Diffractive grating, optical waveguide device, and display device

Abstract

The application discloses a diffraction grating, which comprises a substrate and a plurality of microstructure units formed on the substrate and arranged periodically in two dimensions, wherein a pattern formed by the orthographic projection of the microstructure units on the substrate comprises a first closed pattern; a boundary of the first closed pattern is formed by a smooth closed curve so that the boundary has no sharp vertex; and at least a first curve segment and a second curve segment with negative radius of curvature exist on the boundary so that at least two recesses are formed on the boundary. The application also discloses an optical waveguide device and a display device comprising the diffraction grating. In the technical scheme of the application, the boundary of the microstructure unit constituting the two-dimensional diffraction grating is formed by a smooth closed curve, the boundary has no straight side and sharp vertex, and has recesses, so that the design freedom of the microstructure can be increased, the out-coupling energy can be more uniform, and the image contrast can be improved by reducing scattering.

Description

Technical Field

[0001] This invention belongs to the field of optical display technology, specifically relating to a diffraction grating, an optical waveguide device, and a display device. Background Technology

[0002] In the fields of augmented reality (AR) and mixed reality (MR), compared with display solutions such as Bird Bath (BB, semi-reflective), insect eye (off-axis reflective), and freeform prism, the optical waveguide solution is thinner and lighter and has a larger eye box, thus having a broader application prospect.

[0003] In optical waveguide design, diffractive waveguides are less complex to manufacture than array waveguides using partially reflective films. They also exhibit no dark fringes in the grating pattern when achieving two-dimensional pupil expansion, making them a more attractive option. Currently, diffractive waveguides are mainly based on one-dimensional gratings and two-dimensional gratings. Compared to fully one-dimensional grating waveguide designs, two-dimensional grating waveguide designs can achieve two-dimensional pupil expansion without a transition region, thus providing a larger eyebox and offering greater advantages. Existing two-dimensional grating-based waveguides typically consist of multiple microstructure units arranged periodically along a two-dimensional direction, forming a two-dimensional diffraction grating. These microstructure units have a columnar structure with regular cross-sections such as circles, ellipses, triangles, and parallelograms.

[0004] In the process of implementing the embodiments of the present invention, the inventors found that the two-dimensional diffraction gratings in the above-mentioned related technologies have at least the following problems: (1) The shape of the microstructure unit has few adjustable parameters and low design freedom; (2) When the microstructure unit is circular or elliptical, it is difficult to couple energy; (3) When the microstructure unit is triangular or parallelogram with straight edge boundaries, although it is beneficial to distribute energy to each order so that the energy of each field of view is more uniform, it will also bring about the problem of difficult processing. In particular, the boundaries of these shapes have straight edges and sharp vertices, which easily cause scattering and reduce image contrast. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a diffraction grating, an optical waveguide device, and a display device that can increase the degree of freedom in microstructure design, make the coupled energy more uniform, and help reduce scattering and improve image contrast.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] Substrate;

[0008] Multiple microstructure units are formed on the substrate and arranged periodically along a two-dimensional direction. The pattern formed by the orthographic projection of the microstructure units onto the substrate includes a first closed pattern; wherein,

[0009] The boundary of the first closed shape is formed by a smooth closed curve so that the boundary has no sharp vertices; wherein, there are at least a first curve segment and a second curve segment with a negative radius of curvature on the boundary so that at least two recesses are formed on the boundary.

[0010] In an optional embodiment, the absolute values ​​of the radii of curvature of the first curve segment and the second curve segment are both not less than 5 nm, and the depth of the recess is not less than 5 nm.

[0011] In an optional embodiment, at least one protrusion is also formed on the boundary; the radius of curvature of the third curve segment corresponding to the protrusion on the boundary is not less than 5 nm, and the protrusion height of the protrusion is not less than 5 nm.

[0012] In an optional configuration, the first closed figure is an axisymmetric figure or a rotationally symmetric figure.

[0013] In an optional embodiment, the first closed figure is an axisymmetric figure with at least two axes of symmetry.

