A two-dimensional exit pupil expansion optical waveguide structure

Abstract

The present application relates to the field of optical waveguide structure, specifically to a two-dimensional exit pupil expansion optical waveguide structure. The present application comprises a diffractive optical waveguide substrate and a partially reflective prism array, the diffractive optical waveguide substrate is provided with a first diffractive optical element and a second diffractive optical element, the first diffractive optical element has a periodic structure in the first direction, the second diffractive optical element has a periodic structure, the periodic structure of the second diffractive optical element is at an angle θ with the second direction, so that the light is expanded in the first direction and transmitted in the second direction; the partially reflective prism array is assembled by a plurality of mutually parallel partially reflective prisms, each partially reflective prism has a reflective surface, the reflective surface is coated with a partially reflective film layer, and the reflectivity of the partially reflective film layer increases in the second direction. The present application greatly reduces the difficulty of the process, improves the yield of the product, and at the same time eliminates the common leakage phenomenon and rainbow effect in the traditional two-dimensional exit pupil diffractive optical waveguide.

Description

Technical Field

[0001] This invention belongs to the field of optical waveguide structures, specifically relating to a two-dimensional exit pupil extended optical waveguide structure. Background Technology

[0002] Augmented and mixed reality (AR&MR) waveguide glasses can provide users with virtual content, including text, images, and videos, while also allowing users to view real-world scenes. The two can be integrated and interacted with to meet the needs of users in various fields such as entertainment, consumption, and industrial production.

[0003] To meet the diverse application needs of users in various scenarios, augmented reality and mixed reality waveguide glasses require features such as ease of fabrication, thinness, high brightness, high uniformity, anti-rainbow properties, anti-light leakage, and large eye sockets. To achieve these requirements, current waveguide glasses are mainly divided into two categories: geometric waveguides and diffractive waveguides, each with its own advantages and disadvantages in practical applications.

[0004] To achieve two-dimensional exit pupil expansion and obtain a larger eye socket, geometric array waveguide technology can be applied, such as in patent US2023 / 0013376A1. This technology uses a partial reflection prism array in the first direction to achieve expansion in that direction, and simultaneously uses a partial reflection prism array in the second direction to receive the expanded light from the first direction, thus achieving expansion in both directions. The first and second directions are perpendicular to each other, resulting in a waveguide structure with a large eye socket, high brightness, high uniformity, no rainbow effect, and no light leakage. However, because the entire waveguide structure is assembled from multiple partial reflection prisms in the first and second directions, it places high demands not only on the processing and coating of individual partial reflection mirrors but also on the splicing between all the partial reflection mirrors in the entire waveguide. This results in an extremely low yield for such geometric array waveguides, making mass production and application impossible.

[0005] Diffractive waveguide technology can also be applied. For example, US9,791,696B2 primarily uses diffraction gratings to achieve expansion in two directions. A diffraction grating is used in the first direction to expand the beam, and then another diffraction grating is used in the second direction to receive the beam expanded in the first direction, thus achieving expansion in the second direction. The diffraction grating can be mastered using optical exposure or electron beam technology and etching techniques, and then mass-produced using nanoimprint technology, thereby obtaining waveguide glasses at a lower cost. For example... Figure 1 As shown, optical waveguide technology based on diffraction gratings can also achieve large eye sockets, but it generally suffers from rainbow effects and light leakage. Moreover, compared with geometric optical waveguides, its brightness and uniformity are slightly worse. Summary of the Invention

[0006] The purpose of this invention is to solve the problem that current geometric array optical waveguides require the use of a large number of partially reflecting prism arrays in two directions, resulting in low yield due to excessive manufacturing difficulty, thus preventing mass production and application. It also addresses the rainbow effect and light leakage problems that occur during the use of diffractive optical waveguides, and proposes a two-dimensional exit pupil extended optical waveguide structure.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] The present invention proposes a two-dimensional exit pupil extended optical waveguide structure, comprising a diffractive optical waveguide substrate and a partially reflecting prism array. The diffractive optical waveguide substrate is provided with a first diffractive optical element and a second diffractive optical element. The partially reflecting prism array is located in the light-emitting region of the diffractive optical waveguide substrate and is connected to the diffractive optical waveguide substrate. The first diffractive optical element has a periodic structure in a first direction, and the second diffractive optical element has a periodic structure. The periodic structure of the second diffractive optical element forms an angle θ with the second direction, so that the light extends in the first direction and is transmitted in the second direction. The first direction is perpendicular to the second direction.

