Two-dimensional grating structure, diffractive optical waveguide and display device

Abstract

The invention provides a two-dimensional grating structure, a diffractive optical waveguide and a display device. The two-dimensional grating structure comprises a repeating unit, and the repeating unit comprises a first crystal unit which is projected into a first closed pattern. The first crystal unit comprises a main body part, a first branch part and a second branch part. The projection of the main body portion has a main body profile curve at least partially elliptical. The projection of the first branch portion has a first branch profile curve, at least part of which is a first circle. The projection of the second branch has a second branch profile curve, at least part of which is a second circle. The connecting line between the centers of the first circle and the ellipse and the short axis form a first included angle, the connecting line between the center of the second circle and the center of the ellipse and the short axis form a second included angle, and the first included angle and / or the second included angle are / is smaller than or equal to 90 degrees. The centers of the first circle and the second circle are not on one side of the short shaft simultaneously. The ellipse, the first circle and the second circle form a second closed pattern, and 90% of the first closed pattern is overlapped with the second closed pattern.

Description

Technical Field

[0001] The present application generally relates to the field of micro-nano optical technology, and more specifically to two-dimensional grating structures, diffractive optical waveguides and display devices. Background Art

[0002] With the rapid development of semiconductor technology, the interaction between people and computers is developing rapidly. Among them, augmented reality (AR) display can provide humans with more dimensional information and has received widespread attention. AR glasses are one of the important media in the field of augmented reality display. Diffractive optical waveguides have the advantages of strong mass production, lightness, easy replication, and high processing yield. Compared with the low processing yield of array optical waveguides and the difficulty of mass production of holographic waveguides, surface-embossed diffractive optical waveguides are more ideal solutions for AR glasses and consumer electronic waveguide glasses.

[0003] Diffractive waveguides can be roughly divided into one-dimensional expanded pupil diffractive waveguides and two-dimensional expanded pupil diffractive waveguides. The two-dimensional expanded pupil diffractive waveguide has a two-dimensional grating structure in some gratings in its outcoupling area (that is, there are grating periods in both directions). The signal light level transmitted inside the waveguide will form four levels from the inside of the medium to the interface, including: total reflection level, outcoupling level, left-side splitting level, and right-side splitting level, which can play the role of two-dimensional pupil expansion.

[0004] However, the two-dimensional pupil expansion structure needs to run through the entire outcoupling area. Since the span of the entire outcoupling area is relatively large, it is difficult to achieve a balance between the efficiency and non-uniformity of the entire outcoupling area. Therefore, it is necessary to adjust the above four parameters to achieve the expected overall efficiency and non-uniformity. However, the current two-dimensional grating structure has poor controllability, and the flexibility of changing the above four parameters is low, making it difficult to achieve the expected purpose.

[0005] Therefore, it is necessary to improve the two-dimensional grating structure, the diffractive optical waveguide and the display device to solve at least one technical problem. Summary of the invention

[0006] The present application is proposed to solve at least one of the above problems. Specifically, a first aspect of the present application provides a two-dimensional grating structure, the two-dimensional grating structure comprising an array of repeating units periodically arranged in a horizontal direction and a vertical direction, the horizontal direction is orthogonal to the vertical direction, the repeating unit comprises a first crystal unit, the projection of the first crystal unit on a horizontal plane formed by the horizontal direction and the vertical direction forms a first closed figure, the first crystal unit comprises: A main body portion, wherein the projection of the main body portion on the horizontal plane has a main body contour curve, wherein the main body contour curve is at least partially configured as an elliptical contour curve, wherein the extension direction of the major axis of the ellipse is parallel to the longitudinal direction, and the extension direction of the minor axis of the ellipse is parallel to the transverse direction; a first branch portion, the first branch portion being connected to the main body portion, the projection of the first branch portion on the horizontal plane having a first branch contour curve, and the first branch contour curve being at least partially configured as a first circular contour curve; a second branch portion, the second branch portion being connected to the main body portion, the projection of the second branch portion on the horizontal plane having a second branch contour curve, and the second branch contour curve being at least partially configured as a second circular contour curve; wherein a first angle is formed between a line connecting the center of the first circle and the center of the ellipse and the minor axis, a second angle is formed between a line connecting the center of the second circle and the center of the ellipse and the minor axis, and the first angle and / or the second angle is less than or equal to 90°; and The centers of the first circle and the second circle are not located at one side of the short axis along the longitudinal direction at the same time; and The ellipse, the first circle, and the second circle form a second closed figure, and at least 90% of the first closed figure overlaps with the second closed figure.

[0007] According to the two-dimensional grating structure of the present application, a flexible control method is provided for adjusting the parameters of each level of the two-dimensional grating structure, so that the control autonomy is higher and the adjustable range is larger, which is conducive to obtaining the ideal efficiency and non-uniformity of the two-dimensional grating as a whole.

[0008] Optionally, the first angle and / or the second angle is less than or equal to 80°, and / or One of the first angle and the second angle is less than or equal to 5°.

[0009] Optionally, centers of the first circle and the second circle are respectively located on both sides of the short axis along the longitudinal direction.

[0010] Optionally, a center of one of the first circle and the second circle overlaps with a straight line where the short axis lies.

[0011] Optionally, the size of the first circular radius is r1, the size of the second circular radius is r2, and the size of the short axis is 2b. The minimum distance from the center of the first circle to the contour curve of the ellipse is less than the smaller of r1 / 2 and b / 4, The minimum distance from the center of the second circle to the contour curve of the ellipse is less than the smaller one of r2 / 2 and b / 4.

[0012] Optionally, the minimum distance from the center of the first circle to the contour curve of the ellipse is less than the smaller of r1 / 5 and b / 10, The minimum distance from the center of the second circle to the contour curve of the ellipse is less than the smaller one of r2 / 5 and b / 10.

[0013] Optionally, the center of the first circle and / or the second circle coincides with the contour curve of the ellipse.

[0014] Optionally, the first branch contour curve is at least partially constructed to include two non-concentric contour curves of the first circles, and the centers of the two first circles are respectively located on both sides of the major axis along the transverse direction.

[0015] Optionally, the two first circles are symmetrical with respect to the major axis.

[0016] Optionally, the ratio of the radii of the two first circles is greater than or equal to 0.5 and less than 1.

[0017] Optionally, the ratio of the radii of the two first circles is greater than or equal to 0.8 and less than 1.

[0018] Optionally, the difference between the two first angles is greater than 0 and less than or equal to 20°.

[0019] Optionally, the difference between the two first angles is greater than 0 and less than or equal to 5°.

[0020] Optionally, the second branch contour curve is at least partially constructed to include two non-concentric contour curves of the second circles, and the centers of the two second circles are respectively located on both sides of the major axis along the transverse direction.

