Diffractive optical waveguide

Abstract

The application discloses a diffractive optical waveguide, which comprises a waveguide substrate, the waveguide substrate at least comprising a coupling-in region and a coupling-out region, a coupling-in grating being arranged on or in the waveguide substrate and located in the coupling-in region, a coupling-out grating being arranged on or in the waveguide substrate and located in the coupling-out region, image light being coupled into the waveguide substrate through the coupling-in grating after being incident on the coupling-in region, and being coupled out of the waveguide substrate through the coupling-out grating after being totally reflected between a first surface and a second surface of the waveguide substrate and being transmitted to the coupling-out region, and entering the human eye; a first light-absorbing element is arranged on a side surface between the first surface and the second surface, and is used for absorbing the image light incident on the side surface; and a second light-absorbing element is arranged on the first surface and the second surface, and is used for absorbing the image light scattered through the side surface, at least in a region between the side surface adjacent to the coupling-in region and the coupling-in region. The technical scheme provided by the application can improve the display effect of the diffractive optical waveguide.

Description

Technical Field

[0001] This application relates to the field of augmented reality, and more particularly to a diffractive optical waveguide. Background Technology

[0002] Augmented reality is a technology that blends the real world with virtual information. Augmented reality display systems typically include micro-projectors and optical displays. The micro-projectors provide virtual display content for the augmented reality display system, which is then projected onto the viewer's eyes through the optical displays. The optical displays are usually transparent optical components, so that users can also see the real world through the optical displays at the same time.

[0003] Diffractive waveguides are commonly used in augmented reality optical displays. However, because the sidewalls of the waveguide substrate are formed by laser cutting, their flatness is far inferior to that of the waveguide substrate surface. This significantly affects the propagation of image light, causing light scattering and affecting the clarity of the image. Furthermore, the scattered image light may be diffracted and coupled out again through the grating structure on the waveguide substrate, resulting in dispersion and rainbow stripes, which seriously affects the imaging effect of the diffractive waveguide. Summary of the Invention

[0004] This application provides a diffractive waveguide that can effectively avoid scattering of image light on the sidewall of the waveguide substrate, as well as a series of effects on the imaging effect after scattering.

[0005] A diffractive waveguide includes: a waveguide substrate, the waveguide substrate including at least an insertion region and an exit region; an insertion grating disposed on or within the waveguide substrate and located in the insertion region; and an exit grating disposed on or within the waveguide substrate and located in the exit region. Image light is incident on the insertion region and coupled into the waveguide substrate through the insertion grating. After total internal reflection between a first surface and a second surface of the waveguide substrate, the light is transmitted to the exit region and then coupled out of the waveguide substrate through the exit grating to enter the human eye. A first light-absorbing element is disposed on a side surface between the first surface and the second surface to absorb image light incident on the side surface. A second light-absorbing element is disposed on the first surface and the second surface, at least in the region between the side surface adjacent to the insertion region and the insertion region, to absorb image light scattered by the side surface.

[0006] In practice, both the first light-absorbing element and the second light-absorbing element are light-absorbing material layers. The light-absorbing material layer covers the side to form the first light-absorbing element, and extends from the edge of the side to at least cover the side adjacent to the coupling region and the waveguide substrate surface region between the coupling region to form the second light-absorbing element.

[0007] In practice, the thickness of the first light-absorbing element is greater than 0.3 mm, the transition surface between the first light-absorbing element and the second light-absorbing element is a smooth curved surface, and the dimension of the second light-absorbing element extending from the edge of the side is in the range of 4 mm to 10 mm.

[0008] In practice, the first light-absorbing element is a light-absorbing material layer, and the second light-absorbing element is a three-layer structure, which includes a first metal cylindrical array layer, a second dielectric tetragonal prism array layer and a third metal layer in sequence along the direction away from the surface of the waveguide substrate.

[0009] In practice, the outline shape of the second light-absorbing element is crescent-shaped, and the maximum dimension of the second light-absorbing element in the direction orthogonal to the image light propagation direction is greater than the diameter of the coupling region.

