Two-dimensional pupil-expanding optical waveguide with uniform brightness and display product

Abstract

The utility model discloses a two-dimensional pupil-expanding optical waveguide with uniform brightness and a display product. The optical waveguide has an x direction, a y direction and a z direction which are perpendicular to one another and comprises a coupling-in grating, a first turning grating, a second turning grating and a coupling-out grating, the coupling-in grating is used for coupling-in light and enabling the light to be transmitted to the first turning grating in the y direction, the first turning grating is used for enabling the light to be expanded in the y direction and enabling the light to be transmitted to the second turning grating in the x direction, and the coupling-out grating is used for coupling-out light. The second turning grating is used for expanding the light in the x direction and propagating the light to the out-coupling grating in the y direction, and the out-coupling grating is used for expanding the light in the y direction and coupling out the light; the first turning grating and the second turning grating are volume holographic gratings or polarization volume holographic gratings; the first turning grating is divided into a plurality of sub-regions along the x direction and the y direction, and each sub-region has different refractive index modulation degrees delta n; the second turning grating is divided into a plurality of sub-regions along the x direction and the y direction, and each sub-region has a different refractive index modulation degree delta n.

Description

TECHNICAL FIELD

[0001] The present scheme belongs to the technical field of optical waveguide and specifically relates to a two-dimensional pupil expanding optical waveguide with uniform brightness and a display product. BACKGROUND

[0002] With the further improvement of users' requirements for visual experience, augmented reality (AR) technology emerges as the times require. By superimposing virtual elements on the scene of the real world, AR technology becomes an important bridge connecting the digital world and the physical world. In order to maintain high-quality display effect while ensuring the portability and comfort of AR devices, optical waveguide technology gradually stands out and becomes the most promising optical solution in AR technology.

[0003] Optical waveguide technology is based on the principle of total internal reflection. Light from the light engine is coupled into a high refractive index transparent substrate material (such as glass or resin), and transmitted inside the substrate until it is close to the eye, and then coupled out through a specific optical structure. The core advantage of this technology is that it can greatly optimize the design of the head-mounted device, making the optical system more compact and aesthetic. Compared with other solutions such as prisms and free-form surfaces, optical waveguide technology can reduce the obstruction of external vision, effectively improving the visual experience of the wearer. At the same time, it also improves the weight distribution of the AR device, thereby reducing the fatigue of the user when wearing for a long time and improving the comfort of the device. Therefore, optical waveguide technology has significant advantages in the lightweight and appearance design of AR devices.

[0004] Currently, optical waveguide technology mainly includes two types: geometric optical waveguide and diffractive optical waveguide. The coupling process of geometric optical waveguide mainly depends on refractive and reflective optical elements, such as prisms and mirrors. Array optical waveguide, as one of the most representative solutions in geometric optical waveguide, couples light beams into the waveguide through mirrors. The coupling-out area is composed of a mirror array coated with a semi-transparent and semi-reflective film. Each layer of film will couple part of the light beam out of the waveguide and into the human eye, while the remaining light beam will continue to propagate in the waveguide until the last layer of film completely couples the remaining light beam out of the waveguide and finally into the human eye. Due to the use of geometric optics principles, array optical waveguide can provide extremely high image quality. However, since the number of coated layers of each mirror in the array optical waveguide may be as high as ten or even dozens, the coated mirror needs to be bonded by special glue and cut into the shape of the waveguide at a specific angle, which leads to a complex production process and low yield. In addition, this structure makes it more difficult to achieve two-dimensional pupil expansion, further increasing the manufacturing difficulty and cost.

