Preparation method of volume holographic element, volume holographic element and augmented reality 3D display device

Abstract

The invention provides a preparation method of a volume holographic element, the volume holographic element and an augmented reality 3D display device. The preparation method comprises the following steps: providing a pixelated diffractive lens array and a volume holographic material arranged adjacent to or adjacent to the pixelated diffractive lens array; wherein the pixelated diffraction lens array comprises target diffraction lens sub-units which are distributed in an array; at least one recording step is implemented, and the recording step comprises the steps that a recording light beam is projected to the pixelated diffractive lens array, and the recording light beam is irradiated to one side of the volume holographic material after being emitted by the pixelated diffractive lens array; and projecting a reference light beam to the other side of the volume holographic material, irradiating the reference light beam to the volume holographic material and interfering with the recording light beam to form holographic pixel units in one-to-one correspondence with the target diffraction lens sub-units. The volume holographic element prepared by the preparation method has high diffraction efficiency and high transmittance, and the presented 3D image also has the advantages of low crosstalk, no depth flipping, no self-repetition image and the like.

Description

Technical Field

[0001] The present invention relates to the field of display technologies, and particularly to a method for preparing a volume holographic element, a volume holographic element, and an augmented reality 3D display device. Background Art

[0002] Augmented reality naked-eye 3D (Three-dimensional) display is a new display technology that enables the observation of virtual 3D images integrated with real scenes without wearing any auxiliary devices. As one of the main hardware entrances to the "metaverse", traditional augmented reality display technologies require the use of vision aids such as helmets or glasses, and usually can only display 2D images or 3D images based on binocular parallax, but there is a conflict between vergence and accommodation, which is likely to cause visual fatigue.

[0003] On the other hand, although naked-eye 3D display technology can reconstruct virtual 3D images, it is limited by the contradiction between the transmittance of optical devices and the light utilization rate, and it is difficult to achieve a display effect of virtual-real fusion. For example, a microlens array reconstructs the light field by controlling the direction and focal length of light beams to present a realistic 3D scene to the viewer. However, augmented reality 3D display based on a microlens array requires the use of a semi-transmissive semi-reflective mirror or a compensating mirror to achieve the virtual-real fusion function, resulting in limited transmittance and light efficiency of the system. In addition, this method requires the use of multiple devices such as a microlens array, a convex lens, and a semi-transmissive semi-reflective mirror, with a complex optical path and a large system.

[0004] With the emergence and development of holographic technologies and lasers, holographic optical elements (HOEs) have gradually received extensive attention. Holographic optical elements have been widely used in augmented reality 3D displays due to their advantages such as light weight, thin structure, and easy replication. However, most current augmented reality 3D displays based on holographic optical elements adopt an integral imaging method, that is, using a lens array holographic optical element as a virtual-real fusion device. However, this solution has disadvantages such as image flipping resulting in incorrect depth information and self-repeating images, thereby causing incorrect motion parallax, which has become a key problem in augmented reality 3D displays. Summary of the Invention

[0005] Based on this, the present invention aims to provide an improved method for preparing a volume holographic element, a volume holographic element, and an augmented reality 3D display device to solve at least one of the above problems.

[0006] In a first aspect, the present application provides a method for preparing a volume holographic element, where the volume holographic element includes a substrate and a pixelated information layer disposed on the substrate, and the pixelated information layer includes holographic pixel units distributed in an array;

[0007] The method includes:

[0008] Provide a pixelated diffractive lens array and a volume holographic material disposed adjacent or contiguous to the pixelated diffractive lens array; wherein, the pixelated diffractive lens array includes target diffractive lens sub-units distributed in an array.

[0009] Perform at least one recording step, the recording step including:

[0010] Project a recording beam onto the pixelated diffractive lens array; wherein, after the recording beam exits from the pixelated diffractive lens array, it irradiates one side of the volume holographic material.

[0011] Project a reference beam onto the volume holographic material, the reference beam irradiates the other side of the volume holographic material and interferes with the recording beam to form holographic pixel units corresponding one-to-one to the target diffractive lens sub-units.

[0012] The preparation method of the above volume holographic element projects a recording beam onto a pixelated diffractive lens array, and after exiting from the pixelated diffractive lens array, it irradiates a volume holographic material disposed adjacent or contiguous to the pixelated diffractive lens array. Combining with the reference beam irradiated onto the volume holographic material, the wavefront information of the beam when exiting from the pixelated diffractive lens array is recorded into the holographic pixel units through interference. This is beneficial for forming a volume holographic element with the function of a pixelated diffractive lens array, thereby having a high diffraction efficiency and a high transmittance, reducing the complexity of the optical path of the augmented reality 3D display device, and reducing the use of optical elements; at the same time, the holographic pixel units correspond one-to-one to the target diffractive lens sub-units in the pixelated diffractive lens array, which is beneficial for realizing pixel-by-pixel light field regulation in the subsequent reproduction process, enabling the display optical path to have a high regulation accuracy and a large regulation freedom, thereby reducing the crosstalk of 3D images and overcoming the disadvantages such as depth inversion and self-repeating images in the integral imaging method, and improving the 3D display effect of augmented reality.

