A method for producing a color volume hologram

Abstract

The application discloses a kind of production methods of color volume hologram, it is related to color holographic 3D display field.The present application includes the production of volume holographic color filter array, the preparation of computer sampling color hologram and the device of synthetic volume hologram, among them, volume holographic color filter array is made using volume holographic technology, for computer sampling color hologram is color sampling;Computer sampling color hologram provides low information redundancy color virtual 3D scene information, and volume holographic color filter array is combined to reproduce color 3D image without color crosstalk;Synthetic volume hologram device records the color 3D image reproduced by computer sampling color hologram as color volume hologram that can be reproduced under white light.The present application solves the problem that virtual object is difficult to make volume hologram, and also solves the problems of large amount of calculation caused by color crosstalk and information redundancy of Fresnel color hologram, and realizes the color volume holographic display of virtual three-dimensional scene.

Description

Technical Field

[0001] This invention relates to the field of color holographic 3D display, specifically to a color 3D display technology that combines computational holography and volume holography. In particular, it utilizes a volume holographic color filter array (VH-CFA) as a color separation device, which can realize the conversion from color planar holography to color volume holography, perfectly solving the problem that volume holography is difficult to use for color display of virtual 3D scenes. Background Technology

[0002] Holographic display is considered the ultimate development direction of 3D display technology. Based on the differences in holographic grating structures, holograms are mainly divided into two categories: volume holograms (thick holograms) and planar holograms (thin holograms). Thin holograms use laser light as a light source to illuminate an object. After transmission or reflection (scattering) by the object, an object light wave (W) is formed. When this object light wave (W) encounters another light wave called a reference light (C), interference fringes are formed. These interference fringes are recorded using a photosensitive material, thus obtaining the hologram. The information of the object light wave is encoded in the hologram. When a laser illuminates the hologram, due to diffraction, the outgoing light wave will contain the original object light wave, allowing the image of the object to be reconstructed. For example, the volume hologram generation method disclosed in CN115309023B assumes that a 3D object O is composed of multiple cross-sections, each cross-section being a two-dimensional image, similar to a CT scan image. The Fresnel holograms of each layer of the two-dimensional image are calculated one by one. The holograms of each layer are then input into the spatial light modulator (SLM) in a certain time sequence. The SLM is then illuminated with a beam-expanding laser. As each layer of hologram is input, the SLM reconstructs the reconstructed images of each layer of hologram at the corresponding spatial positions, forming a longitudinal scan of the image plane. If the frame rate of the SLM is fast enough, such that the total scanning time of all sections is less than the visual persistence time of the human eye (about 0.1-0.4 seconds), a complete three-dimensional reconstructed image will be formed.

[0003] Volume holograms possess a three-dimensional striped structure and exhibit wavelength selectivity and multiple recording capabilities, allowing for the reproduction of color images using white light illumination. In contrast, planar holograms are insensitive to wavelength selectivity, are prone to color crosstalk, and struggle to achieve full parallax true-color 3D display under white light illumination. Currently, the relatively mature rainbow holography technology in planar holographic color display can only present horizontal parallax, and the colors change with the viewing angle, making it difficult to realistically reproduce the colors of three-dimensional objects.

[0004] In volume holographic color 3D display technology, the recording process typically requires the pre-preparation of physical models, making it particularly difficult to record large-scale real-world scenes (such as buildings and natural landscapes). Furthermore, recording volume holograms requires the use of monochromatic light with good coherence; when objects are illuminated only with red, green, and blue lasers, the color reproduction differs from the actual colors under ordinary white light illumination. In addition, this technology struggles to handle self-illuminating objects (such as flames and light sources), limiting the application scope of holographic displays and making it difficult to adapt to the current development trends of virtual technology in the era of artificial intelligence.

[0005] Computational holography, capable of reconstructing virtual objects and scenes, has seen steady development in recent years. This technology obtains the object's light field through numerical calculations on 3D computer graphics models and digital images, then generates fringe patterns through numerical interference with a reference light field, thus reconstructing 3D images without the need for actual physical objects. However, printed computational holograms are mostly planar holograms, exhibiting significant color differences under white light illumination. The reconstructed 3D images are prone to ghosting and blurring, making it difficult to achieve full parallax true-color 3D display. Furthermore, computational holography has long been limited by the spatial bandwidth product problem. Under practical display conditions such as screen size and viewing angle, the spatial bandwidth required to generate high-quality holograms is extremely large, posing significant challenges to calculating the object's light field.

