A polarization-based optical holographic encryption method

Abstract

The present invention discloses a polarization-based optical holographic encryption method, which includes: generating an initial field distribution U0 with a random phase and amplitude of X everywhere on the main plane; combining the initial field distribution U0 with the propagation distance to encrypt the field distribution U0 of the information; B Iterate and obtain the sub-hologram H B ; Sub-hologram H formed by encrypted information B Perform phase encoding and obtain H′ B , that is, the encrypted sub-hologram. Multiple encrypted sub-holograms and non-encrypted sub-holograms can be synthesized to obtain the final hologram H. The holographic image of non-encrypted information only needs to be projected in the spatial domain to appear, while the holographic image of encrypted information requires vortex wave plates and polarizers to be decoded at the device level to obtain.

Description

Technical Field

[0001] The present invention relates to the field of optical anti-counterfeiting information encryption, and in particular to an optical holographic encryption method based on polarization. Background Art

[0002] Optical holography is the process of using one or more holograms to reproduce a desired intensity distribution at a specific depth, that is, to reproduce a holographic image at this specific depth.

[0003] Most of the current holographic technologies can only achieve amplitude control, a small part involves phase control, and very few can achieve polarization control of holograms.

[0004] Existing single holograms using holographic encoding technology can only constrain the amplitude and phase of the expected holographic image due to the limitations of scalar optical calculation methods. In addition, mainstream devices such as spatial light modulators and diffractive optical elements cannot achieve multi-polarization control.

[0005] Therefore, there is an urgent need for a polarization-based optical holographic encryption method that can solve one or more of the above problems. Summary of the Invention

[0006] To address one or more problems existing in the prior art, the present invention provides a polarization-based optical holographic encryption method. The present invention employs a technical solution to address the aforementioned problems: a polarization-based optical holographic encryption method comprising: generating an initial field distribution U0 with a random phase and an amplitude of X on a principal plane, wherein the initial field distribution U0 dynamically changes with each use;

[0007] The propagation function from the principal plane to a certain plane is Where i is the imaginary unit, m is the magnification of the output surface relative to the input surface, λ is the wavelength of the incident light, z is the propagation distance, f1 is the frequency domain coordinate, r2 is the optical vector of the display surface, r1 is the optical vector of the input surface, N is the number of pixels in the horizontal or vertical direction, d1 is the pixel size of the input surface, and d2 is the pixel size of the output surface, i.e., the image surface. is the frequency domain interval;

[0008] The field distribution of encrypted information is recorded as field distribution U B , the initial field distribution U0 propagates Z2 distance to reach plane B, then the amplitude distribution of the initial field distribution U0 is replaced by the field distribution U B Target amplitude distribution Keep the phase information unchanged, and then propagate back to the main plane, and then replace the amplitude of the main plane with X, keep the phase unchanged, and iterate several times as needed to obtain the sub-hologram H corresponding to the encrypted information B, each encrypted information forms a corresponding different sub-hologram;

[0009] The sub-hologram H formed for the encrypted information B Phase encoding is performed, and the phase encoding formula is: H′ B =exp(i·(angle(cos(lφ(x,y)))+angle(H B )), where angle function represents the angular distribution in the complex distribution, l is the topological charge of the vortex wave plate, x and y are the one-dimensional coordinates of the principal plane, and φ(x,y)=arctan(y / x).

[0010] In some embodiments, if there is non-encrypted information, the field distribution of the non-encrypted information is recorded as field distribution U A , the initial field distribution U0 propagates Z1 distance to reach plane A, then the amplitude distribution of the initial field distribution U0 is replaced by the field distribution U A Target amplitude distribution Keep the phase information unchanged, and then propagate back to the main plane, and then replace the amplitude of the main plane with X, keep the phase unchanged, and iterate several times as needed to obtain the sub-hologram H corresponding to the non-encrypted information. A Each of the non-encrypted information corresponds to a different sub-hologram.