[0005] Compared with the geometric optical waveguide, the diffraction optical waveguide uses the diffraction effect of the grating to realize the coupling-in and coupling-out of the light beam. The basic working principle is to divide the incident light into multiple diffraction orders through the grating with a periodic structure, and each diffraction order corresponds to a different diffraction angle. By optimizing the design, the diffraction efficiency of a certain specific diffraction order is maximized, thereby realizing the coupling-in and coupling-out of the light. The diffraction optical waveguide has a large degree of design freedom, and can realize two-dimensional pupil expansion by adjusting the period, angle and shape of the grating. Although the diffraction optical waveguide has great development potential, it still faces some challenges in terms of brightness uniformity and other aspects, and technical breakthroughs are urgently needed. Utility model content

[0006] The present scheme aims to overcome at least one of the defects in the prior art, and provides a two-dimensional pupil expansion light waveguide with uniform brightness, so as to easily realize two-dimensional pupil expansion while having high brightness uniformity.

[0007] In order to solve the above technical problems, the following technical solutions are adopted:

[0008] In a first aspect, a two-dimensional pupil expansion light waveguide with uniform brightness is provided. The light waveguide has mutually perpendicular x-direction, y-direction and z-direction, and has a coupling-in region, a turning region and a coupling-out region in the projection plane parallel to the x-direction and the y-direction and perpendicular to the z-direction. The light waveguide includes a coupling-in grating, a first turning grating, a second turning grating and a coupling-out grating. The coupling-in grating is located in the coupling-in region, the first turning grating and the second turning grating are located in the turning region, and the coupling-out grating is located in the coupling-out region. The coupling-in grating is used for coupling-in light and making the light propagate along the y-direction to the first turning grating. The first turning grating is used for expanding the light along the y-direction and making the light propagate along the x-direction to the second turning grating. The second turning grating is used for expanding the light along the x-direction and making the light propagate along the y-direction to the coupling-out grating. The coupling-out grating is used for expanding the light along the y-direction and coupling-out the light. The first turning grating and the second turning grating are both volume holographic gratings or polarization volume holographic gratings. The first turning grating is divided into multiple sub-regions along the x-direction and the y-direction, and each sub-region has a different refractive index modulation degree ; the second turning grating is divided into multiple sub-regions along the x-direction and the y-direction, and each sub-region has a different refractive index modulation degree .

[0009] The present scheme easily realizes two-dimensional pupil expansion by using the first turning grating and the second turning grating which are both volume holographic gratings or polarization volume holographic gratings, and divides the first turning grating and the second turning grating into two dimensions. By modulating the refractive index modulation degree of different sub-regions in the first turning grating , improve the diffraction efficiency of the light propagating from the first turning grating to the second turning grating, reduce the light leaking out of the first turning grating along the y direction, improve the uniformity of the field of view along the x direction, and modulate the refractive index modulation of different sub-regions in the second turning grating , improve the diffraction efficiency of the light propagating from the second turning grating to the out-coupling grating, reduce the light leaking out of the second turning grating along the x direction, improve the uniformity of the field of view along the y direction, and make the entire field of view of the optical waveguide have high brightness uniformity.

[0010] The grating vectors of the first turning grating and the second turning grating may be the same or different. If the grating vectors of the first turning grating and the second turning grating are the same, each sub-region of the first turning grating has the same grating vector along the z direction , and each sub-region of the second turning grating has the same grating vector along the z direction . If the grating vectors of the first turning grating and the second turning grating are different, each sub-region of the first turning grating can have different grating vectors along the z direction , and each sub-region of the second turning grating can have different grating vectors along the z direction . For the case where the grating vectors of the first turning grating and the second turning grating are different, the range of wavelengths and angles of light propagating into the first turning grating can be improved by modulating the grating vectors along the z direction of different sub-regions in the first turning grating , and the range of wavelengths and angles of light propagating into the second turning grating can be improved by modulating the grating vectors along the z direction of different sub-regions in the second turning grating , thereby facilitating the expansion of the field of view (FOV) of the optical waveguide and making the diffraction light intensity at each position of the FOV as uniform as possible, so as to achieve high brightness and high brightness uniformity display effect under large FOV.

[0011] The in-coupling grating and the out-coupling grating are preferably half-mirror arrays, so that the optical waveguide becomes a composite optical waveguide integrating diffraction and array. The half-mirror array can couple in and out image beams based on the principle of geometric optics, and can provide extremely high image quality, so that the optical waveguide has high light efficiency. The composite optical waveguide combines the advantages of high light efficiency of array optical waveguide and easy realization of two-dimensional pupil expansion of diffraction optical waveguide, and can not only easily realize two-dimensional pupil expansion, but also take into account high light efficiency and high brightness uniformity.