[0006] To achieve full parallax true-color 3D scene display using volume holography, existing research has proposed a stacked computational volume hologram technique. This method converts three printed computational holograms corresponding to red, green, and blue wavelengths into volume holograms, and then stacks them to synthesize an overlay of RGB images. However, this technique is complex, with high computational and material costs.

[0007] In summary, existing holographic display technologies still have significant shortcomings in achieving true-color 3D display of virtual objects, and there is an urgent need for a technical solution that can balance the flexibility of computational holography with the high-quality color reproduction capability of volume holography. Summary of the Invention

[0008] To address the above technical problems, this invention proposes a method for fabricating a color volume hologram, comprising: Step S1: Fabricate a volume holographic color filter array. The volume holographic color filter array includes a photosensitive substrate and a filter unit array distributed therein. The photosensitive substrate is a volume holographic recording material. The filter unit array includes three monochrome filter units arranged periodically according to the Bayer array and spatially non-overlapping and closely adjacent to each other. Each monochrome filter unit has the same pixel width and pixel length and contains a volume holographic grating structure. The pixel length is 3 times the pixel width, so that the three monochrome filter units can be merged into a square when placed side by side. The three monochrome colors include red, green and blue. Step S2: Based on the size specifications and arrangement rules of the three monochrome filter units in the volume holographic color filter array, the generation regions of holographic elements are arranged in the fitted color sampling hologram. The color sampling hologram is the same size as the volume holographic color filter array, and each holographic element contains three closely adjacent and non-overlapping sub-holographic elements along the row direction. The size of the sub-holographic elements is consistent with that of the monochrome filter units. The virtual three-dimensional scene of the three-dimensional object is projected along the visual axis direction of the generation region of each holographic element to generate a two-dimensional volume view. Then, the holographic data containing red, green and blue primary color sub-holographic elements is calculated by Fourier transform. It is printed as a pure phase hologram to obtain the computer sampled color hologram. Step S3: Align and bond the computer-sampled color hologram with the volume holographic color filter array to form a composite component. Irradiate the composite component with a three-primary-color mixed laser to reproduce a color 3D original image without color crosstalk. Use this color 3D original image as the object light and introduce reference light to perform interference recording on the holographic recording plate. After chemical processing, the final color volume hologram is obtained.

[0009] Furthermore, the pixel width of the monochrome filtering unit and the sub-holographic element... and pixel length Based on the human eye's resolving limit and the maximum wavelength of the reproduced light It is determined that the following relation is satisfied: , The maximum wavelength of the reproduced light is the wavelength of the red laser. .

[0010] Furthermore, in step S1, the fabrication steps for the volume holographic color filter array include: The volume holographic recording plate is fixed on the first precision displacement stage, and a mask with a binary transmittance structure is set parallel to the incident light side of the volume holographic recording plate on the second precision displacement stage. The mask is formed by creating light-transmitting holes in the alloy plate using laser drilling technology to form light-transmitting units. The light-transmitting units are periodic slit-shaped or dot-shaped arrays with consistent size. The size of the light-transmitting units of the mask in the horizontal direction is one-third of the size of the opaque part. Red, green, and blue lasers are sequentially split, expanded, and collimated before being exposed to the front and back of the volume holographic recording plate in two directions. One beam is incident vertically and the other is incident at an angle. After each exposure, the mask is moved by a fine-tuning bracket to ensure that the three exposure areas do not overlap and are closely connected. After all exposures are completed, the dry plate is developed, fixed, and bleached.

[0011] Furthermore, in step S3, when the composite component is irradiated with a mixed laser of three primary colors, the angle at which the reference light irradiates the holographic recording plate is the same as the angle at which the laser light is incident obliquely from the reverse side of the volume holographic recording plate in step S1.

[0012] Furthermore, the process of creating the computer-sampled color hologram uses the spectral projection method to replace point-by-point object light wave calculation, and the virtual three-dimensional scene is displayed across the entire color sampling hologram plane. The object light distribution of the two-dimensional volume view corresponding to the sub-holographic element at the m-th row and n-th column is as follows: ; ; In the formula, It is a virtual plane located between the virtual 3D scene and the color sampled hologram, where A represents the initial amplitude of the incident light wave, and j indicates that the light wave is described in the complex field. The distance between the color sampling hologram plane and the object plane is denoted by C, which represents the red, green, and blue primary color channels. The operator is... Indicates Fourier transform; It is a window function for sampling holograms from sub-holographic elements; The center coordinates of the green primary dice holographic element are The center coordinates of the red, green, and blue primary color holographic elements are: For red primary color light, ; For green primary color light, ; For blue primary color light: .

