CN117031604A - Volume holographic grating and preparation method thereof, optical waveguide structure and near-eye display device - Google Patents

Abstract

The application provides a volume holographic grating, a preparation method thereof, an optical waveguide structure and a near-eye display device, which are beneficial to improving color cast and rainbow effect. The volume holographic grating comprises a photosensitive base layer and a plurality of grating units arranged on the photosensitive base layer in an array mode, and the grating units comprise a first sub-grating, a second sub-grating and a third sub-grating. The first sub-grating is formed by interference of first coherent light and second coherent light, and an included angle between the first coherent light and a normal line of the photosensitive substrate is more than or equal to 53 degrees and less than or equal to 60 degrees; the second sub-grating is formed by interference of third coherent light and fourth coherent light, and an included angle between the third coherent light and the normal line of the photosensitive substrate is more than or equal to 48 degrees and less than or equal to 70 degrees; the third sub-grating is formed by interference of fifth coherent light and sixth coherent light, and an included angle between the fifth coherent light and the normal line of the photosensitive base layer is more than or equal to 45 degrees and less than or equal to 80 degrees.

Description

Volume holographic grating and preparation method thereof, optical waveguide structure and near-eye display device

Technical Field

The application relates to the technical field of display, in particular to a volume holographic grating, a preparation method thereof, an optical waveguide structure and a near-eye display device.

Background

Related optical technologies of Virtual Reality (VR) and augmented reality (augmented reality, AR) have not only received global attention in recent years, but have also developed at a considerably rapid rate; in addition, the utility of the virtual reality system is also shown in real life, and products or services achieved by virtual reality and augmented reality technologies can be seen in entertainment, medicine, home and military fields.

Examples of applications for virtual reality and augmented reality include various types of display devices, such as: near-Eye Display devices (NEDs) or Head-Mounted Display devices (HMDs). The near-eye display device is similar to glasses in appearance, and can also be called a glasses type display, an image glasses or a head-mounted display device, and mainly comprises a bearing part, a micro-display and an optical system, wherein the micro-display and the optical system are arranged in the bearing part. In the optical system of a near-eye display device, in order to transmit light output from a micro-display to the eye for reception without loss and leakage during transmission, it is necessary to allow the light to proceed into the eye in a total reflection manner within a waveguide in the optical system.

In the related art, in a volumetric holographic grating waveguide display scheme manufactured based on the holographic interference technology, the period of the holographic grating is fixed, and the wavelengths of different colors of light are different. The longer the wavelength, the larger the diffraction angle, so that the diffraction angles of different color lights in the holographic grating are different. In this way, the path length of each time the light with different colors is totally reflected in the light guide will be different, so the number of reflections will be different, and the light distribution and the light efficiency formed at the exit pupil position will be uneven, which will further cause chromatic dispersion (also called rainbow effect).

Disclosure of Invention

Based on this, it is necessary to provide a volume holographic grating, a method for manufacturing the same, an optical waveguide structure, and a near-eye display device, so as to improve color shift and rainbow effects.

An embodiment of a first aspect of the present application provides a volume hologram grating, including a photosensitive substrate and a plurality of grating units arranged on the photosensitive substrate in an array, where the grating units include a first sub-grating, a second sub-grating and a third sub-grating, the first sub-grating is used for diffracting red light, the second sub-grating is used for diffracting green light, and the third sub-grating is used for diffracting blue light. The first sub-grating is formed by interference of first coherent light and second coherent light, the wavelengths of the first coherent light and the second coherent light are the same as those of the red light, an included angle between the first coherent light and the normal line of the photosensitive base layer is more than or equal to 53 degrees and less than or equal to 60 degrees, and the second coherent light is perpendicular to the normal line of the photosensitive base layer; the second sub-grating is formed by interference of third coherent light and fourth coherent light, the wavelengths of the third coherent light and the fourth coherent light are the same as those of the green light, an included angle between the third coherent light and the normal line of the photosensitive base layer is more than or equal to 48 degrees and less than or equal to 70 degrees, and the fourth coherent light is perpendicular to the normal line of the photosensitive base layer; the third sub-grating is formed by interference of fifth coherent light and sixth coherent light, the wavelengths of the fifth coherent light and the sixth coherent light are the same as those of the blue light, an included angle between the fifth coherent light and the normal line of the photosensitive base layer is more than or equal to 45 degrees and less than or equal to 80 degrees, and the sixth coherent light is perpendicular to the normal line of the photosensitive base layer.

In some embodiments, the orthographic projection of the first sub-grating and/or the second sub-grating and/or the third sub-grating on the photosensitive substrate is square, and the side length of the square is greater than or equal to 1 μm and less than or equal to 100 μm.

In some embodiments, the material of the photosensitive base layer includes at least one of holographic polymer dispersed liquid crystal, silver halide, gelatin dichromate, photosensitive polymer.

An embodiment of a second aspect of the present application provides a method for preparing a volume hologram according to the first aspect, including:

providing a photosensitive substrate;

performing interference exposure on the photosensitive base layer by adopting first coherent light and second coherent light to form a first sub-grating, wherein the wavelengths of the first coherent light and the second coherent light are the same as those of the red light, an included angle between the first coherent light and the normal line of the photosensitive base layer is more than or equal to 53 degrees and less than or equal to 60 degrees, and the second coherent light is perpendicular to the normal line of the photosensitive base layer;

exposing the photosensitive substrate by adopting third coherent light and fourth coherent light in an interference way to form a second sub-grating; the wavelength of the third coherent light and the fourth coherent light is the same as that of the green light, an included angle between the third coherent light and the normal line of the photosensitive base layer is more than or equal to 48 degrees and less than or equal to 70 degrees, and the fourth coherent light is perpendicular to the normal line of the photosensitive base layer;

And performing interference exposure on the photosensitive base layer by adopting fifth coherent light and sixth coherent light to form a third sub-grating, wherein the first sub-grating, the second sub-grating and the third sub-grating form a grating unit, the grating units are arrayed on the photosensitive base layer, the wavelength of the fifth coherent light and the wavelength of the sixth coherent light are the same as that of the blue light, an included angle between the fifth coherent light and the normal line of the photosensitive base layer is larger than or equal to 45 degrees and smaller than or equal to 80 degrees, and the sixth coherent light is perpendicular to the normal line of the photosensitive base layer.

