Diffraction gratings, optical waveguide devices, and display devices

Abstract

The present invention relates to a diffraction grating (10), an optical waveguide device, and a display device including the diffraction grating (10). The diffraction grating (10) comprises a substrate (1) and a plurality of microstructure units (2) formed on the substrate (1) and periodically arranged along a two-dimensional direction, the figure formed by orthogonal projection onto the substrate (1) including a first closed figure (21), the boundary of the first closed figure (21) being formed by a single smooth closed curve with no sharp vertices, and the boundary including at least one first curve segment with a negative radius of curvature to form at least one recess (211). This increases the degree of freedom in microstructure design, makes the outgoing coupled energy more uniform, and contributes to reducing scattering and improving image contrast.

Description

[Technical Field]

[0001] This application is in the field of optical displays, and more particularly, diffraction gratings, optical waveguide devices, and display devices. [Background technology]

[0002] In the fields of augmented reality (AR) and mixed reality (MR), compared to display modes such as Bird Bath (BB, semi-reflective semi-transmissive), insect's eye (off-axis reflective), and freeform prism, the optical waveguide mode is lighter and has a larger eyebox, and is therefore expected to be more widely applied.

[0003] Among optical waveguide designs, diffractive optical waveguides have attracted more attention because they are less difficult to manufacture and do not have grid-like dark stripes when achieving two-dimensional pupil expansion compared to array optical waveguides using partial reflection films. Currently, diffractive optical waveguides are primarily classified into optical waveguide designs based on one-dimensional gratings and two-dimensional gratings. Compared to optical waveguide designs based on completely one-dimensional gratings, optical waveguide designs based on two-dimensional gratings have the advantage of being able to achieve two-dimensional pupil expansion without the need for a folding region, thereby providing a larger eyebox. In conventional optical waveguides based on two-dimensional gratings, the two-dimensional diffraction grating is typically composed of multiple microstructure units periodically arranged along a two-dimensional direction. The microstructure units form a columnar structure, and their cross sections have regular shapes such as circles, ellipses, triangles, and parallelograms.

[0004] During the research and development process, the inventors discovered that the two-dimensional diffraction gratings in the above-mentioned related art have at least the following problems: (1) There are few adjustable parameters for the shape of the microstructure units, resulting in low design freedom; (2) If the microstructure units are circular or elliptical, it is difficult to couple energy out; (3) If the microstructure units have straight-sided boundaries, such as triangles or parallelograms, this is advantageous for distributing energy to each level so that the energy of the light rays in each field of view is uniform, but it also causes problems such as difficulty in processing, especially since the boundaries of these shapes have straight sides and sharp vertices, which are prone to scattering and reduce image contrast. Summary of the Invention [Problem to be solved by the invention]

[0005] In view of the above problems, the present application provides a diffraction grating, an optical waveguide device, and a display device that can increase the degree of freedom in microstructure design, make the outgoing coupled energy more uniform, reduce scattering, and contribute to improving image contrast. [Means for solving the problem]

[0006] In order to achieve the above object, the present application provides: A substrate; a plurality of microstructure units formed on the substrate and periodically arranged at intervals along a two-dimensional direction, the microstructure units including a first closed figure in a figure formed by orthogonal projection onto the substrate; The boundary of the first closed figure is formed by a single smooth closed curve so as to have no sharp vertices, and the boundary has at least one first curve segment with a negative radius of curvature so as to form at least one concave portion. A diffraction grating technology is employed.

[0007] In a preferred embodiment, the absolute value of the radius of curvature of the first curved line segment is 5 nm or more, and the recess depth of the recess is 5 nm or more.

[0008] In a preferred embodiment, the boundary also has at least one protrusion formed thereon.

[0009] In a preferred embodiment, the radius of curvature corresponding to the second curved line segment on which the protrusion is formed at the boundary is 5 nm or more, and the protrusion height of the protrusion is 5 nm or more.

[0010] In a preferred embodiment, the first closed figure is an asymmetric figure.

[0011] In a preferred embodiment, within the region enclosed by the boundary, there is also another smooth closed curve so as to form an inner boundary of the first closed figure that has no sharp vertices.