[0013] Furthermore, step S2 also includes obtaining a color sampling hologram using a displacement copy operation, comprising the following steps: Step 21. Merge adjacent red, green, and blue sub-holographic elements to construct a holographic sampling unit, according to the intervals along the column period direction. Spacing in the direction of row period Hologram sampling units are arranged on a plane to obtain an initial sampled hologram array. and All are integer multiples of the length b of the sub-holographic element; Step 22. Displace the generated initial sampled hologram array along the row direction. After each displacement, perform the operation in step 21. Each operation involves a movement distance equal to the length b of a sub-holographic element. Through the above translation and repetition, a row-displaced composite hologram array is obtained. The generated row-displaced composite hologram array is then displaced along the column direction. After each displacement, step 21 is executed. Each operation moves a distance equal to the length b of a sub-holographic element. While moving in the column direction, the row displacement synthesized hologram array also moves to the right by the width a of a sub-holographic element or to the left by the width 2a of two sub-holographic elements.

[0014] Furthermore, the holographic recording plate is a silver halide holographic plate with an emulsion particle size of 4 nm, and its photosensitivity to red, green, and blue wavelengths is configured as 1:1:1.

[0015] Furthermore, in step S3, the alignment and fitting refers to aligning the holographic data of the red, green, and blue sub-holographic elements of the pure phase hologram with the red, green, and blue filter units of the volume holographic color filter array one by one.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention combines computational holography and volume holography, enabling the creation of color volume holograms of virtual 3D scenes without the need for physical models. This breaks through the limitations of traditional volume holography, which relies on physical objects, and adapts to the display needs of virtual content in the AI ​​era.

[0017] 2. By utilizing the narrowband wavelength selectivity of the volume holographic color filter array (VH-CFA), the independent reproduction and synthesis of red, green, and blue colors are achieved, eliminating color crosstalk and reproducing colors realistically and stably.

[0018] 3. By employing computer sampling color hologram technology and utilizing the low-pass filtering characteristics of the human eye for sampling calculation, the calculation of three-dimensional objects is simplified to a Fourier transform of a two-dimensional view, which greatly improves calculation efficiency and reduces hardware costs.

[0019] 4. Compared with stacked computational volume hologram technology, which requires the separate fabrication of three volume holograms before stacking, this invention simplifies the process and reduces material and manufacturing costs by using VH-CFA to bond and convert the sampled hologram in a single step.

[0020] 5. The VH-CFA is made using volume holographic technology and has advantages such as narrow-band spectral response and high environmental stability. It can be mass-produced through optical replication and can be extended to fields with high color accuracy requirements such as professional photography and medical imaging. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the overall production process of the VH-CFA, computer sampling hologram, and color volume hologram of the present invention. Figure 2 Schematic diagram of a volume holographic color filter array; Figure 3 A schematic diagram of the optical path for fabricating a volumetric holographic color filter array; Figure 4 Schematic diagram of a volume holographic color filter mask (MSK); Figure 5 This is a schematic diagram of the mask dimensions; Figure 6 A schematic diagram of exposure for the three primary colors; Figure 7 To create computer-sampled holograms (S-CGHs); Figure 8 A volume view corresponding to a computer-sampled color hologram Hogel; Figure 9 This is a schematic diagram of the holographic sampling unit size; Figure 10 This is a schematic diagram of a horizontal copy of a sampled hologram. Figure 11 For the computer-generated sample hologram after copying; Figure 12 This is a schematic diagram showing the alignment and bonding of VH-CFA and S-CGH; Figure 13 A schematic diagram of VH-CFA-CGH reproduction; Figure 14 For converting computer-sampled color holograms to optical volume holograms, the optical path is as follows: Figure 15 This is a schematic diagram of the optical path for batch copying of VH-CFA. Figure 16 The relationship between the holographic unit and the object's projection viewpoint; Figure 17 The projection of the object point onto the object plane; Figure 18 The spectrum is a VH-CFA filter. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0023] Example This embodiment provides a color 3D display system and fabrication method that combines computational holography and volume holography. The method mainly consists of three core steps: fabrication of a volume holographic color filter array (VH-CFA), compilation of computer-sampled color holograms (S-CGHs), and synthesis of a color volume hologram reproducible in white light using the former two. The specific process is as follows: First, using volume holographic interferometry recording technology and a specially made mask, a volume holographic color filter array (VH-CFA) with narrowband color filtering function is fabricated on a photosensitive material; then, for the virtual 3D scene, using the characteristics of human visual perception, low-information-redundancy computer-sampled color holograms (S-CGHs) are compiled and printed as pure phase holograms; finally, the pure phase holograms are precisely aligned and bonded to the VH-CFA. Under three-primary-color laser illumination, the VH-CFA acts as a beam splitter, guiding light of different wavelengths to the sub-holographic elements corresponding to the pure phase hologram, thereby reproducing a color 3D original image without color crosstalk. Finally, the reproduced color 3D original image is used as the object light, introduced into the reference light, and interfered with on the holographic recording plate to generate the final color volume hologram. This final product can reproduce realistic color 3D scenes under extended white light.

