dimensions such as different wavelengths, polarization state grafting, polarization azimuth angle, and ellipticity), such as... Figure 1 As shown. Increasing the key complexity and encoding space of information encryption can achieve high security and large capacity characteristics, with an information capacity of up to 2. 8 .

[0024] Furthermore, step S1 specifically includes the following processes: First, GPVVB is achieved by superimposing two grafted perfect vortex beams (GPVB) with orthogonal circular polarization states; mathematically, GPVVB is expressed as: here, In the above formula, It is the initial phase. Let be the polarization angle of the incident linearly polarized light. It is the radius. It is the width of the GPVVB ring; N, ln and 𝜓 These represent the number of GPVBs, the topological charge number carried by each vortex beam, and the azimuth angle, respectively; the polarization distribution in a specific region can be represented by the polarization order. To describe; among them l an and l bn The topological charge design parameters for grafted vortex beams GOVBa and GOVBb with orthogonal circular polarization, respectively; It should be noted that, in this invention, the topological charge designed for the grafted perfect vortex beam of two orthogonally circularly polarized states is a conjugate. Therefore m n It can be simplified to m n = l n Alternatively, any other combination of non-conjugate topological loads can be selected; Next, in order to achieve this in a geometrically phased metasurface system at any position ( x j ，y j ，f j The initial phase is generated at () ， Ellipticity is r The label is j For the GPVVB, the required metasurface phase profile is: Representing the j The wavelength of the GPVVB design; d j γ is the period of the conical lens, used to control the ring radius of the vortex beam; γ represents the ellipticity, which determines the ratio of the major axis to the minor axis of the generated PVB. The initial angle is set; , , These correspond to the phases of the grafted perfect vortex beam, the lens, and the conical lens, respectively; the phase distribution of the conical lens produces a Bessel-Gaussian beam, while the phase distribution of the lens can achieve a Fourier transform.

[0025] Furthermore, step S2 specifically includes the following processes: In order to convert linearly polarized light into Q For GPVVBs located at different positions in 3D space, carrying different combinations of color information and topological charge numbers, the required phase profile of the metasurface is as follows: (6) here, j It takes values ​​from 1 to... Q An integer, used to represent the first j Located in ( x j , y j , f j GPVVB at )

[0026] Furthermore, step S3 specifically includes the following processes: Based on the aforementioned phase profile design principle, in order to obtain the optimal design of a high-capacity, high-security optical information encryption metasurface based on a multispectral grafted perfect vector vortex beam, it is necessary to further optimize the parameters such as the number, position, and wavelength of the generated GPVVB. The specific optimization design method is as follows: The number of GPVVBs at different angular positions on a single focal plane or more focal planes in the longitudinal direction are increased. First, under a single operating wavelength, different combinations of topological charge numbers and initial angles are designed for the GPVVBs. The influence of the intensity profile sharpness on the number of GPVVBs, the focal plane position of the GPVVBs, the diameter and ellipticity of the GPVVB beams, the designed combinations of topological charge numbers, and the initial angle is further analyzed. Furthermore, by combining the metalens dispersion manipulation principle, different colors are encoded for different grafted perfect vector vortex beams. The crosstalk between multiple GPVVBs of different colors and positions is studied. The spatial position, ellipticity, different combinations of topological charge numbers, and wavelengths of the GPVVBs are continuously adjusted and optimized. The optimized metasurface single-phase profile with multiple positions in 3D space, carrying multiple wavelength information and topological charge numbers, and ultra-high capacity high-security optical information encryption is designed.

[0027] Furthermore, the sample in step S4 includes a glass substrate and a metasurface composed of TiO2-NPC nanorods with different in-plane orientations on the glass substrate, such as... Figure 2 As shown, based on the Pancharatnam-Berry phase (geometric phase) realization principle, the desired phase profile is achieved by rotating the TiO2-NPC nanorod counterclockwise by half to its current position. The geometric dimensions of the TiO2-NPC nanorod unit structure are then optimized using the finite element method. Figure 3 As shown; The TiO2-NPC nanorod metasurface was prepared using a single-step nanoimprinting technique, such as... Figure 4 As shown, the specific preparation process is as follows: S4-1. A Si template that meets the requirements for metasurface patterning is fabricated using the traditional electron beam lithography method; S4-2. After preparing the Si template, rigid polydimethylsiloxane (h-PDMS) and flexible PDMS are spin-coated and cured onto the Si template in sequence to generate a composite soft template, which is then peeled off from the Si template. S4-3, Further spin-coat TiO2-NPC, which consists of TiO2 particles with a diameter of 30 nm and UV-curable resin (before curing), onto the soft template, and press it onto the glass substrate; S4-4. Use ultraviolet light to irradiate TiO2-NPC to solidify it with the Si template pattern (metasurface pattern). Then peel off the soft template to obtain the desired TiO2-NPC metasurface sample.

