Diffractive optical waveguide, multilayer diffractive optical waveguide and electronic device

Abstract

The application provides a diffractive optical waveguide, a multilayer diffractive optical waveguide and an electronic device to solve the problem of stray light control without increasing the cost by introducing additional devices or by shielding and the like on the premise of ensuring that the user can receive a complete image (FOV). The scheme can realize that the incident light enters the coupling-in area at an angle deviating from the surface normal of the coupling-in area; the incident light is deflected at least once inside the diffractive optical waveguide and then propagates to the coupling-out area through the turning area, and is coupled out from the coupling-out area; after entering the coupling-in area, a part of the light in the field of view (FOV) of at least one wavelength of the light propagates to the lower right of the vertical direction of the diffractive optical waveguide to deviate from the turning area; after being deflected in the turning area, the minimum angle of the light in the FOV outside the circular ring in the K vector space when the light of at least one wavelength leaves the diffractive optical waveguide is greater than 60°.

Description

Technical Field

[0001] This application belongs to the field of optical technology, and more specifically, relates to a diffractive waveguide, a multilayer diffractive waveguide, and an electronic device. Background Technology

[0002] The field of view (FOV) of a single-layer diffraction waveguide (DWG) is limited by the refractive index of the material. To increase the FOV, multiple DWG layers can be stacked. This involves allowing different DWG layers to propagate different FOVs, and the combined FOVs of each layer create a larger image. The maximum FOV that a multi-layer DWG can accommodate is directly proportional to the number of DWG layers. A double-layer DWG made of glass with a refractive index of 1.9 can easily accommodate a 60° FOV. Figure 1 As shown.

[0003] A significant drawback of multilayer DWG is that short-wavelength light will form stray light outside the normal image light angle in large-period DWG layers. This is because short-wavelength light, after being diffracted by large-period SRG, cannot be completely confined within the DWG for total internal reflection. A portion of the FOV (Field of View) light will be reflected or transmitted away from the DWG at large angles and observed by the user. The larger the FOV propagating in a multilayer DWG, the more severe the stray light phenomenon may be.

[0004] Solutions to stray light problems typically involve introducing additional optical components, such as angle- and wavelength-selective absorption films. The presence of these components increases the cost of AR glasses and can also negatively impact the propagation of normal image light, reducing image quality and brightness.

[0005] Therefore, how to suppress stray light from large field-of-view waveguides from entering the user's eyes is a technical problem that urgently needs to be solved. Utility Model Content

[0006] The purpose of this application is to provide a diffractive waveguide, a multilayer diffractive waveguide, and an electronic device to achieve stray light control without introducing additional devices or increasing costs through methods such as occlusion, while ensuring that the user can receive a complete image (FOV).

[0007] To achieve the above objectives, the technical solution adopted in this application is as follows:

[0008] In a first aspect, embodiments of this application provide a diffractive waveguide, which includes a coupling region, a turning region, and a coupling out region. The coupling region is used to receive incident light rays projected by an optomechanical system and to couple the incident light rays into the diffractive waveguide. The incident light rays enter the coupling region at an angle deviating from the surface normal of the coupling region. The incident light rays include light rays of multiple wavelengths.

[0009] The incident light beam is deflected at least once inside the diffractive waveguide, propagates through the turning region to the coupling region, and is coupled out from the coupling region.

[0010] After entering the coupling region, a portion of the light rays of at least one of the multiple wavelengths propagate downward and to the right in the vertical direction of the diffractive waveguide, thus deviating from the turning region.

[0011] After being deflected in the turning region, the minimum angle at which the light of at least one wavelength leaves the diffracting waveguide in the FOV outside the ring in the K-vector space is greater than 60°.

[0012] Because the incident light projected by the optomechanical system into the diffractive waveguide is not incident in a normal manner, that is, the optomechanical system projects the incident light into the diffractive waveguide in a direction deviating from the normal incident angle, or the incident light is incident on the surface of the diffractive waveguide at a certain angle, this can reduce the volume of the entire optical module, and also achieve a larger field of view of the incident light, simplifying the optical path. Since at least one wavelength of the light enters the coupling region, a portion of the light within the field of view (FOV) propagates to the lower right of the vertical direction of the diffractive waveguide to deviate from the turning region. This can prevent this portion of light from becoming stray light and entering the turning region. Since the turning region is for the light to turn and propagate from the coupling region to the coupling region, thereby realizing image transmission, the image quality can be improved by avoiding stray light entering the turning region. Furthermore, after the turning point, the minimum angle at which the light ray (i.e., stray light) leaves the diffractive waveguide in the FOV outside the ring in the K vector space is greater than 60°, which can prevent stray light from entering the human eye.

[0013] In one possible embodiment of this application, the angle between the incident light ray and the surface normal of the diffractive waveguide is 0 to 20°.

[0014] In one possible embodiment of this application, the optical axis of the optomechanism is deflected vertically upward or downward relative to the diffraction waveguide plane, or horizontally to the left or right, or in any combination of two of the above four directions. This allows for more flexible setting of the positional relationship between the optomechanism and the diffraction waveguide, adapting to different installation spaces, and also optimizing optical path efficiency.

[0015] In one possible embodiment of this application, after the light of at least one of the plurality of wavelengths enters the coupling region, a portion of the light within the field of view (FOV) has its propagation direction located in the right-hand region of the vertical direction in the K-vector space, thus deviating from the turning region. This avoids stray light formed by a portion of the light within the field of view of at least one wavelength from entering the turning region and affecting image quality.

