Optical waveguide and extended reality device

Abstract

Disclosed in embodiments of the present invention are an optical waveguide and an extended reality device. The optical waveguide comprises: gratings (101), a first substrate (102), and a second substrate (103); the gratings (101) are arranged on at least one surface of the first substrate (102), and the second substrate (103) is arranged on at least one surface of the first substrate (102); the refractive index of the second substrate (103) is lower than the refractive index of the first substrate (102). The implementation avoids secondary diffraction of light in the optical waveguide, reducing brightness loss of the optical waveguide.

Description

Optical waveguides and extended reality devices

[0001] This disclosure claims priority to Chinese Patent Application No. 2023109618738 filed on August 1, 2023, and the contents of the above-mentioned Chinese patent application disclosure are hereby incorporated by reference in their entirety as a part of this disclosure. Technical Field

[0002] Embodiments of the present disclosure relate to optical waveguides and augmented reality devices. Background Art

[0003] Optical waveguides are crucial components in extended reality (XR) displays, particularly at the heart of augmented reality (AR) display systems. They operate by coupling light from an optical engine into transparent parallel plates. Through total internal reflection, the light propagates losslessly through the plates. Finally, it is guided out through an outcoupling grating at the human eye, allowing the light to merge with the real world.

[0004] Summary of the Invention

[0005] The embodiments of the present disclosure provide an optical waveguide and an augmented reality device.

[0006] In a first aspect, an embodiment of the present disclosure provides an optical waveguide comprising: a grating, a first substrate, and a second substrate; wherein the grating is arranged on at least one side of the first substrate, and the second substrate is arranged on at least one side of the first substrate; and the refractive index of the second substrate is lower than the refractive index of the first substrate.

[0007] In some embodiments, the grating is disposed on a first surface of the first substrate, and the second substrate is disposed on a second surface of the first substrate.

[0008] In some embodiments, the first surface of the first substrate is a surface close to the light source.

[0009] In some embodiments, the second surface of the first substrate is a surface close to the light source.

[0010] In some embodiments, the first substrate and the second substrate are connected to each other by van der Waals forces.

[0011] In some embodiments, the thickness of the second substrate is less than or equal to the thickness of the first substrate.

[0012] In some embodiments, a second substrate is disposed on both sides of the first substrate.

[0013] In some embodiments, the total thickness of the second substrates on both sides of the first substrate is less than or equal to the thickness of the first substrate.

[0014] In some embodiments, the grating is disposed between the first substrate and the second substrate.

[0015] In a second aspect, an embodiment of the present disclosure provides an extended reality device, comprising: the optical waveguide of the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above and other features, advantages, and aspects of the various embodiments of the present disclosure will become more apparent with reference to the following detailed description in conjunction with the accompanying drawings. Throughout the drawings, the same or similar reference numerals represent the same or similar elements. It should be understood that the drawings are schematic and that the originals and elements are not necessarily drawn to scale.

[0017] FIG1 is a schematic structural diagram of an embodiment of an optical waveguide according to the present disclosure;

[0018] FIG2 is a schematic diagram of the structure of an existing optical waveguide;

[0019] FIG3 is a schematic structural diagram of another embodiment of an optical waveguide according to the present disclosure;

[0020] FIG4 is a schematic structural diagram of another embodiment of an optical waveguide according to the present disclosure;

[0021] FIG5 is a schematic structural diagram of another embodiment of an optical waveguide according to the present disclosure;

[0022] FIG6 is a schematic diagram of an extended reality device according to one embodiment of the present disclosure. DETAILED DESCRIPTION

[0023] The present disclosure will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are intended only to illustrate the relevant invention and are not intended to limit the invention. It should also be noted that, for ease of description, only portions relevant to the relevant invention are shown in the accompanying drawings.

[0024] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in the present disclosure may be combined with each other. The present disclosure will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0025] Figure 1 shows a schematic diagram of the structure of an embodiment of an optical waveguide according to the present disclosure. As shown in Figure 1, optical waveguide 100 may include a grating 101, a first substrate 102, and a second substrate 103. The refractive index of second substrate 103 is typically lower than that of first substrate 102 and higher than that of air. An optical waveguide is a dielectric device that guides light waves propagating therein.

