Two-dimensional grating, optical waveguide structure, display module, and electronic device

Abstract

Disclosed in the present invention are a two-dimensional grating, an optical waveguide structure, a display module, and an electronic device. The two-dimensional grating comprises: a substrate and a grating layer, wherein the grating layer comprises several periodically distributed cells, each cell at least including one central lattice point, and the central lattice point being arranged inside the cell and deviating from the geometric center of the cell. Since a central lattice point of the two-dimensional grating provided in the present embodiment is not located at the geometric center point of a cell, and the change in the position of the central lattice point can improve the diffraction efficiency of light in the two-dimensional grating, when the two-dimensional grating is used as a coupling-out grating, the direct coupling-out diffraction efficiency and the pupil-expansion diffraction efficiency can be adjusted, thus improving the diffractive uniformity of a diffraction optical waveguide. Moreover, the method provided in the present embodiment has a simple structure, is easily implemented, and has wide applicability.

Description

Two-dimensional grating, optical waveguide structure, display module and electronic device Technical Field

[0001] The present invention relates to the technical field of diffraction optical equipment, and in particular to a two-dimensional grating, an optical waveguide structure, a display module and an electronic device. Background Art

[0002] In a diffraction optical waveguide device, the light beam emitted from the optical machine module passes through the coupling-in region and is converted from a free-space beam into a light beam transmitted in the optical waveguide substrate in the form of total reflection. The reverse process is performed in the coupling-out region, converting the portion of the light beam transmitted in the form of total reflection into a free-space beam received by the human eye.

[0003] The diffracted light of the two-dimensional grating in the outcoupling area of ​​the diffraction waveguide device can be divided into directly coupled diffracted light and diffracted light coupled out after pupil expansion. Since there is a large energy difference between the diffracted light directly coupled out of the two-dimensional grating and the diffracted light coupled out after pupil expansion, the higher the diffraction efficiency, the higher the exit pupil uniformity. Since the diffraction efficiency of the expanded pupil is lower than the diffraction efficiency of the directly coupled diffraction waveguide device, the two-dimensional grating has the problem of low exit pupil uniformity.

[0004] Summary of the Invention

[0005] The object of the present invention is to provide a two-dimensional grating, an optical waveguide structure, a display module and an electronic device to overcome the defect of low exit pupil uniformity in the two-dimensional grating.

[0006] The technical solutions adopted by the present invention to solve the technical problems are as follows:

[0007] In a first aspect, this embodiment provides a two-dimensional grating comprising: a substrate and a grating layer, wherein the grating layer comprises a plurality of periodically distributed cells; the cells comprise: four edge lattice points and at least one central lattice point; the central lattice point is located inside the cell and deviated from the geometric center of the cell.

[0008] Optionally, the cells are in a parallelogram structure, and the central lattice point is located on a diagonal of the parallelogram structure.

[0009] Optionally, the cells have a diamond-shaped structure.

[0010] Optionally, there are multiple central lattice points, and the central lattice points are arranged in a centrosymmetric and / or axially symmetrical manner.

[0011] Optionally, there are multiple central lattice points, and the multiple central lattice points are arranged asymmetrically.

[0012] Optionally, the shape of each of the central lattice points is a centrosymmetric structure and / or an axially symmetric structure.

[0013] Optionally, the shape of the central lattice point is an asymmetric structure.

[0014] In a second aspect, this embodiment provides an optical waveguide structure, which includes: at least one substrate, an optical waveguide body arranged on the substrate, an in-coupling grating and an out-coupling grating; the out-coupling grating is the two-dimensional grating.

[0015] In a third aspect, this embodiment provides a display module, which includes: the optical waveguide structure described above.

