Information encryption device based on spiral fractional photon orbital angular momentum holography

Abstract

The present invention relates to the field of information encryption technology, and specifically discloses an information encryption device based on spiral fractional-order photon orbital angular momentum holography, comprising a light source module, a first modulation module, a 4f system, a reflector, a second modulation module, and an imaging module. The device realizes the use of spiral fractional-order orbital angular momentum patterns as independent information encoding channels to encrypt information, which supplements integer-order orbital angular momentum pattern channels, greatly increases information channels, and improves the information capacity and encryption security of optical holography.

Description

Technical Field

[0001] The present invention relates to the technical field of information encryption technology, and in particular to an information encryption device based on spiral fractional-order photon orbital angular momentum holography. Background Art

[0002] As modern society's demands for increased communication capacity continue to grow, the utilization of the various dimensions of light is also increasing. Photon orbital angular momentum is widely used to increase communication capacity because it has infinite orthogonal modes, each of which can serve as an independent channel for transmitting information.

[0003] The spiral fractional vortex beam is generated by azimuthal phase scaling based on spiral coordinate transformation. Unlike traditional fractional vortex beams, it has a discontinuous radial phase and exhibits a spiral intensity distribution in the frequency domain.

[0004] Optical holography, a technique that reconstructs information about an object using computer-generated holograms, has been applied to various fields, including optical encryption, 3D display, and data storage. In traditional holography, commonly used parameters, such as light's phase, polarization, and wavelength, have been shown to function as independent channels to increase the capacity of encrypted information. To further enhance the capacity of optical encryption, photon orbital angular momentum holographic encryption has been demonstrated, utilizing photon orbital angular momentum modes as independent channels.

[0005] At present, in the research of photon orbital angular momentum holographic encryption technology, more degrees of freedom are still needed to improve information capacity and security. Spiral fractional photon orbital angular momentum holography provides new ideas in this field. Summary of the Invention

[0006] The present invention provides an information encryption device based on spiral fractional-order photon orbital angular momentum holography, which realizes the use of spiral fractional-order orbital angular momentum patterns as independent information coding channels to encrypt information, which supplements the integer-order orbital angular momentum pattern channels, greatly increases the number of information channels, and improves the information capacity and encryption security of optical holography.

[0007] In order to solve the above problems, the present invention adopts the following technical solutions:

[0008] An information encryption device based on spiral fractional photon orbital angular momentum holography comprises a light source module, a first modulation module, a 4f system, a reflector, a second modulation module and an imaging module.

[0009] The first modulation module includes a first spatial light modulator and a first beam splitter, and the first spatial light modulator is used to load a hologram that generates spiral fractional-order vortex light.

[0010] The second modulation module includes a second spatial light modulator and a second beam splitter, and the second spatial light modulator is used to load a multiplexed hologram carrying encrypted image information.

[0011] The 4f system includes a first lens, an aperture, and a second lens.

[0012] The reflector is located between the second lens and the second beam splitter, and is used to reflect the light beam emitted from the second lens onto the second beam splitter.

[0013] The first spatial light modulator is located on the front focal plane of the first lens.

[0014] The light beam emitted by the light source module is configured to pass through the first beam splitter and reach the first spatial light modulator.

[0015] The light beam is modulated by the first spatial light modulator and filtered by the 4f system, so that when a hologram of a corresponding order is loaded, a spiral fractional vortex beam of a corresponding order can be obtained on the back focal plane of the second lens.

[0016] The spiral fractional-order vortex light beam of corresponding order is modulated by the second spatial light modulator and imaged on the imaging module, wherein the second spatial light modulator is loaded with a multiplexed hologram carrying multiple encrypted image information.

[0017] In the information encryption device based on spiral fractional-order photon orbital angular momentum holography provided by at least one embodiment of the present disclosure, the first spatial light modulator and the second spatial light modulator are both reflective spatial light modulators.