[0012] In a preferred embodiment, the figure formed by orthogonal projection of the microstructure unit onto the substrate further includes a second closed figure having an arbitrary shape.

[0013] In a preferred embodiment, the area of ​​the second closed figure is equal to or less than the area of ​​the first closed figure.

[0014] In a preferred embodiment, the second closed figure has a boundary of a similar shape to that of the first closed figure, and the second closed figure is a figure formed from the first closed figure by at least one of translation, reflection, rotation, and reduction.

[0015] In a preferred embodiment, the arrangement period of the microstructure units in the first dimension and the arrangement period in the second dimension are both within the range of 150 nm to 2 μm.

[0016] In a preferred embodiment, the arrangement period of the microstructure units in the first dimension is not equal to the arrangement period in the second dimension.

[0017] In a preferred embodiment, in the two-dimensional direction in which the microstructure units are periodically arranged, the relatively smallest interior angle of the smallest parallelogram formed by two pairs of shortest opposite sides corresponding to two arrangement periods is within the range of 40° to 90°.

[0018] In a preferred embodiment, the diffraction grating is a surface relief grating or a volume hologram grating, and the thickness of the diffraction grating is in the range of 10 nm to 2 μm.

[0019] In a preferred embodiment, the diffraction grating includes at least two optical material components having different optical properties, the optical properties including at least one of refractive index, absorption property, and birefringence property.

[0020] In a preferred aspect, in the case of the surface relief grating, the region of the microstructure unit is formed at half the thickness of the grating, the region of the microstructure unit in the diffraction grating is configured as a high refractive index portion and other regions surrounding the region of the microstructure unit are configured as low refractive index portions, or the region of the microstructure unit in the diffraction grating is configured as a low refractive index portion and other regions surrounding the region of the microstructure unit are configured as high refractive index portions, and in the case of a volume hologram grating with a gradually changing refractive index, the region of the microstructure unit corresponds to half the thickness of the grating and is the portion surrounded by a contour line corresponding to the average refractive index of the optical material.

[0021] In this application, The base and At least one of an input coupling grating, an output coupling grating, and an intermediate grating provided on the base; The above-described diffraction grating is used in a partial region of at least one of the input coupling grating, the output coupling grating, and the intermediate grating. An optical waveguide device is also provided.

[0022] In a preferred embodiment, one or more coating layers are present on at least one of the sides of the diffraction grating that are closer to the human eye and the side that is farther from the human eye, and one or more coating layers are present on the side that does not have the base grating.

[0023] In a preferred embodiment, the base has a multilayer structure and the diffraction grating has a multilayer structure.

[0024] Furthermore, the present application also provides a display device including the above-mentioned optical waveguide device. [Effects of the Invention]

[0025] In the diffraction grating, optical waveguide device, and display device according to the embodiments of the present application, the boundary of the microstructure unit constituting the two-dimensional diffraction grating is formed by a single smooth closed curve, and the boundary has no straight sides or sharp vertices. The boundary also has at least one first curve segment with a negative radius of curvature, forming at least one recess. This provides the following beneficial effects: (1) The microstructure unit with the above-described shape has many adjustable parameters, allowing for greater design freedom and favorable adjustment of the out-coupling efficiency; (2) The microstructure unit with the above-described shape contributes to uniformly distributing the incident-coupled light rays of each field of view at different positions on the out-coupling grating, so that the energy / color of the out-coupled image is more uniform; and (3) The microstructure unit with the above-described shape has no straight sides or sharp vertices, reducing scattering and improving image contrast. [Brief explanation of the drawings]