[0011] Furthermore, if there is the non-encrypted information, the synthesis formula of the sub-hologram of the encrypted information and the sub-hologram of the non-encrypted information is: H = exp(i·angle(H A +H′ B )).

[0012] In some embodiments, for convenience of calculation, the amplitude X is 1.

[0013] In some embodiments, the initial field distribution U0 = exp(i(2π·random(N,N)-π)), where i is an imaginary unit, random(M,N) represents the generation of an M×N matrix, where all matrix elements are random values ​​0-1, and exp represents an exponential function with the natural constant e as the base.

[0014] In particular, whether to include non-encrypted information, and the amount of encrypted information and non-encrypted information depends on requirements.

[0015] The technical effect achieved by the present invention is that the phase distribution of H obtained after the above synthesis or the H′ of the independent encrypted information B The phase distribution can be a phase-only hologram;

[0016] Take H as an example (including H A and H′B ), where the encrypted information H′ B The number of non-encrypted information H is set to 1. A The number of H phase distributions is also set to 1. The H phase distribution is loaded into the spatial light modulator as the main plane, and the main plane can simultaneously produce different images on two planes at different distances. Among them, a single phase distribution can carry multiple plane information, and after being expanded to more planes, a 3D effect can be produced.

[0017] Non-encrypted information H A The holographic image only needs to be projected in the airspace to appear, and the encrypted information H′ B The holographic image requires vortex wave plate and polarizer to be decoded at the device level; in addition, if a quarter wave plate is used instead of a polarizer, the decoding effect under circular polarization can be achieved, that is, if the encrypted information H′ B If there are multiple holographic images, they will be decoded simultaneously; the number of encrypted information and its polarization states has been expanded to achieve simultaneous encryption of multiple polarizations, multiple depths, and multiple images; the number and position of encrypted information can be adjusted according to actual needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a schematic diagram of information to be synthesized in an embodiment of the present invention;

[0019] Figure 2 A process diagram of information synthesis in an embodiment of the present invention;

[0020] Figure 3 A brief flow chart of an embodiment of the present invention;

[0021] Figure 4 Optical path diagram for observing holographic phase or recording phase to CCD;

[0022] Figure 5 Light path diagram for recovering information on holographic dry plate;

[0023] Figure 6 An example of hologram recovery. DETAILED DESCRIPTION

[0024] To make the above-mentioned objects, features, and advantages of the present invention more readily understood, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. The following description sets forth many specific details to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art can make similar modifications without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0025] The present invention discloses a polarization-based optical holographic encryption method, the embodiments of which are as follows:

[0026] Combine Figure 1-Figure 3 As shown, this embodiment includes common information U A , encrypted information U B and U C , then the polarization-based encoding process for a single hologram is:

[0027] S1, the main plane generates an initial field distribution U0 with a random phase and amplitude of X (in this embodiment, X=1). The initial field distribution U0 will dynamically change each time it is used, wherein the initial field distribution U0=exp(i(2π·random(N,N)-π)), where i is an imaginary unit, random(M,N) represents the generation of an M×N matrix with random values ​​of 0-1 for all matrix elements, and exp represents an exponential function with the natural constant e as the base;

[0028] The propagation function from the principal plane to a certain plane is Where i is the imaginary unit, m is the magnification of the output surface relative to the input surface, λ is the wavelength of the incident light, z is the propagation distance, f1 is the frequency domain coordinate, r2 is the optical vector of the display surface, r1 is the optical vector of the input surface, N is the number of pixels in the horizontal or vertical direction, d1 is the pixel size of the input surface, and d2 is the pixel size of the output surface, i.e., the image surface. is the frequency domain interval;

[0029] In numerical calculations, the two-dimensional Fourier transform is implemented by discrete fast Fourier transform (FFT), the propagation function U(r2) is abbreviated as F(U,d1,d2,z,λ,N), and the angle function is used to represent the angular distribution in the complex distribution, that is, (2π·random(N,N)―π) is simplified;

[0030] S2, for ordinary information U A , which is non-encrypted information, then the field distribution of non-encrypted information is recorded as field distribution U A , the initial field distribution U0 propagates Z1 distance to reach plane A, then the amplitude distribution of the initial field distribution U0 is replaced by the field distribution U A Target amplitude distribution Keep the phase information unchanged, and then propagate back to the main plane, and then replace the amplitude of the main plane with 1, keep the phase unchanged, and iterate several times as needed to obtain the sub-hologram H corresponding to the non-encrypted information. A ;

[0031] It should be noted that each piece of the non-encrypted information corresponds to a different sub-hologram, and this embodiment only sets one.

