An optical waveguide structure and an augmented reality device

Abstract

The application provides an optical waveguide structure and an augmented reality device, relates to the technical field of augmented reality, and comprises an optical waveguide, wherein a protection cover is arranged on the side of the optical waveguide from which forward leakage light is emitted, and a diffraction grating layer is further arranged on the protection cover; the optical waveguide is used for transmitting virtual image light emitted by a light machine to a coupling-out grating of the optical waveguide; the coupling-out light is transmitted into a human eye through the coupling-out grating; and the forward leakage light is transmitted into the diffraction grating layer on the protection cover. The protection cover is added outside the optical waveguide, the diffraction grating layer is arranged on the protection cover to diffract the forward leakage light to a light extinction surface of the protection cover to eliminate the forward leakage light, the design of the optical waveguide itself is not affected, and the compatibility is strong. The diffraction grating layer is simple in design, simple in manufacturing, low in cost and suitable for large-scale production. The forward leakage light is deflected to other directions, meanwhile, external environment light is not affected to be incident into the optical waveguide, the influence on the external environment light entering the optical waveguide is small, and the application is better suitable for a virtual reality fusion scene.

Description

Technical Field

[0001] This application relates to the field of augmented reality technology, specifically to an optical waveguide structure and an augmented reality device. Background Technology

[0002] AR (Augmented Reality) waveguide solutions are characterized by their thinness and excellent display effects, making them the most sought-after by major manufacturers in AR near-eye display devices. According to optical principles, waveguides can be divided into diffractive waveguides and geometric waveguides. Regardless of the type of waveguide structure, they all share a common problem: eye glow, also known as forward light leakage.

[0003] This phenomenon stems from the abnormal leakage of light energy caused by the failure of total internal reflection within the optical waveguide: when light from a virtual image enters the optical waveguide transmission channel through the coupling region, due to surface microstructure defects, material scattering characteristics, or limitations imposed by the coupling grating design, some light rays exceed the critical angle of total internal reflection and leak from the back of the optical waveguide (opposite to the user's face) into the external environment, forming visible light spots in the user's eyes (especially in dark environments or high-brightness display scenarios). This type of light leakage not only causes energy loss but also leads to social embarrassment and privacy exposure (such as revealing the device's usage status) due to the abnormal, visible light emission. Furthermore, in high-risk scenarios (driving, walking at night), it can cause safety hazards due to distraction from the environment or misjudgment by third parties. Therefore, eliminating eye-related light emission has become a key technical challenge for improving the user experience and usability of AR devices. Utility Model Content

[0004] The purpose of this application is to provide an optical waveguide structure and an augmented reality device that can eliminate the phenomenon of forward light leakage to the eye in AR optical waveguides, and has a simple structure, is easy to integrate, and is suitable for mass production.

[0005] In one aspect of this application, an optical waveguide structure is provided, including an optical waveguide, a protective cover is provided on the side of the optical waveguide from which forward light leaks out, and a diffraction grating layer is also provided on the protective cover. The optical waveguide is used to transmit virtual image light emitted by an optical engine to the coupling grating of the optical waveguide, and the coupled light is transmitted to the human eye through the coupling grating. The forward light leaks out and is transmitted to the diffraction grating layer on the protective cover.

[0006] Optionally, the forward light leakage occurs at an angle greater than the critical angle θ for total internal reflection of the protective cover. c directional diffraction, satisfying θ c =arcsin(n1 / n2), where n1 and n2 are the refractive indices of the incident medium and the refracting medium, respectively.

[0007] Optionally, the matte surface of the protective cover is provided with a light-absorbing film, and the forward leakage light transmitted to the protective cover is absorbed by the light-absorbing film.

[0008] Optionally, the matte surface of the protective cover is provided with a frosted glass edge, and forward light leakage transmitted to the protective cover is scattered and released through the frosted glass edge.

[0009] Optionally, the diffraction grating layer satisfies θi and θ t These are the incident angle and the refraction angle of the diffraction grating layer, respectively. s and t p η1 and η2 are the transmission coefficients of S-polarized light and P-polarized light, respectively, and the refractive indices of air and the protective cover, respectively.