[0016] In one possible embodiment of this application, a portion of the FOV of at least one wavelength of light is located in the left region of the vertical direction in the K vector space, where the area is larger than the right region, to ensure that the display uniformity of other wavelengths of light is not affected.

[0017] In one possible embodiment of this application, a portion of the FOV of at least one wavelength of the light is located in the K vector space where the ratio of the area of ​​the left and right regions in the vertical direction is between 1:0 and 1:1.

[0018] In one possible embodiment of this application, the light of at least one wavelength includes blue light;

[0019] After the FOV of the blue light is coupled in, the ratio of the area of ​​the left and right regions in the vertical direction of the K vector space is approximately 1:0.26, so as to ensure that the display uniformity of the red and green wavelengths of light is not affected.

[0020] In one possible embodiment of this application, the grating period of the diffractive waveguide is between 300 nm and 450 nm.

[0021] In one possible embodiment of this application, the vertical distance between the center of the coupling region and the upper boundary of the transition region is at least greater than the diameter of the coupling region. By limiting the vertical distance between the center of the coupling region and the upper boundary of the transition region in the diffractive waveguide, at least most of the light rays propagating downwards and to the right of the diffractive waveguide after coupling can deviate from the transition region. Light rays that do not enter the transition region will be incident on the waveguide sidewall and absorbed by the sidewall absorption layer, and will no longer interact with other grating regions.

[0022] In one possible embodiment of this application, the vertical distance between the center of the coupling region and the upper boundary of the transition region is between 1 mm and 8 mm.

[0023] In one possible embodiment of this application, the transition region includes a first boundary (e.g., the right boundary) and a second boundary (e.g., the left boundary), the second boundary being close to the right boundary of the coupling region;

[0024] The first boundary coincides with or is located to the left of the vertical direction. By setting the turning area to the left of the vertical direction of the optical waveguide, the turning area can be avoided from being directly located at the center of the line of sight, reducing optical path interference and making the coupled light rays cover the human eye's field of vision more evenly.

[0025] In one possible embodiment of this application, the first boundary is located to the left of the vertical direction, and there is an angle between the first boundary and the vertical direction.

[0026] In one possible embodiment of this application, the distance between the first boundary of the turning region and the left boundary of the coupling region is L, where L is less than or equal to 60 mm.

[0027] In one possible embodiment of this application, the distance between the first boundary of the turning region and the left boundary of the coupling region is between 35 and 50 mm.

[0028] Secondly, the embodiments of this application provide a multilayer diffractive waveguide, which is formed by stacking multiple stacked diffractive waveguides. At least one first diffractive waveguide is present among the multiple stacked diffractive waveguides, and the first diffractive waveguide adopts the diffractive waveguide as described in the first aspect.

[0029] The diffractive waveguides in the multiple stacked structures correspond to different wavelength ranges or field-of-view ranges.

[0030] In one possible embodiment of this application, the plurality of stacked diffractive waveguides further include a second diffractive waveguide, wherein the grating periods of the first diffractive waveguide and the second diffractive waveguide are different;

[0031] The grating period of the second diffractive waveguide is between 200nm and 350nm.

[0032] Thirdly, embodiments of this application provide an electronic device, including an optomechanical system, and further including a multilayer diffractive waveguide as described in the second aspect above or any possible implementation thereof, wherein the light-emitting portion of the optomechanical system faces the coupling region of the multilayer diffractive waveguide. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of this application, 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 these drawings without creative effort.

[0034] Figure 1A schematic diagram of the FOV distribution of light rays in DWG with different periods;

[0035] Figure 2 A schematic diagram illustrating the stray light generated by the FOV of short-wavelength light (such as blue light) in a large-period DWG;

[0036] Figure 3 This is a schematic diagram of the grating vector design provided in an embodiment of this application;

[0037] Figure 4 A schematic diagram showing an optical mechanism, as provided in an embodiment of this application, projecting incident light rays into an optical waveguide at a non-normal incident angle;

[0038] Figure 5 This is a schematic diagram of the design structure of each grating region in the optical waveguide provided in the embodiments of this application;

[0039] Figure 6 A schematic diagram illustrating the relative positional relationships of each grating region in an optical waveguide provided in an embodiment of this application;

[0040] Figure 7 This is a schematic diagram of stray light control provided in an embodiment of this application;

[0041] Figure 8 A schematic diagram of the field of view (FOV) of the optomechanical projection onto the waveguide plane provided in an embodiment of this application;

[0042] Figure 9 This is a schematic diagram of the propagation direction of coupled light rays in the waveguide plane provided in an embodiment of this application;

[0043] Figure 10 This is a schematic diagram of the propagation of light rays that have not entered the turning region within the waveguide plane, provided as an embodiment of this application.

[0044] Figure 11 This is a schematic diagram of the FOV of blue light propagation in a long-period DWG layer.

[0045] Figure 12 and Figure 13 These are schematic diagrams showing the relative positions of the various grating regions in an optical waveguide. Detailed Implementation

[0046] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0047] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0048] It should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and 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.

[0049] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, "multiple sets" means two or more sets, "multiple pieces" means two or more pieces, and "multiple" means one or more, unless otherwise explicitly specified.

[0050] Smart glasses incorporating technologies such as augmented reality (AR), virtual reality (VR), and mixed reality (MR) have gained widespread popularity among consumers in recent years. AR glasses, in particular, can display virtual images using diffraction waveguide (DWG) technology. In both AR and VR display technologies, the diffraction waveguide (DWG) is a crucial optical element used to couple images from the display to the user's eyes, enabling thinner and lighter glasses.

