Information encryption and reconstruction method based on spiral cone light beam orbital angular momentum multi-dimensional holographic technology

Abstract

The invention discloses an information encryption and reconstruction method based on a spiral cone light beam orbital angular momentum multi-dimensional holographic technology, and relates to the technical field of optical information processing and information encryption. The method comprises the following steps: discretizing a target image, generating an initial hologram through phase recovery, embedding a spiral cone phase represented by a topological charge l and a radial factor r0 in the hologram, and multiplexing different channels in an orbital angular momentum dimension and / or a spatial azimuth angle dimension, and finally, decryption and reconstruction are completed on the Fourier plane by using a spiral cone light beam conjugated with the encrypted phase. Due to the fact that spiral cone light beams corresponding to different channels are different in l, r0 and azimuth angles, more multiplexing channels with higher distinction degree can be constructed in the same optical aperture, and the problems that in the prior art, the information multiplexing dimension and capacity are limited, coupling interference exists between the channels, the system is complex, and confidentiality is insufficient are solved on the whole.

Description

Technical Field

[0001] This application relates to the fields of optical information processing and information encryption technology, and in particular to an information encryption and reconstruction method based on multi-dimensional holographic technology of spiral conical beam orbital angular momentum. Background Technology

[0002] Against the backdrop of the rapid development of large-scale information transmission and storage, information security and high-speed encrypted transmission technologies are receiving increasing attention. Compared with traditional electronic cryptography, information encryption based on optical physics mechanisms utilizes the multi-dimensional degrees of freedom of the light field in space, such as amplitude, phase, polarization, wavelength, and orbital angular momentum, offering advantages such as strong parallelism, large bandwidth, and strong resistance to electromagnetic interference. Among these, using a light beam carrying orbital angular momentum (OAM) as an information carrier, combined with holographic technology to achieve information recording and reconstruction, is gradually becoming an important direction for optical encryption and high-dimensional information reuse.

[0003] Existing information encryption schemes based on orbital angular momentum and holography typically employ vortex beams with helical phases (such as Laguerre-Gaussian beams) as carriers, achieving OAM multiplexing holography or OAM selective holography by assigning different integer topological charges to different channels. However, these schemes often only utilize integer-order topological charges, with the minimum channel spacing usually not less than 1, resulting in insufficient utilization of the OAM dimension and limited overall information capacity. Simultaneously, the mode field distributions between channels are prone to overlap, making it difficult to effectively suppress crosstalk between channels, and thus difficult to balance the quality and signal-to-noise ratio of the decrypted image. Furthermore, many optical encryption systems use rotationally symmetric vortex beams, whose spatial azimuth degrees of freedom have not been fully utilized as a new multiplexing dimension. Hologram design typically follows traditional sampling laws, with strong constraints on the sampling interval and output spot size, allowing for the reconstruction of a somewhat recognizable image even with incomplete key matching, reducing anti-attack capabilities. In addition, some systems have complex optical path structures, requiring high interference stability, component assembly accuracy, and system cost, hindering engineering applications and widespread adoption.

[0004] Therefore, in the encryption of multi-dimensional holographic information based on orbital angular momentum, the limited dimensions and capacity of information reuse, the difficulty in suppressing crosstalk between channels, and the complex system structure and insufficient confidentiality have become urgent problems to be solved. Summary of the Invention

[0005] This application provides an information encryption and reconstruction method based on the multidimensional holographic technology of orbital angular momentum of a spiral conical beam, aiming to solve the problems of limited information reuse dimension and capacity, difficulty in suppressing crosstalk between channels, and complex system structure and insufficient confidentiality in the existing technology of multidimensional holographic information encryption based on orbital angular momentum.

[0006] A first aspect is a method for information encryption and reconstruction based on multi-dimensional holographic technology of spiral conical beam orbital angular momentum, the method comprising: Discretize at least one target image to be encrypted to obtain a discretized target image; Based on the phase retrieval algorithm, an initial hologram corresponding to each of the discretized target images is generated; For each target image, a spiral conical beam is selected. The initial phase of the spiral conical beam is defined by the product of the spiral phase and the axial conical phase, and by the topological charge number. l and radial factor r 0 Characterization, the topological load number l The values ​​can be integers or fractions; based on the orbital angular momentum dimension and / or spatial azimuth dimension, different spiral conical beam encryption phases are assigned to different multiplexing channels, and the encryption phases of the spiral conical beams are embedded into the corresponding initial holograms to form encryption holograms for each multiplexing channel. The encryption holograms are then superimposed to obtain a multi-dimensional multiplexing encryption hologram. The multidimensional multiplexed encrypted hologram is illuminated using a spiral conic beam conjugate with the encryption phase as a key beam, and reconstructed images corresponding to each target image are obtained on the Fourier plane of the key beam.