[0026] [Figure 1] FIG. 1 is a dot matrix diagram of a diffraction grating according to one or more embodiments. [Figure 2a] 1A-1D illustrate illustrations of shapes of microstructure units in some illustrative embodiments according to one or more embodiments. [Figure 2b] 1A-1D illustrate illustrations of shapes of microstructure units in some illustrative embodiments according to one or more embodiments. [Figure 2c] 1A-1D illustrate illustrations of shapes of microstructure units in some illustrative embodiments according to one or more embodiments. [Figure 2d] 1A-1D illustrate illustrations of shapes of microstructure units in some illustrative embodiments according to one or more embodiments. [Figure 2e] 1A-1D illustrate illustrations of shapes of microstructure units in some illustrative embodiments according to one or more embodiments. [Figure 3] 1 is an illustration of the curvature of a curve of a first closed figure according to one or more embodiments. [Figure 4] 10 is a structural illustration of a recessed portion of a first closed figure according to one or more embodiments. [Figure 5a] 10A-10C illustrate illustrations of shapes of microstructure units in some alternative exemplary embodiments according to one or more embodiments. [Figure 5b] 10A-10C illustrate illustrations of shapes of microstructure units in some alternative exemplary embodiments according to one or more embodiments. [Figure 5c] 10A-10C illustrate illustrations of shapes of microstructure units in some alternative exemplary embodiments according to one or more embodiments. [Figure 5d] 10A-10C illustrate illustrations of shapes of microstructure units in some alternative exemplary embodiments according to one or more embodiments. [Figure 6a] 1A-1D illustrate top view structural schematics of diffraction gratings in some specific embodiments according to one or more embodiments. [Figure 6b] 1A-1D illustrate top view structural schematics of diffraction gratings in some specific embodiments according to one or more embodiments. [Figure 6c] 1A-1D illustrate top view structural schematics of diffraction gratings in some specific embodiments according to one or more embodiments. [Figure 6d] 1A-1D illustrate top view structural schematics of diffraction gratings in some specific embodiments according to one or more embodiments. [Figure 6e] 1A-1D illustrate top view structural schematics of diffraction gratings in some specific embodiments according to one or more embodiments. [Figure 7a] 1A-1D illustrate cross-sectional structural schematics of diffraction gratings in some specific aspects according to one or more embodiments. [Figure 7b] 1A-1D illustrate cross-sectional structural schematics of diffraction gratings in some specific aspects according to one or more embodiments. [Figure 7c] 1A-1D illustrate cross-sectional structural schematics of diffraction gratings in some specific aspects according to one or more embodiments. [Figure 7d]1A-1D illustrate cross-sectional structural schematics of diffraction gratings in some specific aspects according to one or more embodiments. [Figure 7e] 1A-1D illustrate cross-sectional structural schematics of diffraction gratings in some specific aspects according to one or more embodiments. [Figure 7f] 1A-1D illustrate cross-sectional structural schematics of diffraction gratings in some specific aspects according to one or more embodiments. [Figure 8a] 1A-1C illustrate schematic top view structures of diffraction gratings and test results of diffraction effects in two specific cases according to one or more embodiments. [Figure 8b] 1A-1C illustrate schematic top view structures of diffraction gratings and test results of diffraction effects in two specific cases according to one or more embodiments. [Figure 8c] 1A-1C illustrate schematic top view structures of diffraction gratings and test results of diffraction effects in two specific cases according to one or more embodiments. [Figure 8d] 1A-1C illustrate schematic top view structures of diffraction gratings and test results of diffraction effects in two specific cases according to one or more embodiments. [Figure 9] FIG. 1 is a schematic diagram of a top surface structure of a diffraction grating employed in Comparative Example 1 according to one or more embodiments. [Figure 10] 10 illustrates test results of the diffraction effect of Comparative Example 1 according to one or more embodiments. [Figure 11] FIG. 10 is a schematic diagram of a top surface structure of a diffraction grating employed in Comparative Example 2 according to one or more embodiments. [Figure 12] 10 illustrates test results of the diffraction effect of Comparative Example 2 according to one or more embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0027] In order to clarify the objectives, technical aspects and advantages of the present application, the following detailed description of specific embodiments of the present application will be given in conjunction with the drawings. Examples of these preferred embodiments are shown in the drawings. The embodiments of the present application shown in and described by the drawings are merely exemplary, and the present application is not limited to these embodiments.

[0028] 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. In this document, the terminology used in the specification of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application.

[0029] It should be noted that when a component is said to be "mounted on" another component, the component may be directly on the other component or indirectly on the other component.