[0010] In practice, the thickness of the first metal cylindrical array layer is less than the thickness of the second dielectric tetragonal prism array layer, and the thickness of the second dielectric tetragonal prism array layer is less than the thickness of the third metal layer.

[0011] In practice, the cylinder diameter of the first metal cylindrical array layer is smaller than the length and width of the quadrangular prisms of the second dielectric quadrangular prism array layer.

[0012] In an implementable manner, the waveguide substrate further includes a transition region, and a transition grating is disposed on or in the waveguide substrate and located in the transition region. After the image light is incident on the coupling region, it is coupled into the waveguide substrate through the coupling grating and transmitted to the transition region by total internal reflection between the first surface and the second surface of the waveguide substrate. It is then deflected by the transition grating to the coupling region and transmitted, and finally coupled out of the waveguide substrate through the coupling grating and enters the human eye. On the first surface and the second surface, at least in the area between the side adjacent to the transition region and the transition region, a third light-absorbing element is disposed to absorb the image light that reaches the side surface after passing through the transition grating and is scattered by the side surface.

[0013] In practice, the distribution of the third light-absorbing element in a direction orthogonal to the image light propagation direction covers the propagation area of ​​the boundary field of view.

[0014] In practice, the shape pattern of the third light-absorbing element is multiplexed as the information prompt pattern of the diffractive waveguide.

[0015] This application provides a diffractive waveguide. Firstly, a first light-absorbing element is disposed on the sidewall between the first and second surfaces of the waveguide substrate to absorb image light incident on the sidewall, i.e., the sidewall of the waveguide substrate, reducing image light scattering and suppressing the generation of scattered light. Secondly, a second light-absorbing element is disposed on the waveguide substrate surface region adjacent to the coupling region and between the coupling region to absorb image light scattered from the sidewall, suppressing further transmission of already scattered image light. Furthermore, when the diffractive waveguide includes a transition grating, a third light-absorbing element is also disposed on the waveguide substrate surface region adjacent to the transition region and between the transition region to absorb image light that has passed through the transition grating and reached the sidewall and is scattered by the sidewall. Thus, dual suppression of the generation and transmission of scattered image light is achieved, effectively avoiding scattering of image light at the sidewall of the waveguide substrate and the series of effects on imaging effects after scattering.

[0016] Furthermore, the second and third light-absorbing elements set along the propagation path of the scattered image light can both be designed as three-layer structures. When the scattered image light is incident on the three-layer structure, it is incident sequentially on the first metal cylindrical array layer, the second dielectric tetragonal prism array layer, and the third metal layer. The first metal cylindrical array layer is matched with the spatial impedance within the target frequency range, so that the image light is not reflected. The second dielectric tetragonal prism array layer acts as a loss layer to absorb the image light. The thickness of the third metal layer is greater than the skin depth of the image light, so that the image light is not transmitted. In this way, the three-layer structure synergistically suppresses the further transmission of the scattered image light, greatly improving the imaging effect of the diffraction waveguide.

[0017] Furthermore, in some embodiments, a second diffraction grating may be provided in the waveguide substrate surface region between the side adjacent to the coupling region and the coupling region to diffract the image light rays transmitted to the side and the image light rays scattered from the side, thereby suppressing the further transmission of the image light rays that have already been scattered; and a third diffraction grating may be provided in the waveguide substrate surface region between the side adjacent to the turning region and the turning region to diffract the image light rays transmitted to the side through the turning grating and the image light rays that reach the side through the turning grating and are scattered by the side. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 A schematic diagram of a diffractive waveguide provided in an embodiment of this application;

[0020] Figure 2 This is a schematic diagram of another diffractive waveguide structure provided in an embodiment of this application;

[0021] Figure 3 This is a schematic diagram of another diffractive waveguide structure provided in an embodiment of this application;

[0022] Figure 4 This is a schematic diagram of the first view structure of a second light-absorbing element / third light-absorbing element provided in an embodiment of this application;

