A holographic method for producing controllable three-dimensional axial structured light

Abstract

The application discloses a kind of holographic methods for generating controllable three-dimensional axial structured light, the intensity diagram of three-dimensional axial structured light of different period and phase is generated by computer, and depth map is obtained by computer processing, and the propagation from object plane to holographic plane is obtained by means of Fresnel diffraction principle using S-FFT algorithm, the complex amplitude of all slice layers is added, and the hologram is obtained, the phase distribution is extracted from the complex amplitude distribution of hologram, and the phase distribution diagram is obtained, and reconstruction processing is carried out simultaneously;The three-dimensional reconstruction image generated after reconstruction processing is input, and the receiving screen is moved distance corresponding to reconstruction interval, and the axial structured light with 5-6 pixel values of each change is obtained by collecting the focus change.This application simplifies the generation process of three-dimensional axial structured light, improves the operation simplicity and control efficiency while ensuring the beam quality, can accurately control the period and phase distribution of light beam, and meets the strict requirements of different application scenarios on structured light parameters.

Description

Technical Field

[0001] This invention relates to the field of optical imaging, specifically a holographic method for generating controllable three-dimensional axial structured light. Background Technology

[0002] Three-dimensional axial structured light is a beam of light with a cosine intensity distribution along its axis. It is widely used in many high-precision fields, such as high-resolution imaging, 3D image reconstruction, digital holographic imaging, and super-resolution imaging. These high-precision fields have high requirements for the period and phase adjustment of structured light. For example, in the field of super-resolution imaging, it is necessary to precisely control the period and phase of the beam to improve the resolution and detail capture capability of the image.

[0003] However, while some existing technologies can generate three-dimensional axial structured light, their production costs are high, and the adjustment range of period and phase is limited, making the technology complex and resulting in insufficient flexibility in practical applications. Some researchers have used the interference method of concentric ring slit beams to generate structured light, but this technology is not only expensive in terms of equipment, but also difficult to adjust the period and phase for different experimental requirements.

[0004] Currently, no one has attempted to generate three-dimensional axially structured light with controllable period and phase using holographic methods while also controlling costs. Therefore, it is necessary to develop a simple and flexible method for generating three-dimensional axially structured light. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a holographic method for generating controllable three-dimensional axial structured light.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A holographic method for generating controllable three-dimensional axial structured light includes the following steps: Step S1: Generate three-dimensional axial structured light intensity maps with different periods and phases using a computer; Step S2: Generate a depth map using a computer. The depth map is the same size as the three-dimensional axial structured light intensity map. Its depth direction is the direction of light propagation, and the gray value changes linearly from 0 to 255 along the y-axis from top to bottom. Step S3: Combine the three-dimensional axial structured light intensity map with the depth map. Figure 1 The data is input into the computer, where it is sliced ​​to obtain slice layers. Step S4: Using the Fresnel diffraction principle, the propagation from the object plane to the holographic plane is obtained using the S-FFT algorithm. The complex amplitudes of all slice layers are added together to obtain a hologram. The phase distribution is extracted from the complex amplitude distribution of the hologram to obtain a phase distribution map, and reconstruction processing is performed simultaneously. Step S5: Input the phase distribution map into the SLM, and reconstruct the spacing corresponding to the distance the receiving screen moves, and collect the axial structured light with the focus change being 5-6 pixels per frame.

[0007] Optionally, after step S1, the method further includes: specifying the size of the generated multiple three-dimensional axial structured light intensity maps as 512×512, setting the position of the beam at the center, with a width of 3 pixels, generating a corresponding array according to a standard cosine function, where the value in the array corresponds to the light intensity of the structured light at the corresponding position, thereby obtaining the theoretical three-dimensional axial structured light intensity map perpendicular to the propagation direction. There are 3 designed periods, namely 10, 30, and 50, corresponding to the number of bright spots in the three-dimensional axial structured light intensity map. Each period is designed with 4 phases, namely 0°, 120°, 240°, and 360°.

[0008] Optionally, in step S3, the sliced ​​image of the sliced ​​layer is specifically obtained by uniformly cutting the same depth image corresponding to each three-dimensional axial structured light intensity image, and each sliced ​​layer corresponds to 5-6 pixel values.