[0030] Furthermore, in the drawings of the embodiments of the present application, the same or similar symbols correspond to the same or similar parts, and in the description of the present application, the orientations or positional relationships indicated by the terms "up," "down," "left," "right," etc. are based on the orientations or positional relationships shown in the drawings, and are merely intended to facilitate and simplify the description of the present application, and do not indicate or suggest that such devices or elements necessarily have a specific orientation, or must be configured and operated in a specific orientation. Therefore, it should be understood that the terms describing the positional relationships in the drawings are merely for illustrative purposes and should not be understood as limiting the present patent, and that a person skilled in the art may understand the specific meaning of the above terms according to specific circumstances.

[0031] Here again, to avoid obscuring the present application with unnecessary detail, the drawings show only structures and / or processing steps closely related to aspects of the present application, and omit other details less relevant to the present application.

[0032] In an embodiment of the present application, a diffraction grating is first provided. As shown in Fig. 1, the diffraction grating 10 includes a substrate 1 and a plurality of microstructure units 2 formed on the substrate 1 and periodically arranged along two-dimensional directions. Here, the arrangement period of the microstructure units 2 in the first dimensional direction p1 is |p1|, and the arrangement period of the microstructure units 2 in the second dimensional direction p2 is |p2|. Note that the microstructure units 2 are shown as dots in Fig. 1 only to explain the array arrangement structure of the microstructure units 2 on the substrate 1, and do not mean that the microstructure units 2 are circular.

[0033] 1, in the two-dimensional direction in which the microstructure units 2 are periodically arranged, the parallelogram 3 having the smallest area, which is formed by two pairs of shortest opposite sides corresponding to two arrangement periods, has a relatively small interior angle α of 40° to 90°. Since the parallelogram 3 is the repeating unit having the smallest area and the shortest side length, it is defined as a lattice unit, and the relatively small interior angle α of the repeated lattice unit is 40° to 90°.

[0034] 1, the arrangement period |p1| of the microstructure units 2 in the first dimensional direction p1 can be 150 nm to 2 μm, and the arrangement period |p2| of the microstructure units 2 in the second dimensional direction p2 can be 150 nm to 2 μm. In a more preferred embodiment, the arrangement period |p1| of the microstructure units 2 in the first dimensional direction p1 and the arrangement period |p2| of the microstructure units 2 in the second dimensional direction p2 are not equal, i.e., |p1|≠|p2|.

[0035] 2a to 2e respectively show the structural shapes of the microstructure unit 2 in some specific embodiments of the present application. Specifically, as shown in Fig. 2a to 2e, the figure formed by orthogonal projection of the microstructure unit 2 onto the substrate 1 includes a first closed figure 21, the boundary of the first closed figure 21 being formed by surrounding it with a single smooth closed curve so as to have no sharp vertices, and the boundary has at least a first curve segment with a negative radius of curvature so as to form at least one recessed portion 211.

[0036] It should be noted that when observing a non-conductive microstructure, nanoscale metal particles may be sprayed onto the structure to improve accuracy. In this case, when observing the microstructure at high magnification, a particle-like boundary may appear, and the particle diameter is generally between 5 nm and 150 nm. In this application, when determining the boundary, at least one of the microstructure units is present in the field of view during observation, and if the radius of curvature of one segment of the curve during observation is less than 5 nm, it is determined to be a sharp apex.

[0037] Here, the radius of curvature of the curve that constitutes the first closed figure 21 will be specifically explained as follows.

[0038] Referring to Fig. 3, a circular arc is fitted to any segment of the curve, and a straight arrow is created starting from the tangent point and pointing to the center of the circle. When the straight arrow points to the inside of the first closed figure 21, as in r2 pointing to the center O2 in Fig. 3, the curvature is defined as a positive value. When the radius of curvature is large and the center of the circle is outside the first closed figure 21 (when the straight arrow passes through the inside of the first closed figure 21 and then points to the outside), as in r3 pointing to the center O3 in Fig. 3, the curvature is also positive. When the arrow points to the outside of the first closed figure 21, as in r1 pointing to the center O1 in Fig. 3, the curvature is defined as a negative value.