[0018] In the information encryption device based on spiral fractional-order photon orbital angular momentum holography provided by at least one embodiment of the present disclosure, the light source module includes a laser, a beam expander and a linear polarizer.

[0019] The beam expander is located between the laser and the linear polarizer.

[0020] The laser is used to provide a Gaussian beam.

[0021] The linear polarizer is used to control the polarization of the Gaussian beam so that the Gaussian beam matches the working axis of the first spatial light modulator.

[0022] In the information encryption device based on spiral fractional photon orbital angular momentum holography provided by at least one embodiment of the present disclosure, the imaging module includes a third lens and a CCD camera;

[0023] The second spatial light modulator is located on the object focal plane of the third lens, and the CCD camera is located on the image focal plane of the third lens.

[0024] In the information encryption device based on spiral fractional-order photon orbital angular momentum holography provided by at least one embodiment of the present disclosure, the second spatial light modulator is loaded with a Fresnel zone plate.

[0025] The Fresnel zone plate is used to be superimposed with the multiplexed hologram to focus the reconstructed image to different spatial positions.

[0026] In the information encryption device based on spiral fractional-order photon orbital angular momentum holography provided by at least one embodiment of the present disclosure, the aperture is located between the first lens and the second lens.

[0027] The aperture is located on the rear focal plane of the first lens, and the aperture is located on the front focal plane of the second lens.

[0028] The aperture is used to filter out +1-order vortex light.

[0029] In the information encryption device based on spiral fractional photon orbital angular momentum holography provided by at least one embodiment of the present disclosure, the optical path from the second lens to the second spatial light modulator is equal to the focal length of the second lens.

[0030] The beneficial effects of the present invention are: it is possible to use the spiral fractional-order orbital angular momentum mode as an independent information encoding channel to encrypt information, which is a supplement to the integer-order orbital angular momentum mode channel, greatly increases the information channel, and improves the information capacity and encryption security of optical holography. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0032] Figure 1 Schematic diagram of the information encryption device based on spiral fractional photon orbital angular momentum holography.

[0033] Figure 2 This is a grayscale image of the vortex light loaded by the first spatial light modulator in a specific implementation example.

[0034] Figure 3 is the target image of the first specific implementation example.

[0035] Figure 4 This is a flowchart of producing multiplexed holograms according to the first specific implementation example.

[0036] Figure 5Schematic diagram of the light intensity of Gaussian light spot and non-Gaussian light spot in a specific implementation example.

[0037] Figure 6 This is the decrypted image of the first “S” in the target image of the first specific implementation example.

[0038] Figure 7 This is the decrypted image of “Y” in the target image of the first specific implementation example.

[0039] Figure 8 This is the decrypted image of the second “S” in the target image of the first specific implementation example.

[0040] Figure 9 This is the decrypted image of “U” in the target image of the first specific implementation example.

[0041] Figure 10 1 is the phase distribution of spiral fractional orbital angular momentum of different orders and the light intensity distribution in the frequency domain in a specific implementation example.

[0042] Figure 11 Graph showing the functional relationship between the frequency domain spot diameter and the topological charge of the spiral fractional orbital angular momentum in a specific implementation example.

[0043] Figure 12 is the target image of the second specific implementation example.

[0044] Figure 13 This is a flowchart of producing multiplexed holograms according to the second specific implementation example.

[0045] Figure 14 This is the decrypted image of the digital image “1” of the second specific implementation example.

[0046] Figure 15 This is the decrypted image of the digital image “2” of the second specific implementation example.

[0047] Figure 16 This is the decrypted image of the digital image “3” of the second specific implementation example.

[0048] Figure 17 This is the decrypted image of the digital image “4” of the second specific implementation example.

[0049] Figure 18 This is the decrypted image of the digital image “5” of the second specific implementation example.

[0050] Figure 19 This is a flowchart of producing multiplexed holograms according to the third specific implementation example.