[0014] In an alternative embodiment, another smooth closed curve exists within the area enclosed by the boundary to form the inner boundary of the first closed shape, and the inner boundary has no sharp vertices.

[0015] In an optional embodiment, the pattern formed by the orthographic projection of the microstructure unit onto the substrate further includes a second closed pattern of arbitrary shape.

[0016] In an optional configuration, the area of ​​the second closed shape is no greater than the area of ​​the first closed shape.

[0017] In an alternative embodiment, the second closed shape has a boundary with a similar shape to the first closed shape, and the second closed shape is a shape formed by translating and / or mirroring and / or rotating and / or scaling the first closed shape.

[0018] In an optional scheme, the period of the microstructure units arranged in the first dimension and the period of the microstructure units arranged in the second dimension are both in the range of 150nm to 2μm.

[0019] In an optional scheme, the period of the microstructure units arranged in the first dimension is not equal to the period of their arrangement in the second dimension.

[0020] In an optional scheme, in the two-dimensional direction of the periodic arrangement of the microstructure units, in the smallest parallelogram formed by two sets of shortest opposite sides with two arrangement periods, the angle of the relatively small interior angle is in the range of 40° to 90°.

[0021] In an optional embodiment, the diffraction grating is a surface relief grating or a volume holographic grating, and the thickness of the diffraction grating is in the range of 10 nm to 2 μm.

[0022] The present invention also provides an optical waveguide device, comprising:

[0023] Base;

[0024] An input grating and an output grating, and / or an intermediate grating, are disposed on the substrate; wherein,

[0025] A portion of the coupled-in grating and / or the coupled-out grating and / or the intermediate grating employs a diffraction grating as described above.

[0026] Furthermore, the present invention also provides a display device comprising the optical waveguide device described above.

[0027] The diffraction grating, optical waveguide device, and display device provided in this invention have a boundary formed by a smooth closed curve around the microstructure unit constituting the two-dimensional diffraction grating. The boundary has no straight edges or sharp vertices, and at least two curve segments with negative radii of curvature are present on the boundary, resulting in at least two recesses. This achieves the following beneficial effects:

[0028] (1) The microstructure unit with the above shape has many adjustable parameters and rich design freedom, which is conducive to the adjustment of coupling efficiency; (2) The microstructure unit with the above shape helps the light rays of each field of view to be evenly distributed at different positions of the coupling grating, making the energy / color of the coupled image more uniform; (3) The microstructure unit with the above shape does not have straight edges and sharp vertices, which can reduce scattering and improve image contrast. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the dot matrix of the diffraction grating in an embodiment of the present invention;

[0030] Figures 2a to 2g The diagram shows the shape of the microstructure unit in some specific embodiments of the present invention;

[0031] Figure 3 This is an illustration of the curve curvature of the first closed figure in an embodiment of the present invention;

[0032] Figure 4This is a structural illustration of the recessed portion of the first closed pattern in an embodiment of the present invention;

[0033] Figures 5a to 5c The diagram shows the shape of the microstructure unit in some other specific embodiments of the present invention;

[0034] Figures 6a to 6f A top view of the diffraction grating structure in some specific embodiments of the present invention is shown;

[0035] Figures 7a to 7f A cross-sectional structural schematic diagram of a diffraction grating in some specific embodiments of the present invention is shown;

[0036] Figure 8 This is a diagram illustrating the test results of the diffraction effect in a specific case of the present invention;

[0037] Figure 9 This is a diagram illustrating the test results of the diffraction effect in another specific case of the present invention;

[0038] Figure 10 This is a top view of the diffraction grating used in Comparative Case 1 of the present invention.

[0039] Figure 11 This is a diagram illustrating the test results of the diffraction effect in Comparative Case 1 of the present invention;

[0040] Figure 12 This is a top view of the diffraction grating used in Comparative Case 2 of the present invention.

[0041] Figure 13 This is a diagram illustrating the test results of the diffraction effect in Comparative Case 2 of this invention. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the present invention clearer, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Examples of these preferred embodiments are illustrated in the drawings. The embodiments of the present invention shown in and described with reference to the drawings are merely exemplary, and the present invention is not limited to these embodiments.