[0026] The optical properties of a grating (e.g., refractive index) vary periodically in one or more directions, with this period approaching or even exceeding the wavelength of visible light, such as between 200 and 500 nanometers. When the diffracted light's propagation direction perpendicular to the substrate coincides with the original incident light, the grating is a transmission grating. When the diffracted light's propagation direction perpendicular to the substrate is opposite to the original incident light, the grating is a reflection grating.

[0027] Gratings can include refined gratings, such as those with thousands or even tens of thousands of grooves within a 1cm width. These gratings utilize diffraction of transmitted light, known as transmission gratings. Other gratings utilize diffraction of light reflected between two grooves. For example, a grating made by engraving many parallel grooves on a metal-plated surface, where the smooth metal surface between the grooves reflects light, is called a reflection grating.

[0028] As shown in FIG1 , a grating 101 can be provided on at least one side of a first substrate 102. For example, the grating 101 can be a plurality of periodic structures inscribed on the first substrate 102, such as a plurality of parallel grooves. However, the grating 101 is not limited thereto and can also be a plurality of periodic structures added to the first substrate 102, such as a plurality of parallel protrusions.

[0029] As shown in FIG1 , the second substrate 103 can be provided on at least one side of the first substrate 102. For example, the grating 101 and the second substrate 103 can be provided on the same side of the first substrate 102. For example, the second substrate 103 can be connected to the first substrate 102 by gluing. For example, optically clear adhesive (OCA) can be used to bond the first substrate and the second substrate. OCA is a special adhesive used for bonding transparent optical elements (such as lenses, etc.). It is required to be colorless and transparent, have a light transmittance of more than 95%, good bonding strength, be curable at room temperature or medium temperature, and have small curing shrinkage.

[0030] It should be noted that in FIG1 , the grating and the second substrate are arranged on the same surface of the first substrate. This is only a schematic diagram of the optical waveguide. In a specific embodiment, the positional relationship between the grating, the second substrate and the first substrate can be limited according to actual conditions.

[0031] It should also be noted that the grating size in FIG1 is only a schematic diagram, and the actual grating thickness is usually smaller.

[0032] The diffraction efficiency of general optical waveguides is usually low, which limits the brightness provided by the XR optical system. One important reason for the low diffraction efficiency of optical waveguides is that the secondary diffraction of light with the coupling grating causes the coupled light to be decoupled, resulting in brightness loss.

[0033] Please refer to Figure 2, which shows a schematic diagram of a typical optical waveguide structure. In Figure 2, the incident light is diffracted after encountering the grating, enters the optical waveguide substrate, and is reflected. The reflected light is then diffracted again after encountering the grating, coupling out of the waveguide and preventing it from continuing to propagate and entering the human eye.

[0034] This phenomenon is more serious in the design of a monolithic full-color optical waveguide. Since the diffraction angles of the three colors of light, red, green, and blue, are different, blue light propagates at a smaller total internal reflection angle and is more susceptible to secondary diffraction and brightness loss.

[0035] To address this issue, two optical waveguides are typically used for full-color display. One waveguide transmits red and green light, while the other transmits green and blue light. This allows the blue light to propagate at a larger angle, thus avoiding losses caused by secondary diffraction. However, the two-waveguide design increases weight, cost, and process complexity. Therefore, a single full-color waveguide remains a more ideal solution.

[0036] This solution is achieved by fabricating a grating on a first substrate (high refractive index substrate) and setting a second substrate (low refractive index substrate) on the same surface as the grating or on a different surface of the first substrate. Since the refractive index of the second substrate is higher than that of air and lower than that of the first substrate, light is first diffracted by the grating and reflected by the high refractive index substrate. Then, the light enters the low refractive index substrate. Since the propagation angle of the light in the low refractive index substrate is increased, even if the low refractive index substrate is very thin, the propagation distance of the light in the plane can be effectively increased, thereby minimizing the occurrence of secondary diffraction.

[0037] On the other hand, since the material density of the low refractive index substrate is generally low, this layer of substrate will not add too much weight, and the low refractive index substrate has no grating structure, and the process only needs to add a gluing step, so the process complexity is low.

