Mechanically modulated optical encryption system and dynamic holographic image switching method

Abstract

The present invention discloses a mechanically modulated optical encryption system and a dynamic holographic image switching method. The system includes a light source, a composite phase plate, a convex lens and an image acquisition device arranged in sequence. The composite phase plate includes two phase plates arranged in parallel. The two phase plates are encoded with vortex phase information. The image phase is increased on one of the phase plates. At least one of the phase plates is connected to a rotation drive device, which is used to modulate the phase of the corresponding phase plate. The light beam emitted by the light source is modulated by the composite phase plate and outputs vortex light. The topological charge of the vortex light is adjusted by regulating the relative rotation amount of the two phase plates. At the same time, a dynamic holographic image switching method based on the above system is disclosed. The relative rotation angle of the two phase plates is related to the topological charge of the output vortex light. A simple composite phase plate structure is used to realize single-beam multi-topological charge output, reduce system complexity, and store high-density information with only two phase plates at low cost.

Description

Technical Field

[0001] The present invention relates to the field of optical technology, and in particular to a mechanically modulated optical encryption system and a dynamic holographic image switching method. Background Art

[0002] Holographic technology provides a method for reconstructing intensity and phase information and has been achieved using X-rays, electron beams, neutron beams, and optical beams (including surface plasmons). In the field of optics, the different physical dimensions of light, including polarization, wavelength, and time, have been used to provide independent information channels for large-capacity holographic systems. Dynamically adjustable holographic imaging technology is one of the core research directions in the field of optical information. Its goal is to achieve multi-mode image switching through real-time control of physical parameters. It has important applications in fields such as three-dimensional display, optical encryption, and dynamic optical labels. Traditional dynamic holographic technology mostly relies on external modulation methods such as electrically controlled liquid crystals, micro-electromechanical systems, or wavelength tuning. For example, liquid crystal spatial light modulators can achieve dynamic holographic reconstruction by controlling the phase distribution through voltage, but their response speed is limited, and the system is complex and costly.

[0003] In this context, dynamic holographic technology based on mechanical modulation has attracted much attention due to its advantages such as no need for external energy and simple structure. Figure 1 As shown, existing vortex optical encryption systems are typically composed of three core modules: a light source module, a phase modulation module, and an imaging module. The light source module includes a laser and a vortex optical phase modulator, responsible for generating a vortex light field carrying a specific topological charge. The phase modulation module holographically encodes the incident vortex light to achieve information encryption. The imaging module includes an imaging system and an image collector to reconstruct the decrypted image. The vortex optical phase modulator in the light source module can be a spiral phase plate, a liquid crystal spatial light modulator, or a metasurface. The spiral phase plate can only capture light with one topological charge at a time, requiring the incident light to be modulated. Changing the topological charge requires replacing the phase plate, which is very inconvenient. Both liquid crystal spatial light modulators and metasurfaces are expensive, and the liquid crystal spatial light modulator has low energy utilization and slow modulation speed. It requires real-time computer control of the phase diagram, resulting in millisecond-level operation delays, making it difficult to meet high-speed encryption requirements. Metasurfaces only modulate within the visible light range and are significantly affected by temperature and humidity. Metasurfaces require nanofabrication such as electron beam lithography, and the cost of a single piece exceeds 10,000 yuan. Summary of the Invention

[0004] The purpose of the present invention is to provide a mechanically modulated optical encryption system and a dynamic holographic image switching method to solve the above technical problems.

[0005] To achieve the above object, the present invention provides a mechanically modulated optical encryption system, comprising a light source, a composite phase plate, a convex lens, and an image acquisition device arranged in sequence;

[0006] The composite phase plate includes two phase plates arranged in parallel, the two phase plates are encoded with vortex phase information, one of the phase plates increases the image phase, at least one of the phase plates is connected to a rotation drive device, the rotation drive device is used to modulate the phase of the corresponding phase plate, the phase plate opposite to the light source is the first phase plate, the phase plate opposite to the convex lens is the second phase plate, the second phase plate is arranged at the front focal plane position of the convex lens, the image acquisition device is arranged at the back focal plane position of the convex lens, the light beam emitted by the light source is modulated by the composite phase plate and vortex light is output; the topological charge of the vortex light is adjusted by regulating the relative rotation amount of the two phase plates, when the topological charge of the vortex light is consistent with the correct topological charge, the vortex light is converted into a recognizable pattern without crosstalk through the convex lens and the image acquisition device, when the topological charge of the vortex light is inconsistent with the correct topological charge, the vortex light is converted into a blurred image with crosstalk through the convex lens and the image acquisition device.