[0016] In a fourth aspect, this embodiment provides an electronic device, which includes: the display module. Beneficial effects:

[0017] This embodiment discloses a two-dimensional grating, an optical waveguide structure, a display module, and an electronic device. The two-dimensional grating includes: a substrate and a grating layer, and the grating layer includes: a plurality of periodically distributed cells; each cell includes four edge grid points and at least one central grid point, and the central grid point is located inside the cell and deviated from the geometric center of the cell. Since the central grid point of the two-dimensional grating provided by this embodiment is not located at the geometric center point of the cell, and the change in the position of the central grid point can improve the diffraction efficiency of light in the two-dimensional grating, when the two-dimensional grating is used as a coupling grating, the direct coupling diffraction efficiency and the pupil expansion diffraction efficiency can be adjusted, thereby improving the diffraction uniformity of the diffraction optical waveguide. In addition, the method provided by this embodiment has a simple structure, is easy to implement, and has a wide range of applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG1 is a schematic diagram of dot distribution of a two-dimensional grating in the prior art;

[0019] Figure 2 shows the central bright fringe corresponding to the existing two-dimensional dot distribution;

[0020] FIG3 is a schematic structural diagram of a two-dimensional grating in the prior art when the central grid point is a grating morphology;

[0021] FIG4 shows the uniformity distribution corresponding to the waist rhombus in the prior art;

[0022] FIG5 is a schematic diagram of a central grid point translation setting according to an embodiment of the present invention;

[0023] FIG6 is a schematic diagram of central grid point rotation according to an embodiment of the present invention;

[0024] FIG7 is a diagram showing a central grid point rotation and translation structure according to an embodiment of the present invention;

[0025] FIG8 is a schematic diagram of a combination of multiple central grid points in an embodiment of the present invention. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0027] Other embodiments of the present invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. The present invention is intended to cover any variations, uses, or adaptations of the present invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The description and examples are to be considered as exemplary only, with the true scope and spirit of the invention being indicated by the following claims.

[0028] In the fields of augmented reality (AR) and mixed reality (MR), waveguide solutions offer broader application prospects due to their thinner and lighter weight, larger eyebox, and greater visibility compared to bird bath (BB) displays, insect-eye displays, and free-form prism displays. The eyebox refers to the two-dimensional area within which the human eye can fully perceive light within a given field of view (light from every viewing angle is visible) at a given viewing distance.

[0029] Optical waveguide solutions generally include geometric waveguides and diffraction waveguides. Since diffraction waveguides are easier to achieve two-dimensional pupil expansion than geometric waveguides, diffraction waveguides are lighter and thinner than geometric waveguides, and are therefore more suitable for fields such as augmented reality and mixed reality.

[0030] Diffraction waveguides achieve two-dimensional pupil expansion by expanding the exit pupil. While ensuring a compact size and a wide field of view, they also increase the eye's range of motion in both directions, achieving optimal display effects. When using a two-dimensional grating to achieve two-dimensional pupil expansion, light emitted by the optical engine is first coupled into the waveguide via an input grating. After total internal reflection, it is incident on an output grating, a two-dimensional grating. At this point, a portion of the light is diffracted and enters the human eye, while the remaining light is split into two-dimensional, vertical and horizontal reflections that continue to propagate forward before being incident on the output grating again. The light derived from the output grating enters the human eye, thus achieving two-dimensional pupil expansion.

[0031] In a diffraction waveguide, an in-coupling grating converts the free-space beam emitted by the optical machine into a beam that is transmitted by total internal reflection within the waveguide substrate. An out-coupling grating performs the reverse process, converting the portion of the beam transmitted by total internal reflection back into a free-space beam for the human eye. In practical applications, in addition to in-coupling and out-coupling gratings, one or more deflection gratings may be included to redirect the portion of the beam that was transmitted by total internal reflection, allowing it to continue transmitting in the new direction by total internal reflection.

[0032] Since the energy difference between direct coupling and coupling after pupil expansion in a two-dimensional grating is large, the diffraction efficiency of direct coupling is higher than the diffraction efficiency of coupling after pupil expansion. Generally, the higher the diffraction efficiency of coupling after pupil expansion, the better the corresponding brightness uniformity. Therefore, the existing two-dimensional grating has the problem of poor exit pupil uniformity.