[0038] In some optional implementations, the grating 101 may be disposed on the first surface of the first substrate 102 , and the second substrate 103 may be disposed on the second surface of the first substrate 102 , that is, the grating 101 and the second substrate 103 are respectively located on both sides of the first substrate 102 .

[0039] In some optional implementations, the first surface of the first substrate 102 may be the surface close to the light source, that is, the grating 101 is arranged on the surface close to the light source, and the second substrate 103 is arranged on the surface away from the light source.

[0040] Please refer to Figure 3, which is a schematic diagram of the structure of another embodiment of an optical waveguide according to the present disclosure. In Figure 3, a grating 101 is disposed on the side of a first substrate 102 close to the light source, and a second substrate 103 is disposed on the side of the first substrate 102 away from the light source. In this case, the optical waveguide is a transmissive optical waveguide.

[0041] Because the refractive index of the second substrate 103 is higher than that of air and lower than that of the first substrate 102, light is first diffracted by the grating 101 and enters the first substrate 102. However, the presence of the second substrate 103 disrupts total internal reflection at the interface between the first and second substrates 102, allowing the light to enter the second substrate 103. Due to the refractive effect, the propagation angle of the light in the second substrate 103 is increased. This effectively increases the in-plane propagation distance of the light, even if the second substrate 103 is very thin, thereby minimizing secondary diffraction.

[0042] In some optional implementations, the second surface of the first substrate 102 may be the surface close to the light source, that is, the second substrate 103 is disposed on the surface close to the light source, and the grating 101 is disposed on the surface away from the light source.

[0043] Continuing with Figure 4, Figure 4 is a schematic diagram of the structure of another embodiment of an optical waveguide according to the present disclosure. In Figure 4, a grating 101 is disposed on the side of a first substrate 102 away from the light source, and a second substrate 103 is disposed on the side of the first substrate 102 closer to the light source. In this case, the optical waveguide is a reflective optical waveguide.

[0044] Light enters the second substrate 103 and the first substrate 102 in sequence, reflecting off the first substrate 102. At the interface where the first substrate 102 and the second substrate 103 meet, total internal reflection is broken, allowing the light to enter the second substrate 103. Due to the refraction effect, the light propagates through the second substrate 103 at a greater angle. This effectively increases the in-plane propagation distance of the light, even if the second substrate 103 is very thin, minimizing secondary diffraction.

[0045] In some optional implementations, the first substrate 102 and the second substrate 103 can be interconnected by van der Waals forces. Van der Waals forces can also be called intermolecular forces or van der Waals forces. Intermolecular forces have three sources: the interaction between the permanent dipole moments of polar molecules; one polar molecule polarizes another molecule, generating an induced dipole moment and attracting each other; the movement of electrons in the molecule generates a transient dipole moment, which transiently polarizes the adjacent molecule, which in turn enhances the transient dipole moment of the original molecule. This mutual coupling produces an electrostatic attraction. The contributions of these three forces are different, and the third force usually contributes the most. Here, the two substrates are connected to each other by van der Waals forces, further reducing the process complexity of the optical waveguide.

[0046] In some optional implementations, the thickness of the second substrate 103 is generally less than or equal to the thickness of the first substrate 102. Since the propagation angle of light in a low-refractive-index substrate increases, even if the low-refractive-index substrate is very thin, the in-plane propagation distance of light can be effectively increased. By limiting the thickness of the low-refractive-index substrate, the weight of the optical waveguide can be minimized.

[0047] In some optional implementations, a second substrate 103 may be provided on both sides of the first substrate 102. As shown in Figure 5, Figure 5 is a structural schematic diagram of another embodiment of the optical waveguide according to the present disclosure. In Figure 5, the light is first diffracted by the grating 101 and enters the first substrate 102. However, due to the presence of the second substrate 103, the total internal reflection condition is destroyed on the side where the first substrate 102 and the second substrate 103 contact each other, and the light enters the second substrate 103. Due to the refraction effect, the propagation angle of the light in the second substrate 103 becomes larger. After the total internal reflection of the second substrate 103, the light enters the first substrate 102 and then enters the second substrate 103 again. The propagation angle of the light in the second substrate 103 becomes larger again, thereby further avoiding the occurrence of secondary diffraction.