[0051] Diffraction waveguides (DWGs) are a popular solution in current AR technology for implementing optical combiners. A waveguide is a device used to confine light within it for total internal reflection. Diffraction refers to the process by which incident light rays in a DWG, using a surface relief grating (SRG), diffract to enter (couple in) and exit (couple out) the waveguide. The area on the DWG containing the SRG is called the grating region. The grating region where light rays enter is usually called the coupling region, and the grating region where light rays exit is usually called the coupling out region. The coupling region is usually located at the location of the optomechanical system to input the AR image into the waveguide, while the coupling out region is usually located at the location of the human eye to allow the image in the waveguide to leave the waveguide and enter the human eye. Light rays propagate between the coupling region and the coupling out region via total internal reflection.

[0052] In a waveguide, light propagates via total internal reflection. The critical angle for total internal reflection is given by the formula: θ c =arcsin(1 / n). Where n represents the refractive index of the waveguide material, and θ... c The critical angle is indicated by the refractive index. A higher refractive index results in a larger critical angle, meaning the total internal reflection propagation angle that the waveguide can accommodate depends on the refractive index of the waveguide material. A higher refractive index allows for a wider range of light angles, meaning it can display larger image frames. The refractive index of the high-refractive-index glass used in manufacturing DWG (Digital View Glass) is typically between 1.7 and 2.0. Typical maximum field of view (FOV) values ​​allowed for propagation by different refractive index glasses are shown in Table 1. It can be seen that even a high-refractive-index glass of 2.0 only allows a field of view of approximately 40° (e.g., 37° as shown in Table 1) to propagate within the waveguide. On the other hand, the comfortable viewing angle for a single human eye is as high as 60°, meaning that the image frame of a DWG is insufficient to meet the most basic observation needs of the human eye. Further increasing the refractive index of the waveguide material would require moving away from existing glass material systems and using materials with higher refractive indices, such as titanium dioxide and silicon carbide, which would significantly increase the material cost of AR glasses. A more economical solution is to use multilayer diffractive waveguide (DWG) stacking to improve the field of view (FOV). This involves allowing different DWG layers to propagate different FOVs, and the FOVs of each layer are stacked to form a larger image. The maximum FOV that a multilayer DWG can accommodate is positively correlated with the number of DWG layers. For example, a double-layer DWG made of 1.9-refractive-index glass can easily accommodate a 60° FOV, effectively solving the problem of insufficient FOV in a single-layer DWG. Figure 1 As shown, compared to using high-cost ultra-high refractive index materials, the multilayer DWG solution can improve FOV without significantly increasing physical costs, making it more economical.

[0053] Table 1. Maximum FOV allowed for propagation of glass materials with different refractive indices.

[0054]

[0055] A significant characteristic of multilayer DWGs is that the SRGs in each layer have different periods, which is to provide a field of view (FOV) for transmitting different center wavelengths. Figure 1 For example, Figure 1 As shown in (A) and (B), the grating periods of the two DWG layers are 320nm and 430nm, respectively. Figure 1 The grating period of the DWG layer shown in (A) is 320 nm. The wavelength range of blue light is 450 nm–495 nm, and the wavelength range of green light is 495 nm–570 nm. Because their wavelengths are closer to the grating period of 320 nm in the DWG layer, their diffraction efficiency is higher. Figure 1 As can be seen from (A) in the diagram, blue and green light are almost entirely located within the annular zone defined by the two concentric circles, easily satisfying the condition for total internal reflection. Therefore, as shown in Figure (A), Figure 1 The DWG layer shown in (A) is mainly used for propagating blue and green light. The wavelength range of blue and green light is 450 nm to 550 nm. Figure 1 The DWG layer shown in (B) has a period of 430nm. Figure 1 As shown in Figure (B), almost all of the red and green light lies within the annular band defined by the two concentric circles in the figure. Therefore, this DWG layer is mainly used for propagating red and green light. Thus, multiple DWG layers can be used to couple light of different wavelengths separately. However, a significant drawback of multi-layer DWG is that short-wavelength FOVs in large-period DWG layers will form stray light outside the normal image light angle, such as... Figure 1 As shown in (B), some of the blue light rays are located outside the circular band. This is because short-wavelength light, after being diffracted by the large-period SRG, cannot be completely confined to total internal reflection within the DWG. A portion of the FOV light will be reflected or transmitted away from the DWG at a large angle and observed by the user. This process is as follows: Figure 2 As shown: Blue and red light are incident on the SRG1 of the diffractive waveguide at different angles. After entering the diffractive waveguide through SRG1, the blue and red light are reflected and propagated within the waveguide. The blue dashed lines represent stray light rays in the above process. The larger the field of view (FOV) in a multilayer DWG, the more severe the stray light phenomenon may be.

[0056] Solutions to stray light problems typically involve introducing additional optical components, such as angle- and wavelength-selective absorption films. The presence of these components increases the cost of AR glasses and can also negatively impact the propagation of normal image light, reducing image quality and brightness.

[0057] Based on this, this application provides a diffractive waveguide to achieve stray light control and prevent stray light from entering the human eye without increasing costs by introducing additional devices or by blocking, while ensuring that the user can receive a complete image (FOV).