[0023] Figure 5 This is a schematic diagram of a second-view structure of a second light-absorbing element / third light-absorbing element provided in an embodiment of this application;

[0024] Figure 6 This is a schematic diagram of another diffractive waveguide structure provided in an embodiment of this application;

[0025] Figure 7 This is a schematic diagram of another diffractive waveguide structure provided in an embodiment of this application;

[0026] Figure 8 This is a schematic diagram of another diffractive waveguide structure provided in an embodiment of this application;

[0027] Attached image labels:

[0028] 100: Diffractive waveguide;

[0029] 110: Waveguide substrate;

[0030] 120: Coupled-in grating;

[0031] 130: Coupling grating;

[0032] 140: First light-absorbing element;

[0033] 150: Second light-absorbing element;

[0034] 160: Diagonal grating;

[0035] 170: Third light-absorbing element;

[0036] 210: First metal cylindrical array layer;

[0037] 220: Second dielectric tetragonal prism array layer;

[0038] 230: Third metal layer;

[0039] 250: Second diffraction grating;

[0040] 270: Third diffraction grating. Detailed Implementation

[0041] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0042] The technical solution of this application will be described in detail below with reference to specific embodiments. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments.

[0043] This application provides a diffractive waveguide, comprising: a waveguide substrate, the waveguide substrate including at least an insertion region and an exit region, an insertion grating disposed on or within the waveguide substrate and located in the insertion region, and an exit grating disposed on or within the waveguide substrate and located in the exit region, image light incident on the insertion region is coupled into the waveguide substrate through the insertion grating, and after total internal reflection between the first and second surfaces of the waveguide substrate, it is transmitted to the exit region and then coupled out of the waveguide substrate through the exit grating and enters the human eye; a first light-absorbing element is disposed on the side between the first and second surfaces for absorbing image light incident on the side, and a second light-absorbing element is disposed on the first and second surfaces, at least in the region between the side adjacent to the insertion region and the insertion region, for absorbing image light scattered by the side.

[0044] In this application, the diffractive waveguide includes a waveguide substrate with a first surface and a second surface disposed opposite to each other. When image light propagates within the waveguide substrate, it undergoes total internal reflection between the first and second surfaces. The waveguide substrate includes at least an insertion region and an exit region. An insertion grating is disposed within the insertion region, and an exit grating is disposed within the exit region. The insertion and exit gratings can be located on the surface of the waveguide substrate or inside the waveguide substrate. After the image light is incident on the insertion region, it is coupled into the waveguide substrate through the insertion grating, and after total internal reflection within the waveguide substrate, it is transmitted to the exit region and then exits the waveguide substrate through the exit grating before entering the human eye. It is understood that since grating diffraction has multiple diffraction orders, only a portion of the diffraction orders are effectively utilized. (Refer to...) Figure 1Image light rays, after being coupled through the coupling grating 120, generate at least diffraction orders A and B. Diffraction order A is transmitted towards the coupling grating 130 and effectively utilized, while diffraction order B is directly incident on the sidewall of the waveguide substrate in the opposite direction. Since the sidewall of the waveguide substrate is formed by laser cutting, its flatness is far inferior to that of the waveguide substrate surface, which has a significant impact on the propagation of image light rays, leading to scattering of image light rays. In this application, on the one hand, a first light-absorbing element 140 is provided on the sidewall between the first and second surfaces of the waveguide substrate 110 to absorb image light rays incident on the sidewall, and to absorb as much image light rays as possible, reducing scattering of image light rays and suppressing the generation of scattered light rays; on the other hand, on the first and second surfaces of the waveguide substrate 110, at least in the area between the sidewall adjacent to the coupling region and the coupling region, a second light-absorbing element 150 is provided to absorb image light rays transmitted towards the side and image light rays scattered from the side, such as... Figure 1 The middle diffraction order B first enters the second light-absorbing element 150, losing some energy. After being scattered by the sidewall of the waveguide substrate, it re-enters the second light-absorbing element 150. This reduces the scattering of image light incident on the side and suppresses the further transmission of already scattered image light, preventing the scattered image light from returning to the grating area. Thus, dual suppression is achieved in the generation and transmission of scattered image light, effectively avoiding scattering of image light at the sidewall of the waveguide substrate and the series of effects on the imaging effect after scattering.

