Optical waveguide and head-mounted display device

Abstract

The invention discloses an optical waveguide and a head-mounted display device, and relates to the technical field of optical waveguides, and the optical waveguide comprises a waveguide substrate which is provided with a coupling-in grating and a coupling-out grating; the high-reflectivity mirror surface layer is arranged in the waveguide substrate, and the high-reflectivity mirror surface layer is located on the side, away from the coupling-in grating, of the coupling-out grating; incident light enters the waveguide substrate and sequentially passes through the coupling-in grating and the coupling-out grating, and then the propagation direction of residual light pre-entering the side wall of the waveguide substrate is changed through the high-reflectivity mirror surface layer, so that the incident angle of the residual light returning to the coupling-out grating is located outside the effective coupling-out angle range of the coupling-out grating. According to the invention, the edge stray light of the optical waveguide can be effectively suppressed, so that the visual experience of a user is improved.

Description

Technical Field

[0001] This application relates to the field of optical waveguide technology, and in particular to an optical waveguide and a head-mounted display device. Background Technology

[0002] With the rapid development of optical display devices for virtual reality (VR) and augmented reality (AR), optical waveguides have become a core component in this field due to their ability to create a larger eyebox area through pupil expansion technology. However, to ensure uniform pupil expansion, some light energy is transmitted to the edge of the waveguide, thus causing stray light problems.

[0003] Currently, the common method to absorb stray light is to blacken the edges. However, due to the limited refractive index of the inks available and the thinness of the coating layer, the absorption length of the light is limited, so this method is not very effective in suppressing stray light. Summary of the Invention

[0004] The main objective of this application is to provide an optical waveguide and a head-mounted display device that effectively suppresses stray light at the edges of the optical waveguide to improve the user's visual experience.

[0005] To achieve the above objectives, this application proposes an optical waveguide, comprising: A waveguide substrate, wherein the waveguide substrate is provided with an input grating and an output grating; A high-reflectivity mirror layer is disposed within the waveguide substrate, and the high-reflectivity mirror layer is located on the side of the output grating away from the input grating; The incident light enters the waveguide substrate and passes through the coupling grating and the coupling grating in sequence. Then, the propagation direction of the residual light that was about to enter the sidewall of the waveguide substrate is changed by the high-reflectivity mirror layer, so that the incident angle of the residual light when it returns to the coupling grating is outside the effective coupling angle range of the coupling grating.

[0006] In one embodiment, the high-reflectivity mirror layer forms a preset angle with the propagation direction of the residual light rays that are about to enter the sidewall of the waveguide substrate, and the preset angle ranges from 30 degrees to 60 degrees.

[0007] In one embodiment, the preset included angle is set according to the effective coupling angle range, the refractive index of the waveguide substrate, and the initial propagation angle of the residual light.

[0008] In one embodiment, the area where the highly reflective mirror layer is disposed completely covers the propagation range of residual light rays that are about to enter the sidewall of the waveguide substrate.

[0009] In one embodiment, the projected area of ​​the highly reflective mirror layer in the first direction is greater than or equal to the projected area of ​​the coupling grating in the first direction. The first direction refers to the direction that is consistent with or approximately the direction of the residual light rays that are about to enter the sidewall of the waveguide substrate.

[0010] In one embodiment, the waveguide substrate has a thickened portion on the side where the high-reflectivity mirror layer is located.

[0011] In one embodiment, the optical waveguide further includes: An angle selector is disposed in the reflected light path of the high-reflectivity mirror layer. The angle selector is used to absorb light rays reflected by the high-reflectivity mirror layer whose incident angle is within the effective coupling angle range, and to transmit light rays whose incident angle is outside the effective coupling angle range.

[0012] In one embodiment, the waveguide substrate is further provided with a bend grating: The incident light enters the waveguide substrate and passes sequentially through the coupling grating, the turning grating, and the coupling grating. The propagation direction of the residual light that was about to enter the sidewall of the waveguide substrate is changed by the high-reflectivity mirror layer, so that the incident angle of the residual light returning to the coupling grating is outside the effective coupling angle range of the coupling grating.

[0013] In one embodiment, the optical waveguide further includes: An absorption layer is disposed on the side of the high-reflectivity mirror layer opposite to the coupling grating, and the absorption layer is used to absorb light transmitted from the high-reflectivity mirror layer.

[0014] In one embodiment, the optical waveguide further includes: Dissipation section, the dissipation section being formed at the sidewall of the waveguide substrate into which the residual light is to be entered; When the residual light enters the dissipation section, it undergoes multiple reflections within the dissipation section and is gradually absorbed by the dissipation section or leaks out of the dissipation section to the outside.

[0015] In one embodiment, the geometry of the dissipation section is as follows: wedge structure; or, Arc-shaped structure; or, Serrated structure; or, An irregular multi-faceted structure consisting of multiple different facets connected sequentially; or, A free-form surface structure consisting of multiple different curved surfaces connected in sequence.

[0016] In addition, to achieve the above objectives, this application also proposes a head-mounted display device, which includes a device body and an optical waveguide as described above, wherein the optical waveguide is disposed on the device body.

[0017] This application provides an optical waveguide, comprising: a waveguide substrate having an input grating and an output grating; and a highly reflective mirror layer disposed within the waveguide substrate, with the highly reflective mirror layer located on the side of the output grating away from the input grating. Incident light enters the waveguide substrate and passes sequentially through the input and output gratings. The highly reflective mirror layer alters the propagation direction of residual light rays that are about to enter the sidewall of the waveguide substrate, causing the incident angle of the residual light rays returning to the output grating to be outside the effective output angle range of the output grating.

