Diffraction optical waveguide and near-to-eye display equipment

Abstract

The invention provides a diffractive optical waveguide and near-eye display equipment. The diffractive optical waveguide comprises a waveguide substrate, a coupling-in grating and a coupling-out grating group, wherein the coupling-in grating and the coupling-out grating group are arranged on one side surface of the waveguide substrate; the coupling-out grating group comprises at least two coupling-out gratings, and the at least two coupling-out gratings are located on the same side of the waveguide substrate; in the direction away from the coupling-in grating, the at least two coupling-out gratings are sequentially arranged and fixed to the waveguide substrate, and the thickness of the waveguide substrate bearing the coupling-out gratings is gradually reduced. According to the technical scheme, when light is coupled out through different coupling-out gratings, in the area close to the coupling-in grating, the brightness of a single beam of light is high, however, the waveguide substrate is thick, and the number of times of contact between the light and the coupling-out gratings is small; however, in an area far away from the coupling-in grating, the brightness of a single beam of light is weak, but the waveguide substrate is thin, and the contact frequency of the light and the coupling-out grating is large; therefore, the light brightness uniformity of the diffraction optical waveguide coupling-out area can be improved by changing the thickness of the waveguide substrate.

Description

Technical Field

[0001] The present application relates to the technical field of optical devices, and particularly relates to a diffractive optical waveguide and a near-eye display device. Background Art

[0002] Augmented Reality (AR) technology is a technology that combines virtual scenes with the real world. AR devices based on the diffractive optical waveguide solution have advantages such as thin and light finished products, high transmittance, and low mass production costs. Therefore, the diffractive optical waveguide solution is one of the mainstream solutions for AR devices.

[0003] However, for the diffractive optical waveguide in the prior art, when light propagates in the out-coupling grating region, each time the light contacts the out-coupling grating, a part of the energy will leave the waveguide due to diffraction and enter the human eye, and the energy of the light will weaken accordingly. Therefore, the light coupled out at the position on the out-coupling grating that is farther away from the light engine is weaker, which will result in poor light brightness uniformity in the out-coupling region of the diffractive optical waveguide and affect the user experience. Summary of the Invention

[0004] The present application provides a diffractive optical waveguide and a near-eye display device, aiming to improve the light brightness uniformity in the out-coupling region of the diffractive optical waveguide.

[0005] In a first aspect, the present application provides a diffractive optical waveguide, including: a waveguide substrate, an in-coupling grating disposed on one side of the waveguide substrate, and an out-coupling grating group; wherein,

[0006] The out-coupling grating group includes at least two out-coupling gratings, and at least two of the out-coupling gratings are located on the same side of the waveguide substrate;

[0007] Along the direction away from the in-coupling grating, at least two of the out-coupling gratings are arranged in sequence and fixed on the waveguide substrate, and the thickness of the waveguide substrate carrying the out-coupling grating gradually decreases.

[0008] In the above technical solution, when light is coupled out through different out-coupling gratings, in the region closer to the in-coupling grating, the brightness of a single beam of light is stronger, but the waveguide substrate is thicker and the number of times the light contacts the out-coupling grating is less; while in the region farther from the in-coupling grating, the brightness of a single beam of light is weaker, but the waveguide substrate is thinner and the number of times the light contacts the out-coupling grating is more; in this way, the light brightness uniformity in the out-coupling region of the diffractive optical waveguide can be improved by changing the thickness of the waveguide substrate.

[0009] In a possible implementation manner, the waveguide substrate includes a base surface and at least two stepped surfaces oppositely disposed to the base surface;

[0010] Each of the step surfaces is parallel to the base surface, and along the direction away from the coupling grating, the vertical distance between the step surface and the base surface gradually decreases;

[0011] The step surfaces correspond to the coupling gratings one by one;

[0012] Each of the coupling gratings is disposed on one of the step surfaces; alternatively, each of the coupling gratings is disposed on the base surface and opposite to one of the step surfaces.

[0013] In a possible implementation manner, each of the coupling gratings is disposed on one of the step surfaces.

[0014] In a possible implementation manner, along the direction away from the coupling grating, the distance between the nth step surface and the base surface satisfies:

[0015]

[0016] The width of the nth step surface along the direction away from the coupling grating satisfies:

[0017]

[0018] wherein, L0 is the thickness of the waveguide substrate at the coupling grating, h0 is the width of the coupling grating group in the direction away from the coupling grating, Ln is the vertical height between the nth step surface and the (n + 1)th step along the direction away from the coupling grating, hn is the width of the nth step surface along the direction away from the coupling grating, a is the total number of step surfaces; n is a positive integer less than or equal to a.