[0007] In the above scheme, optionally, the spatial sampling interval of the discretization sampling is smaller than the beam unit size on the Fourier plane during the decryption process.

[0008] Optionally, in the above scheme, the multi-dimensional multiplexed encrypted hologram includes a multiplexed dimension based on orbital angular momentum, and the hologram generation and encrypted phase embedding include: A phase retrieval algorithm is used to generate an OAM-preserving hologram that maintains the orbital angular momentum characteristics; By embedding the encrypted phase of the corresponding spiral cone beam into the OAM preserved hologram, an OAM selective hologram is obtained; Multiple OAM selective holograms are superimposed to obtain an OAM multiplexed hologram.

[0009] Optionally, in the above scheme, in the multiplexing channel based on orbital angular momentum, the encrypted phase is determined by the topological charge number. l With radial factor r 0 Joint regulation.

[0010] Optionally, in the above scheme, the multi-dimensional multiplexed encrypted hologram includes a multiplexing dimension based on spatial azimuth, and the encrypted phase embedding and multi-dimensional multiplexing include: The spatial angular range is divided into multiple directional regions, and each directional region corresponds to a directional multiplexing channel. For each multiplexed channel, different spatial rotation angles of the same spiral cone beam pattern are used as the encryption phase of each channel. The rotated spiral cone beam phase is embedded into the corresponding initial hologram to form the encryption hologram of each channel. The encryption holograms of each channel are superimposed to form a rotating multiplexed hologram. The rotating multiplexed hologram constitutes a part of the multidimensional multiplexed encryption hologram. During the decryption and reconstruction process, the key beam is rotated around the optical axis so that the phase orientation of the key beam is consistent with the encryption phase orientation of the corresponding orientation multiplexing channel, and the reconstructed image corresponding to that channel is obtained on the Fourier plane.

[0011] Secondly, an information encryption and reconstruction device based on multi-dimensional holographic technology of spiral conical beam orbital angular momentum is provided, comprising: The module comprises a light source module, a beam modulation module, a holographic module, and an observation module; among which, The light source module is used to output a single-frequency Gaussian mode laser beam; The beam modulation module is connected to the light source module and is used to modulate the Gaussian mode laser beam into a spiral cone beam and output a key beam. The holographic module is used to load a multi-dimensional multiplexed encrypted hologram and illuminate it with the key beam to form a reconstructed light field in the Fourier plane. The observation module is located at the Fourier plane and is used to acquire the reconstructed image corresponding to the reconstructed light field.

[0012] Optionally, in the above scheme, the light source module includes a single-frequency Gaussian mode laser, a first lens, and a second lens. The first lens and the second lens form a telescope system to collimate the laser output beam and adjust the beam's lateral dimension.

[0013] Optionally, in the above scheme, the beam modulation module includes: The system comprises a half-wave plate, a polarizer, a first beam splitter prism, a first spatial light modulator, a third lens, an aperture stop, and a fourth lens; wherein the half-wave plate is used to adjust the polarization direction of the light beam to match the modulation direction of the first spatial light modulator. The first spatial light modulator is a reflective phase-type spatial light modulator, used to load the initial phase of the spiral cone beam and superimpose a blazed grating; The third and fourth lenses are both Fourier lenses and form a 4-f system. The aperture is set on the spectral plane of the 4-f system to select the target diffraction order. The beam modulation module is configured to: pass the beam output from the light source module and polarization-adjusted sequentially through the first spatial light modulator, the third lens, the aperture stop and the fourth lens to form a spiral cone beam, and then output it to the holographic module.

[0014] Optionally, in the above scheme, the holographic module includes a second beam-splitting prism, a second spatial light modulator, and a fifth lens; wherein, The second spatial light modulator is a reflective phase-type spatial light modulator, used to load a pre-calculated phase-only multidimensional multiplexed encrypted hologram; The fifth lens is a Fourier lens, used to perform Fourier transform on the beam modulated by the second spatial light modulator, so that the reconstructed light field is located at the Fourier back focal plane of the fifth lens.

[0015] Optionally, in the above scheme, the observation module includes a neutral density filter and an optical camera. The neutral density filter is disposed between the fifth lens and the optical camera to attenuate the incident light intensity. The optical camera is a charge-coupled device camera, disposed at the Fourier back focal plane of the fifth lens, and is used to record the reconstructed image.