[0007] Preferably, the light source is a laser, and the laser emits a Gaussian beam.

[0008] Preferably, the distance between the first phase plate and the second phase plate is no more than 30 mm, the vortex phase information of the first phase plate and the second phase plate are opposite, and both the first phase plate and the second phase plate are liquid crystal phase plates.

[0009] The specific steps of the dynamic holographic image switching method of the mechanically modulated optical encryption system are as follows:

[0010] Step S1: The light source emits a Gaussian beam, which serves as a detection light source;

[0011] Step S2: adjusting the relative rotation angle of the first phase plate and the second phase plate by a rotation drive device so that the phases of the first phase plate and the second phase plate after relative rotation are superimposed; the Gaussian beam passes through the rotated first phase plate and the second phase plate to generate vortex light of corresponding topological charge;

[0012] Step S3: The vortex light corresponding to the topological charge is Fourier transformed through a convex lens and then converted into an identification pattern or a ring pattern through an image acquisition device. When the topological charge of the vortex light is consistent with the correct topological charge, the image acquisition device restores the Fourier transformed light beam to a Gaussian spot array to form a recognizable pattern without crosstalk. When the topological charge of the vortex light is inconsistent with the correct topological charge, the image acquisition device captures the image as a blurred image with crosstalk.

[0013] Preferably, in step S2, the initial phases of the first phase plate and the second phase plate are and ,in, and Expressed as radial coordinates and angular coordinates in the polar coordinate system respectively.

[0014] Preferably, the rotation angles of the first phase plate and the second phase plate around the optical axis are and , the joint phase after phase superposition The calculation formula is as follows:

[0015] , the phase distribution of vortex light in the polar coordinate system is as follows: ,in, is the topological charge after phase superposition, To achieve the relative rotation angle, the image phase is increased on one of the phase plates.

[0016] Preferably, in step S2, the initial phases of the first phase plate and the second phase plate are respectively as follows:

[0017] ;

[0018] ;

[0019] The first phase plate remains stationary, and the second phase plate rotates. The rotation angle of the second phase plate is , the phases of the first phase plate and the second phase plate after relative rotation are as follows:

[0020] ;

[0021] ;

[0022] Joint Aspect The calculation formula is as follows:

[0023] ;

[0024] ;

[0025] Joint Phase Quantization and offset are performed as follows:

[0026] Quantization: The angle range The step length is Divide into share, , through The phase profiles of the two phase plates are quantized for the step size and are obtained by The fuzzy sector is corrected by integer multiple phase compensation. After quantization, the phase functions of the two phase plates are as follows:

[0027] ;

[0028] ;

[0029] in, is an integer, , is the rounding function, in order to obtain integer topological charge, Needs to be satisfied, , is an integer and should satisfy ;

[0030] Offset: Joint Phase as follows:

[0031] ;

[0032] After simplification, we get:

[0033] ;

[0034] The image phase is increased by the second phase plate. The phase expression of the second phase plate with the increased image phase is as follows:

[0035] ;

[0036] in, is the image phase, is the phase of the second phase plate superimposed with the image phase;

[0037] The combined aspects are as follows:

[0038] ;

[0039] when When the first phase plate and the second phase plate do not rotate relative to each other, the phases cancel each other out, and an image with increased image phase is displayed. When , the result contains vortex phases, and a blurred image with crosstalk is displayed due to the crosstalk between phases.

[0040] Preferably, multiple images are encrypted by superimposing patterns with different rotation phases, and the specific steps are as follows:

[0041] Rotate the initial phase Then the rotation phase is obtained, , is the number of images, and the rotation phase is , the corresponding image phase is superimposed with the corresponding rotation phase to obtain the corresponding image phase as follows:

[0042] ;

[0043] in, For the image phase, The first The image phase, the final phase of the second phase plate is as follows:

[0044] ;

[0045] in, is the final phase of the second phase plate, is the argument function of the complex number, Complex exponential operation function. When the phase plate is rotated to the corresponding angle, the corresponding image will be displayed.