[0024] Step 1: Fabricate a volume holographic color filter array (VH-CFA) The volume holographic color filter array (VH-CFA) includes a photosensitive substrate and an array of filter units distributed within the substrate. The photosensitive substrate is made of a volume holographic recording material exhibiting photorefractive or photopolymerization effects. The filter unit array comprises multiple red, green, and blue filter units arranged periodically according to a Bayer array. These red, green, and blue filter units are spatially non-overlapping and closely adjacent. Each red / green / blue filter unit contains a volume holographic grating structure, which exhibits a periodic modulation distribution of the refractive index within the material. Figure 2 As shown, the basic repeating unit of the filter unit array contains a red filter unit, a green filter unit, and a blue filter unit. The red, green, and blue filter units have the same pixel width and pixel length, and the pixel length is three times the pixel width, so that the red, green, and blue filter units can be merged into a square when placed side by side.

[0025] The manufacturing principle of VH-CFA is as follows: Figure 3 As shown: First, the volume holographic recording substrate (i.e., the photosensitive substrate that has not yet been photosensitive to generate the filter unit array) is fixed on the first precision displacement stage PTT1; a mask MSK with a binary transmittance structure is placed parallel to the incident light side of the volume holographic recording substrate on the second precision displacement stage PTT2; the mask MSK is formed by creating light-transmitting holes in a 0.2 mm thick aluminum alloy plate using laser drilling technology to form light-transmitting units, such as... Figure 4 As shown, its light-transmitting units are periodic slit-like or dot-like arrays of uniform size, used to define the pixel unit size for each exposure. For example, Figure 5 As shown, the size of the light-transmitting unit of the mask in the horizontal direction is one-third of the size of the opaque part.

[0026] Then, turn on the red laser and let the red laser beam pass through... Figure 3 The optical path shown, after beam splitting, beam expansion, and collimation, illuminates the volume holographic recording plate (VHP) from both the front and back sides in two directions, with one beam incident perpendicularly and the other incident obliquely. Two-beam interference occurs in the corresponding light-transmitting region inside the plate, and the red volume holographic grating structure is recorded through this interference recording process. Turn off the red laser Lr, control the first precision displacement stage or the second precision displacement stage, drive the mask and the volume holographic recording plate to generate a first relative displacement, so that the light-transmitting area of ​​the mask moves to align with the unexposed adjacent area on the volume holographic recording plate. Then, the green laser Lg is turned on, and the interference recording process is repeated to record the green volume holographic grating structure in the unexposed adjacent area; Then, the blue laser Lb is turned on, and the interference recording process is repeated to record a blue volume holographic grating structure in the unexposed adjacent area. After each exposure, the mask or volume holographic recording plate is translated using a first or second precision displacement stage to ensure that the three exposure areas do not overlap and are closely connected. After exposure, the volume holographic recording plate is subjected to conventional holographic processing such as development, fixing, and bleaching to obtain the VH-CFA finished product. The VH-CFA produced can remove some components in the spectrum, so that each pixel retains only one color component. This invention utilizes volume holography to produce such a... Figure 6 The VH-CFA shown can meet the narrow bandwidth requirements of color holographic displays. Under white light illumination, the color filter spectrum distribution of the three primary color units is as follows: Figure 18 The device exhibits obvious narrowband color filtering characteristics, with clear separation of the red, green, and blue spectral curves and a full width at half maximum (FWHM) of less than 10 nm, effectively preventing color crosstalk.

[0027] To reduce costs and improve production efficiency, it is possible to... Figure 15 The optical path shown is used for optical replication of the VH-CFA. Using the fabricated VH-CFA as a master template and an unexposed holographic recording plate as the replication material, contact replication is performed under conjugate reference light to obtain a VH-CFA replica with the same performance as the original holographic recording plate, thus enabling mass production.