[0045] It can be understood that a portion of the image light coupled into the grating is directly transmitted toward the sidewall of the waveguide substrate. Before reaching the sidewall of the waveguide substrate, it is first absorbed by the second light-absorbing element, then absorbed by the first light-absorbing element after entering the sidewall, and finally absorbed by the second light-absorbing element after being scattered by the sidewall. In this way, the three-pronged approach can basically prevent the scattered image light from returning to the grating area.

[0046] The specific structure of the diffractive waveguide of this application will be described in detail below with reference to specific embodiments and accompanying drawings.

[0047] In one embodiment, both the first light-absorbing element and the second light-absorbing element are light-absorbing material layers. The light-absorbing material layer covers the side to form the first light-absorbing element, and extends from the edge of the side to at least cover the side adjacent to the coupling region and the waveguide substrate surface region between the coupling region to form the second light-absorbing element.

[0048] refer to Figure 2The diffractive waveguide 100 includes a waveguide substrate 110, on which a coupling grating 120 and a coupling grating 130 are disposed. A light-absorbing material layer is coated on the sidewalls of the waveguide substrate 110 to form a first light-absorbing element 140. The light-absorbing material layer further extends from a portion of the sidewalls of the waveguide substrate 110 toward the surface of the waveguide substrate 110, and at least covers the sidewalls adjacent to the coupling region and the waveguide substrate surface region between the coupling regions to form a second light-absorbing element 150. Of course, the light-absorbing material layer may also extend from all the sidewalls of the waveguide substrate 110 toward the surface of the waveguide substrate 110. The extinction coefficient of the light-absorbing material layer is greater than 0.02, and the difference between the refractive index of the light-absorbing material layer and the refractive index of the waveguide substrate is less than 0.2. The light-absorbing material includes, but is not limited to, one or more of blank ink, graphene, amorphous silicon, and germanium.

[0049] In practice, the thickness of the first light-absorbing element is greater than 0.3 mm. The transition surface between the first and second light-absorbing elements is a smooth curved surface, and the minimum distance between this smooth curved surface and the edge of the waveguide substrate surface is greater than 0.2 mm. The second light-absorbing element extends from the side edge in the range of 4 mm to 10 mm. This allows for the maximum absorption of image light incident on the sidewall of the waveguide substrate and scattered image light.

[0050] It should be noted that the second light-absorbing element is used to absorb as much image light as possible incident upon it, therefore, the placement of the second light-absorbing element should cover the transmission path of the image light across the entire field of view. Generally, the maximum size of the second light-absorbing element in the direction orthogonal to the image light propagation direction should be greater than the diameter of the coupling region.

[0051] In one embodiment, the first light-absorbing element is a light-absorbing material layer, and the second light-absorbing element is a three-layer structure, which includes a first metal cylindrical array layer, a second dielectric tetragonal prism array layer and a third metal layer in sequence along the direction away from the waveguide substrate surface.

[0052] refer to Figure 3 The diffractive waveguide 100 includes a waveguide substrate 110, on which a coupling grating 120 and a coupling grating 130 are disposed. A light-absorbing material layer is coated on the sidewall of the waveguide substrate 110 to form a first light-absorbing element 140. On the surface of the waveguide substrate 110, in the region adjacent to the coupling region and between the coupling region, a three-layer structure is disposed to form a second light-absorbing element 150. (Reference) Figure 4 and Figure 5The two figures are schematic diagrams of the second light-absorbing element 150 from different perspectives. Along the direction away from the waveguide substrate surface, it sequentially includes a first metal cylindrical array layer 210, a second dielectric tetragonal prism array layer 220, and a third metal layer 230. When scattered image light is incident on the three-layer structure, it passes sequentially through the first metal cylindrical array layer, the second dielectric tetragonal prism array layer, and the third metal layer.