[0058] like Figure 4 As shown, Figure 4 This is a schematic diagram of the structure of a diffractive optical waveguide 200 provided in an embodiment of this application. The diffractive optical waveguide 200 includes: a coupling-in region 201, a transition region 202, and a coupling-out region 203.

[0059] The coupling region 201 is used to receive incident light and to couple the incident light into the diffractive waveguide 200. The incident light enters the coupling region 201 at an angle deviating from the surface normal of the coupling region 201. The incident light includes light of multiple wavelengths. For example, the incident light includes light of a first wavelength, light of a second wavelength, and light of a third wavelength. The first wavelength is greater than the second wavelength, which is greater than the third wavelength. For example, the first wavelength is red light, the second wavelength is green light, and the third wavelength is blue light.

[0060] The incident light is deflected at least once inside the diffraction waveguide 200, then propagates through the turning region 202 to the coupling region 203, and is coupled out from the coupling region 203.

[0061] After entering the coupling region, a portion of the light rays of at least one of the multiple wavelengths propagate downwards and to the right in the vertical direction of the diffractive waveguide, thus deviating from the turning region. In this embodiment, at least one wavelength of light can refer to light of a specific wavelength, such as blue light or green light.

[0062] After being deflected in the turning region 202, light of at least one wavelength is located in the field of view (FOV) outside the ring in the K-vector space. If a portion of the FOV of the light is not located in the right-hand region of the vertical direction in the K-vector space before entering the turning region 202, then the minimum angle of the light when leaving the diffractive waveguide is greater than 60°.

[0063] Because the incident light projected by the optomechanical system into the diffractive waveguide is not incident in a normal manner, that is, the optomechanical system projects the incident light into the diffractive waveguide in a direction deviating from the normal incident angle, or the incident light is incident on the surface of the diffractive waveguide at a certain angle, this can reduce the volume of the entire optical module, and also achieve a larger field of view of the incident light, simplifying the optical path. Since at least one wavelength of the light enters the coupling region, a portion of the light within the field of view (FOV) propagates to the lower right of the vertical direction of the diffractive waveguide to deviate from the turning region. This can prevent this portion of light from becoming stray light and entering the turning region. Since the turning region is for the light to turn and propagate from the coupling region to the coupling region, thereby realizing image transmission, the image quality can be improved by avoiding stray light entering the turning region. Furthermore, after the turning point, the minimum angle at which the light ray (i.e., stray light) leaves the diffractive waveguide in the FOV outside the ring in the K vector space is greater than 60°, which can prevent stray light from entering the human eye.

[0064] It should be noted that the incident light can be diffracted in the coupling region 201 and the coupling region 203 to enter the waveguide substrate of the diffracting light waveguide and leave the waveguide substrate. The light entering the waveguide substrate can undergo total internal reflection within the waveguide substrate.

[0065] In some embodiments, the coupling-in region 201, the turning region 202, and the coupling-out region 203 may be disposed on the same side of the diffractive waveguide.

[0066] The coupling region 201 is equipped with a coupling grating, which is used to couple incident light rays into the diffractive waveguide 200. After entering the diffractive waveguide 200, the incident light rays undergo total internal reflection within the waveguide.

[0067] The transition region 202 is used to deflect the propagation angle of incident light rays into the diffraction waveguide 200, thereby changing the propagation direction of the incident light rays. The transition region 202 is equipped with a diffraction grating, such as a surface relief grating or a holographic grating.

[0068] The coupling region 203 is equipped with a coupling grating.

[0069] Along the direction of light propagation within the optical waveguide, the turning region 202 is located between the coupling-in region 201 and the coupling-out region 203, with the turning region 203 located on the side closer to the coupling-in region 201.

[0070] A transition region 202 is set on the side of the waveguide substrate between the coupling region 201 and the coupling region 203. The direction of light propagation is changed by the grating inside the transition region, which can adjust the direction of the optical path in the optical waveguide and increase the number of total internal reflections and the flexibility of the propagation path.

[0071] As an example, the coupling-in grating and coupling-out grating in the embodiments of this application have the same period.

[0072] In one possible embodiment of this application, the angle between the incident ray and the surface normal is 0 to 20°.

[0073] For example, the angle between the incident ray and the surface normal is greater than 0 and less than or equal to 20°, meaning that the incident ray does not enter the diffractive waveguide in a normal incidence manner. In other words, the incident ray enters the diffractive waveguide at a specified angle, which is 0 to 20°.

[0074] In one possible embodiment of this application, the optical axis of the optomechanism is deflected vertically upward or downward relative to the diffraction waveguide plane, or horizontally to the left or right, or to any combination of the above four directions.

[0075] For example, the optical axis of the optical engine is deflected upward in the vertical direction by 10° relative to the diffraction waveguide plane, or the optical axis of the optical engine is deflected downward in the vertical direction by 10° or 5° relative to the diffraction waveguide plane.

[0076] For example, the optical axis of the optical engine is deflected upwards by 10° in both the vertical and horizontal directions relative to the diffraction waveguide plane.

[0077] In one possible embodiment of this application, after the light of at least one of the plurality of wavelengths enters the coupling region, a portion of the light within the field of view (FOV) has its propagation direction located in the right-hand region of the vertical direction in the K-vector space, thus deviating from the turning region. This avoids stray light formed by a portion of the light within the field of view of at least one wavelength from entering the turning region and affecting image quality.