[0021] Optionally, the two second circles are symmetrical with respect to the long axis.

[0022] Optionally, the ratio of the radii of the two second circles is greater than or equal to 0.5 and less than 1.

[0023] Optionally, the ratio of the radii of the two second circles is greater than or equal to 0.8 and less than 1.

[0024] Optionally, the difference between the two second angles is greater than 0 and less than or equal to 20°.

[0025] Optionally, the difference between the two second angles is greater than 0 and less than or equal to 5°.

[0026] Optionally, at least 95% of the first closed figure overlaps with the second closed figure; and / or The first closed figure is formed by Gaussian blurring the second closed figure, so that the first branch contour curve smoothly transitions with the main contour curve, and the second branch contour curve smoothly transitions with the main contour curve.

[0027] Optionally, the repeating unit is constructed as a rectangular repeating unit, the first crystal unit is located at the center of the rectangle, and the four corners of the rectangle are respectively provided with a first branch crystal, a second branch crystal, a third branch crystal and a fourth branch crystal; In a 2×2 array consisting of four repeating units, the first branch crystal, the second branch crystal, the third branch crystal and the fourth branch crystal form a second crystal unit at the middle junction of the four repeating units, and the structure of the second crystal unit is consistent with that of the first crystal unit.

[0028] Optionally, the first crystal unit and / or the second crystal unit is configured as a protrusion or a depression.

[0029] Optionally, the two-dimensional grating structure has a first lattice direction and a second lattice direction, wherein the first lattice direction is parallel to a first diagonal of the rectangle, and the second lattice direction is parallel to a second diagonal of the rectangle; The repeating unit has a first vector direction and a second vector direction, the endpoints of the major axis and the minor axis of the ellipse are connected to form a parallelogram, the parallelogram has two parallel first sides and two parallel second sides, wherein the first vector direction is parallel to the first side, and the second vector direction is parallel to the second side; The angle between the first vector direction and the first lattice direction is less than or equal to 10°, and / or the angle between the second vector direction and the second lattice direction is less than or equal to 10°.

[0030] Optionally, an angle between the first vector direction and the first lattice direction is less than or equal to 5°, and / or an angle between the second vector direction and the second lattice direction is less than or equal to 5°.

[0031] Optionally, the first vector direction is parallel to the first lattice direction, and / or the second vector direction is parallel to the second lattice direction.

[0032] Optionally, an angle between the first lattice direction and the second lattice direction is greater than or equal to 45° and less than or equal to 75°.

[0033] Optionally, the first crystal unit is symmetrical with respect to the long axis, the size of the long axis of the ellipse is 2a, the size of the short axis of the ellipse is 2b, and the angle between the first lattice direction and the longitudinal direction is θ, wherein b=a×tanθ.

[0034] A second aspect of the present application provides a diffraction optical waveguide, comprising the two-dimensional grating structure described in the first aspect.

[0035] Optionally, the diffractive optical waveguide comprises: A waveguide substrate, the waveguide substrate comprising an incoupling region and an outcoupling region; an incoupling grating, disposed on or in the waveguide substrate and located in the incoupling region, configured to couple input light into the waveguide substrate so that the input light propagates in the waveguide substrate by total reflection; An outcoupling grating is arranged on or in the waveguide substrate and located in the outcoupling region, and is used to couple at least a portion of the light propagating to the outcoupling grating out of the waveguide substrate by diffraction, wherein the outcoupling grating includes the two-dimensional grating structure.

[0036] Since the diffraction optical waveguide of the present application includes the aforementioned two-dimensional grating structure, it has basically the same advantages as the two-dimensional grating structure.

[0037] Optionally, a radius of the first circle and / or the second circle is smaller than or equal to half of a period of the coupling-in grating.

[0038] Optionally, a radius of the first circle and / or the second circle is smaller than one third of a period of the coupling-in grating.

[0039] Optionally, a dimension a of the semi-major axis of the ellipse is less than or equal to 1.2 times of half a period of the coupling-in grating.

[0040] Optionally, a dimension b of the semi-major axis of the ellipse is less than or equal to half of a period of the coupling-in grating.

[0041] A third aspect of the present application provides a display device, including: The two-dimensional grating structure described in the first aspect above; or The diffractive optical waveguide described in the second aspect above.

[0042] Since the display device of the present application includes the aforementioned diffraction light waveguide or two-dimensional grating structure, it has substantially the same advantages as the diffraction light waveguide or two-dimensional grating structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0044] Figure 1a A schematic diagram showing a two-dimensional grating structure according to an optional embodiment of the present application; Figure 1b Shows Figure 1a Schematic diagram of the design graphic corresponding to the two-dimensional grating structure; Figure 1c-Figure 1e Shows Figure 1a Schematic diagram of the comparison between the design and processing of the two-dimensional grating structure; Figure 2a-2e A schematic diagram showing a comparison of processing of an optional two-dimensional grating structure of the present application under different Gaussian blur parameters is shown; Figure 3a A schematic diagram showing a first circular shape, a second circular shape and an elliptical shape of a two-dimensional grating structure according to an optional embodiment of the present application is shown; Figure 3b The figure shows the variable range of the centers of the first circle and the second circle of the two-dimensional grating structure relative to the ellipse in an optional embodiment of the present application; Figure 4 A schematic diagram showing the vector direction of a two-dimensional grating structure according to an optional embodiment of the present application; Figure 5 A schematic diagram showing the lattice direction of a two-dimensional grating structure according to an optional embodiment of the present application; Figure 6a-6g A schematic diagram showing a two-dimensional grating structure corresponding to changes in the radii of the first circle and the second circle in an optional embodiment of the present application; Figure 7a Shows Figure 6a , Figure 6b , Figure 6c , Figure 6f and Figure 6g The change diagram of the intermediate total reflection efficiency; Figure 7b Shows Figure 6a , Figure 6b , Figure 6c , Figure 6f and Figure 6g The variation diagram of the light splitting efficiency on both sides; Figure 7c Shows Figure 6a , Figure 6b , Figure 6c , Figure 6f and Figure 6g The change of outcoupling efficiency on both sides after light splitting; Figure 7d Shows Figure 6a , Figure 6b , Figure 6c , Figure 6f and Figure 6g The total reflectivity change diagram on both sides after splitting; Figure 8a-8d A schematic diagram showing a two-dimensional grating structure corresponding to different parameter changes in an optional embodiment of the present application; Figure 9a-9c A schematic diagram showing a comparison of design and processing corresponding to another two-dimensional grating structure is shown; Figure 10a-Figure 10c A schematic diagram showing a comparison of design and processing corresponding to another two-dimensional grating structure is shown; Figure 11a-Figure 11c A schematic diagram showing the comparison of design and processing corresponding to another two-dimensional grating structure is shown; Fig.12 A schematic diagram of a diffractive optical waveguide according to a preferred embodiment of the present application is shown; Fig.13 A schematic diagram of an exemplary display device is shown. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical solutions and advantages of the present application more obvious, the example embodiments according to the present application will be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application, and it should be understood that the present application is not limited to the example embodiments described herein. Based on the embodiments of the present application described in the present application, all other embodiments obtained by those skilled in the art without creative work should fall within the scope of protection of the present application.