[0012] The angle between each mirror surface in the half-mirror array of the in-coupling grating and the out-coupling grating and the y direction β is preferably satisfied: 20°≤ β|≤40°, grating vector of the first turning grating and the second turning grating Preferably, 9 rad / μm≤ ≤25 rad / μm, grating vector of the first turning grating and the second turning grating In the grating K-domain diagram, the angle with the z direction delta Preferably, 90°≤ delta |≤170°, grating vector of the first turning grating and the second turning grating in the z direction Preferably, 1.6 rad / μm≤ ≤4.8 rad / μm, which is conducive to improving the out-coupling efficiency and brightness uniformity. When all the above conditions are met, the out-coupling efficiency of RGB three-color light shows a high level, and its uniformity is also very excellent, which is expected to be applied to AR products to achieve high-quality image effects and provide users with a comfortable viewing experience.

[0013] The optical waveguide can be configured to sequentially stack a first cover plate layer, a first grating layer, and a second grating layer along the z direction, the first turning grating and the second turning grating being located in the first grating layer, and the in-coupling grating and the out-coupling grating being located in the second grating layer. This reasonable structure layer design is helpful to simplify the manufacturing process, reduce production cost, and improve the reliability and stability of the optical waveguide. Especially for a composite optical waveguide, the first turning grating and the second turning grating using volume holographic gratings or polarization volume holographic gratings are formed by different processes than the in-coupling grating and the out-coupling grating using a half-transmission half-reflection mirror array, and the structure layer design is more conducive to the realization of the composite optical waveguide.

[0014] The optical waveguide can also be configured to sequentially stack a first cover plate layer, a first grating layer, a second grating layer, a third grating layer, and a second cover plate layer along the z direction, the first turning grating and the second turning grating being located in the first grating layer and the third grating layer, and the in-coupling grating and the out-coupling grating being located in the second grating layer. This reasonable structure layer design is helpful to simplify the manufacturing process, reduce production cost, and improve the reliability and stability of the optical waveguide. Especially for a composite optical waveguide, the first turning grating and the second turning grating using volume holographic gratings or polarization volume holographic gratings are formed by different processes than the in-coupling grating and the out-coupling grating using a half-transmission half-reflection mirror array, and the structure layer design is more conducive to the realization of the composite optical waveguide.

[0015] Whether the optical waveguide is configured with a third grating layer and a second cover plate layer, the turning region and the out-coupling region can partially overlap to form an overlapping region, the second turning grating being partially located in the overlapping region, and the out-coupling grating being partially located in the overlapping region. Since the light coupled out of the out-coupling grating does not satisfy the Bragg matching condition of the second turning grating, the light coupled out of the out-coupling grating will not be affected by the second turning grating, and thus can be directly coupled out of the optical waveguide to reach the human eye.

[0016] In a second aspect, a display product is provided. The display product comprises a projection light engine and the above-mentioned two-dimensional pupil expanding light waveguide with uniform brightness, and the projection light engine emits an image light beam to the coupling-in region of the light waveguide.

[0017] The light waveguide adopted in the scheme easily realizes two-dimensional pupil expansion through the first turning grating and the second turning grating which are both volume holographic gratings or polarization volume holographic gratings, and the first turning grating and the second turning grating are two-dimensionally partitioned, the refractive index modulation degree of different sub-regions in the first turning grating is modulated , the diffraction efficiency of light rays propagated from the first turning grating to the second turning grating is improved, the light rays leaking out of the first turning grating along the y direction are reduced, and the uniformity of the field of view along the x direction is improved, the refractive index modulation degree of different sub-regions in the second turning grating is modulated , the diffraction efficiency of light rays propagated from the second turning grating to the coupling-out grating is improved, the light rays leaking out of the second turning grating along the x direction are reduced, and the uniformity of the field of view along the y direction is improved, so that the entire field of view of the light waveguide has high brightness uniformity.