[0039] 4, in the first closed figure 21, the absolute value of the radius of curvature of the first curved line segment forming the depression 211 is 5 nm or more (more preferably in the range of 5 nm to 1 μm), and the depression depth d1 of the depression 211 is 5 nm or more. It should be noted that when the magnification is very low, i.e., when the field of view is very wide, for example, there are 100 of the microstructure units in the field of view, and the vicinity of a 5 nm depression is approximately a straight edge, while when the magnification is very high, for example, only one of the microstructure units can be seen in the field of view, and the depression can be observed.

[0040] Based on the above-mentioned diffraction grating 10, a first closed figure 21 is formed by orthogonally projecting the microstructure unit 2 therein onto the substrate 1, and since there is no sharp vertex at its boundary and there is the recessed portion 211, the boundary of the microstructure unit 2 has a concave side, which can effectively improve the uniformity of pupil expansion in different directions compared with a horizontal side or a convex side, and ultimately improve the uniformity of the image seen by the human eye.

[0041] In some other embodiments, in addition to having the above-described recessed portion 211, the first closed figure 21 also has at least one protruding portion formed at the boundary. In a preferred embodiment, the radius of curvature corresponding to the second curved line segment at the boundary where the protruding portion is formed is 5 nm or more (more preferably within a range of 5 nm to 1 μm), and the protruding height of the protruding portion is 5 nm or more. Therefore, the protruding portion complements the recessed portion, increasing the degree of freedom in design and further improving the uniformity of pupil dilation in different directions.

[0042] In some other embodiments, the first closed figure 21 also has another smooth closed curve within the area enclosed by the boundary, so as to form an inner boundary of the first closed figure without sharp vertices. The first closed figure may be understood to have a perforated region, and preferably, the maximum diameter of the perforated region is 5 nm or more.

[0043] In a more preferred embodiment, the first closed figure 21 is an asymmetric figure such as that shown in FIG. 2d.

[0044] 5a to 5d respectively show the structural shape of a microstructure unit 2 in some other specific embodiments of the present application. In some other specific embodiments, the figure formed by orthogonal projection of the microstructure unit 2 onto the substrate 1 may include a second closed figure 22 in addition to the first closed figure 21 described above. The second closed figure 22 may be a figure of any shape, and may be a figure surrounded by one or more straight line segments and / or one or more curved line segments. For example, it may be a circle, an ellipse, a sector, a ring, a polygon, etc., and as shown in FIG. 5d, the second closed figure 22 is a rectangle.

[0045] In a preferred embodiment, the second closed figure 22 may have a boundary of a similar shape to that of the first closed figure 21, and the second closed figure 22 is a figure formed after translation and / or reflection and / or rotation and / or reduction of the first closed figure 21, as shown in Figures 5a to 5c, so that the second closed figure 22 also does not have sharp vertices.

[0046] 6a to 6e show top views of diffraction gratings in some specific embodiments of the present application, where Fig. 6a shows a diffraction grating structure corresponding to the microstructure unit shown in Fig. 2a, Fig. 6b shows a diffraction grating structure corresponding to the microstructure unit shown in Fig. 5a, Fig. 6c shows a diffraction grating structure corresponding to the microstructure unit shown in Fig. 5b, Fig. 6d shows a diffraction grating structure corresponding to the microstructure unit shown in Fig. 5c, and Fig. 6e shows a diffraction grating structure corresponding to the microstructure unit shown in Fig. 5d. As shown in Fig. 6a to 6e, the microstructure units 2 are periodically spaced apart along two-dimensional directions and are not connected to each other when arranged in a two-dimensional array.

[0047] In the above-mentioned diffraction grating of the embodiment of the present 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 sides and no sharp vertices, and at least one recess is formed on the boundary. Based on the microstructure unit of the above-mentioned shape structure, it has many adjustable parameters and a wide design freedom, which is advantageous for adjusting the out-coupling efficiency and contributes to uniformly distributing the incident-coupled light rays of each field of view at different positions on the out-coupling grating, so that the energy / color of the out-coupling image is more uniform. In addition, the absence of straight sides and no sharp vertices can reduce light scattering and improve image contrast.