[0033] As shown in Figures 1 and 2, Figure 1 shows a grating layer in an existing two-dimensional grating with a dot matrix distribution. The minimum structure of the dot matrix is ​​the minimum cell of the two-dimensional grating, which consists of four edge grid points and one center grid point. The cell has two periodic directions, namely period one P1 and period two P2, and two angles, namely angle one and angle two. Figure 2 shows the central bright fringe corresponding to the dot matrix distribution of the two-dimensional grating shown in Figure 1. Because the direct outgoing diffraction efficiency is high under the dot matrix distribution of the two-dimensional grating shown in Figure 1, while the pupil expansion diffraction efficiency is insufficient, a central bright fringe appears in the exit pupil of the two-dimensional grating.

[0034] In order to overcome the central bright lines appearing on the light-emitting surface of the two-dimensional grating, it is necessary to set the internal morphology of the dot matrix under the premise of the existing grating layer setting. As shown in Figure 3, a waisted rhombus 310 can be set at the geometric center position of the cell 30, and the edge grid points are not provided with a grating structure to improve the uniformity of the exit pupil. The corresponding uniformity distribution is shown in Figure 4. However, setting the central grid point to a waisted rhombus requires higher processing accuracy and processing cost, and therefore cannot meet the requirements of low cost and high processing accuracy.

[0035] To overcome the aforementioned issues, this embodiment provides a two-dimensional grating. By positioning the center grid point of a cell in the two-dimensional grating offset from the geometric center of the cell, this improves exit pupil uniformity and overcomes the central bright streaks that appear in the exit pupil. The method provided in this embodiment modifies the geometric shape of the two-dimensional grating by adjusting the location of the center grid point in the cell to control the propagation path of the light signal within the grating. This in turn changes the diffraction efficiency of the two-dimensional grating's pupil expansion coupling, improving the ratio of the direct coupling diffraction efficiency to the pupil expansion coupling diffraction efficiency, thereby enhancing the display uniformity of the diffraction waveguide.

[0036] The two-dimensional grating, optical waveguide structure, display module and electronic device disclosed in this embodiment will be further described below with reference to the accompanying drawings.

[0037] This embodiment discloses a two-dimensional grating, which includes: a substrate and a grating layer arranged on the substrate, the grating layer includes: a plurality of periodically distributed cells; the cell includes: four edge points and at least one central grid point; the central grid point is located inside the cell and deviated from the geometric center of the cell.

[0038] The grating layer disclosed in this embodiment is composed of a number of periodically spaced cells, each of which includes four edge lattice points and at least one central lattice point. To improve the uniformity of the exit pupil of the two-dimensional grating, the central lattice point is offset by a preset distance from the geometric center of the cell to adjust the reflected light of a portion of the incident light beam into the grating layer. When the beam is split into two directions and continues to propagate forward, the reflection direction is changed, thereby increasing the diffraction efficiency when the pupil is expanded and then coupled out. This increases the ratio of the direct coupling diffraction efficiency to the expanded pupil coupling diffraction efficiency, thereby improving the uniformity of the exit pupil.

[0039] Furthermore, the cell includes: four edge lattice points, which are connected in sequence to form a quadrilateral structure of the cell. In order to achieve a periodic arrangement between the cells, the sum of the two adjacent internal angles in the quadrilateral is 180°. With the geometric center point of the cell as the coordinate origin, the position of the straight line where the long diagonal between the cells is located is the position of the x-axis, and the position of the short diagonal among the diagonals is the position of the y-axis, a plane rectangular coordinate system is established. As shown in Figure 5, each cell contains a central lattice point, and each central lattice point deviates from the geometric center point of the cell by a certain distance. The distance from the central lattice point to the geometric center of the cell can be a distance Δy offset from the geometric center of the cell along the y-axis (as shown in the small figure on the far left of Figure 5), or it can be a distance Δx offset from the geometric center of the cell along the x-axis (as shown in the small figure in the middle of Figure 5), or it can be an oblique deviation from the geometric center of the cell by Δx and Δy (as shown in the small figure on the far right of Figure 5).