[0043] To make the objectives, technical solutions, and advantages of the present invention clearer, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Examples of these preferred embodiments are illustrated in the drawings. The embodiments of the present invention shown in and described with reference to the drawings are merely exemplary, and the present invention is not limited to these embodiments.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0045] It should be noted that when a component is referred to as being "set on" another component, it can be directly on the other component or indirectly on that other component.

[0046] It should also be noted that the same or similar reference numerals in the accompanying drawings of the embodiments of the present invention correspond to the same or similar components; in the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the accompanying drawings are only for illustrative purposes and should not be construed as limiting the present patent. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0047] It should also be noted that, in order to avoid obscuring the invention with unnecessary details, only the structures and / or processing steps closely related to the solution according to the invention are shown in the accompanying drawings, while other details that are not closely related to the invention are omitted.

[0048] The present invention first provides a diffraction grating, such as Figure 1 As shown, the diffraction grating 10 includes a substrate 1 and a plurality of microstructure units 2 formed on the substrate 1 and arranged periodically along a two-dimensional direction. The period of the microstructure units 2 arranged in the first dimension p1 is |p1|, and the period of the microstructure units 2 arranged in the second dimension p2 is |p2|. It should be noted that... Figure 1 The microstructure unit 2 is shown as a dot only to illustrate the array arrangement of the microstructure unit 2 on the substrate 1, and does not indicate that the microstructure unit 2 is circular in shape.

[0049] As a preferred option, see Figure 1 In the two-dimensional direction of the periodically arranged microstructure units 2, in the parallelogram 3 with the smallest area formed by two sets of shortest opposite sides in two arrangement periods, the relatively smaller interior angle α has an angle of 40° to 90°. This parallelogram 3 is the smallest repeating unit in terms of area and side length, and is therefore defined as a grating unit. In the repeating grating unit, the relatively smaller interior angle has an angle of 40° to 90°.

[0050] As a preferred option, see Figure 1The period |p1| of the microstructure unit 2 arranged in the first dimension p1 can be set to 150 nm to 2 μm, and the period |p2| of the microstructure unit 2 arranged in the second dimension p2 can be set to 150 nm to 2 μm. In a more preferred embodiment, the periods |p1| of the microstructure unit 2 arranged in the first dimension p1 and the periods |p2| of the microstructure unit 2 arranged in the second dimension p2 are not equal, that is, |p1| ≠ |p2|.

[0051] Figures 2a to 2g The structural shapes of microstructure unit 2 in some specific embodiments of the present invention are shown respectively. Specifically, as shown... Figures 2a to 2g As shown, the pattern formed by the orthographic projection of the microstructure unit 2 onto the substrate 1 includes a first closed pattern 21. The boundary of the first closed pattern 21 is formed by a smooth closed curve so that the boundary has no sharp vertices. The boundary has at least a first curve segment and a second curve segment with a negative radius of curvature so that at least two recesses 211 are formed on the boundary.

[0052] It is worth noting that when observing non-conductive microstructures, nanoscale metal particles may be sprayed onto the structure to improve accuracy. In this case, granular boundaries may appear when observing the microstructure at high magnification, with particle diameters generally between 5 nm and 150 nm. In determining the boundary, this invention requires at least one microstructure unit to be present in the field of view during observation. If the radius of curvature of a curve is less than 5 nm during observation, it is determined to be a sharp vertex.

[0053] The radius of curvature of the curve constituting the first closed figure 21 is explained in detail below:

[0054] See Figure 3 Fit a circular arc to any segment of the curve, and draw a straight arrow with its starting point at the tangent point and pointing towards the center of the circle: when the straight arrow points into the interior of the first closed figure 21, the curvature is defined as a positive value, such as... Figure 3 The middle point points to r2 of the center O2. Even if the radius of curvature is large, the curvature is still positive if the center of the circle is outside the first closed figure 21 (the straight arrow passes through the interior of the first closed figure 21 and then points outward). Figure 3 The middle point points to r3 at the center O3; when the arrow points to the outside of the first closed figure 21, the curvature is defined as a negative value, such as... Figure 3 The middle pointer points to r1 at the center O1.