[0048] In the present embodiment, the diffraction grating 10 may be realized in the form of a surface relief grating or a volume hologram grating. Specifically, the grating thickness is between 10 nm and 2 μm. Figures 7a to 7f show cross-sectional views of diffraction gratings in some specific embodiments of the present application. Here, Figure 7a illustrates the structure of a relief grating with a straight groove envelope, Figure 7b illustrates the structure of a relief grating with a beveled envelope, Figure 7c illustrates the structure of a relief grating with a blazed envelope, Figure 7d illustrates the structure of a relief grating with a stepped envelope, Figure 7e illustrates the structure of a relief grating with a curved envelope, and Figure 7f illustrates the structure of a volume hologram grating.

[0049] In the present embodiment, the diffraction grating 10 is composed of at least two optical materials with different optical properties, including refractive index, absorption, and / or birefringence. Therefore, when the grating is in air, air is also considered an optical material. For materials without birefringence, the optical properties of the material may be comprehensively described by refractive index and absorption. When the two optical materials differ primarily in refractive index, the grating may be divided into a high refractive index portion and a low refractive index portion. Referring to Figures 7a to 7f, the diffraction grating 10 includes a high refractive index portion 101 and a low refractive index portion 102. It should be noted that this illustration may be used to distinguish between two optical materials with different absorption and / or birefringence properties.

[0050] In the case of the surface relief grating, the region of the microstructure unit 2 is preferably formed at a location halfway through the grating thickness. In some specific embodiments, the region of the microstructure unit 2 in the diffraction grating 10 is configured as the high refractive index portion 101, and other regions surrounding the region of the microstructure unit 2 are configured as the low refractive index portion 102, with the refractive index of the high refractive index portion 101 being between 1.5 and 3.0, and the refractive index of the low refractive index portion 102 being between 1.0 and 1.5. In other specific embodiments, the region of the microstructure unit 2 in the diffraction grating 10 is configured as the low refractive index portion 102, but other regions surrounding the region of the microstructure unit 2 are configured as the high refractive index portion 101. In the structures of each diffraction grating 10 shown in Figures 6a to 6e, it may be understood that the dark-colored regions may be configured as high refractive index portions, or the light-colored regions may be configured as high refractive index portions.

[0051] In the case of a volume hologram grating with a gradually changing refractive index, the region of the microstructure unit 2 preferably corresponds to a point halfway through the thickness of the grating, and the part with a refractive index higher than the average refractive index is defined as a high-refractive index part, and the part with a refractive index lower than the average refractive index is defined as a low-refractive index part, with the boundary being a contour line corresponding to the average refractive index of the optical material. Here, the region of the microstructure unit 2 is the part surrounded by the contour line corresponding to the average refractive index of the optical material, and may be configured as either a high-refractive index part or a low-refractive index part.

[0052] Based on the diffraction gratings according to the above-described embodiments, an embodiment of the present application further provides an optical waveguide device, the optical waveguide device comprising a base and an input coupling grating and an output coupling grating provided on the base, the input coupling grating being used to input-couple an external light beam into the base, and the output coupling grating being used to output-couple the light beam from the base. In a further embodiment, the optical waveguide device may comprise an intermediate grating. Here, the diffraction grating according to the embodiment of the present application is used in part or all of the input coupling grating and / or the output coupling grating and / or the intermediate grating. Note that when the diffraction grating according to the embodiment of the present application is applied to an optical waveguide device, the base of the optical waveguide device may be used as a substrate of the diffraction grating, i.e., the base of the optical waveguide device and the substrate of the diffraction grating are integrated.

[0053] In a preferred embodiment, the optical waveguide device has one or more coating layers on the side of the diffraction grating closest to the human eye and / or the side of the diffraction grating far from the human eye, and / or has one or more coating layers on the non-grating side of the base. Furthermore, the base may have a multilayer structure, and the diffraction grating may have a multilayer structure.

[0054] Furthermore, the present application also provides a display device, for example an augmented reality (AR) display device or a mixed reality (MR) display device, comprising an image projection device and an optical waveguide device according to the above-mentioned embodiment of the present application, the image projection device is used to generate image light rays (light rays carrying image information), the image light rays are incident-coupled into a base by an incident-coupling grating, transmitted to an outgoing-coupling grating through the base, and then outgoing-coupled into the base by the outgoing-coupling grating, transmitted to a human eye, and thereby the human eye can observe the corresponding image information.