[0013] In one embodiment, the providing the pixelated diffractive lens array includes: providing a plurality of diffractive lenses; wherein, each diffractive lens has at least one target diffractive lens sub-unit, and the target diffractive lens sub-units in the same diffractive lens have the same focal point; arranging the target diffractive lens sub-units in each diffractive lens in a staggered manner to form the pixelated diffractive lens array.

[0014] In one embodiment, the method includes: performing at least two recording steps, wherein a recording beam in one recording step is a first parallel beam propagating in a first direction; at least one recording beam in other recording steps is a second parallel beam propagating in a second direction, the first parallel beam converges at a first set of viewpoints after passing through the pixelated diffractive lens array, the second parallel beam converges at a second set of viewpoints after passing through the pixelated diffractive lens array, the second direction is different from the first direction, and the second set of viewpoints is not entirely the same as the first set of viewpoints.

[0015] In one embodiment, the reference beam includes a spherical wave beam or a parallel beam.

[0016] In one embodiment, the pixelated diffractive lens array includes a pixelated harmonic diffractive lens array.

[0017] In one embodiment, the method includes: performing at least two recording steps, wherein a recording beam in one recording step is a third parallel beam having a first wavelength; at least one recording beam in other recording steps is a fourth parallel beam having a second wavelength, the viewpoints where the third parallel beam converges after passing through the pixelated diffractive lens array are the same as the viewpoints where the fourth parallel beam converges after passing through the pixelated diffractive lens array, and the second wavelength is different from the first wavelength.

[0018] In one embodiment, the volume holographic material is any one of a photopolymer, a holographic polymer dispersed liquid crystal, a cholesteric liquid crystal, a dichromated gelatin, a silver halide material, and a photorefractive glass.

[0019] In a second aspect, the present application provides a volume holographic element, including: a substrate; a pixelated information layer disposed on the substrate and including holographic pixel units distributed in an array; wherein, the pixelated information layer contains wavefront information of a wavefront formed by the interference of a recording beam and a reference beam after the recording beam passes through the pixelated diffractive lens array; and, the pixelated diffractive lens array includes target diffractive lens sub-units distributed in an array, and the holographic pixel units correspond to the target diffractive lens sub-units one by one.

[0020] Based on the Bragg diffraction condition, the above volume holographic element can have high diffraction efficiency and high transmittance. At the same time, by setting the pixelated information layer and making the holographic pixel units in the pixelated information layer correspond to the target diffractive lens sub-units one by one, it is beneficial to realize pixel-by-pixel light field regulation in the subsequent reproduction process, so that the display optical path has high regulation accuracy and large regulation freedom, thereby reducing the crosstalk of 3D images and overcoming the disadvantages such as depth inversion and self-repeating images in the integral imaging method, and improving the 3D display effect of augmented reality.

[0021] In one embodiment, the pixelated information layer has recording parameters related to the wavefront information, and the recording parameters include at least one of a fringe period and a fringe orientation on a layer section of the pixelated information layer, a pitch of the holographic pixel units, and a shape of the holographic pixel units.

[0022] In one embodiment, the material of the pixelated information layer is any one of a photopolymer, a holographic polymer dispersed liquid crystal, a cholesteric liquid crystal, a dichromated gelatin, a silver halide material, and a photorefractive glass.

[0023] In a third aspect, the present application provides an augmented reality 3D display device, including: a projection module configured to provide a reproduction beam carrying 3D parallax image information; a volume holographic element prepared by the preparation method as described above, disposed on a light-emitting side of the projection module and configured to couple with the reproduction beam and converge the reproduction beam to a plurality of viewpoints; wherein, the projection module is further configured to align pixels of the 3D parallax image irradiated onto the volume holographic element with the holographic pixel units in the volume holographic element one by one during the reproduction process.

[0024] For the above-mentioned augmented reality 3D display device, by using a volume holographic element with the function of a diffractive lens array, high diffraction efficiency and high transmittance can be achieved, the complexity of the augmented display optical path can be reduced, and the use of components can be reduced; meanwhile, during the reproduction process, the pixels of the 3D parallax image can be aligned with the holographic pixel units in the volume holographic element one by one, which is beneficial to realizing pixel-by-pixel light field regulation, enabling the display optical path to have high regulation accuracy and large regulation freedom, thereby reducing crosstalk of the 3D image and overcoming disadvantages such as depth flipping and self-repeating images in the integral imaging method, and improving the 3D display effect of augmented reality. Description of the Drawings

[0025] In order to more clearly illustrate the embodiments of the present specification or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments recorded in the present specification. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0026] Figure 1 It is a schematic structural diagram of a volume holographic element according to an embodiment of the present application;

[0027] Figure 2 It is a flowchart of the steps of a preparation method of a volume holographic element according to an embodiment of the present application;

[0028] Figure 3 It is a front view schematic diagram of a single-viewpoint diffractive lens according to an embodiment of the present application;