[0018] Compared with the prior art, the scheme has the following beneficial effects: the scheme easily realizes two-dimensional pupil expansion through the first turning grating and the second turning grating which are both volume holographic gratings or polarization volume holographic gratings, and the first turning grating and the second turning grating are two-dimensionally partitioned, the refractive index modulation degree of different sub-regions in the first turning grating and the second turning grating is modulated , and the brightness uniformity of the entire field of view is improved. BRIEF DESCRIPTION OF DRAWINGS

[0019] The drawings are only used for illustrative description and cannot be understood as a limitation to the scheme; in order to better illustrate the scheme, some components in the drawings may be omitted, enlarged or reduced, and do not represent the size of the actual product; it is understandable for those skilled in the art that some well-known structures and their descriptions in the drawings may be omitted.

[0020] Figure 1 is a structural schematic diagram of a display product.

[0021] Figure 2 is a top view structure and an optical path schematic diagram of a light waveguide.

[0022] Figure 3 is a partitioning schematic diagram of a first turning grating and a second turning grating of a light waveguide.

[0023] Figure 4 is a grating K domain diagram schematic diagram.

[0024] Figure 5 is a local enlarged schematic diagram of a coupling-in grating and a coupling-out grating.

[0025] Figure 6is a side view structural schematic diagram of an optical waveguide (three-layer structure).

[0026] Figure 7 is a side view structural schematic diagram of an optical waveguide (five-layer structure).

[0027] Figure 8 is a top view structural schematic diagram of an optical waveguide (partially overlapped).

[0028] Figure 9 is a top view structural schematic diagram of a measured optical waveguide.

[0029] Legend: projector 100, optical waveguide 200, coupling-in region 201, turning region 202, coupling-out region 203, coupling-in grating 211, first turning grating 212, second turning grating 213, coupling-out grating 214, first cover plate layer 221, first grating layer 222, second grating layer 223, third grating layer 224, second cover plate layer 225, human eye 300. DETAILED DESCRIPTION

[0030] In order for those skilled in the art to better understand the present scheme, the present scheme will be further described in detail below in conjunction with specific embodiments.

[0031] Figure 1 A possible display product is illustrated, which is configured with a projector 100 and an optical waveguide 200. The projector 100 is similar to a projector, which projects an image light beam with a virtual image into the optical waveguide 200. The optical waveguide 200 transmits and couples out the image light beam from the projector 100 into a human eye 300, forming a virtual image, and realizing different effects such as virtual reality (VR), augmented reality (AR), mixed reality (MR), etc. According to different effects, the display product can be classified into different types. Among them, the VR display product is a carrier of virtual reality technology, which generates a three-dimensional virtual world allowing users to interact with it through computer technology, etc., so that the user has a sense of being there. The AR display product is a carrier of augmented reality technology, which applies virtual information to the real world through computer technology, etc., so that the real environment and virtual objects exist at the same time in real time. The MR display product is a carrier of mixed reality technology, which combines the characteristics of VR and AR, allowing users to interact with real and virtual environments.

[0032] Figures 2-3The possible optical waveguide is illustrated, in which the in-coupling grating 211, the first turning grating 212, the second turning grating 213 and the out-coupling grating 214 are configured. Not only can two-dimensional pupil expansion be easily realized, but also high brightness uniformity is achieved. The optical waveguide is in a three-dimensional rectangular coordinate system, having mutually perpendicular x direction (positive direction of x axis), y direction (positive direction of y axis) and z direction (positive direction of z axis). The optical waveguide and each component thereof (including the in-coupling grating 211, the first turning grating 212, the second turning grating 213, the out-coupling grating 214 and the cover plate layer, the grating layer and the like in the following text) have two opposite surfaces, namely a first surface and a second surface, both of which are parallel to the xOy plane, i.e. parallel to the x direction and the y direction and perpendicular to the z direction.