[0046] In the following description, a large number of specific details are provided to provide a more thorough understanding of the present application. However, it is apparent to those skilled in the art that the present application can be implemented without one or more of these details. In other examples, in order to avoid confusion with the present application, some technical features well known in the art are not described.

[0047] It should be understood that the present application can be implemented in different forms and should not be interpreted as being limited to the embodiments set forth herein. On the contrary, providing these embodiments will make the disclosure thorough and complete, and will fully convey the scope of the present application to those skilled in the art.

[0048] The purpose of the terms used herein is only to describe specific embodiments and is not intended to be limiting of the present application. When used herein, the singular forms "one", "an" and "said / the" are also intended to include plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms "consisting of" and / or "comprising", when used in this specification, determine the presence of the features, integers, steps, operations, elements and / or parts, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, parts and / or groups. When used herein, the term "and / or" includes any and all combinations of the relevant listed items.

[0049] In order to thoroughly understand the present application, a detailed structure will be proposed in the following description to illustrate the technical solution proposed by the present application. The optional embodiments of the present application are described in detail as follows, but in addition to these detailed descriptions, the present application may also have other implementation methods.

[0050] In order to solve the aforementioned technical problems, the first aspect of the present application provides a two-dimensional grating structure, the two-dimensional grating structure includes an array of repeating units 1 arranged periodically in the horizontal and vertical directions, the horizontal direction is orthogonal to the vertical direction, the repeating unit 1 includes a first crystal unit 2, and the projection of the first crystal unit 2 on the horizontal plane forms a first closed figure. The first crystal unit 2 includes a main body 3, a first branch portion 4 and a second branch portion 5.

[0051] The projection of the main body 3 in the horizontal plane formed in the transverse and longitudinal directions has a main body contour curve 8, which is at least partially constructed as a contour curve of an ellipse 9, wherein the extension direction of the major axis of the ellipse 9 is parallel to the longitudinal direction, and the extension direction of the minor axis of the ellipse 9 is parallel to the transverse direction.

[0052] The first branch portion 4 is connected to the main body portion 3 . The projection of the first branch portion 4 on the horizontal plane has a first branch contour curve 6 . The first branch contour curve 6 is at least partially configured as a contour curve of a first circle 10 .

[0053] The second branch portion 5 is connected to the main body portion 3, and the projection of the second branch portion 5 on the horizontal plane has a second branch contour curve 7, and the second branch contour curve 7 is at least partially configured as a contour curve of a second circle 11; The first angle α1 is formed between the line connecting the center of the first circle 10 and the center of the ellipse 9 and the minor axis, and the second angle α2 is formed between the line connecting the center of the second circle 11 and the center of the ellipse 9 and the minor axis, and the first angle α1 and / or the second angle α2 are less than or equal to 90°. The centers of the first circle 10 and the second circle 11 are not located on one side of the minor axis in the longitudinal direction at the same time. The ellipse 9, the first circle 10 and the second circle 11 form a second closed figure, and at least 90% of the first closed figure overlaps with the second closed figure.

[0054] According to the two-dimensional grating structure of the present application, a flexible control method is provided for adjusting the parameters of each level of the two-dimensional grating structure, so that the control autonomy is higher and the adjustable range is larger, which is conducive to obtaining the ideal efficiency and non-uniformity of the two-dimensional grating as a whole.

[0055] The following will refer to Figures 1 to Fig.13 The two-dimensional grating structure, diffraction optical waveguide and display device of the present application are described. Under the premise of no conflict, the features of various embodiments of the present application can be combined with each other.

[0056] refer to Figure 1a-Figure 11c The first aspect of the present application provides a two-dimensional grating structure, which is an array composed of repeating units 1. Figure 5 , a plurality of repeating units 1 are arranged along mutually orthogonal transverse and longitudinal periods, thereby having periodicity in the transverse and longitudinal directions. It can be understood that the two-dimensional grating structure extends on a horizontal plane formed by the transverse and longitudinal directions.

[0057] refer to Figure 1a , Figure 1b and Figure 5 , the repeating unit 1 is constructed as a rectangular repeating unit 1, which includes a first crystal unit 2 and a second crystal unit 16. Among them, the first crystal unit 2 is located at the center of the rectangle. The second crystal unit 16 is composed of a first crystal 12, a second crystal 13, a third crystal 14 and a fourth crystal 15 respectively arranged at the four corners of the rectangle. In a 2×2 array composed of four repeating units 1, the first crystal 12, the second crystal 13, the third crystal 14 and the fourth crystal 15 form the second crystal unit 16 at the middle intersection of the four repeating units 1, and the structure of the second crystal unit 16 is consistent with that of the first crystal unit 2. Preferably, the first crystal unit 2 and / or the second crystal unit 16 are constructed as convex or concave.

[0058] The first crystal unit 2 includes a main body 3, a first branch 4, and a second branch 5, and the first branch 4 and the second branch 5 are both connected to the main body 3. Specifically, the projection of the main body 3 on the above-mentioned horizontal plane has a main body contour curve 8, and the main body contour curve 8 is at least partially configured as a contour curve of an ellipse 9. In other words, the main body contour curve 8 is a part of the contour curve of a certain ellipse 9. The extension direction of the major axis of the ellipse 9 is parallel to the longitudinal direction, and the size of the major axis is 2a, and the extension direction of the minor axis of the ellipse 9 is parallel to the transverse direction, and the size of the minor axis is 2b.

[0059] The projection of the first branch portion 4 on the horizontal plane has a first branch contour curve 6, and the first branch contour curve 6 is at least partially configured as a contour curve of the first circle 10. In other words, the first branch contour curve 6 is a part of the contour curve of the first circle 10. The projection of the second branch portion 5 on the horizontal plane has a second branch contour curve 7, and the second branch contour curve 7 is at least partially configured as a contour curve of the second circle 11. In other words, the second branch contour curve 7 is a part of the contour curve of the second circle 11.

[0060] The first branch contour curve 6 , the second branch contour curve 7 and the main body contour curve 8 together constitute a projection curve of the first crystal unit 2 on a horizontal plane, and the projection curve forms a first closed figure.

