Two-dimensional pupil expanding grating and ar diffraction optical waveguide

Abstract

The application discloses a two-dimensional pupil expanding grating and an AR diffractive optical waveguide. The lattice of the two-dimensional pupil expanding grating is arranged in a hexagonal honeycomb mode and has an internal angle of 120 degrees. The AR diffractive optical waveguide comprises an optical waveguide substrate, a coupling-in grating and the two-dimensional grating. The lattice constant a of the two-dimensional grating and the period P of the coupling-in grating satisfy a=N*P / 3 (N is an integer greater than 1), and the period direction of the coupling-in grating is parallel to one side of the hexagonal honeycomb lattice. The application is designed in the hexagonal honeycomb lattice mode, so that the two-dimensional pupil expansion is realized, the number of microstructure repeating units is significantly reduced, the processing difficulty is reduced, the production yield and mass production capacity are improved, and the advantages of large eye movement range and structural simplification are considered.

Description

Technical Field

[0001] This invention relates to the field of augmented reality technology, and in particular to a two-dimensional pupil-expanding grating and an AR diffraction waveguide. Background Technology

[0002] Augmented Reality (AR) technology can merge virtual information with real-world scenes and has been widely applied in consumer electronics, industrial manufacturing, healthcare, and automotive AR-HUDs. As a core optical component of AR near-eye display devices, the AR diffractive waveguide plays a crucial role in light transmission, pupil expansion, and the coupling and output of virtual information. Its structure and performance directly determine the display performance, wearing comfort, portability, and mass production cost of AR devices.

[0003] Currently, AR diffractive waveguides based on surface-embossed gratings have become the mainstream technology solution for near-eye displays due to their advantages such as small size, light weight, superior optical performance, and strong mass production capabilities. The pupil-expanding grating is the core component of the AR diffractive waveguide. Its function is to expand the light beam coupled into the waveguide in both horizontal and vertical directions to match the range of human eye movement, ensuring that users can still clearly see the virtual image when their head moves slightly.

[0004] Existing AR diffractive waveguides with two-dimensional exit pupil expansion capabilities are mainly divided into two categories: The first type consists of three parts: a one-dimensional coupling grating, a one-dimensional bend grating, and a one-dimensional coupling grating. The bend grating and the coupling grating together achieve two-dimensional pupil expansion in both the horizontal and vertical directions. However, in this type of scheme, the light path from the coupling grating through the bend grating to the coupling grating is relatively long, resulting in significant energy loss. Furthermore, the presence of the bend grating not only introduces additional light leakage and rainbow patterns but also limits the area of ​​the coupling grating, affecting the eye-tracking range and other performance indicators of the AR waveguide system.

[0005] The second type consists of a one-dimensional coupling grating and a two-dimensional coupling grating arranged in a triangular lattice. The lattice lines of this two-dimensional grating form an equilateral triangle with a 60° interior angle. Light rays are directly incident on the two-dimensional grating after passing through the coupling grating, simultaneously achieving two-dimensional pupil expansion and coupling. AR waveguide systems based on this two-dimensional grating exhibit relatively low propagation loss and a large eye-tracking range. However, the triangular lattice arrangement in this scheme results in an excessively high density of repeating microstructure units in the two-dimensional grating. These densely packed and numerous microstructures impose stringent requirements on morphological consistency and dimensional accuracy, leading to high fabrication difficulty, low production yield, and hindering large-scale mass production.

[0006] Therefore, there is an urgent need for a two-dimensional pupil expansion solution to overcome the shortcomings of existing triangular lattice two-dimensional grating microstructures, such as high density and high manufacturing difficulty, while meeting the requirements of AR diffractive waveguides for excellent optical performance and large-scale mass production. Summary of the Invention

[0007] The purpose of this invention is to provide a two-dimensional pupil-expanding grating. By optimizing the arrangement of the grating lattice, the number of repeating microstructure units is reduced, thereby achieving two-dimensional pupil expansion while lowering the processing difficulty and improving production yield and mass production capability. This solution effectively overcomes the technical problems of existing multi-grating combination schemes, such as high light loss, light leakage, and obvious rainbow patterns, as well as the technical problems of dense arrangement of triangular lattice two-dimensional gratings, high processing difficulty, and low yield. It also has the advantages of simple structure, good process compatibility, and large eye movement range.

[0008] Another object of the present invention is to provide an AR diffraction waveguide incorporating the two-dimensional pupil grating.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: a two-dimensional pupil-expanding grating, wherein the grating lattice adopts a hexagonal honeycomb arrangement, the connecting lines of the hexagonal honeycomb lattice form a regular hexagonal structure, and have 120° interior angles.

[0010] Optionally, the microstructure of the two-dimensional pupil grating can be any three-dimensional structure.