[0016] Compared with the prior art, this application has at least the following beneficial effects: (1) Significantly improved information capacity and multiplexing density. Traditional OAM holographic technology is limited by integer topological charge number, with fixed channel spacing and low multiplexing density. This invention uses spiral conical phase as encryption carrier and achieves ultra-dense orbital angular momentum multiplexing through the coordinated control of topological charge number l (which can support integer and fractional) and radial factor r0. By assigning differentiated l and r0 parameters to different channels, the overlap between modes is effectively reduced, the topological charge number resolution is improved, and the channel capacity within the same optical aperture is significantly expanded.

[0017] (2) Enhanced security and simplified system structure. The spiral mode field characteristics of the spiral conical beam generate low-intensity cluttered diffraction spots during non-conjugate decryption, significantly increasing the difficulty of illegal cracking compared to the regular vortex rings of traditional vortex beams. Simultaneously, by breaking through the Nyquist sampling interval strategy (discretizing the sampling interval to be smaller than the Fourier plane spot size), channel crosstalk is further suppressed. Furthermore, the phase-matching mechanism based on a single optical path throughout the process eliminates the need for complex aperture filter arrays, achieving a "what you see is what you get" reconstruction effect and reducing system complexity and cost.

[0018] (3) Expanded spatial dimension reuse capability. Utilizing the asymmetry of the spiral cone beam, this invention innovatively introduces a spatial azimuth angle reuse dimension. By dividing the beam cross-section into multiple azimuth regions and using different rotation angles of the same spiral cone pattern as encryption phases, an azimuth angle reuse channel is constructed. During decryption, the phase azimuth of the key beam must be strictly matched, making this technology particularly suitable for non-reconfigurable holographic scenarios such as phase plates and metasurfaces, significantly improving the practicality and flexibility of the solution.

[0019] In summary, the present invention provides an information encryption and reconstruction method based on the multi-dimensional holographic technology of spiral conical beam orbital angular momentum. Through multi-parameter control of the spiral conical beam and precise matching of the holographic phase, it achieves synergistic optimization of information capacity, security and system integration, providing an innovative solution for high-dimensional optical encryption. Attached Figure Description

[0020] Figure 1 A schematic diagram of OAM multiplexing holographic encryption based on a spiral conical beam and a schematic diagram of spatial rotation multiplexing holographic encryption are provided for one embodiment of this application; Figure 2 A schematic diagram of an experimental apparatus for OAM holographic information encryption technology based on a spiral conical beam, provided as an embodiment of this application; Figure 3 This is a schematic diagram of an OAM multiplexing holographic encryption scheme provided in one embodiment of this application; Figure 4 This is an OAM multiplexing holographic decryption and reconstruction result diagram provided in one embodiment of this application; Figure 5 This is a schematic diagram of a spatial rotation multiplexing holographic encryption scheme provided in one embodiment of this application; Figure 6 This is a spatial rotation multiplexing holographic decryption and reconstruction result image provided in one embodiment of this application; Figure label: 101: Schematic diagram of OAM multiplexing holographic encryption; 102: Schematic diagram of spatial rotation multiplexing holographic encryption; 201: Laser; 202: First lens; 203: Second lens; 204: Half-wave plate; 205: Polarizer; 206: First beam splitter prism; 207: First spatial light modulator; 208: Third lens; 209: Aperture; 210: Fourth lens; 211: Second beam splitter prism; 212: Second spatial light modulator; 213: Fifth lens; 214: Neutral density filter; 215: CCD camera; 301: Discrete The target image after transformation: 302: OAM preserved hologram; 303: Spiral cone encrypted phase; 304: OAM selective hologram; 305: OAM multiplexed hologram; 401-403: Numerical simulation results; 404-406: Experimental results; 501: Spatial rotation multiplexed hologram; 502: Fourier lens; 503: Reconstruction results; 504: Six-phase spatial division scheme; 505: Rotated encrypted phase; 506: Selected original target image; 601-606: Numerical simulation results; 607-612: Experimental results. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0022] In the description of this application: unless otherwise stated, "a plurality of" means two or more. The terms "first," "second," "third," etc., in this application are intended to distinguish the objects referred to and do not have any special meaning in terms of technical connotation (e.g., they should not be construed as an emphasis on importance or order). Expressions such as "including," "comprising," and "having" also mean "not limited to" (certain units, components, materials, steps, etc.).

