Diffraction image superimposer, display device module and head-mounted display device

Abstract

The present application discloses a diffraction image superimposer that can increase the exit pupil size and improve user experience. The diffraction image superimposer includes: a first diffraction optical element (DOE) and a second DOE, wherein the first DOE is parallel to the second DOE; a first incident point of the first DOE and a second incident point of the second DOE have the same grating vector, the first incident point is used to convert an incident light satisfying the Bragg condition into a first diffracted light and a first transmitted light, the first transmitted light is incident on the second incident point, and the second incident point is used to convert the first transmitted light into a second diffracted light.

Description

Technical Field

[0001] The present application relates to the field of optics, and in particular to a diffraction image superimposer, a display device module, and a head-mounted display device. Background Art

[0002] Augmented reality (AR) near-eye display technology is a wearable display system that uses a specific optical system to allow the human eye to see both real scenes and computer-generated virtual scenes. In an AR system, computing components analyze and process the real scene observed by the user. Then, using near-eye display technology, the generated virtual augmented information is overlaid onto the real scene, achieving a seamless fusion of real and virtual scenes and assisting users with a deeper and more comprehensive understanding of the real world. As one of the core technologies of AR devices, near-eye display technology has become a research hotspot in both industry and academia.

[0003] The core task of AR near-eye display technology is to perform virtual-real superposition, that is, to allow real-world light and virtual image light to pass through simultaneously and reach the human eye. Near-eye display technology based on diffraction optics has become a research hotspot in recent years because it can effectively reduce the size and weight of optical components. The AR near-eye projection solution based on the Maxwell observation principle and the diffractive image combiner (DIC) can significantly improve the field of view (FoV) of AR near-eye display, that is, the angle of the virtual image presentation range relative to the human eye, for example, more than 80 degrees.

[0004] Due to the angular bandwidth of DIC devices, the pixel size of SLM-type image source devices, or the optical path limitations of the laser beam retinal scanning mechanism, the exit pupil size of AR near-eye projection solutions based on the Maxwell observation principle and DIC devices is relatively small, for example, 1 mm. Since the human pupil and the eyebox must have a spatial overlap in order to see the virtual image, a too small eyebox can easily cause users to lose the image, seriously reducing the user experience. Summary of the Invention

[0005] The embodiment of the present application provides a diffraction image superimposer based on micro-nano optical technology, which is used to expand the system exit pupil size and improve the user experience.

[0006] In a first aspect, an embodiment of the present application provides a diffraction image superimposer, comprising: a first diffraction optical element (DOE) and a second DOE, wherein the first DOE is parallel to the second DOE; a first incident point of the first DOE and a second incident point of the second DOE have the same grating vector, the first incident point is used to convert an incident light satisfying a Bragg condition into a first diffracted light and a first transmitted light, the first transmitted light is incident on the second incident point, and the second incident point is used to convert the first transmitted light into a second diffracted light.

[0007] The diffraction image superimposer provided in an embodiment of the present application includes at least two layers of diffraction optical elements (DOEs). The first incident point of the first DOE can be used to convert incident light with a projection angle within the Bragg domain into a first diffraction ray and a first transmitted ray, wherein the first diffraction ray constitutes the first exit pupil of the system. The first transmitted ray can be incident on the second incident point of the second DOE. The second incident point converts the incident first transmitted ray into a second diffraction ray, and the second diffraction ray constitutes the second exit pupil of the system. Because the grating vector of the first incident point is the same as the grating vector of the second incident point, the second diffraction ray is parallel to the first diffraction ray. The exit pupil size determined based on the first exit pupil and the second exit pupil is larger than the exit pupil size of a diffraction image superimposer having only a single layer of diffraction optical elements. Therefore, the exit pupil size of the diffraction image superimposer provided in the present application is increased, and users are less likely to lose images, which can improve the user experience.

[0008] The light incident under the Bragg condition is incident at the first incident point, and the first transmitted light propagates to the second incident point and is incident, which can ensure that the first diffracted light and the second diffracted light are parallel to each other, and no crosstalk occurs when the user observes the virtual image.

[0009] In a possible implementation of the first aspect, the first DOE is provided with a first grating region, and the second DOE is provided with a second grating region. The first grating region is used to convert a first parallel incident light beam with a projection angle within the Bragg domain into a first diffracted light beam and a first transmitted light beam. The first diffracted light beam converges at a first focal point. The first transmitted light beam is incident on the second grating region. The second grating region is used to convert the first transmitted light beam into a second diffracted light beam. The second diffracted light beam converges at a second focal point. The distance from the first focal point to the diffraction image superimposer is equal to the distance from the second focal point to the diffraction image superimposer.

[0010] In a possible implementation of the first aspect, the first DOE is provided with a first grating region, and the second DOE is provided with a second grating region. The first grating region is configured to convert a first parallel incident light beam with a projection angle within the Bragg domain into a first diffracted light beam and a first transmitted light beam. The first diffracted light beam is diffracted and converged at a first focal point. The first transmitted light beam is incident on the second grating region. The second grating region is configured to convert the first transmitted light beam into a second diffracted light beam. The second diffracted light beam is diffracted and converged at a second focal point. The distance from the first focal point to the diffraction image superimposer is equal to the distance from the second focal point to the diffraction image superimposer. The first incident point is located in the first grating region, and the second incident point is located in the second grating region. The diffraction structure of the first grating region and the diffraction structure of the second grating region are proportionally scaled. Specifically, in the plane direction of the DOE extension, the diffraction structure of the second grating region is a proportional enlargement of the diffraction structure of the first grating region.

[0011] In the diffraction image superimposer provided in the embodiments of the present application, the distance from the first focal point to the diffraction image superimposer is equal to the distance from the second focal point to the diffraction image superimposer, and both are located on the same side of the diffraction image superimposer. That is, the line connecting the first and second focal points is parallel to the plane where any DOE of the diffraction image superimposer is located. Therefore, the field of view angle formed by the diffracted light beams of the first DOE and the field of view angle formed by the diffracted light beams of the second DOE are the same. The virtual images presented to the user by light beams emitted from the same image point after diffraction by different DOEs overlap, and crosstalk does not occur.

[0012] In a possible implementation manner of the first aspect, the incident light and the first diffracted light are located on the same side of the first DOE; or, the incident light and the first diffracted light are located on different sides of the first DOE.

[0013] In the diffraction image superimposer provided in an embodiment of the present application, if each DOE is implemented using a reflective DOE, the incident light and the first diffracted light are located on the same side of the first DOE, that is, the micro-projection engine and the human eye observing the user can be located on the same side; if each DOE is implemented using a transmissive DOE, the incident light and the first diffracted light are located on different sides of the first DOE, that is, the micro-projection engine and the human eye observing the user can be located on different sides. As a result, different near-eye display projection schemes can be designed, thereby improving the flexibility of the scheme implementation.

[0014] In a possible implementation of the first aspect, the first DOE is a micro-nano optical device, including a volume holographic grating VHG, a surface relief grating SRG, a metasurface or a microlens array; the second DOE is a micro-nano optical device, including a volume holographic grating VHG, a surface relief grating SRG, a metasurface or a microlens array.

[0015] The diffraction image superimposer provided in the embodiment of the present application can have various types of diffraction optical elements, thereby increasing the diversity of the implementation scheme.

[0016] In a possible implementation of the first aspect, the DIC further includes a third DOE parallel to the second DOE, the second DOE is located between the first DOE and the third DOE, a third incident point of the third DOE has the same grating vector as the second incident point, the second incident point is further used to convert the first transmitted light into a second diffracted light and a second transmitted light, the second transmitted light is incident on the third incident point, and the third grating area is used to convert the second transmitted light into a third diffracted light.

[0017] The diffraction image superimposer provided in an embodiment of the present application may include a third DOE, and the third incident point on the third DOE has the same grating vector as the second incident point and the first incident point. The emitted third diffraction light constitutes a third sub-exit pupil, which can further expand the exit pupil size. In addition, the emitted second diffraction light and the third diffraction light are parallel to each other. The light emitted from the same image point appears as the same virtual image in the user's eyes after being diffracted by different DOEs, and no crosstalk occurs.

