Diffractive optical waveguide

Abstract

The present application discloses a diffractive optical waveguide. The diffractive optical waveguide comprises: a waveguide substrate, a surface of the waveguide substrate being provided with a light ray coupling functional region, and the light ray coupling functional region at least comprising an in-coupling region and an out-coupling region; an auxiliary structure, provided in a region of the surface of the waveguide substrate other than the light ray coupling functional region, the auxiliary structure comprising multiple auxiliary units, and the auxiliary units being used to cancel interference of reflected light formed when ambient light is incident on the auxiliary structure. The technical solution provided in the present application can reduce undesirable surface reflection generated on the surface of a diffractive optical waveguide.

Description

A diffractive optical waveguide Technical Field

[0001] This application relates to the field of augmented reality, and more particularly to a diffractive optical waveguide. Background Technology

[0002] Augmented reality is a technology that blends the real world with virtual information. Augmented reality display systems typically include micro-projectors and optical displays. The micro-projectors provide virtual display content for the augmented reality display system, which is then projected onto the viewer's eyes through the optical displays. The optical displays are usually transparent optical components, so that users can also see the real world through the optical displays at the same time.

[0003] Diffractive waveguides are a common method for implementing optical displays. However, the waveguide substrate is usually smooth and flat, and when ambient light shines on the waveguide surface, it will be reflected. This surface reflection can cause unwanted interference to users of augmented reality devices and external viewers. Summary of the Invention

[0004] This application provides a diffractive waveguide and near-eye display device, which can set an auxiliary structure in other areas of the waveguide substrate surface except for the light coupling functional area, and the auxiliary structure is specially designed to make the interference of reflected light formed when ambient light is incident on the auxiliary structure cancel each other out, thereby reducing unwanted surface reflection.

[0005] This application provides a diffractive optical waveguide, which includes: a waveguide substrate, the surface of which is provided with a light coupling functional region; the light coupling functional region includes at least an insertion region and an exit region; and auxiliary structures are provided on other regions of the waveguide substrate surface other than the light coupling functional region, the auxiliary structures including a plurality of auxiliary units, the auxiliary units being used to cause the reflected light formed when ambient light is incident on the auxiliary structure to interfere destructively.

[0006] This application provides a diffractive waveguide, wherein an auxiliary structure is disposed on the waveguide substrate surface excluding the light coupling functional region. This auxiliary structure includes several auxiliary units. The auxiliary units are cleverly designed so that the reflected light rays formed when ambient light is incident on the auxiliary structure interfere with each other destructively, thereby reducing the reflectivity of the waveguide surface and minimizing unwanted surface reflections. Furthermore, the auxiliary units are arranged periodically within the auxiliary structure, and the period of this auxiliary structure is designed to be smaller than the grating period of any grating structure within the light coupling functional region, to avoid affecting the transmission and imaging of image light within the light coupling functional region. The relationship between the periodic structures on the waveguide substrate surface is further defined to avoid ghosting caused by light loops with different main image angles. Furthermore, the period of the auxiliary structure is defined to be smaller than, or even much smaller than, the wavelength of the incident ambient light, and the height of the auxiliary units is synergistically constrained by the refractive index of the waveguide substrate and the wavelength of the ambient light, achieving destructive interference of reflected light. This enables the antireflection effect to maintain high performance over a wide wavelength range and incident angle range. In addition, the auxiliary unit can also be implemented as a two-dimensional structure. The two-dimensional auxiliary unit has a smaller difference in light response to different polarization states and can play the same weakening effect for different polarization states. Attached Figure Description

[0007] To more clearly illustrate the technical solutions in the embodiments of this utility model, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0008] Figure 1 is a schematic diagram of a diffractive waveguide provided in an embodiment of this application;

[0009] Figure 2 is a schematic diagram of another diffractive waveguide provided in an embodiment of this application;

[0010] Figure 3 is a schematic diagram of the reflectivity of an auxiliary structure provided in this application as a function of wavelength under different incident angles;

[0011] Figure 4 is a schematic diagram of the reflectivity of another auxiliary structure provided in the embodiments of this application as a function of wavelength under different incident angles;

[0012] Figure 5 is a schematic diagram of the reflectivity of another auxiliary structure provided in the embodiments of this application as a function of wavelength under different incident angles;

[0013] Figure 6 is a schematic diagram of the reflectivity of another auxiliary structure provided in the embodiments of this application as a function of wavelength under different incident angles;

[0014] Figure 7 is a schematic diagram of the reflectivity of another auxiliary structure provided in the embodiments of this application as a function of wavelength under different incident angles;

[0015] Figure 8 is a side view of a diffractive waveguide provided in an embodiment of this application;

[0016] Figure 9 is a schematic diagram of the grating parameter settings of the coupling grating provided in an embodiment of this application;

[0017] Figure 10 is a schematic diagram comparing the changes in incoming and leaked light measured by a helical toothed grating in the coupling grating provided in the embodiment of this application.

[0018] Figure 11 shows the light leakage ratio of the helical teeth at different depths with different normal angles in the central field of view provided in the embodiments of this application;

[0019] Figure 12 is a schematic diagram of another diffractive waveguide architecture and the corresponding K-domain diagram provided in an embodiment of this application;

[0020] Figure 13 is a schematic diagram of another diffractive waveguide architecture and the corresponding K-domain diagram provided in an embodiment of this application;

[0021] Figure 14 is a schematic diagram of the structure of various diffractive waveguides provided in the embodiments of this application;

[0022] Figure 15 is a schematic diagram of the structure of a second light-absorbing element / third light-absorbing element provided in an embodiment of this application;

[0023] Figure 16 is a schematic diagram of the actual shape of a coupling region provided in an embodiment of this application;

[0024] Figure 17 is a schematic diagram of a diffraction structure in a coupling region provided in an embodiment of this application;

[0025] Figure 18 is a schematic diagram of the assembly of a diffractive waveguide and an optomechanic provided in an embodiment of this application; Detailed Implementation

[0026] 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 some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0027] Currently, diffractive waveguides couple, transmit, and image light through grating structures on their surfaces. The areas of the waveguide surface without grating structures are smooth and flat; reflections from ambient light in these areas can interfere with users of augmented reality devices and external viewers. To address this issue, existing technologies typically deposit anti-reflection coatings on the waveguide surface to reduce reflection. However, if anti-reflection coatings are deposited on the grating structure without region selection, waveguide performance degrades; conversely, if region selection is performed to avoid the grating structure, the process becomes extremely complex, significantly increasing manufacturing costs. Therefore, this application provides a novel technical approach to address undesirable surface reflections on waveguide surfaces.

[0028] The technical solution of this application will be described in detail below with reference to specific embodiments. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments.

[0029] This application provides a diffractive optical waveguide, which includes: a waveguide substrate, and a light coupling functional region disposed on the surface of the waveguide substrate; the light coupling functional region includes at least a coupling-in region and a coupling-out region; and auxiliary structures disposed on other regions of the waveguide substrate surface other than the light coupling functional region, the auxiliary structures including a plurality of auxiliary units, the auxiliary units being used to cause the reflected light rays formed when ambient light is incident on the auxiliary structures to interfere with each other destructively.

[0030] The light coupling functional region is a collection of regions containing optical elements required to guide image light rays through the waveguide substrate for imaging, including but not limited to coupling-in regions, turning regions, and coupling-out regions. The light coupling functional region can be multiple discrete regions, or interconnected continuous regions, or combinations thereof. For example, a coupling-in optical element is disposed within the coupling-in region of the light coupling functional region to couple image light rays into the waveguide substrate; a coupling-out optical element is disposed within the coupling-out region of the light coupling functional region to couple image light rays out of the waveguide substrate. Optionally, the optical elements within the light coupling functional region are all diffractive optical elements, such as diffraction gratings, and have a periodic structure.

[0031] In this application, an auxiliary structure is provided on the waveguide substrate surface of the diffractive waveguide, excluding the light coupling functional region. The auxiliary structure includes several auxiliary units. Each auxiliary unit in the auxiliary structure is cleverly designed so that the reflected light formed when ambient light is incident on the auxiliary structure interferes with each other, thereby reducing the reflectivity of the waveguide surface and reducing unwanted surface reflection.

[0032] In practice, the auxiliary units in the auxiliary structure are arranged periodically, and the period of the auxiliary structure is less than the grating period of any grating structure in the light coupling functional region.

[0033] It is understandable that when the auxiliary units in the auxiliary structure are arranged periodically, the periodic structure will diffract light. Therefore, adding an auxiliary structure to the surface of the waveguide substrate may affect the original image light transmission within the waveguide substrate. In this embodiment, the period of the auxiliary structure is limited to be less than the grating period of any grating structure within the light coupling functional region, which can reduce this effect to a certain extent.

[0034] Further implementably, the periodic structures on the waveguide substrate surface satisfy the following:

[0035] in, Let the wave vector of the image light rays be... It is the sum of the grating vectors of each periodic structure that the image light passes through before being coupled out during its propagation within the light coupling functional region. For the grating vector of the auxiliary structure, The refractive index of the waveguide substrate, The wavelength of the light rays in the image.

[0036] Specifically, the periodic structures on the waveguide substrate surface include grating structures within the light coupling functional region and auxiliary structures outside the light coupling functional region. Image rays (wave vector is...) Before being coupled out after incident on the coupling region within the light coupling functional region, the wave vector changes after passing through a series of grating structures within the light coupling functional region and auxiliary structures outside the light coupling functional region. ,when When the image light rays become evanescent waves, they decay rapidly and thus will not couple out through the coupling region to form a light loop with an angle different from the main image, thereby avoiding the generation of ghost images. For example, the light coupling functional region includes a coupling-in region and a coupling-out region. Before being coupled out, the image light rays must pass through at least the coupling-in grating (grating vector). The coupling effect may also occur through the coupling-out grating (one of the grating vectors). or The pupil dilation effect; the light coupling functional area includes the coupling-in region, the turning region, and the coupling-out region. Before being coupled out, the image light rays must pass through at least the coupling-in grating (grating vector). The coupling effect may also occur through a deflection grating (grating vector). (This has a pupil-dilating effect.)