[0053] In this embodiment, when the image light is incident on the first metal cylindrical array layer, the image light is not reflected because the first metal cylindrical array layer matches the spatial impedance within the target frequency range. The image light is then incident on the second dielectric tetragonal prism array layer, which acts as a loss layer to absorb the image light, greatly reducing the energy of the image light. The thickness of the third metal layer is greater than the skin depth of the image light, preventing the image light from being transmitted. This suppresses the transmission of the image light and prevents the scattered image light from returning to the grating region, greatly improving the imaging effect of the diffraction waveguide.

[0054] In practice, the outline shape of the second light-absorbing element is crescent-shaped, and the maximum size of the second light-absorbing element in the direction orthogonal to the image light propagation direction is greater than the diameter of the coupling region.

[0055] In practice, the thickness of the first metal cylindrical array layer is less than the thickness of the second dielectric tetragonal prism array layer, and the thickness of the second dielectric tetragonal prism array layer is less than the thickness of the third metal layer.

[0056] For example, the thickness of the first metal cylindrical array layer ranges from 20 to 50 nm, the thickness of the second dielectric tetragonal prism array layer ranges from 50 to 100 nm, and the thickness of the third metal layer ranges from 100 to 150 nm.

[0057] In practice, the cylinder diameter of the first metal cylindrical array layer is smaller than the length and width of the quadrangular prisms of the second dielectric quadrangular prism array layer.

[0058] For example, the cylinder diameter of the first metal cylindrical array layer ranges from 60 to 100 nm, and the length and width of the prisms of the second dielectric tetragonal prism array layer range from 150 to 200 nm.

[0059] For example, the material of the second dielectric prism array layer can be vanadium dioxide.

[0060] The first metal cylindrical array layer and the second dielectric tetragonal prism array layer are structural unit array layers. There are gaps between the structural units. These gaps can be filled with dielectric materials with a refractive index of 1 to 1.5, such as air, SiO2, MgF2, glue, etc.

[0061] In this application, the waveguide substrate further includes a transition region. A transition grating is disposed on or in the waveguide substrate and located in the transition region. After the image light is incident on the coupling region, it is coupled into the waveguide substrate through the coupling grating and transmitted to the transition region by total internal reflection between the first and second surfaces of the waveguide substrate. It is then deflected by the transition grating and transmitted to the output region, and finally coupled out of the waveguide substrate through the output grating and enters the human eye. On the first and second surfaces, at least in the area between the side adjacent to the transition region and the transition region, a third light-absorbing element is disposed to absorb the image light that reaches the side through the transition grating and is scattered by the side.

[0062] In some embodiments, the waveguide substrate may further include a transition region, within which a transition grating is disposed. The transition grating may be located on the surface of the waveguide substrate or inside the waveguide substrate. After image light is incident on the coupling region, it is coupled into the waveguide substrate through the coupling grating and then transmitted to the transition region via total internal reflection within the waveguide substrate. After being deflected by the transition grating to the output region, it is transmitted again via the output grating and exits the waveguide substrate to enter the human eye. It can be understood that when image light is acted upon by the transition grating, part of it is deflected to the output region, while part continues to propagate along its original direction. This part of the image light that continues to propagate along its original direction will eventually be incident on the sidewall of the waveguide substrate and reflected. Therefore, in this application, a third light-absorbing element is also disposed on the first and second surfaces, at least in the region between the sidewall adjacent to the transition region and the transition region, to absorb the image light that reaches the sidewall after passing through the transition grating and is scattered by the sidewall.

[0063] The third light-absorbing element is the same as the second light-absorbing element. It can be a light-absorbing material layer or a three-layer structure consisting of a first metal cylindrical array layer, a second dielectric quadrangular prism array layer, and a third metal layer in sequence along the direction away from the waveguide substrate surface.