[0009] The partial reflection prism array is composed of several parallel partial reflection prisms arranged along a second direction. Each partial reflection prism has a reflective surface facing the diffraction waveguide substrate, and the reflective surface is coated with a partial reflection film.

[0010] Furthermore, the diffractive waveguide substrate and the partially reflective prism array are made of wafer material.

[0011] Furthermore, the first and second diffractive optical elements are surface relief gratings or volume holographic gratings.

[0012] Furthermore, when the first and second diffractive optical elements are surface-embossed gratings, the manufacturing process is as follows:

[0013] The first and second diffractive optical elements are imprinted on the diffractive waveguide substrate.

[0014] Furthermore, when the first and second diffractive optical elements are volume holographic gratings, they are obtained by performing double-beam interference exposure on the diffractive waveguide substrate.

[0015] Furthermore, the partially reflective prism array is bonded to the diffractive waveguide substrate using a refractive index matching liquid.

[0016] Furthermore, the reflective films of different parts of the reflective prism have different reflectivities, which increase sequentially along the second direction.

[0017] Furthermore, the periodicity of the periodic structure of the first diffractive optical element ranges from 200 nm to 500 nm, and the periodicity of the periodic structure of the second diffractive optical element ranges from 180 nm to 350 nm.

[0018] Furthermore, the included angle θ ranges from 30° to 60°.

[0019] Furthermore, the refractive index of the wafer material is n = 1.5 to 2.5.

[0020] Compared with the prior art, the significant advantages of this invention are:

[0021] 1. In this invention, diffractive optical elements are used only in the first direction, and a partial reflection prism array structure is used in the second direction, which greatly reduces the process difficulties and low yield caused by using a partial reflection prism array structure in both directions.

[0022] 2. In this invention, a partial reflection prism array structure is used instead of diffractive optical elements in the first extension direction, which avoids light leakage and rainbow effect in diffractive waveguides. At the same time, by controlling the reflectivity of the coating layer of the partial reflection prism, the efficiency and uniformity of the coupled beam can also be improved. Attached Figure Description

[0023] Figure 1 This refers to the light leakage phenomenon in traditional two-dimensional exit pupil diffraction waveguides in existing technologies.

[0024] Figure 2 This is a schematic diagram of a two-dimensional exit pupil extended optical waveguide structure according to the present invention;

[0025] Figure 3 This is a schematic diagram of the structure of the partial reflective array prism of the present invention;

[0026] Figure 4 This is an optical path diagram of the two-dimensional exit pupil extended waveguide structure of the present invention;

[0027] Figure 5 This is a schematic diagram of the structure of the second embodiment of the present invention.

[0028] Explanation of reference numerals in the attached figures: 1. Diffraction grating; 11. Diffraction waveguide substrate; 11-1. First diffraction optical element; 11-2. Second diffraction optical element; 12. Partial reflection prism array; S1. Reflective surface. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0030] First embodiment, such as Figure 2 As shown, a two-dimensional exit pupil extended waveguide structure includes a diffractive waveguide substrate 11 and a partially reflecting prism array 12. The diffractive waveguide substrate 11 is provided with a first diffractive optical element 11-1 and a second diffractive optical element 11-2. The partially reflecting prism array 12 is located in the light-emitting region of the diffractive waveguide substrate 11 and is connected to the diffractive waveguide substrate 11. The partially reflecting prism array 12 and the diffractive waveguide substrate 11 are bonded together by a refractive index matching liquid.

[0031] The first diffractive optical element 11-1 and the second diffractive optical element 11-2 can be either surface relief gratings or volume holographic gratings. The first diffractive optical element 11-1 has a periodic structure in the first direction (+X direction), with a period ranging from 200 nm to 500 nm. The first diffractive optical element 11-1 is responsible for coupling the light emitted from the optomechanism into the optical waveguide, where it undergoes total internal reflection transmission. The second diffractive optical element 11-2 has a periodic structure with a period ranging from 180 nm to 350 nm. Its periodic structure forms an angle θ with the second direction (-Y direction), with θ ranging from 30° to 60°. Furthermore, the periodic structure of the first diffractive optical element 11-1 and the second diffractive optical element 11-2 is on the plane formed by the first direction and the second direction. The light emission direction of the second diffractive optical element 11-2 is the second direction. That is, the unit cell in the periodic structure of the second diffractive optical element 11-2 gradually approaches the first diffractive optical element 11-1 in the opposite direction of the second direction, so that the light can be extended in the +X direction and transmitted in the -Y direction at the same time, reaching the partial reflection prism array 12.