[0018] Therefore, the technical solution provided in this application, by setting a highly reflective mirror layer in the waveguide substrate and placing it on the side of the coupling-out grating away from the coupling-in grating, ensures that residual light rays about to enter the sidewall of the waveguide substrate will have their propagation direction altered by the highly reflective mirror layer as they are coupled out of the coupling-out grating. This results in the incident angle of these residual rays returning to the coupling-out grating being outside the effective coupling-out angle range of the grating. Consequently, even if these residual rays return to the coupling-out grating, they will not be coupled out of the grating to the eyepiece because their incident angle is outside the effective coupling-out angle range. This effectively suppresses stray light from the edge of the optical waveguide, thereby improving the user's visual experience. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0020] Figure 1 A diagram illustrating the diffraction principle of light when the edge of the optical waveguide provided in this embodiment is rough; Figure 2 A diagram illustrating the diffraction principle of light rays when the edge of the optical waveguide provided in this embodiment is smooth; Figure 3 This is a schematic diagram of the optical waveguide provided in the first embodiment of this application; Figure 4 A schematic diagram illustrating the principle of how the highly reflective mirror layer in the first embodiment of this application changes the propagation direction of residual light. Figure 5 This is a vector diagram of the optical coupler when light propagates through an optical waveguide, provided in the fifth embodiment of this application. Figure 6A schematic diagram of the structure of the dissipation section provided in the first example of this application; Figure 7 A schematic diagram of the structure of the dissipation section provided in the second example of this application; Figure 8 A schematic diagram of the structure of the dissipation section provided in the third example of this application; Figure 9 A schematic diagram of the structure of the dissipation section provided in the fourth example of this application.

[0021] The purpose, features, and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings.

[0022] Explanation of icon numbers: 10. Waveguide substrate; 20. High-reflectivity mirror layer; 11. Coupled-in grating; 12. Coupled-out grating; 13. Turning grating; φ, Preset angle. Detailed Implementation

[0023] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0024] It should be noted that all directional indicators (such as up, down, left, right, front, back, etc.) in the embodiments of this application are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicator will also change accordingly.

[0025] Furthermore, the use of terms such as "first" and "second" in this application is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. Additionally, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. When the combination of technical solutions is contradictory or impossible to implement, such a combination of technical solutions should be considered non-existent and not within the scope of protection claimed in this application.

[0026] With the rapid development of virtual reality and augmented reality technologies, the performance requirements for optical display devices (such as smart head-mounted displays) are also increasing. As a key component of these optical display devices, the design of optical waveguides has a crucial impact on the user's visual experience. For optical waveguide devices, the exit pupil is often expanded in one or two directions, a process known as pupil expansion. This allows a smaller entrance pupil to create a larger effective eyebox at the eye's end.

[0027] However, in practical applications, to ensure uniform pupil dilation, a significant amount of light energy is typically transmitted to the tail end and further propagated until it reaches the edge of the optical waveguide. This phenomenon causes several problems, one of the more significant being stray light at the edge of the optical waveguide. For example... Figure 1 As shown, when the edge is relatively rough, the light energy reaching the edge will return in the form of diffuse reflection. Many of these rays can satisfy the total internal reflection conditions of the upper and lower boundaries of the optical waveguide, thus successfully returning to the coupling region and forming a diffuse stray light noise floor. The other part of the rays, because they do not satisfy the total internal reflection conditions of the upper and lower boundaries, will quickly leak out after several reflections.

[0028] It should be noted that since optical waveguides are usually made of materials with high refractive index, the higher the refractive index, the smaller the critical angle of total internal reflection, and the more stray light can be successfully returned. Even if some special designs use optical waveguide substrates with low refractive index (such as resin substrates with a refractive index of about 1.6), a considerable amount of reflected light can still be successfully returned, which is usually higher than 40% according to calculations. Therefore, it also has a significant impact on imaging quality.

[0029] Currently, the common method to absorb stray light is to blacken the edges. However, due to the limited refractive index of the inks available and the thinness of the coating layer, the absorption length of the light is limited, so this method is not very effective in suppressing stray light.

[0030] It is worth noting that when the edges of the optical waveguide are relatively smooth, specular reflection occurs, which allows more stray light to return smoothly. For example... Figure 2 As shown, once the edge approaches specular reflection, according to simple geometric relationships, the returned light will 100% meet the total internal reflection condition, forming strong stray light. More seriously, if the tail light energy brought by the pupil expansion design is relatively strong, then the returned stray light will have an uncontrollable and significant impact on the display's color, field uniformity, and other performance characteristics, thus causing the product to fail.

[0031] Based on this, the first embodiment of this application proposes an optical waveguide, please refer to... Figure 3 Optical waveguides may include: Waveguide substrate 10, waveguide substrate 10 is provided with coupling grating 11 and coupling grating 12; A high-reflectivity mirror layer 20 is disposed within the waveguide substrate 10, and the high-reflectivity mirror layer 20 is located on the side of the output grating 12 away from the input grating 11. The incident light enters the waveguide substrate 10 and passes through the input grating 11 and the output grating 12 in sequence. The high-reflectivity mirror layer 20 changes the propagation direction of the residual light that is about to enter the sidewall of the waveguide substrate 10, so that the incident angle of the residual light when it returns to the output grating 12 is outside the effective output angle range of the output grating 12.