[0018] In a possible implementation of the first aspect, the third DOE includes a third grating region. The first grating region is configured to convert a first parallel incident light beam with a projection angle within the Bragg domain into a first diffracted light beam and a first transmitted light beam. The first diffracted light beam converges at a first focal point. The first transmitted light beam enters the second grating region. The second grating region is configured to convert the first transmitted light beam into a second diffracted light beam and a second transmitted light beam. The second diffracted light beam converges at a second focal point. The second transmitted light beam enters the third grating region. The third grating region is configured to convert the third transmitted light beam into a third diffracted light beam. The third diffracted light beam is diffracted and converges at a third focal point. The distance from the third focal point to the diffraction image superimposer is equal to the distance from the second focal point to the diffraction image superimposer and the distance from the first focal point to the diffraction image superimposer. The third incident point is located in the third grating region. The diffraction structure of the third grating region is proportionally scaled to the diffraction structure of the second grating region.

[0019] In the diffraction image superimposer provided in the embodiments of the present application, the distances from the third focal point to the diffraction image superimposer, the distances from the second focal point to the diffraction image superimposer, and the distances from the first focal point to the diffraction image superimposer are all equal, and the first, second, and third focal points are all located on the same side of the diffraction image superimposer. That is, the plane containing the first, second, and third focal points is parallel to the plane where any DOE of the diffraction image superimposer is located. Therefore, the field of view angle formed by the third diffracted beam is the same as the field of view angle formed by the second diffracted beam and the field of view angle formed by the first diffracted beam. That is, the field of view angles formed by each diffracted beam formed by the incident beam within the Bragg domain after diffraction by multiple DOEs are the same. Therefore, the virtual images presented to the user by beams emitted from the same image point after diffraction by different DOEs overlap, and crosstalk does not occur.

[0020] The diffraction image superimposer provided in the embodiment of the present application can achieve a crosstalk-free pupil expansion effect while maintaining the system field of view size unchanged by introducing a multi-layer diffraction structure and designing the corresponding relationship between the diffraction structures of each layer.

[0021] In a possible implementation manner of the first aspect, the diffraction image superimposer further includes: a substrate disposed between the first DOE and the second DOE, wherein the upper and lower surfaces of the substrate are optically parallel.

[0022] The diffraction image superimposer provided in the embodiment of the present application can fill a substrate between the multi-layer diffraction optical elements, thereby providing a certain optical path and facilitating the expansion of the exit pupil size.

[0023] In a possible implementation manner of the first aspect, the substrate material is an optically transparent material, and the optically transparent material includes glass or optical plastic.

[0024] The diffraction image superimposer provided in the embodiment of the present application can have a substrate that can be made of a variety of materials, thereby increasing the diversity of the implementation scheme.

[0025] In a possible implementation manner of the first aspect, a diffraction efficiency of the first DOE is lower than a diffraction efficiency of the second DOE.

[0026] In a possible implementation manner of the first aspect, a diffraction efficiency of the second DOE is lower than a diffraction efficiency of the third DOE.

[0027] The diffraction image superimposer provided in the embodiment of the present application can adjust the intensity of the diffracted light of each layer of diffraction optical elements by designing the diffraction efficiency of different diffraction optical elements, so that the light intensity of each sub-exit pupil is close, which can improve the user experience.

[0028] A second aspect of an embodiment of the present application provides a display device module, characterized in that it includes a micro-projection engine and a diffraction image superimposer as described in any one of the first aspect and various implementation methods; the micro-projection engine is used to project incident light in the Bragg domain to the diffraction image superimposer; the first diffraction light constitutes a first sub-exit pupil, the second diffraction light constitutes a second sub-exit pupil, and the exit pupils of the display device module include the first sub-exit pupil and the second sub-exit pupil.

[0029] In a possible implementation of the second aspect, the micro-projection engine includes a planar image source device or a scanning image source device, the planar image source device includes a spatial light modulator (SLM) image source device and an incoherent planar micro image source, and the scanning image source device includes a laser beam scanning (LBS) device.

[0030] In a possible implementation manner of the second aspect, the display device module further includes a frame, and the frame is used to fix the micro-projection engine and the diffraction image superimposer.

[0031] In a possible implementation manner of the second aspect, the display device module further includes at least one of the following: a communication device, a processor, and a power supply device.

[0032] A third aspect of an embodiment of the present application provides an augmented reality (AR) device, characterized in that it includes the display device module described in any one of the second aspect and various implementation methods.

[0033] A fourth aspect of an embodiment of the present application provides a virtual reality (VR) device, characterized in that it includes the display device module described in any one of the second aspect and various implementation methods.

[0034] A fifth aspect of an embodiment of the present application provides a near-eye display device, characterized in that it includes the display device module described in any one of the second aspect and various implementation methods.

[0035] A sixth aspect of an embodiment of the present application provides a head-mounted display device, characterized in that it includes a left-eye display and a right-eye display; the left-eye display includes a diffraction image superimposer as described in any one of the first aspect and various implementations; the right-eye display includes a diffraction image superimposer as described in any one of the first aspect and various implementations.

[0036] It can be seen from the above technical solutions that the embodiments of the present application have the following advantages:

[0037] The diffraction image superimposer provided in an embodiment of the present application includes at least two layers of diffractive optical elements (DOEs). The first DOE includes a first grating region having the same diffraction structure as the second grating region of the second DOE. The first DOE and the second DOE can convert incident light with a projection angle within the Bragg domain into diffracted light, forming a first sub-exit pupil and a second sub-exit pupil, respectively. Therefore, compared with a DIC having only one DOE, the exit pupil size can be expanded. The larger exit pupil size can accommodate differences in pupil distances between different users, avoid image loss caused by eye movement, and improve the user experience.

[0038] The display device module provided in an embodiment of the present application includes an image overlay display DIC having at least two layers of mutually parallel diffractive optical elements (DOEs). The first DOE includes a first grating region having the same diffraction structure as the second grating region of the second DOE, and can convert image light projected by a micro-projection engine toward the DIC to generate a first sub-exit pupil and a second sub-exit pupil, respectively. The second layer of DOE replicates and translates the exit pupil formed by the first layer of DOE. Thus, compared to a DIC having only one layer of DOE, the exit pupil size can be expanded. The larger exit pupil size can accommodate differences in pupil distances between different users, and can also avoid image loss caused by eye movement, thereby improving the user experience.

[0039] Furthermore, in the DIC comprising at least two DOE layers, the first grating region of the first DOE corresponds to the second grating region of the second DOE: the incident point of light under the Bragg condition on the first grating region has the same grating vector as the incident point on the second grating region. Therefore, light projected onto the DIC from any image point on the real image plane with an incident angle within the Bragg domain is converted into nearly parallel light after passing through the multi-layer diffractive optical elements of the diffraction image superimposer and entering the human eye, where it corresponds to a single image point on the retina. This achieves crosstalk-free pupil expansion. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A schematic diagram of a user wearing a head-mounted display device;

[0041] Figure 2 A schematic diagram of a head-mounted display device;

[0042] Figure 3 This is a schematic diagram of an embodiment of a near-eye display system in an embodiment of the present application;

[0043] Figure 4 Schematic diagram of the field of view angle and exit pupil size of the near-eye display system in an embodiment of the present application;

[0044] Figure 5 Schematic diagram of the basic components of a diffraction image superimposer;

[0045] Figure 6a It is a near-eye display system based on the SLM micro-projection engine;

[0046] Figure 6b It is a near-eye display system based on an incoherent planar image source micro-projection engine;

[0047] Figure 6c It is a near-eye display system based on LBS micro-projection engine;

[0048] Figure 7a This is a schematic diagram of an embodiment of a display device module in an embodiment of the present application;

[0049] Figure 7b This is a schematic diagram of light transmission of a display device module in an embodiment of the present application;

[0050] Figure 7c Schematic diagram of the display device module projecting light toward the DIC within the effective angle in an embodiment of the present application;

[0051] Figure 7d This is a schematic diagram of another embodiment of a display device module in an embodiment of the present application;

[0052] Figure 8 Schematic diagram of diffraction efficiency design of a display device module in an embodiment of the present application;

[0053] Figure 9a A schematic diagram of an optical path of a display device module in an embodiment of the present application;

[0054] Figure 9b This is another optical path schematic diagram of the display device module in an embodiment of the present application;

[0055] Figure 10a Schematic diagram of a method for manufacturing a diffraction structure in an embodiment of the present application;

[0056] Figure 10b Another schematic diagram of the method for manufacturing a diffraction structure in an embodiment of the present application;

[0057] Figure 11 Another schematic diagram of the method for manufacturing a diffraction structure in an embodiment of the present application;

[0058] Figure 12 Schematic diagram of the relationship between the grating vector, reference light and object light in the embodiment of the present application. DETAILED DESCRIPTION

[0059] The following describes the embodiments of the present application in conjunction with the accompanying drawings. Obviously, the embodiments described are only part of the embodiments of the present application, rather than all the embodiments. Those skilled in the art will appreciate that with the development of technology and the emergence of new scenarios, the technical solutions provided in the embodiments of the present application are also applicable to similar technical problems.