[0055] In the examples of this application, the following comparative tests were also carried out.

[0056] (1) Example 1: Based on the optical waveguide device described in the examples of the present application, the diffraction grating according to the examples of the present application, specifically the diffraction grating with the structure shown in FIG. 8a, is adopted as the output coupling grating therein. Then, the diffraction effect of the output coupling grating is tested, and the test results are shown in FIG. 8b.

[0057] (2) Example 2: Based on the optical waveguide device described in the examples of the present application, the output coupling grating therein is a diffraction grating according to the examples of the present application, specifically, a diffraction grating having the structure shown in Figure 8c (the microstructure unit in Figure 8c is different from the microstructure unit in Figure 8a in that one protrusion is added to the original recess). Then, the diffraction effect of the output coupling grating is tested, and the test results are shown in Figure 8d.

[0058] (3) Comparative Example 1: Refer to the prior art. Example 1 The output coupling grating in the optical waveguide device uses a diffraction grating with the structure shown in Figure 9, in which the boundaries of the microstructure units are elliptical. The diffraction effect of the output coupling grating in Comparative Example 1 was then tested, and the test results are shown in Figure 10.

[0059] (4) Comparative Example 2: Refer to the prior art. Example 1 The output coupling grating in the optical waveguide device adopts the diffraction grating structure shown in FIG. 11, in which the boundary of the microstructure unit is also elliptical, and the rotation angle is Comparative Example 1 Different from the above, the diffraction effect of the output coupling grating of Comparative Example 2 was then tested, and the test results are shown in FIG.

[0060] It should be noted that although only nine microstructures are shown schematically in Figures 8a, 8c, 9, and 11, in actual testing, a large-area array of microstructures is used.

[0061] In optical waveguides using two-dimensional diffraction gratings, if the pupil expansion efficiency is low and the outgoing coupling efficiency is high, uneven bright fringes are likely to occur in the center. Therefore, the quality of a two-dimensional diffraction grating can be evaluated using the pupil expansion efficiency and outgoing coupling efficiency. Two-dimensional gratings that can be used in optical waveguides must have as high a pupil expansion efficiency as possible, but their outgoing coupling efficiency is not very high. Based on the above test results, the diffraction effect of the conventional diffraction grating structure shown in Figure 9 is shown in Figure 10, where the diffraction efficiency in pupil expansion direction 1 is relatively low, the outgoing coupling efficiency is relatively high, and there is a bright fringe in the center. The diffraction effect of the conventional diffraction grating structure shown in Figure 11 is shown in Figure 12, where the outgoing coupling efficiency is reduced in some areas, but the diffraction efficiency in both pupil expansion directions is low, and there is still a bright fringe in the center. On the other hand, the diffraction effects of the diffraction gratings according to the embodiments of the present invention shown in Figures 8a and 8c are shown in Figures 8b and 8d. Compared with Figures 10 and 12, Figures 8b and 8d have lower outcoupling efficiencies and higher diffraction efficiencies in both pupil expansion directions, effectively avoiding the central bright fringe, improving the uniformity seen by the human eye and increasing the image contrast. The microstructure shown in Figure 8c differs from the microstructure shown in Figure 8a in that a protrusion is added to the original recess, dividing the original recess into two recesses. Comparing the effects of Figures 8b and 8d, the added protrusion increases both the outcoupling efficiency and the diffraction efficiencies in both pupil expansion directions by about 2%, while maintaining a relatively low outcoupling efficiency and a relatively high pupil expansion efficiency. By optimizing the combination of the recesses and protrusions, the diffraction effect can be further improved.

[0062] From the above, in the diffraction grating, optical waveguide device, and display device according to the above-mentioned embodiments of the present application, the boundary of the microstructure unit constituting the two-dimensional diffraction grating is formed by surrounding it with a single smooth closed curve, the boundary has no straight sides and no sharp vertices, and the boundary has at least a first curve segment with a negative radius of curvature so that at least one recess is formed, which increases the degree of freedom in microstructure design and makes the outgoing coupled energy more uniform, contributing to reducing scattering and improving image contrast.