[0032] The iterative process is as follows: 1. The initial field distribution U0 propagates Z1 distance to reach plane A, then U A =F(U0,d0,d1,z1,λ,N);

[0033] 2. Replace the amplitude distribution of the initial field distribution U0 with the field distribution U A Target amplitude distribution At this time

[0034] 3. Keep the phase information unchanged and propagate back to the main plane. Then U0=F(U A ,d1,d0,―z1,λ,N);

[0035] 4. Replace the amplitude of the principal plane with 1, keeping the phase unchanged, then U0 = exp(i·angle(U0));

[0036] 5. Repeat the iteration several times as needed, then H A Equal to U0 obtained after several iterations.

[0037] S3, for the encrypted information U B , the initial field distribution U0 propagates Z2 distance to reach plane B, then the amplitude distribution of the initial field distribution U0 is replaced by the field distribution U B Target amplitude distribution Keep the phase information unchanged, and then propagate back to the main plane, and then replace the amplitude of the main plane with 1, keep the phase unchanged, and iterate several times as needed to obtain the sub-hologram H corresponding to the encrypted information. B ;

[0038] The iterative process is as follows: 1. The initial field distribution U0 propagates Z2 distance to reach plane B, then U B =F(U0,d0,d2,z2,λ,N);

[0039] 2. Replace the amplitude distribution of the initial field distribution U0 with the field distribution U B Target amplitude distribution At this time

[0040] 3. Keep the phase information unchanged and propagate back to the main plane. Then U0=F(U B ,d2,d0,―z2,λ,N);

[0041] 4. Replace the amplitude of the principal plane with 1, keeping the phase unchanged, then U0 = exp(i·angle(U0));

[0042] 5. Repeat the iteration several times as needed, then H BEqual to U0 obtained after several iterations.

[0043] S4, for the encrypted information U C , the initial field distribution U0 propagates Z3 distance to reach the C plane, then the amplitude distribution of the initial field distribution U0 is replaced by the field distribution U C Target amplitude distribution Keep the phase information unchanged, and then propagate back to the main plane, and then replace the amplitude of the main plane with 1, keep the phase unchanged, and iterate several times as needed to obtain the sub-hologram H corresponding to the encrypted information. C ;

[0044] The iterative process is as follows: 1. The initial field distribution U0 propagates Z3 distance to reach the C plane, then U C =F(U0,d0,d3,z3,λ,N);

[0045] 2. Replace the amplitude distribution of the initial field distribution U0 with the field distribution U C Target amplitude distribution At this time

[0046] 3. Keep the phase information unchanged and propagate back to the main plane. Then U0=F(U C ,d3,d0,―z3,λ,N);

[0047] 4. Replace the amplitude of the principal plane with 1, keeping the phase unchanged, then U0 = exp(i·angle(U0));

[0048] 5. Repeat the iteration several times as needed, then H C Equal to U0 obtained after several iterations.

[0049] S5, the above three relatively independent iterative processes obtain three different holograms H A 、H B and H C , where U0 in each iterative process changes dynamically. A As an explicit hologram containing ordinary information, no encoding is required; H B and H C It is a hologram that needs to be encrypted. After encoding, it needs to use vortex wave plates and polarizers to decode it. Then H B and H C The phase encoding is: H′ B =exp(i·(angle(cos(lφ(x,y)))+angle(H B )), H′ C=exp(i·(angle(sin(―lφ(x,y)))+angle(H C ));

[0050] Where l is the topological charge of the vortex wave plate. Accurate decoding is only possible when a specific vortex wave plate that matches the encoding situation is used. x and y are the one-dimensional coordinates of the principal plane, respectively, and φ(x,y)=arctan(y / x).