[0032] It should be noted that the waveguide substrate 10 is a transparent dielectric layer that constrains and guides light propagation through the principle of total internal reflection. The coupling grating 11 is responsible for efficiently coupling the incident light into the waveguide interior and ensuring that the light propagates within the waveguide under the condition of total internal reflection. The coupling grating 12 is responsible for efficiently coupling the light that has already propagated within the waveguide under total internal reflection out of the waveguide and directing it towards the human eye. A portion of the grating region of the coupling grating 11 can be disposed on the upper or lower surface of the waveguide substrate 10, and at least a portion of the grating region of the coupling grating 11 is disposed within the waveguide substrate 10; this embodiment does not impose specific limitations on this. Similarly, a portion of the grating region of the coupling grating 12 can be disposed on the upper or lower surface of the waveguide substrate 10, and at least a portion of the grating region of the coupling grating 12 is disposed within the waveguide substrate 10; this embodiment does not impose specific limitations on this.

[0033] If a portion of the grating regions of the input grating 11 and the output grating 12 are located on the upper surface of the waveguide substrate 10, both operate in transmission mode, primarily guiding the direction of light by manipulating the transmission diffraction order (e.g., m=+1 order). If a portion of the grating regions of the input grating 11 and the output grating 12 are located on the lower surface of the waveguide substrate 10, both operate in reflection mode, primarily guiding the direction of light by manipulating the reflection diffraction order (e.g., m=-1 order).

[0034] Additionally, it should be noted that the effective coupling angle range refers to the range of incident angles of the guided mode light that can be coupled out by the coupling grating 12 to the eyebox to form an effective image. The effective coupling angle range can be determined by analyzing parameters such as the period, duty cycle, and shape of the coupling grating 12, or it can be directly obtained through optical testing equipment. This embodiment does not impose specific limitations on this. The high-reflectivity mirror layer 20 is an optical thin film or structure with extremely high reflectivity (typically >95%) and extremely low absorption and transmission loss in the target wavelength band. It can be formed by physical vapor deposition of a metal thin film or by alternating deposition of dielectric materials with different refractive indices of multiple dielectric films. This embodiment does not impose specific limitations on this. Among them, metal thin films are usually made of aluminum, silver or gold, which generate strong ohmic loss at the interface due to their high free electron density, thereby achieving high reflectivity over a wide angle and a wide band; multilayer dielectric films are usually composed of alternating high refractive index materials such as titanium oxide and hafnium oxide with low refractive index materials such as silicon oxide and magnesium fluoride, with each layer having an optical thickness of one-quarter of the target wavelength, which can achieve an extremely high reflectivity of close to 99.9% in a specific band through the constructive interference effect.

[0035] It is understandable that, among the rays coupled out by the coupling grating 12, the residual rays that were about to enter the sidewall of the waveguide substrate 10, after being reflected by the high-reflectivity mirror layer 20, will have their guided mode angle changed to fall outside the effective coupling angle range of the coupling grating 12. For example, please refer to... Figure 4 After the residual light is redirected by the high-reflectivity mirror layer 20, because its incident angle is outside the effective coupling angle range of the coupling grating 12, it will not be coupled to the eye box by the coupling grating 12, but will directly pass through the coupling grating 12 to oscillate up and down in the waveguide substrate 10.

[0036] When the high-reflectivity mirror layer 20 changes the propagation direction of the residual light rays pre-entering the sidewall of the waveguide substrate 10, so that the incident angle of the residual light rays returning to the coupling grating 12 is outside the effective coupling angle range of the coupling grating 12, the high-reflectivity mirror layer 20 can change the propagation vector of the residual light rays pre-entering the sidewall of the waveguide substrate 10, so that the changed propagation vector of the residual light rays is perpendicular or approximately perpendicular to the modulated vector of the coupling grating 12 on the plane of the waveguide substrate 10. This embodiment does not specifically limit this.

[0037] The fact that the propagation vector of the modified residual light is approximately perpendicular to the modulated vector of the coupling grating 12 on the plane of the waveguide substrate 10 means that the angle between the propagation vector of the modified residual light and the modulated vector of the coupling grating 12 is within a certain vertical angle range (e.g., 85 degrees to 95 degrees).

[0038] The high-reflectivity mirror layer 20 alters the propagation vector of residual light to be perpendicular or nearly perpendicular to the modulated vector of the coupling grating 12. Consequently, residual light cannot undergo diffraction beyond the zeroth order when passing through the coupling grating 12 (i.e., only zeroth-order diffraction occurs), thus preventing residual light from being modulated into the eye box. This results in more stable image quality in the exit pupil area, preventing uncontrollable and significant impacts on display performance such as color and field uniformity (e.g., avoiding bright spot phenomena).

[0039] In one feasible implementation, to ensure that the residual light, after passing through the highly reflective mirror layer 20, can have its propagation direction altered so that its incident angle upon return is outside the effective coupling angle range of the coupling grating 12, please refer to... Figure 3 The propagation direction of the residual light rays from the high-reflectivity mirror layer 20 to the sidewall of the pre-entering waveguide substrate 10 can be set to a preset angle φ, which is less than 90 degrees.

[0040] Furthermore, in one feasible implementation, to ensure that all residual light rays, after changing their propagation direction through the high-reflectivity mirror layer 20, return to an incident angle outside the effective coupling angle range of the coupling grating 12, the preset included angle φ can be set according to the effective coupling angle range, the refractive index of the waveguide substrate 10, and the initial propagation angle of the residual light rays.

[0041] The initial propagation angle of the residual ray is the angle between the residual ray and the waveguide plane before it first reaches the highly reflective mirror layer 20.