[0033] The optical waveguide is made of a material with high refractive index, which itself serves as a high refractive index medium, and the surrounding air serves as a low refractive index medium. The two surfaces of the optical waveguide serve as the interface between the high refractive index medium and the low refractive index medium. When light is incident from the high refractive index medium to the interface with the low refractive index medium, the absolute value of the incident angle is greater than the critical angle of total reflection theta c The light with the absolute value of the incident angle greater than the critical angle of total reflection will be completely reflected back, thereby propagating forward along the medium extension direction in the form of back-and-forth reflection in the high refractive index medium.

[0034] The projection of the optical waveguide in the xOy plane or a plane parallel to the xOy plane, i.e. a plane parallel to the x direction and the y direction and perpendicular to the z direction, can be divided into the in-coupling region 201, the turning region 202 and the out-coupling region 203. The in-coupling grating 211 is located in the in-coupling region 201, used for coupling the image beam into the optical waveguide, so that the image beam can propagate in the optical waveguide in the form of back-and-forth reflection and propagate along the y direction to the first turning grating 212. The first turning grating 212 is located in the turning region, used for changing the propagation direction of the image beam in the optical waveguide, so that the image beam can propagate along the x direction to the second turning grating 213 and expand the beam range in the y direction, realizing one-dimensional pupil expansion. The second turning grating 213 is also located in the turning region, used for changing the propagation direction of the image beam in the optical waveguide, so that the image beam can propagate along the y direction to the out-coupling grating 214 and expand the beam range in the x direction, realizing two-dimensional pupil expansion. The out-coupling grating 214 is located in the out-coupling region 203, used for coupling the image beam out of the optical waveguide, so that the image beam propagating in the optical waveguide in the form of back-and-forth reflection can exit to the outside of the optical waveguide, enter the human eye and expand the beam range in the y direction.

[0035] The first turning grating 212 and the second turning grating 213 can be volume holographic grating (VHG) or polarization volume holographic grating (PVG). The volume holographic grating and the polarization volume holographic grating have a refractive index modulation degree. and raster vector , raster vector It can be expressed as:

[0036]

[0037] in, is the grating vector along the x direction, that is, the grating vector Component in the x direction; is the grating vector along the y direction, that is, the grating vector Component in the y direction; is the grating vector along the z direction, that is, the grating vector Component in the z direction.

[0038] The first turning grating 212 can be divided into M*N sub-regions with equal or non-equal spacing along the x-direction and the y-direction, for example, 4*2 sub-regions (e.g. Figure 3 ), each sub-region has a different refractive index modulation By modulating the refractive index of different sub-regions in the first turning grating 212 , which can improve the diffraction efficiency of light propagating from the first turning grating 212 to the second turning grating 213, reduce the light leaking out of the first turning grating 212 along the y direction, and improve the uniformity of the field of view along the x direction. Similarly, the second turning grating 213 can also be divided into P*Q sub-regions with equal or unequal spacing along the x and y directions, for example, 4*4 (such as Figure 3 ), each sub-region has a different refractive index modulation By modulating the refractive index of different sub-regions in the second turning grating 213 , can improve the diffraction efficiency of the light propagating from the second turning grating 213 to the outcoupling grating 214, reduce the light leaking out of the second turning grating 213 along the x-direction, and improve the uniformity of the field of view along the y-direction. As a result, the brightness uniformity of the entire field of view of the optical waveguide is improved. Specifically, the refractive index modulation degree of each sub-region of the first turning grating 212 is The refractive index modulation degree of each sub-region of the second turning grating 213 can be increased in sequence along the y direction. The refractive index of each sub-region of the first turning grating 212 and the second turning grating 213 is modulated by the degree of the refractive index of each sub-region of the first turning grating 212 and the second turning grating 213. It needs to be independently regulated according to actual conditions and does not necessarily strictly follow a certain law of change.