[0029] Figure 4 Schematic diagram of the division of the target diffractive lens sub-unit in a single-viewpoint diffractive lens according to an embodiment of the present application;

[0030] Figure 5 Schematic diagram of the composition of a pixelated diffractive lens array according to an embodiment of the present application;

[0031] Figure 6 is Figure 5 Schematic diagram of the operation of the pixelated diffractive lens array shown;

[0032] Figure 7 Schematic diagram of the preparation system of a volume holographic element according to an embodiment of the present application;

[0033] Figure 8 Schematic diagram of the preparation of a volume holographic element according to an embodiment of the present application;

[0034] Figure 9 Schematic diagram of the preparation of a space multiplexing type volume holographic element according to an embodiment of the present application;

[0035] Figure 10 Schematic diagram of the preparation of a wavelength multiplexing type volume holographic element according to an embodiment of the present application;

[0036] Figure 11 Schematic diagram of the preparation of a volume holographic element using a parallel reference beam according to an embodiment of the present application;

[0037] Figure 12 Schematic diagram of the operation of an augmented reality 3D display device according to an embodiment of the present application;

[0038] Figure 13 is Figure 12 Effect diagram of the operation of the augmented reality 3D display device shown;

[0039] Figure 14 Schematic diagram of the operation of an augmented reality 3D display device according to another embodiment of the present application.

[0040] Description of component labels:

[0041] 100, volume holographic element; 110, substrate; 120, pixelated information layer; 121, holographic pixel unit; 100', space multiplexing type volume holographic element; 200, single-viewpoint diffractive lens; 300, pixelated diffractive lens array; 310, target diffractive lens sub-unit; 300', equivalent pixelated diffractive lens array; 400, holographic dry plate; 500, projection module. Detailed implementation manners

[0042] In order to make the above objects, features, and advantages of the present invention more obvious and understandable, the following will describe the specific embodiments of the present invention in detail with reference to the accompanying drawings. Many specific details are set forth in the following description in order to fully understand the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0043] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention.

[0044] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of the present invention, the meaning of "a plurality" is at least two, such as two, three, etc., unless otherwise specifically and clearly defined.

[0045] It should be noted that when an element is referred to as "fixed to" or "disposed on" another element, it can be directly on the other element or there may also be an intermediate element. When an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be an intermediate element at the same time. The terms "vertical", "horizontal", "upper", "lower", "left", "right" and similar expressions used herein are only for the purpose of illustration and do not represent the only implementation.

[0046] Before introducing the technical solutions provided by the embodiments of the present application, the basic principles and technical terms involved in the present application will be introduced first.

[0047] 1. Bragg diffraction principle: When the wavelength of electromagnetic radiation or subatomic particle waves is close to the atomic spacing length of the incident crystal sample, Bragg diffraction will occur, and the incident object will be scattered by the atoms in the system in a mirror form and will undergo constructive interference as shown by Bragg's law.

[0048] 2. Diffraction efficiency: The ratio of the light intensity in a certain diffraction direction to the incident light intensity.

[0049] 3. Volume holographic grating element (hereinafter referred to as volume holographic element): The photoresist film on the substrate is exposed by the bright and dark interference fringes formed by two coherent light beams (recording beam and reference beam), so that the interference fringes are recorded in the volume holographic material. Among them, the interference fringes contain the wavefront information of the light beam. The volume holographic element usually works under the Bragg diffraction condition. When the incident light beam satisfies the Bragg diffraction condition, the volume holographic element will have extremely high diffraction efficiency. On the other hand, the Bragg diffraction condition has very strict requirements on the angle and wavelength of the incident light beam. Once it cannot be satisfied, the diffraction efficiency will drop rapidly.

[0050] 4. Wavefront: The surface formed by the equal-phase points in the light beam, perpendicular to the propagation direction of each point of the light beam, can be used to describe the phase distribution of light, the change of light intensity, and the propagation direction of light. For example, the wavefront of a parallel light beam is a plane, and the wavefront of the light beam emitted by a point light source is a sphere (also called a spherical wave light beam). Generally, after the light beam passes through the medium, the wavefront is no longer the original shape and will carry a lot of information reflecting the characteristics of the medium.

[0051] Traditional augmented reality display technologies require wearing vision aids such as helmets or glasses, and usually can only display 2D images or 3D images based on binocular parallax. The latter has vergence-accommodation conflict and is prone to cause visual fatigue. The augmented reality 3D display technology based on a microlens array needs to use a semi-transmissive semi-reflective mirror or a compensating mirror to achieve the virtual-real fusion function, resulting in limited transmittance and optical efficiency of the system. Moreover, this method requires multiple devices such as a microlens array, a convex lens, and a semi-transmissive semi-reflective mirror, with a complex optical path and a large system.

[0052] In addition, most of the augmented reality 3D display technologies based on holographic optical elements adopt the integral imaging method, using a holographic optical element with the function of a microlens array as a virtual-real fusion device, having disadvantages such as image flipping caused by the symmetry of the image acquisition and display optical paths and self-repeating images caused by the structure of the microlens itself, thus resulting in incorrect motion parallax.

