Volume holographic optical waveguide and volume holographic grating preparation method thereof
The holographic grating formed by the interference of three coherent laser beams solves the problems of ghosting and poor light uniformity in two-dimensional pupil-expanding waveguides, achieving a larger field of view and eye-tracking range, which is suitable for AR devices.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- JIANGXI LIANHAO OPTOELECTRONIC CO LTD
- Filing Date
- 2023-12-20
- Publication Date
- 2026-04-28
AI Technical Summary
Existing two-dimensional pupil-expanding waveguide sheets suffer from problems such as ghosting, poor light uniformity, and small field of view, making it difficult to meet the needs of AR devices.
A holographic grating is formed by interfering three coherent laser beams. By setting a two-dimensional pupil-expanding grating region on the waveguide substrate and combining the linear polarization state modulation of the three coherent laser beams, two-dimensional and mesh-like propagation of light can be achieved, increasing the field of view and improving the uniformity of light.
It achieves miniaturized AR devices with a larger eye-tracking range and field of view, while the emitted images have less ghosting and better uniformity, making them suitable for AR glasses and AR headsets.
Smart Images
Figure CN121934263A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of display device technology, and in particular to a volume holographic waveguide and a method for fabricating a volume holographic grating thereof. Background Technology
[0002] Augmented Reality (AR) technology uses computer graphics and visualization techniques to create virtual objects that do not exist in the physical world and accurately "place" them in the physical world, presenting users with a new environment with a richer perceptual experience. AR technology has enormous potential application value in many fields, such as industrial manufacturing, maintenance, medical, military, entertainment, and education. In the AR industry chain, lenses (such as waveguides) that have both transparency and imaging / light guiding effects are the most critical components for the implementation of AR hardware.
[0003] In existing technologies, most waveguide display devices are fabricated using volume holographic gratings. These waveguide display devices mainly consist of one-dimensional and two-dimensional pupil-expanding waveguides. One-dimensional pupil-expanding waveguides exhibit less ghosting and better uniformity, but their optical engine size is relatively large. Two-dimensional pupil-expanding waveguides can have a very small optical engine size, but fabricating them generally requires two or three grating regions (e.g., ...). Figure 1 As shown, since diffraction occurs in each grating area, and some grating deformation is inevitable when using laser interference to photograph waveguide sheets, the cumulative tolerance results in poor display effect (ghosting, poor light uniformity) and the image is not bright enough under the same conditions. Summary of the Invention
[0004] Therefore, the purpose of this invention is to provide a volume holographic waveguide and a method for fabricating the volume holographic grating, so as to achieve two-dimensional propagation of light and pupil expansion through only a single diffraction region, and make the image have small ghosting and good uniformity when it is emitted after propagation, while having a larger eye movement range and a larger field of view.
[0005] In a first aspect, the present invention provides a volume holographic optical waveguide, comprising a waveguide substrate and a two-dimensional pupil-expanding grating region disposed on the waveguide substrate, wherein the grating region is used for coupling in light rays, deflecting light rays, and coupling out light rays.
[0006] More preferably, a holographic grating formed by the interference exposure of three coherent laser beams K1, K2 and K3 is provided in the grating area; wherein the directions of K2 and K3 are at the same angle with the Z-axis and the projections of K2 and K3 on the XOY plane are at different angles with the X-axis.
[0007] More preferably, when the optical engine is incident on the grating region in the direction of K1, the light diffracted by the grating region in the same direction as K2 and K3 continues to propagate in the grating region after total internal reflection.
[0008] More preferably, when the grating region receives light in the same direction as K2, it generates light in the K4 and K3 directions; when the grating region receives light in the same direction as K3, it generates light in the K4 and K2 directions. Specifically, the light in the K4 direction is in the same direction as K1 and couples out of the waveguide. A portion of the light in the K2 direction continues to propagate by total internal reflection in the K2 direction, and so on, continuing to propagate and diffract within the waveguide. Similarly, a portion of the light in the K3 direction continues to propagate by total internal reflection in the K3 direction, and so on, continuing to propagate and diffract within the waveguide.
[0009] More preferably, at least one of the three coherent laser beams K1, K2 and K3 is set as linearly polarized light.