An embodiment of a third aspect of the present application provides an optical waveguide structure, including an optical waveguide, and a first volume holographic grating and a second volume holographic grating that are disposed at intervals on the same side of the optical waveguide, where the first volume holographic grating and the second volume holographic grating are the volume holographic gratings of the first aspect; the first volume holographic grating is configured to couple light of a corresponding color into the optical waveguide through the first sub-grating, the second sub-grating and the third sub-grating of the first volume holographic grating, the second volume holographic grating is configured to couple light of a corresponding color out of the optical waveguide through the first sub-grating, the second sub-grating and the third sub-grating of the second volume holographic grating, and the optical waveguide is used for generating total internal reflection of the light coupled into the optical waveguide, wherein the total internal reflection times of the red light, the green light and the blue light in the optical waveguide are the same.

In some embodiments, the optical waveguide has a thickness of 0.5mm or greater and 10mm or less.

In some embodiments, the length of the optical waveguide is greater than or equal to 50mm and less than or equal to 80mm.

In some embodiments, the optical waveguide includes a first surface and a second surface disposed opposite each other in a thickness direction thereof; the first volume holographic grating and the second volume holographic grating are reflection-type volume holographic gratings, the first volume holographic grating and the second volume holographic grating are positioned on the first surface, and external light is incident to the first volume holographic grating through the second surface;

in some embodiments, the first volume holographic grating and the second volume holographic grating are transmissive volume holographic gratings, the first volume holographic grating and the second volume holographic grating being located at the first surface through which external light is incident into the optical waveguide.

In some embodiments, the included angle between the first coherent light and the normal line of the photosensitive base layer, the included angle between the third coherent light and the normal line of the photosensitive base layer, and the included angle between the fifth coherent light and the normal line of the photosensitive base layer are the same, and the first volume holographic grating and the second volume holographic grating are symmetrically arranged.

In some embodiments, the optical waveguide includes a first section, a second section, and a third section extending in sequence along a length direction thereof, the first volume hologram grating disposed on the first section, the second volume hologram grating disposed on the third section, the second section including a first optical fiber, a second optical fiber, and a third optical fiber disposed in a stack;

the first optical fiber is configured to perform total internal reflection on red light coupled by the first volume holographic grating, the second optical fiber is configured to perform total internal reflection on green light coupled by the first volume holographic grating, and the third optical fiber is configured to perform total internal reflection on blue light coupled by the first volume holographic grating.

An embodiment of a fourth aspect of the present application provides an optical waveguide structure, including an optical waveguide, and a third volume hologram grating, a fourth volume hologram grating, and a fifth volume hologram grating, where the third volume hologram grating and the fifth volume hologram grating are the volume hologram gratings according to the first aspect. The fourth volume holographic grating comprises a photosensitive base layer and a plurality of grating units which are arranged on the photosensitive base layer in an array manner, wherein the grating units comprise a first sub-grating, a second sub-grating and a third sub-grating, the first sub-grating is used for diffracting red light, the second sub-grating is used for diffracting green light, the third sub-grating is used for diffracting blue light, the first sub-grating is formed by interference of first coherent light and second coherent light, the incidence angle of the first coherent light is identical to the incidence angle of the second coherent light, the second sub-grating is formed by interference of third coherent light and fourth coherent light, the incidence angle of the third coherent light is identical to the incidence angle of the fourth coherent light, the third sub-grating is formed by interference of fifth coherent light and sixth coherent light, and the incidence angle of the fifth coherent light is identical to the incidence angle of the sixth coherent light. The optical waveguide comprises a third surface and a fourth surface which are oppositely arranged along the length direction of the optical waveguide, the third volume holographic grating is arranged on the third surface, and the fourth volume holographic grating is arranged on the fourth surface; the optical waveguide comprises a first optical fiber, a second optical fiber and a third optical fiber which are stacked; the first optical fiber is configured to perform total internal reflection on the red light transmitted by the third volume holographic grating, the second optical fiber is configured to perform total internal reflection on the green light transmitted by the third volume holographic grating, and the third optical fiber is configured to perform total internal reflection on the blue light transmitted by the third volume holographic grating;

The fourth volume holographic grating is configured to couple light of a corresponding color out of the optical waveguide through the first sub-grating, the second sub-grating and the third sub-grating of the fourth volume holographic grating;

the fifth volume holographic grating is arranged on the coupling-out light path of the fourth volume holographic grating so as to transmit the coupled-out light into human eyes.

An embodiment of a fifth aspect of the present application proposes a near-eye display device comprising a micro-display and the optical waveguide structures of the third and fourth aspects, the micro-display being configured to emit image light of a corresponding color to be displayed to the optical waveguide structure.

In the application, the same volume holographic grating can respectively control the diffraction angles and the total reflection paths of different colors of light. And when the diffraction angle of the first sub-grating, the diffraction angle of the second sub-grating and the diffraction angle of the third sub-grating are respectively in the above ranges, the total internal reflection times of the light of different colors in the optical waveguide can be controlled to be the same, so that the light efficiency and the light distribution at the pupil position are relatively uniform. In addition, the light distribution at the exit pupil position is more uniform due to the three sub-gratings pixelation. Thus, the uniformity of the distribution of emergent light and the uniformity of light efficiency are improved, and the rainbow effect is improved.

Drawings

FIG. 1 is a schematic diagram of a volume hologram according to an embodiment of the present application;

FIG. 2 is a schematic diagram of an exposure structure of a reflection type volume hologram according to an embodiment of the present application;

FIG. 3 is a schematic diagram showing an exposure structure of a transmission type volume hologram according to an embodiment of the present application

FIG. 4 is a schematic diagram of a process for preparing a volume hologram according to an embodiment of the present application;

FIG. 5 is a schematic view of an optical waveguide structure according to an embodiment of the present application;

FIG. 6 is a schematic view of another optical waveguide structure according to an embodiment of the present application;

FIG. 7 is a schematic view of another exposure structure of a reflective volume hologram grating of an optical waveguide structure according to an embodiment of the present application;

FIG. 8 is a schematic structural view of an optical waveguide structure including the reflective volume hologram grating shown in FIG. 7;

FIG. 9 is a schematic view of another optical waveguide structure according to an embodiment of the present application;

fig. 10 is a schematic view of another structure of an optical waveguide structure according to an embodiment of the present application.

The reference numerals are as follows:

100-volume holographic gratings; 110-a photosensitive base layer; 120-grating units; 120 a-a first sub-grating; 120 b-a second sub-grating; 120 c-a third sub-grating; l1-first coherent light; l2-second coherent light; l3-third phase dry light; l4-fourth coherent light; l5-fifth coherent light; l6-sixth coherent light;

10-an optical waveguide structure; 11-an optical waveguide; 11 a-a first surface; 11 b-a first surface; 11 c-a third surface; 11 d-fourth surface; 111-a first section; 112-a second section; 112 a-a first optical fiber; 112 b-a second optical fiber; 112 c-a third optical fiber; 113-a third section; 12-a first volume holographic grating; 13-a second volume holographic grating; 14-a third volume holographic grating; 15-a fourth volume holographic grating; 16-fifth volume holographic grating.