[0061] The oval 9, the first circle 10 and the second circle 11 can form a second closed figure, and at least 90% of the first closed figure overlaps with the second closed figure. In other words, the first closed figure and the second closed figure have a mismatch of at most 10%.

[0062] Preferably, at least 95% of the first closed figure overlaps with the second closed figure. In other words, the first closed figure and the second closed figure have a mismatch of at most 5%.

[0063] It can be understood that the above-mentioned ellipse 9, the first circle 10 and the second circle 11 can form a second closed figure, which has a more precise shape and is the shape used when designing a two-dimensional grating structure. The projection of the actual processed shape of the first crystal unit 2 forms the above-mentioned first closed figure. The above-mentioned difference may be caused by processing errors, or it may be formed after corresponding deformation due to the difficulty of processing the designed shape. For example, the above-mentioned mismatch can be understood as the degree of difference between the designed shape and the actual shape. As shown in reference Figure 1c , Figure 1d and Figure 1e The embodiment shown, referring to Figure 9a , Figure 9b and Fig.9c The embodiment shown, Fig.10a , Fig.10b and Fig.10c The embodiment shown and Fig.11a , Fig.11b and Fig.11c In the illustrated embodiment, the design pattern and the processed pattern have a certain mismatch due to a certain smoothing process, such as the Gaussian smoothing process described in detail below.

[0064] Specifically, since the smoother the edge curve of the micro-nano optical structure is, the more convenient it is to process, the design shape can be smoothed, such as by Gaussian Blur processing, so that the first branch contour curve 6 and the main contour curve 8 can transition smoothly, and the second branch contour curve 7 and the main contour curve 8 can transition smoothly.

[0065] Exemplarily, Gaussian blur processing uses the following expression: , phase_blur=phase×G(u,v).

[0066] The degree of smoothing can be adjusted by adjusting the parameter σ, which can range from 0 to 200 nm.

[0067] For example Figure 2a-2e The processed morphologies of the two-dimensional grating of the same structure after Gaussian smoothing of σ=0nm, σ=50nm, σ=100nm, σ=150nm, and σ=200nm are shown respectively, and the intermediate coupling-out ratio, intermediate total reflectivity, left splitting ratio, right splitting ratio, left coupling-out ratio after splitting, right coupling-out ratio after splitting, left total reflectivity after splitting, and right total reflectivity after splitting are tested, refer to Table 1.

[0068] Table 1 σ value Intermediate coupling rate Intermediate total reflectivity Left side splitting ratio Right side splitting ratio The left outcoupling rate after splitting The right outcoupling rate after splitting Total reflectivity on the left after splitting Total reflectivity on the right after splitting 0 nm 0.0130242 0.7634561 0.0954785 0.0954785 0.0197893 0.0197893 0.7717537 0.7717537 50 nm 0.0127868 0.7556363 0.0984849 0.0984849 0.0203795 0.0203795 0.7730443 0.7730443 100 nm 0.0124594 0.7518135 0.0994473 0.0994473 0.0206109 0.0206109 0.7765957 0.7765957 150 nm 0.0121043 0.7501972 0.0996084 0.0996084 0.0206977 0.0206977 0.7797774 0.7797774 200 nm 0.0119694 0.7507194 0.0992244 0.0992244 0.0206561 0.0206561 0.7813922 0.7813922 It can be seen from Table 1 that the overall optical performance does not change much, so Gaussian blur processing can be used to improve the processability and robustness of the structure.

[0069] In addition, reference Figure 3a , a first angle α1 is formed between the line connecting the center of the first circle 10 and the center of the ellipse 9 and the minor axis, a second angle α2 is formed between the line connecting the center of the second circle 11 and the center of the ellipse 9 and the minor axis, and the first angle α1 and / or the second angle α2 are less than or equal to 90°. It can be understood that the first circle 10 and / or the second circle 11 can be set at the vertex of the major axis of the ellipse 9, or can be set away from the vertex of the major axis. Preferably, the first angle α1 and / or the second angle α2 are less than or equal to 80°.

[0070] As an optional embodiment, the center of the first circle 10 and / or the second circle 11 coincides with the contour curve of the ellipse 9, thereby the position of the center of the first circle 10 and / or the second circle 11 can be adjusted along the contour curve of the ellipse 9.

[0071] As another optional embodiment, the center of the first circle 10 and / or the second circle 11 may deviate from the contour curve of the ellipse 9 by a certain distance. Exemplarily, the size of the radius of the first circle 10 is r1, the size of the radius of the second circle 11 is r2, the minimum distance from the center of the first circle 10 to the contour curve of the ellipse 9 is less than the smaller of r1 / 2 and b / 4, and the minimum distance from the center of the second circle 11 to the contour curve of the ellipse 9 is less than the smaller of r2 / 2 and b / 4. Preferably, the minimum distance from the center of the first circle 10 to the contour curve of the ellipse 9 is less than the smaller of r1 / 5 and b / 10, and the minimum distance from the center of the second circle 11 to the contour curve of the ellipse 9 is less than the smaller of r2 / 5 and b / 10. Figure 3b As shown, the center of the first circle 10 and the center of the second circle can be adjusted between a small ellipse inside the contour curve of the ellipse 9 and a large ellipse outside the contour curve of the ellipse 9 .

[0072] As an implementation, the centers of the first circle 10 and the second circle 11 are not located at the same side of the minor axis in the longitudinal direction. For example, the center of the first circle 10 overlaps with the straight line where the minor axis is located, and the center of the second circle 11 is located at the side of the minor axis in the longitudinal direction. Alternatively, the center of the second circle 11 overlaps with the straight line where the minor axis is located, and the center of the first circle 10 is located at the side of the minor axis in the longitudinal direction.

[0073] Alternatively, the centers of the first circle 10 and the second circle 11 are located on both sides of the short axis in the longitudinal direction. In this case, the centers of the first circle 10 and the second circle 11 may both be far from the short axis, or one of the centers of the first circle 10 and the second circle 11 may be closer to the short axis. Exemplarily, one of the first angle α1 and the second angle α2 is less than or equal to 5°.

[0074] As a preferred embodiment, in order to further improve the flexibility of the design and increase the adjustable parameters, the first branch contour curve 6 is at least partially constructed as a contour curve including two non-concentric first circles 10, and the centers of the two first circles 10 are respectively located on both sides of the long axis along the horizontal direction, and / or the second branch contour curve 7 is at least partially constructed as a contour curve including two non-concentric second circles 11, and the centers of the two second circles 11 are respectively located on both sides of the long axis along the horizontal direction.