[0010] More preferably, at least one of the three coherent laser beams K1, K2, and K3 is linearly polarized as both S-polarized and P-polarized, and the S-polarized component Ks and the P-polarized component Kp satisfy: Ks 2 +Kp 2 =1.
[0011] More preferably, the horizontal field of view (HFOV) of the volume holographic waveguide satisfies: 10° < HFOV.
[0012] This invention utilizes a single grating region on a waveguide substrate to achieve two-dimensional pupil expansion. This grating region allows light to propagate in a mesh-like pattern, resulting in a small ghosting and high uniformity in the emitted image. Furthermore, it minimizes the size of the optomechanical components while maintaining a large field of view. Simultaneously, the use of a holographic grating formed by three coherent laser interference exposure further increases the waveguide's field of view. Moreover, by controlling the linear polarization states of the three coherent laser beams, the refractive index distribution of the grating region can exhibit different periodic arrangements and morphologies in the X and Y directions. This also allows for variations in the diffraction efficiency of different orders of the grating at different locations within the grating region, making it more suitable for applications in AR glasses, AR headsets, and other fields.
[0013] Secondly, the present invention provides a method for fabricating a volume holographic grating, wherein the volume holographic grating is used in a volume holographic waveguide, the volume holographic waveguide includes a waveguide substrate and a two-dimensional pupil-expanding grating region disposed on the waveguide substrate, the grating region being the volume holographic grating, and the method for fabricating the volume holographic grating includes: providing a holographic photosensitive material; exposing the holographic photosensitive material once using three coherent laser beams K1, K2, and K3 to obtain the volume holographic grating on the holographic photosensitive material; wherein the directions of K2 and K3 have the same angle with the Z-axis, and the projections of K2 and K3 onto the XOY plane have different angles with the X-axis.
[0014] More preferably, when the optical engine is incident on the grating region in direction K1, the grating region diffracts light in the same direction as K2 and K3, which continues to propagate in the grating region after total internal reflection; when the grating region receives light in the same direction as K2, it generates light in directions K4 and K3, and when the grating region receives light in the same direction as K3, it generates light in directions K4 and K2; wherein, the light in direction K4 is in the same direction as K1 and is coupled out of the waveguide, a portion of the light in direction K2 continues to propagate in direction K2 with total internal reflection and so on, and a portion of the light in direction K3 continues to propagate in direction K3 with total internal reflection and so on, and so on, and so on, within the waveguide.
[0015] More preferably, at least one of the three coherent laser beams K1, K2 and K3 is set as linearly polarized light.
[0016] More preferably, at least one of the three coherent laser beams K1, K2, and K3 is linearly polarized as both S-polarized and P-polarized, and the S-polarized component Ks and the P-polarized component Kp satisfy: Ks 2 +Kp 2 =1.
[0017] Compared to existing technologies, the advantages of this invention are as follows: By using three coherent laser beams to form a single grating region with two-dimensional pupil expansion through a single exposure, and by enabling light to propagate in a mesh-like pattern, the emitted image not only exhibits minimal ghosting and good uniformity, but also allows for a small optical engine size and a large field of view (horizontal field of view exceeding 10° and diagonal field of view exceeding 20°), thereby enabling a larger eyebox and achieving lightweight AR devices. Simultaneously, by controlling the linear polarization state of the three coherent laser beams, the refractive index distribution of the grating region can exhibit different periodic arrangements and morphologies in the X and Y directions, and the diffraction efficiency of different orders of the grating at different locations within the grating region can vary, thereby better controlling the uniformity of the emitted light and making it more suitable for applications in AR glasses, AR headsets, and other fields. Attached Figure Description
[0018] Figure 1 This is a schematic diagram of light propagation in a two-dimensional pupil-expanding waveguide in the prior art.
[0019] Figure 2 This is a refractive index distribution diagram of a grating obtained by dual-beam exposure in a two-dimensional pupil-expanding waveguide, as described in the prior art.
[0020] Figure 3 This is a schematic diagram showing the diffraction efficiency of a grating obtained by dual-beam exposure in a two-dimensional pupil-expanding waveguide in the prior art, corresponding to each incident angle in glass with a refractive index of n = 1.5286.
[0021] Figure 4 This is a schematic diagram of the structure of a volume holographic optical waveguide according to the present invention.