Detailed Description

In order that the above objects, features and advantages of the invention will be readily understood, a more particular description of the invention will be rendered by reference to the appended drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. The present invention may be embodied in many other forms than described herein and similarly modified by those skilled in the art without departing from the spirit of the invention, whereby the invention is not limited to the specific embodiments disclosed below.

In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings are merely for convenience in describing the present invention and simplifying the description, and do not indicate or imply that the device or element being referred to must have a specific orientation, be configured and operated in a specific orientation, and therefore should not be construed as limiting the present invention.

Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include at least one such feature. In the description of the present invention, the meaning of "plurality" means at least two, for example, two, three, etc., unless specifically defined otherwise.

In the present invention, unless explicitly specified and limited otherwise, the terms "mounted," "connected," "secured," and the like are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; either directly or indirectly, through intermediaries, or both, may be in communication with each other or in interaction with each other, unless expressly defined otherwise. The specific meaning of the above terms in the present invention can be understood by those of ordinary skill in the art according to the specific circumstances.

In the present invention, unless expressly stated or limited otherwise, a first feature "up" or "down" a second feature may be the first and second features in direct contact, or the first and second features in indirect contact via an intervening medium. Moreover, a first feature being "above," "over" and "on" a second feature may be a first feature being directly above or obliquely above the second feature, or simply indicating that the first feature is level higher than the second feature. The first feature being "under", "below" and "beneath" the second feature may be the first feature being directly under or obliquely below the second feature, or simply indicating that the first feature is less level than the second feature.

It will be understood that when an element is referred to as being "fixed" or "disposed" on another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and the like are used herein for illustrative purposes only and are not meant to be the only embodiment.

As shown in fig. 1, an embodiment of the first aspect of the present application proposes a volume hologram grating 100. The volume hologram grating 100 includes a photosensitive substrate 110 and a plurality of grating units 120 arranged on the photosensitive substrate 110 in an array, wherein the grating units 120 include a first sub-grating 120a, a second sub-grating 120b and a third sub-grating 120c, the first sub-grating 120a is used for diffracting red light, the second sub-grating 120b is used for diffracting green light, and the third sub-grating 120c is used for diffracting blue light. As shown in fig. 2, the first sub-grating 120a is formed by interference of the first coherent light L1 and the second coherent light L2, the wavelength of the first coherent light L1 and the wavelength of the second coherent light L2 are the same as that of the red light, an included angle α between the first coherent light L1 and the normal line of the photosensitive base layer 110 is greater than or equal to 53 ° and less than or equal to 60 °, and the second coherent light L2 is perpendicular to the normal line of the photosensitive base layer 110. The second sub-grating 120b is formed by interference of third coherent light L3 and fourth coherent light L4, the wavelengths of the third coherent light L3 and the fourth coherent light L4 are the same as those of the green light, an included angle between the third coherent light L3 and a normal line of the photosensitive base layer 110 is greater than or equal to 48 ° and less than or equal to 70 °, and the fourth coherent light L4 is perpendicular to the normal line of the photosensitive base layer 110. The third sub-grating 120c is formed by interference of the fifth coherent light L5 and the sixth coherent light L6, the wavelengths of the fifth coherent light L5 and the sixth coherent light L6 are the same as those of the blue light, an included angle between the fifth coherent light L5 and the normal line of the photosensitive base layer 110 is greater than or equal to 45 ° and less than or equal to 80 °, and the sixth coherent light L6 is perpendicular to the normal line of the photosensitive base layer 110.

In the present application, the volume hologram grating 100 includes a photosensitive base layer 110 and a plurality of grating units 120. Further, the grating unit 120 includes a first sub-grating 120a, a second sub-grating 120b, and a third sub-grating 120c. That is, the first sub-grating 120a, the second sub-grating 120b, and the third sub-grating 120c constitute a structure similar to that of a display sub-pixel, and the volume hologram grating 100 realizes pixelation.

The present application sequentially performs three interference exposures on the photosensitive substrate 110 to form a plurality of grating units 120 including a first sub-grating 120a, a second sub-grating 120b, and a third sub-grating 120c. Specifically, the first sub-grating 120a is formed by interference of the first coherent light L1 and the second coherent light L2. The wavelengths of the first coherent light L1 and the second coherent light L2 are the same as those of the red light, an included angle between the first coherent light L1 and a normal line of the photosensitive base layer 110 is more than or equal to 53 ° and less than or equal to 60 °, and the second coherent light L2 is perpendicular to the normal line of the photosensitive base layer 110. In this way, by the interference exposure of the first coherent light L1 and the second coherent light L2, the first sub-grating 120a can transmit or reflect the red light vertically incident on the first sub-grating 120a at a diffraction angle of 53 ° to 60 °. As shown in fig. 2, when the first coherent light L1 and the second coherent light L2 are incident and interfere from opposite side surfaces of the photosensitive base layer 110, the first sub-grating 120a is formed as a reflective grating. As shown in fig. 3, when the first coherent light L1 and the second coherent light L2 are incident and interfere from the same side surface of the photosensitive base layer 110, the first sub-grating 120a is formed as a transmissive grating.

Further, the second sub-grating 120b is formed by interference of the third coherent light L3 and the fourth coherent light L4. The wavelength of the third coherent light L3 and the fourth coherent light L4 is the same as the wavelength of the green light, an included angle between the third coherent light L3 and the normal line of the photosensitive base layer 110 is greater than or equal to 48 ° and less than or equal to 70 °, and the fourth coherent light L4 is perpendicular to the normal line of the photosensitive base layer 110. In this way, by the interference exposure of the third coherent light L3 and the fourth coherent light L4, the second sub-grating 120b can transmit or reflect green light vertically incident on the second sub-grating 120b at a diffraction angle of 48 ° to 70 °. As shown in fig. 2, when the third coherent light L3 and the fourth coherent light L4 are incident and interfere from the opposite side surfaces of the photosensitive base layer 110, the second sub-grating 120b is formed as a reflective grating; as shown in fig. 3, when the third coherent light L3 and the fourth coherent light L4 are incident and interfere from the same side surface of the photosensitive base layer 110, the second sub-grating 120b is formed as a transmissive grating.