[0028] The size design of the red, green, and blue filter units in the VH-CFA is based on the following principle: When light passes through the VH-CFA filter and is then sampled and reconstructed by a computer-sampled color hologram, each sampling unit essentially acts as a small aperture. According to the principle of optical diffraction, light diffuses after passing through this small aperture, forming a diffraction spot. Let the width and height of the sampling unit in the sampled color hologram be α. h b h The reconstructed image points have diffraction diffusion angles in the length and width directions as follows: in, To reproduce the wavelength of light, and The diffraction spread angles in the length and width directions are given. To ensure the observer sees a continuous, smooth image, rather than isolated bright spots (i.e., to avoid the screen-door effect or noticeable pixelation), the size of the diffraction spot produced by a single sampling unit must be less than or equal to the resolving power of the human eye. The diffraction spread angles of the reproduced image points in the length and width directions must not exceed the resolving power of the human eye. Therefore , The smaller the aperture of the sampling unit, the larger the diffraction spot, and the larger the diffraction spread angle of the reconstructed image point in the width direction. Therefore, the maximum diffraction spread angle cannot be greater than the human eye's resolving angle. , , In addition, wavelength The longer the diffraction spot The larger the wavelength, the better, as the wavelengths of the three primary colors of red, green, and blue are respectively... The red wave is the largest, so its wavelength is taken as the maximum value. At that time, the width and length of the filter unit of VH-CFA are as follows: , It can ensure smooth image reproduction for all wavelengths.

[0029] The selection of suitable lasers and photosensitive substrate materials is very important. The performance of blue, green and red solid-state lasers produced in China that can be used for color hologram imaging is shown in Table 1 from top to bottom.

[0030] Table 1 Lasers for Color Volume Holographic Recording The size of the light-transmitting unit in the photomask is the same as that of the filtering unit, and the angular resolution limit of the human eye is... Then the size of the light-transmitting hole in the mask is: The photosensitive substrate material for the volume holographic recording plate is the French Ultimate 04 silver halide holographic plate, with an emulsion particle size of 4 nm, making it particularly suitable for fabricating color Denisyuk volume holographic color filter arrays. The sensitive wavelength can be customized according to user needs. A key feature is that, when fabricating volume holographic color filter arrays, the photosensitive sensitivity for red, green, and blue wavelengths can be configured to 1:1:1, which facilitates the imaging of volume holographic color filter arrays. Table 2 shows the performance parameters of Ultimate 04 customized according to the laser wavelength in Table 1.

[0031] Table 2 Photosensitive substrate materials Step 2: Compile computer-sampled color holograms (S-CGHs) In this step, low-information-redundancy S-CGHs are created for the virtual 3D scene and output as pure phase holograms.

[0032] A color sampling hologram is composed of an array of small holographic elements (Hogels). Each holographic element contains three closely adjacent, non-overlapping sub-holographic elements along the horizontal (row) direction. The size of the sub-holographic elements is the same as the size of the aperture of the mask, i.e., the width of the sub-holographic element is: Sub-holographic element height: .

[0033] Each holographic element records information from a 3D object projected along a differentiated specific viewing axis onto a plane perpendicular to that viewing axis, generating a corresponding 2D volume view. Three sub-holographic elements record the red component projection of the object from this viewpoint: a green sub-holographic element records the green component projection, and a blue sub-holographic element records the blue component projection. Then, a Fourier transform is performed on the 2D volume view to obtain the complex amplitude distribution of the light waves of that holographic element on the color-sampled hologram plane.

[0034] The differentiated specific visual axis direction of each holographic element is the direction that starts from the same fixed reference point in the three-dimensional object and points to the corresponding holographic element on the color sampled hologram.

[0035] The three-dimensional object is a digitized spatial three-dimensional virtual object. In a color-sampled hologram, different holographic elements have different perspectives relative to the recorded object. This embodiment uses the visual axis projection method to replace the traditional point-by-point object wavelet calculation. That is, the three-dimensional object is projected onto its vertical plane along the visual axis direction of each holographic element, generating a 2D volume view corresponding to that holographic element. Subsequently, only the wavelet distribution of this 2D view needs to be obtained using Fourier transform, such as... Figure 8As shown in ac, the volume view corresponding to different holographic elements is given. This method avoids tedious point-by-point calculations, thus significantly improving the calculation speed of holograms.