[0078] Specifically, such as Figure 3 As shown in (b) in the figure, Figure 3 As can be seen in the long-period DWG layer, due to the longer wavelength and smaller diffraction angle of red light, the K-vector of red light is more easily concentrated in the left effective region. That is, after red light is coupled in, its field of view is entirely located on the left side of the vertical direction of the K-vector space, and the red light is located in the annular zone shown. This indicates that all the red light rays can pass through the turning region of the diffraction waveguide and then be coupled out through the coupling region to enter the human eye. Blue light, on the other hand, has a shorter wavelength and a larger diffraction angle, and its K-vector distribution is relatively dispersed. Therefore, after blue light is coupled in, a portion of its field of view is located on the left side of the vertical direction of the K-vector space, allowing it to enter the turning region, while a portion of the blue light's FOV is located on the right side of the vertical direction of the K-vector space, unable to enter the turning region. Furthermore, the area of ​​the light rays in the left region is larger than that in the right region, indicating that most of the blue light's FOV can enter the turning region, while a small portion of the blue light's FOV will not. Figure 3 In (b), the FOV located to the right of the vertical direction in the K vector space after coupling propagation has a propagation angle along the lower right direction in the waveguide plane, as shown in the figure. Figure 5 The blue and green light are shown in the schematic diagram of the waveguide plane.

[0079] The K-vector is the wave vector of light propagating in the waveguide. Its direction and magnitude determine whether light can couple into or out of the diffractive waveguide.

[0080] The K vector on the left side of the vertical direction usually corresponds to the effective coupling region of the grating, such as the diffraction order that satisfies the Bragg condition, while the region on the right may have reduced diffraction efficiency or even fail to couple due to excessively large or small angles.

[0081] In one possible embodiment of this application, a portion of the FOV of at least one wavelength of the light ray is located in the K vector space where the area of ​​the left-hand region in the vertical direction is greater than the area of ​​the right-hand region.

[0082] In one possible embodiment of this application, a portion of the FOV of at least one wavelength of the light is located in the K vector space where the ratio of the area of ​​the left and right regions in the vertical direction is between 1:0 and 1:1.

[0083] In one possible embodiment of this application, the light of at least one wavelength includes blue light;

[0084] After the FOV of the blue light is coupled in, the ratio of the area of ​​the left and right regions in the vertical direction of the K vector space is approximately 1:0.26.

[0085] In one possible embodiment of this application, the diffractive waveguide in this embodiment can refer to a large-period DWG, where the grating period of the DWG is between 300nm and 450nm.

[0086] The grating period refers to the physical distance between adjacent grooves of a grating. A grating period of 300nm to 450nm in a DWG means that the periods of both the input and output gratings of the DWG are designed within this range.

[0087] In one possible embodiment of this application, such as Figure 6 As shown, the vertical distance d between the center of the coupling region 201 and the upper boundary of the transition region 202 in the vertical direction (i.e., the Y-axis) is at least greater than the diameter of the coupling region 201. This ensures that the incident light rays, after being coupled into the coupling region, propagate along the lower right side of the optical waveguide plane with a sufficiently long distance to deviate from the transition region.

[0088] By limiting the distance between the center of the coupling region and the upper boundary of the transition region in the vertical direction of the diffractive waveguide, light rays propagating downwards and to the right of the diffractive waveguide after coupling can completely deviate from the transition region, i.e., not enter the transition region at all. The light rays that do not enter the transition region will be incident on the waveguide sidewall and absorbed by the sidewall absorption layer, and will no longer interact with other grating regions.

[0089] As an example, in the embodiments of this application, such as Figure 6 As shown, taking the transition zone 202 as an example, which may include an upper boundary, a lower boundary, a left boundary, and a right boundary, the upper boundary can refer to the uppermost edge line in the vertical direction (i.e., the positive Y-axis direction) of the two-dimensional plane. The lower boundary can refer to the lowermost edge line in the vertical direction (i.e., the negative Y-axis direction) of the two-dimensional plane. The left boundary can refer to the leftmost edge line in the horizontal direction (i.e., the negative X-axis direction) of the two-dimensional plane. The right boundary can refer to the rightmost edge line in the horizontal direction (i.e., the positive X-axis direction) of the two-dimensional plane.

[0090] As an example, up, down, left, and right are coordinates relative to the cross-section of the diffracting waveguide. Typically, the wide side of the waveguide can be defined as the horizontal direction (X-axis), and the narrow side as the vertical direction (Y-axis).

[0091] In one possible embodiment of this application, such as Figure 6 As shown, the vertical distance d between the center of the coupling region 201 and the upper boundary of the transition region 202 is between 1 mm and 8 mm.

[0092] In one possible embodiment of this application, the transition region includes a first boundary (e.g., the right boundary) and a second boundary (e.g., the left boundary), the second boundary being close to the coupling region 203;

[0093] The first boundary coincides with or is located to the left of the vertical direction. Since the right boundary of the turning region coincides with or is located to the left of the vertical direction, it ensures that light rays propagating along the lower right of the optical waveguide plane after coupling will not enter the turning region.

[0094] In one possible embodiment of this application, the first boundary is located to the left of the vertical direction, and there is an angle between the first boundary and the vertical direction.

[0095] In one possible embodiment of this application, the distance between the first boundary of the transition region and the left boundary of the coupling region is L, where L is less than or equal to 60 mm.

[0096] In one possible embodiment of this application, the distance between the right boundary of the transition zone and the left boundary of the coupling zone is between 35 and 50 mm.

[0097] In one possible embodiment of this application, the distance between the human eye and the waveguide coupling region (Eyerelief) should be greater than 14 mm, typically 14 to 20 mm.