[0060] The terms "first", "second", etc. in the specification and claims of this application and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate so that the embodiments described herein can be implemented in a sequence other than that illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or modules is not necessarily limited to those steps or modules clearly listed, but may include other steps or modules that are not clearly listed or that are inherent to these processes, methods, products or devices. The naming or numbering of steps in this application does not mean that the steps in the method flow must be executed in the time or logical sequence indicated by the naming or numbering. The process steps that have been named or numbered can be changed in the execution order according to the technical purpose to be achieved, as long as the same or similar technical effects can be achieved.

[0061] To facilitate understanding, the technical terms involved in this application are first introduced:

[0062] Diffraction grating: A diffraction grating, also known as a grating, is an optical device or structure that can periodically modulate the amplitude or phase, or both, of incident light. It includes transmission gratings (transmitted light is modulated) and reflection gratings (reflected light is modulated).

[0063] Grating vector: The grating vector at any point on a diffraction structure is defined as the difference between the wave vectors of the object and reference beams at that point during the diffraction structure's fabrication. The spatial distribution of the grating vectors on a diffraction structure determines the selectivity of each point on the structure for the angle and wavelength of incident light, as well as the direction of the diffracted light. A diffraction optics concept corresponding to the grating vector is the grating period. Changes in the grating vector are reflected in changes in the grating period structure. Numerically, the product of the grating period and the grating vector at any point on the diffraction structure is equal to 2π.

[0064] Bragg domain: The diffraction structure prepared based on micro-nano processing technologies such as VHG, SRG, and metasurface has angle selectivity for incident light. Only when the incident angle of the incident light is within a neighborhood range of the Bragg angle will it be redirected by the diffraction structure. Otherwise, it will pass through the diffraction structure in a straight line. The neighborhood range of the Bragg angle is the Bragg domain.

[0065] Angular bandwidth of the grating: The diffraction structure prepared based on technologies such as VHG, SRG, and metasurface has angular selectivity for the incident light. Only when the incident angle of the incident light is within the Bragg domain will it be redirected by the diffraction structure. The projected light outside the angular bandwidth can pass through the grating without being redirected. The angular bandwidth of the grating is used to represent the size of the Bragg domain, that is, the angular range of the incident light that can be redirected by the diffraction structure.

[0066] Diffraction efficiency refers to the ratio of the light intensity in a certain diffraction direction to the incident light intensity. Diffraction efficiency is related to various parameters such as the refractive index and thickness of the material.

[0067] Exit pupil: The image formed by the aperture of an optical system in the optical system's image space is called the system's "exit pupil," also known as the eye's field of view, exit pupil, or often simply referred to as the eyebox. Exit pupil size is used to measure the size of a system's "exit pupil."

[0068] Figure 1 A schematic diagram of a head-mounted display device 100 worn by a user 102 is shown. The head-mounted display device 100 can be used to display augmented reality images and physical objects in a real-world background scene. The head-mounted display device 100 can include a frame 104 for positioning the device at a target viewing position relative to the eyes of the user 102.

[0069] Figure 2 Show Figure 1 A schematic diagram of a head mounted display device 100 is shown in FIG. Figure 2 As shown in FIG, the see-through head mounted display device 100 includes a right eye display 200a and a left eye display 200b. Each see-through display (right eye display 200a or left eye display 200b) can be used to display virtual images to the user and allow the user to view the real world environment. For example, each see-through display may include a display device for emitting display light through an optical structure to reach the user's eyes, and the display device may also allow light from the real world environment to reach the user's eyes. In addition, Figure 2 Schematically, a microphone 202 is shown that can be used to output acoustic information to the user. Such acoustic information can take any suitable form, including but not limited to computer-generated speech output in an appropriate language (such as selected by the user), tones or other sounds that are not specific to any language, and / or any other suitable sound. In some embodiments, other types of output can be provided by the head-mounted display device 100, such as haptic / touch output.

[0070] The left-eye display 200b and the right-eye display 200a may be positioned at viewing positions relative to the eyes via one or more fastening mechanisms of the frame 104. For example, Figure 2As shown, the frame 104 can be supported by the user's ears via earpieces 206 and by the user's nose via nose bridge 208 to reduce sliding of the frame 104. It will be understood that Figure 2 The supports shown (e.g., earpieces 206, nosepieces, and nose bridge 208) are exemplary in nature, and the see-through display of the head-mounted see-through display device may be positioned at the viewing position via any suitable mechanism. For example, additional supports may be utilized, and / or Figure 2 One or more of the supports shown can be removed, replaced, and / or expanded to position the see-through display in the viewing position. Additionally, the see-through display can be positioned in the viewing position by mechanisms other than supports that physically contact the user, and this application is not limited thereto.

[0071] Below is an introduction to the relationship between field of view and exit pupil size in near-eye display systems. Please refer to Figure 3 , is a schematic diagram of an embodiment of a near-eye display system in an embodiment of the present application.

[0072] The image formed by the aperture stop of the optical system in the image space of the optical system is called the "exit pupil" of the system. The micro-projection engine projects a virtual image from the side to the DIC device. On the one hand, the DIC device redirects the incident light within its characteristic angle range directly to the exit pupil position (such as V1 and V2) through diffraction. At the same time, it also allows the external real-world light that falls outside the characteristic angle range and characteristic wavelength range (such as R1) to pass through the DIC transparently and enter the pupil of the human eye without being affected, thereby completing the virtual and real superposition operation.

[0073] The size S of the DIC device is limited by the size of the lens and cannot be too large, generally not exceeding 50 mm; the exit pupil distance D is limited by the physiological structure of the human face (face shape, eyebrows, eyelashes, etc.) and is generally greater than 20 mm; the diffraction angle of the image point on the object plane is limited by the pixel spacing of the image source device and is usually very small, such as around 8 degrees (°); the eyebox is mainly limited by the diffraction angle of the SLM image source device and the angular bandwidth of the DIC device. Currently, the actual system usually does not exceed 3 mm; the FoV is limited by the size S of the DIC device, the exit pupil distance D and the eyebox size. Currently, the actual system usually does not exceed 80°.

[0074] See also Figure 4 , which is a schematic diagram of the field of view angle and exit pupil size of the near-eye display system in an embodiment of the present application.

[0075] The field of view is the angular range of the image presented by the human eye. The user will not be able to see the image outside this angular range. The exit pupil is a spatial area. When the intersection of the eye pupil and this area is not empty, the light emitted by all pixels on the image plane can be seen, that is, the complete image can be seen; otherwise, the complete image cannot be seen.

[0076] Since the pupil and the eyebox must overlap in space to see the virtual image, the user's pupil needs to overlap with the eyebox in order to see the virtual image. If the pupil moves and the overlapping area with the eyebox disappears, the image will be lost, seriously reducing the user experience. Figure 3 As shown in the figure, if the field of view is large, the eyeball usually needs to rotate to fully observe the image within the field of view. Understandably, a larger FoV requires a larger eyebox to match. Because the human pupil and the eyebox must spatially overlap to see the virtual image, if the eyebox is too small, the user will easily lose the image, seriously degrading the user experience.

[0077] The following is an introduction to commonly used near-eye display systems. Please continue to refer to Figure 3 The near-eye display system shown.