[0010] Optionally, the forward-leaking light, after passing through the diffraction grating layer, is transmitted within the protective cover via total internal reflection, and the distance L between the light source and the foreground after each total internal reflection satisfies L = 2*h*tan(θ). diff ), h is the distance from the grating diffraction layer to the extinction surface of the protective cover, θ diff Represents the diffraction angle.

[0011] Optionally, the diffraction grating layer is a volume holographic grating layer, satisfying n²*sinθ. m -n1*sinθ in = mλ / d, n1 and n2 are the refractive indices of the incident and diffracting media, respectively, θ in and θ m λ and d are the incident angle and the diffraction angle of the m-th diffraction order, respectively, where λ is the incident wavelength and d is the grating period.

[0012] Optionally, the diffraction grating layer is a surface relief grating layer, wherein the grating period d of the surface relief grating layer is 591.8 nm, the duty cycle f is 0.268, the depth h is 293.2 nm, and the refractive index n2 of the grating is 1.9.

[0013] Optionally, the diffraction grating layer of the protective cover is configured to correspond to the coupling grating of the optical waveguide.

[0014] In another aspect of this application, an augmented reality device is provided, comprising: the optical waveguide structure described above.

[0015] The optical waveguide structure and augmented reality device provided in this application add a protective cover to the outside of the optical waveguide. A diffraction grating layer is set on the protective cover to diffract the forward leakage light to the extinction surface of the protective cover to eliminate the forward leakage light. This does not affect the design of the optical waveguide itself and has strong compatibility. The design of the diffraction grating layer is simple, easy to manufacture, and low in cost, making it suitable for mass production. By deflecting the forward leakage light to other directions, it does not affect the incident ambient light into the optical waveguide, minimizing the impact on ambient light entering the optical waveguide, and making it better suited for virtual reality fusion scenarios. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 It is an existing AR diffractive waveguide structure;

[0018] Figure 2 This is a schematic diagram of the optical waveguide structure provided in the embodiments of this application;

[0019] Figure 3 This is a diagram showing the arrangement of volume holographic grating diffraction in Embodiment 1 of this application;

[0020] Figure 4 This is a graph showing the change in diffraction efficiency of the volume holographic grating as a function of the incident angle in Embodiment 1 of this application;

[0021] Figure 5 This is a schematic diagram of the surface relief grating layer structure of Embodiment 2 of this application;

[0022] Figure 6 This is a diffraction efficiency diagram of the surface relief grating layer in Embodiment 2 of this application.

[0023] Icons: 1-Input grating; 2-Turn grating; 3-Output grating; 4-Eye box; S0-Output light; S1-Forward leakage light; S2-Ambient light; 10-Optical waveguide; 100-Output grating; 11-Protective cover; 110-Diffraction grating layer; 20-Human eye. Detailed Implementation

[0024] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings.

[0025] In the description of this application, it should be noted that the terms "inner" and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product is in use. They are used only for the convenience of describing this application and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0026] It should also be noted that, unless otherwise explicitly specified and limited, the terms "setup" and "connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0027] Geometric waveguides achieve pupil expansion through multiple semi-transparent and semi-reflective mirror arrays, while diffractive waveguides achieve pupil expansion based on diffraction gratings, which can be further subdivided into SRG, VHG, and PVG according to the grating type. However, regardless of the waveguide structure, forward leakage is a current problem.

[0028] like Figure 1 As shown, Figure 1 This is a common AR diffractive waveguide structure (similar to geometric waveguides, but using a semi-transparent, semi-reflective mirror array instead of regional gratings). The virtual image light emitted by the optomechanical system is coupled into the waveguide by the coupling grating 1, then undergoes secondary pupil expansion via the deflection grating 2 and the output grating 3, ultimately forming a virtual image that blends with the external environment at the eye box 4, resulting in the output light S0. However, typically on the back side of the output grating 3, some light exceeds the critical angle for total internal reflection, causing forward leakage light S1 to leak from the back of the waveguide into the external environment, forming a visible light spot in the user's eye. When an observer stands opposite the user and observes their eyes, the user's eye emission is clearly visible, which negatively impacts user privacy.