[0042] When setting the preset angle φ based on the effective coupling angle range, the refractive index of the waveguide substrate 10, and the initial propagation angle of the residual light, the critical angle of total internal reflection of the waveguide substrate 10 can be calculated first using the refractive index of the waveguide substrate 10. Then, the target reflection angle can be determined using the critical angle of total internal reflection and the effective coupling angle range (the target reflection angle needs to be outside the effective coupling angle range and needs to be less than the critical angle of total internal reflection). After that, the preset angle φ can be calculated using the target reflection angle and the initial propagation angle of the residual light (e.g., half of the difference between the target reflection angle and the initial propagation angle of the residual light can be used as the preset angle φ).

[0043] In one feasible implementation, to ensure that all residual light rays coupled from the coupling grating 12 to the sidewalls of the pre-entry waveguide substrate 10 can enter the high-reflectivity mirror layer 20, the area of ​​the high-reflectivity mirror layer 20 can be configured to completely cover the propagation range of the residual light rays from the sidewalls of the pre-entry waveguide substrate 10. This design ensures that backlight rays emitted from any position of the coupling grating 12 will be reflected by the high-reflectivity mirror layer 20, so that the propagation angle of residual light rays in all directions can be changed by the high-reflectivity mirror layer 20. In practical use, the high-reflectivity mirror layer 20 can be designed as a rectangle, trapezoid, or other geometry that matches the projected shape of the coupling grating 12; this embodiment does not specifically limit this.

[0044] When the area where the high-reflectivity mirror layer 20 is set completely covers the propagation range of the residual light that is about to enter the sidewall of the waveguide substrate 10, in one feasible embodiment, the orthogonal projection area of ​​the high-reflectivity mirror layer 20 in the first direction can be set to be greater than or equal to the orthogonal projection area of ​​the coupling grating 12 in the first direction. The first direction can be a direction that is consistent with or approximately similar to the direction of the residual light rays that are about to enter the sidewall of the waveguide substrate 10, or it can be a direction that is consistent with or approximately similar to the normal direction of the sidewall of the waveguide substrate 10 (specifically, the sidewall of the waveguide substrate 10 where stray light is about to enter).

[0045] It should be noted that the direction approximating the residual ray direction of the pre-entry waveguide substrate 10 sidewall refers to a direction whose angle with the residual ray direction of the pre-entry waveguide substrate 10 sidewall is within a certain angular range (e.g., within ±5 degrees). Similarly, the direction approximating the normal direction of the waveguide substrate 10 sidewall refers to a direction whose angle with the normal direction of the waveguide substrate 10 sidewall is within a certain angular range (e.g., within ±5 degrees).

[0046] This embodiment establishes a clear and reliable geometric design principle by setting the orthographic projection area of ​​the high-reflectivity mirror layer 20 in the first direction to be greater than or equal to the orthographic projection area of ​​the coupling grating 12 in the same direction. This geometric design principle ensures that all light rays emitted backward from the entire region of the coupling grating 12 are spatially intercepted and have their propagation direction changed by the high-reflectivity mirror layer 20 along their path toward the waveguide sidewall.

[0047] Based on the above, this embodiment provides an optical waveguide, including: a waveguide substrate 10, which is provided with an insertion grating 11 and an exit grating 12; and a high-reflectivity mirror layer 20, which is disposed within the waveguide substrate 10 and located on the side of the exit grating 12 away from the insertion grating 11. Incident light enters the waveguide substrate 10 and passes sequentially through the insertion grating 11 and the exit grating 12. The high-reflectivity mirror layer 20 then changes the propagation direction of residual light rays that are about to enter the sidewall of the waveguide substrate 10, so that the incident angle of the residual light rays returning to the exit grating 12 is outside the effective exit angle range of the exit grating 12.

[0048] Therefore, the technical solution provided in this embodiment provides a highly reflective mirror layer 20 in the waveguide substrate 10, positioned on the side of the coupling grating 12 away from the coupling in grating 11. This ensures that residual light rays that are about to enter the sidewall of the waveguide substrate 10 will have their propagation direction altered by the highly reflective mirror layer 20, so that the incident angle of these residual rays returning to the coupling grating 12 is outside the effective coupling angle range of the coupling grating 12. Thus, even if these residual rays return to the coupling grating 12, they will not be coupled to the eyepiece because their incident angle is outside the effective coupling angle range of the coupling grating 12. This effectively suppresses stray light from the edge of the optical waveguide, improving the user's visual experience.

[0049] Based on the first embodiment described above, a second embodiment of the optical waveguide of this application is proposed. In the second embodiment, in order to ensure that all residual light rays can have their propagation direction changed after passing through the high-reflectivity mirror layer 20, so that the incident angle when they return is outside the effective coupling angle range of the coupling grating 12, the propagation direction of the residual light rays that are pre-entering the sidewall of the waveguide substrate 10 can be set to a preset angle φ. The value of the preset angle φ is in the range of 30 degrees to 60 degrees.

[0050] Alternatively, the placement azimuth angle of the high-reflectivity mirror layer 20 on the waveguide substrate 10 can be set to a range of 30 degrees to 60 degrees, where the placement azimuth angle is the angle between the high-reflectivity mirror layer 20 and the target axis direction. The target axis direction refers to the direction that is parallel to the base plane of the waveguide substrate 10 and perpendicular to the line connecting the center of the coupling grating 11 to the center of the coupling grating 12.