[0009] Optionally, in step S4, the propagation from the object plane to the holographic plane is obtained using the S-FFT algorithm based on the Fresnel diffraction principle. The complex amplitudes of all slice layers are summed to obtain a hologram. The phase distribution is extracted from the complex amplitude distribution of the hologram to obtain a phase distribution map. Specifically, this includes: Step S41: Based on the Fresnel diffraction principle, calculate the diffraction process of the light wave in the near field: , In the above formula, These are the planar coordinate systems for the diffraction plane and the observation plane, respectively. For the object plane function, For wave number, The wavelength of light. The diffraction distance. The complex amplitude obtained from diffraction. i It is the imaginary unit. F Fourier transform; Step S42: Calculate the complex amplitude of each slice layer using the S-FFT algorithm, and superimpose the complex amplitudes of all slice layers to obtain a hologram. The S-FFT algorithm switches between the frequency domain and the spatial domain by alternately using FFT and IFFT. In the frequency domain, the transfer function is applied to simulate free space propagation. In the spatial domain, the refractive index change is considered. Through multiple iterations of this process, the propagation result of the light field from the object plane to the holographic plane is finally calculated. Step S43: Extract the phase distribution from the complex amplitude distribution of the hologram to obtain the phase distribution map: , In the above formula, F -1 This is the inverse Fourier transform. This is a superposition of all complex amplitudes.

[0010] Optionally, the reconstruction process in step S4 specifically includes: Step S44: Based on the phase distribution map generated above, the reconstruction process of the spatial light field is simulated by anti-Fresnel diffraction, and the simulated three-dimensional reconstructed image is output.

[0011] Compared with the prior art, the present invention has the following beneficial effects: This invention utilizes the Fresnel diffraction principle to generate three-dimensional axial structured light. It allows for precise control of the beam's period and phase distribution, meeting the stringent requirements of different application scenarios for structured light parameters. Compared to existing concentric ring-slit interference methods, this invention requires no expensive equipment, resulting in lower costs. Furthermore, the three-dimensional axial structured light intensity map employs different periods and phases, significantly expanding the adjustment range of period and phase, and offering greater flexibility and adaptability. This method simplifies the generation process of three-dimensional axial structured light, significantly improving ease of operation and control efficiency while ensuring beam quality. It facilitates applications in high-resolution imaging, three-dimensional image reconstruction, digital holographic imaging, and super-resolution imaging, providing an efficient and economical solution for related research and practice. Attached Figure Description

[0012] Figure 1 This is an experimental process diagram of a holographic method for generating controllable three-dimensional axial structured light in an embodiment of the present invention; Figure 2 This is a schematic diagram of a holographic method for generating controllable three-dimensional axial structured light in an embodiment of the present invention; Figure 3 This is an experimental result diagram of a holographic method for generating controllable three-dimensional axial structured light in an embodiment of the present invention. Detailed Implementation

[0013] To better demonstrate the advantages and innovations of this invention and to clearly illustrate its technical solution, the embodiments of this invention will be further described in detail below with reference to the accompanying drawings.

[0014] Example 1 like Figure 1 and Figure 2 As shown, this invention provides a holographic method for generating controllable three-dimensional axial structured light, comprising the following steps: Step S1: Generate three-dimensional axial structured light intensity maps with different periods and phases using a computer; Step S2: Generate a depth map using a computer. The depth map is the same size as the three-dimensional axial structured light intensity map. Its depth direction is the direction of light propagation, and the gray value changes linearly from 0 to 255 along the y-axis from top to bottom. Step S3: Combine the three-dimensional axial structured light intensity map with the depth map. Figure 1 The data is input into the computer, where it is sliced ​​to obtain slice layers. Step S4: Using the Fresnel diffraction principle, the propagation from the object plane to the holographic plane is obtained using the S-FFT algorithm. The complex amplitudes of all slice layers are added together to obtain a hologram. The phase distribution is extracted from the complex amplitude distribution of the hologram to obtain a phase distribution map, and reconstruction processing is performed simultaneously. Step S5: Input the phase distribution map into the SLM (Spatial Light Modulator), and move the receiving screen to correspond to the reconstruction spacing to acquire axial structured light with focus changes of 5-6 pixels per frame.