[0022] Figure 5 This is a schematic diagram showing the diffraction efficiency of a grating obtained by three-beam exposure in a glass with a refractive index of n = 1.5286 in a volume holographic waveguide according to the present invention at each incident angle.
[0023] Figure 6 This is a refractive index distribution diagram of a volume holographic grating of the present invention when all three beams K1, K2, and K3 are p-beams.
[0024] Figure 7 This is a schematic diagram of the diffraction efficiency of a volume holographic grating of the present invention at each incident angle of the (-1, -1) and (1, -1) orders when all three beams K1, K2, and K3 are p-beams.
[0025] Figure 8 This is a refractive index distribution diagram of a volume holographic grating of the present invention when K1 and K3 are both P-beams and K2 (s, p) = (0.8, 0.6).
[0026] Figure 9 This is a schematic diagram of the diffraction efficiency of the (-1, -1) and (1, -1) order incident angles of a volume holographic grating of the present invention when K1 and K3 are both P-beams and K2 beam (s, p) = (0.8, 0.6). Detailed Implementation
[0027] To make the objectives, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Several embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of the present invention will be thorough and complete.
[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Throughout this specification, the same reference numerals refer to the same elements.
[0029] like Figure 1The diagram shown is a schematic of light propagation in a two-dimensional pupil-expanding waveguide in the prior art. The two-dimensional pupil-expanding waveguide includes an input grating region (IN region), a folding grating region (Folding region), and an output grating region (OUT region). The IN region is obtained by interfering and exposing two coherent beams K1 and K2, the Folding region is obtained by interfering and exposing two coherent beams K2 and K3, and the OUT region is obtained by interfering and exposing two coherent beams K3 and K1.
[0030] like Figure 2 The figure shows the refractive index distribution of a grating obtained using dual-beam exposure in a two-dimensional pupil-expanding waveguide according to existing technology. It can be seen from the figure that the refractive index in the X direction exhibits a periodic arrangement, while the refractive index in the Y direction remains constant. Meanwhile, as shown... Figure 3 The figure shows a schematic diagram of the diffraction efficiency of a grating obtained by dual-beam exposure in a two-dimensional pupil-expanding waveguide in the prior art, corresponding to various incident angles in glass with a refractive index of n = 1.5286. As can be seen from the figure, with 40% diffraction efficiency as the HFOV (horizontal field of view) determination point, the HFOV of the grating is approximately 6°.
[0031] from Figure 1 , Figure 2 and Figure 3 As can be seen from the existing technology of a two-dimensional pupil-expanding waveguide, due to the existence of multiple grating regions and the diffraction of each grating region, the outgoing image is prone to ghosting and the uniformity of the outgoing light is poor. At the same time, the waveguide has a small field of view, which is not conducive to the widespread application of waveguides.
[0032] To this end, this invention proposes a volume holographic waveguide, which includes a waveguide substrate 1 and a grating region 2 disposed on the waveguide substrate 1. The grating region 2 can be used to couple incoming light, deflect incoming light, and couple out incoming light, thereby achieving two-dimensional pupil expansion.
[0033] In some embodiments, the grating region 2 can be directly fabricated on the waveguide substrate 1, or it can be pre-fabricated on the holographic photosensitive material, and then the holographic photosensitive material carrying the grating structure is combined with the waveguide substrate 1. No limitation is made here.
[0034] As a further optimization of this embodiment of the invention, a holographic grating formed by the interference exposure of three coherent laser beams K1, K2, and K3 is provided in the grating region 2. The directions of K2 and K3 have the same angle (represented by Theta) with the Z-axis, and the projections of K2 and K3 onto the XOY plane have different angles (represented by phi) with the X-axis. It should be noted that in this embodiment of the invention, the direction of K1 is not limited; K1 can be parallel to the Z-axis or form a certain angle with the Z-axis, such as 0–5°, greater than 5°, or even greater than 15°. Similarly, the angles of K2 and K3 with the Z-axis are not limited; for example, the angles of K2 and K3 with the Z-axis can be 0–10°, greater than 10°, or even greater than 40°.
[0035] In practical applications, when the optical engine is incident on the grating region 2 in the direction of K1, the grating region 2 will diffract to produce light in the same direction as K2 and K3, and continue to propagate and diffract within the grating region 2 through total internal reflection in the waveguide substrate 1.