[0029] Currently, there are two main approaches to addressing forward light leakage. The first is to use external elimination methods, such as adding traditional light-shielding layers and polarization filtering outside the waveguide. However, these methods have limitations. For example, using traditional light-shielding layers adds sunglasses-like lenses to the outside of AR glasses, affecting aesthetics, increasing size, and causing the wearer to see the external environment in a darker light (similar to sunglasses), thus hindering observation. Polarization filtering modulates the forward leakage light and ambient light into different polarization states, thus precisely eliminating forward leakage. However, modulating the polarization state affects the transmittance of external light. Furthermore, the optomechanical light source used with the waveguide must be polarized, increasing system complexity and cost. Additionally, laser light sources themselves have technical issues such as speckle. The second approach involves optimizing the waveguide's gratings to weaken or deflect the reverse-outgoing light from the gratings to other, less observable angles. Firstly, this increases the design complexity of the waveguide, as each grating is interconnected; any change to one grating requires adjustments to the entire grating layout. Secondly, this optimization causes the optimal grating parameters for optical indicators such as display brightness and uniformity to deviate, which inevitably affects the imaging quality of the optical waveguide.

[0030] In view of this, the present application provides an optical waveguide structure that can eliminate the phenomenon of forward light leakage S1 to the eye in AR optical waveguide 10. This technology needs to be simple and easy to integrate, suitable for mass production, and have a minimal impact on key display indicators such as volume, size, brightness and transmittance of optical waveguide 10.

[0031] Specifically, please refer to Figure 2 As shown, this application embodiment provides an optical waveguide structure, including an optical waveguide 10. A protective cover 11 is provided on the side of the optical waveguide 10 from which forward leakage light S1 is emitted. A diffraction grating layer 110 is also provided on the protective cover 11. The optical waveguide 10 is used to transmit the virtual image light emitted by the optical engine to the coupling grating 100 of the optical waveguide 10. The coupling light S0 is transmitted to the human eye 20 through the coupling grating 100, and the forward leakage light S1 is transmitted to the diffraction grating layer 110 on the protective cover 11.

[0032] The protective cover 11 protects the surface of the optical waveguide 10 and prevents damage during wiping. A diffraction grating layer 110 is provided on the protective cover 11. The size and position of the diffraction grating layer 110 are consistent with the forward leakage S1 region that is to be eliminated. Usually, the most obvious area of ​​forward leakage S1 is the coupling grating 100 region. Therefore, the size and position of the diffraction grating layer 110 in this application are set to be consistent with the coupling grating 100.

[0033] The diffraction grating layer 110 can be a volume holographic grating film, or a one-dimensional or two-dimensional surface relief grating, or other micro-nano structures with the same function.

[0034] The diffraction grating layer 110 can be placed on the inner side of the protective cover 11 facing the optical waveguide 10, on the outer side away from the optical waveguide 10, or inside the protective cover 11.

[0035] The function of the diffraction grating layer 110 is to divert the incident forward leakage light S1 at an angle greater than the critical angle θ for total internal reflection of the protective cover 11. c directional diffraction, θ c =arcsin(n1 / n2), where n1 and n2 are the refractive indices of the incident and refracting media, respectively. There is an air layer between the optical waveguide 10 and the protective cover 11, so the forward leakage light S1 will propagate to the edge of the protective cover 11 in the form of total internal reflection.

[0036] from Figure 2 It can be seen that the matte surface of the protective cover 11 is used to emit forward light leakage S1 in order to eliminate forward light leakage S1. For example, the matte surface is located at the edge of the protective cover 11, and a light-absorbing film is provided at the edge of the protective cover 11, i.e. the matte surface. The forward light leakage S1 enters the protective cover 11 through the diffraction grating layer 110 and is transmitted. After being transmitted to the light-absorbing film, the forward light leakage S1 is absorbed by pasting black glue or by blackening the surface.

[0037] Alternatively, a frosted glass edge can be used, where the edge of the protective cover 11, i.e. the matte surface, is provided with a frosted glass edge, so that the forward leakage light S1 transmitted to the edge of the protective cover 11 is scattered and released to the outside of the edge of the optical waveguide 10.

[0038] Through the two methods described above, forward light leakage S1 will not leak from the corresponding position of the diffraction grating layer 110 on the protective cover 11 into the external environment, thereby achieving the function of eliminating forward light leakage S1.