[0055] As a preferred option, see Figure 3 and Figure 4In the first closed pattern 21, the absolute value of the radius of curvature of the first curve segment and the second curve segment forming the recess 211 is not less than 5 nm (more preferably in the range of 5 nm to 1 μm), and the recess depth d1 of the recess 211 is not less than 5 nm. Further, the radii of curvature of the first curve segment and the second curve segment can be the same or different. It is worth noting that when the magnification is very low, i.e., when the field of view is large, for example, when there are 100 microstructure units in the field of view, the area near the 5 nm recess is approximately a straight edge; when the magnification is very high, for example, when only one microstructure unit is visible in the field of view, the recess can be observed.

[0056] Based on the diffraction grating 10 as described above, the microstructure unit 2 therein is projected onto the substrate 1 to form a first closed pattern 21. There are no sharp vertices on its boundary and there is a recess 211. Thus, there is a concave edge on the boundary of the microstructure unit 2. The concave edge, compared with the flat edge or the convex edge, can effectively improve the uniformity of pupil expansion in different directions and improve the uniformity of the final image viewed by the human eye.

[0057] In other embodiments, in the first closed pattern 21, in addition to the recessed portion 211 as described above, at least one protrusion is also formed on the boundary. Preferably, the radius of curvature of the third curve segment corresponding to the protrusion on the boundary is not less than 5 nm (more preferably in the range of 5 nm to 1 μm), and the protrusion height is not less than 5 nm. Thus, the protrusion, as a supplement to the recessed portion, increases design freedom and can further improve the uniformity of pupil dilation in different directions.

[0058] In some other embodiments, within the region enclosed by the boundary of the first closed pattern 21, there is another smooth closed curve forming the inner boundary of the first closed pattern, and the inner boundary has no sharp vertices. It can be understood that the first closed pattern has a punched-out region, preferably with a maximum diameter of not less than 5 nm.

[0059] In a preferred embodiment, the first closed figure 21 is an axisymmetric figure or a rotationally symmetric figure. For example, such as Figures 2a to 2d The first closed figure 21 shown is an axisymmetric figure, such as Figure 2f The first closed figure 21 shown is a rotationally symmetric figure, as follows: Figure 2e The first closed figure 21 shown is both an axisymmetric figure and a rotationally symmetric figure.

[0060] In a more preferred embodiment, the first closed figure 21 is an axisymmetric figure with at least two axes of symmetry. For example, such as Figures 2a to 2c as well as Figure 2eThe first closed figure 21 shown is both vertically symmetrical and horizontally symmetrical.

[0061] Based on the preferred embodiment, the boundary pattern of the microstructure unit 2 is a symmetrical pattern, which can reduce the difficulty of the fabrication process and further improve the uniform distribution of light in each field of view.

[0062] Figures 5a to 5c The structural shapes of the microstructure unit 2 in some other specific embodiments of the present invention are shown. In some other specific embodiments, the pattern formed by the orthographic projection of the microstructure unit 2 onto the substrate 1 may include a second closed pattern 22 in addition to the first closed pattern 21 described above. The second closed pattern 22 can be of any shape, and can be a pattern enclosed by one or more straight line segments and / or one or more curved line segments. For example, it can be a circle, ellipse, sector, ring, or polygon, etc.

[0063] In some specific embodiments, the boundary of the second closed shape 22 is also formed by a smooth closed curve so that the boundary has no sharp vertices. The boundary has at least a first curve segment and a second curve segment with negative radii of curvature, resulting in at least two recesses on the boundary. Figure 5a As shown. In a preferred embodiment, the second closed shape 22 can be a boundary with a similar shape to the first closed shape 21. The second closed shape 22 is a shape formed by translating and / or mirroring and / or rotating and / or scaling the first closed shape 21, such as... Figure 5b As shown. In some other specific embodiments, the second closed shape 22 can also be a boundary with a completely different shape from the first closed shape 21, such as... Figure 5c As shown, the second closed shape 22 is a square.