[0078] The near-eye display system is usually composed of a micro-projection engine, a DIC device and a frame structure for fixing the two. In addition, it can also include related communication components, information processing components and power supply devices, etc., which are not limited here.

[0079] Micro-projection engines, also known as handheld projectors, offer advantages such as small size, high brightness, and low noise. They have broad application prospects in small businesses, home entertainment, and near-eye display devices. Micro-projection engines can be implemented using either planar or point-image source devices, each of which is described below.

[0080] Planar image source devices include various spatial light modulator (SLM) image source devices, such as liquid crystal on silicon (LCoS) microdisplays and digital micro-mirror displays (DMD) microdisplays, as well as various incoherent planar image sources, such as light-emitting diode (LED) microdisplays, organic light-emitting diode (OLED) microdisplays, and liquid crystal displays (LCD) microdisplays.

[0081] Point image source devices mainly include laser beam scanning (LBS) microdisplays.

[0082] Diffractive image combiner (DIC), hereinafter referred to as DIC device, can modulate the wavefront of light waves and precisely control the direction of the incident light. Figure 5 , a schematic diagram of the basic components of a diffractive image superimposer. A DIC device consists of an optically transparent lens-shaped substrate, also known as a lens substrate, and a diffractive optical element (DOE) layer located on the substrate surface. The transparent substrate can typically be glass or optical plastic, with good optical parallelism between the two surfaces of the substrate. The DOE can be a volume holographic grating (VHG) attached to the surface (top or bottom) of the transparent substrate, a surface rising grating (SRG) fabricated directly on the transparent substrate through photolithography, or a metasurface. The DOE element exhibits angle selectivity and wavelength selectivity for incident light. That is, only when the incident angle and wavelength of the incident light fall within the characteristic angle range and characteristic wavelength range of the DOE element will it be redirected to a predetermined direction by the diffraction effect of the DOE element. Otherwise, the incident light can pass through the DOE element in a straight line without being affected.

[0083] In the AR near-eye projection solution based on the Maxwell observation principle and DIC devices, the micro-projection engine projects a virtual image from the side to the DIC device. On the one hand, the DIC device redirects the incident light within its characteristic angle range directly to the observer's pupil position, i.e., the exit pupil position, through diffraction (through the design of the system optical path and DOE elements, the incident angle of the image light projected by the micro-projection engine falls within the characteristic angle range of the DOE element at the incident point). At the same time, it also allows the light from the external real world to pass through the DIC unaffected and transparently into the observer's pupil (through the design of the system optical path and DOE elements, the incident angle of the external real-world light falls outside the characteristic angle range of the DOE element at the incident point), thereby completing the virtual-real superposition operation.

[0084] See below. Figures 6a-6c , introduces the limiting factors of Eyebox in different types of micro-projection engines respectively.

[0085] Figure 6a It is a near-eye display system based on the SLM micro-projection engine. The SLM device modulates the incident coherent light, generates a real image plane of the visible image through diffraction, and projects it onto the DIC device. The DIC device converges the parallel light beams of each image point on the image plane along the same projection direction to an exit pupil point through diffraction. The distance between the exit pupil points generated by the marginal light beams projected by each image point to the DIC constitutes the system's exit pupil (Eyebox), which is composed of Figure 6aIt can be seen intuitively that the exit pupil size is limited by the diffraction angle of each image point and the angular bandwidth of the grating in the DIC device. Since the image point diffraction angle is limited by the pixel spacing of the image source device, it is usually very small, generally less than 8°, and the angular bandwidth of the DIC device is generally less than 10°. Therefore, the exit pupil of the system is extremely small, only 1 mm to 3 mm.

[0086] Figure 6b This is a near-eye display system based on an incoherent planar image source micro-projection engine. The image source surface is the image surface. The effective angular range of light projected by each image point to the DIC is mainly constrained by the angular bandwidth of the DIC device, that is, the Bragg domain. Due to the angular selectivity of the DIC, the projected light outside the Bragg domain can pass through the DIC transparently without being redirected to the exit pupil position, and the problem of a small exit pupil also exists.

[0087] Figure 6c This near-eye display system, based on an LBS micro-projection engine, uses a semiconductor laser as its light source. The intensity and spectrum of the outgoing laser beam are modulated according to the image information. A micro-scanning mirror scans the modulated incident laser beam in a two-dimensional time series and projects it onto a DIC device. Diffraction from the DIC device redirects the light and focuses it at the pupil, where it is then propagated to the retina for imaging. The system's exit pupil is approximately a point.

[0088] Depend on Figures 6a-6c It can be seen that due to the angular bandwidth of the DIC device, the pixel size of the image source device or the optical path limitations of the laser beam retinal scanning mechanism, the eyebox size in the DIC-based AR near-eye display system is too small, seriously affecting the user experience.

[0089] In order to expand the exit pupil size and improve the user experience, the embodiment of the present application provides a display device module. Figures 7a-7d The structure and optical path of the display device module are introduced respectively.

[0090] like Figure 7a Figure 1 is a schematic diagram of an embodiment of a display device module according to an embodiment of the present application. The DIC device in this display device module includes a substrate 101, a first diffraction structure 103, and a second diffraction structure 102. Furthermore, 104 represents the system exit pupil, 105 represents the human eye's observation range, and 106 represents the real image plane projected by the micro-projection engine.

[0091] The first diffraction structure 103 is parallel to the second diffraction structure 102. Optionally, the first diffraction structure 103 may be a volume holographic grating (VHG), a surface relief grating (SRG), a metasurface, or a microlens array, which is not specifically limited herein, and the first diffraction structure 102 may be a volume holographic grating (VHG), a surface relief grating (SRG), a metasurface, or a microlens array, which is not specifically limited herein.

[0092] Optionally, the substrate 101 is an optically transparent medium, including glass, optical plastic, and other materials, and the upper and lower surfaces of the substrate 101 have good optical parallelism.

[0093] Optionally, a substrate 101 is not provided between the first diffraction structure 103 and the first diffraction structure 102, and the first diffraction structure 103 and the first diffraction structure 102 need to be supported by a supporting component such as a frame structure so that the first diffraction structure 103 is parallel to the first diffraction structure 102. In this implementation, the light transmitted from the first diffraction structure 103 propagates through the air to the first diffraction structure 102. Since the refractive index of air is smaller than that of the optically transparent medium, a larger offset distance can be obtained.

[0094] Optionally, the micro-projection engine can be a planar image source device or a point image source device, with no specific limitations here. Planar image source devices include SLM image source devices, such as LCoS microdisplays and DMD microdisplays, or incoherent planar micro-image sources, such as OLED microdisplays and LCD microdisplays. Point image source devices include LBS-based laser scanning microdisplays.

[0095] The corresponding light transmission process is as follows Figure 7b As shown in the figure, assume that light ① and light ⑥ are two edge rays of a parallel beam carrying the entire image information emitted by the real image plane projected by the micro-projection engine. Light ① strikes point A of the first-layer diffraction structure, where it splits into two rays: positive-first-order diffraction light ② and zero-order transmitted light ③. Zero-order transmitted light ③ strikes point B of the second-layer diffraction structure and similarly splits into two rays: positive-first-order diffraction light ④ and zero-order transmitted light ⑤. Through the design and processing of the diffraction structure, the grating vectors at points A and B are identical, ensuring that light rays ② and ④ emerge as parallel rays. The horizontal distance between light rays ② and ④ at the exit pupil position 104 is the distance between points A and A'. Similarly, light ⑥ strikes point C and splits into two rays: positive-first-order diffraction light ⑦ and zero-order transmitted light ⑧. Zero-order transmitted light ⑧ strikes point D of the second-layer diffraction structure and similarly splits into two rays: positive-first-order diffraction light ⑨ and zero-order transmitted light ⑩. By designing and processing the diffraction structure, the grating vectors at points C and D are identical, ensuring that light rays ⑦ and ⑨ emerge as parallel rays. The distance between points C and C' is the same as the distance between points A and A', which is the amount of exit pupil expansion. Light rays ② and ⑦ converge at point E within the first sub-exit pupil corresponding to the first layer of the diffraction structure and enter the human eye. The human eye observes the image information of the entire image plane carried by the parallel beams. Simultaneously, light rays ④ and ⑨ converge at point E' within the expanded sub-exit pupil corresponding to the second layer of the grating and enter the human eye. When the human eye moves to point E', it can also observe the complete image information.