[0015] Specifically, after step S1, the method further includes: specifying the size of the generated multiple three-dimensional axial structured light intensity maps as 512×512, setting the beam position at the center, and using a width of 3 pixels. A corresponding array is generated according to a standard cosine function, where the values ​​in the array correspond to the light intensity of the structured light at the corresponding position. This yields the theoretical intensity map of the three-dimensional axial structured light perpendicular to the propagation direction. Three sets of periods are designed: 10, 30, and 50, corresponding to the number of bright spots in the three-dimensional axial structured light intensity map. Each set of periods has four phases: 0°, 120°, 240°, and 360°.

[0016] Specifically, in step S3, the sliced ​​images of the sliced ​​layers are obtained by uniformly cutting the same depth map corresponding to each three-dimensional axial structured light intensity map, and each sliced ​​layer corresponds to 5-6 pixel values.

[0017] Specifically, step S4 includes: Step S41: Based on the Fresnel diffraction principle, calculate the diffraction process of the light wave in the near field: , In the above formula, These are the planar coordinate systems for the diffraction surface and the observation surface, respectively. The object plane function; For wave number, ; The wavelength of light; This is the diffraction distance; The complex amplitude is obtained from diffraction; i It is the imaginary unit, used to describe the wave and phase of light; F Fourier transform; Step S42: Calculate the complex amplitude of each slice layer using the S-FFT algorithm, and superimpose the complex amplitudes of all slice layers to obtain a hologram. The S-FFT algorithm switches between the frequency domain and the spatial domain by alternately using FFT and IFFT. In the frequency domain, the transfer function is applied to simulate free space propagation. In the spatial domain, the refractive index change is considered. Through multiple iterations of this process, the propagation result of the light field from the object plane to the holographic plane is finally calculated. Step S43: Extract the phase distribution from the complex amplitude distribution of the hologram to obtain the phase distribution map: , In the above formula, F -1 This is the inverse Fourier transform. Superimpose all complex amplitudes; Step S44: Based on the phase distribution map generated above, the reconstruction process of the spatial light field is simulated by anti-Fresnel diffraction, and the simulated three-dimensional reconstructed image is output.

[0018] Specifically, the experimental setup used in step S5 includes: a He-Ne laser (model DH-HN300, manufactured by Daheng Optics, wavelength 632.8 nm), a polarizer, a beam expander lens group (16x magnification, f = 25 mm and f = 400 mm plano-convex lenses), an NDF center density filter, an SLM (EXULUS-4K1, Thorlabs, resolution: 3840 × 2160, pixel pitch: 3.74µm, refresh rate: 30 Hz), a BS beam splitter, a CCD camera (23.5 fps, MER2-503-23 ​​GM, manufactured by Daheng Imaging), a 4f system (consisting of two 75 mm plano-convex lenses used to perform Fourier transform of the light field), and a receiving screen.

[0019] A He-Ne laser emits a red laser beam. A reflector adjusts the direction of the red laser beam, and a beam expander amplifies the beam. An NDF (neutral density filter) controls the light intensity. A polarizer generates a polarized beam. After being expanded by the beam expander, the polarized beam is redirected by a beam splitter (BS) to project perpendicularly onto the effective display area of ​​the SLM (Spark Laser Monitor), forming a specific light field distribution. A phase distribution map is then loaded into the SLM to modulate the incident red laser beam. The modulated light is reflected back to the 4f system, where a receiving screen is set up, and a CCD camera captures the image.

[0020] The feasibility and scientific validity of the method of the present invention will be further verified and explained below with the help of flowcharts from actual experiments.

[0021] In this embodiment, a three-dimensional axial structured light intensity map and a depth map are generated by computer to complete the generation and reconstruction of the three-dimensional axial structured light. The generated three-dimensional axial structured light intensity map is set with the beam position centered and the width of 3 pixels, and a depth map with gray values ​​that change linearly along the y-axis is generated. The three-dimensional axial structured light intensity map and the depth map are sliced, and the complex amplitude of all slices is calculated by Fresnel diffraction to obtain a hologram. The phase distribution is extracted from the complex amplitude distribution of the hologram. The phase distribution map is loaded onto the SLM, and the structured light with axial focusing change is collected by adjusting the position of the receiving screen.