[0051] Then a single hologram is synthesized, hologram H = exp(i·angle(H A +H′ B +H′ C )), the phase distribution of H is a phase-only hologram. This phase is loaded into the spatial light modulator as the main plane, which can simultaneously produce different images on three planes A, B, and C at different distances.

[0052] Combine Figure 2 As shown, U A 、U B and U C The image information in are patterns, letters and numbers, which are synthesized and output as the holographic image in H through the above process.

[0053] Combine Figure 3 As shown, the simplified synthesis process of the above embodiment is: the initial field distribution U0 is combined with U A The sub-hologram H will be generated A ; Initial field distribution U0 combined with U B The sub-hologram H will be generated B , then H B Phase encoding is performed to obtain B′ B ; Initial field distribution U0 combined with U C The sub-hologram H will be generated C , then H C Phase encoding is performed to obtain B′ C ;H A , B′ B and H′ C Finally, the hologram H is synthesized.

[0054] Specifically, the observation process of the hologram H in the above embodiment is as follows: Figure 4As shown, the laser light emitted by the first laser 100 passes through the first electronic shutter (or polarizer) 101, which is electrically connected to the first computer 106 to control the exposure time. The laser light passes through the first diverging lens 102 and the first converging lens 103 and is modulated into parallel light. The parallel light passes through the first polarization beam splitter prism 104 and hits the first spatial light modulator 105. The first spatial light modulator 105 is electrically connected to the first computer 106. The first computer 106 loads the generated hologram into the first spatial light modulator, so that the first spatial light modulator can output light with phase information. The light passes through the 4f system composed of the first lens 107, the first aperture 108, and the second lens 109 to filter out the zero-order speckle.

[0055] The light hitting the observation screen 112 can be directly observed by the human eye 113 or captured by the camera 114. The camera 114 is electrically connected to the first computer 106 and obtains the reconstructed holographic image from the first computer 106 in real time. If the first device 110 (vortex wave plate) and the second device 111 (polarizer or quarter wave plate) are not added, that is, polarization decoding is not performed, then only ordinary information U can be obtained. A If the vortex wave plate 110 and the polarizer 111 are added to obtain linearly polarized light, then the information U can be observed. B or U C If the vortex wave plate 110 and the quarter wave plate 111 are added, circularly polarized light is obtained, and the circularly polarized light can be decomposed into linearly polarized light in two directions, then the information U can be observed at the same time. B and U C .

[0056] Specifically, the observation process of the hologram H in the above embodiment can also be as follows: Figure 5 As shown, the calculated hologram is recorded on the holographic dry plate 204. The laser light emitted by the second laser 200 is modulated into parallel light through the second aperture 201, the second diverging lens 202, and the second converging lens 203, and then hits the second observation screen 207. At this time, it can be directly observed by the human eye 208, and the only information observed is U A A vortex wave plate 205 and a second device 206 (polarizer or quarter wave plate) are added between the holographic dry plate 204 and the second observation screen 207. If the second device 206 is a polarizer, linear polarized light is obtained, and the information U can be observed. B or U C If the second device 206 is a quarter wave plate, circularly polarized light is obtained, which can be decomposed into linearly polarized light in two directions, and then the information U can be observed at the same time B and U C .

[0057] Combine Figure 6 As shown, Figure 6 Figure a is a schematic diagram of the hologram restored using plane light. It can be seen that there is only a pattern in figure a, namely U A can be observed, and U B and U C None of them can be observed; Figure 6 Figure b is a schematic diagram of the hologram restored using s-polarized light. It can be seen that there are only letters in Figure b, namely U B can be observed, and U A and U C None of them can be observed; Figure 6 Figure c is a schematic diagram of the hologram restored using left-handed circularly polarized light. It can be seen that there are letters and numbers in Figure c, namely U B and U C can be observed, and U A Cannot be observed.