[0096] It should be noted that the light incident point in the first diffraction structure 103, for example, point A, can be understood as the first grating region of the first diffraction structure, and the light incident point in the second diffraction structure 102, for example, point B, can be understood as the second grating region of the second diffraction structure. The microscopic physical structure of the grating region can determine the grating vector. The grating vectors at points A and B are the same, that is, the diffraction structure of the first grating region is the same as the diffraction structure of the second grating region.

[0097] For the light carrying image information projected from the image plane to the DIC, Figure 7b The optical path only shows the propagation path of a parallel beam propagating in one direction. In fact, the light projected from the image plane to the DIC is limited to an effective angle by the angular bandwidth of the DIC. The following is an example of a near-eye display system based on an SLM micro-projection engine. If the micro-projection engine is based on an SLM device, the effective angle will be further limited by the diffraction angle of the SLM device, that is, the effective angle should not be greater than the diffraction angle. For the optical path propagation after considering the effective angle, please refer to Figure 7c .

[0098] Figure 7c In the figure, each image point on the image plane projects light onto the DIC within the effective aperture angle. For the sake of clarity, only two light rays at the edge of the aperture angle are drawn in the figure. In the figure, the left edge light rays emitted by each image point on the image plane are diffracted by the first layer of diffraction structure and then converge at the left edge point M of the sub-exit pupil 107. The right edge light rays emitted by each image point are diffracted by the first layer of diffraction structure and then converge at the right edge point N of the sub-exit pupil 107. The area between the left and right edge points is the sub-exit pupil 107 corresponding to the first layer of diffraction structure. This is also the exit pupil that can be achieved by the single-layer diffraction structure DIC. Since the DIC device in the embodiment of the present application has a multi-layer diffraction structure, the light rays projected onto the DIC within the effective aperture angle by each image point on the image plane will be diffracted and converged into the expanded sub-exit pupil 108 after propagating to the second layer of diffraction structure. That is, the human eye can also see the complete projected image in the sub-exit pupil 108. It should be pointed out that there may be a hole area 109 (i.e., an area through which no image light passes) between the sub-exit pupil 107 and the sub-exit pupil 108. However, in order to ensure that the human eye does not lose the image field of view when continuously moving between the sub-exit pupil 107 and the sub-exit pupil 108, the size of the hole area 109 needs to be smaller than the size of the human eye pupil. That is, to ensure that when the human eye continuously moves within the system exit pupil synthesized by areas 107, 108, and 109, there is always a sub-exit pupil area that overlaps with the human eye pupil.

[0099] It should be noted that the distances from sub-exit pupils 107 and 108 to the DIC device, i.e., the exit pupil distances, are identical. They can be adjacent on the pre-designed exit pupil plane, or a void region 109 of a certain size can exist. The specific dimensions are not limited here. Optionally, the size of void region 109 is less than or equal to 3 mm.

[0100] It should be noted that Figures 7a-7c The DIC devices in the illustrated display device module are all designed with a double-layer diffraction structure. Optionally, the DIC device can include three or more layers of diffraction structure. The number of layers of the diffraction structure can be determined according to the actual pupil expansion size requirements and the thickness requirements of the DIC device. The specific number is not limited here. The following is an example of a DIC device including a three-layer diffraction structure. Figure 7d , is a schematic diagram of another embodiment of the display device module in the embodiment of the present application.

[0101] On the basis of the aforementioned two-layer diffraction structure DIC device, a layer of substrate material (optional) and diffraction structure is added to expand the third sub-exit pupil at the exit pupil position, further increasing the size of the system exit pupil, such as Figure 7d By continuing to increase the number of substrate materials and diffraction structure layers, more sub-exit pupils can be expanded to achieve a larger system exit pupil size.

[0102] Based on the above analysis, the human eye can always observe image information when moving within the exit pupil range of the synthetic system extended by the multi-layer diffraction structure DIC device. In addition, since the light rays projected by a single image point on the image plane within the Bragg domain remain approximately parallel after passing through the multi-layer diffraction structure, they form a unique image point on the retina after entering the human eye. Therefore, even if the human eye pupil overlaps with the two sub-exit pupils at the same time during movement, crosstalk will not occur.

[0103] Figure 8 Schematic diagram of diffraction efficiency design of a display device module in an embodiment of the present application;

[0104] Taking the propagation path of light projected from a single image point on the image plane into the effective aperture angle of the DIC after passing through a three-layer diffraction structure as an example, the following further explains the physical parameters related to the pupil expansion effect of the multi-layer diffraction structure.

[0105] See also Figure 8Light ray I1A1 projected onto the DIC device from any image point I1 on the image plane is split into two at the incident point A1 of the first diffraction structure. One ray is redirected by the diffraction structure to point E1 within the first sub-exit pupil, while the other, following the law of refraction, continues to propagate to the incident point A2 of the second diffraction structure. At A2, the ray is split into two again. One ray is redirected by the diffraction structure, passes through the exit point B1 of the first diffraction structure, and then exits to point E2 within the second sub-exit pupil. The other ray continues to propagate to the incident point A3 of the third diffraction structure. There, it is redirected by the diffraction structure, passes through the exit point B2 of the second diffraction structure, and then exits to point E3 within the third sub-exit pupil after exiting the first diffraction structure. It should be noted that the light is diffracted only at points A1, A2, and A3. Because the incident angles of the light at points B1, B2, and C1 fall outside the angular bandwidth of the grating structure, the light can pass directly through points B1, B2, and C1. By designing the diffraction efficiencies of the diffraction structures at locations A1, A2, and A3, for example, to 30%, 50%, and 100%, respectively, it is possible to achieve approximately the same light intensity at locations E1, E2, and E3. It should be noted that the specific values ​​of the diffraction efficiencies of each diffraction structure are not limited herein.

[0106] Please continue to refer to Figure 8 The presence of the second-layer diffraction structure introduces light B1E2 into the second sub-exit pupil. B1E2 is parallel to the diffraction light A1E1 generated by the first-layer diffraction structure, and both correspond to the same light ray I1A1 incident on the DIC device. The distance A1B1 between the two exit points at the DIC device is the exit pupil expansion introduced by the second-layer diffraction structure. Its value is related to the thickness and refractive index of the first and second diffraction structures and the substrate between them, as well as the Bragg incident angle θ0 of the diffraction structure. Similarly, the presence of the third-layer diffraction structure introduces light C1E3 into the third sub-exit pupil. C1E3 is parallel to the exit light A1E1 corresponding to the first-layer diffraction structure and the exit light B1E2 corresponding to the second-layer diffraction structure, and corresponds to the same light ray I1A1 incident on the DIC device. The distance C1B1 between C1E3 and B1E2 at the DIC device's exit point is the pupil expansion introduced by the third diffractive structure. Its value is related to the thickness and refractive index of the second and third diffractive structures and the substrate between them, as well as the Bragg angle of incidence θ0 of the diffractive structure. Taking the pupil expansion A1B1 introduced by the second diffractive structure as an example, simple geometric calculations yield:

[0107] A1B1=d=(tan(π-θ s )+tanθ r )

[0108] Where d is the total thickness of the first and second diffraction structures and the substrate between them; θ sis the diffraction angle, which is related to the system FoV size and the spatial distribution of the grating vector; θ r is the refraction angle of the incident light when it enters the diffraction structure from air. Assuming that the refractive index of the diffraction structure and the base material are both n, then

[0109] The following describes the specific calculation method of the exit pupil size. Figure 9a and Figure 9b .

[0110] Figure 9a A schematic diagram of an optical path of a display device module in an embodiment of the present application; Figure 9b FIG. 2 is another optical path schematic diagram of a display device module in an embodiment of the present application.

[0111] Assuming a VHG grating as the diffraction structure, with a single-layer grating structure diameter of d = 50mm and an exit pupil distance of r = 30mm, the geometric relationship: 2*tan(θ / 2) = d / r yields a system field of view angle θ of 80°. Calculating the angular bandwidth of this non-periodic grating based on Kognick diffraction theory (assuming monochromatic incident light in this example), we find that the angular bandwidth corresponding to the position with the minimum grating period is 2°, and the angular bandwidth corresponding to the position with the maximum grating period is 8°. Because the entire field of view must be observed at the exit pupil, the calculation is based on the angular bandwidth corresponding to the position with the minimum grating period.