[0022] First, using computer simulation and a holographic reconstruction system, three-dimensional axial structured light intensity maps with different periods and phases were generated. The image size was 512×512, and three periods were designed: 10, 30, and 50, corresponding to the number of bright spots in the intensity map. Four phases were designed for each period: 0°, 120°, 240°, and 360°. Simultaneously, a depth map was generated, also 512×512, with its depth direction corresponding to the direction of light propagation. The grayscale value varied linearly from top to bottom along the y-axis, ranging from 0 to 255. The generated three-dimensional axial structured light intensity maps and depth maps were matched in the computer and sliced ​​to obtain sliced ​​layers. The sliced ​​images of these layers were then filled and resized to 900×900 before being used for holographic calculations.

[0023] In holographic computation, based on the Fresnel diffraction principle, the S-FFT algorithm is used to calculate the propagation from the object plane to the holographic plane. A hologram is generated by layer-by-layer superposition of the complex amplitudes of all slices. The phase distribution is extracted from the complex amplitude distribution of the hologram to obtain the phase distribution map. Subsequently, the phase distribution map is input into the SLM for optical field modulation. A He-Ne laser (model DH-HN300, manufactured by Daheng Optics, wavelength 632.8 nm) was used in the experiment, emitting a red laser beam with a wavelength of 632.8 nm as the light source. The SLM has 256 gray levels. After the red laser beam modulated by the SLM with a CGH (Computer-Generated Holograms) is loaded, the red laser beam is reflected through a 4f system.

[0024] Finally, the reconstructed images were acquired using a Daheng Imaging CCD camera (23.5 fps, model MER2-503-23 ​​GM, manufactured by Daheng Imaging). Experimental results show that the three-dimensional axial structured light generated by this method exhibits significant focusing changes on the receiving screen, and different combinations of periods (10, 30, 50) and phases (0°, 120°, 240°, 360°) all yielded corresponding light field distributions.

[0025] Due to interference factors such as beam diffraction in actual experimental equipment, there may be slight focusing deviations between the reconstructed image acquired by the CCD camera and the simulation image.

[0026] Reconstruction and Experimental Results Presentation: like Figure 3 As shown, the simulated 3D reconstructed images demonstrate the distribution of 3D axial structured light with a period of 10 and phases of 0° and 360°. Figures (a1) to (o1) and (a2) to (o2) indicate the light field distribution at different depths, where the light intensity exhibits an axial cosine distribution and shows significant controllability at different phases (e.g., 0° and 360°). The phase and intensity information of the reconstructed 3D axial structured light at different depths are consistent with the theoretical design, indicating that the method of this invention can accurately achieve the generation of structured light with controllable period and phase. The results show that the method of this invention, through the combination of Fresnel diffraction and holography, maintains high light field resolution during reconstruction and can achieve focused changes in the light field by controlling the phase. Analysis of the axial structured light obtained from the simulated 3D reconstructed images and actual experiments verifies the effectiveness and flexibility of the method of this invention under various combinations of period and phase, meeting the practical application requirements for 3D light field generation and control.

[0027] In summary, the method of this invention generates three-dimensional axial structured light intensity maps and depth maps with different periods and phases using a computer. The computer then processes these maps to obtain slice layers. Using the Fresnel diffraction principle and the S-FFT algorithm, the propagation from the object plane to the holographic plane is obtained. The complex amplitudes of all slice layers are summed to obtain a hologram. The phase distribution is extracted from the complex amplitude distribution of the hologram to obtain a phase distribution map. Simultaneously, reconstruction processing is performed. The three-dimensional reconstructed image generated after reconstruction processing is input, and the distance the receiving screen moves corresponds to the reconstruction interval. Axial structured light with a focus change of 5-6 pixels per image is acquired.

[0028] This method can precisely control the period and phase distribution of the beam, meeting the stringent requirements of structured light parameters in various application scenarios. Compared to existing concentric annular slit interferometry methods, this invention requires no expensive equipment and is cost-effective; at the same time, its period and phase adjustment range is significantly expanded, and the control is more flexible and adaptable. This method simplifies the generation process of three-dimensional axial structured light, significantly improving ease of operation and control efficiency while ensuring beam quality. It facilitates the promotion and application of this method in fields such as high-resolution imaging, three-dimensional image reconstruction, digital holographic imaging, and super-resolution imaging, providing an efficient and economical solution for related research and practice.