[0039] Grating vectors of the first turning grating 212 and the second turning grating 213 They can be the same or different. If the grating vectors of the first turning grating 212 and the second turning grating 213 are If the same, each sub-region of the first turning grating 212 has the same grating vector along the z direction Each sub-region of the second turning grating 213 has the same grating vector along the z direction If the grating vectors of the first turning grating 212 and the second turning grating 213 Different, each sub-region of the first turning grating 212 may have a different grating vector along the z direction. Each sub-region of the second turning grating 213 may have a different grating vector along the z direction. The grating vectors of each sub-region of the first turning grating 212 and the second turning grating 213 along the z direction are The grating vectors along the z direction of different sub-regions in the first turning grating 212 are modulated. , which can improve the selection range of the wavelength and angle of the light propagating into the first turning grating 212 by the first turning grating 212; by modulating the grating vectors along the z direction of different sub-regions in the second turning grating 213 , which can improve the selection range of the wavelength and angle of the second turning grating 213 for the light propagating into the second turning grating 213; thereby helping to expand the field of view (FOV) of the optical waveguide, making the diffracted light intensity at each position of the FOV as uniform as possible, thereby achieving high brightness and high brightness uniformity display effects under a large FOV.

[0040] Raster Vector There is an angle between the grating K-domain image and the z-direction delta ,like Figure 4 The grating vectors of the first turning grating 212 and the second turning grating 213 Best to meet: 9 rad / μm≤ ≤25 rad / μm, grating vectors of the first turning grating 212 and the second turning grating 213 The angle with the z direction in the grating K-domain diagram delta It is best to meet: 90°≤| delta|≤170°, grating vectors of the first turning grating 212 and the second turning grating 213 along the z direction Preferably, 1.6 rad / µm≤ ≤4.8 rad / µm, which is conducive to improving the out-coupling efficiency and brightness uniformity.

[0041] The in-coupling grating 211 and the out-coupling grating 214 can be a half-mirror array, thereby making the optical waveguide a composite optical waveguide integrating diffraction and array. The in-coupling grating 211 and the out-coupling grating 214 can also be a surface relief grating, a volume holographic grating or a polarization volume holographic grating, thereby making the optical waveguide a diffractive optical waveguide. In contrast, the half-mirror array of the former couples in and out the image light beams based on the principle of geometric optics, which can provide extremely high image quality, making the optical waveguide have high light efficiency. The composite optical waveguide combines the advantages of high light efficiency of the array optical waveguide and the ease of realizing two-dimensional pupil expansion of the diffractive optical waveguide, which not only can easily realize two-dimensional pupil expansion, but also can balance high light efficiency and high brightness uniformity. There is an included angle between each mirror surface of the half-mirror array and the y direction β As shown in Figure 5 , the included angle β Preferably, 20°≤ β ≤40°, which is conducive to improving the out-coupling efficiency and brightness uniformity.

[0042] The optical waveguide can be configured as a three-layer structure, as shown in Figure 6 . Figure 6 The optical waveguide is configured with a first cover plate layer 221, a first grating layer 222 and a second grating layer 223, which are sequentially stacked along the z direction. The first turning grating 212 and the second turning grating 213 are configured in the first grating layer 222, and the in-coupling grating 211 and the out-coupling grating 214 are configured in the second grating layer 223. This reasonable structure layering design helps to simplify the manufacturing process, reduce production costs, and improve the reliability and stability of the optical waveguide. Especially for the composite optical waveguide, the first turning grating 212 and the second turning grating 213 using the volume holographic grating or the polarization volume holographic grating are formed by different processes respectively from the in-coupling grating 211 and the out-coupling grating 214 using the half-mirror array, and the structure layering design is more conducive to the realization of the composite optical waveguide.