[0112] Taking a two-layer diffraction structure DIC device as an example, the system composition, optical path, and related physical parameters are shown in the figure below. Figure 9a In the figure, the light emitted from the image point I, the light within the diffraction angle range of 2° can be transmitted to the exit pupil position through diffraction. If the observed virtual image is imaged at infinity, that is, the projected real image is located at the front focal plane of the diffraction structure, that is, the object distance is equal to 30mm, the corresponding Bragg incident angle θ0 is 60°, that is, the angles between the two edge rays and the plane of the diffraction optical element are 29° and 31° respectively. The exit pupil size corresponding to the single-layer grating structure, that is, the size of a single sub-exit pupil, can be calculated as: 15 / tan29°-15 / tan31°=2mm. (tan29°=0.554, tan30°=0.577, tan31°=0.601, here it is assumed that the light incident at the Bragg angle, that is, the solid line in the figure, is located at the angle bisector position of the edge ray. The deviation of the incident position may cause the emergent light to be not perfectly parallel light. Since the deviation is small, it will not cause perception by the human eye). Figure 9b The light ① in Figure 9aThe solid line corresponds to the light ray. Light ray ① is incident on the two grating structures and diffracts separately. Because the grating vectors at points A and B are identical, the exiting rays ② and ③ are parallel. Assuming a total thickness d of 2 mm for the diffraction structure and substrate, and a material refractive index n of 1.5, the distance between the centers of the two sub-exit pupils, points A and C, can be calculated based on the light propagation geometry to be approximately 3 mm, resulting in an expanded system exit pupil size of 5 mm.

[0113] It's important to note that the combined thickness and refractive index of two adjacent diffractive structures and the substrate between them, as well as the preset Bragg angle of incidence, determine the amount of exit pupil expansion achieved with each additional diffractive structure layer. Selecting different design parameters yields varying system exit pupil sizes, which can be tailored to actual needs.

[0114] If the same parameters as above are used to increase the diffraction structure of the DIC device from 2 layers to 3 layers, an exit pupil expansion of 3 mm can be obtained again, that is, the system exit pupil can be further expanded to 8 mm.

[0115] From this, it can be deduced that if the display device module includes N layers of mutually parallel diffraction structures, the thickness and refractive index of the substrates between the diffraction structures are the same, the exit pupil size of the single-layer diffraction structure is D, and the exit pupil size of the two-layer diffraction structure is D+K, then the exit pupil size of the N-layer diffraction structure is: D+(N-1)K.

[0116] The following describes a method for fabricating the diffraction structure in the above-mentioned DIC device, taking a DIC device including two layers of VHG gratings as an example.

[0117] First, we introduce the fabrication method of a DIC device containing two layers of VHG gratings when the near-eye display system uses a micro-projection engine based on an SLM device. To achieve the function of off-axis light convergence of the VHG grating, each layer of the VHG grating can be fabricated by interferometric exposure of a spherical wave and a parallel light wave with a specific tilt angle on a photopolymer film. Figure 10a The two-layer VHG grating must simultaneously meet the Bragg condition that for incident light, the grating vectors at the corresponding incident points of the second-layer VHG grating and the first-layer VHG grating are the same. To meet this condition, a possible fabrication method is as follows:

[0118] (1) Determine the thickness and refractive index of the VHG grating and substrate, the Bragg incident angle, and the exit pupil distance;

[0119] (2) The spatial position of the two interfering light waves is fixed and remains unchanged during the processing of the two-layer grating, thereby ensuring that each layer of the grating has the same field of view (aperture angle);

[0120] (3) Cut two layers of volume holographic film of the same size and shape, and prepare two pieces of the same base material.

[0121] (4) The first layer of volume holographic film is attached to the lower surface of the first substrate and exposed to two interfering light waves to obtain the first layer of VHG grating. This step requires ensuring that the spatial position and spatial attitude angle of the first layer of volume holographic film ensure that the parallel reference light wave enters the first layer of volume holographic film at the Bragg angle, and the distance from the convergent focus position of the converging spherical object light wave to the first layer of volume holographic film is the preset exit pupil distance.

[0122] (5) The second layer of volume holographic film is attached to the upper surface of the second substrate and exposed to two interfering light waves to obtain the second layer of VHG grating. This step requires ensuring that the spatial attitude angle of the second layer of volume holographic film is exactly the same as that of the first layer of volume holographic film, but the displacement in the normal direction of the film plane relative to the first layer of film is equal to the thickness of the substrate.

[0123] (6) The second layer of VHG grating is separated from the second substrate and attached to the upper surface of the first substrate at a specific offset relative to the attachment position of the first layer of VHG grating. This can obtain the desired DIC device consisting of two layers of VHG gratings. For incident light that meets the Bragg condition, the grating vectors are the same at the corresponding incident points of the second layer of VHG grating and the first layer of VHG grating. The specific offset displacement when attaching the second layer of VHG grating can be obtained by simple calculation based on parameters such as the Bragg incident angle, the thickness and refractive index of the grating and substrate, and the law of diffraction of light in geometric optics.

[0124] The following is a further explanation based on the above processing steps. Figure 11 , is another schematic diagram of the method for manufacturing the diffraction structure in an embodiment of the present application.

[0125] In the aforementioned step (5), the spatial position relationship between the second layer VHG grating and the first layer VHG grating after exposure is as follows: Figure 11 As shown in (a), in order to clearly show the relative spatial positions of the two during exposure, they are placed in the same spatial coordinate system. The first layer of VHG grating corresponds to Figure 11 The smaller circular gray area on the lower surface of the substrate in (a) corresponds to the second layer of VHG grating. Figure 11 The larger circular gray area on the substrate surface in (a) shows that the micro-nano diffraction structure of the second layer of VHG grating is proportionally magnified compared to the first layer of VHG grating. The magnification factor K and the design parameters of the DIC device: aperture angle θ a , the exit pupil distance L (the distance from the DIC device to the human pupil), the thickness d of the two layers of volume holographic film and the substrate between them, and the refractive index n. The specific relationship is as follows:

[0126]

[0127] Among them, Δr can be calculated by the following formula:

[0128]

[0129] In step (6), for two layers of VHG gratings attached to the upper and lower surfaces of the same substrate, the grating vectors of the incident light satisfying the Bragg condition at the corresponding incident points of the two gratings must be equal. To achieve this requirement, the center O1 of the first grating layer and the center Q2 of the second grating layer must be offset along the substrate surface by a distance s before attachment, as shown in the following example: Figure 11 (b) The value of s is related to the Bragg angle θ o , the thickness d of the two layers of volume holographic film and the substrate between them is related to the refractive index n. The specific relationship is as follows:

[0130]

[0131] It should be noted that because the micro-nano diffraction structure of the second VHG grating is proportionally slightly magnified compared to the first layer, the equality of the grating vectors of the two grating layers at the corresponding incident points of the Bragg incident light is not strictly equal in the mathematical sense. After the Bragg incident light is redirected by the two grating layers, it becomes two parallel light rays. The exiting DIC is also not strictly parallel in the mathematical sense, but is approximately equal and parallel in the sense of human eye perception.

[0132] It should be pointed out that the above-mentioned fabrication process is only one feasible method for obtaining a DIC device containing two layers of VHG gratings, and is not the only method. Other fabrication methods are not listed here one by one.

[0133] If the diffraction structure is an SRG device or a metasurface device, the spatial distribution of the two-layer grating vectors can be determined based on the thickness and refractive index of the grating and the substrate, the Bragg incident angle, the exit pupil distance and other parameters, the off-axis convergent light requirements to be achieved, and the requirement that the grating vectors at the corresponding incident points of the second-layer diffraction structure and the first-layer diffraction structure for the incident light that meets the Bragg condition are the same. The desired two-layer diffraction structure can be obtained by processing through etching or nanoimprinting technology. The specific processing process will not be introduced in detail here.