[0023] In one embodiment, such as Figure 1 As shown, a method for information encryption and reconstruction based on multi-dimensional holographic technology of spiral conical beam orbital angular momentum is provided. The method includes: Discretize at least one target image to be encrypted to obtain a discretized target image; Based on the phase retrieval algorithm, an initial hologram corresponding to each of the discretized target images is generated; For each target image, a spiral conical beam is selected. The initial phase of the spiral conical beam is defined by the product of the spiral phase and the axial conical phase, and by the topological charge number. l and radial factor r 0 Characterization, the topological load number lThe values ​​can be integers or fractions; based on the orbital angular momentum dimension and / or spatial azimuth dimension, different spiral conical beam encryption phases are assigned to different multiplexing channels, and the encryption phases of the spiral conical beams are embedded into the corresponding initial holograms to form encryption holograms for each multiplexing channel. The encryption holograms are then superimposed to obtain a multiplexing encryption hologram. The multiplexed encrypted hologram is illuminated using a spiral conic beam conjugate with the encryption phase as a key beam, and reconstructed images corresponding to each target image are obtained on the Fourier plane of the key beam.

[0024] In this embodiment, the spatial sampling interval of the discretization sampling is smaller than the beam element size on the Fourier plane during the decryption process.

[0025] In this embodiment, the multi-dimensional multiplexed encrypted hologram includes a multiplexed dimension based on orbital angular momentum, and the hologram generation and encrypted phase embedding include: A phase retrieval algorithm is used to generate an OAM-preserving hologram that maintains the orbital angular momentum characteristics; By embedding the encrypted phase of the corresponding spiral cone beam into the OAM preserved hologram, an OAM selective hologram is obtained; Multiple OAM selective holograms are superimposed to obtain an OAM multiplexed hologram.

[0026] In this embodiment, in the multiplexed channel based on orbital angular momentum, the encrypted phase is determined by the topological charge number. l With radial factor r 0 Joint regulation.

[0027] In this embodiment, the multi-dimensional multiplexed encrypted hologram includes a multiplexing dimension based on spatial azimuth angle, and the encrypted phase embedding and multi-dimensional multiplexing include: The spatial angular range is divided into multiple directional regions, and each directional region corresponds to a directional multiplexing channel. For each multiplexed channel, different spatial rotation angles of the same spiral cone beam pattern are used as the encryption phase of each channel. The rotated spiral cone beam phase is embedded into the corresponding initial hologram to form the encryption hologram of each channel. The encryption holograms of each channel are superimposed to form a rotating multiplexed hologram. The rotating multiplexed hologram constitutes a part of the multidimensional multiplexed encryption hologram. During the decryption and reconstruction process, the key beam is rotated around the optical axis so that the phase orientation of the key beam is consistent with the encryption phase orientation of the corresponding orientation multiplexing channel, and the reconstructed image corresponding to that channel is obtained on the Fourier plane.

[0028] In one embodiment, a method for information encryption and reconstruction based on multi-dimensional holographic technology of spiral conical beam orbital angular momentum is provided, including the following steps: Encryption process: S1. Target image discretization: Discretize the target image to be encrypted by sampling. S2. Hologram Generation: Based on the phase retrieval algorithm, an initial hologram corresponding to the target image is generated; S3. Encrypted Phase Embedding: The phase of the spiral cone beam is embedded as an encrypted phase into the initial hologram to form an encrypted hologram; Decryption process: The encrypted hologram is illuminated using a spiral conical beam conjugate with the encrypted phase as a key beam, and the target image is reconstructed and obtained on the Fourier plane of the key beam.

[0029] In this embodiment, a spiral cone phase is used as the encryption phase, and the topological charge number is... l It can take integer or fractional values, and there can be arbitrary topological load intervals between channels.

[0030] In this embodiment, in the target image discretization step, the sampling interval is set to be smaller than the beam element size on the spectral plane during the decryption process.

[0031] In this embodiment, during information encryption, the encryption phase is simultaneously affected by the topological charge number. l and radial factor r 0 Control; during the decryption process, a beam of light with conjugate parameters needs to be correctly incident in order to successfully reconstruct the target image.

[0032] In this embodiment, parameters can be coordinated and adjusted. l and r 0 Reduce the degree of overlap between modes and suppress crosstalk between channels.

[0033] In this embodiment, dense multiplexing holography based on orbital angular momentum can be realized.

[0034] In this embodiment, the asymmetry of the spiral cone beam pattern is utilized to divide multiple azimuth multiplexing channels according to different azimuth angles, and different spatial rotation angles of the same spiral cone pattern are used as the encryption phases of different channels; during decryption, the corresponding target image can only be reconstructed when the phase azimuth of the demodulated beam matches the phase azimuth of the encryption mask.