Further, the third sub-grating 120c is formed by interference of the fifth coherent light L5 and the sixth coherent light L6, the wavelengths of the fifth coherent light L5 and the sixth coherent light L6 are the same as those of the blue light, an included angle between the fifth coherent light L5 and a normal line of the photosensitive base layer 110 is greater than or equal to 45 ° and less than or equal to 80 °, and the sixth coherent light L6 is perpendicular to the normal line of the photosensitive base layer 110. In this way, by the interference exposure of the fifth coherent light L5 and the sixth coherent light L6, the third sub-grating 120c can transmit or reflect the blue light vertically incident on the third sub-grating 120c at a diffraction angle of 45 ° to 80 °. As shown in fig. 2, when the fifth coherent light L5 and the sixth coherent light L6 are incident and interfere from the opposite side surfaces of the photosensitive base layer 110, the third sub-grating 120c is formed as a reflective grating; as shown in fig. 3, when the fifth coherent light L5 and the sixth coherent light L6 are incident and interfere from the same side surface of the photosensitive base layer 110, the third sub-grating 120c is formed as a transmissive grating.

Although the transmissive grating or the reflective grating may be formed according to the direction of the interference light. However, it is necessary to ensure that the first sub-grating 120a, the second sub-grating 120b, and the third sub-grating 120c are all transmissive in the same volume hologram 100; alternatively, the first sub-grating 120a, the second sub-grating 120b, and the third sub-grating 120c are all reflective.

In the present application, the first sub-grating 120a, the second sub-grating 120b, and the third sub-grating 120c are pixelated by performing interference exposure on the photosensitive substrate 110 in several passes. The first sub-grating 120a may control the diffraction angle of red light, the second sub-grating 120b may control the diffraction angle of green light, and the third sub-grating 120c may control the diffraction angle of blue light, so that the same volume hologram 100 may control the diffraction angles and total reflection paths of light of different colors, respectively. In addition, when the diffraction angles of the first sub-grating 120a, the second sub-grating 120b, and the third sub-grating 120c are respectively in the above ranges, the total internal reflection times of the light beams of different colors in the optical waveguide 11 can be controlled to be the same, so that the light efficiency and the light distribution at the pupil position are relatively uniform. In addition, the light distribution at the exit pupil position is more uniform due to the three sub-gratings pixelation. Thus, the uniformity of the distribution of emergent light and the uniformity of light efficiency are improved, and the rainbow effect is improved.

In some embodiments, as shown in fig. 1, the orthographic projection of the first sub-grating 120a on the photosensitive substrate 110 is square, and the side length of the square is greater than or equal to 1 μm and less than or equal to 100 μm. The size of the first sub-grating 120a depends on the machining precision of the laser light during machining. When the orthographic projection of the first sub-grating 120a is square, the convenience of laser exposure is improved. In addition, when the side length of the square satisfies the above range, on one hand, the convenience of laser exposure is further improved, and on the other hand, the area of the first sub-grating 120a is not excessively large, thereby further improving the uniformity of the distribution of the outgoing light.

In some embodiments, as shown in fig. 1, the orthographic projection of the second sub-grating 120b on the photosensitive substrate 110 is square, and the side length of the square is greater than or equal to 1 μm and less than or equal to 100 μm. In this way, on the one hand, the convenience of laser exposure is improved, and on the other hand, the area of the second sub-grating 120b is not excessively large, so that the uniformity of the distribution of the outgoing light is improved.

In some embodiments, as shown in fig. 1, the orthographic projection of the third sub-grating 120c on the photosensitive substrate 110 is square, and the side length of the square is greater than or equal to 1 μm and less than or equal to 100 μm. In this way, on the one hand, the convenience of laser exposure is improved, and on the other hand, the area of the third sub-grating 120c is not excessively large, so that the uniformity of the distribution of the outgoing light is improved.

In some embodiments, as shown in fig. 1, the shapes and sizes of the first sub-grating 120a, the second sub-grating 120b, and the third sub-grating 120c are all the same, which is beneficial to further improving the convenience of laser exposure.

In some embodiments, the material of the photosensitive base layer 110 includes at least one of holographic polymer dispersed liquid crystal, silver halide, gelatin dichromate, photosensitive polymer. The photosensitive substrate 110 made of the above material can record interference fringes formed by two beams of interference light, so as to form a sub-grating meeting the requirement of exposure angle. Such materials are common, thereby facilitating a reduction in the manufacturing cost of the volume hologram grating 100.

As shown in fig. 4, an embodiment of the second aspect of the present application proposes a method for manufacturing a volume hologram grating 100, including:

providing a photosensitive base layer 110;

performing interference exposure on the photosensitive base layer 110 by adopting first coherent light L1 and second coherent light L2 to form a first sub-grating 120a, wherein the wavelength of the first coherent light L1 and the wavelength of the second coherent light L2 are the same as that of red light, an included angle between the first coherent light L1 and the normal line of the photosensitive base layer 110 is more than or equal to 53 degrees and less than or equal to 60 degrees, and the second coherent light L2 is perpendicular to the normal line of the photosensitive base layer 110;

Performing interference exposure on the photosensitive substrate 110 by adopting third coherent light L3 and fourth coherent light L4 to form a second sub-grating 120b; wherein, the wavelengths of the third coherent light L3 and the fourth coherent light L4 are the same as the wavelength of the green light, the included angle between the third coherent light L3 and the normal line of the photosensitive base layer 110 is more than or equal to 48 ° and less than or equal to 70 °, and the fourth coherent light L4 is perpendicular to the normal line of the photosensitive base layer 110;

the fifth coherent light L5 and the sixth coherent light L6 are adopted to carry out interference exposure on the photosensitive base layer 110 to form a third sub-grating 120c, the first sub-grating 120a, the second sub-grating 120b and the third sub-grating 120c form a grating unit 120, the grating units 120 are arrayed on the photosensitive base layer 110, wherein the wavelength of the fifth coherent light L5 and the wavelength of the sixth coherent light L6 are the same as that of the blue light, and an included angle between the fifth coherent light L5 and the normal line of the photosensitive base layer 110 is more than or equal to 45 degrees and less than or equal to 80 degrees, and the sixth coherent light L6 is perpendicular to the normal line of the photosensitive base layer 110.