[0064] Figures 6a to 6f A top view of a diffraction grating according to some specific embodiments of the present invention is shown. Figure 6a What is shown is as follows Figure 2a The diffraction grating structure corresponding to the microstructure unit shown is Figure 6b What is shown is as follows Figure 2c The diffraction grating structure corresponding to the microstructure unit shown is Figure 6c What is shown is as follows Figure 2e The diffraction grating structure corresponding to the microstructure unit shown is Figure 6e What is shown is as follows Figure 5a The diffraction grating structure corresponding to the microstructure unit shown is Figure 6f What is shown is as follows Figure 5c The diffraction grating structure corresponding to the microstructure unit shown. For example... Figures 6a to 6fAs shown, the microstructure units 2 are arranged at periodic intervals along the two-dimensional direction and are not connected to each other when arranged in a two-dimensional array.

[0065] The diffraction grating described above in this embodiment of the invention has a boundary formed by a smooth closed curve surrounding the microstructure unit constituting the two-dimensional diffraction grating. There are no straight edges or sharp vertices on the boundary, and there are at least a first curve segment and a second curve segment with a negative radius of curvature on the boundary, resulting in at least two recesses on the boundary. The microstructure unit based on the above shape structure has many adjustable parameters, rich design freedom, which is conducive to the adjustment of coupling efficiency and helps to achieve uniform distribution of the coupled light rays from each field of view at different positions of the coupling grating, making the energy / color of the coupled image more uniform. Furthermore, since there are no straight edges or sharp vertices, light scattering can be reduced, thereby improving image contrast.

[0066] In this embodiment of the invention, the diffraction grating 10 described above can be implemented as a surface relief grating or as a volume holographic grating. Specifically, the thickness of the grating is between 10 nm and 2 μm. Figures 7a to 7f Cross-sectional views of diffraction gratings in some specific embodiments of the present invention are shown. Among them, Figure 7a This is a structural diagram of an embossed grating with a straight groove envelope. Figure 7b This is a structural diagram of an embossed grating with a helical tooth envelope. Figure 7c A structural diagram of an embossed grating with a shimmering envelope. Figure 7d A structural diagram of a relief grating enveloping a stepped surface. Figure 7e A structural diagram of a relief grating with curved envelope. Figure 7f A structural diagram of a volumetric holographic grating.

[0067] In this embodiment of the invention, the diffraction grating 10 is composed of at least two optical materials with different optical properties, including refractive index, and / or absorption properties, and / or birefringence. Therefore, if the grating is in air, air is also considered an optical material. For materials that do not exhibit birefringence, their optical properties can be comprehensively described by their refractive index and absorption properties. When the two optical materials differ primarily in their refractive index, the grating can be divided into a high-refractive-index portion and a low-refractive-index portion. See also... Figures 7a to 7f The diffraction grating 10 includes a high refractive index portion 101 and a low refractive index portion 102. It is worth noting that this illustration can also be used to distinguish between two optical materials with different absorption characteristics and / or different birefringence characteristics.

[0068] For the surface-embossed grating, the microstructure unit 2 region is preferably formed at half the thickness of the grating. In some specific embodiments, the microstructure unit 2 region in the diffraction grating 10 is set as the high refractive index portion 101, and the other regions surrounding the microstructure unit 2 region are set as the low refractive index portion 102, wherein the refractive index of the high refractive index portion 101 is between 1.5 and 3.0, and the refractive index of the low refractive index portion 102 is between 1.0 and 1.5. In other specific embodiments, the microstructure unit 2 region in the diffraction grating 10 is set as the low refractive index portion 102, while the other regions surrounding the microstructure unit 2 region are set as the high refractive index portion 101. This can be understood as follows: Figures 6a to 6f In the structure of each diffraction grating 10 shown, the dark area can be set as the high refractive index part, or the light area can be set as the high refractive index part.