[0035] In this embodiment, the identification features of the reconstruction result in the image reconstruction step are: when decryption is performed using a conjugate key beam, clear and discrete Gaussian spots appear on the observation surface; when decryption is performed using a non-conjugate key beam, stray light with low unit intensity and disorder appears on the observation surface.

[0036] The purpose of this embodiment is to design an optical OAM holographic encryption scheme with high information capacity, high security, and low system complexity. To achieve the above objective, this embodiment provides a multi-dimensional holographic encryption method based on a spiral conical beam.

[0037] Specifically, based on the tunable intrinsic parameters and non-rotational symmetry of the spiral conical beam, this method respectively invented OAM multiplexing holographic encryption and spatial rotation multiplexing holographic encryption. At the operational level, the encryption process includes: target image discretization, hologram generation based on a phase retrieval algorithm, and embedding the encrypted phase; the decryption process requires illuminating the hologram with a key beam to obtain the reconstruction result on the corresponding Fourier plane.

[0038] Furthermore, this method breaks through the limitation of sampling interval when discretizing the target image, that is, the sampling interval can be smaller than the beam unit size on the spectral surface.

[0039] Furthermore, the proposed holographic architecture includes OAM-preserving holography, OAM-selective holography, and OAM-reusable holography.

[0040] Furthermore, the OAM-preserving hologram is obtained using an optimized Grechberg-Saxton phase retrieval algorithm; the OAM-selective hologram is obtained by embedding an encrypted phase into the OAM-preserving hologram; and the OAM-multiplexed hologram is obtained by superimposing multiple OAM-selective holograms.

[0041] For the OAM multiplexing holographic encryption scheme, the topological charge number of the spiral cone beam used for encryption breaks through the integer limitation, integrating the integer topological charge number and the fractional topological charge number under a unified framework, that is, the topological charge number interval between adjacent channels can be arbitrarily set.

[0042] Furthermore, during information encryption, the encryption phase is simultaneously affected by the topological charge number. l and radial factor r 0 Control; during the decryption process, a beam of light with conjugate parameters needs to be correctly incident in order to successfully reconstruct the target image.

[0043] Furthermore, to achieve dense reuse of OAM, parameters can be coordinated and adjusted. l and r 0 When between patterns l and r0 When there is a negative correlation, the overlap between modes is the lowest, the crosstalk suppression effect is better, and the corresponding multiplexing holographic effect is also better.

[0044] For the spatial rotation multiplexing holographic encryption scheme, the asymmetry of the spiral cone beam pattern is utilized to divide different azimuth multiplexing channels in the spatial dimension according to different azimuth angles, and different rotation results of the same spiral cone pattern are used as encryption phases. The target image can only be successfully reconstructed when the phase of the demodulated beam corresponds to the phase orientation of the encryption mask.

[0045] For feature identification of the reconstruction results, when the target image is successfully reconstructed, clear and discrete Gaussian spots will appear on the observation surface in different topological charge number channels and azimuth channels; otherwise, stray light will appear on the observation surface.

[0046] To achieve the above effects, the present invention provides an information encryption device for OAM holography of a spiral conical beam, specifically including: a light source module, a beam modulation module, a holographic module and an imaging module.

[0047] The light source module includes a single-frequency Gaussian mode laser, a first lens, and a second lens. The first lens and the second lens form a telescope system for beam collimation and lateral dimension control.

[0048] The beam modulation module includes a half-wave plate, a polarizer, a first beam splitter prism, a first spatial light modulator, a third lens, an aperture, and a fourth lens. The half-wave plate is used to adjust the polarization direction of the light to match the modulation direction of the spatial light modulator panel, thereby achieving maximum modulation efficiency. The first spatial light modulator is a reflective phase-type modulator used to load the initial phase of the spiral conical beam and superimpose a blazed grating. The third and fourth lenses are both Fourier lenses and together form a 4-f system. The aperture is placed on the second focal plane of the 4-f system to filter out the target diffraction orders.

[0049] The holographic module includes a second beam-splitting prism, a second spatial light modulator, and a fifth lens. The second spatial light modulator is also a reflective phase-type modulator, used to load a pre-calculated phase-only hologram; the fifth lens is a Fourier lens, and the reconstruction result is located at its Fourier back focal plane.

[0050] The observation module includes a neutral density filter and an optical camera. The neutral density filter can continuously and adjustablely attenuate the light intensity to avoid overexposure during observation; the optical camera usually uses a charge-coupled device (CCD), which, when placed on the Fourier back focal plane of the fifth lens, allows for the observation and recording of the reconstruction results.