[0051] Figure 20 This is the decrypted image of the letter image “O” of the third specific implementation example.

[0052] Figure 21 This is the decrypted image of the letter image “A” of the third specific implementation example.

[0053] Figure 22 This is the decrypted image of the letter image “M” of the third specific implementation example.

[0054] In the picture:

[0055] 1. Laser; 2. Beam expander; 3. Linear polarizer; 4. First spatial light modulator; 5. First beam splitter; 6. First lens; 7. Aperture; 8. Second lens; 9. Reflector; 10. Second spatial light modulator; 11. Second beam splitter; 12. Third lens; 13. CCD camera. DETAILED DESCRIPTION

[0056] The technical solutions in the embodiments will be described clearly and completely below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments, rather than all the embodiments.

[0057] Example

[0058] like Figure 1 As shown, an information encryption device based on spiral fractional photon orbital angular momentum holography includes: a light source module, a first modulation module, a 4f system, a reflector 9, a second modulation module and an imaging module.

[0059] Specifically, the first modulation module includes a first spatial light modulator 4 and a first beam splitter 5. The first spatial light modulator 4 is used to load a hologram that generates spiral fractional-order vortex light.

[0060] Specifically, the second modulation module includes a second spatial light modulator 10 and a second beam splitter 11. The second spatial light modulator 10 is used to load the multiplexed hologram carrying encrypted image information.

[0061] Specifically, the 4f system includes a first lens 6, an aperture 7 and a second lens 8; a reflector 9 is located between the second lens 8 and the second beam splitter 11, and the reflector 9 is used to reflect the light beam emitted from the second lens 8 to the second beam splitter 11; the first spatial light modulator 4 is located on the front focal plane of the first lens 6.

[0062] Specifically, the light beam emitted by the light source module is configured to pass through the first beam splitter 5 and reach the first spatial light modulator 4; the light beam is modulated by the first spatial light modulator 4 and filtered by the 4f system, so that when a hologram of a corresponding order is loaded, a spiral fractional-order vortex beam of a corresponding order can be obtained on the back focal plane of the second lens 8; the spiral fractional-order vortex beam of a corresponding order is modulated by the second spatial light modulator and imaged on the imaging module, wherein the second spatial light modulator is loaded with a multiplexed hologram carrying multiple encrypted image information.

[0063] In this embodiment, both the first spatial light modulator 4 and the second spatial light modulator 10 are reflective spatial light modulators.

[0064] In this embodiment, the light source module includes a laser 1, a beam expander 2 and a linear polarizer 3; the beam expander 2 is located between the laser 1 and the linear polarizer 3; the laser 1 is used to provide a Gaussian beam; the linear polarizer 3 is used to control the polarization of the Gaussian beam so that the Gaussian beam matches the working axis of the first spatial light modulator 4.

[0065] In this embodiment, the aperture 7 is located between the first lens 6 and the second lens 8; the aperture 7 is located on the rear focal plane of the first lens 6, and the aperture 7 is located on the front focal plane of the second lens 8; the aperture 7 is used to filter the +1-order vortex light; the optical path from the second lens 8 to the second spatial light modulator 10 is equal to the focal length of the second lens 8.

[0066] In some embodiments, the imaging module includes a third lens 12 and a CCD camera 13 ; the second spatial light modulator 10 is located on the object focal plane of the third lens 12 , and the CCD camera 13 is located on the image focal plane of the third lens 12 .

[0067] In some embodiments not shown, the second spatial light modulator has a Fresnel zone plate, which is used to superimpose with the multiplexed hologram to focus the reconstructed image to different spatial positions, replacing the function of the third lens.

[0068] Therefore, the imaging module in this embodiment only includes a CCD camera.

[0069] Three specific implementation examples of encrypting and decrypting multiple images are provided below.

[0070] like Figure 2-9 As shown in the first specific implementation example, the four letters "S", "Y", "S" and "U" are subjected to spiral fractional orbital angular momentum multiplexing at non-overlapping positions in the picture.