[0134] The working process of the near-eye display system composed of a DIC device with a two-layer diffraction structure and a micro-projection engine based on an SLM device manufactured using the aforementioned process is as follows:

[0135] (1) The SLM device within the micro-projection engine modulates the incident coherent light, producing a real image through diffraction. The real image is located within one focal length of the DIC device. In addition to the SLM device, the micro-projection engine may also include necessary beam shaping, spatial filtering, and optical path guidance devices, which are not described in detail here.

[0136] (2) The light from each point of the real image continues to be projected toward the DIC device, and the projection angle of the micro-projection engine is adjusted so that the angle at which the projected light is incident on the surface of the first diffraction structure of the DIC device is within the Bragg domain.

[0137] (3) Part of the incident light is diffracted inside the first layer of diffraction structure, and the diffracted light converges in the first sub-exit pupil area. If a VHG device is used, the diffraction structure can be processed by interfering the exposure of the convergent spherical wave generated by the parallel light wave passing through the convex lens and the parallel light wave with a specific tilt angle on the photopolymer film material to achieve the function of off-axis convergent light.

[0138] (4) Part of the incident light continues to propagate through the first layer of diffraction structure, reaches the surface of the second layer of grating structure and is diffracted, and the diffracted light converges in the second sub-exit pupil area. The distance between the second sub-exit pupil area and the first sub-exit pupil area and the DIC device is the same, and the two can be adjacent in space, or there can be a certain size of gap. However, in order to ensure that the human eye pupil does not lose the image field of view in the process of continuously moving from one sub-exit pupil area to another sub-exit pupil area, the size of the gap must be smaller than the size of the human eye pupil. In summary, the design of the two-layer diffraction structure replicates the exit pupil of the single-layer diffraction structure while ensuring that the system field of view angle is not affected, thereby expanding the system exit pupil size.

[0139] It should be noted that if the micro-projection engine of the near-eye display system is based on an incoherent planar image source, the display plane of the micro-projection engine is the real image plane. The manufacturing method of the diffraction structure in the display device module is similar to that of the SLM micro-projection engine, and the details will not be repeated here.

[0140] When the micro-projection engine for a near-eye display system is based on a point-scanning image source like LBS, the image light incident on the DIC device is a spherical light wave centered at the laser source's incident point on the MEMS scanning mirror. The fabrication method for the diffraction structure of this DIC device differs from that of the DIC device used in the aforementioned micro-projection engine with a surface image source. The following describes the fabrication process for a DIC device compatible with an LBS micro-projection engine, using a DIC device with a two-layer VHG diffraction structure as an example.

[0141] In order to realize the function of off-axis convergent light, a convergent spherical wave (generated by parallel light waves passing through a convex lens) and a divergent spherical wave (generated by parallel light waves passing through a concave lens) can be used to perform interference exposure on both sides of the volume holographic film at a specific tilt angle. Please refer to Figure 10b The two-layer VHG grating must simultaneously meet the Bragg condition that for incident light, the grating vectors at the corresponding incident points of the second-layer VHG grating and the first-layer VHG grating are the same. To meet this condition, a possible fabrication method is as follows:

[0142] (1) Determine the thickness and refractive index of the VHG grating and substrate, the Bragg incident angle, and the exit pupil distance;

[0143] (2) The spatial positions of the two interfering light waves are fixed and remain unchanged during the processing of the two-layer grating, thereby ensuring that the processed grating layers have the same numerical aperture;

[0144] (3) Cut two layers of volume holographic film of the same size and shape, and prepare two pieces of the same base material.

[0145] (4) The first layer of volume holographic film is attached to the lower surface of the first substrate and exposed to two interfering light waves to obtain the first layer of VHG grating. This step requires ensuring that the spatial position and spatial attitude angle of the first layer of volume holographic film ensure that the parallel reference light wave enters the first layer of volume holographic film at the Bragg angle, and the distance from the convergent focus position of the converging spherical object light wave to the first layer of volume holographic film is the preset exit pupil distance.

[0146] (5) The second layer of volume holographic film is attached to the upper surface of the second substrate and exposed to two interfering light waves to obtain a second layer of VHG grating. This step requires ensuring that the spatial attitude angle of the second layer of volume holographic film is exactly the same as that of the first layer of volume holographic film, but the displacement in the vertical direction of the film plane relative to the first layer of film is equal to the thickness of the substrate.

[0147] (6) The second layer of VHG grating is separated from the second substrate and attached to the upper surface of the first substrate at a specific offset relative to the attachment position of the first layer of VHG grating. This can obtain the desired DIC device consisting of two layers of VHG gratings. For incident light that meets the Bragg condition, the grating vectors are the same at the corresponding incident points of the second layer of VHG grating and the first layer of VHG grating. The specific offset displacement when attaching the second layer of VHG grating can be obtained by simple calculation based on parameters such as the Bragg incident angle, the thickness and refractive index of the grating and substrate, and the law of diffraction of light in geometric optics.

[0148] It should be pointed out that the above-mentioned fabrication process is only one feasible method for obtaining a DIC device containing two layers of VHG gratings, and is not the only method. Other fabrication methods are not listed here one by one.

[0149] If the diffraction structure is an SRG device or a metasurface device, the spatial distribution of the two-layer grating vectors can be determined based on the thickness and refractive index of the grating and the substrate, the Bragg incident angle, the exit pupil distance and other parameters, the off-axis convergent light requirements to be achieved, and the requirement that the grating vectors at the corresponding incident points of the second-layer diffraction structure and the first-layer diffraction structure for the incident light that meets the Bragg condition are the same. The desired two-layer diffraction structure can be obtained by processing through etching or nanoimprinting technology. The specific processing process will not be introduced in detail here.

[0150] The DIC device, manufactured using the aforementioned process and comprising two layers of diffraction structures, and a near-eye display system with a micro-projection engine based on an LBS device operate as follows: The modulated laser beam carrying image information is redirected by a MEMS scanning mirror. The light propagation path within a MEMS scanning cycle is projected onto the DIC device in the form of a spherical light wave incident from the side, with the center of the spherical light wave being the point of incidence of the modulated laser beam on the MEMS scanning mirror. After being redirected by the MEMS scanning mirror, each incident light beam entering the DIC device is split into two by the diffraction structure at the point of incidence of the first diffraction structure. One beam is redirected by the diffraction structure and converges to the first sub-exit pupil position, while the other beam continues to propagate to the second diffraction structure, where it is redirected by this structure and converges to the second sub-exit pupil position. Therefore, the human eye can see the complete image at both the first and second sub-exit pupil positions. By designing the two-layer diffraction structure, the incident light has the same grating vector at the incident point of the first diffraction structure and the incident point of the second diffraction structure. Therefore, the incident light is parallel after passing through the two-layer diffraction structure and exiting the DIC device. After being converged by the human eye, it forms a unique corresponding point on the retina. Therefore, even if the first and second sub-exit pupils overlap with the human eye pupil at the same time, no crosstalk phenomenon will be observed. In order to ensure that there is no loss of image field when the human eye pupil moves continuously between the first and second sub-exit pupils, the size of the gap between the two sub-exit pupils should be smaller than the size of the human eye pupil. After meeting the above requirements, the total size of the two sub-exit pupils and the gap between them is the system exit pupil size.

[0151] See also Figure 12 , is a schematic diagram of the relationship between the grating vector and the reference light and the object light in the embodiment of the present application. The following is an introduction to the design of the diffraction efficiency during the diffraction structure processing.

[0152] In order to ensure that the incident light projected onto the two-layer diffraction structure is as bright as possible when it is diffracted and emitted into the two sub-exit pupils, the diffraction efficiency of the two-layer diffraction structure needs to be designed, and the diffraction efficiency of the first-layer diffraction structure needs to be appropriately reduced so that only a portion of the incident light is diffracted into the first sub-exit pupil after reaching the first-layer diffraction structure, and the remaining portion continues to propagate toward the second-layer diffraction structure and is diffracted into the second sub-exit pupil at the second-layer diffraction structure with maximum diffraction efficiency. For a two-layer grating, one possible diffraction efficiency arrangement is that the target diffraction efficiency of the first-layer diffraction structure is 50%, and the target diffraction efficiency of the second-layer diffraction structure is 100%. If a three-layer diffraction structure is used, the target diffraction efficiencies of the first, second, and third-layer diffraction structures can be 30%, 50%, and 100%, respectively. In short, for a multi-layer diffraction structure, the diffraction efficiency of each layer of the diffraction structure can be designed so that the brightness of the image field seen by the human eye from each sub-exit pupil is basically the same. The specific values ​​of the diffraction efficiency of each layer of the diffraction structure are not limited here.