[0051] Compared with the prior art, this embodiment has the following beneficial effects: The OAM holographic architecture in this embodiment uses a spiral cone phase as the encryption phase. Compared to traditional OAM beams, the phase definition of a spiral cone beam makes it easier to uniformly reuse integer and fractional topological charges, theoretically enabling ultra-dense orbital angular momentum reuse, thereby significantly improving information capacity.

[0052] Benefiting from the spiral mode field characteristics of the spiral conical beam itself, during non-conjugate incident decryption, the observation surface does not form a distinct vortex ring shape, but rather a low-intensity and chaotic diffraction pattern. This increases the difficulty of inferring the original information from the reconstruction result in cases of key mismatch, thus improving information security. Furthermore, this characteristic avoids the aperture filter array commonly used in existing methods, simplifying the system's computational complexity and achieving a "what you see is what you get" reconstruction effect. The introduced breakthrough sampling interval strategy demonstrates a significant advantage in suppressing mode crosstalk, further enhancing the system's information security.

[0053] This embodiment utilizes the asymmetry of the spiral conical beam pattern to achieve spatial rotation multiplexing, further expanding the multiplexing dimension and effectively increasing information capacity. This strategy is particularly suitable for applications where holograms cannot be reconfigured (e.g., systems based on phase plates or traditional metasurfaces), and has greater practicality.

[0054] In one embodiment, an OAM multiplexing holographic encryption scheme is provided; in another embodiment, a spatial rotation multiplexing holographic encryption scheme is provided.

[0055] The experimental apparatus used to implement the above two schemes is as follows: Figure 2 As shown. In this embodiment, a Gaussian mode beam with a wavelength of 532 nm output from laser 201 is collimated and expanded by lens groups 202 and 203, and its polarization state is adjusted by half-wave plate 204 and polarizer 205 before being incident on spatial light modulator 207 via beam splitter prism 206. The initial phase of the spiral conical beam used as the key is loaded into spatial light modulator 207. After modulation, the beam is reflected by beam splitter prism 204, and then spectrally filtered by lens 208, aperture 209, and lens 210 to obtain the desired diffraction order. It is then reflected by beam splitter prism 211 to spatial light modulator 212. A multiplexed hologram is loaded into spatial light modulator 212. The hologram is illuminated by the key beam, and then subjected to Fourier transform by lens 213. The result of decryption and reconstruction can be observed and recorded by CCD camera 215.

[0056] like Figure 3 As shown, the OAM multiplexing scheme selects the uppercase English letters "N", "K" and "U" as target images and assigns them to different topology charge number channels for multiplexing, encryption and decryption reproduction.

[0057] Specifically, the image information of the three independent OAM information channels (for convenience, they are set as channel 1, channel 2 and channel 3 respectively, the same below) are “N”, “K” and “U” respectively, and are discretized to retain the OAM characteristics (301); the sampling interval of the discretization here can break the sampling law, the purpose of which is to make the light field distribution of the reconstruction result more chaotic when the key does not match, making the image information difficult to predict and improving information security.

[0058] The discretized target image is used to obtain an OAM-preserved hologram (302) through an optimized Grechberg-Saxton phase retrieval algorithm. Further, the topological charge numbers of the spiral conical beams used for encryption in channels 1, 2, and 3 are respectively set to... l 1 = 2.8、 l 2 = 3 and l 3 = 3.2, and the corresponding radial factors are set as follows: r 01 = 3.2×10 -3 , r 02 = 3×10 -3 and r 03 = 2.8 × 10 -3 (303) can be obtained l and r 0 The correlation is negative. The OAM-preserved holograms from the three channels are superimposed with the corresponding encrypted spiral cone beams to obtain an OAM-selective hologram (304). The superposition of the three OAM-selective holograms generates an OAM multiplexed hologram (305).

[0059] During decryption, conjugate beams of encryption phases from different channels are incident onto the multiplexed hologram to reconstruct the corresponding results, such as... Figure 3 As shown in the diagram, sections 401-403 present the numerical simulation results, while sections 404-406 present the corresponding experimental results. It can be seen that the reconstructed letters "N", "K", and "U" have distinct shape features, clear images, and good agreement between theoretical and experimental results.

[0060] like Figure 5As shown, Embodiment 2 employs a six-phase spatial rotational multiplexing holographic encryption scheme. Specifically, in the spatial dimension, a circle (0~2π) is uniformly divided into six regions. The image information of the six channels are the uppercase English letters "O", "P", "T", "I", "C", and "S", and the spiral cone phases used for encryption in each channel are of the same distribution, but they have different azimuth angles after rotation. The holograms of all channels are superimposed to generate a rotational multiplexing hologram. Thus, during reconstruction, as the key beam illuminates the hologram and rotates one revolution, decryption will be achieved successively in the six directions.