[0053] The augmented reality 3D display device provided by the embodiment of the present application adopts a volume holographic element with the function of a pixelated diffractive lens array. Based on the Bragg diffraction condition, it has high wavelength selectivity and angle selectivity. When the reproduction light projected by the projector has the same wavelength and the same incident angle as the reference light, the reproduction light can undergo Bragg diffraction and converge to multiple viewpoints with a high diffraction efficiency, thereby forming a virtual 3D image. For the ambient light emitted by real objects, it can directly pass through, achieving the display effect of augmented reality. At the same time, the image pixels of the reproduction light projected by the projector can be aligned one by one with the holographic pixel units on the volume holographic element, which is conducive to realizing per-pixel light field control, enabling the display optical path to have high control accuracy and a large control freedom, reducing the crosstalk of the 3D image, overcoming the shortcomings such as depth inversion and self-repeating images in the integral imaging method, and further improving the augmented reality 3D display effect.

[0054] Next, the inventive concept of the present application will be introduced in turn from the volume holographic element, the preparation method and preparation system of the volume holographic element, and the augmented reality 3D display device.

[0055] Volume holographic element

[0056] As Figure 1 、 Figures 3 to 6 shown, the embodiment of the present application provides a volume holographic element 100, including a substrate 110; a pixelated information layer 120 disposed on the substrate 110, including holographic pixel units 121 distributed in an array; wherein, the pixelated information layer 120 contains the wavefront information of the wavefront formed by the interference of the recording light beam emitted from the pixelated diffractive lens array 300 and the reference light beam; and, the pixelated diffractive lens array 300 includes target diffractive lens sub-units 310 distributed in an array, and the holographic pixel units 121 correspond to the target diffractive lens sub-units 310 one by one.

[0057] Exemplarily, the substrate 110 can be prepared from materials with good transmittance, such as polyester film, glass, etc. The pixelated information layer 120 can be prepared from any one of volume holographic materials such as photopolymer, holographic polymer dispersed liquid crystal, cholesteric liquid crystal, dichromated gelatin, silver halide material, and photorefractive glass. Among them, the photopolymer has the characteristics of spatial multiplexing and multi-wavelength response, and the refractive index modulation degree of the holographic polymer dispersed liquid crystal and cholesteric liquid crystal is higher, which can further improve the diffraction efficiency.

[0058] Exemplarily, after the recording light beam exits through the pixelated diffractive lens array 300, it will interfere with the reference light beam to form a new wavefront. The wavefront information of the new wavefront (such as phase distribution, light intensity change, propagation direction, etc.) will be synchronously recorded by the volume holographic material on the substrate 110. After the volume holographic material recording the wavefront information is cured, heated, and degassed, the pixelated information layer 120 can be obtained. The pixelated information layer 120 has recording parameters related to the wavefront information, and the recording parameters can include at least one of the fringe period and fringe orientation on the layer section of the pixelated information layer 120, the pitch of the holographic pixel units 121, and the shape of the holographic pixel units 121. Optionally, the angle between the fringes on the layer section of the pixelated information layer 120 and the plane where the substrate 110 is located ranges from 0° to 85°, and the period interval between the fringes is approximately half of the wavelength of the recording light beam.

[0059] Exemplarily, as Figures 3 to 6 shown, the pixelated diffractive lens array 300 includes a plurality of target diffractive lens sub-units 310, and each target diffractive lens sub-unit 310 is respectively taken from different single-viewpoint gray diffractive lenses 200 (hereinafter simply referred to as diffractive lenses 200).

[0060] Specifically, in order to obtain the pixelated diffractive lens array 300, the single-viewpoint diffractive lens 200 can be designed first. Taking the remainder of 2π or 2πP for the phase function of the spherical and aspherical refractive lenses, the gray diffractive lens phase diagram of the given design can be obtained. Among them, the design parameters of the refractive lens can be expressed by the optical quadratic surface formula, and the calculated quadratic surface height H(r) is collapsed, where r is the surface rotation radius. The phase of each collapse is 2π or 2πP, where P is a positive integer, that is, the harmonic diffraction coefficient. The corresponding collapse height can be expressed by the following formula: where λ is the central wavelength and n is the refractive index of the medium. Then, taking the remainder of the quadratic surface height H(r) with respect to the collapse height d and translating the coordinate axes according to the position of the viewpoint, the diffractive lens 200 as shown in Figure 3 can be designed. As Figure 3 shown, each diffractive lens 200 can be regarded as a series of Fresnel lens structures with different off-axis amounts, and the four diffractive lenses 200 have different focal points respectively, and the focal length is 500 mm for all.