[0039] The diffraction grating layer 110 of the protective cover 11 is the core optical device for eliminating forward light leakage S1. Its diffraction efficiency directly affects the efficiency of eliminating forward light leakage S1. Therefore, the efficiency of the designed diffraction grating directly determines the degree of light leakage elimination.

[0040] Furthermore, not all of the forward leakage light S1 is incident orthogonally onto the protective cover 11. Therefore, the diffraction grating layer 110 also needs to have a certain angular bandwidth to diffract the forward leakage light S1 incident at other angles. According to Fresnel's formula:

[0041]

[0042] Where, θ i and θ t These represent the incident angle and the refraction angle of the diffraction grating layer 110, respectively. s and t p η1 and η2 are the transmission coefficients of S-polarized light and P-polarized light, respectively, and the refractive indices of air and protective cover 11 are, respectively.

[0043] Regardless of whether the optical engine emits polarized light, when the incident angle θ i As t gradually increases from 0 degrees (corresponding to normal incidence), s Monotonically decreasing, t p First increase slightly, then decrease gradually. For unpolarized light, its transmittance is taken as t. s and t p The average value. Therefore, in general, the larger the incident angle of the forward leakage S1, the lower its transmittance. Therefore, the angular bandwidth of the diffraction grating layer 110 does not need to be particularly large. Eliminating the forward leakage S1 mainly refers to the leakage in the vertical direction.

[0044] On the other hand, the forward-leaking light S1, after passing through the diffraction grating layer 110, propagates towards the edge of the protective cover 11 via total internal reflection. The distance the light travels after each total internal reflection is called the "step size," and its expression is as follows:

[0045] L=2*h*tan(θ diff ) formula (3);

[0046] Where h represents the distance from the grating diffraction layer to the rear surface of the protective cover 11, θ diff Represents the diffraction angle.

[0047] Calculations show that the step size is relatively small compared to the size of the diffraction grating layer 110. This means that a portion of the forward leakage light S1 needs to undergo several total internal reflections before leaving the diffraction grating layer 110. Each time this portion of forward leakage light S1 is repeatedly incident on the diffraction grating layer 110, some of its energy will be reversed and coupled out by the diffraction grating layer 110, and re-incidentally onto the coupling grating 100 of the optical waveguide 10. According to the principle of optical path reversibility, the light re-incidentally onto the coupling grating 100 will travel along the original transmission path to the turning grating and the coupling grating, so it has little impact on the final image observed by the human eye 20.

[0048] To further reduce the impact of the reverse coupling of the diffraction grating layer 110, the step size can be increased, for example, by increasing the thickness of the protective cover 11 or increasing the diffraction angle of the diffraction grating layer 110.

[0049] Figure 2 The green arrow represents ambient light S2. When it is incident on the diffraction grating layer 110 in the reverse direction, a portion of its energy is diffracted into the protective cover 11. It should be noted that ambient light S2 is a broadband light source, such as sunlight spectrum and LED emission spectrum, both outdoors and indoors. To reduce the influence of the diffraction grating layer 110 on ambient light S2, the grating should be designed only for the peak wavelength bandwidth of the optomechanical system.

[0050] Furthermore, for forward light leakage S1 around the eye, the main extinction direction is forward light leakage (corresponding to perpendicular incidence), consistent with the previously mentioned view that the grating angle bandwidth does not need to be too large. However, the incident angle bandwidth of ambient light S2 is typically very large, so the diffraction grating layer 110 has relatively little impact on ambient light S2. On the other hand, when a typical AR waveguide (without the diffraction grating layer 110) is used in the external environment, the coupling grating 100 will also diffract a portion of the ambient light S2, but the transmittance of the waveguide 10 can still reach 90%, which also demonstrates that the diffraction grating layer 110 has relatively little impact on ambient light S2.

[0051] Finally, the geometric waveguide 10 can also solve the light leakage problem using the solution proposed in this application. The forward light leakage S1 is reduced by the protective cover 11 with the diffraction grating layer 110, and the principle is the same as the process described above.

[0052] The design principle of the AR waveguide structure for eliminating eye emission proposed in this application is as described above. The diffraction grating layer 110 can be a volume holographic grating film, a one-dimensional or two-dimensional surface relief grating, or other micro / nano structures with the same function. To better understand this application, two representative structural designs are provided, employing a volume holographic grating and a surface relief grating, respectively.