[0043] The optical waveguide can also be configured as a five-layer structure, as shown in Figure 7 . Figure 7The optical waveguide shown is not only configured with the first cover layer 221, the first grating layer 222 and the second grating layer 223, but also configured with the third grating layer 224 and the second cover layer 225, which are sequentially stacked along the z direction. The first turning grating 212 and the second turning grating 213 are configured in the first grating layer 222 and the third grating layer 224, and the in-coupling grating 211 and the out-coupling grating 214 are configured in the second grating layer 223. This reasonable structure layer design helps to simplify the manufacturing process, reduce production cost, improve the reliability and stability of the optical waveguide. Especially for the composite optical waveguide, the first turning grating 212 and the second turning grating 213 using volume holographic gratings or polarization volume holographic gratings are formed by different processes respectively, and the structure layer design is more conducive to the realization of the composite optical waveguide. For the first grating layer 222 and the third grating layer 224, one of them can be configured with the first turning grating 212 and the other with the second turning grating 213, or both of them can be configured with the first turning grating 212 and the second turning grating 213.

[0044] Whether the optical waveguide is configured as a three-layer structure or a five-layer structure, the turning region 202 can partially overlap with the out-coupling region 203 to form an overlapping region, such as Figure 8 The second turning grating 213 is partially located in the overlapping region, and the out-coupling grating 214 is also partially located in the overlapping region, and the two overlap or spatially overlap in the overlapping region. Since the light coupled out of the out-coupling grating 214 does not satisfy the Bragg matching condition of the second turning grating 213, the light coupled out of the out-coupling grating 214 will not be affected by the second turning grating 213, and thus can be directly coupled out of the optical waveguide to reach the human eye.

[0045] Whether the composite optical waveguide is configured as a three-layer structure or a five-layer structure, whether the second turning grating 213 and the out-coupling grating 214 have no overlap or partial overlap, the grating vectors of the first turning grating 212 and the second turning grating 213 in each sub-region along the z direction are the same or different, and the angle between each mirror surface of the half-transmission half-reflection mirror array used as the in-coupling grating 211 and the out-coupling grating 214 and the y direction β is preferably satisfied: 20°≤| β ≤40°, the grating vectors of the first turning grating 212 and the second turning grating 213 are preferably satisfied: 9 rad / μm≤ ≤25 rad / μm, the grating vectors of the first turning grating 212 and the second turning grating 213 in the grating K domain diagram and the z direction delta are preferably satisfied: 90°≤|delta |≤170°, the grating vector of the first turning grating 212 and the second turning grating 213 along the z direction Best to meet: 1.6 rad / μm≤ ≤4.8 rad / μm, which is conducive to improving outcoupling efficiency and brightness uniformity. When all the above conditions are met, the outcoupling efficiency of the three colors of RGB light is high, and its uniformity is also excellent. It is expected to be applied to AR products to achieve high-quality image effects and provide users with a comfortable viewing experience.

[0046] by Figure 9 Taking the composite optical waveguide shown in FIG as an example, it is configured as a five-layer structure, the coupling-in grating 211 and the coupling-out grating 214 are selected from a semi-transparent and semi-reflective mirror array and are configured in the second grating layer 223, the first turning grating 212 and the second turning grating 213 are selected from a volume holographic grating and the grating vector Similarly, the first turning grating 212 is configured on the first grating layer 222 and is divided into 3*2 sub-regions, each sub-region having a different refractive index modulation degree. and the same raster vector along the z direction The second turning grating 213 is configured on the third grating layer 224 and is divided into 2*4 sub-regions, each sub-region having a different refractive index modulation degree. and the same raster vector along the z direction , the angle between the coupling-in grating 211 and the coupling-out grating 214 β , the grating vectors of the first turning grating 212 and the second turning grating 213 , angle delta and raster vector The test results show that the brightness uniformity of red light R reaches 49.36%, and the luminous efficiency percentage reaches 1.6%; the brightness uniformity of blue light B reaches 65.81%, and the luminous efficiency percentage reaches 8.5%; the brightness uniformity of green light G reaches 60.64%, and the luminous efficiency percentage reaches 3.8%.

[0047] Obviously, the above embodiments of this solution are merely examples for the purpose of clarifying this solution and are not intended to limit the implementation of this solution. Those skilled in the art will be able to make other variations or modifications based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this solution shall be included within the scope of protection of the claims of this solution.