[0061] Continuing to refer to Figure 4 , each diffractive lens 200 is discretized into a plurality of target diffractive lens sub-units 1a, 1b, 1c, 1d, ……, and the target diffractive lens sub-units (such as 1a, 1b, 1c, 1d, ……) in the same diffractive lens 200 have the same viewpoint (focal point). Staggering the target diffractive lens sub-units in each diffractive lens 200 can form the one as shown in Figure 5The pixelated diffractive lens array 300 as shown. Optionally, the area of each diffractive lens 200 can be 40×40 mm 2 , and the size of the target diffractive lens sub-unit can be 200×200 μm 2 , and there are 200×200 target diffractive lens sub-units in total. To ensure the correct original phase distribution, each diffractive lens 200 only retains one quarter of the number of target diffractive lens sub-units, and the rest are discarded. For example, for the diffractive lens 200 with the first viewing point, only the sub-units at the corresponding positions of 1a, 1b, 1c, 1d,... can be retained, and the rest are discarded, and so on for other diffractive lenses 200. Thus, the area of the pixelated diffractive lens array 300 should also be 40×40 mm 2 . Figure 6 Fig. shows a working schematic diagram of the pixelated diffractive lens array 300. It can be seen that the incident light can be converged to 4 viewing points after passing through the pixelated diffractive lens array 300, and the angular interval between two adjacent viewing points is 3°.

[0062] Exemplarily, "the holographic pixel unit 121 corresponds to the target diffractive lens sub-unit 310 one by one" means that during the formation of the holographic pixel unit 121, when the recording light beam exits from a target diffractive lens sub-unit 310, it interferes with the reference light beam to perform photolithographic exposure on the volume holographic material to form a holographic pixel unit 121, thereby recording the wavefront information of the exiting light beam in a holographic pixel unit 121, and this holographic pixel unit 121 can be considered to correspond to this target diffractive lens sub-unit 310. Thus, each formed holographic pixel unit 121 can be considered to correspond to each target diffractive lens sub-unit 310 one by one.

[0063] The above-mentioned volume holographic element 100 can have high diffraction efficiency and high transmittance based on the Bragg diffraction condition. At the same time, by setting the pixelated information layer 20 and making the holographic pixel units 121 in the pixelated information layer 20 correspond to the target diffractive lens sub-units 310 one by one, it is beneficial to realize pixel-by-pixel light field regulation during the subsequent reproduction process, enabling the display optical path to have high regulation accuracy and large regulation freedom, thereby reducing the crosstalk of 3D images, overcoming the disadvantages such as depth inversion and self-repeating images in the integral imaging method, and improving the display effect of augmented reality.

[0064] Preparation method and preparation system of volume holographic element

[0065] As Figure 2 and Figure 7 shown, the embodiments of the present application provide a preparation method and a preparation system of a volume holographic element, and the related structures can still be referred to Figure 1 , Figures 3 to 6 . Among them, the preparation method includes:

[0066] S100. Provide a pixelated diffractive lens array 300 and a volume holographic material disposed adjacent to or contiguous with the pixelated diffractive lens array; wherein the pixelated diffractive lens array includes target diffractive lens sub-units 310 distributed in an array.

[0067] Exemplarily, the volume holographic material can be coated on a transparent substrate to form a holographic dry plate 400, and is disposed adjacent to or contiguous with the pixelated diffractive lens array 300. That is to say, the side of the holographic dry plate 400 coated with the volume holographic material can face the uneven structure surface of the pixelated diffractive lens array 300, and the two are very close or in direct contact. Optionally, the holographic dry plate 400 is disposed closely to the pixelated diffractive lens array 300 to ensure the accuracy of wavefront information recording. It should be noted that, for simplicity of description, the "irradiating the holographic dry plate 400" described below can also be understood as "irradiating the volume holographic material".

[0068] Exemplarily, as Figures 3 to 6 shown, step S100 may include: S110. Provide a plurality of diffractive lenses 200; wherein each diffractive lens 200 has at least one target diffractive lens sub-unit 310, and the target diffractive lens sub-units 310 in the same diffractive lens 200 have the same focal point; S120. Interleave the target diffractive lens sub-units 310 in each diffractive lens 200 to form a pixelated diffractive lens array 300. The specific formation method of the pixelated diffractive lens array 300 can be referred to the description of the volume holographic element in the foregoing text, and will not be elaborated here.

[0069] S200. Perform at least one recording step, and the recording step includes: projecting a recording beam onto the pixelated diffractive lens array 300, and after the recording beam exits from the pixelated diffractive lens array 300, irradiating one side of the volume holographic material; projecting a reference beam onto the other side of the volume holographic material, and the reference beam irradiates the volume holographic material and interferes with the recording beam to form holographic pixel units 121 corresponding one-to-one to the target diffractive lens sub-units 310.

[0070] Exemplarily, the diffraction efficiency of the volume holographic element 100 can be analyzed first, and then the relevant parameters of the holographic dry plate 400 and the recording beam and the reference beam (such as the incident angle of the reference beam, the thickness of the volume holographic material, the refractive index modulation degree, etc.) can be obtained.