[0053] The following are several examples:

[0054] In Embodiment 1, the volume holographic grating has the advantages of easy assembly, low cost, and easy mass production. In actual use, the volume holographic grating is used as the diffraction grating layer 110, and the arrangement is as follows. Figure 3 As shown. For ease of description, in this embodiment, the optical waveguide 10 is a single green waveguide 10, and both the optical waveguide 10 and the protective cover 11 are made of glass with a refractive index of 1.51. The function of the diffraction grating layer 110 is to diffract the forward leakage light S1 with a wavelength of 532nm at a direction of 57°, which is greater than the critical angle of total internal reflection of 41°. The volume holographic grating is manufactured by dual-beam exposure, and the principle is as follows. Figure 3 As shown.

[0055] The two beams are the reference beam K. R and signal light K S As can be seen from the principle of volume holographic gratings, the angles of the reference light and the signal light recorded on the photosensitive material are θ and θ, respectively. R =0° and signal light θ S =57°, and the recorded beam wavelength is 532nm.

[0056] From the grating equation: n²*sinθ m -n1*sinθ in= mλ / d, where n1 and n2 represent the refractive indices of the incident and diffracting media, respectively, and θ in and θ m λ represents the incident angle and the diffraction angle of the m-th diffraction order, respectively. λ represents the incident wavelength, d represents the grating period, the air refractive index is 1, and the glass substrate refractive index is 1.51. Substituting the above data into the formula, we can find that the volume holographic grating period is 420.1 nm.

[0057] According to prior literature [coupled wave theory for thick hologram gratings, Kogelnik, 1969], the diffraction efficiency of the volume holographic grating in Example 1 as a function of the incident angle is shown in the curve. Figure 4 As shown, by Figure 4 It can be seen that the peak diffraction efficiency of the volume holographic grating exceeds 80%, and the angular bandwidth is about 15°, which means that the diffraction grating layer 110 can diffract leakage light within an angular range of -10 degrees to 10 degrees to the light-absorbing layer. Therefore, using the grating of Embodiment 1 can eliminate 80% of the forward leakage light S1, while the eliminated forward leakage light S1 gradually decreases as the angle increases.

[0058] It should be noted that the volume holographic grating is manufactured using green light with a wavelength of 532nm, and therefore is only suitable for eliminating forward light leakage S1 of a single green waveguide 10. For the full-color waveguide 10, diffraction grating layers 110 of other wavelengths need to be manufactured accordingly. This can be achieved by attaching multilayer volume holographic grating films to the protective cover 11, or by manufacturing a composite grating as the diffraction grating layer 110 through multiple exposures.

[0059] In Embodiment 2, a surface-embossed grating layer can also be used as a diffraction grating layer 110 to achieve the same function. The basic structure of the surface-embossed grating layer is as follows: Figure 5 As shown.

[0060] The surface relief grating used in this embodiment has a period d of 591.8 nm, a duty cycle f of 0.268, a depth h of 293.2 nm, and a refractive index n2 of 1.9.

[0061] The diffraction efficiency of the surface relief grating layer is calculated based on rigorous coupled-wave theory [previous literature: Stable implementation of the rigorous coupled-wave analysis for surface-relief gratings: enhanced transmittance matrix approach, M.G. Moharam et al., 1995]. Figure 6As shown, in the 460nm–620nm wavelength range, the -1st order diffraction efficiency of the surface relief grating exceeds 40%. Due to the symmetry of the grating, the -1st order diffraction efficiency is equal to the +1st order diffraction efficiency, which means that the surface relief grating can diffract more than 80% of the energy of the forward leakage light S1 into the absorption layer. On the other hand, the 0th order diffraction efficiency of the diffraction grating represents the energy that can pass through the grating. It can be seen that in most regions, the 0th order diffraction efficiency is less than 15%, which means that the forward leakage light S1 is greatly weakened.

[0062] Typically, surface-embossed gratings have a large wavelength bandwidth, so only one layer of surface-embossed grating is needed to eliminate forward light leakage S1 in the RGB three colors. In this embodiment, the surface-embossed grating can be mass-produced on the protective cover 11 using nanoimprint technology, serving as a diffraction grating layer 110 to reduce forward light leakage S1.