[0061] The corresponding reconstruction results are as follows Figure 6 As shown, 601-606 present the numerical simulation results, and 607-612 present the corresponding experimental results. It can be seen that the reconstructed letters "O", "P", "T", "I", "C" and "S" have obvious shape features, clear images, and good agreement between theoretical and experimental results.

[0062] In the two embodiments described above, the spiral cone phase parameters used for encryption and the spatial orientation division are not limited to those shown above. Numerical simulations and experimental verification demonstrate that, through appropriate parameter selection, the OAM multiplexing scheme can achieve a topological charge resolution of 0.01 and an azimuth resolution of π / 16, significantly improving information capacity compared to traditional multiplexing holographic methods.

[0063] In one embodiment, an information encryption and reconstruction device based on multi-dimensional holographic technology of spiral conical beam orbital angular momentum is provided, comprising: The module comprises a light source module, a beam modulation module, a holographic module, and an observation module; among which, The light source module is used to output a single-frequency Gaussian mode laser beam; The beam modulation module is connected to the light source module and is used to modulate the Gaussian mode laser beam into a spiral cone beam and output a key beam. The holographic module is used to load a multi-dimensional multiplexed encrypted hologram and illuminate it with the key beam to form a reconstructed light field in the Fourier plane. The observation module is located at the Fourier plane and is used to acquire the reconstructed image corresponding to the reconstructed light field.

[0064] In this embodiment, the light source module includes a single-frequency Gaussian mode laser, a first lens, and a second lens. The first lens and the second lens form a telescope system to collimate the laser output beam and adjust the beam's lateral dimension.

[0065] In this embodiment, the beam modulation module includes: The system comprises a half-wave plate, a polarizer, a first beam splitter prism, a first spatial light modulator, a third lens, an aperture stop, and a fourth lens; wherein the half-wave plate is used to adjust the polarization direction of the light beam to match the modulation direction of the first spatial light modulator. The first spatial light modulator is a reflective phase-type spatial light modulator, used to load the initial phase of the spiral cone beam and superimpose a blazed grating; The third and fourth lenses are both Fourier lenses and form a 4-f system. The aperture is set on the spectral plane of the 4-f system to select the target diffraction order. The beam modulation module is configured to: pass the beam output from the light source module and polarization-adjusted sequentially through the first spatial light modulator, the third lens, the aperture stop and the fourth lens to form a spiral cone beam, and then output it to the holographic module.

[0066] In this embodiment, the holographic module includes a second beam-splitting prism, a second spatial light modulator, and a fifth lens; wherein, The second spatial light modulator is a reflective phase-type spatial light modulator, used to load a pre-calculated phase-only multidimensional multiplexed encrypted hologram; The fifth lens is a Fourier lens, used to perform Fourier transform on the beam modulated by the second spatial light modulator, so that the reconstructed light field is located at the Fourier back focal plane of the fifth lens.

[0067] In this embodiment, the observation module includes a neutral density filter and an optical camera. The neutral density filter is disposed between the fifth lens and the optical camera to attenuate the incident light intensity. The optical camera is a charge-coupled device (CCD) camera, disposed at the Fourier back focal plane of the fifth lens, and is used to record the reconstructed image.

[0068] The specific implementation details of each module can be found in the above description of the information encryption method based on the multi-dimensional holographic technology of spiral conical beam orbital angular momentum, and will not be repeated here.

[0069] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

Claims

1. A method for information encryption and reconstruction based on multi-dimensional holographic technology of spiral conical beam orbital angular momentum, characterized in that, The method includes: Discretize at least one target image to be encrypted to obtain a discretized target image; Based on the phase retrieval algorithm, an initial hologram corresponding to each of the discretized target images is generated. For each target image, a spiral conical beam is selected. The initial phase of the spiral conical beam is defined by the product of the spiral phase and the axial conical phase, and by the topological charge number. l and radial factor r 0 Characterization, the topological load number l The values ​​can be integers or fractions; based on the orbital angular momentum dimension and / or spatial azimuth dimension, different spiral conical beam encryption phases are assigned to different multiplexing channels, and the encryption phases of the spiral conical beams are embedded into the corresponding initial holograms to form encryption holograms for each multiplexing channel. The encryption holograms are then superimposed to obtain a multi-dimensional multiplexing encryption hologram. The multidimensional multiplexed encrypted hologram is illuminated using a spiral conic beam conjugate with the encryption phase as a key beam, and reconstructed images corresponding to each target image are obtained on the Fourier plane of the key beam.