[0011] Optionally, the microstructure of the two-dimensional pupil grating can be any one of the following: cylindrical, frustum, conical, elliptical cylinder, frustum, elliptical cone, triangular prism, triangular frustum, square prism, square frustum, pentagonal prism, pentagonal frustum, hexagonal prism, and hexagonal frustum.

[0012] Optionally, the microstructures of the two-dimensional pupil grating are arranged in isolation from each other or partially connected to each other.

[0013] Optionally, the microstructure of the two-dimensional pupil grating is a protruding structure on the surface of the medium, or a recessed structure formed inside the medium.

[0014] An AR diffractive optical waveguide, comprising: An optical waveguide substrate; A coupling grating is disposed on the upper or lower surface of the optical waveguide substrate. The coupling grating is a one-dimensional grating with a period of P. A two-dimensional pupil-expanding grating is disposed on the upper or lower surface of the optical waveguide substrate; Wherein, the hexagonal honeycomb lattice constant 'a' of the two-dimensional pupil grating satisfies: a = N × P / 3, where N is an integer greater than 1; preferably, the integer N is 2. The periodic direction of the coupling grating is parallel to any side of the hexagonal honeycomb lattice of the two-dimensional pupil grating; The optical waveguide substrate is a layer of parallel medium with a refractive index of 1.5 to 2.8 and a thickness of 0.3 mm to 1.5 mm; The type of the coupled grating is one of the following: rectangular grating, blazed grating, stepped grating, meta-grating, sawtooth grating, or tilted grating, and its period P is 250 to 500 nm. The overall area of ​​the coupled grating is smaller than the area of ​​the two-dimensional pupil grating.

[0015] The working principle of this invention's AR diffractive waveguide: Light emitted from the optomechanism of the near-eye display system enters the waveguide substrate through a one-dimensional grating. Typically, the light propagates along the first or -1st order diffraction angle direction and undergoes total internal reflection upon encountering the waveguide interface. The light propagates forward between the upper and lower parallel interfaces of the waveguide substrate via total internal reflection until it reaches the two-dimensional pupil-expanding grating region. After entering the two-dimensional pupil-expanding grating, the light splits into two parts: one part is diffracted through the grating and exits the waveguide substrate, entering the human eye through the external air to form a virtual image; the other part is diffracted and reflected to different propagation orders in different directions, continuing to maintain total internal reflection propagation within the waveguide substrate, and then reflected back into the two-dimensional pupil-expanding grating, repeating the transmission coupling and reflection propagation. Through multiple cycles of diffraction and total internal reflection, the light beam completes pupil expansion in both horizontal and vertical directions, achieving a two-dimensional pupil-expanding effect and entering the human eye. The near-eye display device is AR glasses or an ARHUD.

[0016] The beneficial effects of this invention are: the two-dimensional pupil grating using a hexagonal honeycomb lattice has a more dispersed arrangement of microstructure repeating units compared to the traditional triangular lattice, and the same area contains fewer microstructure repeating units, thus significantly reducing the difficulty of the processing technology, significantly improving the production yield, and making it suitable for mass production.

[0017] The architecture of "one-dimensional coupled grating + single hexagonal honeycomb lattice two-dimensional grating" is adopted, which eliminates the need to set up independent turning gratings, shortens the optical path transmission distance, effectively reduces optical transmission energy loss, and avoids the additional light leakage and rainbow pattern problems caused by turning gratings.

[0018] A single two-dimensional pupil-expanding grating simultaneously completes two-dimensional pupil expansion and coupling in both horizontal and vertical directions, which can increase the effective coupling area, expand the eye movement range, and improve the user's wearing and observation experience.

[0019] The optical waveguide substrate and grating parameters have a wide range of values, and are compatible with various substrate materials such as glass, resin and silicon carbide. This enables the lens to be designed to be thin and light, and is suitable for various near-eye display terminals such as AR glasses and AR-HUD. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the hexagonal honeycomb lattice two-dimensional pupil-expanding grating and the corresponding AR diffraction waveguide planar structure in this invention.

[0021] Figure 2This is a simulation diagram of the two-dimensional pupil expansion of the AR diffraction waveguide based on a hexagonal honeycomb lattice two-dimensional grating in this invention. Specific Implementation

[0022] The present invention will be further described in detail below with reference to specific embodiments.

[0023] Appendix Figure 1 This is an embodiment of the present invention, which discloses a two-dimensional pupil-expanding grating and an AR diffraction waveguide. A light source with a center emission wavelength of 525nm is selected to construct the AR diffraction waveguide of the present invention: the waveguide substrate is a parallel dielectric plate with a refractive index of 1.8 and a thickness of 1mm.

[0024] The coupling grating is set on the upper surface of the optical waveguide substrate. It has a size of 2mm×2mm and is a one-dimensional rectangular line grating with a period of P=395nm, a duty cycle (linewidth / period) of 40%, a line height of 180nm, and a refractive index of 1.8.