The method for preparing the volume hologram grating 100 according to the embodiment of the present application is used for preparing the volume hologram grating 100 according to the first aspect. In the present application, the first sub-grating 120a, the second sub-grating 120b, and the third sub-grating 120c are pixelated by performing interference exposure on the photosensitive substrate 110 in several passes. The included angle between the first coherent light L1 and the normal line of the photosensitive substrate 110 is greater than or equal to 53 ° and less than or equal to 60 °, and the second coherent light L2 is perpendicular to the normal line of the photosensitive substrate 110. In this way, by the interference exposure of the first coherent light L1 and the second coherent light L2, the first sub-grating 120a formed can diffract the red light vertically incident on the first sub-grating 120a at a diffraction angle of 53 ° to 60 °. The included angle between the third coherent light beam L3 and the normal line of the photosensitive substrate 110 is more than or equal to 48 degrees and less than or equal to 70 degrees, and the fourth coherent light beam L4 is perpendicular to the normal line of the photosensitive substrate 110. In this way, by the interference exposure of the third coherent light L3 and the fourth coherent light L4, the second sub-grating 120b formed can diffract green light vertically incident on the second sub-grating 120b at a diffraction angle of 48 ° to 70 °. The included angle between the fifth coherent light L5 and the normal line of the photosensitive base layer 110 is greater than or equal to 45 ° and less than or equal to 80 °, and the sixth coherent light L6 is perpendicular to the normal line of the photosensitive base layer 110. In this way, by the interference exposure of the fifth coherent light L5 and the sixth coherent light L6, the third sub-grating 120c formed can diffract blue light vertically incident on the third sub-grating 120c at a diffraction angle of 45 ° to 80 °. In this way, the same volume hologram 100 can control the diffraction angles and the total reflection paths of different colors of light, respectively. In addition, when the diffraction angles of the first sub-grating 120a, the second sub-grating 120b, and the third sub-grating 120c are respectively in the above ranges, the total internal reflection times of the light beams of different colors in the optical waveguide 11 can be controlled to be the same, so that the light efficiency and the light distribution at the pupil position are relatively uniform. In addition, the light distribution at the exit pupil position is more uniform due to the three sub-gratings pixelation. Thus, the uniformity of the distribution of emergent light and the uniformity of light efficiency are improved, and the rainbow effect is improved.

An embodiment of the third aspect of the present application proposes an optical waveguide structure 10. As shown in fig. 5, the optical waveguide structure 10 includes an optical waveguide 11, and a first volume hologram grating 12 and a second volume hologram grating 13 disposed at a distance from the same side of the optical waveguide 11, where the first volume hologram grating 12 and the second volume hologram grating 13 are the volume hologram grating 100 according to the first aspect. The first volume holographic grating 12 is configured to couple light of a corresponding color into the optical waveguide 11 through the first sub-grating 120a, the second sub-grating 120b and the third sub-grating 120c of the first volume holographic grating 12, the second volume holographic grating 13 is configured to couple light of a corresponding color out of the optical waveguide 11 through the first sub-grating 120a, the second sub-grating 120b and the third sub-grating 120c of the second volume holographic grating 13, the optical waveguide 11 is used for generating total internal reflection of the light coupled into it, wherein the total internal reflection times of red light, green light and blue light within the optical waveguide 11 are the same.

The optical waveguide structure 10 according to the embodiment of the present application uses the volume hologram grating 100 described in the first aspect as the coupling-in grating and the coupling-out grating, respectively. Wherein the first volume holographic grating 12 is an incoupling grating and the second volume holographic grating 13 is an outcoupling grating. Further, the first volume hologram grating 12 may control the diffraction angle of the light of different colors and the total reflection path of the light of different colors within the optical waveguide 11 through the first sub-grating 120a, the second sub-grating 120b, and the third sub-grating 120c of the first volume hologram grating 12, respectively. The second volume hologram 13 may sequentially receive the corresponding color light through the first sub-grating 120a, the second sub-grating 120b, and the third sub-grating 120c of the second volume hologram 13 and couple it out of the optical waveguide 11. Meanwhile, the total internal reflection times of red light, green light and blue light in the optical waveguide 11 are the same. Thus, the light efficiency of the pupil position is uniform. And the three sub-gratings are pixelated, so that the light distribution at the exit pupil position is uniform. Thus, the uniformity of the distribution of emergent light and the uniformity of light efficiency are improved, and the rainbow effect is improved.

Although the first volume hologram grating 12 and the second volume hologram grating 13 are the volume hologram grating 100 according to the first aspect. However, the sub-grating arrangement of the first volume hologram grating 12 and the sub-grating arrangement of the second volume hologram grating 13 may be the same or different. That is, the arrangement rule of the first, second, and third sub-gratings 120a, 120b, and 120c in each volume hologram grating 100 may be set according to the magnitude of the diffraction angle and the actual condition of total internal reflection within the optical waveguide 11. For ease of understanding, the description is specifically provided with reference to the accompanying drawings. As shown in fig. 5, in the first volume hologram grating 12, the first sub-grating 120a, the second sub-grating 120b, and the third sub-grating 120c are arranged in this order along the longitudinal direction of the optical waveguide 11. The diffraction angle of the first sub-grating 120a diffracts red light is α, the diffraction angle of the second sub-grating 120b diffracts green light is β, the diffraction angle of the third sub-grating 120c diffracts blue light is θ, and α > β > θ. The total internal reflection times of the red light, green light, and blue light in the optical waveguide 11 are the same (7 times in fig. 5). In this way, when light is coupled out from the optical waveguide 11 to the second volume hologram grating 13, the arrangement rule of the first sub-grating 120a, the second sub-grating 120b, and the third sub-grating 120c on the second volume hologram grating 13 is different from the arrangement rule of the first sub-grating 120a, the second sub-grating 120b, and the third sub-grating 120c in the first volume hologram grating 12. Specifically, the second sub-grating 120b, the third sub-grating 120c, and the first sub-grating 120a are sequentially arranged along the length direction of the light beam. The reason for this difference is that the light of different colors changes its coupling-out position on the second volume hologram 13 due to the difference in diffraction angle and total reflection times. Therefore, in practice, after the arrangement rule of each sub-grating of the first volume hologram grating 12 is determined, the arrangement rule of the first sub-grating 120a, the second sub-grating 120b, and the third sub-grating 120c of the second volume hologram grating 13 needs to be flexibly set according to the positions of light coupling out of different colors, so that the first sub-grating 120a of the second volume hologram grating 13 couples out red light, the second sub-grating 120b couples out green light, and the third sub-grating 120c couples out blue light. It is easy to understand that when the diffraction angles of the first sub-grating 120a, the second sub-grating 120b, and the third sub-grating 120c are the same, the sub-grating arrangement structure of the first volume hologram grating 12 and the sub-grating arrangement structure of the second volume hologram grating 13 are the same.

In some embodiments, the thickness of the optical waveguide 11 is 0.5mm or more and 10mm or less. When the thickness of the optical waveguide 11 satisfies the above range, on one hand, it is advantageous to improve the light and thin performance of the optical waveguide structure 10, and on the other hand, it is advantageous to reasonably set the total internal reflection times within the length range of the optical waveguide 11, thereby reducing the difficulty in building the optical waveguide structure 10.