[0040] The two-dimensional grating disclosed in this embodiment alters the geometric shape of the grating layer within the two-dimensional grating by positioning the central lattice point within the cell away from the geometric center of the cell. This altered geometry alters the propagation path of the light beam input into the grating layer within the two-dimensional grating, thereby changing the diffraction efficiency of the pupil-expanding outcoupling of the two-dimensional grating. The deviation of the central lattice point from the geometric center changes the propagation direction of the light beam propagating within the two-dimensional grating, directly or indirectly increasing the transmission distance and, consequently, the pupil-expanding outcoupling energy. This increases the ratio of the direct-outcoupling diffraction efficiency to the pupil-expanding outcoupling diffraction efficiency, thereby improving the display uniformity of the diffraction waveguide.

[0041] As shown in FIG6 , the shape of the cell can be a parallelogram, and the angle 1 (θ1) and angle 2 (θ2) formed by the lines connecting the four edge grid points of the cell can be any combination of acute angles and obtuse angles. However, in order for the cells to be arranged periodically, the sum of angle 1 and angle 2 must be 180°. As shown in FIG1 , the cells in the two-dimensional grating disclosed in this embodiment also have two periodic directions, namely period 1 (P1) and period 2 (P2). The range of period 1 and period 2 is generally between 100nm and 600nm.

[0042] In the plane rectangular coordinate system established as shown in Figure 5, the length of the longest diagonal line between the four edge grid points of the cell is defined as The length of the short diagonal line between the four edge points of the cell is defined as Then we can get the distance of the central grid point from the geometric center of the cell: the value range of Δy is ±D2 / 2, and the value range of Δx is ±D1 / 2.

[0043] In practice, to achieve better uniformity, within this coordinate system, better uniformity improvement can be achieved when the central grid points are located on a diagonal line. In one embodiment, the optimal uniformity improvement can be achieved when the central grid points are located midway between the major or minor axis of the diagonal line. Specifically, the number of central grid points located on the diagonal line can be one or more.

[0044] Furthermore, the shape of the cell can be a rhombus, that is, the parallelogram formed by connecting the four edge lattice points in sequence is a rhombus, and when the central lattice point is located on the long axis of the rhombus structure, the maximum value of the preset distance is half of the long axis of the rhombus structure; when the central lattice point is located on the short axis of the rhombus structure, the maximum value of the preset distance is half of the short axis of the rhombus structure.

[0045] As shown in Figure 6, when it is necessary to obtain multiple different center grid point settings, this can be achieved by rotating the current center grid point by a certain angle, thereby obtaining cellular structures with the center grid point at different positions. For example, the cell can be rotated 30 degrees with the cell's geometric center point as the rotation center to obtain another cellular structure with the center grid point being centrosymmetric to the current center grid point. Furthermore, by using different rotation angles, cellular structures with multiple center grid points at different positions can be obtained, and thus cellular structures with the center grid point at different positions can be obtained.

[0046] When there is only one central point in a cell, you can translate the central point to another location within the cell to obtain a cell with a central point at a different location. For example, you can translate the central point to the other side of the geometric center to obtain a cell shape with a central point on the other side of the geometric center.

[0047] In specific implementation, the position of the central grid point can be moved to other positions by using translation and rotation at the same time, so as to obtain the cell shape with the central grid point at different positions.

[0048] Furthermore, as shown in FIG. 7 and FIG. 8 , there may be multiple central lattice points in a cell, and the central lattice points may be arranged symmetrically or asymmetrically.