[0028] Furthermore, the metasurface prepared in step S4 is subjected to detection using a multispectral grafted perfect vector vortex beam. The specific operation process of step S5 is as follows: The intensity distribution of grafted perfect vector vortex beams carrying different combinations of topological charge, initial angle, and wavelength information generated at different positions on multiple longitudinal planes is examined. If the polarization order combination, wavelength, and initial angle information of each grafted perfect vector vortex beam generated by the metasurface can be clearly displayed, it proves that the metasurface can be further applied to information encryption. If these information cannot be clearly displayed, the metasurface design is further optimized according to the optimization method in step S3 until the polarization order combination, wavelength, and initial angle information of each grafted perfect vector vortex beam can be clearly measured. The specific testing method is as follows: A tunable supercontinuum laser (SuperK EXTREME, NKT Photonics) is used as the incident light source; a polarizer and a quarter-wave plate are placed in front of the sample to control the polarization state of the incident light; the angle between the transmission axis of the polarizer and the fast axis of the quarter-wave plate is adjusted to 45° to achieve right-hand circularly polarized light incident; on the transmission side, an achromatic objective with a magnification of ×40 is used to observe the light field distribution on the focal plane of the superlens; another set of quarter-wave plates and analyzers are placed behind the objective, their fast axes and transmission axes being parallel to the fast axes and transmission axes of the quarter-wave plate and polarizer in front of the sample, respectively, which can completely filter out the circularly polarized light that has not undergone polarization conversion, and a color CCD is used to collect the light field of the part that has undergone circular polarization conversion; Figure 5 , Figure 6 and 7 As shown, when RCP polarized light is incident, all grafted vector vortex beams designed in this invention will be fully displayed, and the light intensity distribution on the entire vortex beam will be uniform. When measuring the polarization distribution on the grafted vector vortex beam, it is necessary to remove the two quarter-wave plates in the experimental device at the same time, adjust the polarizer transmission axis to the horizontal direction and the analyzer transmission axis to the vertical direction, which can also completely filter out the light field that has not undergone circular polarization conversion.

[0029] The above embodiments illustrate the basic principles and features of the present invention, but are merely preferred embodiments and are not limited to these embodiments. Those skilled in the art, inspired by this patent, can make many modifications and improvements without departing from the spirit and scope of the claims, all of which fall within the scope of protection of the present invention. Therefore, the scope of this patent and its protection should be determined by the appended claims.

Claims

1. A high-security optical information encryption method based on a grafted vector vortex beam, characterized in that: Comprising the following steps: S1, obtaining the super surface phase profile distribution of a single single-wavelength GPVVB based on spin multiplexing and topological charge grafting method; S2, obtaining the super surface single phase profile distribution of multiple multi-color GPVVBs based on super lens dispersion manipulation, space and phase multiplexing; S3, further optimizing the number, position, wavelength and other parameters of the generated GPVVBs; S4, preparing a super surface sample according to the phase profile; S5, testing the super surface sample prepared in step S4; S6, for the super surface obtained in step S5 which can clearly display the polarization order combination, wavelength and initial angle information on each grafted perfect vector vortex beam, information encryption coding is carried out to form a unique password book, realizing high security and super capacity information encryption.

2. The high-security optical information encryption method based on grafted vectorial vortex beams according to claim 1, characterized in that: Step S1 specifically includes the following process: First, GPVVB is realized by superposition of two grafted perfect vortex beams (GPVB) with orthogonal circular polarization states; from a mathematical point of view, GPVVB is represented as: Here, In the above formula, is the initial phase, is the polarization angle of the incident linearly polarized light, is the radius, is the width of the GPVVB ring; N, ln and 𝜓 respectively represent the number of GPVBs, the topological charge number carried by each vortex beam, and the azimuthal angle; the polarization distribution of a specific region can be described by the polarization order ; wherein l an and l bn correspond to the topological charge design parameters of the grafted vortex beams GOVBa and GOVBb with orthogonal circular polarizations, respectively; It needs to be particularly pointed out that in the application, for the grafted perfect vortex beam of two orthogonal circular polarization states, the conjugate topological charge number Therefore, m n Can be simplified as m n = l n Other topological charge combinations not conjugate can also be selected. Next, in order to achieve this in a geometrically phased metasurface system at any position ( x j ，y j ，f j The initial phase is generated at () ， Ellipticity is r The label is j For the GPVVB, the required metasurface phase profile is: representing the wavelength of the j d j is the period of the conical lens, which is used to control the ring radius of the vortex beam; γ represents the ellipticity, which determines the ratio of the major axis and the minor axis of the generated PVB; is the initial angle set; , , respectively correspond to the phases of the grafted perfect vortex beam, the lens and the conical lens; the phase distribution of the conical lens generates a Bessel-Gauss beam, while the phase distribution of the lens can realize Fourier transform.​ 3. The high-security optical information encryption method based on grafted vectorial vortex beams according to claim 2, characterized in that: Step S2 specifically includes the following process: In order to convert linearly polarized light into Q The phase profile of the desired metasurface is: （6） Here, j is an integer valued 1 to Q , used to indicate the j th GPVVB located at ( x j , y j , f j ).