[0071] The four letters "S", "Y", "S" and "U" are multiplexed in spiral fractional orbital angular momentum at non-overlapping positions in the image. Figure 3 is the target image. Figure 4 This is the process of generating a multiplexed hologram. The four letters "S", "Y", "S" and "U" of the target image are first sampled, and then the corresponding four holograms are generated by the GS algorithm. Then, four spiral phase plates with orders l = -1.2, l = -2, l = -2.7 and l = -3.3 are used to superimpose these four holograms for encoding, thereby obtaining four selective holograms. Combining these four holograms can obtain a multiplexed hologram. The multiplexed hologram is loaded onto the second spatial light modulator 10. If the first spatial light modulator 4 is loaded with a phase plate conjugated to a certain encoding order, a spiral fractional-order vortex beam conjugated to the encoding order can be obtained. When the beam is irradiated onto the second spatial light modulator 10, it can be observed on the CCD camera 13 that the pixel points of the corresponding letters are Gaussian point distributions, while the pixel points of other letters are still a spiral intensity distribution. Figure 5 Comparing the two intensities, since the intensity of the Gaussian point is much higher than that of the spiral point, we only need to set a threshold for filtering to obtain the encrypted letter image. Figure 6-Figure 9 The decrypted images obtained by the CCD camera 13 are obtained by illuminating the multiplexed hologram with vortex light of l=1.2, l=2, l=2.7 and l=3.3 respectively and filtering.

[0072] When sampling the target image, the sampling interval should be ensured to be larger than the frequency domain spot diameter of the incident spiral fractional orbital angular momentum beam. Figure 10 is the phase distribution of different fractional orders and the intensity distribution in the frequency domain, d is the diameter of the frequency domain spot, which is defined as the spacing at 30% of the peak value of the spot. Figure 11 The figure shows the functional relationship between the frequency domain spot diameter and the topological charge. Only when the sampling interval is larger than the frequency domain spot diameter can the characteristics of the incident light be preserved at every pixel, meaning that each pixel has a spot shape identical to the incident light's frequency domain. Otherwise, if the sampling interval is too small, the spots between pixels will interfere with each other, thus destroying the characteristics of the incident light and ultimately introducing crosstalk into the encryption system.

[0073] like Figures 12 to 18 As shown in the second specific implementation example, the five numbers "1", "2", "3", "4" and "5" are subjected to spiral fractional orbital angular momentum multiplexing at the overlapping positions of the picture.

[0074] The five numbers "1", "2", "3", "4" and "5" are multiplexed in spiral fractional orbital angular momentum at overlapping positions in the image. Figure 12 is the target image. Figure 13This is the generation process of the multiplexed hologram. Similar to the first part, five spiral fractional-order phase plates with l = -5.9, l = -3.1, l = -1.2, l = 2.8 and l = 4.3 are randomly selected to encode five digital pictures "1", "2", "3", "4" and "5". Figures 14-18 The decrypted images obtained by the CCD camera 13 are obtained by illuminating the multiplexed hologram with vortex light of l=1.2, l=2, l=2.7 and l=3.3 respectively and filtering.

[0075] like Figures 19 to 22 As shown, in a third specific implementation example, the three letters "O", "A" and "M" are subjected to three-dimensional spiral fractional orbital angular momentum multiplexing at overlapping positions in the picture.