[0019] In a possible implementation manner, for at least one of the coupling gratings, in the direction away from the coupling grating, the coupling efficiency of the coupling grating gradually increases.

[0020] In a possible implementation manner, the waveguide substrate further includes a stepped surface for connecting two adjacent step surfaces;

[0021] The stepped surface is an extinction surface.

[0022] In a possible implementation manner, the number of the step surfaces is less than or equal to 5.

[0023] In a possible implementation manner, the vertical distance between any one of the step surfaces and the base surface is not less than 1 / 3 of the thickness of the waveguide substrate at the position of the coupling grating.

[0024] In a possible implementation manner, the waveguide substrate further includes a stepped surface for connecting two adjacent step surfaces;

[0025] The stepped surface is a total reflection surface.

[0026] In a second aspect, the present application provides a near-eye display device, including a near-eye display device body and any one of the diffraction optical waveguides as described above provided on the near-eye display device body.

[0027] For the diffraction optical waveguide adopted by the above near-eye display device, when light is coupled out through different output gratings, in the area closer to the input grating, the brightness of a single beam of light is stronger, but the waveguide substrate is thicker and the number of times the light contacts the output grating is less; while in the area farther from the input grating, the brightness of a single beam of light is weaker, but the waveguide substrate is thinner and the number of times the light contacts the output grating is more; in this way, the brightness uniformity of the light in the output area of the diffraction optical waveguide can be improved by changing the thickness of the waveguide substrate. Description of the Drawings

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings required for use in the embodiments will be briefly introduced below. The drawings here are incorporated into the specification and constitute a part of this specification. These drawings show the embodiments that conform to the present disclosure and are used together with the specification to illustrate the technical solutions of the present disclosure. It should be understood that the following drawings only show some embodiments of the present disclosure and should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can also be obtained based on these drawings without creative efforts.

[0029] Figure 1 Overall schematic diagram of the diffraction optical waveguide provided by the present application;

[0030] Figure 2 Schematic diagram of the dimensions of the output grating and the waveguide substrate in the embodiment of the present application;

[0031] Figure 3 Schematic diagram showing that the stepped surface is a total reflection surface in the embodiment of the present application. Detailed Embodiments

[0032] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings.

[0033] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in one or more embodiments of this specification should have the ordinary meaning understood by those of ordinary skill in the art to which this disclosure pertains. The terms "first", "second" and similar terms used in one or more embodiments of this specification do not denote any order, quantity or importance, but are only used to distinguish different components. Words such as "including" or "comprising" mean that the elements or objects appearing before this word cover the elements or objects listed after this word and their equivalents, without excluding other elements or objects. Words such as "connected" or "coupled" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right", etc. are only used to represent relative position relationships, and when the absolute position of the object being described changes, the relative position relationship may also change accordingly.

[0034] To facilitate the understanding of the diffractive optical waveguide provided in the embodiments of the present application, its application scenario will be described first. The diffractive optical waveguide provided in the embodiments of the present application can be applied to near-eye display devices, especially as a part of the display component in near-eye display devices.

[0035] Augmented Reality (AR) technology is a technology that combines virtual scenes with the real world. AR devices based on the diffractive optical waveguide solution have advantages such as thin and light finished products, high transmittance, and low mass production costs. Therefore, the diffractive optical waveguide solution is one of the mainstream solutions for AR devices.

[0036] However, for the diffractive optical waveguides in the prior art, when light propagates in the outcoupling grating region, each time the light contacts the outcoupling grating, a part of the energy will leave the waveguide and enter the human eye due to diffraction, and the energy of the light will weaken accordingly. Therefore, the light coupled out at positions on the outcoupling grating that are farther away from the light engine is weaker, which will result in poor light brightness uniformity in the outcoupling region of the diffractive optical waveguide and affect the user experience.

[0037] Based on this, the present application provides a diffractive optical waveguide and a near-eye display device, aiming to improve the light brightness uniformity in the outcoupling region of the diffractive optical waveguide, thereby enhancing the user experience. The diffractive optical waveguide provided by the present application will be specifically introduced below with reference to the accompanying drawings.