[0071] Figure 7 shows a schematic diagram of the system for preparing the volume holographic element of the present application. As Figure 7As shown, the pixelated diffractive lens array 300 is closely attached to the holographic plate 400. The incident laser first passes through the electronic shutter and then is separated into two beams by the beam splitter. One of the beams is expanded by the pinhole filter to eliminate stray light and then collimated by a collimating lens to form a parallel beam (recording beam), which then vertically enters the pixelated diffractive lens array 300. After exiting the pixelated diffractive lens array 300, it irradiates one side of the holographic plate 400. The other beam is expanded by the pinhole filter to eliminate stray light (forming the reference beam) and irradiates the other side of the holographic plate 400 in the form of a spherical wave, interfering with the recording beam passing through the pixelated diffractive lens array 300, and recording the wavefront information of the beam exiting the pixelated diffractive lens array 300 on the holographic plate 400. Among them, the optical path and intensity of the recording beam and the reference beam are kept consistent, and the dashed arrow indicates the wavefront information of the recorded light field. Figure 8 It shows that before recording using the holographic plate 400, the recording beam can converge to four original converging viewpoints after exiting the pixelated diffractive lens array 300.

[0072] Optionally, in this embodiment, the wavelength of the laser can be 442 nm, the incident angle α of the reference beam is greater than or equal to 65°, for example, it can be 69.86°, the thickness of the volume holographic material is about 15 μm, the refractive index modulation is 0.015, and the exposure of the recording beam is 30 mJ / cm 2 , and the exposed holographic plate 400 is subjected to ultraviolet curing for 3 min with a mercury lamp at a power of 1 kW, and finally placed in an oven at 100 °C for 15 min of heating to remove bubbles, and finally the volume holographic element 100 can be obtained.

[0073] Optionally, the laser is a monochromatic light source with a certain coherence length and needs to meet the conditions of holographic exposure. The types of this kind of laser generally include argon ion gas lasers, helium cadmium lasers, single longitudinal mode semiconductor lasers, etc.

[0074] Optionally, the volume holographic material is any one of photopolymers, holographic polymer dispersed liquid crystals, cholesteric liquid crystals, dichromated gelatin, silver halide materials, photorefractive glasses. Among them, photopolymers have the characteristics of spatial multiplexing and multi-wavelength response, and the refractive index modulation of holographic polymer dispersed liquid crystals and cholesteric liquid crystals is higher, which can further improve the diffraction efficiency.

[0075] The preparation method of the above-mentioned volume holographic element can form a volume holographic element 100 with the function of a pixelated diffractive lens array, thereby having a high diffraction efficiency and a high transmittance, reducing the complexity of the enhanced display optical path, and reducing the use of components. At the same time, the holographic pixel units 121 correspond one-to-one with the target diffractive lens sub-units 310 in the pixelated diffractive lens array 300, which is conducive to realizing pixel-by-pixel light field regulation in the subsequent reproduction process, enabling the display optical path to have a high regulation accuracy and a large regulation freedom, thereby reducing the crosstalk of 3D images, overcoming the disadvantages such as depth inversion and self-repeating images in the integral imaging method, and improving the display effect of augmented reality.

[0076] In some embodiments of the present application, for volume holographic materials with multiplexing characteristics (such as photopolymers), the above recording steps can be repeated in different recording forms, and multiple holograms can be recorded on the volume holographic material, so that the volume holographic element meets the application requirements of different scenarios.

[0077] Optionally, the first parallel beam propagating in the first direction can converge at a first set of viewpoints after passing through the pixelated diffractive lens array, and the second parallel beam propagating in the second direction can converge at a second set of viewpoints after passing through the pixelated diffractive lens array. The second direction is different from the first direction, and the second set of viewpoints is not completely the same as the first set of viewpoints. Therefore, the preparation method may include: implementing at least two recording steps; wherein, the recording beam in one recording step is the first parallel beam; at least one recording beam in other recording steps is the second parallel beam. As Figure 9 As shown, before recording using the holographic dry plate 400, the vertically incident first parallel beam can form four converging viewpoints after exiting, and the obliquely incident second parallel beam can form another four different converging viewpoints after exiting, forming a total of eight spatially multiplexed converging viewpoints. By continuously recording the wavefront information in the vertically incident and obliquely incident scenarios twice, a spatially multiplexed volume holographic element can be formed. This spatially multiplexed volume holographic element has more converging viewpoints, which is conducive to improving the angular resolution.

[0078] Optionally, the pixelated diffractive lens array 300 includes a pixelated harmonic diffractive lens array. Using a pixelated harmonic diffractive lens array can overcome the chromatic aberration problem in traditional diffractive lenses, which is conducive to preparing a wavelength multiplexing type volume holographic element with multi-wavelength response.