In some embodiments, the length of the optical waveguide 11 is 50mm or more and 80mm or less. When the length of the waveguide 11 satisfies the above range, on one hand, it is beneficial to control the light output of different colors of light after the light is totally internally reflected for the same number of times to be more uniform, and on the other hand, the size of the optical waveguide structure 10 can be adapted to the use requirement of personnel.

In some embodiments, as shown in fig. 5, the optical waveguide 11 includes a first surface 11a and a second surface 11b that are disposed opposite in a thickness direction thereof. The first volume hologram grating 12 and the second volume hologram grating 13 are reflection volume hologram gratings 100, the first volume hologram grating 12 and the second volume hologram grating 13 are located on the first surface 11a, and external light is incident on the first volume hologram grating 12 through the second surface 11b. In the present embodiment, the first volume hologram grating 12 and the second volume hologram grating 13 are reflection type volume hologram gratings 100. That is, when external light is incident on the first volume hologram grating 12 or the second volume hologram grating 13, the light is reflected at a predetermined angle and then totally internally reflected within the optical waveguide 11.

In some embodiments, the optical waveguide 11 may be made of optical glass, polymethyl methacrylate (PMMA), polystyrene (PS), polycarbonate (PC), cyclic Olefin Copolymer (COC), cyclic olefin polymer, or the like. Typically, the refractive index is greater than 1.5 to ensure good total internal reflection.

In a specific embodiment, as shown in fig. 5, a first volume hologram grating 12 and a second volume hologram grating 13 are disposed on a first surface 11a of the optical waveguide 11 at intervals, both of which are reflective gratings. The first sub-grating 120a, the second sub-grating 120b, and the third sub-grating 120c of the first volume hologram grating 12 are sequentially arranged along the propagation direction of the light. The first sub-grating 120a diffracts red light at a diffraction angle α of 53 °, the second sub-grating 120b diffracts green light at a diffraction angle β of 48 °, and the third sub-grating 120c diffracts blue light at a diffraction angle θ of 45 °. The optical waveguide 11 has a thickness of 5mm and a length of 53mm. The total internal reflection times of the red light, green light and blue light in the optical waveguide 11 are 7 times. When the three colors of light are coupled out from the optical waveguide 11 to the second volume hologram grating 13, the arrangement rule of the first sub-grating 120a, the second sub-grating 120b, and the third sub-grating 120c on the second volume hologram grating 13 is that the second sub-grating 120b, the third sub-grating 120c, and the first sub-grating 120a of the second volume hologram grating 13 are sequentially arranged along the propagation direction of the light. Thus, the light efficiency and the light distribution of the pupil position are uniform. In addition, the light distribution at the exit pupil position is more uniform due to the three sub-gratings pixelation. Thereby being beneficial to improving the uniformity of the distribution of emergent light and the uniformity of light efficiency, and further being beneficial to improving the rainbow effect.

In other embodiments, as shown in fig. 6, the first volume hologram grating 12 and the second volume hologram grating 13 are transmissive volume hologram gratings 100, and the first volume hologram grating 12 and the second volume hologram grating 13 are located on the first surface 11a, and external light is incident into the optical waveguide 11 through the first volume hologram grating 12. In this embodiment, when external light is incident on the first volume holographic grating 12, the light will first pass through the first volume holographic grating 12, then total internal reflection occurs in the optical waveguide 11, and finally the coupled light is coupled out by the second volume holographic grating 13 and deflected by a predetermined angle, so that the coupled light is vertically incident on the human eye.

In some embodiments, as shown in fig. 7 and 8, the included angle α (i.e. the diffraction angle α) between the first coherent light L1 and the normal line of the photosensitive base layer 110, the included angle β (i.e. the diffraction angle β) between the third coherent light L3 and the normal line of the photosensitive base layer 110, and the included angle θ (i.e. the diffraction angle θ) between the fifth coherent light L5 and the normal line of the photosensitive base layer 110 are all the same, and the first volume hologram grating 12 and the second volume hologram grating 13 are symmetrically disposed. In this embodiment, the diffraction angles of the first sub-grating 120a, the second sub-grating 120b, and the third sub-grating 120c for the light of the corresponding colors are all the same. Thus, the light with different colors is totally internally reflected in the optical waveguide 11 in a parallel light mode, so that convenience in controlling total internal reflection times is improved, uniformity of light emission is further improved, and color red effect is improved. In addition, the first volume holographic grating 12 and the second volume holographic grating 13 are symmetrically arranged, so that the second volume holographic grating 13 can couple out different color lights with multiple total internal reflection corresponding to the first volume holographic grating 12 and the second volume holographic grating 13, and the convenience in arrangement of the first volume holographic grating 12 and the second volume holographic grating 13 is further improved.

In some embodiments, as shown in fig. 9, the optical waveguide 11 includes a first section 111, a second section 112, and a third section 113 that extend in sequence along the length thereof. The first volume hologram grating 12 is disposed on the first section 111, the second volume hologram grating 13 is disposed on the third section 113, and the second section 112 includes a first optical fiber 112a, a second optical fiber 112b, and a third optical fiber 112c that are stacked. The first optical fiber 112a is configured to perform total internal reflection for the red light coupled into the first volume hologram 12, the second optical fiber 112b is configured to perform total internal reflection for the green light coupled into the first volume hologram 12, and the third optical fiber 112c is configured to perform total internal reflection for the blue light coupled into the first volume hologram 12.

In this embodiment, the optical waveguide 11 is divided into three sections. Wherein the first section 111 and the third section 113 are used for arranging volume holographic gratings to couple in and out light of different colors. The second section 112 is used to achieve total internal reflection of light of different colors. Specifically, the second section 112 includes a first optical fiber 112a, a second optical fiber 112b, and a third optical fiber 112c that are stacked. Thus, the first optical fiber 112a may control the total internal reflection path of red light, the second optical fiber 112b may control the total internal reflection path of green light, and the third optical fiber 112c may control the total internal reflection path of blue light. When the diffraction angles of the light beams with different colors coupled by the first volume hologram grating 12 are different, the total internal reflection times and paths of the light beams with three colors in the three optical fibers can be consistent by respectively adjusting the refractive indexes in the optical fiber 112a, the second optical fiber 112b and the third optical fiber 112c. Thus, the light extraction efficiency and the uniformity of light extraction distribution are further improved, and the rainbow phenomenon is further improved.

Alternatively, the first optical fiber 112a, the second optical fiber 112b, and the third optical fiber 112c may be single-mode optical fibers, or multimode optical fibers, which is not limited in the present application. Further, when the first optical fiber 112a, the second optical fiber 112b and the third optical fiber 112c are single mode optical fibers, the diameter of the optical fiber core is 5 to 10um, and the thickness of the external insulation layer of the optical fiber core is 25 to 100um. When the first optical fiber 112a, the second optical fiber 112b and the third optical fiber 112c are multimode optical fibers, the diameter of the optical fiber core is 50 to 75um, and the thickness of the external insulation layer of the optical fiber core is 25 to 100um.