2. The method according to claim 1, characterized in that, The spatial sampling interval of the discretized sampling is smaller than the beam element size on the Fourier plane during the decryption process.

3. The method according to claim 1, characterized in that, The multi-dimensional multiplexed encrypted hologram includes a multiplexed dimension based on orbital angular momentum, and the hologram generation and encrypted phase embedding include: A phase retrieval algorithm is used to generate an OAM-preserving hologram that maintains the orbital angular momentum characteristics; By embedding the encrypted phase of the corresponding spiral cone beam into the OAM preserved hologram, an OAM selective hologram is obtained; Multiple OAM selective holograms are superimposed to obtain an OAM multiplexed hologram.

4. The method according to claim 1, characterized in that, In orbital angular momentum-based multiplexing channels, the encrypted phase is determined by the topological charge number. l With radial factor r 0 Joint regulation.

5. The method according to claim 1, characterized in that, The multi-dimensional multiplexed encrypted hologram includes a multiplexing dimension based on spatial azimuth angle, and the encrypted phase embedding and multi-dimensional multiplexing include: The spatial angular range is divided into multiple directional regions, and each directional region corresponds to a directional multiplexing channel. For each multiplexed channel, different spatial rotation angles of the same spiral cone beam pattern are used as the encryption phase of each channel. The rotated spiral cone beam phase is embedded into the corresponding initial hologram to form the encryption hologram of each channel. The encryption holograms of each channel are superimposed to form a rotating multiplexed hologram. The rotating multiplexed hologram constitutes a part of the multidimensional multiplexed encryption hologram. During the decryption and reconstruction process, the key beam is rotated around the optical axis so that the phase orientation of the key beam is consistent with the encryption phase orientation of the corresponding orientation multiplexing channel, and the reconstructed image corresponding to that channel is obtained on the Fourier plane.

6. An information encryption and reconstruction device based on multi-dimensional holographic technology of spiral conical beam orbital angular momentum, used to implement the information encryption method according to any one of claims 1 to 5, characterized in that, include: The module comprises a light source module, a beam modulation module, a holographic module, and an observation module; among which, The light source module is used to output a single-frequency Gaussian mode laser beam; The beam modulation module is connected to the light source module and is used to modulate the Gaussian mode laser beam into a spiral cone beam and output a key beam. The holographic module is used to load a multi-dimensional multiplexed encrypted hologram and illuminate it with the key beam to form a reconstructed light field in the Fourier plane. The observation module is located at the Fourier plane and is used to acquire the reconstructed image corresponding to the reconstructed light field.

7. The apparatus according to claim 6, characterized in that, The light source module includes a single-frequency Gaussian mode laser, a first lens, and a second lens. The first lens and the second lens form a telescope system to collimate the laser output beam and adjust the beam's lateral dimension.

8. The apparatus according to claim 6, characterized in that, The beam modulation module includes: The system comprises a half-wave plate, a polarizer, a first beam splitter prism, a first spatial light modulator, a third lens, an aperture stop, and a fourth lens; wherein the half-wave plate is used to adjust the polarization direction of the light beam to match the modulation direction of the first spatial light modulator. The first spatial light modulator is a reflective phase-type spatial light modulator, used to load the initial phase of the spiral cone beam and superimpose a blazed grating; The third and fourth lenses are both Fourier lenses and form a 4-f system. The aperture is set on the spectral plane of the 4-f system to select the target diffraction order. The beam modulation module is configured to: pass the beam output from the light source module and polarization-adjusted sequentially through the first spatial light modulator, the third lens, the aperture stop and the fourth lens to form a spiral cone beam, and then output it to the holographic module.

9. The apparatus according to claim 6, characterized in that, The holographic module includes a second beam-splitting prism, a second spatial light modulator, and a fifth lens; wherein... The second spatial light modulator is a reflective phase-type spatial light modulator, used to load a pre-calculated phase-only multidimensional multiplexed encrypted hologram; The fifth lens is a Fourier lens, used to perform Fourier transform on the beam modulated by the second spatial light modulator, so that the reconstructed light field is located at the Fourier back focal plane of the fifth lens.

10. The apparatus according to claim 6, characterized in that, The observation module includes a neutral density filter and an optical camera. The neutral density filter is disposed between the fifth lens and the optical camera to attenuate the incident light intensity. The optical camera is a charge-coupled device camera and is disposed at the Fourier back focal plane of the fifth lens to record the reconstructed image.

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