[0063] Although the present application has been shown and described with reference to particular embodiments, it will be understood by those skilled in the art that various changes in form and detail can be made therein without departing from the spirit and scope of the present application, which is defined by the claims and equivalents thereof.

Claims

1. A substrate; a plurality of microstructure units formed on the substrate and periodically arranged at intervals along a two-dimensional direction, the microstructure units including a first closed figure in a figure formed by orthogonal projection onto the substrate; The boundary of the first closed figure is formed by a single smooth closed curve so as to have no sharp vertices, and the boundary includes at least a first curve segment having a negative radius of curvature so as to form at least one concave portion. Diffraction grating.

2. the absolute value of the radius of curvature of the first curved line segment is 5 nm or more, and the recess depth of the recess is 5 nm or more; 2. The diffraction grating of claim 1.

3. At least one protrusion is also formed on the boundary.

2. The diffraction grating of claim 1.

4. a radius of curvature corresponding to the second curved line segment on which the protrusion is formed at the boundary is 5 nm or more, and a protrusion height of the protrusion is 5 nm or more; 4. The diffraction grating of claim 3.

5. the first closed figure is an asymmetric figure; 2. The diffraction grating of claim 1.

6. Within the area enclosed by the boundary, there is also another smooth closed curve, so as to form an inner boundary of the first closed figure that does not have a sharp vertex.

2. The diffraction grating of claim 1.

7. The figure formed by orthogonal projection of the microstructure unit onto the substrate further includes a second closed figure having an arbitrary shape. The diffraction grating according to any one of claims 1 to 6.

8. The area of ​​the second closed figure is equal to or less than the area of ​​the first closed figure.

8. The diffraction grating of claim 7.

9. the second closed figure has a boundary of a similar shape to that of the first closed figure, and the second closed figure is a figure formed by performing at least one of translation, reflection, rotation, and reduction on the first closed figure.

9. The diffraction grating of claim 8.

10. The arrangement period of the microstructure units in the first dimension and the arrangement period of the microstructure units in the second dimension are both within a range of 150 nm to 2 μm.

2. The diffraction grating of claim 1.

11. the arrangement period of the microstructure units in the first dimension is not equal to the arrangement period in the second dimension; 11. The diffraction grating of claim 10.

12. In the two-dimensional direction in which the microstructure units are periodically arranged, the smallest parallelogram formed by two pairs of shortest opposite sides corresponding to two arrangement periods has a relatively small interior angle within a range of 40° to 90°.

2. The diffraction grating of claim 1.

13. The diffraction grating is a surface relief grating or a volume hologram grating, and the thickness of the diffraction grating is in the range of 10 nm to 2 μm.

2. The diffraction grating of claim 1.

14. the diffraction grating includes at least two types of optical material components having different optical properties, the optical properties including at least one of a refractive index, an absorption property, and a birefringence property; 14. The diffraction grating of claim 13.

15. In the case of the surface relief grating, the region of the microstructure unit is formed at a location halfway through the grating thickness, the region of the microstructure unit in the diffraction grating is configured as a high refractive index portion and other regions surrounding the region of the microstructure unit are configured as low refractive index portions, or the region of the microstructure unit in the diffraction grating is configured as a low refractive index portion and other regions surrounding the region of the microstructure unit are configured as high refractive index portions, and in the case of a volume hologram grating with a gradually changing refractive index, the region of the microstructure unit corresponds to a location halfway through the grating thickness and is a portion surrounded by a contour line corresponding to the average refractive index of the optical material.

15. The diffraction grating of claim 14.

16. The base and At least one of an input coupling grating, an output coupling grating, and an intermediate grating provided on the base; The diffraction grating according to any one of claims 1 to 15 is used in a partial region of at least one of the input coupling grating, the output coupling grating, and the intermediate grating. Optical waveguide device.

17. one or more coating layers are present on at least one of the side of the diffraction grating that is closer to the human eye and the side that is farther from the human eye, and one or more coating layers are present on the side that does not have the base grating; 17. The optical waveguide device of claim 16.

18. The base has a multilayer structure, and the diffraction grating has a multilayer structure.

17. The optical waveguide device of claim 16.

19. The optical waveguide device according to any one of claims 16 to 18 is provided. Display equipment.

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