[0046] Therefore, the present invention adopts the above-mentioned mechanically modulated optical encryption system and dynamic holographic image switching method, which has the following beneficial effects: a composite phase plate structure is used to realize single-beam multi-topological charge output, reducing system complexity, and only two phase plates are needed to store high-density information. Only ordinary Gaussian beams are needed to complete encryption without the need for complex light sources; the mechanical structure is more stable, faster, more repeatable, and low-cost.

[0047] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is a schematic diagram of the existing vortex optical encryption system;

[0049] Figure 2 A schematic diagram of a mechanically modulated optical encryption system;

[0050] Figure 3 This is the image acquired after the second phase plate is rotated 40°;

[0051] Figure 4 This is the image acquired after the second phase plate is rotated 80°;

[0052] Figure 5 This is the image acquired after the second phase plate is rotated 120°;

[0053] Figure 6 This is the image acquired after the second phase plate is rotated 160°. DETAILED DESCRIPTION

[0054] In the description of the present invention, it should be noted that the terms "upper", "lower", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or the orientations or positional relationships in which the inventive product is usually placed when in use. These are only for the convenience of describing the present invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on the present invention. In the description of the present invention, it should also be noted that, unless otherwise expressly specified and limited, the terms "setting", "installation" and "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be a communication between the internal parts of two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0055] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0056] like Figure 2 As shown, a mechanically modulated optical encryption system is characterized by comprising a light source, a composite phase plate, a convex lens and an image acquisition device arranged in sequence.

[0057] The light source in this embodiment is a laser, which emits a Gaussian beam.

[0058] The composite phase plate comprises two phase plates arranged side by side. The spacing between the first and second phase plates is no greater than 30mm. A smaller spacing improves the superposition effect; a spacing greater than 30mm prevents phase superposition. Therefore, the spacing between the two phase plates is adjusted based on actual conditions; this embodiment uses a spacing of 10mm. The vortex phase information of the first and second phase plates is opposite. Both the first and second phase plates are liquid crystal phase plates. Liquid crystal phase plates have a small pixel pitch, low zero-order diffraction, and high energy efficiency. Liquid crystal phase plates are also inexpensive and reusable after molding. Vortex phase information is encoded on the two phase plates, and at least one of the phase plates is connected to a rotation drive device, which is used to modulate the phase of the corresponding phase plate. The phase plate opposite to the light source is the first phase plate, and the phase plate opposite to the convex lens is the second phase plate. The second phase plate is arranged at the front focal plane position of the convex lens, and the image acquisition device is arranged at the back focal plane position of the convex lens. The light beam emitted by the light source is modulated by the composite phase plate and outputs vortex light; the topological charge of the vortex light is adjusted by regulating the relative rotation amount of the two phase plates. When the topological charge of the vortex light is consistent with the correct topological charge, the vortex light is converted into an identification pattern through the convex lens and the image acquisition device. When the topological charge of the vortex light is inconsistent with the correct topological charge, the vortex light is converted into a ring pattern through the convex lens and the image acquisition device.

[0059] It should be noted that the rotation drive device is implemented by a mechanical structure, which is more stable, faster, and has high repeatability. For example, a motor is used to directly engage the phase plate for rotation, or the phase plate is indirectly rotated through transmission parts such as gears, racks, chains or connecting rods under the action of driving parts such as motors or telescopic parts. In this embodiment, the specific structure of the rotation is no longer limited.

[0060] The dynamic holographic image switching method based on the above-mentioned mechanically modulated optical encryption system has the following specific steps:

[0061] Step S1: The light source emits a Gaussian beam, which is used as a detection light source. Encryption can be completed using only an ordinary Gaussian beam without the need for complex light source modulation.

[0062] Step S2: The rotation drive adjusts the relative rotation angle of the first and second phase plates, causing them to overlap in phase. The Gaussian beam, after passing through the rotated first and second phase plates, generates vortex light with corresponding topological charges. This composite phase plate structure enables the output of multiple topological charges in a single beam, reducing system complexity.

[0063] The initial phases of the first phase plate and the second phase plate are and ,in, and Expressed as radial coordinates and angular coordinates in the polar coordinate system respectively.

[0064] Case where both phase plates have rotation drives:

[0065] Both the first phase plate and the second phase plate can be rotated around the optical axis:

[0066] The rotation angles of the first phase plate and the second phase plate around the optical axis are and , the joint phase after phase superposition The calculation formula is as follows:

[0067] , the phase distribution of vortex light in the polar coordinate system is as follows: ,in, is the topological charge after phase superposition, is the relative rotation angle.