[0075] It can be understood that, as an optional embodiment, two first circles 10 and one second circle 11 can be provided. In this embodiment, the center of the second circle 11 is preferably located on the straight line where the long axis is located, and preferably one second circle 11 is provided at the vertex of the long axis.

[0076] As another optional embodiment, two second circles 11 and one first circle 10 may be provided. In this embodiment, the center of the first circle 10 is preferably located on the straight line where the long axis is located, and preferably one first circle 10 is provided at the vertex of the long axis.

[0077] As yet another optional implementation, two second circles 11 and two first circles 10 may be provided.

[0078] The sizes and positions of the two first circles 10 may be the same, for example, they may be symmetrical with respect to the long axis. Figure 6a-6g as well as Figure 8a-8d , both show embodiments in which two identical first circles and two identical second circles are provided.

[0079] in Figure 6a-6g In the seven embodiments, the first angle α1 and the second angle α2 are both 75°, the major axis of the ellipse is 130 nm, and the smaller angle of the rhombus formed by the major axis and the minor axis of the ellipse is 60°. Figure 6a The radii of the first circle and the second circle are both 20 nm. Figure 6b Relative to Figure 6a Only the radius of the second circle was adjusted, where the radius of the first circle was 20 nm and the radius of the second circle was 40 nm. Figure 6c The radius of the first circle is 40nm, and the radius of the second circle is 20nm. Figure 6d The radii of the first circle and the second circle are both 40 nm. Figure 6e The radius of the first circle is 60 nm, and the radius of the second circle is 40 nm. Figure 6f In the figure, the radius of the first circle is 40 nm and the radius of the second circle is 60 nm. Figure 6g The radius of the first circle and the second circle are both 60nm. Figure 6a to Figure 6g Tests were performed on the middle outcoupling rate, middle total reflectance, left side splitting rate, right side splitting rate, left side outcoupling rate after splitting, right side outcoupling rate after splitting, left side total reflectance after splitting, and right side total reflectance after splitting, refer to Table 2.

[0080] Table 2 Example Intermediate coupling rate Intermediate total reflectivity Left side splitting ratio Right side splitting ratio The left outcoupling rate after splitting The right outcoupling rate after splitting Total reflectivity on the left after splitting Total reflectivity on the right after splitting Figure 6a 0.00356753 0.941286727 0.023425034 0.023425112 0.005832209 0.005832216 0.939476964 0.939476964 Figure 6b 0.003974451 0.923004713 0.031936042 0.031938776 0.008020374 0.008019603 0.923177498 0.923178475 Figure 6c 0.003762235 0.927493132 0.02988394 0.029892878 0.007480276 0.007479101 0.927114063 0.927108961 Figure 6d 0.003495085 0.907891095 0.039609596 0.039609756 0.009253025 0.009253078 0.912284129 0.912284129 Figure 6e 0.003741915 0.890623651 0.045985722 0.04597503 0.011315982 0.01131754 0.898180775 0.898188121 Figure 6f 0.003465002 0.890652632 0.047235881 0.047247274 0.011801193 0.011799714 0.89821854 0.8982112 Figure 6g 0.002849236 0.868031752 0.056627535 0.056627691 0.01373504 0.013735104 0.883485102 0.883485102 It can be seen from Table 2 that, by simply adjusting the radius of the first circle and / or the second circle, the other parameters can be adjusted approximately linearly while the intermediate outcoupling efficiency remains unchanged, thereby achieving a balance among the above eight indicators.

[0081] For example, reference Figure 7a-7d , respectively showing Figure 6a , Figure 6b , Figure 6c , Figure 6f and Figure 6g The graphs of total reflection efficiency in the middle, light splitting efficiency on both sides, outcoupling efficiency on both sides after light splitting, and total reflectivity on both sides after light splitting are shown in Figure 1. It can be seen that the four parameters of total reflection efficiency in the middle, light splitting efficiency on both sides, outcoupling efficiency on both sides after light splitting, and total reflectivity on both sides after light splitting basically show a linear trend as the radius of the first circle and the second circle center changes.

[0082] Figure 8a-8d In addition to the change in the radius of the first circle 10 and / or the second circle 11, the illustrated embodiment also involves the change in the first angle α1 and / or the second angle α2, as well as the change in the major axis size of the ellipse 9 (the angle of the smaller internal angle of the rhombus formed by the vertices of the ellipse 9 remains unchanged). Figure 8a The major axis of the middle ellipse is 130 nm, the radius of the first circle is 60 nm, the radius of the second circle is 40 nm, and the first angle and the second angle are both 90°. Figure 8b The major axis of the middle ellipse is 130 nm, the radius of the first circle is 40 nm, the radius of the second circle is 40 nm, and the first angle and the second angle are both 60°. Figure 8c The major axis of the middle ellipse is 170 nm, the radius of the first circle is 50 nm, the radius of the second circle is 50 nm, and the first angle and the second angle are both 60°. Figure 8d The major axis of the middle ellipse is 220 nm, the radius of the first circle is 80 nm, the radius of the second circle is 20 nm, the first angle is 50°, and the second angle is 75°.

[0083] For the above Figures 8a to 8d Tests were performed on the middle outcoupling rate, middle total reflectance, left side splitting rate, right side splitting rate, left side outcoupling rate after splitting, right side outcoupling rate after splitting, left side total reflectance after splitting, and right side total reflectance after splitting, refer to Table 3.

[0084] Table 3 Example Intermediate coupling rate Intermediate total reflectivity Left side splitting ratio Right side splitting ratio The left outcoupling rate after splitting The right outcoupling rate after splitting Total reflectivity on the left after splitting Total reflectivity on the right after splitting Figure 8a 0.003235759 0.908421534 0.039881996 0.039883634 0.010498091 0.010497871 0.90879565 0.908794633 Figure 8b 0.005653531 0.91161343 0.034438175 0.034438027 0.009536941 0.009536988 0.918282714 0.918282713 Figure 8c 0.006359762 0.820957494 0.07242785 0.07242785 0.019048157 0.019048157 0.859039527 0.859039527 Figure 8d 0.003719898 0.74110121 0.115339876 0.115339876 0.027959944 0.027959944 0.773941426 0.773941426 It can be seen from Table 3 that the span of the middle total reflectivity is about 74% to 91%, the span of the splitting efficiency on both sides is about 4% to 11.5%, the span of the middle outcoupling efficiency is about 0.3% to 0.7%, and the outcoupling efficiency and total reflectivity on both sides after splitting are also in an enlarged adjustment span, which brings a high degree of design freedom in the two-dimensional pupil expansion area.

[0085] The sizes and / or positions of the two first circles 10 may also be different. For example, the ratio of the radii of the two first circles 10 is greater than or equal to 0.5 and less than 1, and further, the ratio of the radii of the two first circles 10 is greater than or equal to 0.8 and less than 1. The difference between the two first angles α1 is greater than 0 and less than or equal to 20°, and further, the difference between the two first angles α1 is greater than 0 and less than or equal to 5°.