[0069] For a volume holographic grating with a gradually changing refractive index, the microstructure unit 2 region is preferably located at half the thickness of the grating. Using the contour line corresponding to the mean refractive index of the optical material as the boundary, the portion with a refractive index greater than the mean refractive index is defined as the high refractive index portion, and the portion with a refractive index less than the mean refractive index is defined as the low refractive index portion. Specifically, the microstructure unit 2 region, which is the portion enclosed by the contour line corresponding to the mean refractive index of the optical material, can be designated as either a high refractive index portion or a low refractive index portion.

[0070] Based on the diffraction grating provided in the above embodiments, this invention also provides an optical waveguide device. The optical waveguide device includes a substrate and a coupling grating and a coupling grating disposed on the substrate. The coupling grating is used to couple an external light beam into the substrate, and the coupling grating is used to couple the light beam out of the substrate. In a further embodiment, the optical waveguide device may further include an intermediate grating. Wherein, part or all of the region of the coupling grating and / or the coupling grating and / or the intermediate grating employs the diffraction grating provided in this invention. It should be noted that when the diffraction grating provided in this invention is applied to the optical waveguide device, the substrate of the optical waveguide device can be directly reused as the substrate of the diffraction grating; that is, the substrate of the optical waveguide device and the substrate of the diffraction grating are integral.

[0071] In an optional embodiment, in the optical waveguide device, the diffraction grating has one or more layers of coating on the side near and / or away from the human eye, and / or the substrate has one or more layers of coating on the side without the grating. Further, the substrate may be a multilayer structure, and the diffraction grating may be a multilayer structure.

[0072] Furthermore, the present invention also provides a display device, such as an augmented reality (AR) display device or a mixed reality (MR) display device. The display device includes a projection device and an optical waveguide device as provided in the above embodiments. The projection device generates image rays (rays carrying image information). The image rays are coupled into the substrate by a coupling grating, transmitted through the substrate to a coupling grating, coupled out of the substrate by the coupling grating, and transmitted to the human eye, enabling the human eye to observe the corresponding image information.

[0073] The embodiments of the present invention also included the following comparative tests:

[0074] (1) Example 1: Based on the optical waveguide device described in this embodiment of the invention, the coupling grating adopts the diffraction grating provided in this embodiment of the invention, specifically adopting as follows: Figure 6a The diffraction grating with the structure shown was used, and then the diffraction effect of the coupled grating was tested. The test results are as follows. Figure 8 As shown.

[0075] (2) Example 2: In the optical waveguide device described in the embodiment of the present invention, the coupling grating adopts the diffraction grating provided in the embodiment of the present invention, specifically adopting as follows: Figure 6b The diffraction grating with the structure shown was used, and then the diffraction effect of the coupled grating was tested. The test results are as follows. Figure 9 As shown.

[0076] (3) Comparative Example 1: Referring to the prior art, the coupling grating in the optical waveguide device of step (1) is adopted as follows: Figure 10 The diffraction grating with the structure shown has circular boundaries for its microstructure units. The diffraction effect of the coupling grating in Comparative Example 1 was then tested, and the results are as follows: Figure 11 As shown.

[0077] (4) Comparative Example 2: Referring to the prior art, the coupling grating in the optical waveguide device of step (1) is adopted as follows: Figure 12 The diffraction grating with the structure shown has elliptical boundaries for its microstructure units. The diffraction effect of the coupling grating in Comparative Example 2 was then tested, and the results are as follows: Figure 13 As shown.

[0078] It should be noted that, Figure 10 , Figure 12 Only nine microstructures are shown, but in practice, a large-area array of microstructures is used for testing.

[0079] For optical waveguides using two-dimensional diffraction gratings, low pupil expansion efficiency and high coupling efficiency can easily lead to unevenness in the central bright fringe. Therefore, the quality of a two-dimensional diffraction grating can be evaluated using both pupil expansion efficiency and coupling efficiency. Two-dimensional gratings suitable for optical waveguides should have the highest possible pupil expansion efficiency while maintaining a relatively low coupling efficiency. Based on the above test results: Based on existing technology, using... Figure 10 and Figure 12 The existing diffraction grating structure shown is as follows: Figure 11 and Figure 13 The diffraction effect diagram shows that high efficiency in the two pupil expansion directions and low efficiency in the coupling direction cannot be satisfied simultaneously, thus easily leading to uneven visual effects such as a central bright stripe. The diffraction grating based on this invention, however, is as follows... Figure 8 and Figure 9 The diffraction effect diagram shows that the diffraction efficiency in both pupil directions is improved, while the coupling efficiency is also moderate, which is conducive to achieving a uniform visual effect and higher image contrast.