[0076] The three letters "O", "A" and "M" are multiplexed in three-dimensional spiral fractional orbital angular momentum at the overlapping positions of the image. Figure 19 This is the process of generating a multiplexed hologram. Unlike the previous one, during the encryption process, the hologram obtained through sampling and the GS algorithm is superimposed not only with a spiral phase plate but also with a Fresnel zone plate. Spiral fractional phase plates with l = -1.2, l = -2.1, and l = -2.8 are used with FZPs with focal lengths of f = 60, f = 130, and f = 200 mm, respectively, to encode images "O," "A," and "M," thereby generating holograms with selectivity for orbital angular momentum and imaging distance. Combining these three selective holograms yields a multiplexed hologram. The role of different Fresnel zone plates is to focus the reconstructed image to different spatial locations, replacing the role of the third lens 12. Therefore, the third lens 12 can be omitted in this embodiment, meaning that the imaging module consists solely of the CCD camera 13. Only when a vortex beam of the correct decoding order illuminates the second spatial light modulator 10 can a reconstructed image be obtained at the correct imaging distance. For example, when a beam with an l = 2.1 is incident on the multiplexed hologram, the reconstructed image "O" can only be obtained at an imaging distance of 60 mm. The imaging distance refers to the distance from the second spatial light modulator 10 to the CCD camera 13. This further improves the security of information encryption.

[0077] In this example, the order used to encode the spiral fractional orbital angular momentum is not limited to the order used above, and can be any fractional order or integer order. The minimum channel spacing can reach 0.6, which greatly improves the information capacity compared to the traditional integer decomposition orbital angular momentum holographic encryption system.

[0078] Although the embodiments of the present application have been shown and described above, the scope of protection of the present invention is not limited thereto, and any changes or substitutions that are not conceivable through creative work should be included in the scope of protection of the present invention; unless expressly stated, any elements, actions or instructions used in this document should not be interpreted as critical or necessary.

Claims

1. An information encryption device based on spiral fractional photon orbital angular momentum holography, characterized in that: include: Light source module, first modulation module, 4f system, reflector, second modulation module and imaging module; The first modulation module includes a first spatial light modulator and a first beam splitter, wherein the first spatial light modulator is used to load a hologram that generates spiral fractional vortex light; The second modulation module includes a second spatial light modulator and a second beam splitter, and the second spatial light modulator is used to load a multiplexed hologram carrying encrypted image information; The 4f system includes a first lens, an aperture, and a second lens; The reflector is located between the second lens and the second beam splitter, and is used to reflect the light beam emitted from the second lens onto the second beam splitter; The first spatial light modulator is located on the front focal plane of the first lens; The light beam emitted by the light source module is configured to pass through the first beam splitter and reach the first spatial light modulator; The light beam is modulated by the first spatial light modulator and filtered by the 4f system, so that when a hologram of a corresponding order is loaded, a spiral fractional vortex beam of a corresponding order can be obtained on the back focal plane of the second lens; The spiral fractional-order vortex beam of the corresponding order is modulated by a second spatial light modulator and imaged on the imaging module, wherein the second spatial light modulator is loaded with a multiplexed hologram carrying multiple encrypted image information; The second spatial light modulator is loaded with a Fresnel zone plate; The Fresnel zone plate is used to be superimposed with the multiplexed hologram to focus the reconstructed image to different spatial positions.

2. The information encryption device based on spiral fractional photon orbital angular momentum holography according to claim 1, characterized in that: The first spatial light modulator and the second spatial light modulator are both reflective spatial light modulators.

3. The information encryption device based on spiral fractional photon orbital angular momentum holography according to claim 1, characterized in that: The light source module includes a laser, a beam expander and a linear polarizer; The beam expander is located between the laser and the linear polarizer; The laser is used to provide a Gaussian beam; The linear polarizer is used to control the polarization of the Gaussian beam so that the Gaussian beam matches the working axis of the first spatial light modulator.

4. The information encryption device based on spiral fractional photon orbital angular momentum holography according to claim 3, characterized in that: The aperture is located between the first lens and the second lens; The aperture is located on the back focal plane of the first lens, and the aperture is located on the front focal plane of the second lens; The aperture is used to filter out +1-order vortex light.

5. The information encryption device based on spiral fractional photon orbital angular momentum holography according to claim 1, characterized in that: An optical distance from the second lens to the second spatial light modulator is equal to a focal length of the second lens.

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