[0037] In this embodiment, the auxiliary unit included in the auxiliary structure outside the light coupling functional region can be a one-dimensional structure or a two-dimensional structure. When the auxiliary unit is implemented as a two-dimensional auxiliary unit, the difference in light response to different polarization states is small, and it can play an equal role in reducing the intensity of light for different polarization states.

[0038] Specifically, when the auxiliary unit is a one-dimensional auxiliary unit, the grating vector is When the auxiliary unit is a two-dimensional auxiliary unit, the grating vector includes and , In for and One of them.

[0039] For example, the light coupling functional region includes a coupling-in region and a coupling-out region. When the auxiliary unit is implemented as a two-dimensional auxiliary unit, the image light wave vector... / / ,or, / The ray coupling functional region includes an insertion region, a turning region, and an exit region. Similarly, when the auxiliary unit is implemented as a two-dimensional auxiliary unit, the image ray wave vector... / / ,or, / .

[0040] In this embodiment, on the one hand, the period of the auxiliary structure outside the optical coupling functional region is designed to be smaller than the grating period of any grating structure within the optical coupling functional region, thereby reducing the impact of the auxiliary structure on the original optical path and imaging. On the other hand, the auxiliary structure is designed so that the reflected light rays formed when ambient light is incident on the auxiliary structure interfere destructively, thereby reducing the reflectivity of the waveguide surface and minimizing unwanted surface reflections. This solves the problem of reflection interference without generating other negative impacts. Furthermore, the relationship between the periodic structures on the waveguide substrate surface is defined to avoid the auxiliary structure's influence on the original optical path and imaging.

[0041] In another embodiment, although the relationships between the periodic structures on the waveguide substrate surface do not satisfy those defined in the foregoing embodiments, forming a light loop with an angle different from the main image, if the formed ghost image is not within the field of view, or the brightness of the ghost image is insufficient to affect the imaging effect, it is still a specific implementation scheme to be protected by this application. Additionally, the auxiliary units in the auxiliary structure can also be randomly arranged.

[0042] In practice, the auxiliary units are protruding structures, and there are dielectric gaps between each auxiliary unit. The refractive index of the auxiliary units is greater than the refractive index of the dielectric gaps. In this application, it can be assumed that when the auxiliary units are arranged periodically, the dielectric gaps between the auxiliary units are also arranged periodically.

[0043] Specifically, when the auxiliary unit is a one-dimensional structure, the medium gap between the one-dimensional auxiliary units is a strip-shaped structure extending in the same direction. When the medium gap is an air gap, the air gap forms a groove between the protruding structures (auxiliary units). The longitudinal section of the protruding structure can be triangular, quadrilateral, or stepped, etc., where the quadrilateral can be a parallelogram, or a quadrilateral that is narrower at the top and wider at the bottom, etc.

[0044] When the auxiliary unit is a two-dimensional structure, the two-dimensional auxiliary unit is a protruding structure, and the medium gap between the two-dimensional auxiliary units or the two-dimensional auxiliary units is a regular shape. Specifically, the two-dimensional auxiliary unit can be a cylindrical structure, an elliptical cylindrical structure, a polygonal base cylindrical structure, a conical structure, an elliptical cone structure, or a polygonal base cone structure, and the cross-section of the two-dimensional auxiliary unit can be circular, elliptical, polygonal, etc.; or, the medium gap can be a cylindrical structure, an elliptical cylindrical structure, a polygonal base cylindrical structure, an inverted cone structure, an inverted elliptical cone structure, or a polygonal top inverted cone structure; the cross-section of the medium gap can be circular, elliptical, polygonal, etc.

[0045] It should be noted that when the two-dimensional auxiliary unit is a cylindrical, elliptical cylindrical, or polygonal base cylinder structure, the dimensions of the two-dimensional auxiliary unit along the direction away from the waveguide substrate can be the same or different. When they are different, the dimensions of the two-dimensional auxiliary unit gradually decrease along the direction away from the waveguide substrate. When the two-dimensional auxiliary unit is a conical, elliptical conical, or polygonal base cone structure, the dimensions of the two-dimensional auxiliary unit gradually decrease along the direction away from the waveguide substrate. When the dielectric gap is a cylindrical, elliptical cylindrical, or polygonal base cylinder structure, the dimensions of the dielectric gap along the direction away from the waveguide substrate can be the same or different. When they are different, the dimensions of the dielectric gap gradually increase along the direction away from the waveguide substrate. When the dielectric gap is an inverted conical, inverted elliptical conical, or polygonal top inverted conical structure, the dimensions of the dielectric gap gradually increase along the direction away from the waveguide substrate.

[0046] For example, referring to Figures 1 and 2, a grating structure 120 is provided in the light coupling functional region on the surface of the waveguide substrate 110, and an auxiliary structure 130 is provided in the region outside the light coupling functional region. The auxiliary structure 130 includes a plurality of auxiliary units 131, and there are dielectric gaps 132 between the auxiliary units 131. The auxiliary units 131 and the dielectric gaps 132 are arranged periodically.

[0047] As can be seen, in Figures 1 and 2, the auxiliary unit 131 is a raised structure, and the medium gap 132 is implemented as an air gap between the raised structures. In Figure 1, the auxiliary unit 131 is a cylindrical structure with a circular cross-section; in Figure 2, the medium gap 132 is a quadrilateral base column structure with a quadrilateral cross-section.

[0048] Further implementably, the period of the auxiliary structure is less than the wavelength of ambient light, and the height of the auxiliary unit ranges from [...]. , ],in, The wavelength of ambient light, The refractive index of the waveguide substrate, Allowable height deviation.

[0049] Specifically, when the difference between the period of the auxiliary structure and the wavelength of the ambient light reaches a certain level, the ambient light incident on the auxiliary structure will not produce higher-order reflections, but only zero-order reflections and zero-order transmissions, theoretically equivalent to a uniform thin film. Thus, when designing the parameters of the auxiliary structure to achieve destructive interference of the reflected light rays incident on the auxiliary structure, the principle of thin-film interference can be referenced. The refractive index of the waveguide substrate is designed to be approximately equal to the square of the refractive index of the auxiliary structure, and the product of the height of the auxiliary unit and the refractive index of the auxiliary structure is designed to be approximately an odd multiple of a quarter wavelength. Furthermore, considering the stability of the auxiliary unit, the process flow, and manufacturing costs, in this embodiment, the product of the height of the auxiliary unit and the refractive index of the auxiliary structure is designed to be approximately equal to a quarter wavelength, i.e., the height of the auxiliary unit... Basically equal to It should be noted that absolute equality is not required here; a certain degree of deviation is allowed. For the allowable height deviation, i.e. and The difference is no greater than max( That's all. For example, The possible values ​​are 0-20nm.

[0050] In this application, the period of the auxiliary structure is less than the wavelength of ambient light, specifically less than or equal to half the wavelength. Ambient light is visible light with a wavelength range of 400 nanometers (nm) to 760 nanometers (nm).

[0051] In practice, the refractive index of the auxiliary structure Refractive index relative to waveguide substrate The following equation applies between them:

[0052]

[0053] in, For the duty cycle of the auxiliary unit, The dielectric constant of the auxiliary unit, The dielectric constant of the dielectric gap is... This represents the allowable refractive index deviation.

[0054] Specifically, when designing an auxiliary structure as an equivalent thin film, the equivalent refractive index of the auxiliary structure should be obtained based on the refractive index of the auxiliary unit, the refractive index of the interlayer, and the duty cycle of the auxiliary unit. The refractive index of the redesigned waveguide substrate is approximately equal to the square of the refractive index of the auxiliary structure, thus obtaining... Basically equal to Similarly, absolute equality is not required here; a certain degree of deviation is allowed. Among these, For the allowable refractive index deviation, i.e., and The difference is no greater than max( That's it. Furthermore, after selecting the waveguide substrate material, the auxiliary unit material, and the dielectric material, , and That is, it is determined, thus obtaining the duty cycle of the auxiliary unit. and , and The relationship, and then the allowable refractive index deviation. Convert to allowable duty cycle deviation For example, The possible values ​​are 0-15%.

[0055] For example, the waveguide substrate has a refractive index of 1.8, the two-dimensional auxiliary unit has a refractive index of 1.8, and the dielectric gap is an air gap with a refractive index of 1. Without auxiliary structures on the waveguide substrate surface, the reflectivity is 8%. In a specific example, the two-dimensional auxiliary unit is designed as a cylindrical structure with a diameter of 120 nm, a height of 100 nm, a period of 150 nm in both directions, and a duty cycle of 50%. Figure 3 shows the variation of reflectivity with wavelength at different incident angles. As can be seen from Figure 3, at incident angles of 0° (black solid line), 20° (dark gray solid line), and 40° (light gray solid line), within the wavelength range of 400 nm to 700 nm, the reflectivity can be reduced to less than 2%, and further within the wavelength range of 450 nm to 650 nm, the reflectivity can be reduced to less than 1%. In another specific example, the air gap between the two-dimensional auxiliary units is designed as a square-bottomed columnar structure with a side length of 110 nm and a height of 100 nm. The period in both directions is 150 nm, and the duty cycle is 46%. Figure 4 shows the variation of reflectivity with wavelength at different incident angles. As can be seen from Figure 4, at incident angles of 0° (black solid line), 20° (dark gray solid line), and 40° (light gray solid line), within the wavelength range of 400 nm to 700 nm, the reflectivity can be reduced to less than 2%. Furthermore, within the wavelength range of 450 nm to 650 nm, the reflectivity can be reduced to less than 1%.