[0098] The following describes in detail how multilayer DWGs with the above characteristics avoid the formation of stray light or prevent stray light from entering the user's eyes after it has formed. Figure 7 The diagram illustrates the propagation process of various wavelengths in a long-period DWG. The refractive index of the DWG is n, k in and θ in These are the magnitude and direction of the grating vector coupled into the SRG on the DWG, k out and θ out These are the magnitude and direction of the grating vector coupled out of the DWG and the SRG, respectively. The magnitude and direction of the grating vector are determined by the closed triangle formed by the coupled-in and coupled-out vectors. The relationship between the grating vector magnitude k and the grating period P is as follows:

[0099] like Figure 7 As shown, when the optical engine is incident directly onto the plane of the DWG, the FOV of a certain wavelength of light emitted from the optical engine is represented by the projection angles (half-angles) in the horizontal and vertical directions as φ. x and φ y That is, the FOV of the light rays projected by the optical engine has an angular range of -φ in the horizontal direction. x ~φ x The vertical angle range is -φ y ~φ y When the optical engine deflects by Δφ in both the horizontal and vertical directions... x and Δφ y At that time, the FOV of the light rays transmitted by the optomechanism has angular ranges of (-φ) in the horizontal and vertical directions, respectively. x +Δφ x )~(φ x +Δφ x ) and (-φ y +Δφ y )~(φ y +Δφ y ).

[0100] In the field of view (FOV) projected by the optomechanical system, light with wavelength λ, after being diffracted by the aforementioned coupled grating, propagates within the diffracted waveguide plane. The maximum angle formed between the right side of the vertical direction of the waveguide plane and the vertical direction within the waveguide plane is θ. r It satisfies

[0101] When the result of the expression on the right side of the above equation is less than 0, it means that the light of that wavelength will propagate entirely in the lower left direction after being coupled into the waveguide. When the result of the expression on the right side of the above equation is greater than 0, it means that at least a portion of the field of view (FOV) of the light of that wavelength will propagate in the lower right direction after being coupled into the waveguide, and the angle between the propagation angle of this portion of the FOV and the vertical direction of the waveguide plane is between 0 and θ. r Within the range. θ r For example, it is around 10°, and generally does not exceed 20°.

[0102] by Figure 7 Taking (a) as an example, the FOV of the red light, after being coupled into the diffractive waveguide through the coupling region, is entirely located on the left side of the vertical direction in the K-vector space. This means that the red light will propagate entirely along the lower left direction after being coupled into the diffractive waveguide. A portion of the green light's FOV propagates along the lower left direction of the diffractive waveguide after coupling, while a portion of the green light's FOV is located on the right side of the vertical direction in the K-vector space. This portion of the green light's FOV, as shown... Figure 7 The rectangular region is shown in (b). This means that part of the FOV of the green light will propagate downwards and to the right after being coupled into the diffracting waveguide. The angle between the rightmost ray of this part of the FOV of the green light and the vertical direction when it propagates in the waveguide plane is θ. r The propagation within the waveguide plane corresponding to the above process is as follows: Figure 9 As shown. Within the waveguide plane, the entire FOV of the red light propagates downwards to the left. A portion of the FOV of the green light propagates downwards to the left within the diffraction waveguide, and another portion of the FOV propagates downwards to the right within the diffraction waveguide. The maximum angle between the rightmost ray of the downward-to-right green light and the vertical direction of the waveguide plane is θ. r .

[0103] Generally, the coupling region has a certain size. When the coupling region is circular with a radius r, the vertical distance d between the center of the coupling region and the upper boundary of the transition region should satisfy: dtanθ r ≥r; or, if the coupling zone can be slightly offset by Δx in the horizontal direction, then the vertical distance d from the center of the coupling zone to the upper boundary of the transition zone should satisfy:

[0104] dtanθ r ≥r-Δx

[0105] like Figure 10 As shown, taking the FOV of green light as an example again. When the above conditions are met, and the right boundary of the transition region is entirely located to the left of the vertical direction of the diffracting waveguide plane, the green light, after being coupled into the FOV, propagates along the lower right at all angles (0 to θ). rAt least a portion of the angle can completely deviate from the transition zone, i.e., it does not enter the transition zone at all. After coupling, the light rays that do not enter the transition zone will be incident on the waveguide sidewall and absorbed by the sidewall absorption layer, and will no longer interact with other grating areas.

[0106] In one possible embodiment of this application, the vertical distance d between the center of the coupling region and the upper boundary of the transition region is between 1 and 8 mm. This distance can be adjusted within this range based on the shape design of the lens and frame.

[0107] Since some of the FOVs in the aforementioned green light do not enter the transition region, the FOVs of the green light that do not enter the transition region will not continue to propagate to the next grating region, i.e., the coupling region, in the long-period DWG. The corresponding propagation process in the K-vector space is as follows: Figure 7 As shown in (B) in the diagram. After the green light's FOV is coupled in, a portion of the FOV does not enter the turning region. This portion of the FOV is exactly the FOV that would normally form stray light after passing through the grating. Therefore, the entire process of the green light's FOV propagating in this DWG will no longer form stray light.