[0086] The sizes and / or positions of the two second circles 11 may also be different. For example, the ratio of the radii of the two second circles 11 is greater than or equal to 0.5 and less than 1, and further, the ratio of the radii of the two second circles 11 is greater than or equal to 0.8 and less than 1. The difference between the two second angles α2 is greater than 0 and less than or equal to 20°, and further, the difference between the two second angles α2 is greater than 0 and less than or equal to 5°.

[0087] refer to Figure 5 The two-dimensional grating structure has a first lattice direction D1 and a second lattice direction D2, wherein the first lattice direction D1 is parallel to the first diagonal of the rectangular repeating unit 1, and the second lattice direction D2 is parallel to the second diagonal of the rectangular repeating unit 1.

[0088] refer to Figure 4 , the repeating unit 1 has a first vector direction G1 and a second vector direction G2. The above-mentioned vector direction is also called "grating vector". Its direction is parallel to the direction along which the structure of the grating changes / arranges periodically, and is consistent with the propagation direction of the positive first-order diffraction light of the grating. For example, in the present application, the endpoints of the long axis and the endpoints of the short axis of the ellipse 9 of the first crystal unit 2 form a parallelogram, and the parallelogram has two parallel first sides 17 and two parallel second sides 18. Among them, the first side 17 is connected to the second side 18, the first vector direction G1 is parallel to the first side 17, and the second vector direction G2 is parallel to the second side 18.

[0089] As an optional embodiment, the first vector direction G1 is parallel to the first lattice direction D1, and the second vector direction G2 is parallel to the second lattice direction D2. As another optional embodiment, the first vector direction G1 may not be parallel to the first lattice direction D1, and the second vector direction G2 may not be parallel to the second lattice direction D2, for example, the angle between the first vector direction G1 and the first lattice direction D1 is less than or equal to 10°, and the angle between the second vector direction G2 and the second lattice direction D2 is less than or equal to 10°. Further, the angle between the first vector direction G1 and the first lattice direction D1 is less than or equal to 5°, and the angle between the second vector direction G2 and the second lattice direction D2 is less than or equal to 5°.

[0090] Optionally, the angle between the first lattice direction D1 and the second lattice direction D2 is greater than or equal to 45° and less than or equal to 75°. Preferably, the first crystal unit 2 is symmetrical with respect to the long axis, and the angle between the first lattice direction D1 and the longitudinal direction is θ, wherein the long axis and the short axis of the ellipse 9 satisfy the following relationship b=a×tanθ.

[0091] The second aspect of the present application further provides a diffractive optical waveguide 100 for optical pupil expansion, wherein: Fig.12An example of a diffractive light guide 100 for optical pupil expansion according to an embodiment of the present invention is schematically shown, namely, a diffractive light guide 100. Fig.12 As shown, the diffractive optical waveguide 100 includes a waveguide substrate 110. The waveguide substrate 110 may be made of glass, optical plastic or other optically transmissive materials.

[0092] Optionally, the waveguide substrate 110 may have a substantially flat first surface 111 and a second surface 112, wherein the first surface 111 and the second surface 112 are opposite to each other, wherein the first surface 111 may refer to a surface of a display device having the waveguide substrate 110 facing an observer's eyes. The waveguide substrate 110 may propagate light in a direction substantially parallel to the first surface 111 and the second surface 112 by total internal reflection.

[0093] Optionally, the shape of the waveguide substrate 110 may be any suitable shape, for example, it may be rectangular, dumbbell-shaped or butterfly-shaped. The thickness of the waveguide substrate 110 may be any suitable thickness, for example, the thickness of the waveguide substrate 110 is greater than or equal to 0.4 mm and less than or equal to 2 mm. The waveguide substrate 110 in this thickness range can provide good optical properties without being too thick and heavy to affect the user's experience. It is worth mentioning that the thickness of the waveguide substrate 110 may refer to the size of the waveguide substrate 110 in a direction substantially perpendicular to the first surface 111 and the second surface 112.

[0094] Optionally, the waveguide substrate 110 includes an incoupling region and an outcoupling region. The diffraction optical waveguide 100 of the present application further includes an incoupling grating 120 and an outcoupling grating. The incoupling grating 120 and the outcoupling grating 130 may be located on the same side of the waveguide substrate 110, for example, both are arranged on the first surface 111 of the waveguide substrate 110, or may be located on different sides, that is, respectively on the first surface 111 and the second surface 112.

[0095] The coupling-in grating 120 is disposed on or in the waveguide substrate 110 and is located in the coupling-in region, and is configured to couple input light into the waveguide substrate 110 so that it propagates in the waveguide substrate 110 through total reflection, so as to propagate the light toward the coupling-out grating.

[0096] The coupling grating 120 may be a one-dimensional grating, such as a linear grating (also referred to as a straight tooth grating), or may be a slanted tooth grating, a non-blazed grating, or other suitable types of gratings, or the coupling grating 120 may also be a metasurface coupling structure. In some examples, the coupling grating 120 is a one-dimensional grating, a two-dimensional grating, or is composed of two gratings with different grating vectors. The coupling grating 120 may be an optical element including a periodic structure, which may be manufactured by any suitable micro-fabrication process. For example, a grating may be manufactured on the surface of the waveguide substrate 110 or inside thereof by photolithography technology, or a grating may be manufactured on the waveguide substrate 110 by nano-imprinting to form a surface relief diffraction grating. Optionally, the period of the coupling grating 120 may be 350nm-600nm, or other suitable period lengths.

[0097] The out-coupling grating is arranged on or in the waveguide substrate, and the out-coupling grating is located in the out-coupling area. The out-coupling grating is used to couple at least a portion of the light propagating therein out of the waveguide substrate by diffraction, so that the eyes of the viewer can receive the coupled-out light. When the light entering the coupling-in grating 120 is, for example, image light projected by a projector, the light coupled out from the out-coupling grating 130 is at least a portion of the image light, and the out-coupling grating 130 guides the portion of the image light to the eyes of the viewer, so that the eyes of the viewer can see the image projected by the projector. Among them, the out-coupling grating 130 plays a role in expanding the pupil. After receiving the thinner incident light beam from the coupling-in grating, the out-coupling grating continuously diffracts the expanded light beam in two directions in the plane and simultaneously partially couples the light out of the waveguide substrate, thereby achieving the role of expanding the pupil in the plane, so that the observer can observe the display information carried by the incident light beam in a larger window EB (eyebox).