[0048] It should be noted that the optical waveguide in Figure 5 is only a schematic structural diagram, and the grating position can be set according to actual conditions. For example, the grating can be set between the first substrate and the second substrate on the side of the first substrate away from the light source, or the grating can be set on both sides of the first substrate.

[0049] In some optional implementations, the total thickness of the second substrate 103 on both sides of the first substrate 102 is generally less than or equal to the thickness of the first substrate 102. Because the propagation angle of light in a low-refractive-index substrate increases, even if the low-refractive-index substrate is very thin, the in-plane propagation distance of light can be effectively increased. By limiting the total thickness of the two low-refractive-index substrates, the weight of the optical waveguide can be minimized.

[0050] In some optional implementations, the grating 101 may be disposed between the first substrate 102 and the second substrate 103. If a second substrate is disposed on both sides of the first substrate, a grating may be disposed between each first substrate and the second substrate.

[0051] The optical waveguide provided by the disclosed embodiments includes a grating, a first substrate, and a second substrate. The grating is disposed on at least one side of the first substrate, and the second substrate is disposed on at least one side of the first substrate. The refractive index of the second substrate is lower than that of the first substrate, thereby preventing secondary diffraction of light in the optical waveguide and reducing brightness loss. Furthermore, since the material density of a low-refractive-index substrate is generally low, this substrate layer does not add excessive weight. Furthermore, since the low-refractive-index substrate lacks a grating structure, the manufacturing process only requires the addition of a gluing step, thus reducing process complexity.

[0052] FIG6 shows a schematic diagram of an embodiment of an extended reality device according to the present disclosure. As shown in FIG6 , the extended reality device may include the optical waveguide described in the embodiment of the present disclosure. The optical waveguide described in the embodiment of the present disclosure includes a first substrate and a second substrate having a lower refractive index than the first substrate. Since the propagation angle of light in the low-refractive-index substrate becomes larger, the propagation distance of light in the plane is effectively increased, and the secondary diffraction of light in the optical waveguide is avoided. When the user uses the extended reality device including the optical waveguide, more light enters the human eye, reducing the brightness loss. In addition, since the material density of the low-refractive-index substrate is generally low, this layer of substrate will not add too much weight, and the low-refractive-index substrate does not have a grating structure. Therefore, the process only needs to add a gluing step, so the process complexity is low.

[0053] The above description is merely a preferred embodiment of the present disclosure and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in the embodiments of the present disclosure is not limited to the technical solutions formed by a specific combination of the above-mentioned technical features, but should also encompass other technical solutions formed by any combination of the above-mentioned technical features or their equivalents without departing from the above-mentioned inventive concept. For example, a technical solution formed by mutually replacing the above-mentioned features with (but not limited to) technical features with similar functions disclosed in the embodiments of the present disclosure.

Claims

1. An optical waveguide comprising: A grating, a first substrate and a second substrate; in The grating is arranged on at least one side of the first substrate, and the second substrate is arranged on at least one side of the first substrate; The refractive index of the second substrate is lower than the refractive index of the first substrate.

2. The optical waveguide according to claim 1, wherein The grating is disposed on a first surface of the first substrate, and the second substrate is disposed on a second surface of the first substrate.

3. The optical waveguide according to claim 2, wherein: The first surface of the first substrate is a surface close to the light source.

4. The optical waveguide according to claim 2, wherein: The second surface of the first substrate is a surface close to the light source.

5. The optical waveguide according to any one of claims 2 to 4, wherein: The first substrate and the second substrate are connected to each other by van der Waals force.

6. The optical waveguide according to any one of claims 2 to 5, wherein: The thickness of the second substrate is less than or equal to the thickness of the first substrate.

7. The optical waveguide according to claim 1, wherein The second substrate is disposed on both sides of the first substrate.

8. The optical waveguide according to claim 7, wherein The total thickness of the second substrates on both sides of the first substrate is less than or equal to the thickness of the first substrate.

9. The optical waveguide according to claim 1, wherein The grating is disposed between the first substrate and the second substrate.

10. An extended reality device, comprising: An optical waveguide as claimed in any one of claims 1 to 9.

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