[0068] Case of second phase plate with rotation drive:

[0069] The initial phases of the first phase plate and the second phase plate are as follows:

[0070] ;

[0071] ;

[0072] The first phase plate remains stationary, and the second phase plate rotates. The rotation angle of the second phase plate is , the phases of the first phase plate and the second phase plate after relative rotation are as follows:

[0073] ;

[0074] ;

[0075] Joint Aspect The calculation formula is as follows:

[0076] ;

[0077] ;

[0078] In order to solve the problem of two topological charges in the fan-shaped area, the light will be diffracted onto the rings of different radii. Quantization and offset are performed as follows:

[0079] Quantization: The angle range The step length is Divide into share, , through The phase profiles of the two phase plates are quantized for the step size and are obtained by The fuzzy sector is corrected by integer multiple phase compensation. After quantization, the phase functions of the two phase plates are as follows:

[0080] ;

[0081] ;

[0082] in, is an integer, , is the rounding function, in order to obtain integer topological charge, Needs to be satisfied, , is an integer and should satisfy ;

[0083] Offset: Joint Phase as follows:

[0084] ;

[0085] when When the joint phase Simplifying the formula we can get:

[0086] ;

[0087] when and When , the phase distribution is equivalent, then the joint phase The simplified process is as follows:

[0088] ;

[0089] The image phase is increased by the second phase plate. The phase expression of the second phase plate with the increased image phase is as follows:

[0090] ;

[0091] in, is the image phase, is the phase of the second phase plate superimposed with the image phase;

[0092] The combined aspects are as follows:

[0093] ;

[0094] when When the first phase plate and the second phase plate do not rotate relative to each other, the phases cancel each other out, and an image with increased image phase is displayed. When , the result contains vortex phases, and a blurred image with crosstalk is displayed due to the crosstalk between phases.

[0095] Multiple images are encrypted by superimposing patterns with different rotation phases. The specific steps are as follows:

[0096] Rotate the initial phase Then the rotation phase is obtained, , is the number of images, and the rotation phase is , the corresponding image phase is superimposed with the corresponding rotation phase to obtain the corresponding image phase as follows:

[0097] ;

[0098] in, For the image phase, The first The image phase, the final phase of the second phase plate is as follows:

[0099] ;

[0100] in, is the final phase of the second phase plate, is the argument function of the complex number, Complex exponential operation function. When the phase plate is rotated to the corresponding angle, the corresponding image will be displayed.

[0101] Step S3: The vortex light corresponding to the topological charge undergoes Fourier transformation through a convex lens and is then converted into an identification pattern or a ring pattern through an image acquisition device. When the topological charge of the vortex light is consistent with the correct topological charge, the image acquisition device restores the Fourier transformed light beam to a Gaussian spot array to form an identification pattern. When the topological charge of the vortex light is inconsistent with the correct topological charge, the image acquisition device captures the image as a ring pattern.

[0102] In order to verify the effect of this embodiment, a simulation experiment was conducted. Two images were superimposed on the second phase plate. The rotation angles of the two images were 40° and 80° respectively. Figure 3-Figure 6 As shown in the figure, it can be seen that the two images can be clearly seen at rotation angles of 40° and 80°, but when the rotation angles are 120° and 160°, crosstalk occurs, making the points of the image circular, and the two images are superimposed, and a clear and recognizable image cannot be obtained, and cannot be identified.

[0103] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A mechanically modulated optical encryption system, characterized in that: It includes a light source, a composite phase plate, a convex lens and an image acquisition device which are arranged in sequence; The composite phase plate includes two phase plates arranged in parallel, the two phase plates are encoded with vortex phase information, multiple image phases are added to one of the phase plates, at least one of the phase plates is connected to a rotation drive device, the rotation drive device is used to modulate the phase of the corresponding phase plate, the phase plate opposite to the light source is the first phase plate, the phase plate opposite to the convex lens is the second phase plate, the second phase plate is arranged at the front focal plane position of the convex lens, the image acquisition device is arranged at the back focal plane position of the convex lens, the light beam emitted by the light source is modulated by the composite phase plate and vortex light is output; the topological charge of the vortex light is adjusted by regulating the relative rotation amount of the two phase plates, and the joint phase generated by the superposition of the first phase plate and the second phase plate is modulated. Quantization and offset are performed. When the topological charge of the vortex light is consistent with the correct topological charge, the vortex light is converted into a recognizable pattern without crosstalk through a convex lens and an image acquisition device. The recognizable pattern is formed by a Gaussian spot array, and there is no crosstalk between the points of the Gaussian spot array. When the topological charge of the vortex light is inconsistent with the correct topological charge, the vortex light is converted into a blurred image with crosstalk through a convex lens and an image acquisition device.