[0098] In some embodiments, the out-coupling grating can be manufactured by any suitable micro-manufacturing process. For example, the grating can be manufactured on the surface or in the waveguide substrate 110 by photolithography, or the grating can be manufactured on the waveguide substrate 110 by nano-imprinting, thereby forming a surface relief diffraction grating. It is worth mentioning that the shape of the various gratings shown in the present application is the shape of the top surface parallel to the surface of the optical waveguide (that is, the surface on which the out-coupling grating or the in-coupling grating 120 is provided), which can be the cross-sectional shape cut by a plane substantially parallel to the surface of the optical waveguide, or can be the projection shape on a plane parallel to the surface of the optical waveguide.

[0099] In some embodiments, the out-coupling grating may be a two-dimensional grating, for example, the two-dimensional grating structure provided in the present application may be used. When the out-coupling grating in the diffraction optical waveguide 100 includes the two-dimensional grating structure of the first aspect, the radius of the first circle 10 and / or the second circle 11 in the two-dimensional grating structure is less than or equal to half of the period of the in-coupling grating. Preferably, the radius of the first circle 10 and / or the second circle 11 is less than one-third of the period of the in-coupling grating.

[0100] As an optional embodiment, the size a of the major semi-axis of the ellipse 9 is less than or equal to 1.2 times of half the period of the coupling-in grating. Preferably, the size a of the major semi-axis of the ellipse 9 is less than or equal to half the period of the coupling-in grating.

[0101] On the other hand, Fig.13 As shown, the present application further provides a display device 800, which may include the aforementioned diffraction optical waveguide 100, wherein the description of the diffraction optical waveguide 100 may refer to the above text and will not be repeated here.

[0102] The display device 800 may be any device including the aforementioned diffractive optical waveguide 100, for example, Fig.13 As shown, the display device 800 may be a near-eye display device, which may include: a lens 820 and a frame 810 for holding the lens close to the eye, wherein the lens 820 includes the above-mentioned diffractive optical waveguide 100.

[0103] According to the display device of the present application, after the human eye wears the optical waveguide display device, the perception of the brightness change of light from different incident directions is more moderate, the light in the field of view is brighter, and at the same time, it also avoids large changes in brightness and darkness of the image observed by the human eye when moving in the window of the diffraction optical waveguide, thereby improving the display effect of the display device including the diffraction optical waveguide, thereby enhancing the user experience.

[0104] In some examples, such as Fig.13As shown, the display device may further include an optical machine 830. Optionally, the optical machine 830 may project image light toward the diffraction waveguide 100, for example, toward the region where the coupling grating 120 of the diffraction waveguide 100 is located. The optical machine 830 may be a micro display such as a laser beam scanner (Laser Beam Scanning, LBS), digital light processing (Digital Light Procession, DLP), digital micromirror device (Digital Micromirror Device, DMD), liquid crystal on silicon (Liquid Crystal On Silicon, LCOS), micro electromechanical system (Micro Electro Mechanical System, MEMS), organic light emitting diode (Organic Light Emitting Diode, OLED), MicroLED optical machine, etc., and the light emitted by the optical machine 830 is visible light.

[0105] Furthermore, the display device may also include a driving device, which is used to drive the optical machine 830 to project the image light onto the coupling grating 120 of the diffraction light waveguide 100, wherein the driving device may include a driving circuit, and the driving circuit may include a MOS tube, a capacitor, a resistor or other suitable components. The display device may also include a controller, which may be electrically connected to the driving circuit, and control the driving device via the controller to drive the optical machine 830 to project the image light onto the coupling grating 120 of the diffraction light waveguide.

[0106] Optionally, the area of ​​the coupling region can be greater than or equal to the spot area of ​​the light projected to the coupling region by the optical machine 830. Optionally, the optical axis of the image light projected by the optical machine 830 is perpendicular to the surface of the waveguide substrate 110 of the diffraction optical waveguide to ensure the quality of the final imaging.

[0107] The light (e.g., image light) projected by the optical machine 830 toward the diffraction light waveguide 100 is coupled to the waveguide substrate 110 through the coupling-in grating 120 for total reflection to the coupling-out, and then coupled out through the coupling-out grating to enter the eyes of the viewer of the near-eye device, thereby enabling the viewer to see the image projected by the optical machine 830.

[0108] In some embodiments, the display device is an augmented reality display device or a virtual reality display device, wherein the augmented reality display device includes but is not limited to augmented reality (AR) glasses, vehicle-mounted head-up display (HUD) and other devices.

[0109] It should be noted that the above embodiments illustrate rather than limit the present application, and that those skilled in the art may devise alternative embodiments without departing from the scope of the appended claims. In the claims, any reference symbol between brackets should not be constructed as a limitation to the claims. The present application may be implemented by means of hardware including several different elements and by means of a suitably programmed computer. In a unit claim that lists several devices, several of these devices may be embodied by the same hardware item. The use of the words first, second, and third, etc. does not indicate any order. These words may be interpreted as names.

Claims

1. A two-dimensional grating structure, characterized in that: The two-dimensional grating structure includes an array of repeating units periodically arranged in a horizontal direction and a vertical direction, wherein the horizontal direction is orthogonal to the vertical direction, and the repeating unit includes a first crystal unit, wherein the projection of the first crystal unit on a horizontal plane formed by the horizontal direction and the vertical direction forms a first closed figure, and the first crystal unit includes: A main body portion, wherein the projection of the main body portion on the horizontal plane has a main body contour curve, wherein the main body contour curve is at least partially configured as an elliptical contour curve, wherein the extension direction of the major axis of the ellipse is parallel to the longitudinal direction, and the extension direction of the minor axis of the ellipse is parallel to the transverse direction; a first branch portion, the first branch portion being connected to the main body portion, the projection of the first branch portion on the horizontal plane having a first branch contour curve, and the first branch contour curve being at least partially configured as a first circular contour curve; a second branch portion, the second branch portion being connected to the main body portion, the projection of the second branch portion on the horizontal plane having a second branch contour curve, and the second branch contour curve being at least partially configured as a second circular contour curve; wherein a first angle is formed between a line connecting the center of the first circle and the center of the ellipse and the minor axis, a second angle is formed between a line connecting the center of the second circle and the center of the ellipse and the minor axis, and the first angle and / or the second angle is less than or equal to 90°; and The centers of the first circle and the second circle are not located at one side of the short axis along the longitudinal direction at the same time; and The ellipse, the first circle, and the second circle form a second closed figure, and at least 90% of the first closed figure overlaps with the second closed figure.

2. The two-dimensional grating structure according to claim 1, characterized in that: The first angle and / or the second angle is less than or equal to 80°, and / or One of the first angle and the second angle is less than or equal to 5°.