[0036] The process of obtaining the complex amplitude distribution of light waves of each holographic element on the color sampling hologram plane can be achieved using... Figure 16 Note that in the diagram, a cube represents the object to be recorded, and ABCDEFG represent the six vertices of the cube. The plane... It is a virtual plane located between the object and the color-sampled hologram: the object plane. It is the color-sampled hologram plane. The shape of an object viewed from different positions on the color-sampled hologram can be considered as the object's shape along the corresponding viewing axis. Projection onto a plane.

[0037] For example in Holographic elements on a plane When viewing an object, what you see are the vertices ABCDEFG of the cube along the ZE direction on the plane. The two-dimensional image (view) projected upwards is: A'B'C'D'E'F'G'. The holographic element at point E records the information of this view.

[0038] Reference Figure 17 Let the view distribution seen from observation point E be as follows: C represents the red, green, and blue primary color channels. The analog wavelength... When monochromatic light illuminates the view, the light waves emitted by the view cover the entire color-sampled hologram plane. The diffraction distribution produced on It can be expressed by the following formula: (1) In the formula, A represents the initial amplitude of the incident light wave, and j indicates that the light wave is described using the complex domain. The operator represents the distance between the color-sampled hologram plane and the object plane. Indicates Fourier transform; A color sampling hologram is composed of multiple small holographic elements (Hogels) arranged in an array. Let the index of the holographic element array at observation point E be the m-th row and n-th column. The light waves emitted by the view then cover the entire color sampling hologram plane. The object light distribution of the sub-holographic element at the m-th row and n-th column is , Equation (1) only calculates the object light distribution within a rectangular frame of width a and length b at observation point E: (2) In the formula, It is a window function for the sub-holographic element sampled hologram (this function represents a hologram with a center point x). hEC ,y hEC A rectangular hole indicates a... (Sampling). Let the center coordinates of the green primary dichroic element be... and set The center coordinates of the red, green, and blue primary color holographic elements are: For red primary color light, (3-1) For green primary color light, (3-2) For blue primary color light: (3-3) A sub-hologram is formed by interfering the reference light with the object light wave represented by equation (2).

[0039] The optimal size of each sub-holographic element is determined based on the following principle: The reconstruction of a hologram is essentially the diffraction process of the object light wave as shown in equation (2), and the distribution of the reconstructed image... By performing an inverse Fourier transform on equation (2), we obtain: (4) According to the properties of the Fourier transform, the above equation can be expanded as follows: (5) In the formula, the symbol This represents convolution.

[0040] In the formula That is the original view The likeness, and (6) In the formula, , It is the diffraction angle, which is generally taken as the Rayleigh criterion. , When the diffraction spot can be distinguished, at this time: (7) Let the distance between the color sampling hologram plane and the image point be... Equation (7) means that, due to the diffraction effect of the sampling aperture, a geometric point will diffuse into a light spot, the size of which is: (8) Diffraction distribution and view of sampling aperture After convolution, the view will be made The size of each image point is consistent with the image spot in equation (8).

[0041] If the image spot size in equation (8) is smaller than the resolving limit of the human eye, it has no practical significance for the display and will only increase the redundancy of information, thereby increasing the computational load. However, if it is larger than the resolving limit of the human eye, a blurred reconstructed image will be seen. An optimal choice is to make the size of the reconstructed image spot exactly meet the resolving limit of the human eye. Let the resolving angle of the human eye be θ. The observation distance is (When calculating holograms, follow this design), the size of the image spots that the human eye can distinguish is: (9) To ensure that the image spot is resolvable in both the x and y directions, the diffraction size of the image spot in the x direction is selected. As the size of the image spot, i.e. Therefore, the optimal size 'a' of the sub-holographic element in the horizontal direction can be derived: (10) Finally, based on the size specifications and arrangement rules of the red, green, and blue filter units in the VH-CFA (Volume Holographic Color Filter Array), this step samples and arrays the three sub-holographic elements of all holographic elements to synthesize a single color sampled hologram. Fourier transform is then used to obtain the light wave distribution of all holographic elements, thereby obtaining computer-generated sampled holograms (S-CGHs) (e.g., Figure 7 (As shown). Subsequently, the S-CGHs data were printed onto holographic photosensitive material using a high-resolution direct-write system. After chemical processing such as development and fixing, the data was converted into a pure phase hologram.