[0056] For example, the waveguide substrate has a refractive index of 1.5, the two-dimensional auxiliary unit has a refractive index of 1.5, and the dielectric gap is an air gap with a refractive index of 1. Without auxiliary structures on the waveguide substrate surface, the reflectivity is 6%. In a specific example, the air gap between the two-dimensional auxiliary units is designed as a square-bottomed columnar structure with a side length of 105 nm and a height of 105 nm. The period in both directions is 150 nm, and the duty cycle is 50%. Figure 5 shows the variation of reflectivity with wavelength at different incident angles. As can be seen from Figure 5, at incident angles of 0° (black solid line), 20° (dark gray solid line), and 40° (light gray solid line), within the wavelength range of 400 nm to 700 nm, the reflectivity can be reduced to less than 1%.

[0057] For example, the waveguide substrate has a refractive index of 2.0, the two-dimensional auxiliary unit has a refractive index of 2.0, and the dielectric gap is an air gap with a refractive index of 1. Without auxiliary structures on the waveguide substrate surface, the reflectivity is 11%. In a specific example, the air gap between the two-dimensional auxiliary units is designed as a square-bottomed columnar structure with a side length of 115 nm and a height of 94 nm. The period in both directions is 150 nm, and the duty cycle is 41%. Figure 6 shows the variation of reflectivity with wavelength at different incident angles. As can be seen from Figure 6, at incident angles of 0° (black solid line), 20° (dark gray solid line), and 40° (light gray solid line), the reflectivity can be reduced to less than 2% within the wavelength range of 400 nm to 700 nm, and to less than 1% within the wavelength range of 450 nm to 650 nm.

[0058] In this application, it is feasible that the refractive index of the two-dimensional auxiliary element can be the same as the refractive index of the waveguide substrate. Alternatively, the refractive index of the two-dimensional auxiliary element can be different from the refractive index of the waveguide substrate.

[0059] For example, the waveguide substrate has a refractive index of 2.0, the two-dimensional auxiliary unit has a refractive index of 2.4, and the dielectric gap is an air gap with a refractive index of 1. Without auxiliary structures on the waveguide substrate surface, the reflectivity is 20%. In a specific example, the air gap between the two-dimensional auxiliary units is designed as a square-bottomed columnar structure with a side length of 130 nm, a height of 100 nm, a period of 150 nm in both directions, and a duty cycle of 25%. The reflectivity variation with wavelength at different incident angles is shown in Figure 7. As can be seen from Figure 7, at incident angles of 0° (black solid line), 20° (dark gray solid line), and 40° (light gray solid line), the reflectivity can be reduced to less than 2% within the wavelength range of 400 nm to 700 nm, and to less than 1% within the wavelength range of 450 nm to 650 nm.

[0060] In the above embodiments, auxiliary structures are provided on the surface of the waveguide substrate of the diffractive waveguide, in areas other than the light coupling functional region. These auxiliary structures consist of several periodically arranged two-dimensional auxiliary units. To maintain high performance of the anti-reflection effect over a wide wavelength range and incident angle range, the period of the auxiliary structure is designed to be smaller than, or even much smaller than, the incident ambient light wavelength. Furthermore, the height of the auxiliary units is constrained by both the refractive index of the waveguide substrate and the ambient light wavelength to achieve destructive interference of the reflected light. In addition, these two-dimensional auxiliary units exhibit small differences in response to light of different polarization states, thus providing equal attenuation for light of different polarization states. Further, the period of the auxiliary structure is designed to be smaller than the grating period of any grating structure within the light coupling functional region to reduce the influence of the auxiliary structure on the original optical path and imaging. In some embodiments, the relationship between the periodic structures on the waveguide substrate surface is further defined to avoid the auxiliary structure's influence on the original optical path and imaging.

[0061] In this application, the two-dimensional auxiliary units included in the auxiliary structure are the smallest structural units of the auxiliary structure. The two-dimensional auxiliary units have the same shape and size, which can simplify the process and reduce manufacturing costs.

[0062] Furthermore, the entire waveguide surface in this application has microstructures, so there is no adhesive overflow problem when fabricated using nanoimprinting. Alternatively, the adhesive overflow ring can be extended beyond the outer contour of the diffractive waveguide and removed by cutting. This avoids the problem that the waveguide surface only has microstructures in the light coupling functional area, and adhesive overflow rings are formed around the microstructure area during the imprinting process, which affects the performance of the diffractive waveguide.

[0063] Furthermore, in practical use of electronic devices including diffractive waveguides, referring to Figure 8, on the one hand, the light 210 emitted by the optomechanical system 200 propagates into the waveguide substrate 110 after diffraction by the coupling grating 121. When the light 210 reaches the coupling grating 123 and is diffracted out by the coupling grating 123, the coupled light is divided into two parts: one part, 212, enters the user's eye, while the other part, 211, leaks into the external environment, resulting in light leakage. On the other hand, the light 301 emitted by the external light source 300 is incident on the coupling grating 123 and enters the user's eye after diffraction by the coupling grating 123. This part of the light 302 is prone to producing a rainbow effect. Based on this, this application can reduce light leakage and the rainbow effect by adjusting the tooth profile parameters of the coupling grating 123, changing the ratio of the light 212 entering the eye and the leaking light 211, as well as the amount of external light 302 entering the eye. Specifically, the tooth profile of the coupling grating is helical; the helical tooth angle of the coupling grating is θ, the tooth height is h, and the grating period is p, satisfying the helical tooth relationship: 0.9m*p≤ h*tanθ≤1.1m*p; where m is a positive integer greater than or equal to 1. The helical tooth angle refers to the angle between the helical tooth and the normal to the waveguide substrate.

[0064] Referring to Figure 9, the coupling grating 123 is a helical grating with a helical angle of θ, a tooth height of h, and a grating period of p. The refractive index of the waveguide substrate 110 is n1, the refractive index of the coupling grating 123 is n2, and the refractive index of air is n3. In this case, the coupling grating 123 can be considered as consisting of upper and lower grating parts, each with a tooth height of h / 2, and the horizontal offset between the two helical grating parts is p / 2. The first portion of the light ray 311 emitted by the external light source 300 is diffracted by the helical grating of the lower part of the coupling grating 123 to form the first diffracted light ray 312, while the second portion of the light ray 321 emitted by the external light source 300 is diffracted by the helical grating of the upper part of the coupling grating 123 to form the second diffracted light ray 322. The first portion of the light ray 311 and the second portion of the light ray 321 are emitted from the same light source and have the same phase. After diffraction, the phase difference between the first diffracted ray 312 and the second diffracted ray 322 consists of two parts. One part is due to the optical path difference, with a magnitude of 2π / λ * optical path difference. Since the optical path difference is very small, this part of the phase difference is close to 0. The other part is due to the phase difference caused by the misalignment of the grating period, which is approximately 180 degrees. Therefore, the first diffracted ray 312 and the second diffracted ray 322 will undergo destructive interference, making the sum of their total electric fields approximately equal to zero, thus significantly reducing the rainbow effect. As an example, when the grating period of the coupled grating 123 (hedge grating) is 300 nm, and the helical tooth angle is set to 62 degrees, the calculated helical tooth height h is 159 nm, resulting in the strongest destructive interference and the weakest rainbow effect. In this case, a slight sacrifice of rainbow effect can be made by adjusting the helical tooth height h to around 140 nm, which can achieve the best light leakage suppression effect. That is, with a grating period of 300nm, a helical tooth angle θ of 62 degrees and a helical tooth height h of 140nm, the rainbow and light leakage of the waveguide substrate 120 are reduced to a very low level, which can greatly improve the user's viewing experience and usage experience.

[0065] For example, Figure 10 is a schematic diagram comparing the changes in incoming light and leakage light measured by using a helical toothed grating for the coupling grating. Specifically, referring to Figure 10(a), when the coupling grating 123 uses the helical toothed grating shown in Figure 9, the ratio of incoming light 212 to leakage light 211 first increases and then tends to stabilize with the grating depth (grating tooth height h). The larger the grating tooth height h, the larger the ratio of incoming light 212 to leakage light 211, and the less leakage light. As shown in Figure 10(b), for the helical toothed grating, another major factor affecting the leakage ratio is the angle θ of the helical tooth, that is, the angle between the helical tooth and the normal of the waveguide substrate. In the range of 0~75°, the larger the helical tooth angle θ, the lower the diffraction efficiency of leakage light 211, while the diffraction efficiency of incoming light 212 is still relatively high, indicating that the lower the leakage ratio, the better the leakage suppression effect. Therefore, the grating provided in this embodiment of the invention uses a larger helical tooth angle θ, which can reduce the leakage ratio, thereby weakening leakage light and rainbow effect. In other embodiments, the coupling grating can also employ Bragg diffraction of a volume holographic grating, and in a surface relief grating, the oblique teeth have a large aspect ratio, which also has a significant effect on suppressing light leakage.

[0066] Figure 11 shows the light leakage ratio of the helical teeth at different depths with different normal angles in the central field of view provided in this embodiment of the application. Referring to Figure 11, the helical tooth depth is the tooth height, and the unit is nm (nanometer). It can be seen that when the helical tooth angle θ is large, the depth required to achieve the highest light leakage ratio is the smallest. According to this curve, the optimal combination of helical tooth angle θ and tooth height h can be obtained. For example, when the helical tooth angle θ of the coupling grating 123 is set to 62 degrees, the light leakage suppression ratio is the highest when its tooth height h is 140 nm. That is, when the parameters of the helical tooth grating of the coupling grating 123 are configured such that the helical tooth height multiplied by the tangent of the tilt angle is equal to or close to an integer multiple of the helical tooth period, the principle of interference cancellation can be used to effectively reduce the intensity of the rainbow.