[0079] Optionally, the viewpoints where the third parallel beam with the first wavelength converges after passing through the pixelated diffractive lens array are the same as the viewpoints where the fourth parallel beam with the second wavelength converges after passing through the pixelated diffractive lens array. The second wavelength is different from the first wavelength. Therefore, the preparation method includes: implementing at least two recording steps; wherein, the recording beam in one recording step is the third parallel beam, and at least one recording beam in other recording steps is the fourth parallel beam. AsFigure 10 As shown, before recording using the holographic plate 400, after the red parallel light beam, the green parallel light beam, and the blue parallel light beam exit from the pixelated diffractive lens array 300, four identical wavelength-division multiplexed converging viewpoints can be respectively formed. By continuously recording the wavefront information under the incident scenes of the red parallel light beam, the green parallel light beam, and the blue parallel light beam three times, a wavelength-division multiplexed volume holographic element can be formed, and this wavelength-division multiplexed volume holographic element can respond to the red wavelength, the green wavelength, and the blue wavelength.

[0080] In some embodiments of the present application, the reference beam includes a spherical wave beam or a parallel beam. As Figure 11 shown, a collimating lens can be used to Figure 7 modulate the spherical wave reference beam in

[0081] an enhanced reality 3D display device

[0082] As Figure 12 shown, an embodiment of the present application provides an enhanced reality 3D display device, including: a projection module 500 configured to provide a reproduction beam carrying 3D parallax image information; a volume holographic element 100 prepared according to the preparation method described above, disposed on the light-emitting side of the projection module 500, and configured to couple with the reproduction beam and converge the reproduction beam to multiple viewpoints; wherein, the projection module 500 is further configured to align the pixels of the 3D parallax image irradiated on the volume holographic element with the holographic pixel units in the volume holographic element one by one during the reproduction process.

[0083] Exemplarily, the wavelength of the reproduction beam is the same as the wavelength of the reference beam; and, the incident angle of the reproduction beam irradiated on the volume holographic element 100 is the same as the incident angle of the reference beam irradiated on the volume holographic material. In this way, it is beneficial to ensure that the reproduction beam better satisfies the Bragg diffraction condition, thereby ensuring the diffraction efficiency. Among them, the incident angle can be expressed as the angle formed by the incident beam and the surface normal of the volume holographic element 100.

[0084] Exemplarily, the projection module includes a projector and a pose adjustment mechanism for adjusting the pose of the projector. The projection angle of the projector can be adjusted through the pose adjustment mechanism. Exemplarily, an image pixel adjustment mechanism can also be provided inside the projection module to adjust the relative position of the image pixels and the holographic pixel units during the reproduction process. Exemplarily, a corresponding program can also be preset inside the projection module to automatically correct the deviation when the image pixels and the holographic pixel units deviate, so as to ensure that the image pixels and the holographic pixel units are aligned one by one.

[0085] As Figure 12As shown, the reproduced light beam is scattered by the volume holographic element 100 to the observer side and converges to four viewpoints (the convergence viewpoints 1 of the reproduced light beam), which is equivalent to passing through the pixelated diffractive lens array 300. That is to say, the volume holographic element 100 can be equivalent to the equivalent pixelated diffractive lens array 300'. By aligning the multi-viewpoint image pixels with the holographic pixel units one by one, it is conducive to realizing pixel-by-pixel light field regulation, enabling the display optical path to have high regulation accuracy and large regulation freedom, thereby reducing the crosstalk of 3D images and overcoming the shortcomings such as depth inversion and self-repeating images in the integral imaging method, and improving the 3D display effect of augmented reality.

[0086] Optionally, the angular interval between adjacent viewpoints among the multiple viewpoints where the reproduced light beam converges ranges from 2° to 4°, for example, it can be 2°, 2.5°, 3°, 3.5°, 4°. If the angular interval is too large, there will be dark areas and discontinuity when viewing the 3D image; if the angular interval is too small, there will be crosstalk when viewing the 3D image and the viewpoints will overlap each other. By setting an appropriate angular interval, the continuity when viewing the 3D image can be ensured while avoiding crosstalk between 3D images.

[0087] Figure 13 The working effect diagram of the augmented reality 3D display device using the volume holographic element 100 is shown. It can be seen that the projected "36 km / h" (virtual 3D image) and the right-turn arrow have a good virtual-real fusion effect with the actual toy car (real object) behind, and as the viewing angle changes, the 3D virtual image provides natural motion parallax without problems of self-repeating images and depth inversion.

[0088] In some embodiments of the present application, the reproduced light beam includes a spherical wave beam or a parallel beam. As Figure 14 shown, a collimating lens can be added to the light-emitting side of the projection module 500, thereby increasing the projection type of the reproduced light beam. Continuing to refer to Figure 14 , when the parallel reproduced light beam irradiates the space-division multiplexing type volume holographic element 100' with the same wavelength and the same incident angle as the reference beam, eight convergence viewpoints (the convergence viewpoints 2 of the reproduced light beam) can be formed on the observer side. That is to say, the space-division multiplexing type volume holographic element 100' can also be equivalent to the equivalent pixelated diffractive lens array 300', thereby realizing the augmented reality 3D display effect with high angular resolution.

[0089] In summary, the augmented reality 3D display device proposed in the present application has the advantages of high diffraction efficiency, high transmittance, no depth inversion, and no self-repeating images, and can provide correct depth information. In addition, due to the large regulation freedom and high precision of the volume holographic element of the present application for the light field, the presented 3D image also has the characteristic of low crosstalk. The optical path of the augmented reality 3D display device of the present application is simple and requires fewer devices, and can be applied to fields such as in-vehicle display, exhibition, and education.