[0080] In summary, the diffraction grating, optical waveguide device, and display device provided by the present invention as described in the above embodiments have a boundary formed by a smooth closed curve surrounding the microstructure unit constituting the two-dimensional diffraction grating. There are no straight edges or sharp vertices on the boundary, and there are at least a first curve segment and a second curve segment with a negative radius of curvature on the boundary, which forms at least two recesses on the boundary. This increases the degree of freedom in microstructure design, makes the coupled energy more uniform, and helps to reduce scattering and improve image contrast.

[0081] Although the invention has been shown and described with reference to specific embodiments, those skilled in the art will understand that various changes in form and detail may be made herein without departing from the spirit and scope of the invention as defined by the claims and their equivalents.

Claims

1. A diffraction grating, characterized in that, include: Substrate; Multiple microstructure units are formed on the substrate and arranged periodically along a two-dimensional direction. The pattern formed by the orthographic projection of the microstructure units onto the substrate includes a first closed pattern; wherein, The boundary of the first closed shape is formed by a smooth closed curve so that the boundary has no sharp vertices; wherein, there are at least a first curve segment and a second curve segment with negative radii of curvature on the boundary so that at least two recesses are formed on the boundary; the absolute values ​​of the radii of curvature of the first curve segment and the second curve segment are both not less than 5nm, and the recess depth of the recess is not less than 5nm; Within the area enclosed by the boundary, there exists another smooth closed curve to form the inner boundary of the first closed shape, and the inner boundary has no sharp vertices.

2. The diffraction grating according to claim 1, characterized in that, At least one protrusion is also formed on the boundary; the radius of curvature of the third curve segment corresponding to the protrusion on the boundary is not less than 5 nm, and the protrusion height of the protrusion is not less than 5 nm.

3. The diffraction grating according to any one of claims 1-2, characterized in that, The first closed figure is an axisymmetric figure or a rotationally symmetric figure.

4. The diffraction grating according to claim 3, characterized in that, The first closed figure is an axisymmetric figure with at least two axes of symmetry.

5. The diffraction grating according to claim 1, characterized in that, The pattern formed by the orthographic projection of the microstructure unit onto the substrate also includes a second closed pattern of arbitrary shape.

6. The diffraction grating according to claim 5, characterized in that, The area of ​​the second closed figure is not greater than the area of ​​the first closed figure.

7. The diffraction grating according to claim 6, characterized in that, The second closed figure has a boundary with a similar shape to the first closed figure, and the second closed figure is a figure formed by translating and / or mirroring and / or rotating and / or scaling the first closed figure.

8. The diffraction grating according to claim 1, characterized in that, The period of the microstructure units arranged in the first dimension and the period of their arrangement in the second dimension are both in the range of 150 nm to 2 μm.

9. The diffraction grating according to claim 8, characterized in that, The period of the microstructure units arranged in the first dimension is not equal to the period of their arrangement in the second dimension.

10. The diffraction grating according to claim 1, characterized in that, In the two-dimensional direction of the periodic arrangement of the microstructure units, in the smallest parallelogram formed by two sets of shortest opposite sides with two arrangement periods, the relatively small interior angle is in the range of 40° to 90°.

11. The diffraction grating according to claim 1, characterized in that, The diffraction grating is a surface relief grating or a volume holographic grating, and the thickness of the diffraction grating is in the range of 10nm~2μm.

12. An optical waveguide device, characterized in that, include: Base; An input grating and an output grating, and / or an intermediate grating, are disposed on the substrate; wherein, A portion of the coupled-in grating and / or the coupled-out grating and / or the intermediate grating employs a diffraction grating as described in any one of claims 1-11.

13. A display device, characterized in that, Includes the optical waveguide device as described in claim 12.

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