[0064] refer to Figure 6 and Figure 7 The diffractive waveguide 100 includes a waveguide substrate 110, on which a coupling grating 120, a coupling grating 130, and a transition grating 160 are disposed. A light-absorbing material layer is covered on the sidewall of the waveguide substrate 110 to form a first light-absorbing element 140. On the surface of the waveguide substrate 110, in the region between the side adjacent to the coupling region and the coupling region, a three-layer structure is disposed to form a second light-absorbing element 150. On the surface of the waveguide substrate 110, in the region between the side adjacent to the transition region and the transition region, a third light-absorbing element 170 is disposed.

[0065] In practice, the distribution of the third light-absorbing element in a direction orthogonal to the image light propagation direction covers the propagation area of ​​the boundary field of view. It should be noted that the third light-absorbing element is designed to absorb as much image light as possible incident on it, so its position must cover the transmission path of the entire field of view image light.

[0066] In practice, the shape pattern of the third light-absorbing element is multiplexed as an information prompt pattern for the diffractive waveguide.

[0067] It's understandable that the high visibility of light-absorbing elements would affect the appearance of the diffractive waveguide. Generally, during the assembly of diffractive waveguide modules, the coupling region is usually encapsulated inside the module and is not visible to the outside. Therefore, the second light-absorbing element near the sidewall of the waveguide substrate in the coupling region is also not visible and does not require additional consideration. However, the third light-absorbing element, located near the sidewall of the waveguide substrate in the transition region, is exposed. Its shape and pattern can be reused to design information prompts that would otherwise be displayed on the diffractive waveguide, such as product names or brand logos.

[0068] In another embodiment, ion implantation, such as Fe, C, Si, Ti, etc., can also be performed in the waveguide substrate region covered by the second and third light-absorbing elements. The transmittance of the waveguide substrate in the ion-implanted region is reduced, and the image light can be absorbed when it is transmitted therein. When it passes through this region and is incident on the sidewall of the waveguide substrate again, part of the light energy has been consumed, so that the image light is consumed before scattering, which can further improve the imaging effect of the diffraction waveguide.

[0069] In another embodiment, a fourth light-absorbing element can be disposed on the waveguide substrate surface in the region between the side adjacent to the coupling region and the coupling region. This fourth light-absorbing element is used to absorb image light that reaches the side after passing through the coupling grating and is scattered by the side. The fourth light-absorbing element is the same as the second light-absorbing element and can be a light-absorbing material layer, or a three-layer structure comprising a first metal cylindrical array layer, a second dielectric tetragonal prism array layer, and a third metal layer sequentially along the direction away from the waveguide substrate surface.

[0070] In another possible implementation, the second and / or third light-absorbing element can be replaced with a diffraction grating. Before reaching the sidewall of the waveguide substrate, the image light passes through the diffraction grating and is diffracted out of the waveguide substrate, reducing scattering caused by the image light incident on the side. The scattered image light is then diffracted out of the waveguide substrate again after incident on the diffraction grating. Preferably, the outgoing direction of the light is away from the eyebox position, so that the outgoing light does not enter the human eye. The diffraction grating has high coupling efficiency to couple the scattered image light out of the waveguide substrate as much as possible. Specifically, it can be implemented as a zigzag grating or a blazed grating, or of course, a high-efficiency straight-tooth grating.

[0071] In practice, when the second light-absorbing element is replaced with a diffraction grating, the grating vector of the diffraction grating and the grating vector of the coupled grating satisfy the light coupling condition, and vector closure is not required. When the diffraction waveguide is assembled into the module, if the diffraction grating is encapsulated inside the module and not visible to the outside, there are no requirements for the light emission direction.

[0072] In practice, when the third light-absorbing element is replaced with a diffraction grating, the grating vector of the diffraction grating, the grating vector of the coupled grating, and the grating vector of the folding grating satisfy the light coupling condition, and vector closure is not required.