[0051] It is understandable that both of the above implementation methods essentially ensure that the high-reflectivity mirror layer 20 can produce a sufficiently large directional change in the residual light by limiting its tilt state. Specifically, the preset angle φ directly defines the geometric relationship between the mirror and the direction of light propagation, while the placement azimuth angle defines the orientation of the mirror in the waveguide substrate coordinate system. According to the principles of geometric optics, when the preset angle φ or the placement azimuth angle is set between 30 and 60 degrees, the incident angle of the residual light incident on the high-reflectivity mirror layer 20 (the angle between the light and the mirror normal) will be correspondingly limited to the required target angle range. According to the law of reflection, after reflection, the propagation direction of the light will undergo a significant deflection within a certain angle range. This angle change is sufficient to ensure that regardless of the initial guiding mode angle of the residual light, its new guiding mode angle after reflection can deterministically deviate from the effective coupling angle range of the coupling grating 12, thus preventing it from being coupled back to the eyepiece to form stray light.

[0052] Based on the first and / or second embodiments described above, a third embodiment of the optical waveguide of this application is proposed. In the third embodiment, the waveguide substrate 10 has a thickened portion on the side where the high-reflectivity mirror layer 20 is provided.

[0053] After the high-reflectivity mirror layer 20 changes the propagation direction of the residual light, there are two possibilities: one is that the residual light can oscillate up and down in the waveguide substrate 10 after being reflected by the high-reflectivity mirror layer 20; the other is that the residual light can directly escape from the waveguide after being reflected by the high-reflectivity mirror layer 20.

[0054] Understandably, the critical angle for total internal reflection changes when the waveguide is locally thickened. As a result, light reflected back from the highly reflective mirror layer 20 is more likely to enter the waveguide interface at an angle smaller than the critical angle in the thicker waveguide region. This allows it to escape the waveguide more effectively and be captured by any potential absorption layer, rather than being further guided, thus improving the robustness of stray light suppression.

[0055] Alternatively, the waveguide substrate 10 can be configured to have a gradually varying thickness in the region near the high-reflectivity mirror layer 20, forming a smoothly transitioning wedge-shaped region rather than an abrupt, stepped thickening. This gradually increasing wedge design allows the waveguide thickness to gradually and uniformly increase from the main region (i.e., the waveguide substrate 10 region where the coupling grating 11 and the coupling grating 12 are located) to the ends, thereby avoiding light pattern disturbances caused by abrupt thickness changes.

[0056] The design parameters for the wedge-shaped region can include the wedge angle length and the maximum thickness difference. The wedge angle length refers to the distance from the point where the thickness begins to change to the end, and can typically be designed as the diameter of several guided mode spots within the waveguide. The maximum thickness difference can be determined based on the required range of critical angle variation. The advantage of this gradually changing thickness structure is that, during the propagation of residual light within the wedge-shaped region, the total internal reflection condition gradually changes, allowing the light to transition to the escape state more smoothly. This reduces scattering and mode coupling caused by abrupt interface changes, thereby further reducing the risk of generating new stray light.

[0057] Based on the first, second, and / or third embodiments described above, a fourth embodiment of the optical waveguide of this application is proposed. In the fourth embodiment, the optical waveguide may further include: An angle selector is located in the reflected light path of the high-reflectivity mirror layer 20. The angle selector is used to absorb light rays reflected by the high-reflectivity mirror layer 20 whose incident angle is within the effective coupling angle range, and to transmit light rays whose incident angle is outside the effective coupling angle range.

[0058] It should be noted that the angle selector can be a multilayer dielectric film filter, a volume holographic grating, or other optical elements that have a high selectivity for the incident angle of light. This embodiment does not specifically limit this.

[0059] When designing the angle selector, in order to enable it to "absorb light reflected from the high-reflectivity mirror layer 20 whose incident angle is within the effective coupling angle range and transmit light whose incident angle is outside the effective coupling angle range", when it is a multilayer dielectric film filter, two materials that are transparent in the set wavelength band and have a large difference in refractive index can be selected first, such as high-refractive-index titanium dioxide and low-refractive-index silicon dioxide. Then, optical thin film design software can be used to design the filter with the effective coupling angle range of the coupling grating 12 as the central design condition. Specifically, for light whose incident angle is within the effective coupling angle range, the reflectivity is designed to be higher than the first preset threshold (e.g., 95%), and for light whose incident angle is outside the effective coupling angle range, the transmittance is designed to be higher than the second preset threshold (e.g., 90%). When the angle selector is a volume holographic grating, the photosensitive recording medium, such as dichromate gelatin or photopolymer, can be selected first. Then, based on the Bragg condition, the center value or a specific value of the effective coupling angle range of the coupling grating 12 is set as the Bragg angle. The grating period is calculated by combining the system operating wavelength and the average refractive index of the photosensitive recording medium. Next, a dual-beam interference exposure optical path is built. By precisely adjusting the angle between the two coherent beams, they are made to interfere at the photosensitive recording medium and produce fringes that conform to the design period. After that, the substrate coated with the photosensitive recording medium is exposed to form a volume phase grating inside the photosensitive recording medium. The necessary post-processing, such as development, fixing, and curing, is performed according to the characteristics of the medium to finally obtain the required angle selector.

[0060] In this embodiment, an angle selector is set in the reflected light path of the high-reflectivity mirror layer 20. The selector can absorb light reflected by the high-reflectivity mirror layer 20 whose incident angle is within the effective coupling angle range and transmit light whose incident angle is outside the effective coupling angle range. As a result, stray light at the edge of the optical waveguide can be suppressed more effectively, thereby further improving the user's visual experience.