[0067] Implementably, the coupling grating can be implemented as a one-dimensional grating or a two-dimensional grating. When the coupling grating is a two-dimensional grating, it is tilted along the same direction or along at least two different directions. The cross-sectional shape of the coupling grating is one or a combination of elliptical, rhomboid, or two-dimensional shapes. Furthermore, the tooth profile of the folding grating includes straight teeth or helical teeth; when the tooth profile of the folding grating is helical, the parameter configuration of the folding grating also satisfies the aforementioned helical tooth relationship.

[0068] It is understood that diffractive waveguides using grating structures for exit pupil expansion will have multiple expansion paths, resulting in numerous rays with equal optical path differences propagating in the same direction. These rays will experience constructive or destructive interference when coupled to the human eye, causing bright and dark fringes in the displayed image, significantly affecting the display effect. Based on this, the diffractive waveguide provided in this application further includes: a coupling grating for coupling light from the entire field of view into the waveguide substrate; and a transition grating including at least a first transition grating and a second transition grating, wherein the first transition grating deflects light from a first field of view towards the output grating, and the second transition grating deflects light from a second field of view towards the output grating, the union of the first and second field of view forming the complete field of view; wherein the first and second transition gratings are located on different sides of the output grating; or, the first and second transition gratings are located on the same side of the output grating, and are offset from each other.

[0069] It should be noted that the light transmitted through the diffractive waveguide in this application has a certain field of view. The field of view of all the light rays coupled into the waveguide substrate through the coupling grating is the complete field of view. The first and second bending gratings each deflect a portion of the complete field of view. The first bending grating is used to deflect the light rays in the first field of view towards the coupling grating, and the second bending grating is used to deflect the light rays in the second field of view towards the coupling grating. The union of the first and second field of view ranges is the complete field of view. Preferably, the first and second field of view ranges do not overlap. For example, the complete field of view is -15° to 15°, the first field of view range is -15° to 5°, and the second field of view range is -5° to 15°; or, the complete field of view is -15° to 15°, the first field of view range is -15° to 0°, and the second field of view range is 0° to 15°.

[0070] In one embodiment, the first bend grating and the second bend grating are located on different sides of the output grating. For example, FIG12 shows a schematic diagram of the architecture of a diffractive waveguide and the corresponding K-domain diagram in one embodiment. The diffractive waveguide 100 includes a waveguide substrate 110, and the surface of the waveguide substrate 110 is provided with an input grating 121, a first bend grating 122-1, a second bend grating 122-2, and an output grating 123. The first bend grating 122-1 and the second bend grating 122-2 are respectively located on different sides of the output grating 123.

[0071] In practice, after light is coupled into the waveguide substrate, it is transmitted via total internal reflection along a first direction. A steering optical element is disposed along the optical path in the first direction. The steering optical element is used to deflect light from a second field of view toward a second deflection grating, while the light from the first field of view continues to be transmitted along the first direction to the first deflection grating. The steering optical element is a serrated grating, which is tilted toward the direction of light transmission so that the diffraction efficiency of the diffraction order deflected toward the second deflection grating is much greater than the diffraction efficiency of the diffraction order transmitted along the original direction.

[0072] It should be noted that, in this application, the transmission direction of light rays after being coupled into the waveguide substrate by the coupling grating and then propagating towards the deflection grating is defined as the first direction. Referring to Figure 12(a), after the light rays are coupled into the waveguide substrate 110 by the coupling grating 121, they are propagated by total internal reflection along the first direction, that is, towards the first deflection grating 122-1. During the transmission of light rays towards the first deflection grating 122-1, a portion of the light rays within the field of view will first pass through the deflecting optical element 124 and be deflected by the second deflection grating 122-2 for transmission towards the output grating 123; the other portion of the light rays within the field of view will not pass through the deflecting optical element 124 and will directly transmit to the first deflection grating 122-1 for transmission towards the output grating 123. Thus, the light rays of the complete field of view are divided into two parts according to the field of view, and each part is propagated to the output grating 123 along different paths. It is understood that the width of the deflection grating is positively correlated with the field of view of the light it deflects. The larger the field of view of the light to be deflected by the deflection grating, the wider the width of the deflection grating; and the wider the width of the deflection grating, the more times the light is deflected, which may lead to more severe undesirable interference effects. In this embodiment, the first deflection grating 122-1 and the second deflection grating 122-2, which are respectively disposed on different sides of the coupling grating 123, transmit light with different field of view through different paths. This can reduce the width of the deflection grating on a single transmission path, thereby improving or even eliminating undesirable interference effects, and thus improving the display effect of the diffractive waveguide.

[0073] Implementably, the vector direction of the grating vector of the second deflection grating is the same as the vector direction of the grating vector of the deflection optics. For example, referring to Figure 12(b), which shows a K-domain diagram of light transmission under the diffractive waveguide architecture shown in Figure 12(a), the grating vector coupled into the grating is... The grating vector of the first folding grating is The grating vector of the second folding grating is The grating vector of the coupled grating is and The grating vector of the steering optical element is The first deflection grating 122-1 is located to the right of the output grating 123, and the second deflection grating 122-2 is located above the output grating 123. The effective output area of ​​light in the first field of view is to the left of the output grating 123, and the effective output area of ​​light in the second field of view is to the right of the output grating 123. After the light is coupled into the waveguide substrate 110 through the input grating 121, it is transmitted downwards toward the first deflection grating 122-1. A portion of the light in the field of view encounters the steering optical element 124 and needs to be deflected to the upper left to be transmitted toward the second deflection grating 122-2. After the light reaches the second deflection grating 122-2, it needs to be deflected toward the right side of the output grating 123. When the vector direction of the grating vector of the second deflection grating 122-2 is the same as the vector direction of the grating vector of the steering optical element 124, the transmission direction of the light does not change after passing through the steering optical element 124 and the second deflection grating 122-2, and it can be transmitted toward the right side of the output grating. In another embodiment, the vector direction of the grating vector of the second deflection grating may be different from that of the grating vector of the steering optics, but it is still necessary to ensure that the light rays in the second field of view, after reaching the second deflection grating, are deflected toward the right side of the coupling grating, and transmitted through the effective coupling area of ​​the light rays in the second field of view. Moreover, the light rays in each field of view should reach their corresponding effective coupling area in the coupling grating to avoid vignetting.

[0074] In another embodiment, the first folding grating and the second folding grating are located on the same side of the coupling grating, and the first folding grating and the second folding grating are offset from each other.

[0075] Referring, to FIG13, a schematic diagram of a diffractive waveguide architecture and a corresponding K-domain diagram are shown in one embodiment. The diffractive waveguide 100 includes a waveguide substrate 110. A coupling-in grating 121, a first bend grating 122-1, a second bend grating 122-2, and a coupling-out grating 123 are disposed on the surface of the waveguide substrate 110. The first bend grating 122-1 and the second bend grating 122-2 are located on the same side of the coupling-out grating 123, and are staggered. The first bend grating 122-1 and the second bend grating 122-2 are not spaced apart in a second direction perpendicular to the first direction, so that all light rays entering the complete field of view of the waveguide substrate can be deflected to the coupling-out grating 123.

[0076] In practice, after the light is coupled into the waveguide substrate, it is transmitted by total internal reflection along a first direction, and the first and second folding gratings are offset from each other in the first direction. Referring to Figure 13(a), after the light is coupled into the waveguide substrate 110 from the coupling grating 121, it is transmitted by total internal reflection along the first direction, that is, towards the first folding grating 122-1. During the transmission of the light towards the first folding grating 122-1, a portion of the light in the field of view will first reach the first folding grating 122-1 and be deflected by the first folding grating 122-1 towards the coupling grating 123; the other portion of the light in the field of view will travel a longer distance by total internal reflection to reach the second folding grating 122-2 and be deflected by the second folding grating 122-2 towards the coupling grating 123; thus, the light in the complete field of view is divided into two parts according to the field of view, which are transmitted to the coupling grating 123 along different paths.

[0077] Implementably, the vector angle of the grating vector of the first folding grating is greater than the vector angle of the grating vector of the second folding grating. For example, referring to Figure 13(b), which shows a K-domain diagram of light transmission under the diffractive waveguide architecture shown in Figure 13(a), the grating vector coupled into the grating is... The grating vector of the first folding grating is The grating vector of the second folding grating is The grating vector of the coupled grating is and The first and second folding gratings 122-1 and 122-2 are both located to the right of the coupling grating 123, with the second folding grating 122-2 being farther from the coupling grating 123. The folding grating farther from the coupling grating requires a larger vector deflection angle to deflect the light to the coupling grating. Therefore, the vector angle of the grating vector of the first folding grating is greater than that of the second folding grating. Here, the vector angle of the grating vector is the angle between the grating vector direction and Kx.

[0078] Preferably, the vector angle of the grating vector of the first folding grating is greater than the vector angle of the grating vector of the second folding grating, and the vector angle of the grating vector of the second folding grating is greater than 40°.

[0079] In practice, the grating vectors of the coupled grating, the first folding grating, and the second folding grating satisfy the following relationship:

[0080]

[0081] in, The grating vector coupled into the grating. The grating vector of the first folding grating. The grating vector of the second folding grating. denoted as , where is the refractive index of the waveguide substrate.

[0082] It should be noted that the first and second bending gratings are staggered for two reasons: firstly, to create two different paths for light transmission; and secondly, to prevent interference caused by light deflected by the first bending grating continuing to be affected by the second bending grating. The grating vectors of the coupled grating, the first bending grating, and the second bending grating satisfy... At this time, the optical paths of the two folding gratings will not interfere with each other.

[0083] In practice, the first and second bend gratings have different grating directions, and the coupling grating is a two-dimensional grating. It can be understood that the first and second bend gratings deflect light rays propagating in different directions towards the coupling grating, therefore the vector directions of the grating vectors of the first and second bend gratings should be different. Since the light rays propagating along both paths enter the waveguide substrate through the same coupling grating, the coupling grating needs to have at least two grating vectors with different directions to couple the light rays from both paths out of the waveguide substrate. and , making and At this point, the coupled grating can be realized as a two-dimensional grating.