[0029] It should be understood that the above description of the preferred embodiments is quite detailed, but it should not be considered as a limitation on the scope of protection of this invention. Those skilled in the art, under the guidance of this invention, can make substitutions or modifications without departing from the scope of protection of the claims of this invention, and all such substitutions or modifications fall within the scope of protection of this invention. The scope of protection of this invention should be determined by the appended claims.

Claims

1. A holographic method for generating controllable three-dimensional axial structured light, characterized in that, Includes the following steps: Step S1: Generate three-dimensional axial structured light intensity maps with different periods and phases using a computer; Step S2: Generate a depth map using a computer. The depth map is the same size as the three-dimensional axial structured light intensity map. Its depth direction is the direction of light propagation, and the gray value changes linearly from 0 to 255 along the y-axis from top to bottom. Step S3: Input the three-dimensional axial structured light intensity map and depth map into the computer, perform slicing processing, and obtain slice layers; Step S4: Using the Fresnel diffraction principle, the propagation from the object plane to the holographic plane is obtained using the S-FFT algorithm. The complex amplitudes of all slice layers are added together to obtain a hologram. The phase distribution is extracted from the complex amplitude distribution of the hologram to obtain a phase distribution map, and reconstruction processing is performed simultaneously. Step S5: Input the phase distribution map into the SLM, and move the receiving screen to correspond to the reconstruction spacing to acquire axial structured light with focus changes of 5-6 pixels per frame; After step S1, the method further includes: specifying the size of the generated multiple three-dimensional axial structured light intensity maps as 512×512, setting the position of the beam at the center, with a width of 3 pixels, generating a corresponding array according to the standard cosine function, and the value in the array corresponds to the light intensity of the structured light at the corresponding position, thereby obtaining the theoretical three-dimensional axial structured light intensity map perpendicular to the propagation direction. There are 3 sets of designed periods, namely 10, 30, and 50, corresponding to the number of bright spots in the three-dimensional axial structured light intensity map. Each set of periods is designed with 4 sets of phases, namely 0°, 120°, 240°, and 360°. In step S3, the sliced ​​image of the sliced ​​layer is specifically obtained by uniformly cutting the same depth image corresponding to each three-dimensional axial structured light intensity image, and each sliced ​​layer corresponds to 5-6 pixel values.

2. The method according to claim 1, characterized in that, In step S4, the propagation from the object plane to the holographic plane is obtained using the Fresnel diffraction principle and the S-FFT algorithm. The complex amplitudes of all slice layers are summed to obtain a hologram. The phase distribution is extracted from the complex amplitude distribution of the hologram to obtain a phase distribution map. Specifically, this includes: Step S41: Based on the Fresnel diffraction principle, calculate the diffraction process of the light wave in the near field: ， In the above formula, These are the planar coordinate systems for the diffraction plane and the observation plane, respectively. For the object plane function, For wave number, The wavelength of light. The diffraction distance. The complex amplitude obtained from diffraction. i It is the imaginary unit. F Fourier transform; Step S42: Calculate the complex amplitude of each slice layer using the S-FFT algorithm, and superimpose the complex amplitudes of all slice layers to obtain a hologram. The S-FFT algorithm switches between the frequency domain and the spatial domain by alternately using FFT and IFFT. In the frequency domain, the transfer function is applied to simulate free space propagation. In the spatial domain, the refractive index change is considered. Through multiple iterations of this process, the propagation result of the light field from the object plane to the holographic plane is finally calculated. Step S43: Extract the phase distribution from the complex amplitude distribution of the hologram to obtain the phase distribution map: ， In the above formula, F -1 This is the inverse Fourier transform. This is a superposition of all complex amplitudes.

3. The method according to claim 2, characterized in that, The reconstruction process in step S4 specifically includes: Step S44: Based on the phase distribution map generated above, the reconstruction process of the spatial light field is simulated by anti-Fresnel diffraction, and the simulated three-dimensional reconstructed image is output.

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