[0036] Specifically, such as Figure 4 As shown, the bulk holographic waveguide includes a waveguide substrate 1 and a grating region 2 disposed on the waveguide substrate 1. The grating region 2 is a holographic grating formed by interference exposure of three coherent laser beams K1, K2 and K3. When the optical engine incident on a certain position of the grating region 2 in direction K1, the grating region 2 will diffract light in the same direction as K2 and K3, and continue to propagate to other positions of the grating region 2 through total internal reflection in the waveguide substrate 1. When the grating region 2 at other positions receives light in the same direction as K2, it will generate light in the directions K4 and K3. The light in the direction K4 is in the same direction as K1 and will couple out of the volume holographic waveguide and enter the human eye. At the same time, a portion of the light in the direction K2 will continue to propagate through total internal reflection in the direction K2, and so on, continuing to propagate and diffract within the volume holographic waveguide. When the grating region 2 at other positions receives light in the same direction as K3, it will generate light in the directions K4 and K2. The light in the direction K4 is in the same direction as K1 and will couple out of the volume holographic waveguide and enter the human eye. At the same time, a portion of the light in the direction K3 will continue to propagate through total internal reflection in the direction K3, and so on, continuing to propagate and diffract within the volume holographic waveguide. This forms a pattern as shown in the image. Figure 4 The net-like light trail shown.
[0037] like Figure 5As shown in the figure, this embodiment of the invention provides a schematic diagram of the diffraction efficiency of a grating obtained by three-beam exposure in a glass with a refractive index of n = 1.5286 for each incident angle in a volume holographic waveguide (where the azimuth angles of K1 are Theta = 14°, phi = 0°; the azimuth angles of K2 are Theta = 50°, phi = 0°; and the azimuth angles of K3 are Theta = 50°, phi = 90°). It can be seen from the figure that, using 40% diffraction efficiency as the HFOV criterion, the HFOV of the grating is greater than 10°, which is 67% higher than the HFOV of the grating obtained by two-beam exposure.
[0038] As a further optimization of this embodiment of the invention, at least one of the three coherent laser beams K1, K2, and K3 used to expose and form the grating region 2 is set as linearly polarized light. For example, all three coherent laser beams are P-polarized light, all are S-polarized light, partially P-polarized light and partially S-polarized light, partially P-polarized light and partially S-polarized light and P-polarized light with a certain polarization ratio, and partially S-polarized light and partially S-polarized light and P-polarized light with a certain polarization ratio. The S-polarized light component Ks and the P-polarized light component Kp satisfy: Ks 2 +Kp 2 =1, such as K1 and K3 being P-polarized beams, and the S-polarized and P-polarized components of K2 being (s, p) = (0.8, 0.6). In other words, the three coherent laser beams can use the same linear polarization state or different linear polarization states, depending on the application scenario of the holographic waveguide.
[0039] In this embodiment of the invention, since adjusting the linear polarization state of the three exposure beams does not change the period of the light in the XYZ directions, the volume holographic grating can generate light in the K4 and K3 directions when it receives light in the same direction as K2, and generate light in the K4 and K2 directions when it receives light in the same direction as K3. The light in the K4 direction is in the same direction as K1 and couples out of the waveguide. A portion of the light in the K2 direction continues to propagate by total internal reflection in the K2 direction and continues to propagate and diffract within the waveguide in this manner. A portion of the light in the K3 direction continues to propagate by total internal reflection in the K3 direction and continues to propagate and diffract within the waveguide in this manner. This process continues within the waveguide, propagating and diffracting in a mesh-like pattern. Simultaneously, depending on the linear polarization states of the three exposure beams, the resulting volume holographic grating will differ, affecting the diffraction efficiency of each order of the grating. For instance, when K1 and K3 are both P-beams, and K2 is both S-polarized and P-polarized with a certain polarization ratio, and the higher the proportion of S-polarized light, the stronger the diffraction efficiency of each order of the light produced in the same direction as K2 when the optical engine is incident on the volume holographic grating in the K1 direction, while the weaker the diffraction efficiency of each order of the light produced in the same direction as K3.