[0090] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0091] The above-described embodiments only express several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A method for preparing a volume holographic element, characterized in that, The volume holographic element includes a substrate and a pixelated information layer disposed on the substrate, and the pixelated information layer includes holographic pixel units distributed in an array; The method includes: Providing a pixelated diffractive lens array and a volume holographic material disposed adjacent to or in contact with the pixelated diffractive lens array; wherein, the pixelated diffractive lens array includes target diffractive lens sub-units distributed in an array; Performing at least one recording step, and the recording step includes: Projecting a recording beam onto the pixelated diffractive lens array, and after the recording beam exits from the pixelated diffractive lens array, it irradiates one side of the volume holographic material; Projecting a reference beam onto the volume holographic material, and the reference beam irradiates the other side of the volume holographic material and interferes with the recording beam to form holographic pixel units corresponding one by one to the target diffractive lens sub-units.

2. The preparation method of the volume holographic element according to claim 1, characterized in that, The providing of the pixelated diffractive lens array includes: Providing a plurality of diffractive lenses; wherein each diffractive lens has at least one target diffractive lens sub-unit, and the target diffractive lens sub-units in the same diffractive lens have the same focal point; Staggering the target diffractive lens sub-units in each of the diffractive lenses to form the pixelated diffractive lens array.

3. The preparation method of the volume holographic element according to claim 1, characterized in that, The method includes: Performing at least two recording steps, wherein the recording beam in one recording step is a first parallel beam propagating in a first direction; at least one of the recording beams in other recording steps is a second parallel beam propagating in a second direction, the first parallel beam converges at a first set of viewpoints after exiting from the pixelated diffractive lens array, the second parallel beam converges at a second set of viewpoints after exiting from the pixelated diffractive lens array, the second direction is different from the first direction, and the second set of viewpoints is not entirely the same as the first set of viewpoints.

4. The method for preparing a volume holographic element according to claim 1, wherein, The reference beam includes a spherical wave beam or a parallel beam.

5. The preparation method of the volume holographic element according to claim 1, characterized in that, The pixelated diffractive lens array includes a pixelated harmonic diffractive lens array.

6. The method for preparing a volume holographic element according to claim 1, characterized in that, The method includes: Performing at least two recording steps, wherein the recording beam in one recording step is a third parallel beam having a first wavelength; at least one of the recording beams in other recording steps is a fourth parallel beam having a second wavelength, the viewpoints at which the third parallel beam converges after exiting from the pixelated diffractive lens array are the same as the viewpoints at which the fourth parallel beam converges after exiting from the pixelated diffractive lens array, and the second wavelength is different from the first wavelength.

7. The method for preparing a volume holographic element according to any one of claims 1 to 6, characterized in that, The volume holographic material is any one of a photopolymer, a holographic polymer dispersed liquid crystal, a cholesteric liquid crystal, a dichromated gelatin, a silver halide material, and a photorefractive glass.

8. A volume holographic element, characterized in that, Including: A substrate; A pixelated information layer disposed on the substrate, including holographic pixel units distributed in an array; Wherein, the pixelated information layer contains wavefront information of a wavefront formed by the interference of a recording beam after exiting from a pixelated diffractive lens array and a reference beam; And, the pixelated diffractive lens array includes target diffractive lens sub-units distributed in an array, and the holographic pixel units correspond one by one to the target diffractive lens sub-units.

9. The volume holographic element according to claim 8, wherein The pixelated information layer has recording parameters related to the wavefront information, and the recording parameters include at least one of a fringe period and a fringe orientation on a layer section of the pixelated information layer, a pitch of the holographic pixel units, and a shape of the holographic pixel units.

10. The volume holographic element according to claim 8, characterized in that, The material of the pixelated information layer is any one of a photopolymer, a holographic polymer dispersed liquid crystal, a cholesteric liquid crystal, a dichromated gelatin, a silver halide material, and a photorefractive glass.

11. An augmented reality 3D display device, characterized in that, Comprising: A projection module configured to provide a reproduction beam carrying 3D parallax image information; A volume holographic element prepared by the preparation method according to any one of claims 1 to 8, disposed on an outgoing light side of the projection module, and configured to couple with the reproduction beam and converge the reproduction beam to a plurality of viewpoints; Wherein, The projection module is further configured to align pixels of the 3D parallax image irradiated onto the volume holographic element with the holographic pixel units in the volume holographic element during the reproduction process.

12. The augmented reality 3D display device according to claim 11, wherein The wavelength of the reproduction beam is consistent with the wavelength of the reference beam; and An incident angle of the reproduction beam irradiated onto the volume holographic element is consistent with an incident angle of the reference beam irradiated onto the volume holographic material.

13. The augmented reality 3D display device according to claim 11, wherein The reproduction beam includes a spherical wave beam or a parallel beam.

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