[0025] A two-dimensional pupil-expanding grating is set on the upper surface of the optical waveguide substrate, with a size of 28mm×22mm. It adopts cylindrical microstructure units arranged in a hexagonal honeycomb lattice with an interior angle of 120°. Taking N=2, the lattice constant a=263.3nm is calculated by formula. The refractive index of the cylindrical medium is 1.8, the radius is 100nm, and the height is 200nm.

[0026] The right side of the coupling grating area and the left side of the two-dimensional pupil grating area are horizontally spaced 7mm apart, and the overall structure is symmetrically arranged along the horizontal central axis.

[0027] like Figure 2 As shown, TE-polarized light with a wavelength of 525 nm is incident perpendicularly on the coupling grating region on the upper surface of the waveguide substrate. It propagates along the +1 order transmission direction into the waveguide substrate, undergoes total internal reflection at the lower surface, and then propagates to the upper surface. It undergoes another total internal reflection at the upper surface and then propagates to the lower surface. After repeated total internal reflections on both the upper and lower surfaces of the waveguide substrate, the light propagates along the principal axis to the two-dimensional grating region. When the light is incident on the two-dimensional grating, part of the light is transmitted through the grating into the outside air, while the rest is reflected by the grating at different angles and continues to propagate through total internal reflection in the planar waveguide substrate. This process repeats until the light encounters the grating again, resulting in another transmission-coupling and reflection propagation. This cycle continues until two-dimensional pupil expansion and light coupling are achieved. The two-dimensional pupil expansion results (detector area 16 mm × 14 mm) obtained by joint simulation of an AR diffraction waveguide based on a hexagonal honeycomb lattice two-dimensional grating using rigorous coupled-wave analysis and ray tracing methods are shown in the figure. Figure 2 As shown.

[0028] Those skilled in the art should understand that the present invention is not limited to the specific embodiments described above. The above embodiments are only used to illustrate the technical solutions of the present invention. Any equivalent changes, substitutions, and improvements made to the grating lattice arrangement, microstructure morphology, waveguide substrate parameters, and grating parameters of the present invention within the spirit and principle of the present invention should fall within the protection scope of the present invention.

Claims

1. A two-dimensional pupil-expanding grating, characterized in that, The grating lattice of the two-dimensional pupil grating is arranged in a hexagonal honeycomb pattern. The lines connecting the hexagonal honeycomb lattice form a regular hexagon with 120° interior angles.

2. The two-dimensional pupil-expanding grating according to claim 1, characterized in that, The microstructure of the two-dimensional pupil grating can be any three-dimensional structure.

3. The two-dimensional pupil-expanding grating according to claim 2, characterized in that, The microstructure of the two-dimensional pupil-expanding grating is any one of the following: cylindrical, frustum, conical, elliptical cylindrical, frustum, elliptical conical, triangular prism, frustum, square prism, square frustum, pentagonal prism, pentagonal frustum, hexagonal prism, and hexagonal frustum.

4. The two-dimensional pupil-expanding grating according to claim 1, characterized in that, The microstructures of the two-dimensional pupil grating are arranged in isolation from each other or partially connected to each other.

5. The two-dimensional pupil-expanding grating according to claim 1, characterized in that, The microstructure of the two-dimensional pupil grating is either a raised structure protruding from the surface of the medium or a recessed structure recessed inside the medium.

6. An AR diffractive optical waveguide, characterized in that, include: An optical waveguide substrate; A coupling grating is disposed on the upper or lower surface of the optical waveguide substrate. The coupling grating is a one-dimensional grating with a period of P. A two-dimensional pupil-expanding grating as described in any one of claims 1-5 is disposed on the upper or lower surface of the optical waveguide substrate; Wherein, the hexagonal honeycomb lattice constant 'a' of the two-dimensional pupil grating satisfies: a = N × P / 3, where N is an integer greater than 1; The periodic direction of the coupled grating is parallel to any side of the hexagonal honeycomb lattice of the two-dimensional pupil grating.

7. The AR diffractive waveguide according to claim 6, characterized in that, The integer N takes the value of 2.

8. The AR diffractive waveguide according to claim 6, characterized in that, The optical waveguide substrate is a layer of parallel medium with a refractive index of 1.5 to 2.8 and a thickness of 0.3 to 1.5 mm.

9. The AR diffractive waveguide according to claim 6, characterized in that, The coupled grating is one of the following types: rectangular grating, blazed grating, stepped grating, meta-grating, sawtooth grating, or tilted grating, with a period P of 250 to 500 nm.

10. The AR diffractive waveguide according to claim 6, characterized in that, The overall area of ​​the coupled grating is smaller than the area of ​​the two-dimensional pupil grating.

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