[0084] The diffractive waveguide provided in the foregoing embodiments has an insertion grating, a deflection grating, and an exit grating disposed on the substrate surface. The insertion grating is used to couple light into the waveguide substrate and then transmit it toward the deflection grating. The deflection grating is used to deflect the transmission direction of the light, so that the light is transmitted toward the exit grating, so that the light is coupled out of the waveguide substrate and enters the human eye through the exit grating. Since the wider the deflection grating, the more times the light is deflected, the more serious the undesirable interference effect may be. In this application, the deflection grating includes at least a first deflection grating and a second deflection grating. At least two deflection gratings transmit light of different field ranges through different paths. This can change the transmission of a part of the field of view light to other paths. Compared with the existing method of transmitting the entire field of view light through one path, it can reduce the width of the deflection grating required for a single transmission path, improve or even eliminate undesirable interference effects, thereby improving the display effect of the diffractive waveguide. Furthermore, since the light is divided into at least two parts according to the field of view and propagates along different paths, the design of the coupling grating can also be optimized by dividing the field of view into at least two parts. The coupling region corresponding to the light in the first field of view is optimized according to the grating structures along the path traversed by the first field of view; the coupling region corresponding to the light in the second field of view is optimized according to the grating structures along the path traversed by the second field of view.

[0085] The diffractive waveguide provided in this application further includes: a waveguide substrate comprising a first surface and a second surface disposed opposite to each other; a first light-absorbing element disposed on the side between the first surface and the second surface for absorbing image light incident on the side; and a second light-absorbing element disposed on the first surface and the second surface, at least in the region between the side adjacent to the coupling region and the coupling region, for absorbing image light scattered by the side.

[0086] It is understandable that, since grating diffraction has multiple diffraction orders, only some of the diffraction orders are effectively utilized. When the image light is coupled into the grating, at least diffraction orders A and B are generated. Diffraction order A is transmitted towards the grating and is effectively utilized, while diffraction order B is directly incident on the sidewall of the waveguide substrate in the opposite direction. Since the sidewall of the waveguide substrate is formed by laser cutting, its flatness is far less than that of the waveguide substrate surface, which will have a significant impact on the propagation of the image light, resulting in the scattering of the image light. In this application, on the one hand, a first light-absorbing element is provided on the side wall between the first and second surfaces of the waveguide substrate to absorb image light incident on the side wall, and to absorb as much image light as possible, reduce the scattering of image light, and suppress the generation of scattered light. On the other hand, on the first and second surfaces of the waveguide substrate, at least in the area between the side wall adjacent to the coupling region and the coupling region, a second light-absorbing element is provided to absorb image light transmitted toward the side and image light scattered from the side. Diffraction order B first incident on the second light-absorbing element, loses some energy, and then is scattered by the side wall of the waveguide substrate before incident on the second light-absorbing element again. This can reduce the scattering caused by image light incident on the side and suppress the further transmission of image light that has already been scattered, preventing the scattered image light from returning to the grating region. Thus, the generation and transmission of scattered image light are suppressed in two ways, effectively avoiding the scattering of image light on the side wall of the waveguide substrate and the series of effects on the imaging effect after scattering.

[0087] It can be understood that a portion of the image light coupled into the grating is directly transmitted toward the sidewall of the waveguide substrate. Before reaching the sidewall of the waveguide substrate, it is first absorbed by the second light-absorbing element, then absorbed by the first light-absorbing element after entering the sidewall, and finally absorbed by the second light-absorbing element after being scattered by the sidewall. In this way, the three-pronged approach can basically prevent the scattered image light from returning to the grating area.

[0088] In one embodiment, both the first light-absorbing element and the second light-absorbing element are light-absorbing material layers. The light-absorbing material layer covers the side to form the first light-absorbing element, and extends from the edge of the side to at least cover the side adjacent to the coupling region and the waveguide substrate surface region between the coupling region to form the second light-absorbing element.

[0089] Referring to Figure 14(a), the diffractive waveguide 100 includes a waveguide substrate 110, on which a coupling grating 121 and a coupling grating 123 are disposed. A light-absorbing material layer is coated on the sidewalls of the waveguide substrate 110 to form a first light-absorbing element 140. The light-absorbing material layer further extends from a portion of the sidewalls of the waveguide substrate 110 toward the surface of the waveguide substrate 110, and at least covers the sidewalls adjacent to the coupling region and the waveguide substrate surface region between the coupling regions to form a second light-absorbing element 150. The light-absorbing material layer may also extend from all sidewalls of the waveguide substrate 110 toward the surface of the waveguide substrate 110. The extinction coefficient of the light-absorbing material layer is greater than 0.02, and the difference between the refractive index of the light-absorbing material layer and the refractive index of the waveguide substrate is less than 0.2. The light-absorbing material includes, but is not limited to, one or more of blank ink, graphene, amorphous silicon, and germanium.

[0090] In practice, the thickness of the first light-absorbing element is greater than 0.3 mm. The transition surface between the first and second light-absorbing elements is a smooth curved surface, and the minimum distance between this smooth curved surface and the edge of the waveguide substrate surface is greater than 0.2 mm. The dimension of the second light-absorbing element extending from the side edge ranges from 4 mm to 10 mm. This allows for the absorption of image light incident on the sidewall of the waveguide substrate and scattered image light as much as possible. It should be noted that, since the second light-absorbing element is used to absorb as much image light as possible, its placement should cover the transmission path of image light across the entire field of view. Generally, the maximum dimension of the second light-absorbing element in the direction orthogonal to the image light propagation direction should be greater than the diameter of the coupling region.

[0091] In one embodiment, the first light-absorbing element is a light-absorbing material layer, and the second light-absorbing element is a three-layer structure, which includes a first metal cylindrical array layer, a second dielectric tetragonal prism array layer and a third metal layer in sequence along the direction away from the waveguide substrate surface.

[0092] Referring to Figure 14(b), the diffractive waveguide 100 includes a waveguide substrate 110, on which a coupling grating 121 and a coupling grating 123 are disposed. A layer of light-absorbing material is covered on the sidewall of the waveguide substrate 110 to form a first light-absorbing element 140. On the surface of the waveguide substrate 110, in the area between the sidewall adjacent to the coupling region and the coupling region, a three-layer structure is disposed to form a second light-absorbing element 150.

[0093] Referring to Figure 15, Figures (a) and (b) in Figure 15 are schematic diagrams of the structure of the second light-absorbing element 150 from different viewpoints. Along the direction away from the waveguide substrate surface, it sequentially includes a first metal cylindrical array layer 510, a second dielectric tetragonal prism array layer 520, and a third metal layer 530. When scattered image light is incident on the three-layer structure, it passes sequentially through the first metal cylindrical array layer 510, the second dielectric tetragonal prism array layer 520, and the third metal layer 530.

[0094] In this embodiment, when the image light is incident on the first metal cylindrical array layer, the image light is not reflected because the first metal cylindrical array layer matches the spatial impedance within the target frequency range. The image light is then incident on the second dielectric tetragonal prism array layer, which acts as a loss layer to absorb the image light, greatly reducing the energy of the image light. The thickness of the third metal layer is greater than the skin depth of the image light, preventing the image light from being transmitted. This suppresses the transmission of the image light and prevents the scattered image light from returning to the grating region, greatly improving the imaging effect of the diffraction waveguide.

[0095] In practice, the outline shape of the second light-absorbing element is crescent-shaped, and the maximum size of the second light-absorbing element in the direction orthogonal to the image light propagation direction is greater than the diameter of the coupling region.

[0096] In practice, the thickness of the first metallic cylindrical array layer is less than the thickness of the second dielectric tetragonal prism array layer, and the thickness of the second dielectric tetragonal prism array layer is less than the thickness of the third metallic layer. The thickness of the first metallic cylindrical array layer ranges from 20 to 50 nm, the thickness of the second dielectric tetragonal prism array layer ranges from 50 to 100 nm, and the thickness of the third metallic layer ranges from 100 to 150 nm.

[0097] In practice, the cylinder diameter of the first metal cylindrical array layer is smaller than the length and width of the prisms in the second dielectric tetragonal prism array layer. The cylinder diameter of the first metal cylindrical array layer ranges from 60 to 100 nm, and the length and width of the prisms in the second dielectric tetragonal prism array layer range from 150 to 200 nm.

[0098] For example, the material of the second dielectric prism array layer can be vanadium dioxide.

[0099] The first metal cylindrical array layer and the second dielectric tetragonal prism array layer are structural unit array layers. There are gaps between the structural units. These gaps can be filled with dielectric materials with a refractive index of 1 to 1.5, such as air, SiO2, MgF2, glue, etc.

[0100] In this application, the waveguide substrate further includes a transition region, within which a transition grating is disposed. A third light-absorbing element is disposed on the first and second surfaces of the waveguide substrate, at least in the region between the side adjacent to the transition region and the transition region, to absorb image light rays that have passed through the transition grating and are scattered by the side. It is understood that when the image light rays are acted upon by the transition grating, a portion is deflected towards the coupling region, while the portion continues to propagate along its original direction. This portion of the image light rays that continues to propagate along its original direction eventually incident on the sidewall of the waveguide substrate and is reflected. Therefore, in this application, a third light-absorbing element is also disposed on the first and second surfaces, at least in the region between the side adjacent to the transition region and the transition region, to absorb image light rays that have passed through the transition grating and are scattered by the side.

[0101] The third light-absorbing element is the same as the second light-absorbing element, and can be a light-absorbing material layer, or a three-layer structure consisting of a first metal cylindrical array layer, a second dielectric tetragonal prism array layer, and a third metal layer in sequence along the direction away from the waveguide substrate surface. In Figures 14(c) and (d), the diffractive waveguide 100 includes a waveguide substrate 110, on which a coupling grating 121, a coupling grating 123, and a transition grating 122 are disposed. A light-absorbing material layer is covered on the sidewall of the waveguide substrate 110 to form a first light-absorbing element 140. On the surface of the waveguide substrate 110, in the area between the side adjacent to the coupling region and the coupling region, a three-layer structure is disposed to form a second light-absorbing element 150. On the surface of the waveguide substrate 110, in the area between the side adjacent to the transition region and the transition region, a third light-absorbing element 170 is disposed.