2. The mechanically modulated optical encryption system according to claim 1, wherein: The light source is a laser, which emits a Gaussian beam.

3. The mechanically modulated optical encryption system according to claim 2, wherein: The distance between the first phase plate and the second phase plate is no more than 30 mm. The vortex phase information of the first phase plate and the second phase plate are opposite. Both the first phase plate and the second phase plate are liquid crystal phase plates.

4. A dynamic holographic image switching method for a mechanically modulated optical encryption system according to any one of claims 1 to 3, characterized in that: The specific steps are as follows: Step S1: The light source emits a Gaussian beam, which serves as a detection light source; Step S2: adjusting the relative rotation angle of the first phase plate and the second phase plate by a rotation drive device so that the phases of the first phase plate and the second phase plate after relative rotation are superimposed; the Gaussian beam passes through the rotated first phase plate and the second phase plate to generate vortex light of corresponding topological charge; Step S3: The vortex light corresponding to the topological charge is Fourier transformed through a convex lens and then converted into an identification pattern or a ring pattern through an image acquisition device. When the topological charge of the vortex light is consistent with the correct topological charge, the image acquisition device restores the Fourier transformed light beam to a Gaussian spot array to form a recognizable pattern without crosstalk. When the topological charge of the vortex light is inconsistent with the correct topological charge, the image acquisition device captures the image as a blurred image with crosstalk.

5. The method for dynamic holographic image switching in an optical encryption system based on mechanical modulation according to claim 4, characterized in that: In step S2, the initial phases of the first phase plate and the second phase plate are and ,in, and Expressed as radial coordinates and angular coordinates in the polar coordinate system respectively.

6. The method for dynamic holographic image switching in an optical encryption system based on mechanical modulation according to claim 5, characterized in that: The rotation angles of the first phase plate and the second phase plate around the optical axis are and , the joint phase after phase superposition The calculation formula is as follows: , the phase distribution of vortex light in the polar coordinate system is as follows: ,in, is the topological charge after phase superposition, To achieve the relative rotation angle, the image phase is increased on one of the phase plates.

7. The method for dynamic holographic image switching in an optical encryption system based on mechanical modulation according to claim 5, characterized in that: In step S2, the initial phases of the first phase plate and the second phase plate are as follows: The first phase plate remains stationary, and the second phase plate rotates. The rotation angle of the second phase plate is , the phases of the first phase plate and the second phase plate after relative rotation are as follows: Joint Aspect The calculation formula is as follows: ； ； Joint Phase Quantization and offset are performed as follows: Quantization: The angle range The step length is Divide into share, , through The phase profiles of the two phase plates are quantized for the step size and are obtained by The fuzzy sector is corrected by integer multiple phase compensation. After quantization, the phase functions of the two phase plates are as follows: in, is an integer, , is the rounding function, in order to obtain integer topological charge, Needs to be satisfied, , is an integer and should satisfy ; Offset: Joint Phase as follows: After simplification, we get: The image phase is increased by the second phase plate. The phase expression of the second phase plate with the increased image phase is as follows: in, is the image phase, is the phase of the second phase plate superimposed with the image phase; The combined aspects are as follows: when When the first phase plate and the second phase plate do not rotate relative to each other, the phases cancel each other out, and an image with increased image phase is displayed. When , the result contains vortex phases, and a blurred image with crosstalk is displayed due to the crosstalk between phases.

8. The method for dynamic holographic image switching in an optical encryption system based on mechanical modulation according to claim 7, characterized in that: Multiple images are encrypted by superimposing patterns with different rotation phases. The specific steps are as follows: Rotate the initial phase Then the rotation phase is obtained, , is the number of images, and the rotation phase is , the corresponding image phase is superimposed with the corresponding rotation phase to obtain the corresponding image phase as follows: in, For the image phase, The first The image phase, the final phase of the second phase plate is as follows: in, is the final phase of the second phase plate, is the argument function of the complex number, Complex exponential operation function. When the phase plate is rotated to the corresponding angle, the corresponding image will be displayed.

Images