3. The two-dimensional grating structure according to claim 1, characterized in that: The centers of the first circle and the second circle are respectively located on both sides of the short axis along the longitudinal direction.

4. The two-dimensional grating structure according to claim 1, characterized in that: A center of one of the first circle and the second circle overlaps with a straight line where the minor axis is located.

5. The two-dimensional grating structure according to claim 1, characterized in that: The size of the first circular radius is r1, the size of the second circular radius is r2, and the size of the short axis is 2b. The minimum distance from the center of the first circle to the contour curve of the ellipse is less than the smaller of r1 / 2 and b / 4, or the minimum distance from the center of the first circle to the contour curve of the ellipse is less than the smaller of r1 / 5 and b / 10, The minimum distance from the center of the second circle to the contour curve of the ellipse is less than the smaller of r2 / 2 and b / 4, or the minimum distance from the center of the second circle to the contour curve of the ellipse is less than the smaller of r2 / 5 and b / 10.

6. The two-dimensional grating structure according to claim 5, characterized in that: The center of the first circle and / or the second circle coincides with the contour curve of the ellipse.

7. The two-dimensional grating structure according to any one of claims 1 to 6, characterized in that: The first branch contour curve is at least partially constructed to include two non-concentric contour curves of the first circles, and the centers of the two first circles are respectively located on both sides of the major axis along the transverse direction.

8. The two-dimensional grating structure according to claim 7, characterized in that: The two first circles are symmetrical with respect to the long axis.

9. The two-dimensional grating structure according to claim 7, characterized in that: The ratio of the radii of the two first circles is greater than or equal to 0.5 and less than 1, or the ratio of the radii of the two first circles is greater than or equal to 0.8 and less than 1.

10. The two-dimensional grating structure according to claim 7, characterized in that: The difference between the two first angles is greater than 0 and less than or equal to 20°, or the difference between the two first angles is greater than 0 and less than or equal to 5°.

11. The two-dimensional grating structure according to any one of claims 1 to 6, characterized in that: The second branch contour curve is at least partially constructed to include two non-concentric contour curves of the second circles, and the centers of the two second circles are respectively located on both sides of the major axis along the transverse direction.

12. The two-dimensional grating structure according to claim 11, characterized in that: The two second circles are symmetrical with respect to the major axis.

13. The two-dimensional grating structure according to claim 11, characterized in that: The ratio of the radii of the two second circles is greater than or equal to 0.5 and less than 1, or the ratio of the radii of the two second circles is greater than or equal to 0.8 and less than 1.

14. The two-dimensional grating structure according to claim 10, characterized in that: The difference between the two second angles is greater than 0 and less than or equal to 20°, or the difference between the two second angles is greater than 0 and less than or equal to 5°.

15. The two-dimensional grating structure according to claim 1, characterized in that: At least 95% of the first closed figure overlaps with the second closed figure; and / or The first closed figure is formed by Gaussian blurring the second closed figure, so that the first branch contour curve smoothly transitions with the main contour curve, and the second branch contour curve smoothly transitions with the main contour curve.

16. The two-dimensional grating structure according to any one of claims 1 to 6, characterized in that: The repeating unit is constructed as a rectangular repeating unit, the first crystal unit is located at the center of the rectangle, and the four corners of the rectangle are respectively provided with a first branch crystal, a second branch crystal, a third branch crystal and a fourth branch crystal; In a 2×2 array consisting of four repeating units, the first branch crystal, the second branch crystal, the third branch crystal and the fourth branch crystal form a second crystal unit at the middle junction of the four repeating units, and the structure of the second crystal unit is consistent with that of the first crystal unit.

17. The two-dimensional grating structure according to claim 16, characterized in that: The first crystal unit and / or the second crystal unit is configured as a projection or a depression.

18. The two-dimensional grating structure according to claim 16, characterized in that: The two-dimensional grating structure has a first lattice direction and a second lattice direction, wherein the first lattice direction is parallel to a first diagonal of the rectangle, and the second lattice direction is parallel to a second diagonal of the rectangle; The repeating unit has a first vector direction and a second vector direction, the endpoints of the major axis and the minor axis of the ellipse are connected to form a parallelogram, the parallelogram has two parallel first sides and two parallel second sides, wherein the first vector direction is parallel to the first side, and the second vector direction is parallel to the second side; The angle between the first vector direction and the first lattice direction is less than or equal to 10°, and / or the angle between the second vector direction and the second lattice direction is less than or equal to 10°.

19. The two-dimensional grating structure according to claim 18, characterized in that: The angle between the first vector direction and the first lattice direction is less than or equal to 5°, and / or the angle between the second vector direction and the second lattice direction is less than or equal to 5°.

20. The two-dimensional grating structure according to claim 18, characterized in that: The first vector direction is parallel to the first lattice direction, and / or the second vector direction is parallel to the second lattice direction.

21. The two-dimensional grating structure according to claim 18, characterized in that: An angle between the first lattice direction and the second lattice direction is greater than or equal to 45° and less than or equal to 75°.

22. The two-dimensional grating structure according to claim 18, characterized in that: The first crystal unit is symmetrical with respect to the long axis, the size of the long axis of the ellipse is 2a, the size of the short axis of the ellipse is 2b, and the angle between the first lattice direction and the longitudinal direction is θ, where b=a×tanθ.

23. A diffractive optical waveguide, characterized in that: Comprising a two-dimensional grating structure according to any one of claims 1-22.

24. The diffractive optical waveguide according to claim 23, characterized in that: The diffractive optical waveguide comprises: A waveguide substrate, the waveguide substrate comprising an incoupling region and an outcoupling region; an incoupling grating, disposed on or in the waveguide substrate and located in the incoupling region, configured to couple input light into the waveguide substrate so that the input light propagates in the waveguide substrate by total reflection; An outcoupling grating is arranged on or in the waveguide substrate and located in the outcoupling region, and is used to couple at least a portion of the light propagating to the outcoupling grating out of the waveguide substrate by diffraction, wherein the outcoupling grating includes the two-dimensional grating structure.

25. The diffractive optical waveguide according to claim 24, characterized in that: The radius of the first circle and / or the second circle is smaller than or equal to half of the period of the coupling-in grating, or the radius of the first circle and / or the second circle is smaller than one third of the period of the coupling-in grating.

26. The diffractive optical waveguide according to claim 24, characterized in that: The dimension a of the semi-major axis of the ellipse is less than or equal to 1.2 times of half the period of the coupling-in grating, or the dimension a of the semi-major axis of the ellipse is less than or equal to half the period of the coupling-in grating.

27. A display device, characterized in that: include: The two-dimensional grating structure according to any one of claims 1 to 22; or A diffractive optical waveguide according to any one of claims 23 to 26.

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