[0058] It should be pointed out that the information transmission of the holographic image includes amplitude information and phase information, that is, three-dimensional information can be transmitted. The technical solution of the present application can also realize the encryption, transmission and decoding of amplitude information and phase information.

[0059] In summary, the present invention realizes the non-encrypted information H A The holographic image only needs to be projected in the airspace to appear, and the encrypted information H′ B The holographic image requires vortex wave plate and polarizer to be decoded at the device level; in addition, if a quarter wave plate is used instead of a polarizer, the decoding effect under circular polarization can be achieved, that is, if the encrypted information H′ B If there are multiple holographic images, they will be decoded simultaneously; the number of encrypted information and its polarization states has been expanded to achieve simultaneous encryption of multiple polarizations, multiple depths, and multiple images; the number and position of encrypted information can be adjusted according to actual needs.

[0060] The embodiments described above merely represent one or more embodiments of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art may make various modifications and improvements without departing from the scope of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A polarization-based optical holographic encryption method, characterized in that: include: The main plane generates an initial field distribution U0 with a random phase and an amplitude of X everywhere. The initial field distribution U0 will change dynamically each time it is used. The propagation function from the principal plane to a certain plane is Where i is the imaginary unit, m is the magnification of the output surface relative to the input surface, λ is the wavelength of the incident light, z is the propagation distance, f1 is the frequency domain coordinate, r2 is the optical vector of the display surface, r1 is the optical vector of the input surface, N is the number of pixels in the horizontal or vertical direction, d1 is the pixel size of the input surface, and d2 is the pixel size of the output surface, i.e., the image surface. is the frequency domain interval; The field distribution of encrypted information is recorded as field distribution U B , the initial field distribution U0 propagates Z2 distance to reach plane B, then the amplitude distribution of the initial field distribution U0 is replaced by the field distribution U B Target amplitude distribution Keep the phase information unchanged, and then propagate back to the main plane, and then replace the amplitude of the main plane with X, keep the phase unchanged, and iterate several times as needed to obtain the sub-hologram H corresponding to the encrypted information B , each encrypted information forms a corresponding different sub-hologram; The sub-hologram H formed for the encrypted information B Phase encoding is performed, and the sub-hologram H B Execute the phase encoding to obtain the encrypted information H′ B , the phase encoding formula is: H′ B =exp(i·(angle(cos(lφ(x,y)))+angle(H B )), where angle function represents the angular distribution in the complex distribution, l is the topological charge of the vortex wave plate, x and y are the one-dimensional coordinates of the principal plane, and φ(x,y)=arctan(y / x).

2. The polarization-based optical holographic encryption method according to claim 1, characterized in that: If there is non-encrypted information, the field distribution of the non-encrypted information is recorded as field distribution U A , the initial field distribution U0 propagates Z1 distance to reach plane A, then the amplitude distribution of the initial field distribution U0 is replaced by the field distribution U A Target amplitude distribution Keep the phase information unchanged, and then propagate back to the main plane, and then replace the amplitude of the main plane with X, keep the phase unchanged, and iterate several times as needed to obtain the sub-hologram H corresponding to the non-encrypted information. A Each of the non-encrypted information corresponds to a different sub-hologram.

3. The polarization-based optical holographic encryption method according to claim 2, characterized in that: If there is the non-encrypted information, the synthesis formula of the sub-hologram of the encrypted information and the sub-hologram of the non-encrypted information is: H = exp(i·angle(H A +H′ B )).

4. The polarization-based optical holographic encryption method according to claim 1, characterized in that: The amplitude X is 1.

5. The polarization-based optical holographic encryption method according to claim 1, characterized in that: The initial field distribution U0=exp(i(2π·random(M,N)-π)), where i is an imaginary unit, random(M,N) represents the generation of an M×N matrix, the matrix elements of which are all random values ​​0-1, and exp represents an exponential function with the natural constant e as the base.

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