[0153] The diffraction efficiency of the diffraction structure is jointly determined by parameters such as the reference light vector Kr and the reference light incident angle θr, the object light vector Ks and the object light incident angle θs, the grating vector K and the grating vector angle φ, the refractive index spatial modulation degree and thickness of the volume holographic film, and the deviation of the incident angle θi of the projected light of the micro-projection engine from the Bragg reference angle θr.

[0154] The following uses VHG as an example to explain how to achieve the target diffraction efficiency during diffraction device processing. Diffractive optical elements are designed based on Bragg diffraction conditions, and the diffraction equation is described by the Kogdenk principle of coupled light waves. The figure below illustrates the geometric relationship between the reference light vector Kr and the reference light incident angle θr, the object light vector Ks and the object light incident angle θs, and the grating vector K and the grating vector angle φ. These angles are the angles between the physical quantities and the z-axis, with the z-axis direction being the normal to the grating plane.

[0155] When the incident light satisfies the Bragg condition, that is, when the incident light vector is equal to the reference light vector Kr, the grating achieves maximum diffraction efficiency, otherwise, the diffraction efficiency decreases. Specifically, the phase mismatch factor is described as:

[0156] δ=ΔθKsin(φ-θ i )

[0157] Δθ is the incident angle θ of the projected light i Bragg reference angle θ r The deviation of , the coupling strength ν of the grating and the Bragg mismatch parameter ξ are expressed as follows:

[0158]

[0159]

[0160] Δn is the spatial modulation of the refractive index of the material, and d is the thickness of the diffractive thin film material.

[0161] The calculation formula for the diffraction efficiency of a reflective diffractive optical element is:

[0162]

[0163] Based on the above relationship, the target diffraction efficiency of each layer of the diffraction grating can be customized to ensure that the light intensity of each sub-exit pupil is consistent. When the user's pupil moves relative to the user, the light intensity of the image obtained from different sub-exit pupils is consistent, which can improve the user experience.

[0164] Those skilled in the art will clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0165] In the several embodiments provided in this application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are merely schematic. For example, the division of the units is merely a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or units, which can be electrical, mechanical or other forms.

[0166] The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of these units may be selected to achieve the purpose of this embodiment according to actual needs.

[0167] In addition, the functional units in the various embodiments of the present application may be integrated into a single processing unit, or each unit may exist physically separately, or two or more units may be integrated into a single unit. The aforementioned integrated units may be implemented in the form of hardware or software functional units.

[0168] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present application is essentially or the part that contributes to the prior art or all or part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including a number of instructions for enabling a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the method described in each embodiment of the present application. The aforementioned storage medium includes: various media that can store program codes, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk.

[0169] As described above, the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A diffraction image superimposer, characterized in that: Applicable to a near-eye display device, comprising: a first diffractive optical element DOE and a second DOE, wherein the first DOE is parallel to the second DOE; The grating vector of the first incident point of the first DOE is the same as the second incident point of the second DOE. The first incident point is used to convert the incident light satisfying the Bragg condition into a first diffraction light and a first transmitted light. The first transmitted light is incident on the second incident point, and the second incident point is used to convert the first transmitted light into a second diffraction light.

2. The diffraction image superimposer according to claim 1, wherein: The first DOE is provided with a first grating region, and the second DOE is provided with a second grating region. The first incident point is located in the first grating region, and the second incident point is located in the second grating region. The first grating region is used to convert a first parallel incident light beam with a projection angle within the Bragg domain into a first diffracted light beam and a first transmitted light beam. The first diffracted light beam converges at a first focal point, and the first transmitted light beam is incident on the second grating region. The second grating region is used to convert the first transmitted light beam into a second diffracted light beam, and the second diffracted light beam converges at a second focal point. The distance from the first focal point to the diffraction image superimposer is equal to the distance from the second focal point to the diffraction image superimposer.

3. The diffraction image superimposer according to claim 1 or 2, characterized in that: The incident light and the first diffracted light are located on the same side of the first DOE; or, The incident light and the first diffracted light are located on different sides of the first DOE.

4. The diffraction image superimposer according to claim 1 or 2, characterized in that: The first DOE includes a volume holographic grating VHG, a surface relief grating SRG, a metasurface or a microlens array; The second DOE includes a volume holographic grating VHG, a surface relief grating SRG, a metasurface or a microlens array.

5. The diffraction image superimposer according to any one of claims 1 to 4, characterized in that: The diffraction image superimposer also includes a third DOE parallel to the second DOE, the second DOE is located between the first DOE and the third DOE, the third incident point of the third DOE has the same grating vector as the second incident point, the second incident point is also used to convert the first transmitted light into a second diffracted light and a second transmitted light, the second transmitted light is incident on the third incident point, and the third grating area is used to convert the second transmitted light into a third diffracted light.

6. The diffraction image superimposer according to claim 5, characterized in that: The third DOE is provided with a third grating region. The first grating region is used to convert a first parallel incident light beam with a projection angle within the Bragg domain into a first diffracted light beam and a first transmitted light beam. The first diffracted light beam converges at a first focal point. The first transmitted light beam is incident on the second grating region. The second grating region is used to convert the first transmitted light beam into a second diffracted light beam and a second transmitted light beam. The second diffracted light beam converges at a second focal point. The second transmitted light beam is incident on the third grating region. The third grating region is used to convert the third transmitted light beam into a third diffracted light beam. The third diffracted light beam is diffracted and converges at a third focal point. The distance from the third focal point to the diffraction image superimposer is equal to the distance from the second focal point to the diffraction image superimposer and the distance from the first focal point to the diffraction image superimposer.

7. The diffraction image superimposer according to any one of claims 1 to 6, characterized in that: The diffraction image superimposer further comprises: A substrate is disposed between the first DOE and the second DOE, wherein upper and lower surfaces of the substrate are optically parallel.

8. The diffraction image superimposer according to claim 7, characterized in that: The substrate material is an optically transparent material, and the optically transparent material includes glass or optical plastic.

9. The diffraction image superimposer according to any one of claims 1 to 8, characterized in that: The diffraction efficiency of the first DOE is lower than the diffraction efficiency of the second DOE.

10. The diffraction image superimposer according to any one of claims 5 to 9, characterized in that: The diffraction efficiency of the second DOE is lower than the diffraction efficiency of the third DOE.

11. A display device module, characterized in that: Applicable to a near-eye display device, comprising a micro-projection engine and a diffraction image superimposer according to any one of claims 1 to 10; The micro-projection engine is used to project incident light with an angle within the Bragg domain toward the diffraction image superimposer; The first diffraction light constitutes a first sub-exit pupil, the second diffraction light constitutes a second sub-exit pupil, and the exit pupil of the display device module includes the first sub-exit pupil and the second sub-exit pupil.

12. The display device module according to claim 11, wherein: The micro-projection engine includes a plane image source device or a point image source device. The plane image source device includes a spatial light modulator (SLM) image source device and an incoherent plane micro image source. The point image source device includes a laser beam scanning (LBS) device.

13. The display device module according to claim 11 or 12, characterized in that: The display device module further includes a frame, which is used to fix the micro-projection engine and the diffraction image superimposer.

14. The display device module according to any one of claims 11 to 13, characterized in that: The display device module further includes at least one of the following: a communication device, a processor, and a power supply device.

15. An augmented reality (AR) device, characterized in that: The device comprises the display device module according to any one of claims 11 to 14.

16. A virtual reality (VR) device, characterized in that: The device comprises the display device module according to any one of claims 11 to 14.

17. A near-eye display device, characterized in that: The device comprises the display device module according to any one of claims 11 to 14.

18. A head-mounted display device, characterized in that: including a left-eye display and a right-eye display; The left-eye display comprises a diffractive image superimposer as claimed in any one of claims 1 to 10; The right-eye display comprises a diffractive image superimposer as claimed in any one of claims 1 to 10.

Images