4. The high-security optical information encryption method based on grafted vectorial vortex beams according to claim 3, characterized in that: Step S3 specifically includes the following process: On the basis of the above phase profile design principle, in order to obtain the optimal design of the super capacity high security optical information encryption super surface based on multi-spectrum grafted perfect vector vortex beam, further optimization design is needed for the number, position, wavelength and other parameters of the generated GPVVBs, and the specific optimization design method is: Increase the number of GPVVBs at different angular positions on a single focal plane or increase more focal planes in the longitudinal direction, and first design different topological charge combinations and initial angles for GPVVBs at a single operating wavelength, further analyze the influence of GPVVB number, GPVVB position on the focal plane, GPVVB beam diameter, ellipticity, designed topological charge combination and initial angle on the intensity profile clarity; further combine the super lens dispersion manipulation principle to encode different colors for different grafted perfect vector vortex beams, study the crosstalk between multiple GPVVBs of different colors and different positions, and continuously adjust and optimize the spatial position, ellipticity, different topological charge combinations and wavelength of GPVVBs, and design the optimal super surface single phase profile of GPVVBs at multiple positions in 3D space, carrying multiple wavelength information and topological charge number, and super capacity high security optical information encryption.

5. The high-security optical information encryption method based on grafted vectorial vortex beams according to claim 4, characterized in that: The sample in step S4 includes a glass substrate and a super surface composed of TiO2-NPC nanorods with different in-plane orientations on the glass substrate, based on the Pancharatnam-Berry phase (geometric phase) implementation principle, the required phase profile is realized by rotating the TiO2-NPC nanorods counterclockwise by half of the required phase profile at the location, and the finite element method is used to optimize the geometric size of the TiO2-NPC nanorod unit structure; The preparation of TiO2-NPC nanorod super surface adopts single-step nanoimprinting technology, and the specific preparation process is as follows: S4-1, use traditional electron beam lithography method to process Si template meeting the pattern requirements of super surface; S4-2, after the Si template is prepared, a hard polydimethylsiloxane (h-PDMS) and a flexible PDMS are successively spin-coated and cured on the Si template to generate a composite soft template (Soft mode), and the soft template is peeled off from the Si template; S4-3, a TiO2-NPC composed of TiO2 particles with a diameter of 30 nm and an ultraviolet light-cured resin (before curing) is further spin-coated on the soft template and pressed onto a glass substrate; S4-4, the TiO2-NPC is cured in a pattern of the Si template (super surface pattern) by irradiation with ultraviolet light, and then the soft template is peeled off, so that a required TiO2-NPC super surface sample is obtained.

6. The high-security optical information encryption method based on grafted vectorial vortex beams according to claim 5, characterized in that: The super surface prepared in step S4 is subjected to detection of multispectral grafted perfect vector vortex beams, and the specific operation process of step S5 is as follows: The light intensity distribution of the grafted perfect vector vortex beams carrying different combinations of topological charge, initial angle and wavelength information generated by the sample at different positions of multiple planes in the longitudinal direction is detected; if the polarization order combination, wavelength and initial angle information on each grafted perfect vector vortex beam generated by the super surface can be clearly displayed, it is proved that the super surface can be further applied to information encryption; if these information cannot be clearly displayed, the super surface design is further optimized according to the optimization method of step S3 until the polarization order combination, wavelength and initial angle information on each grafted perfect vector vortex beam can be clearly tested. The specific detection method is as follows: a tunable super-continuum laser (SuperK EXTREME, NKT Photonics) is used as an incident light source; a polarizer and a 1 / 4 wave plate are placed in front of the sample to control the polarization state of the incident light; the angle between the transmission axis of the polarizer and the fast axis of the 1 / 4 wave plate is adjusted to 45°, so that right circularly polarized light can be incident; on the transmission side, a ×40 magnification achromatic objective is used to observe the light field distribution on the focal plane of the super lens; another set of 1 / 4 wave plate and analyzer is placed behind the objective, and their fast axes and transmission axes are parallel to the fast axis and transmission axis of the 1 / 4 wave plate and the polarizer in front of the sample, respectively, so that the circularly polarized light that has not undergone polarization conversion can be completely filtered out, and a color CCD is used to collect the light field that has undergone circular polarization conversion; when RCP polarized light is used as the incident light, all the grafted vector vortex beams designed by us can be completely displayed, and the light intensity distribution on the entire vortex beam is uniform; when the polarization distribution of the grafted vector vortex beam is measured, the two 1 / 4 wave plates in the experimental device are removed at the same time, the transmission axis direction of the polarizer is adjusted to be horizontal, and the transmission axis direction of the analyzer is adjusted to be vertical, so that the light field that has not undergone circular polarization conversion can also be completely filtered out.

Images