[0108] refer to Figure 7 (c) and Figure 11 Because blue light has a shorter wavelength, a small portion of the blue light's field of view (FOV) can still enter the transition region of the long-period DWG layer and form stray light. This stray light forms in a short area immediately after the light couples into the transition region, concentrated at the top of the transition region, and exits in the direction of... Figure 11 To the left of the center, the range of the emission angle is θ. l ~90°. θ can be changed by adjusting the magnitude and direction of the K vector in the coupling region SRG. l The value of θ. For example, when the period of the coupling region SRG is 357nm and the vector direction forms a 176° angle with the positive x-axis (counterclockwise is positive), the minimum angle of stray light formed by the blue light FOV is approximately θ. l =64°. Therefore, under certain Eyeelief conditions, when the distance between the inflection zone and the coupling zone does not exceed a certain threshold, all stray light formed by the FOV of blue light will not enter the human eye. Let L be the distance between the right boundary of the inflection zone and the left boundary of the coupling zone, and when it satisfies:

[0109] L≤Eyerelief×tanθ l hour,

[0110] Stray light generated by the blue light field of view (FOV) will not enter the human eye. Although the human eye has a certain physical size, and the waveguide allows the eye to move within a certain range (Eyebox) during normal use, this range generally does not exceed the left boundary of the coupling region. Therefore, taking the aforementioned distance L as the threshold satisfies normal usage conditions. Typically, the value of Eyeelief is between 14 and 20 mm; the larger the Eyeelief, the less likely stray light is to enter the human eye. Assuming Eyeelief = 20 mm, θ... l =64°, then the distance L between the right boundary of the transition zone and the left boundary of the coupling zone needs to be less than 41mm. Preferably, L can be limited to between 35 and 50mm, depending on the shape design of the lens and frame and the minimum angle θ of the actual stray light. l The distance L between the transition zone and the coupling zone is adjusted within this range.

[0111] like Figure 12 As shown, Figure 12 Taking a circular coupling region with a diameter of 3 mm, a distance D between the center of the coupling region and the upper boundary of the transition region of 5.5 mm, and a distance 40.5 mm between the left boundary of the coupling region and the right boundary of the transition region as an example, the optimal optical deflection angle for this diffractive waveguide is a deflection of 10° in both the horizontal and vertical directions. Figures 8-10 The center is deflected by 10° in both the x-axis and y-axis directions. Figure 12 What is shown is the raster area setup for a long-period DWG layer; the setup for a short-period DWG layer can be the same as... Figure 12 They are the same. The period range of each grating region in the short-period DWG layer is between 200 and 350 nm, while the period range of each grating region in the long-period DWG layer is between 300 and 450 nm.

[0112] like Figure 13 As shown, Figure 13 Taking a circular coupling region with a diameter of 2mm, a distance D between the center of the coupling region and the upper boundary of the transition region of 4.2mm, and a distance 36.8mm between the left boundary of the coupling region and the right boundary of the transition region as an example, the optimal deflection angle for the optomechanics of this waveguide is a horizontal deflection of 5° to 15°. Figure 7 In sections 8 and 9, the grating regions are deflected 5° to 15° towards the x-axis. The morphology and relative positional relationships of each grating region are as follows: Figure 13 As shown. With Figure 12 The difference in the illustrated embodiments is that, Figure 13 The size of the coupling region shown in the embodiment is smaller than Figure 12 The dimensions of the coupling region shown allow for a shorter vertical distance d between the coupling region and the transition region. Furthermore, Figure 13In the illustrated embodiment, the right boundary of the transition zone is not along the vertical direction, but rather close to the vertical direction and entirely located to the left of the vertical direction. The angle formed between the right boundary of the transition zone and the vertical direction is 2.8°. Figure 13 What is shown is the raster area setup for a long-period DWG layer; the setup for a short-period DWG layer can be the same as... Figure 13 They are the same. The period range of each grating region in the short-period DWG layer is between 200 and 350 nm, while the period range of each grating region in the long-period DWG layer is between 300 and 450 nm.

[0113] This application embodiment also provides a multilayer diffractive waveguide, which is formed by stacking multiple diffractive waveguides in a stacked manner. At least one first diffractive waveguide is present among the multiple stacked diffractive waveguides. The first diffractive waveguide adopts the structure of the diffractive waveguide as described in the above embodiment. The diffractive waveguides in different layers of the multiple stacked diffractive waveguides correspond to different wavelength ranges or field of view ranges.

[0114] In one possible embodiment of this application, the multiple stacked diffractive waveguides further include a second diffractive waveguide, wherein the grating periods of the first diffractive waveguide and the second diffractive waveguide are different; wherein the grating period of the second diffractive waveguide is between 200nm and 350nm.

[0115] It is understandable that the first diffractive waveguide can refer to a large-period DWG, while the second diffractive waveguide can refer to a short-period diffractive waveguide.

[0116] The structure and layout of the second diffractive waveguide can refer to the structure of the first diffractive waveguide described above, and will not be repeated here. Since the short-period layer DWG theoretically does not generate stray light, the shape and relative positions of the grating regions such as the coupling-in region, transition region, and coupling-out region on the short-period layer DWG can be the same as or different from those of the long-period layer DWG. However, it is necessary to ensure that all FOV angles missing in the long-period layer DWG can propagate normally in the short-period layer DWG, thereby ensuring the integrity of the FOV for all wavelengths after the two DWG layers are superimposed.

[0117] This application also provides an electronic device, including an optomechanical system and a multilayer diffractive waveguide as described in any of the above embodiments, wherein the light-emitting part of the optomechanical system faces the coupling region 202 of the multilayer diffractive waveguide.