[0102] In practice, the distribution position 610 of the third light-absorbing element in a direction orthogonal to the image light propagation direction covers the propagation area of ​​the boundary field of view. It should be noted that the third light-absorbing element is designed to absorb as much image light as possible incident on it, so its design position needs to cover the transmission path of the image light across the entire field of view.

[0103] In practice, the shape pattern of the third light-absorbing element can be reused to design an information display pattern for the diffractive waveguide. It is understood that the high visibility of the light-absorbing element would affect the appearance of the diffractive waveguide. The third light-absorbing element, located near the sidewall of the waveguide substrate at the turning point, is exposed, and its shape pattern can be reused to design an information display pattern originally intended to be displayed on the diffractive waveguide, such as a product name or brand logo.

[0104] In another embodiment, ion implantation, such as Fe, C, Si, Ti, etc., can also be performed in the waveguide substrate region covered by the second and third light-absorbing elements. The transmittance of the waveguide substrate in the ion-implanted region is reduced, and the image light can be absorbed when it is transmitted therein. When it passes through this region and is incident on the sidewall of the waveguide substrate again, part of the light energy has been consumed, so that the image light is consumed before scattering, which can further improve the imaging effect of the diffraction waveguide.

[0105] In another embodiment, a fourth light-absorbing element can be disposed on the waveguide substrate surface in the region between the side adjacent to the coupling region and the coupling region. This fourth light-absorbing element is used to absorb image light that reaches the side after passing through the coupling grating and is scattered by the side. The fourth light-absorbing element is the same as the second light-absorbing element and can be a light-absorbing material layer, or a three-layer structure comprising a first metal cylindrical array layer, a second dielectric tetragonal prism array layer, and a third metal layer sequentially along the direction away from the waveguide substrate surface.

[0106] In another possible implementation, the second and / or third light-absorbing element can be replaced with a diffraction grating. Before reaching the sidewall of the waveguide substrate, the image light passes through the diffraction grating and is diffracted out of the waveguide substrate, reducing scattering caused by the image light incident on the side. The scattered image light is then diffracted out of the waveguide substrate again after incident on the diffraction grating. Preferably, the outgoing direction of the light is away from the eyebox position, so that the outgoing light does not enter the human eye. The diffraction grating has high coupling efficiency to couple the scattered image light out of the waveguide substrate as much as possible. Specifically, it can be implemented as a zigzag grating or a blazed grating, or of course, a high-efficiency straight-tooth grating.

[0107] In practice, when the second light-absorbing element is replaced with a diffraction grating, the grating vector of the diffraction grating and the grating vector of the coupled grating satisfy the light coupling condition, and vector closure is not required. When the diffraction waveguide is assembled into the module, if the diffraction grating is encapsulated inside the module and not visible to the outside, there are no requirements for the light emission direction.

[0108] In practice, when the third light-absorbing element is replaced with a diffraction grating, the grating vector of the diffraction grating, the grating vector of the coupled grating, and the grating vector of the folding grating satisfy the light coupling condition, and vector closure is not required.

[0109] Augmented reality display systems based on diffraction optics typically include an optomechanical system and a diffractive waveguide. A common approach in the design and assembly of the optomechanical system and the diffractive waveguide is to match the size of the coupling region to the exit pupil size of the optomechanical system, aligning the exit pupil position of the optomechanical system with the coupling plane of the diffractive waveguide. However, due to alignment errors, the exit pupil position of the optomechanical system and the coupling plane of the diffractive waveguide cannot be perfectly aligned, causing the optomechanical system to deviate from its initially designed working distance. This results in reduced coupling efficiency, which directly affects brightness and significantly limits the improvement of uniformity. To address this issue, this application also provides a coupling design method for a diffractive waveguide, used to design the coupling region of the diffractive waveguide provided in the aforementioned embodiments. This coupling design method specifically includes:

[0110] S100, acquire the pupil size of the optical engine, the first field of view in the first direction, the second field of view in the second direction, and the assembly error threshold of the working distance of the optical engine.

[0111] The optical engine is used to project light carrying image information within a predetermined field of view. In this application, the optical engine can be of different types, such as uLED, LCOS, DLP, LBS, OLED, etc.

[0112] Specifically, this involves obtaining the field of view in two different directions. One of these directions is referred to as the first direction below, and the field of view in that direction is the first field of view. The other direction is referred to as the second direction below, and the field of view in that direction is the second field of view.

[0113] In augmented reality display systems, the virtual display screen is generally a two-dimensional image. The field of view of a two-dimensional image typically includes a vertical field of view, a horizontal field of view, and a diagonal field of view. In this application, to better design the coupling region and maximize the reception of light from all fields of view, optimization is performed according to the diagonal field of view. For example, the first field of view in the first direction is one of the diagonal field of view ranges, and the second field of view in the second direction is the other diagonal field of view range. In particular, when the vertical and horizontal field of view angles are the same size, the first and second directions are orthogonal.

[0114] The assembly error threshold for the working distance of an optomechanical system refers to the critical value of the error between the actual working distance of the optomechanical system and the preset working distance when assembling the optomechanical system and the diffractive waveguide into a module. Here, the value of the assembly error threshold can be the maximum allowable distance between the exit pupil position of the optomechanical system and the coupling plane.

[0115] S200, the basic region of the coupling region is a circular area with the pupil size as its diameter.

[0116] Based on the current assembly viewpoint, the exit pupil position of the optical engine is aligned with the coupling plane of the diffractive waveguide. In this application, the circular region formed with the pupil size as the diameter is used as the basic region for the coupling region.

[0117] S301, based on the first field of view and the assembly error threshold, determine the first deviation distance of the base region in the positive direction of the first direction and the second deviation distance in the negative direction of the first direction.

[0118] S302, based on the second field of view and the assembly error threshold, determine the third deviation distance of the base region in the positive direction of the second direction and the fourth deviation distance in the negative direction of the second direction.

[0119] There is no fixed order between steps S301 and S302.

[0120] In practice, the field of view angle in the positive direction of the first direction within the first field of view is: The field of view in the negative direction of the first direction is The field of view angle in the positive direction of the second direction within the second field of view is... The field of view in the positive direction of the first direction is The first deviation distance is The second deviation distance is The third deviation distance is The fourth deviation distance is , This is the assembly error threshold.

[0121] Specifically, let's take the example where both the field of view in the first direction and the field of view in the second direction are diagonal field of view. Since the two diagonal field of view are the same, when the optical axis of the optical engine is perpendicular to the coupling plane, the field of view angles in the positive direction of the first direction, the negative direction of the first direction, the positive direction of the second direction, and the negative direction of the second direction are all the same, and all are half-diagonal field of view angles. However, when the optical axis of the optical engine is not perpendicular to the coupling plane, the field of view angles in the four directions will be different, requiring corresponding conversion based on the tilt direction and tilt angle of the optical axis. It should be noted that the field of view angle here refers to the size of the angle formed by the corresponding field of view.

[0122] For example, referring to FIG16, a circular region with the pupil size as its diameter is first used as the base region 610 of the coupling region. Then, based on the first field of view and the assembly error threshold, the first deviation distance of the base region 610 of the coupling region in the positive direction of one of the diagonal directions is determined. The second offset distance of the base region 610 of the coupling region in the negative direction of one of the diagonal directions. Based on the second field of view and the assembly error threshold, the third deviation distance of the base region 610 of the coupling region in the positive direction of another diagonal direction is determined. The fourth offset distance of the base region 610 of the coupling region in the negative direction of another diagonal direction. .

[0123] S400, the base region is deviated from the base region by a first deviation distance, a second deviation distance, a third deviation distance, and a fourth deviation distance in the positive and negative directions of the first direction and the positive and negative directions of the second direction, respectively, to obtain auxiliary regions of four coupled regions.

[0124] For example, continuing to refer to FIG16, in this embodiment, the base region 610 of the coupling region is offset by a first deviation distance in the positive direction of one of the diagonal directions. The first auxiliary region 621 is obtained; the second offset distance of the base region 610 of the coupled region in the negative direction of one of the diagonal directions is obtained. The second auxiliary region 622 is obtained; the third offset distance of the base region 610 of the coupled region in the positive direction of another diagonal direction is obtained. The third auxiliary region 623 is obtained; the fourth offset distance of the base region 610 of the coupled region is in the negative direction of another diagonal direction. The fourth auxiliary region 624 is obtained.

[0125] S600, the region formed by the outer contours of the four auxiliary regions is the actual region of the coupling region.

[0126] For example, continuing to refer to FIG16, in this embodiment, an external tangent contour is formed by using the outer vertices of the first auxiliary region 621, the second auxiliary region 622, the third auxiliary region 623, and the fourth auxiliary region 624 as tangent points, and the area enclosed by the external tangent contour is the actual region 630 of the coupling region. The external tangent contour can be, for example, a rounded quadrilateral, with the rounded corner radius being consistent with the exit pupil radius of the optical engine.

[0127] This application provides a coupling design method for a diffractive optical waveguide. The shape of the coupling region is designed based on the pupil size, field of view, and assembly error threshold of the optical engine's working distance. On the basis of the base region that matches the pupil size, auxiliary regions compatible with the assembly error threshold are determined in four directions of the coupling plane according to the corresponding field of view. The area formed by the outer contours of the four auxiliary regions is then used as the actual area of ​​the coupling region, so as to receive light from the full field of view emitted by the optical engine. This can improve the coupling efficiency caused by alignment errors and effectively improve the coupling efficiency.