[0042] Specifically, the process of synthesizing a single color sampled hologram includes the following steps: Step 21: Merge adjacent red (R), green (G), and blue (B) sub-holographic elements to construct a holographic sampling unit. This is done according to the intervals along the column period direction. Spacing in the direction of row period Hologram sampling units are arranged on a plane to obtain an initial sampled hologram array. and All are integer multiples of the length b of the sub-holographic element, and the specific mathematical expression is: as well as ,in and All values ​​are positive integers greater than 1. This step reduces the amount of subsequent computation by increasing the spacing between holographic sampling units. Figure 9 Showing when and A schematic diagram of the size of the holographic sampling unit at that time.

[0043] Step 22: Displace the initial sampled hologram array generated in Step 21 along the row direction. After each displacement, perform the operation in Step 21. Each operation involves a movement distance equal to the length *b* of a sub-holographic element. Through the above translation and repetition, a row-shifted synthetic hologram array is obtained, as shown below. Figure 10 As shown.

[0044] Step 23: Displace the row-shifted composite hologram array generated in Step 22 along the column direction. After each displacement, execute the operation in Step 21, and then execute... Each operation involves a movement distance equal to the length *b* of a sub-holographic element. Simultaneously with the column-wise movement, the row-shifted composite hologram array also moves to the right by the width *a* of a sub-holographic element or to the left by the width *2a* of two sub-holographic elements. Through this combined vertical and horizontal displacement, the final computer-generated sampled hologram is obtained, as shown below. Figure 11 As shown.

[0045] Step 24: Print the final computer-generated sampled hologram onto a holographic plate using a holographic printer, and process it into a phase-type hologram.

[0046] Step 3: Reconstruction of the color 3D image and synthesis of the final volumetric hologram In the stages of color 3D image reconstruction and final volume hologram synthesis, the pre-processed phase hologram is first precisely aligned and bonded to the volume holographic color filter array (VH-CFA). This means that each RGB sub-holographic element of the phase hologram is aligned with one RGB filter unit in the VH-CFA, forming a structure like... Figure 12 The composite component shown is (VH-CFA-CGH); subsequently, the composite component is illuminated with white light, a mixture of the red, green, and blue primary color lasers used in recording VH-CFA, and the mixed laser light... Figure 14 The optical path in the process is split into two paths after beam splitting, beam expansion, and collimation. In one optical path, the mixed laser beam illuminates the VH-CFA in the same direction as the oblique incident light during VH-CFA fabrication. The Bragg diffraction selective separation of the three primary colors is achieved using the corresponding RGB filter unit of the VH-CFA. These primary colors are then used to illuminate the corresponding sub-holographic elements in the phase-type hologram, thus reproducing a pair of color 3D original images (I) without color crosstalk. r and conjugate first image I i ( Figure 13 The reproduced color 3D original image ( As the object light, in another optical path, the mixed laser is guided into a reference beam and the original color 3D image ( The two light rays meet on a new holographic recording plate, causing them to form interference fringes (the recording light path is as follows). Figure 14As shown, the holographic recording plate uses a high-sensitivity color volume holographic material (such as Ultimate 04). Finally, after exposure, development, fixing and other chemical treatments, the final color volume hologram is obtained. This finished product inherits the characteristics of volume holograms and can directly reproduce realistic and color-crosstalk-free color 3D scenes under ordinary extended white light sources (such as halogen lamps or LED white light), thus effectively solving the technical problems of traditional virtual objects being difficult to produce volume holograms and Fresnel color holograms having color crosstalk and large computational load.

[0047] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method of making a color volume hologram, characterized by, Includes the following steps: Step S1: Fabricate a volume holographic color filter array. The volume holographic color filter array includes a photosensitive substrate and a filter unit array distributed therein. The photosensitive substrate is a volume holographic recording material. The filter unit array includes three monochrome filter units arranged periodically according to the Bayer array and spatially non-overlapping and closely adjacent to each other. Each monochrome filter unit has the same pixel width and pixel length and contains a volume holographic grating structure. The pixel length is 3 times the pixel width, so that the three monochrome filter units can be merged into a square when placed side by side. The three monochrome colors include red, green and blue. Step S2: Based on the size specifications and arrangement rules of the three monochrome filter units in the volume holographic color filter array, the generation regions of holographic elements are arranged in the fitted color sampling hologram. The color sampling hologram is the same size as the volume holographic color filter array, and each holographic element contains three closely adjacent and non-overlapping sub-holographic elements along the row direction. The size of the sub-holographic elements is consistent with that of the monochrome filter units. The virtual three-dimensional scene of the three-dimensional object is projected along the visual axis direction of the generation region of each holographic element to generate a two-dimensional volume view. Then, the holographic data containing red, green and blue primary color sub-holographic elements is calculated by Fourier transform. It is printed as a pure phase hologram to obtain the computer sampled color hologram. Step S3: Align and bond the computer-sampled color hologram with the volume holographic color filter array to form a composite component. Irradiate the composite component with a three-primary-color mixed laser to reproduce a color 3D original image without color crosstalk. Use this color 3D original image as the object light and introduce reference light to perform interference recording on the holographic recording plate. After chemical processing, the final color volume hologram is obtained.