[0040] In some common AR application scenarios, such as Figure 6 The figure shows the refractive index distribution of a volume holographic grating provided in an embodiment of the present invention when all three beams K1, K2, and K3 are p-beams, meaning the three coherent laser beams can use the same linear polarization state. As can be seen from the figure, its refractive index distribution exhibits a periodic arrangement in both the X and Y directions, consistent with... Figure 2 Compared to the dual-beam configuration shown, the refractive index distribution exhibits a unique morphology and is symmetrical with respect to both the X and Y directions. Meanwhile, as... Figure 7 The diagram illustrates the diffraction efficiency of a volume holographic grating at various incident angles (-1, -1) and (1, -1) when all three beams (K1, K2, and K3) are p-beams, according to an embodiment of the present invention. As can be seen from the diagram, the diffraction efficiency at each incident angle is identical for both (-1, -1) and (1, -1) orders. Furthermore, with 40% diffraction efficiency as the HFOV (horizontal field of view) criterion, the grating's HFOV is greater than 10°, indicating a larger horizontal field of view. Of course, the same result would be obtained if all three beams (K1, K2, and K3) were s-beams.
[0041] In some AR glasses applications, due to differences in human eye habits and requirements for image uniformity, it is often necessary to have a higher horizontal field of view (HFOV) than a higher vertical field of view (VFOV). Furthermore, the diffraction efficiency of gratings at different locations within the waveguide must vary, and even the diffraction efficiency of different orders of gratings at the same location must differ. This is to ensure that the brightness and color accuracy of the image observed by the human eye within the entire eyebox area are uniform. For example, the (1st, -1st) order diffraction efficiency must be greater than the (-1st, -1st) order diffraction efficiency. Figure 8 The figure shows the refractive index distribution of a volume holographic grating provided in an embodiment of the present invention when K1 and K3 are both P-beams and K2 beam (s, p) = (0.8, 0.6), i.e., the three coherent laser beams use different linear polarization states. It can be seen from the figure that the refractive index distribution exhibits different periodic arrangements in the X and Y directions, which is consistent with... Figure 6 The three beams shown are all p-beams, but their refractive index distributions are significantly different and asymmetrical relative to the X and Y directions. Meanwhile, as... Figure 9 The figure shows a schematic diagram of the diffraction efficiency of a volume holographic grating provided in an embodiment of the present invention at various incident angles for the (-1, -1) and (1, -1) orders when K1 and K3 are both P-beams and K2 beam (s, p) = (0.8, 0.6). As can be seen from the figure, compared with... Figure 7 Compared to p-beams, the diffraction efficiency of the (1, -1) order is greatly improved, while the diffraction efficiency of the (-1, -1) order is reduced. Furthermore, with 40% diffraction efficiency as the HFOV (horizontal field of view) determination point, the HFOV of the grating is greater than 10°.
[0042] This invention, through the provision of a single grating region on a waveguide substrate capable of achieving two-dimensional pupil expansion, allows light to propagate in a mesh-like pattern. This not only results in minimal ghosting and good uniformity in the emitted image but also enables a small optomechanical size and a large field of view. Furthermore, the use of a holographic grating formed by three coherent laser interference exposure further increases the waveguide's field of view. Moreover, by controlling the linear polarization states of the three coherent laser beams, the refractive index distribution of the grating region can exhibit different periodic arrangements and morphologies in the X and Y directions. Additionally, the diffraction efficiencies of different orders of the grating at different locations within the grating region can vary, making it more suitable for applications in AR glasses, AR headsets, and other fields.
[0043] This invention also provides a method for fabricating a volume holographic grating, which can be used in a volume holographic waveguide. This invention provides a volume holographic waveguide comprising a waveguide substrate and a two-dimensional pupil-expanding grating region disposed on the waveguide substrate, wherein the grating region is the volume holographic grating. The following provides a method for fabricating a volume holographic grating, comprising the following steps:
[0044] Step 1: Provide holographic photosensitive materials.
[0045] Step two involves exposing the holographic photosensitive material once using three coherent laser beams, K1, K2, and K3, to obtain a volume holographic grating on the material. Specifically, the directions of K2 and K3 are at the same angle to the Z-axis, but the projections of K2 and K3 onto the XOY plane are at different angles to the X-axis.