[0032] The partial reflection prism array 12 is assembled from several parallel partial reflection prisms, which are arranged along the -Y direction, such as... Figure 3As shown, each partially reflecting prism has a reflective surface S1 facing the diffractive waveguide substrate. A partially reflective film is deposited on the reflective surface S1, enabling both light reflection and transmission, thus allowing the light beam to expand in the second direction and couple out to the human eye. The reflectivity of the partially reflective film on each reflective surface S1 increases sequentially along the second direction to obtain a uniformly coupled outgoing light beam. On one hand, light incident on the reflective surface S1 of the partially reflecting prism can be reflected and coupled out from the two-dimensional exit pupil expansion waveguide structure; on the other hand, light can pass through the reflective surface S1 and propagate in the -Y direction, thus achieving light expansion in the -Y direction. The diffractive waveguide substrate 11 and the partially reflecting prism array 12 are combined to form a waveguide structure, achieving light expansion in both directions, thereby obtaining the desired eye socket size.

[0033] like Figure 4 As shown, the region where the first diffractive optical element 11-1 is located is the coupling region, which is responsible for coupling the light emitted from the optomechanical system into the two-dimensional exit pupil extended waveguide structure. The region where the second diffractive optical element 11-2 is located is the first extension region, which is responsible for extending the light coupled into the two-dimensional exit pupil extended waveguide structure in the +X direction. The region where the partial reflection prism array 12 is located is the coupling region, which is responsible for extending the beam in the -Y direction and coupling the beam out.

[0034] In this invention, the extension in the first direction utilizes a second diffractive optical element 11-2, and the extension and coupling in the second direction utilize a partially reflecting prism array 12. If the first diffractive optical element 11-1 and the second diffractive optical element 11-2 in the diffractive waveguide substrate 11 are surface-mounted gratings, a mask pattern of the diffractive optical element can be obtained on photoresist through optical exposure or electron beam exposure. Then, ion etching is used to deposit the pattern on the photoresist onto the diffractive waveguide substrate. Finally, nanoimprint lithography is used for mass replication to obtain the first diffractive optical element 11-1 and the second diffractive optical element 11-2 on the diffractive waveguide substrate, which is then cut into... Figure 2 The shape shown or any other arbitrary shape. The diffractive waveguide substrate 11 is made of wafer material. If the first diffractive optical element 11-1 and the second diffractive optical element 11-2 are volume holographic gratings, they can be obtained by double-beam interference exposure. The partial reflection prism array 12 can be formed by cutting, grinding, polishing, and coating the wafer and then bonding it. The wafer used for imprinting or exposing the diffractive waveguide substrate 11 is the same as that used for the partial reflection prism array 12. The refractive index n of the wafer material is 1.5 to 2.5. The thickness t of the diffractive waveguide substrate 11 and the partial reflection prism array 12 satisfies: t = 0.5 mm to 4 mm.

[0035] In this invention, since the second diffractive optical element 11-2 is responsible for the propagation of light in the first direction, there is no need to use a partial reflection prism array for propagation. The partial reflection prism array 12 is responsible for the propagation and coupling of light in the second direction. Therefore, in the entire two-dimensional exit pupil waveguide structure, only the partial reflection prisms used in the partial reflection prism array 12 need to be spliced ​​and assembled. Compared with the traditional two-dimensional exit pupil geometric array waveguide, this greatly reduces the difficulty of the process and improves the product yield. At the same time, since the coupling region uses a partial reflection prism array, compared with the traditional two-dimensional exit pupil diffractive waveguide structure, firstly, the beam is coupled only in the direction of the human eye (+Z direction), and there is no beam coupling in the opposite direction (-Z direction). Therefore, there is no light leakage phenomenon that is common in traditional two-dimensional exit pupil diffractive waveguides. In traditional two-dimensional exit pupil diffractive waveguides, since the coupling region uses a diffraction grating 1, which has both transmission and reflection orders, while coupling the beam from the waveguide to the human eye, it also couples the beam to the outside world. Figure 1 As shown; secondly, ambient light cannot interact with the partial reflection prism array 12 in the coupling region, so there is no rainbow effect that is common in diffractive waveguides, that is, the dispersion effect generated when ambient light interacts with the diffractive optics in the coupling region.