2. The manufacturing method according to claim 1, characterized in that, The pixel width of the monochrome filter unit and the sub-hologram element and the pixel length , in accordance with the angular resolution limit of the human eye and the maximum value of the wavelength of the reproduction light is determined, satisfying the relationship: , The maximum value of the wavelength of the reproduction light is the wavelength of red laser light, .

3. The manufacturing method according to claim 1, characterized in that, In step S1, the fabrication steps for the volume holographic color filter array include: The volume holographic recording plate is fixed on the first precision displacement stage, and a mask with a binary transmittance structure is set parallel to the incident light side of the volume holographic recording plate on the second precision displacement stage. The mask is formed by creating light-transmitting holes in the alloy plate using laser drilling technology to form light-transmitting units. The light-transmitting units are periodic slit-shaped or dot-shaped arrays with consistent size. The size of the light-transmitting units of the mask in the horizontal direction is one-third of the size of the opaque part. Red, green, and blue lasers are used to irradiate the volume holographic recording plate from both sides of the front and back after beam splitting, beam expansion, and collimation. The volume holographic recording plate is exposed in two directions, with one beam incident vertically and the other incident at an angle. After each exposure, the mask is moved by fine-tuning the support to ensure that the three exposure areas do not overlap and are closely connected. After all exposures are completed, the dry plate is developed, fixed, and bleached.

4. The manufacturing method according to claim 3, characterized in that, In step S3, when the composite component is irradiated with a mixed laser of three primary colors, the angle at which the reference light irradiates the holographic recording plate is the same as the angle at which the laser light is incident obliquely from the reverse side of the volume holographic recording plate in step S1.

5. The manufacturing method according to claim 1, characterized in that, The computer-sampled color hologram compilation process uses the spectral projection method to replace point-by-point object light wave calculation, and the virtual three-dimensional scene is displayed on the entire color sampling hologram plane. The object light distribution of the two-dimensional volume view corresponding to the sub-holographic element at the m-th row and n-th column is as follows: ； ； In the formula, It is a virtual plane located between the virtual 3D scene and the color sampled hologram, where A represents the initial amplitude of the incident light wave, and j indicates that the light wave is described in the complex field. The distance between the color sampling hologram plane and the object plane is denoted by C, which represents the red, green, and blue primary color channels. The operator is... Indicates Fourier transform; It is a window function for sampling holograms from sub-holographic elements; The center coordinates of the green primary dice holographic element are The center coordinates of the red, green, and blue primary color holographic elements are: For red primary color light, ; For green primary color light, ; For blue primary color light: .

6. The manufacturing method according to claim 5, characterized in that, Step S2 further includes obtaining a color sampled hologram using a displacement copy operation, including the following steps: Step 21. Merge adjacent red, green, and blue sub-holographic elements to construct a holographic sampling unit, according to the intervals along the column period direction. Spacing in the direction of row period Hologram sampling units are arranged on a plane to obtain an initial sampled hologram array. and All are integer multiples of the length b of the sub-holographic element; Step 22. Displace the generated initial sampled hologram array along the row direction. After each displacement, perform the operation in step 21. Each operation involves a movement distance equal to the length b of a sub-holographic element. Through the above translation and repetition, a row-displaced composite hologram array is obtained. The generated row-displaced composite hologram array is then displaced along the column direction. After each displacement, step 21 is executed. Each operation moves a distance equal to the length b of a sub-holographic element. While moving in the column direction, the row displacement synthesized hologram array also moves to the right by the width a of a sub-holographic element or to the left by the width 2a of two sub-holographic elements.

7. The manufacturing method according to claim 1, characterized in that, In step S3, the alignment and fitting refers to aligning the holographic data of the red, green, and blue sub-holographic elements of the pure phase hologram with the red, green, and blue filter units of the volume holographic color filter array one by one.

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