[0128] Furthermore, the coupling design method for diffractive waveguides provided in this application also includes:

[0129] S501, for the first auxiliary region obtained by deviating the base region from the positive direction of the first direction by a first deviation distance, design a diffraction structure in the non-overlapping region of the first auxiliary region and the base region to optimize the efficiency of the field rays in the positive direction of the first direction within the first field of view.

[0130] S502, for the second auxiliary region obtained by deviating the base region from the negative direction of the first direction by a second deviation distance, design a diffraction structure in the non-overlapping region of the second auxiliary region and the base region to optimize the efficiency of the field rays in the negative direction of the first field of view within the first field of view.

[0131] S503, for the third auxiliary region obtained by deviating the base region from the positive direction of the second direction by a third deviation distance, design a diffraction structure in the non-overlapping region of the third auxiliary region and the base region to optimize the efficiency of the field rays in the positive direction of the first direction within the second field of view.

[0132] S504, for the fourth auxiliary region obtained by deviating the base region from the fourth deviation distance in the negative direction of the second direction, design the diffraction structure in the non-overlapping region of the fourth auxiliary region and the base region to optimize the efficiency of the field rays in the negative direction of the second direction within the second field of view.

[0133] The order of steps S501, S502, S503, and S504 is not fixed. It can be understood that the areas where the auxiliary regions do not overlap with the base region separate the light-affected areas of different fields of view, allowing for targeted modulation based on the corresponding field of view. For example, the non-overlapping area between the first auxiliary region and the base region separates the light-affected area of ​​the positive direction of the horizontal field of view's edge, where the diffraction structure can be optimized to meet the efficiency requirements of the light rays in the positive direction of the horizontal field of view's edge. Similarly, the non-overlapping area between the fourth auxiliary region and the base region separates the light-affected area of ​​the negative direction of the vertical field of view's edge, where the diffraction structure can be optimized to meet the efficiency requirements of the light rays in the negative direction of the vertical field of view's edge.

[0134] In practice, among the first, second, third, and fourth auxiliary regions, the diffraction efficiency in the auxiliary region where the direction deviating from the base region matches the direction of light transmission is lower than the diffraction efficiency in the auxiliary region where the direction deviating from the base region does not match the direction of light transmission.

[0135] Specifically, since light rays will be re-intruded into the coupling region during transmission, causing losses, and the light rays incident in the auxiliary region whose direction deviates from the base region and does not match the light transmission direction travel a farther distance and suffer greater losses compared to the light rays incident in the auxiliary region whose direction deviates from the base region and matches the light transmission direction, the diffraction efficiency in the auxiliary region whose direction deviates from the base region and matches the light transmission direction is designed to be lower than that in the auxiliary region whose direction deviates from the base region and does not match the light transmission direction, in order to improve the uniformity of the field of view of the coupling.

[0136] In the above embodiments, the areas where the auxiliary regions do not overlap with the basic regions are separated into light action areas of different fields of view. In this way, the non-overlapping parts can be independently divided into light modulation units corresponding to different fields of view, so as to realize directional control based on a specific field of view and optimize the field of view uniformity performance in light coupling.

[0137] Furthermore, the coupling design method for diffractive waveguides provided in this application also includes:

[0138] S610 calculates the number of interactions between the light ray and the base region of the coupling region based on the incident angle and center wavelength of the light ray, the period and refractive index of the diffraction structure, and the thickness and refractive index of the waveguide substrate.

[0139] S620 partitions the base region of the coupled region according to the number of times it is applied.

[0140] It is understandable that for light rays emitted from different fields of view from the optomechanical system, the number of interactions with the diffraction structure in the coupling region is inconsistent, and the coupling efficiency of the light rays is determined by the diffraction efficiency of multiple interactions. This will lead to a decrease in angular uniformity and affect the uniformity of the subsequently coupled field of view.

[0141] In this embodiment, the base region of the coupling region is divided into zones based on the number of interactions between the light rays and the diffraction structure. After zoning, the type and parameters of the diffraction structure within each zone are used as variables for optimization, thereby improving the uniformity and brightness of the light field after light rays from different fields of view pass through the coupling region. During the zoning process, the minimum number of zones is the number of interactions between the central field of view ray and the base region of the coupling region, and the maximum number of zones is the number of interactions between the boundary field of view ray and the base region of the coupling region in the opposite direction of the light transmission direction.

[0142] Implementable, S620, includes:

[0143] S621, by acquiring various light spot maps of the interaction between the light rays and the base region of the coupled region;

[0144] S622, subtract adjacent spot patterns to partition the base region of the coupled region.

[0145] In the above embodiments, the base region of the coupling region is further divided into zones according to the number of times the light interacts with the base region, which can further improve the coupling efficiency, brightness and uniformity.

[0146] In the aforementioned embodiments, the basic region of the coupled region and the outer region of the basic region are partitioned and optimized based on different approaches. S501, S502, S503, and S504 are partition optimizations of the basic region of the coupled region, while S610 and S620 are partition optimizations of the outer region of the basic region. The order of these two optimizations is not limited. This allows for the optimization of field uniformity from different perspectives.

[0147] In some embodiments, when a two-dimensional diffraction structure is provided in the diffraction waveguide, including an input region and an output region, the output uniformity is often difficult to achieve because the light from the two-dimensional pupil cannot cover the corner of the output region near the input region. This application adds turning regions on both sides of the output region, creating two additional optical paths, allowing light to enter the output region from three directions, thus improving output uniformity. Furthermore, the diffraction structure in the input region is specifically designed to meet the diffraction efficiency requirements of the three optical paths.

[0148] In one embodiment, the coupling design method for diffractive waveguides provided in this application further includes:

[0149] S711, determine the shape, size and arrangement period of the diffraction units;

[0150] S712 uses diffraction units arranged in a hexagonal array to fill the actual area of ​​the coupling region;

[0151] S713, for each diffraction unit, the rotation is performed with the angle between the line connecting the center of the diffraction unit and the actual center of the coupled region and the horizontal direction as the rotation angle;

[0152] S714 divides the actual region of the coupling region into two parts in the direction of light transmission, and replaces the diffraction structure in the part away from the direction of light transmission with the diffraction structure in the part close to the direction of light transmission.

[0153] In practice, the diffraction unit is a rectangular pillar, the length of which ranges from 80 to 200 nm, the width of which ranges from 40 to 200 nm, the height of which ranges from 200 to 400 nm, and the arrangement period of which ranges from 200 to 500 nm.

[0154] For example, the actual region of the coupling region is divided into left and right parts along the light transmission direction. For each diffraction unit in the coupling region, the rotation angle of the diffraction unit is the angle between the line connecting the center of the diffraction unit and the center of the actual region of the coupling region and the horizontal direction. The long side of the rotated diffraction unit is orthogonal to one of the diffraction directions. When the left half of the coupling region is close to the coupling region, the left half of the coupling region is copied to the right half of the coupling region to improve the diffraction efficiency of the diffraction orders propagating to the right by using the diffraction efficiency of each order of the newly allocated diffraction structure; when the right half of the coupling region is close to the coupling region, the right half of the coupling region is copied to the left half of the coupling region to improve the diffraction efficiency of the diffraction orders propagating to the left by using the diffraction efficiency of each order of the newly allocated diffraction structure.

[0155] In another embodiment, the coupling design method for the diffractive waveguide provided in this application further includes:

[0156] S721, determine the shape, size and arrangement period of the diffraction unit, and the shape and size of the basic functional unit;

[0157] S722 uses diffraction elements arranged in a hexagonal array to fill the basic functional units;

[0158] S723, for each diffraction unit, the rotation is performed with the angle between the line connecting the center of the diffraction unit and the center of the basic functional unit and the horizontal direction as the rotation angle;

[0159] S724, in the direction of light transmission, half of the basic functional unit closest to the direction of light transmission is taken as a structural replication unit, and the structural replication unit is used to fill the actual area of ​​the coupling region.

[0160] In practice, the functional replication unit is rectangular in shape, with the size of the rectangle ranging from 30 to 60. The shape and size of the diffraction unit are consistent with those of the aforementioned embodiment.

[0161] For example, referring to Figure 17, this figure illustrates the design of the coupling region under the architecture described above, which adds turning regions on both sides of the coupling region. The basic functional unit 420 is defined as rectangular. Diffraction units 401 are arranged in a hexagonal array to fill the basic functional unit 420. For each diffraction unit in the left half of the coupling region, the rotation angle of the diffraction unit is the angle between the line connecting the center of the diffraction unit and the actual center of the coupling region and the horizontal direction. The long side of the rotated diffraction unit is orthogonal to one of the diffraction directions. In the light transmission direction, half of the basic functional unit 420 closest to the light transmission direction (the right half of the basic functional unit 420) is taken as the structure replication unit 421, which is used to fill the actual region of the coupling region.

[0162] In this embodiment, the computational cost of optimization is reduced by using functional replication units to replicate and fill the coupling region. When designing the shape and size of the basic functional units, since the basic functional units are the targets of optimization, their size should not be too large to avoid losing the advantage of reducing the computational cost of optimization, nor should their size be too small to avoid failing to achieve the purpose of redistributing the diffraction efficiency of each level of the diffraction structure.

[0163] In the above embodiments, combined with the architecture of the diffractive waveguide, the diffraction structure in the actual region of the coupling area is designed to have multiple diffraction orders, and the diffraction efficiency of each order of the diffraction structure is redistributed by the modulation of the diffraction unit, which can further improve the coupling efficiency, brightness and uniformity.

[0164] In summary, after completing the coupling design according to the proposed method for diffractive waveguide coupling, good coupling efficiency can be achieved when assembling the diffractive waveguide with the optomechanical system, within the assembly error threshold of the optomechanical working distance. The coupling plane of the diffractive waveguide can be exactly at the exit pupil position of the optomechanical system, or it can be between the exit position and the exit pupil position, or it can be outside the exit pupil position.