[0036] Second embodiment, such as Figure 5 As shown, a two-dimensional exit pupil expansion waveguide structure includes a diffractive waveguide substrate 11 and a partial reflection prism array 12. 11-1 is a first diffractive optical element responsible for coupling light into the waveguide and achieving total internal reflection transmission. 11-2 is a second diffractive optical element responsible for expanding light in the first direction (+Y direction) and transmitting the light to the region of the partial reflection prism array 12. The partial reflection prism array 12 is composed of partial reflection prisms, each with a reflective surface S1 facing the diffractive waveguide substrate 11. The reflective surface S1 is coated with a corresponding partial reflection film layer. The reflectivity of different partial reflection prism films is different, generally increasing gradually with the beam expansion direction. The region of the partial reflection prism array 12 is responsible for expanding light in the second direction (+X direction) and coupling light out of the two-dimensional exit pupil expansion waveguide structure to enter the human eye. The main difference between the second embodiment and the first embodiment is that the first and second directions are different, corresponding to the left and right eyes in practical applications. Other identical structures can be found in the first embodiment.

[0037] The first and second directions are not limited to the two schemes described in the first and second embodiments, and may have other variations, such as the first direction being the +X direction and the second direction being the +Z direction, all of which are within the scope of protection of this application.

[0038] The embodiments described above are merely illustrative of one or more implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this invention should be determined by the appended claims.

Claims

1. A two-dimensional exit pupil extended optical waveguide structure, characterized in that, The device includes a diffractive waveguide substrate and a partially reflecting prism array. The diffractive waveguide substrate is provided with a first diffractive optical element and a second diffractive optical element. The partially reflecting prism array is located in the light-emitting region of the diffractive waveguide substrate and is connected to the diffractive waveguide substrate. The first diffractive optical element has a periodic structure in a first direction, and the second diffractive optical element has a periodic structure. The periodic structure of the second diffractive optical element forms an angle θ with the second direction, so that the light extends in the first direction and is transmitted in the second direction. The first direction is perpendicular to the second direction. The partial reflection prism array is composed of several parallel partial reflection prisms arranged along a second direction. Each partial reflection prism has a reflective surface facing the diffraction waveguide substrate, and the reflective surface is coated with a partial reflection film.

2. The two-dimensional exit pupil extended optical waveguide structure according to claim 1, characterized in that, The diffractive waveguide substrate and the partial reflective prism array are made of wafer material.

3. The two-dimensional exit pupil extended optical waveguide structure according to claim 2, characterized in that, The first and second diffractive optical elements are surface relief gratings or volume holographic gratings.

4. The two-dimensional exit pupil extended optical waveguide structure according to claim 3, characterized in that, When the first and second diffractive optical elements are surface-embossed gratings, the manufacturing process is as follows: The first and second diffractive optical elements are imprinted on the diffractive waveguide substrate.

5. The two-dimensional exit pupil extended optical waveguide structure according to claim 3, characterized in that, When the first and second diffractive optical elements are volume holographic gratings, they are obtained by performing double-beam interference exposure on a diffractive waveguide substrate.

6. The two-dimensional exit pupil extended optical waveguide structure according to claim 1, characterized in that, The partially reflective prism array is bonded to the diffractive waveguide substrate using a refractive index matching liquid.

7. The two-dimensional exit pupil extended optical waveguide structure according to claim 1, characterized in that, Different reflective prisms have different reflectivity in their partial reflective film layers, and the reflectivity increases sequentially along the second direction.

8. The two-dimensional exit pupil extended optical waveguide structure according to claim 1, characterized in that, The periodicity of the periodic structure of the first diffractive optical element ranges from 200 nm to 500 nm, and the periodicity of the periodic structure of the second diffractive optical element ranges from 180 nm to 350 nm.

9. The two-dimensional exit pupil extended optical waveguide structure according to claim 1, characterized in that, The included angle θ ranges from 30° to 60°.

10. The two-dimensional exit pupil extended optical waveguide structure according to claim 2, characterized in that, The refractive index of the wafer material is n = 1.5 to 2.5.

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