An embodiment of the fourth aspect of the present application proposes an optical waveguide structure 10. As shown in fig. 10, the optical waveguide structure 10 includes an optical waveguide 11, and a third volume hologram grating 14, a fourth volume hologram grating 15, and a fifth volume hologram grating 16, and the third volume hologram grating 14 and the fifth volume hologram grating 16 are the volume hologram gratings 100 according to the first aspect. The fourth volume hologram grating 15 includes a photosensitive substrate 110 and a plurality of grating units 120 arranged on the photosensitive substrate 110 in an array, wherein the grating units 120 include a first sub-grating 120a, a second sub-grating 120b and a third sub-grating 120c, the first sub-grating 120a is used for diffracting red light, the second sub-grating 120b is used for diffracting green light, and the third sub-grating 120c is used for diffracting blue light. The first sub-grating 120a is formed by interference of the first coherent light L1 and the second coherent light L2, the first coherent light L1 has an incident angle identical to that of the second coherent light L2, the second sub-grating 120b is formed by interference of the third coherent light L3 and the fourth coherent light L4, the third coherent light L3 has an incident angle identical to that of the fourth coherent light L4, the third sub-grating 120c is formed by interference of the fifth coherent light L5 and the sixth coherent light L6, and the fifth coherent light L5 has an incident angle identical to that of the sixth coherent light L6. The optical waveguide 11 includes a third surface 11c and a fourth surface 11d which are disposed opposite to each other in the longitudinal direction thereof, the third volume hologram grating 14 is disposed on the third surface 11c, and the fourth volume hologram grating 15 is disposed on the fourth surface 11d. The optical waveguide 11 includes a first optical fiber 112a, a second optical fiber 112b, and a third optical fiber 112c that are stacked. The first optical fiber 112a is configured to perform total internal reflection for red light transmitted by the third volume hologram grating 14, the second optical fiber 112b is configured to perform total internal reflection for green light transmitted by the third volume hologram grating 14, and the third optical fiber 112c is configured to perform total internal reflection for blue light transmitted by the third volume hologram grating 14. The fourth volume hologram grating 15 is configured to couple light of a corresponding color out of the optical waveguide 11 through the first sub-grating 120a, the second sub-grating 120b, and the third sub-grating 120c of the fourth volume hologram grating 15. The fifth volume hologram 100 is disposed on the coupling-out light path of the fourth volume hologram 100 to transmit the coupling-out light to the human eye.

In the present application, three transmissive volume hologram gratings 100 are used. The third volume hologram grating 14 and the fifth volume hologram grating 16 are the volume hologram gratings according to the first aspect. The fourth volume hologram grating 15 is different from the third volume hologram grating 14 and the fifth volume hologram grating 16 in that the incidence angles of two coherent light beams of the fourth volume hologram grating 15 are the same at the time of interference exposure. Thus, as shown in fig. 10, when the red light is perpendicularly incident to the first optical fiber 112a through the first sub-grating 120a, the red light is totally reflected within the first optical fiber 112a at the diffraction angle α. When the red light enters the first sub-grating 120a of the fourth volume hologram grating 15 at the diffraction angle α, the red light passes through the first sub-grating 120a of the fourth volume hologram grating 15 at the same diffraction angle α due to the same incidence angle of the two coherent light beams of the first sub-grating 120a, thereby forming the optical path diagram shown in fig. 10. Blue light and green light are the same. Thus, the optical waveguide 11 transmits light through the first optical fiber 112a, the second optical fiber 112b, and the third optical fiber 112c, which are stacked, and the three transmissive volume hologram gratings. Further, the first optical fiber 112a may control the total internal reflection path of red light, the second optical fiber 112b may control the total internal reflection path of green light, and the third optical fiber 112c may control the total internal reflection path of blue light. When the diffraction angles of the light beams with different colors coupled out by the first volume hologram grating 12 are different, the total internal reflection times and paths of the light beams with three colors in the three optical fibers can be consistent by respectively adjusting the refractive indexes in the optical fiber 112a, the second optical fiber 112b and the third optical fiber 112 c. Thus, the light-emitting efficiency and the uniformity of light-emitting distribution are improved, and the rainbow phenomenon is improved.

An embodiment of the fifth aspect of the present application proposes a near-eye display device comprising a micro-display and the optical waveguide structure 10 of the third and fourth aspects. The micro display is configured to emit image light of a corresponding color to be displayed to the optical waveguide structure 10. For example, the micro display may be a self-luminous Active Device (Active Device), such as a mini light emitting diode (mine LED), a micro light emitting diode (micro-LED), or the like, or a liquid crystal display Device requiring illumination by an external light source, such as: transmissive liquid crystal displays and reflective liquid crystal on silicon (Liquid Crystal On Silicon (LCOS)) projectors, as well as digital micromirror arrays (Digital micro mirror Device, DMD) based on microelectromechanical systems (Microelectromechanical Systems, DMD) technology, digital micromirror arrays being the core of digital light source processing (Digital Light Processing, DLP) and laser beam scanners (Laser Beam Scanner, LBS), etc.

The near-eye display device of the present application uses the optical waveguide structure 10 described in the third aspect and the fourth aspect, thereby being advantageous for improving the light extraction efficiency and the uniformity of the light extraction distribution, and further being advantageous for improving the rainbow phenomenon.

The technical features of the above-described embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above-described embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.

The above examples illustrate only a few embodiments of the invention, which are described in detail and are not to be construed as limiting the scope of the invention. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the invention, which are all within the scope of the invention. Accordingly, the scope of protection of the present invention is to be determined by the appended claims.

Claims (10)

1. The volume holographic grating is characterized by comprising a photosensitive base layer and a plurality of grating units which are arranged on the photosensitive base layer in an array manner, wherein each grating unit comprises a first sub-grating, a second sub-grating and a third sub-grating, the first sub-grating is used for diffracting red light, the second sub-grating is used for diffracting green light, and the third sub-grating is used for diffracting blue light;

The first sub-grating is formed by interference of first coherent light and second coherent light, an included angle between the first coherent light and the normal line of the photosensitive base layer is more than or equal to 53 degrees and less than or equal to 60 degrees, and the second coherent light is perpendicular to the normal line of the photosensitive base layer;

the second sub-grating is formed by interference of third coherent light and fourth coherent light, an included angle between the third coherent light and the normal line of the photosensitive base layer is more than or equal to 48 degrees and less than or equal to 70 degrees, and the fourth coherent light is perpendicular to the normal line of the photosensitive base layer;

the third sub-grating is formed by interference of fifth coherent light and sixth coherent light, an included angle between the fifth coherent light and the normal line of the photosensitive base layer is larger than or equal to 45 degrees and smaller than or equal to 80 degrees, and the sixth coherent light is perpendicular to the normal line of the photosensitive base layer.