[0118] Optionally, the deflection direction of the optomechanic relative to the vertical direction of the diffractive waveguide can be upward or downward, or the deflection direction of the optomechanic relative to the horizontal direction of the diffractive waveguide can be left or right, or deflection in any combination of any two of the above four directions.

[0119] It should be noted that electronic devices can be AR glasses, virtual reality (VR) glasses, extended reality (XR) glasses, artificial intelligence (AI) glasses, or mixed reality (MR) glasses, etc.

[0120] It should be noted that the optical waveguides in AR / VR devices are used in near-eye display systems (such as Microsoft HoloLens and Magic Leap). The light image generated by the micro-projection chip is coupled into the optical waveguide and transmitted to the human eye through total internal reflection, realizing a thin, wide field of view virtual image overlay (replacing the traditional mirror solution).

[0121] Because the multilayer diffractive waveguide in any of the above embodiments can emit stray light formed after at least a portion of the incident light enters the multilayer diffractive waveguide at a large angle, all stray light will not enter the human eye. This solution does not require the introduction of other optical devices; stray light control can be achieved solely through the ingenious design of the grating vector and the shape of the grating region.

[0122] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A diffractive optical waveguide, characterized in that, The diffractive waveguide includes a coupling region, a turning region, and a coupling out region. The coupling region is used to receive incident light rays projected by an optomechanical system and to couple the incident light rays into the diffractive waveguide. The incident light rays enter the coupling region at an angle deviating from the surface normal of the coupling region. The incident light rays include light rays of multiple wavelengths. The incident light beam is deflected at least once inside the diffractive waveguide, propagates through the turning region to the coupling region, and is coupled out from the coupling region. After entering the coupling region, a portion of the light rays of at least one of the multiple wavelengths propagate downward and to the right in the vertical direction of the diffractive waveguide, thus deviating from the turning region. After being deflected in the turning region, the minimum angle at which the light of at least one wavelength leaves the diffracting waveguide in the FOV outside the ring in the K-vector space is greater than 60°.

2. The diffractive waveguide according to claim 1, characterized in that, The angle between the incident ray and the surface normal is 0 to 20°.

3. The diffractive waveguide according to claim 1, characterized in that, The optical axis of the optical engine is deflected vertically upward or downward relative to the plane of the diffractive waveguide, or horizontally to the left or right, or to any combination of any two of the above four directions.

4. The diffractive waveguide according to claim 1, characterized in that, After entering the coupling region, light rays of at least one wavelength among the plurality of wavelengths have a portion of the light rays within the field of view (FOV) whose propagation direction is located in the right-hand region of the vertical direction in the K-vector space, thus deviating from the turning region.

5. The diffractive waveguide according to claim 4, characterized in that, A portion of the FOV of at least one wavelength of the light ray lies in the area of ​​the left region in the vertical direction of the K vector space that is larger than the area of ​​the right region.

6. The diffractive waveguide according to claim 5, characterized in that, A portion of the FOV of the light of at least one wavelength lies in the K vector space where the ratio of the area of ​​the left and right regions in the vertical direction is between 1:0 and 1:

1.

7. The diffractive waveguide according to claim 5, characterized in that, The light of at least one wavelength includes blue light; After the FOV of the blue light is coupled in, the ratio of the area of ​​the left and right regions in the vertical direction of the K vector space is 1:0.

26.

8. The diffractive waveguide according to any one of claims 1 to 7, characterized in that, The grating period of the diffractive waveguide is between 300 nm and 450 nm.

9. The diffractive waveguide according to any one of claims 1 to 7, characterized in that, The vertical distance between the center of the coupling zone and the upper boundary of the turning zone is at least greater than the diameter of the coupling zone.

10. The diffractive waveguide according to claim 9, characterized in that, The vertical distance between the center of the coupling zone and the upper boundary of the transition zone is between 1 mm and 8 mm.

11. The diffractive waveguide according to any one of claims 1 to 7, characterized in that, The transition zone includes a first boundary and a second boundary, with the second boundary being close to the coupling zone; The first boundary coincides with the vertical direction or is located to the left of the vertical direction.

12. The diffractive waveguide according to claim 11, characterized in that, The first boundary is located to the left of the vertical direction, and there is an angle between the first boundary and the vertical direction.

13. The diffractive waveguide according to claim 12, characterized in that, The distance between the first boundary of the transition zone and the left boundary of the coupling zone is L, where L is less than or equal to 60 mm.

14. The diffractive waveguide according to claim 11, characterized in that, The distance between the first boundary of the transition zone and the left boundary of the coupling zone is between 35 and 50 mm.

15. A multilayer diffractive optical waveguide, characterized in that, The multilayer diffractive waveguide is formed by stacking multiple diffractive waveguides, and at least one first diffractive waveguide is present among the multiple stacked diffractive waveguides. The first diffractive waveguide is a diffractive waveguide as described in any one of claims 1 to 14. The diffractive waveguides in the multiple stacked structures correspond to different wavelength ranges or field-of-view ranges.

16. The multilayer diffractive waveguide according to claim 15, characterized in that, The plurality of stacked diffractive waveguides also include a second diffractive waveguide, wherein the grating periods of the first diffractive waveguide and the second diffractive waveguide are different; The grating period of the second diffractive waveguide is between 200nm and 350nm.

17. An electronic device comprising an optomechanic, characterized in that, It also includes a multilayer diffractive waveguide as described in any one of claims 15 or 16, wherein the light-emitting portion of the optomechanism faces the coupling region of the multilayer diffractive waveguide.

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