[0049] When the central grid points are arranged symmetrically, they can be rotationally symmetric, translationally symmetric, or both centrally symmetric and axially symmetric. For example, the arrangement of multiple central grid points is a square array. For example, a 4×4 array, in which case the central grid points are axially symmetric. For example, if a cell contains four central grid points, the four central grid points are located at four azimuths of the geometric center of the cell, and are at the same distance from the geometric center. For example, they are located directly above, directly below, directly to the left, and directly to the right of the geometric center, and the distances from the central grid points in the four directions to the geometric center are equal. Then, the arrangement of the four central grid points is symmetrical with the geometric center as the center.

[0050] When the central grid points are not symmetrical, some of the central grid points can be axially symmetrical and some of the central grid points can be centrosymmetric. When any two central grid points are centrosymmetric, the angle of rotation along the centrosymmetric point can be 0-360 degrees.

[0051] Specifically, the arrangement of the central grid points within the cell can be achieved by first shifting the central grid point set at a geometric position away from the cell center by a preset distance, and then performing multiple translations and / or rotations to obtain a cell shape with multiple central grid points at different positions. Alternatively, one or more central grid points can be added to the cell, and the multiple central grid points can be arranged at different positions, either at any position within the cell or at multiple positions arranged in a regular pattern. Then, one or more of the central grid points can be individually translated and / or rotated to obtain a cell shape with multiple additional central grid points at different positions than the previous positions.

[0052] Furthermore, as shown in FIG8 , the shape of each central grid point can be a centrosymmetric structure and / or an axisymmetric structure. The central grid points can be a circular or square centrosymmetric structure, or a rhombus, ellipse, or any other non-rotationally symmetric structure. The improvement in the exit pupil uniformity of the grating can be achieved by simply ensuring that the central grid points are offset from the geometric center of the cell.

[0053] For example, if the central grid point is a circle, then the shapes of the central grid points are centrosymmetric, with multiple circular central grid points distributed around the geometric center point. Alternatively, if the central grid point is a rectangle, triangle, or regular pentagon, then the shapes of the central grid points are axisymmetric.

[0054] As shown in FIG8 , when the central grid points have a certain shape, such as a rectangle, it can also be set so that the long sides of the rectangles are parallel to each other, and the short sides of the rectangles are parallel to each other, that is, the rectangles are arranged in sequence. Alternatively, the sides of the rectangles are not parallel, and the rectangles are staggered at a certain distance to achieve regulation of the diffraction efficiency of the pupil-expanded outgoing diffraction light. For example, the central grid points of the rectangles are arranged in the same manner, and the central grid points of the rectangles can be obtained by translation. As shown in FIG8 , the central grid points of the three rectangles are asymmetric and cannot be obtained by translation, so the central grid points of the three rectangles shown in FIG8 are staggered.

[0055] Furthermore, the shape of the central grid point can also be other centrally symmetrical or axially symmetrical shapes such as a cylinder, an ellipse or a truncated cone. The shapes of multiple central grid points can be the same or different.

[0056] For example, multiple cylindrical center points and multiple rectangular center points can be set in the same cell. The center points of the multiple cylindrical centers can be distributed in a centrosymmetric or axisymmetric manner, the center points of the multiple rectangular centers can be distributed in a centrosymmetric or axisymmetric manner, and the center points of the multiple cylindrical centers and the center points of the multiple rectangular centers can be distributed in a centrosymmetric or axisymmetric manner, or they can be distributed in a non-centrosymmetric or axisymmetric manner.

[0057] Furthermore, the shapes of the central grid points can be asymmetrical, with each central grid point having a different shape and each having an irregular shape. For example, a scalene triangle, a non-isosceles trapezoid, etc. In specific implementations, some central grid points can be symmetrical, while others can be asymmetrical.

[0058] The two-dimensional grating disclosed in this embodiment improves the uniformity of the grating by setting a central grid point that deviates from the geometric center of the cell on the basis of the existing two-dimensional grating lattice. At the same time, multiple central grid points can be introduced. Through the arrangement, combination, translation and rotation of the multiple central grid points, the efficiency ratio of the direct coupling diffraction efficiency and the pupil expansion diffraction efficiency is improved, thereby enhancing the pupil expansion uniformity of the two-dimensional grating and improving the central bright fringe effect.