[0165] Preferably, when the coupling plane of the diffractive waveguide is positioned between the exit position and the exit pupil position of the optomechanism, the propagation distance of field rays with relatively small diffraction angles within the coupling region is shortened, further improving the overall coupling efficiency. For example, referring to Figure 18, it can be seen that the coupling plane 601 of the diffractive waveguide 600 is located between the plane 501 of the optomechanism 200 and the exit pupil position 502. The dashed line rays have smaller diffraction angles than the solid line rays. Compared to scenarios where the coupling plane of the diffractive waveguide is exactly at the exit pupil position of the optomechanism, or outside the exit pupil position of the optomechanism, the propagation distance within the coupling region is shorter.

[0166] On the other hand, this application also provides an augmented reality display device, which includes a diffractive waveguide and an optomechanical system as described in any of the foregoing embodiments.

[0167] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit it. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this utility model.

Claims

1. A diffractive optical waveguide, characterized by, The diffractive waveguide includes: A waveguide substrate, wherein a light coupling functional region is provided on the surface of the waveguide substrate; the light coupling functional region includes at least a coupling-in region and a coupling-out region; and auxiliary structures are provided on other regions of the waveguide substrate surface other than the light coupling functional region, wherein the auxiliary structures include a plurality of auxiliary units, and the auxiliary units are used to cause the reflected light rays formed when ambient light is incident on the auxiliary structures to interfere with each other destructively.

2. The diffractive optical waveguide of claim 1, wherein, The auxiliary units in the auxiliary structure are arranged periodically, and the period of the auxiliary structure is less than the grating period of any grating structure in the light coupling functional region; or, the auxiliary units in the auxiliary structure are arranged randomly.

3. The diffractive waveguide according to claim 2, characterized in that, The periodic structures on the waveguide substrate surface satisfy the following: wherein for the wave vector of the image light, a sum of grating vectors of each periodic structure that the image light ray passes through before being coupled out within the light ray coupling function region, for the grating vector of the auxiliary structure, the refractive index of the waveguide substrate, The wavelength of the light rays in the image.

4. The diffractive optical waveguide of claim 2, wherein, The auxiliary unit is a protruding structure, and there are medium gaps between each auxiliary unit. The medium gaps are arranged periodically, and the refractive index of the auxiliary unit is greater than the refractive index of the medium gap.

5. The diffractive optical waveguide of claim 4, wherein, The period of the auxiliary structure is less than the wavelength of ambient light, and the height of the auxiliary unit is in the range of , ] wherein is the wavelength of ambient light, is the refractive index of the waveguide substrate, is the allowable height deviation.

6. The diffractive optical waveguide of claim 5, wherein, The equivalent refractive index of the auxiliary structure The refractive index of the waveguide substrate satisfies the following equation: wherein duty cycle for the auxiliary unit, for the dielectric constant of the auxiliary unit, for the dielectric constant of the medium gap, This represents the allowable refractive index deviation.

7. The diffractive optical waveguide of claim 1, wherein, A coupling grating is provided in the coupling region, and the tooth profile of the coupling grating is helical; the helical tooth angle of the coupling grating is θ, the tooth height is h, and the grating period is p, satisfying the helical tooth relationship: 0.9m*p≤ h*tanθ≤1.1m*p; m is a positive integer greater than or equal to 1.

8. The diffractive optical waveguide of claim 1, wherein, The light coupling functional region further includes a turning region. An insertion grating is disposed within the insertion region, a turning grating is disposed within the turning region, and an output grating is disposed within the output region. The insertion grating is used to couple light rays from the entire field of view into the waveguide substrate. The turning grating includes at least a first turning grating and a second turning grating. The first turning grating is used to deflect light rays from a first field of view towards the output grating, and the second turning grating is used to deflect light rays from a second field of view towards the output grating. The union of the first and second field of view constitutes the complete field of view. The first and second turning gratings are located on different sides of the output grating; or, the first and second turning gratings are located on the same side of the output grating, and are offset from each other.

9. The diffractive optical waveguide of claim 8, wherein, After the light is coupled into the waveguide substrate, it is transmitted by total internal reflection along the first direction. A steering optical element is provided in the optical path along the first direction. The steering optical element is used to deflect the light in the second field of view to the second deflection grating. The light in the first field of view continues to be transmitted along the first direction to the first deflection grating.

10. The diffractive optical waveguide of claim 8, wherein, After the light is coupled into the waveguide substrate, it is transmitted by total internal reflection along a first direction. The first folding grating and the second folding grating are offset from each other in the first direction. The grating vectors of the coupled grating, the first folding grating, and the second folding grating satisfy the following relationship: wherein, for the grating vector of the in-coupling grating, for the grating vector of the first turning grating, for the grating vector of the second turning grating, is the refractive index of the waveguide substrate.

11. The diffractive optical waveguide of claim 1, wherein, The waveguide substrate includes a first surface and a second surface disposed opposite to each other; a first light-absorbing element is disposed on the side between the first surface and the second surface for absorbing image light incident on the side; and a second light-absorbing element is disposed on the first surface and the second surface, at least in the region between the side adjacent to the coupling region and the coupling region, for absorbing image light scattered by the side.

12. The diffractive optical waveguide of claim 11, wherein, Both the first light-absorbing element and the second light-absorbing element are light-absorbing material layers. The light-absorbing material layer covers the side to form the first light-absorbing element, and extends from the edge of the side to at least cover the waveguide substrate surface region adjacent to the coupling region and the coupling region to form the second light-absorbing element.

13. The diffractive optical waveguide of claim 11, wherein, The first light-absorbing element is a light-absorbing material layer, and the second light-absorbing element is a three-layer structure, which includes a first metal cylindrical array layer, a second dielectric tetragonal prism array layer and a third metal layer in sequence along the direction away from the surface of the waveguide substrate.

14. The diffractive optical waveguide of claim 1, wherein, The design method for the coupling region includes the following steps: The assembly error thresholds for the optical engine's pupil size, field of view in two different directions, and working distance are obtained. A circular region with the pupil size as its diameter is used as the base region of the coupling region. Based on the field of view of one of the two directions and the assembly error threshold, a first deviation distance in the positive direction and a second deviation distance in the negative direction of the base region in that one direction are determined. Based on the field of view of the other direction and the assembly error threshold, a third deviation distance in the positive direction and a fourth deviation distance in the negative direction of the other direction are determined. The base region is deviated from the first deviation distance, the second deviation distance, the third deviation distance, and the fourth deviation distance in the positive and negative directions of one direction and the positive and negative directions of the other direction, respectively, to obtain four auxiliary regions of the coupling region. The region formed by the outer contours of the four auxiliary regions is the actual region of the coupling region.

15. The diffractive optical waveguide of claim 14, wherein, The design method for the coupling region further includes the following steps: Determine the shape, size, and arrangement period of the diffraction units; The actual area of ​​the coupling region is filled by arranging the diffraction units in a hexagonal array. For each diffraction unit, the rotation is performed with the angle between the line connecting the center of the diffraction unit and the actual center of the coupled region and the horizontal direction as the rotation angle; The actual region of the coupling area is divided into two parts in the direction of light transmission, and the diffraction structure in the part away from the direction of light transmission is replaced with the diffraction structure in the part close to the direction of light transmission.

16. A diffractive optical waveguide, characterized by include: A waveguide substrate includes at least one coupling grating and one coupling grating; the coupling grating is used to couple image light into the waveguide substrate for total internal reflection transmission, and the coupling grating is used to couple the image light transmitted within the waveguide substrate for total internal reflection to enter the human eye; The tooth profile of the coupling grating is helical; the helical tooth angle of the coupling grating is θ, the tooth height is h, and the grating period is p, satisfying the helical tooth relationship: 0.9m*p≤ h*tanθ≤1.1m*p; m is a positive integer greater than or equal to 1.

17. The diffractive optical waveguide of claim 16, wherein, The surface of the waveguide substrate is provided with a light coupling functional region; the light coupling functional region includes at least a coupling-in region and a coupling-out region; the coupling-in region is provided with the coupling-in grating, the coupling-out region is provided with the coupling-out grating, and the other regions on the surface of the waveguide substrate other than the light coupling functional region are provided with auxiliary structures, the auxiliary structures including a plurality of auxiliary units, the auxiliary units being used to cause the reflected light rays formed when ambient light is incident on the auxiliary structure to interfere with each other destructively.

18. The diffractive optical waveguide of claim 16, wherein, The waveguide substrate includes a first surface and a second surface disposed opposite to each other; a first light-absorbing element is disposed on the side between the first surface and the second surface for absorbing image light incident on the side; and a second light-absorbing element is disposed on the first surface and the second surface, at least in the region between the side adjacent to the coupling region and the coupling region, for absorbing image light scattered by the side.

19. The diffractive optical waveguide of claim 16, wherein, The diffractive waveguide further includes a deflection grating, wherein the coupling grating is used to couple light rays from the complete field of view into the waveguide substrate; the deflection grating includes at least a first deflection grating and a second deflection grating, wherein the first deflection grating is used to deflect light rays from a first field of view toward the coupling grating, and the second deflection grating is used to deflect light rays from a second field of view toward the coupling grating, wherein the union of the first field of view and the second field of view constitutes the complete field of view; wherein the first deflection grating and the second deflection grating are located on different sides of the coupling grating; or, the first deflection grating and the second deflection grating are located on the same side of the coupling grating, and the first deflection grating and the second deflection grating are offset from each other.

20. The diffractive optical waveguide of claim 16, wherein, The design method for the coupling region includes the following steps: The assembly error thresholds for the optical engine's pupil size, field of view in two different directions, and working distance are obtained. A circular region with the pupil size as its diameter is used as the base region for the coupling region. Based on the field of view in the two directions and the assembly error thresholds, four auxiliary regions for the coupling region are obtained. The region formed by the outer contours of the four auxiliary regions is used as the actual region for the coupling region.

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