[0046] After obtaining the volume holographic grating, the volume holographic grating is placed on the waveguide substrate. When an optical engine incident light in direction K1 onto a certain position of a volume holographic grating, the grating diffracts to produce light in the same directions as K2 and K3. This light then undergoes total internal reflection in the waveguide substrate and continues to propagate to other positions within the grating. When other positions of the volume holographic grating receive light in the same direction as K2, they generate light in directions K4 and K3. The light in direction K4 is the same as the direction of K1 and couples out of the volume holographic waveguide into the eye. Simultaneously, a portion of the light in direction K2 continues to propagate via total internal reflection in the K2 direction, and this process continues within the volume holographic waveguide for propagation and diffraction. When other positions of the volume holographic grating receive light in the same direction as K3, they generate light in the same directions as K2. The light in direction K4 is the same as the direction of K1 and couples out of the volume holographic waveguide into the eye. Simultaneously, a portion of the light in direction K3 continues to propagate via total internal reflection in the K3 direction, and this process continues within the volume holographic waveguide for propagation and diffraction. This process forms a... Figure 4 The net-like light trail shown.
[0047] In some embodiments, the holographic photosensitive material can be disposed on the waveguide substrate before exposure processing to obtain a grating region on the waveguide substrate capable of achieving two-dimensional pupil expansion. The materials of the waveguide substrate and the holographic photosensitive material are not limited here; that is, the waveguide substrate can be any light-transmitting material such as glass, resin, or optical waveguide, and the holographic photosensitive material can be a holographic photosensitive emulsion. Furthermore, the holographic photosensitive emulsion can be made of photopolymer, silver halide, dichromate gelatin, photorefractive material, photoanisotropic material, or any other photosensitive material that can be used to record interference fringes after exposure.
[0048] In some embodiments, at least one of the three coherent laser beams K1, K2, and K3 used to form the bulk holographic grating is linearly polarized. Examples include all three coherent laser beams being P-polarized, all being S-polarized, partially P-polarized and partially S-polarized, partially P-polarized and partially S-polarized with a certain polarization ratio, and partially S-polarized and partially S-polarized with a certain polarization ratio. The S-polarized component Ks and the P-polarized component Kp satisfy: Ks 2 +Kp 2 =1, meaning that the three coherent laser beams can use the same linear polarization state or different linear polarization states, depending on the application scenario of the holographic waveguide.
[0049] In this embodiment of the invention, since adjusting the linear polarization state of the three exposure beams does not change the period of the light in the XYZ directions, the volume holographic grating can generate light in the K4 and K3 directions when it receives light in the same direction as K2, and generate light in the K4 and K2 directions when it receives light in the same direction as K3. The light in the K4 direction is in the same direction as K1 and couples out of the waveguide. A portion of the light in the K2 direction continues to propagate by total internal reflection in the K2 direction and continues to propagate and diffract within the waveguide in this manner. A portion of the light in the K3 direction continues to propagate by total internal reflection in the K3 direction and continues to propagate and diffract within the waveguide in this manner. This process continues within the waveguide, propagating and diffracting in a mesh-like pattern. Simultaneously, depending on the linear polarization states of the three exposure beams, the resulting volume holographic grating will differ, affecting the diffraction efficiency of each order of the grating. For instance, when K1 and K3 are both P-beams, and K2 is both S-polarized and P-polarized with a certain polarization ratio, and the higher the proportion of S-polarized light, the stronger the diffraction efficiency of each order of the light produced in the same direction as K2 when the optical engine is incident on the volume holographic grating in the K1 direction, while the weaker the diffraction efficiency of each order of the light produced in the same direction as K3.
[0050] Of course, when using three coherent laser beams (K1, K2, and K3) to form a volumetric holographic grating through interferometry, in addition to controlling the linear polarization state of the three coherent laser beams, it is also necessary to control parameters such as exposure intensity and exposure time. Since the adjustment of parameters such as exposure intensity and exposure time is a conventional method for controlling the refractive index and diffraction efficiency of the grating, and the resulting refractive index distribution pattern exhibits periodic changes in both the X and Y directions, it will not be elaborated upon here.
[0051] This invention employs a single exposure using three coherent laser beams to form a single grating region capable of two-dimensional pupil expansion. This grating region allows light to propagate in a mesh-like pattern, resulting in less ghosting and better uniformity in the emitted image. Furthermore, it allows for a small optical engine size and a large field of view, enabling a larger eyebox and a lighter AR device. Simultaneously, by controlling the linear polarization states of the three coherent laser beams, the refractive index distribution of the grating region can exhibit different periodic arrangements and morphologies in the X and Y directions. This also allows for varying diffraction efficiencies at different orders of the grating at different locations within the grating region, thereby better controlling the uniformity of the emitted light and making it more suitable for applications such as AR glasses and AR headsets.