[0061] Based on the first, second, third, and / or fourth embodiments described above, a fifth embodiment of the optical waveguide of this application is proposed. In this fifth embodiment, please refer to... Figure 3 The waveguide substrate 10 may also be provided with a bend grating 13: The incident light enters the waveguide substrate 10 and passes through the coupling grating 11, the turning grating 13 and the coupling grating 12 in sequence. After passing through the high-reflectivity mirror layer 20, the propagation direction of the residual light that was about to enter the sidewall of the waveguide substrate 10 is changed, so that the incident angle of the residual light when it returns to the coupling grating 12 is outside the effective coupling angle range of the coupling grating 12.

[0062] It should be noted that the deflection grating 13 is typically positioned between the input grating 11 and the output grating 12. Its main function is to deflect the light path within the waveguide plane, achieving two-dimensional pupil expansion. The period and orientation of the deflection grating 13 are specially designed to control the direction of light propagation. In practical applications, the deflection grating 13 can be fabricated using the same process as the input grating 11 / output grating 12, but its diffraction efficiency distribution needs to be optimized separately to ensure uniform light energy distribution.

[0063] Understandably, when the waveguide substrate 10 is also equipped with a deflection grating 13, after the incident light enters the waveguide substrate 10 and passes sequentially through the coupling grating 11, the deflection grating 13, and the coupling grating 12, the residual light rays that pre-entered the sidewall of the waveguide substrate 10 and exited from the coupling grating 12 will also pass through the high-reflectivity mirror layer 20 and have their propagation direction changed. This ensures that the incident angle of these residual rays returning to the coupling grating 12 is outside the effective coupling angle range of the coupling grating 12. Therefore, even if these residual rays return to the coupling grating 12, they will not be coupled to the eyepiece by the coupling grating 12 because the incident angle is outside the effective coupling angle range of the coupling grating 12. This effectively suppresses stray light at the edge of the optical waveguide, thereby improving the user's visual experience.

[0064] For example, the optical waveguide provided in this embodiment, when propagating light, can be referred to as an optical coupler vector diagram. Figure 5 , specifically: The vector sum of the coupling grating vector k1, the turning grating vector k2, and the coupling out grating vector k3 in the waveguide substrate 10 is zero. When the coupling out grating vector k3 is modulated to an upward direction or a downward direction, the vector sum of the coupling out grating vector k3 and the reflected grating vector k4 is zero. Therefore, after the residual light changes its propagation direction through the high-reflectivity mirror layer 20, it can oscillate up and down within the waveguide substrate 10 to form fields of view such as FOV1 and FOV2. The specific oscillation effect can be referred to... Figure 4 .

[0065] It should be noted that this example is only for the purpose of assisting in understanding this application and does not constitute a limitation on the optical waveguide of this application. Other technical solutions based on this concept are all within the protection scope of this application.

[0066] Based on the first, second, third, and / or fourth embodiments described above, a fifth embodiment of the optical waveguide of this application is proposed. In the fifth embodiment, the optical waveguide may further include: An absorption layer is disposed on the side of the high-reflectivity mirror layer 20 away from the coupling grating 12. The absorption layer is used to absorb light transmitted from the high-reflectivity mirror layer 20.

[0067] It should be noted that the absorption layer can be a light-absorbing ink coating layer, a metal thin film absorption layer, etc., and this embodiment does not specifically limit it. The light-absorbing ink coating layer is typically formed by dispersing carbon black particles in an organic solvent, and the coating thickness can range from 10 micrometers to 100 micrometers. The metal thin film absorption layer can be prepared by sputtering light-absorbing metals such as nickel and chromium, and the thickness can range from 0.1 micrometers to 1 micrometer. In practical applications, the absorbance of the absorption layer should be greater than 95% to ensure sufficient absorption effect.

[0068] In this embodiment, an absorption layer is provided on the side of the high-reflectivity mirror layer 20 away from the coupling grating 12 to absorb the light transmitted from the high-reflectivity mirror layer 20, thereby effectively preventing the transmitted light from continuing to propagate in the optical waveguide, so as to more effectively suppress stray light at the edge of the optical waveguide and further enhance the user's visual experience.

[0069] Based on the first, second, third, fourth, fifth, and / or sixth embodiments described above, a seventh embodiment of the optical waveguide of this application is proposed. In the seventh embodiment, the highly reflective mirror layer 20 can be composed of an electrowetting material, a magnetorheological material, or other smart materials that respond to external fields. Therefore, by changing the voltage, magnetic field, or other physical fields applied to the material, the curvature, tilt angle, and even reflectivity of the highly reflective mirror layer 20 can be continuously adjusted.

[0070] In this embodiment, the highly reflective mirror layer 20 can be composed of electrowetting materials, magnetorheological materials, or other smart materials that respond to external fields, giving it dynamically adjustable characteristics. This allows the optical waveguide to adapt to different application scenarios. For example, when displaying high-brightness content, the reflectivity of the highly reflective mirror layer 20 can be increased to enhance stray light suppression; in augmented reality scenarios requiring higher light transmittance, the reflectivity of the highly reflective mirror layer 20 can be appropriately reduced to improve the visibility of the real world. Furthermore, the parameters of the highly reflective mirror layer 20 can be automatically adjusted based on the detected stray light intensity.

[0071] Based on the first, second, third, fourth, fifth, sixth and / or seventh embodiments described above, an eighth embodiment of the optical waveguide of this application is proposed. In the eighth embodiment, considering that the high-reflectivity mirror layer 20 will also absorb some light energy when reflecting residual light, a heat dissipation layer can be provided on the side of the high-reflectivity mirror layer 20 away from the coupling grating 12.

[0072] It should be noted that the heat dissipation layer can be a graphene layer, metal foil, or other highly thermally conductive materials, and this embodiment does not specifically limit it.