2. The volume hologram grating according to claim 1, wherein the orthographic projection of the first sub-grating and/or the second sub-grating and/or the third sub-grating on the photosensitive base layer is a square, and the side length of the square is greater than or equal to 1 μm and less than or equal to 100 μm.

3. A method of producing a volume hologram grating according to any of claims 1-2, comprising:

Providing a photosensitive substrate;

performing interference exposure on the photosensitive base layer by adopting first coherent light and second coherent light to form a first sub-grating, wherein an included angle between the first coherent light and the normal line of the photosensitive base layer is more than or equal to 53 degrees and less than or equal to 60 degrees, and the second coherent light is perpendicular to the normal line of the photosensitive base layer;

exposing the photosensitive substrate by adopting third coherent light and fourth coherent light in an interference way to form a second sub-grating; the included angle between the third coherent light and the normal line of the photosensitive base layer is more than or equal to 48 degrees and less than or equal to 70 degrees, and the fourth coherent light is perpendicular to the normal line of the photosensitive base layer;

and performing interference exposure on the photosensitive base layer by adopting fifth coherent light and sixth coherent light to form a third sub-grating, wherein the first sub-grating, the second sub-grating and the third sub-grating form a grating unit, the grating units are arranged on the photosensitive base layer in an array manner, an included angle between the fifth coherent light and the normal line of the photosensitive base layer is greater than or equal to 45 degrees and less than or equal to 80 degrees, and the sixth coherent light is perpendicular to the normal line of the photosensitive base layer.

4. An optical waveguide structure, characterized by comprising an optical waveguide, and a first volume holographic grating and a second volume holographic grating which are arranged on the same side surface of the optical waveguide at intervals, wherein the first volume holographic grating and the second volume holographic grating are the volume holographic gratings according to any one of claims 1-2;

The first volume holographic grating is configured to couple light of a corresponding color into the optical waveguide through the first sub-grating, the second sub-grating and the third sub-grating of the first volume holographic grating, the second volume holographic grating is configured to couple light of a corresponding color out of the optical waveguide through the first sub-grating, the second sub-grating and the third sub-grating of the second volume holographic grating, and the optical waveguide is used for generating total internal reflection of the light coupled into the optical waveguide, wherein the total internal reflection times of the red light, the green light and the blue light in the optical waveguide are the same.

5. The optical waveguide structure according to claim 4, wherein a thickness of the optical waveguide is 0.5mm or more and 10mm or less;

and/or, the length of the optical waveguide is greater than or equal to 50mm and less than or equal to 80mm.

6. The optical waveguide structure according to claim 4, wherein the optical waveguide includes a first surface and a second surface disposed opposite to each other in a thickness direction thereof;

the first volume holographic grating and the second volume holographic grating are reflection-type volume holographic gratings, the first volume holographic grating and the second volume holographic grating are positioned on the first surface, and external light is incident to the first volume holographic grating through the second surface;

Or the first volume holographic grating and the second volume holographic grating are transmission-type volume holographic gratings, the first volume holographic grating and the second volume holographic grating are positioned on the first surface, and external light is incident into the optical waveguide through the first volume holographic grating.

7. The optical waveguide structure according to claim 4, wherein an included angle between the first coherent light and a normal line of the photosensitive base layer, an included angle between the third coherent light and a normal line of the photosensitive base layer, and an included angle between the fifth coherent light and a normal line of the photosensitive base layer are all the same, and the first volume hologram grating and the second volume hologram grating are symmetrically arranged.

8. The optical waveguide structure according to claim 4, wherein the optical waveguide includes a first section, a second section, and a third section extending in order along a length direction thereof, the first volume hologram grating being provided on the first section, the second volume hologram grating being provided on the third section, the second section including a first optical fiber, a second optical fiber, and a third optical fiber that are stacked;

the first optical fiber is configured to perform total internal reflection on red light coupled by the first volume holographic grating, the second optical fiber is configured to perform total internal reflection on green light coupled by the first volume holographic grating, and the third optical fiber is configured to perform total internal reflection on blue light coupled by the first volume holographic grating.

9. An optical waveguide structure, characterized by comprising an optical waveguide and a third volume hologram grating, a fourth volume hologram grating and a fifth volume hologram grating, wherein the third volume hologram grating and the fifth volume hologram grating are the volume hologram gratings according to any one of claims 1 to 2;

the fourth volume holographic grating comprises a photosensitive base layer and a plurality of grating units which are arranged on the photosensitive base layer in an array manner, wherein the grating units comprise a first sub-grating, a second sub-grating and a third sub-grating, the first sub-grating is used for diffracting red light, the second sub-grating is used for diffracting green light, the third sub-grating is used for diffracting blue light, the first sub-grating is formed by interference of first coherent light and second coherent light, the incidence angle of the first coherent light is identical to the incidence angle of the second coherent light, the second sub-grating is formed by interference of third coherent light and fourth coherent light, the incidence angle of the third coherent light is identical to the incidence angle of the fourth coherent light, the third sub-grating is formed by interference of fifth coherent light and sixth coherent light, and the incidence angle of the fifth coherent light is identical to the incidence angle of the sixth coherent light; the optical waveguide comprises a third surface and a fourth surface which are oppositely arranged along the length direction of the optical waveguide, the third volume holographic grating is arranged on the third surface, and the fourth volume holographic grating is arranged on the fourth surface;

The optical waveguide comprises a first optical fiber, a second optical fiber and a third optical fiber which are stacked;

the first optical fiber is configured to perform total internal reflection on the red light transmitted by the third volume holographic grating, the second optical fiber is configured to perform total internal reflection on the green light transmitted by the third volume holographic grating, and the third optical fiber is configured to perform total internal reflection on the blue light transmitted by the third volume holographic grating;

the fourth volume holographic grating is configured to couple light of a corresponding color out of the optical waveguide through the first sub-grating, the second sub-grating and the third sub-grating of the fourth volume holographic grating;

the fifth volume holographic grating is arranged on the coupling-out light path of the fourth volume holographic grating so as to transmit the coupled-out light into human eyes.

10. A near-eye display device comprising a micro-display and an optical waveguide structure according to any of claims 4-9, the micro-display being configured to emit image light of a corresponding color to be displayed to the optical waveguide structure.