[0063] In summary, the optical waveguide structure provided in this application adds a protective cover 11 to the outside of the optical waveguide 10. A diffraction grating layer 110 is provided on the protective cover 11 to diffract the forward leakage light S1 to the extinction surface of the protective cover 11 to eliminate the forward leakage light S1. This does not affect the design of the optical waveguide 10 itself and has strong compatibility. The design of the diffraction grating layer 110 is simple. If a volume holographic grating is used, it can be exposed on a large scale on a film material, and then cut and transferred to the protective cover 11, which is simple to manufacture, low in cost, and suitable for mass production. Furthermore, by optimizing the diffraction grating layer 110, the forward leakage light S1 is deflected to other directions without affecting the incident ambient light S2 into the optical waveguide 10. The impact on the ambient light S2 entering the optical waveguide 10 is small, making it better suited for virtual reality fusion scenarios.

[0064] On the other hand, embodiments of this application also disclose an augmented reality device, including an optical waveguide structure as described above. For example, the augmented reality device may be AR glasses, etc.

[0065] This augmented reality device includes the same structure and beneficial effects as the optical waveguide structure in the foregoing embodiments. The structure and beneficial effects of the optical waveguide structure have been described in detail in the foregoing embodiments and will not be repeated here.

[0066] The above description is merely an embodiment of this application and is not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. An optical waveguide structure, characterized in that, include: An optical waveguide is provided with a protective cover on the side of the forward-leaking light-transmitting waveguide. A diffraction grating layer is also provided on the protective cover. The optical waveguide is used to transmit virtual image light emitted by the optical engine to the coupling grating of the optical waveguide. The coupled light is transmitted to the human eye through the coupling grating. The forward-leaking light is transmitted to the diffraction grating layer on the protective cover.

2. The optical waveguide structure according to claim 1, characterized in that, The forward light leakage occurs at a rate greater than the critical angle θ for total internal reflection of the protective cover. c directional diffraction, satisfying θ c =arcsin(n1 / n2), where n1 and n2 are the refractive indices of the incident medium and the refracting medium, respectively.

3. The optical waveguide structure according to claim 1, characterized in that, The matte surface of the protective cover is provided with a light-absorbing film, and forward-leaking light transmitted to the protective cover is absorbed by the light-absorbing film.

4. The optical waveguide structure according to claim 1, characterized in that, The matte surface of the protective cover is provided with a frosted glass edge, and the forward light transmitted to the protective cover is scattered and released through the frosted glass edge.

5. The optical waveguide structure according to any one of claims 1 to 4, characterized in that, The diffraction grating layer satisfies θ i and θ t These are the incident angle and the refraction angle of the diffraction grating layer, respectively. s and t p η1 and η2 are the transmission coefficients of S-polarized light and P-polarized light, respectively, and the refractive indices of air and the protective cover, respectively.

6. The optical waveguide structure according to any one of claims 1 to 4, characterized in that, The forward-leaking light, after passing through the diffraction grating layer, is transmitted within the protective cover via total internal reflection. After each total internal reflection, the distance L between the light source and the foreground satisfies L = 2h * tan(θ). diff ), h is the distance from the grating diffraction layer to the extinction surface of the protective cover, θ diff Represents the diffraction angle.

7. The optical waveguide structure according to claim 1, characterized in that, The diffraction grating layer is a volume holographic grating layer that satisfies n²*sinθ. m -n1*sinθ in = mλ / d, n1 and n2 are the refractive indices of the incident and diffracting media, respectively, θ in and θ m λ and d are the incident angle and the diffraction angle of the m-th diffraction order, respectively, where λ is the incident wavelength and d is the grating period.

8. The optical waveguide structure according to any one of claims 1 to 4, characterized in that, The diffraction grating layer is a surface relief grating layer with a grating period d of 591.8 nm, a duty cycle f of 0.268, a depth h of 293.2 nm, and a refractive index n2 of 1.

9.

9. The optical waveguide structure according to any one of claims 1 to 4, characterized in that, The diffraction grating layer of the protective cover is correspondingly arranged with the coupling grating of the optical waveguide.

10. An augmented reality device, characterized in that, Includes the optical waveguide structure according to any one of claims 1 to 9.

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