[0073] In this embodiment, by providing a heat dissipation layer on the side of the high-reflectivity mirror layer 20 that is away from the coupling grating 12, thermal deformation or thermal stress caused by local heating of the optical waveguide can be effectively prevented, thereby ensuring the stability of the optical waveguide imaging quality and its service life.

[0074] Based on the first, second, third, fourth, fifth, sixth, seventh, and / or eighth embodiments described above, a ninth embodiment of the optical waveguide of this application is proposed. In the ninth embodiment, the optical waveguide further includes: Dissipation section, the dissipation section being formed at the sidewall of the waveguide substrate into which the residual light is to be entered; When the residual light enters the dissipation section, it undergoes multiple reflections within the dissipation section and is gradually absorbed by the dissipation section or leaks out of the dissipation section to the outside.

[0075] In this embodiment, at the sidewall of the waveguide substrate where the residual light is pre-entered, the dissipation part seals the upper and lower end faces of the optical waveguide.

[0076] In this embodiment, a dissipation section is formed on the edge side of the main body of the optical waveguide structure, that is, the dissipation section is formed at the sidewall of the waveguide substrate into which the residual light is to be entered. The dissipation section seals the upper and lower end surfaces of the optical waveguide. When the residual light enters the dissipation section, the residual light is reflected multiple times within the dissipation section and is gradually absorbed by the dissipation section or leaks from the dissipation section to the outside. During the reflection process, it is weakened and absorbed multiple times, so that the residual light can be completely or almost completely dissipated in the dissipation section. This avoids stray light from returning to the coupling grating modulation and entering the eye box, and prevents uncontrollable and significant impacts on the display performance such as color and field uniformity of the displayed image (e.g., avoiding the generation of bright spots).

[0077] In some embodiments, the geometry of the dissipation section is as follows: wedge structure; or, Arc-shaped structure; or, Serrated structure; or, An irregular multi-faceted structure consisting of multiple different facets connected sequentially; or, A free-form surface structure consisting of multiple different curved surfaces connected in sequence.

[0078] In one example, please refer to the appendix. Figure 6 The dissipation section has a wedge-shaped geometry. When residual light enters the wedge-shaped dissipation section, it undergoes multiple reflections within the structure. Some residual light is gradually absorbed by the dissipation section, while some leaks out to the outside (the residual light leaking out is the...). Figure 6The stray light (as shown in the diagram) is gradually weakened and absorbed during reflection, so that all or almost all of the residual light can be dissipated within the wedge structure, thereby preventing stray light from returning to the coupling grating and modulating back into the eye box, thus making the imaging quality of the exit pupil area more stable.

[0079] Furthermore, in another example, please refer to the appendix. Figure 7 The dissipation section has a sawtooth-shaped geometry. Similarly, when residual light enters the sawtooth-shaped dissipation section, it undergoes multiple reflections within the structure. Some residual light is gradually absorbed by the dissipation section, while some leaks out to the outside (the residual light leaking out is the...). Figure 7 The stray light (as shown in the diagram) is gradually weakened and absorbed during reflection, so that all or almost all of the residual light can be dissipated within the sawtooth structure, thereby preventing stray light from returning to the coupling grating and modulating into the eye box, thus making the imaging quality of the exit pupil area more stable.

[0080] In yet another example, please refer to the appendix. Figure 8 The dissipative section has an irregular multi-faceted structure consisting of multiple different facets connected sequentially. Similarly, when residual light enters the dissipative section belonging to this irregular multi-faceted structure, the residual light undergoes multiple reflections within the structure. Some of the residual light is gradually absorbed by the dissipative section, while some gradually leaks out to the outside (the residual light leaking out to the outside is the...). Figure 8 The stray light (as shown in the diagram) is gradually weakened and absorbed during reflection, so that all or almost all of the residual light can be dissipated within the irregular multi-faceted structure, thereby preventing stray light from returning to the coupling grating and modulating back into the eye box, thus making the imaging quality of the exit pupil area more stable.

[0081] In another example, please refer to the appendix. Figure 9 The dissipation section has an arc-shaped geometry. Similarly, when residual light enters the arc-shaped dissipation section, it undergoes multiple reflections within the section and is gradually absorbed or leaks to the outside (the residual light leaking to the outside is the...). Figure 9 The stray light (as shown in the diagram) is weakened and absorbed multiple times during reflection, so that all or almost all of the residual light can be dissipated in the dissipation section, thereby preventing the stray light from returning to the coupling grating modulation and entering the eye box, thus making the imaging quality of the exit pupil area more stable.

[0082] Of course, the geometry of the dissipation section can also be a freeform surface structure (not shown) consisting of multiple different curved surfaces connected in sequence. Similarly, when residual light enters the dissipation section belonging to this freeform surface structure, the residual light is reflected multiple times within the dissipation section and is gradually absorbed by the dissipation section or leaks from the dissipation section to the outside. During the reflection process, it is weakened and absorbed multiple times, so that the residual light can be completely or almost completely dissipated within the dissipation section, thereby preventing stray light from returning to the coupling grating modulation and entering the eye box, thus making the imaging quality of the exit pupil area more stable.

[0083] For example, the dissipation section is made of waveguide material. Further, the surface of the dissipation section (i.e., the surface of the waveguide material) can be roughened or roughened, or the surface of the dissipation section can be a micro-nano metasurface. This allows the surface of the dissipation section to scatter or diffuse the residual light when it reaches the surface of the dissipation section. During multiple reflections, the stray light is weakened and homogenized, becoming more dispersed in all directions. Its energy distribution is more discrete, resulting in a reduction in the intensity of the residual light. This facilitates better attenuation and absorption of stray light by the dissipation section, further improving the imaging quality of the exit pupil region.