Claims

1.A two-dimensional pupil expanding light waveguide with uniform brightness, characterized in that, the light waveguide has x, y and z directions perpendicular to each other, and a projection in a plane parallel to the x and y directions and perpendicular to the z direction has a coupling-in region, a turning region and a coupling-out region; the light waveguide comprises a coupling-in grating, a first turning grating, a second turning grating and a coupling-out grating, the coupling-in grating is located in the coupling-in region, the first and second turning gratings are located in the turning region, and the coupling-out grating is located in the coupling-out region; the coupling-in grating is configured to couple-in light and propagate the light along the y direction to the first turning grating, the first turning grating is configured to expand the light along the y direction and propagate the light along the x direction to the second turning grating, the second turning grating is configured to expand the light along the x direction and propagate the light along the y direction to the coupling-out grating, and the coupling-out grating is configured to expand the light along the y direction and couple-out the light. The first turning grating and the second turning grating are both volume holographic gratings or polarization volume holographic gratings; the first turning grating is divided into a plurality of sub-regions along the x direction and the y direction, and each sub-region has a different refractive index modulation ; the second turning grating is divided into a plurality of sub-regions along the x direction and the y direction, and each sub-region has a different refractive index modulation . 2.The two-dimensional pupil expanding light waveguide with uniform brightness according to claim 1, characterized in that, a grating vector of the first turning grating and the second turning grating identical, each sub-region of the first turning grating has the same grating vector in the z direction identical, each sub-region of the second turning grating has the same grating vector in the z direction . 3.The two-dimensional pupil expanding light waveguide with uniform brightness according to claim 1, characterized in that, a grating vector of the first turning grating and the second turning grating different, each sub-region of the first turning grating has a different grating vector in the z direction different, each sub-region of the second turning grating has a different grating vector in the z direction . 4.The two-dimensional pupil expanding light waveguide with uniform brightness according to claim 1, characterized in that, the coupling-in grating and / or the coupling-out grating is an array of half-transmission half-reflection mirrors. 5.The two-dimensional pupil expanding light waveguide with uniform brightness according to claim 4, characterized in that, An angle of each mirror surface in the half-transmission half-reflection mirror array with the y direction β satisfies: 20°≤ β ≤40°, a grating vector of the first turning grating and the second turning grating satisfies: 9 rad / μm≤ ≤25 rad / μm, a grating vector of the first turning grating and the second turning grating An angle with the z direction in a grating K domain map δ satisfies: 90°≤ δ ≤170°, a grating vector of the first turning grating and the second turning grating along the z direction satisfies: 1.6 rad / μm≤ ≤4.8 rad / μm. 6.The two-dimensional pupil expanding light waveguide with uniform brightness according to any one of claims 1 to 5, characterized in that, the light waveguide comprises a first cover plate layer, a first grating layer and a second grating layer stacked in sequence along the z direction, the first and second turning gratings are located in the first grating layer, and the coupling-in grating and the coupling-out grating are located in the second grating layer. 7.The two-dimensional pupil expanding light waveguide with uniform brightness according to claim 6, characterized in that, the turning region and the coupling-out region partially overlap to form an overlapping region, the second turning grating is partially located in the overlapping region, and the coupling-out grating is partially located in the overlapping region. 8.The two-dimensional pupil expanding light waveguide with uniform brightness according to any one of claims 1 to 5, characterized in that, the light waveguide comprises a first cover plate layer, a first grating layer, a second grating layer, a third grating layer and a second cover plate layer stacked in sequence along the z direction, the first and second turning gratings are located in the first and third grating layers, and the coupling-in grating and the coupling-out grating are located in the second grating layer. 9.The two-dimensional pupil expanding light waveguide with uniform brightness according to claim 8, characterized in that, the turning region and the coupling-out region partially overlap to form an overlapping region, the second turning grating is partially located in the overlapping region, and the coupling-out grating is partially located in the overlapping region. 10.A display product comprising a projection light machine, characterized in that, the display product further comprises the two-dimensional pupil expanding light waveguide with uniform brightness according to any one of claims 1 to 9, and the projection light machine emits an image light beam to the coupling-in region of the light waveguide.

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