[0052] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.
[0053] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.
Claims
1. A volume holographic optical waveguide, characterized in that, It includes a waveguide substrate and a two-dimensional pupil grating region disposed on the waveguide substrate, the grating region being used for coupling in light rays, deflecting light rays, and coupling out light rays.
2. The volume holographic waveguide according to claim 1, characterized in that, The grating area is provided with a holographic grating formed by the interference exposure of three coherent laser beams K1, K2 and K3; wherein, the directions of K2 and K3 are at the same angle to the Z-axis, and the projections of K2 and K3 on the XOY plane are at different angles to the X-axis.
3. The volume holographic waveguide according to claim 2, characterized in that, When the optical engine is incident on the grating region in the direction of K1, the light generated by the diffraction of the grating region in the same direction as K2 and K3 continues to propagate in the grating region after total internal reflection.
4. The volume holographic waveguide according to claim 3, characterized in that, When the grating region receives light in the same direction as K2, it generates light in the directions of K4 and K3. When the grating region receives light in the same direction as K3, it generates light in the directions of K4 and K2. Among them, the light in the direction of K4 is in the same direction as K1 and the light in the direction of K4 is coupled out of the waveguide. A portion of the light in the direction of K2 continues to propagate by total internal reflection in the direction of K2 and continues to propagate and diffract in the waveguide in the same manner. A portion of the light in the direction of K3 continues to propagate by total internal reflection in the direction of K3 and continues to propagate and diffract in the waveguide in the same manner.
5. The volume holographic waveguide according to claim 2, characterized in that, At least one of the three coherent laser beams K1, K2, and K3 is set as linearly polarized light.
6. The volume holographic optical waveguide according to claim 5, characterized in that, Of the three coherent laser beams K1, K2, and K3, at least one is linearly polarized as both S-polarized and P-polarized, and the S-polarized component Ks and the P-polarized component Kp satisfy: Ks 2 +Kp 2 =1.
7. The volume holographic waveguide according to claim 1, characterized in that, The horizontal field of view (HFOV) of the volume holographic waveguide satisfies: 10° < HFOV.
8. A method for fabricating a volume holographic grating, characterized in that, The volume holographic grating is used in a volume holographic waveguide, the volume holographic waveguide includes a waveguide substrate and a two-dimensional pupil-expanding grating region disposed on the waveguide substrate, the grating region being the volume holographic grating, and the method for fabricating the volume holographic grating includes: Provide holographic photosensitive materials; The holographic photosensitive material is exposed once using three coherent laser beams K1, K2 and K3 to obtain the volume holographic grating on the holographic photosensitive material; Among them, the directions of K2 and K3 have the same angle with the Z-axis, and the projections of K2 and K3 onto the XOY plane have different angles with the X-axis.
9. The method for fabricating a volume holographic grating according to claim 8, characterized in that, When the optical engine is incident on the grating region in direction K1, the grating region diffracts light in the same direction as K2 and K3, which continues to propagate in the grating region after total internal reflection. When the grating region receives light in the same direction as K2, it generates light in directions K4 and K3. When the grating region receives light in the same direction as K3, it generates light in directions K4 and K2. Among them, the light in direction K4 is in the same direction as K1 and is coupled out of the waveguide. A portion of the light in direction K2 continues to propagate in direction K2 with total internal reflection and so on, continuing to propagate and diffract in the waveguide. A portion of the light in direction K3 continues to propagate in direction K3 with total internal reflection and so on, continuing to propagate and diffract in the waveguide.
10. The method for fabricating a volume holographic grating according to claim 8, characterized in that, At least one of the three coherent laser beams K1, K2, and K3 is set as linearly polarized light.
11. The method for fabricating a volume holographic grating according to claim 8, characterized in that, Of the three coherent laser beams K1, K2, and K3, at least one is linearly polarized as both S-polarized and P-polarized, and the S-polarized component Ks and the P-polarized component Kp satisfy: Ks 2 +Kp 2 =1.