[0073] For example, refer to Figure 8 The diffractive waveguide 100 includes a waveguide substrate 110. A coupling grating 120, a coupling grating 130, and a transition grating 160 are disposed on the waveguide substrate 110. A first light-absorbing element 140 is formed by covering the sidewalls of the waveguide substrate 110 with a layer of light-absorbing material. A second diffraction grating 250 is disposed on the surface of the waveguide substrate 110, in the region adjacent to the coupling region and between the coupling region. A third diffraction grating 270 is disposed on the surface of the waveguide substrate 110, in the region adjacent to the transition region and between the transition region. The third diffraction grating 270 can be adjacent to the transition grating 160 to increase overall integrity.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this invention.

Claims

1. A diffractive optical waveguide, characterized in that, include: A waveguide substrate, comprising at least an insertion region and an exit region, wherein an insertion grating is disposed on or within the waveguide substrate and located in the insertion region, and an exit grating is disposed on or within the waveguide substrate and located in the exit region; image light is incident on the insertion region and coupled into the waveguide substrate through the insertion grating, and after total internal reflection between the first and second surfaces of the waveguide substrate, it is transmitted to the exit region and then coupled out of the waveguide substrate through the exit grating and enters the human eye; A first light-absorbing element is provided on the side between the first surface and the second surface to absorb image light incident on the side. A second light-absorbing element is provided on the first surface and the second surface, at least in the area between the side adjacent to the coupling region and the coupling region, to absorb image light scattered by the side.

2. The diffractive waveguide according to claim 1, characterized in that, Both the first light-absorbing element and the second light-absorbing element are light-absorbing material layers. The light-absorbing material layer covers the side to form the first light-absorbing element, and extends from the edge of the side to at least cover the waveguide substrate surface region adjacent to the coupling region and the coupling region to form the second light-absorbing element.

3. The diffractive waveguide according to claim 2, characterized in that, The thickness of the first light-absorbing element is greater than 0.3 mm, the transition surface between the first light-absorbing element and the second light-absorbing element is a smooth curved surface, and the dimension of the second light-absorbing element extending from the edge of the side is in the range of 4 mm to 10 mm.

4. The diffractive waveguide according to claim 1, characterized in that, The first light-absorbing element is a light-absorbing material layer, and the second light-absorbing element is a three-layer structure, which includes a first metal cylindrical array layer, a second dielectric tetragonal prism array layer and a third metal layer in sequence along the direction away from the surface of the waveguide substrate.

5. The diffractive waveguide according to claim 4, characterized in that, The outline shape of the second light-absorbing element is crescent-shaped, and the maximum size of the second light-absorbing element in the direction orthogonal to the image light propagation direction is greater than the diameter of the coupling region.

6. The diffractive waveguide according to claim 4, characterized in that, The thickness of the first metal cylindrical array layer is less than the thickness of the second dielectric tetragonal prism array layer, and the thickness of the second dielectric tetragonal prism array layer is less than the thickness of the third metal layer.

7. The diffractive waveguide according to claim 4, characterized in that, The diameter of the cylinder in the first metal cylindrical array layer is smaller than the length and width of the prism in the second dielectric tetragonal prism array layer.

8. The diffractive waveguide according to claim 1, characterized in that, The waveguide substrate further includes a transition region. A transition grating is disposed on or within the waveguide substrate and located in the transition region. After image light is incident on the coupling region, it is coupled into the waveguide substrate through the coupling grating and transmitted to the transition region by total internal reflection between the first and second surfaces of the waveguide substrate. It is then deflected by the transition grating and transmitted to the output region, and finally coupled out of the waveguide substrate through the output grating and enters the human eye. A third light-absorbing element is disposed on the first and second surfaces, at least in the area between the side adjacent to the transition region and the transition region, for absorbing image light that has passed through the transition grating to the side and is scattered by the side.

9. The diffractive waveguide according to claim 8, characterized in that, The distribution of the third light-absorbing element in a direction orthogonal to the image light propagation direction covers the propagation area of ​​the boundary field of view.

10. The diffractive waveguide according to claim 8, characterized in that, The shape pattern of the third light-absorbing element is reused as the information prompt pattern of the diffractive waveguide.

Images