[0084] Furthermore, in one embodiment, a light-absorbing film layer can be deposited on the surface of the dissipation section, ink can be applied (i.e., matte varnish ink), and a certain anti-reflection material can be attached, thereby further reducing the returned stray light, so that the stray light returning to the eye box is reduced or completely eliminated, and the imaging quality of the exit pupil area is further improved.

[0085] In this embodiment, a dissipation section can be formed on the sidewall of the waveguide substrate near the re-turning grating side, so that any residual light incident on the dissipation section can be "blocked" within the dissipation section, thereby effectively enhancing the robustness and reliability of the entire stray light suppression scheme, so as to more effectively suppress stray light at the edge of the optical waveguide, and further improve the user's visual experience.

[0086] In addition, this application embodiment also provides a head-mounted display device, which may include a device body and an optical waveguide as described in the above embodiment, the optical waveguide being disposed on the device body.

[0087] It should be noted that head-mounted display devices may include, but are not limited to, head-mounted display devices such as Mixed Reality (MR) devices (e.g., MR glasses or MR helmets), Augmented Reality (AR) devices (e.g., AR glasses or AR helmets), Virtual Reality (VR) devices (e.g., VR glasses or VR helmets), Extended Reality (XR) devices, or some combination thereof.

[0088] It is understood that since the above-mentioned optical waveguide is used in the head-mounted display device, the embodiments of the head-mounted display device include all the technical solutions of all the above-mentioned optical waveguide embodiments, and the technical effects achieved are exactly the same, so they will not be repeated here.

[0089] The above description is merely a preferred embodiment of this application and does not limit the patent scope of this application. Any equivalent structural transformations made based on the content of this application's specification and drawings under the concept of this application, or direct / indirect applications in other related technical fields, are included within the patent protection scope of this application.

Claims

1. An optical waveguide, characterized in that, include: A waveguide substrate, wherein the waveguide substrate is provided with an input grating and an output grating; A high-reflectivity mirror layer is disposed within the waveguide substrate, and the high-reflectivity mirror layer is located on the side of the output grating away from the input grating; The incident light enters the waveguide substrate and passes through the coupling grating and the coupling grating in sequence. Then, the propagation direction of the residual light that was about to enter the sidewall of the waveguide substrate is changed by the high-reflectivity mirror layer, so that the incident angle of the residual light when it returns to the coupling grating is outside the effective coupling angle range of the coupling grating.

2. The optical waveguide as described in claim 1, characterized in that, The high-reflectivity mirror layer forms a preset angle with the propagation direction of the residual light rays that are about to enter the sidewall of the waveguide substrate, and the preset angle ranges from 30 degrees to 60 degrees.

3. The optical waveguide as described in claim 2, characterized in that, The preset included angle is set according to the effective coupling angle range, the refractive index of the waveguide substrate, and the initial propagation angle of the residual light.

4. The optical waveguide as described in claim 1, characterized in that, The area where the highly reflective mirror layer is set completely covers the propagation range of residual light that is about to enter the sidewall of the waveguide substrate.

5. The optical waveguide as described in claim 1, characterized in that, The projected area of ​​the highly reflective mirror layer in the first direction is greater than or equal to the projected area of ​​the coupling grating in the first direction. The first direction refers to the direction that is consistent with or approximately the direction of the residual light rays that are about to enter the sidewall of the waveguide substrate.

6. The optical waveguide as described in claim 1, characterized in that, The waveguide substrate has a thickened portion on the side where the high-reflectivity mirror layer is located.

7. The optical waveguide as described in any one of claims 1 to 6, characterized in that, The optical waveguide also includes: An angle selector is disposed in the reflected light path of the high-reflectivity mirror layer. The angle selector is used to absorb light rays reflected by the high-reflectivity mirror layer whose incident angle is within the effective coupling angle range, and to transmit light rays whose incident angle is outside the effective coupling angle range.

8. The optical waveguide as described in any one of claims 1 to 6, characterized in that, The waveguide substrate is also provided with a bending grating: The incident light enters the waveguide substrate and passes sequentially through the coupling grating, the turning grating, and the coupling grating. The propagation direction of the residual light that was about to enter the sidewall of the waveguide substrate is changed by the high-reflectivity mirror layer, so that the incident angle of the residual light returning to the coupling grating is outside the effective coupling angle range of the coupling grating.

9. The optical waveguide as described in any one of claims 1 to 6, characterized in that, The optical waveguide also includes: An absorption layer is disposed on the side of the high-reflectivity mirror layer opposite to the coupling grating, and the absorption layer is used to absorb light transmitted from the high-reflectivity mirror layer.

10. The optical waveguide as described in any one of claims 1 to 6, characterized in that, The optical waveguide also includes: Dissipation section, the dissipation section being formed at the sidewall of the waveguide substrate into which the residual light is to be entered; When the residual light enters the dissipation section, it undergoes multiple reflections within the dissipation section and is gradually absorbed by the dissipation section or leaks out of the dissipation section to the outside.

11. The optical waveguide as described in claim 10, characterized in that, The geometry of the dissipation unit is as follows: wedge structure; or, Arc-shaped structure; or, Serrated structure; or, An irregular multi-faceted structure consisting of multiple different facets connected sequentially; or, A free-form surface structure consisting of multiple different surfaces connected in sequence.

12. A head-mounted display device, characterized in that, The head-mounted display device includes a device body and an optical waveguide as described in any one of claims 1 to 11, wherein the optical waveguide is disposed on the device body.

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