[0059] While disclosing the above-mentioned two-dimensional grating, this embodiment also provides an optical waveguide structure, which includes: at least one substrate, an optical waveguide body arranged on the substrate, an in-coupling grating and an out-coupling grating; the out-coupling grating is the two-dimensional grating.

[0060] In a specific implementation, the period 1 and period 2 of the two-dimensional grating are between 100nm and 600nm, the groove depth of the grating layer in the two-dimensional grating is between 10nm and 2μm, and the refractive index of the material of the grating layer microstructure is generally between 1.3-2.0.

[0061] Furthermore, the optical waveguide structure may have one or more layers of substrates, and the material of the substrate may be glass, resin, plastic, transparent ceramic or a combination of the above materials.

[0062] In addition to the aforementioned optical waveguide structure, this embodiment also discloses a display module comprising the aforementioned optical waveguide structure. The optical waveguide structure provided in this embodiment, combined with a projection device, forms a display module; the display module can be used in XR devices and HUDs. The optical waveguide structure disclosed in this embodiment, due to the provision of the disclosed two-dimensional grating, can achieve excellent exit pupil uniformity, thereby achieving superior display quality.

[0063] Based on the above-mentioned display module, this embodiment further provides an electronic device, which includes the above-mentioned display module. The electronic device can be a device such as AR glasses or an AR helmet that uses a diffraction optical waveguide to output images.

[0064] The two-dimensional grating disclosed in this embodiment improves the uniformity of the grating by setting a central grid point that is translated or rotated from the geometric center, based on the existing two-dimensional grating lattice. The method of this embodiment can also be configured to introduce multiple central grid points, and obtain more cell shapes through the permutation, combination, translation, and rotation of multiple central grid points. Grating layers are constructed using cell arrangements of various shapes, and the constructed grating layers are then used to manufacture two-dimensional gratings. This can achieve an improvement in the efficiency ratio of direct coupling diffraction efficiency (STE) and expanded pupil diffraction efficiency (EPE) using the reconstructed two-dimensional grating, thereby improving the uniformity of pupil expansion and reducing the central bright streak effect.

[0065] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or N embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0066] It is understandable that the above embodiments are exemplary and should not be construed as limiting the present application. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A two-dimensional grating, characterized in that: include: A substrate and a grating layer, wherein the grating layer includes a plurality of periodically distributed cells; the cells include: four edge grid points and at least one central grid point; The location of the central grid point is: set inside the cell and deviated from the geometric center of the cell.

2. The two-dimensional grating according to claim 1, characterized in that: The unit cells are in a parallelogram structure, and the central grid point is located on the diagonal line of the parallelogram structure.

3. The two-dimensional grating according to claim 2, characterized in that: The cell has a rhombus structure.

4. The two-dimensional grating according to claim 1, characterized in that: There are multiple central lattice points, and the central lattice points are arranged in centrosymmetry and / or axisymmetry.

5. The two-dimensional grating according to claim 1, characterized in that: There are multiple central lattice points, and the multiple central lattice points are arranged asymmetrically.

6. The two-dimensional grating according to any one of claims 1 to 5, characterized in that: The shape of the central lattice point is a centrosymmetric structure and / or an axially symmetric structure.

7. The two-dimensional grating according to claims 1-5, characterized in that: The shape of the central lattice point is an asymmetric structure.

8. An optical waveguide structure, characterized in that: include: At least one substrate, an optical waveguide body arranged on the substrate, an in-coupling grating and an out-coupling grating; the out-coupling grating is a two-dimensional grating as claimed in any one of claims 1-7.

9. A display module, characterized in that: include: The optical waveguide structure as claimed in claim 8.

10. An electronic device, characterized in that: include: The display module as claimed in claim 9.

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