[0038] Refer to Figure 1 , Figure 1 which is the overall schematic diagram of the diffractive optical waveguide provided by the present application. Figure 1The optical path is indicated by a solid line with an arrow in the figure. The diffractive optical waveguide provided by the present application includes a waveguide substrate 3, an input grating 1 provided on one side of the waveguide substrate 3, and an output grating group 2. Among them, the input grating 1 is used to couple light into the waveguide substrate 3. Specifically, the light emitted by the image light source irradiates the input grating 1 and will diffract at the input grating 1 and enter the waveguide substrate 3. At this time, the light that meets the total reflection condition in the waveguide substrate 3 is repeatedly reflected in the waveguide substrate 3, and some light will gradually move away from the input grating 1 and propagate toward the area where the output grating group 2 is located during the reflection process.

[0039] The output grating group 2 includes at least two output gratings 2, and at least two output gratings 2 are located on the same side of the waveguide substrate 3. Each output grating 2 is respectively carried by the waveguide substrate 3. In the direction away from the input grating 1, at least two output gratings 2 are arranged in parallel in sequence and are respectively fixed on the waveguide substrate 3, and the thickness of the waveguide substrate 3 carrying the output grating 2 gradually decreases.

[0040] The position where the output grating 2 is located is the output area of the diffractive optical waveguide. Here, the thickness of the waveguide substrate 3 carrying the output grating 2 gradually decreases, which is for different output gratings 2. That is, for two output gratings 2, the output grating 2 farther from the input grating 1 has a smaller thickness of the waveguide substrate 3 carrying it. Specifically, the number of output gratings 2 can be two, three, four, five or more. The change in the thickness of the waveguide substrate 3 can be achieved by grinding the waveguide substrate 3 and other methods.

[0041] The waveguide substrate 3 has two opposite sides, and the two sides are parallel to each other. When the light entering the waveguide substrate 3 is neither perpendicular nor parallel to the two opposite sides of the waveguide substrate 3, it can be repeatedly reflected in the waveguide substrate 3. If the incident angle of the incident light is biased toward the position where the output grating group 2 is located, the light will gradually propagate toward the direction where the output grating group 2 is located during the repeated reflection process. When the light reaches the area where the output grating group 2 is located, for each beam of light, it will contact the output grating 2 when reflected to the side where the output grating 2 is located. After the light contacts the output grating 2, some light is coupled out through the output grating 2, and some light continues to be totally reflected at the output grating 2 and continues to be repeatedly reflected in the waveguide substrate 3.

[0042] During the propagation of the light, each time it contacts the output grating 2, some light is coupled out of the diffractive optical waveguide, and the brightness of the light will also decrease accordingly. That is, in the area where the output grating 2 is located, as the light gradually moves away from the output grating 2, the brightness of the light in the waveguide substrate 3 will also gradually decrease.

[0043] During the process of the light repeatedly reflecting within the waveguide substrate 3, based on the principle of total internal reflection, the incident angle and the exit angle of the light relative to the side surface of the waveguide substrate 3 will not change. Therefore, within a unit distance in the direction away from the coupling grating 1, the greater the thickness of the waveguide substrate 3, the fewer the number of times the light repeatedly reflects within this unit distance, which means the fewer the number of times the light contacts the output coupling grating 2 within this unit distance. Conversely, the smaller the thickness of the waveguide substrate 3, the more the number of times the light repeatedly reflects within this unit distance, which also means the more the number of times the light contacts the output coupling grating 2.

[0044] In the diffractive optical waveguide provided by this application, the output coupling grating 2 group includes at least two output coupling gratings 2, and in the direction away from the input coupling grating 1, the thickness of the waveguide substrate 3 carrying different output coupling gratings 2 gradually decreases. From the above description, the smaller the thickness of the waveguide substrate 3, the more the number of times the light contacts the output coupling grating 2 within a unit distance. For the output coupling grating 2 closer to the input coupling grating 1, the brightness of the light when it contacts the output coupling grating 2 is higher, the thickness of the waveguide substrate 3 is thicker, and the number of times the light contacts the output coupling grating 2 is fewer; while for the output coupling grating 2 farther from the input coupling grating 1, the brightness of the light when it contacts the output coupling grating 2 is lower, the thickness of the waveguide substrate 3 is thinner, and the number of times the light contacts the output coupling grating 2 is more; during this process, as the light gradually moves away from the input coupling grating 1, the brightness of the light gradually decreases, and at the same time, the number of times the light contacts the output coupling grating 2 is gradually increased, compensating for the decrease in the brightness of a single beam of light with the increased number of output couplings, so as to achieve the purpose of improving the brightness uniformity of the light in the output region of the diffractive optical waveguide, and further enhancing the user experience.

[0045] As an optional implementation manner, when specifically setting the waveguide substrate 3, the waveguide substrate 3 includes a base surface 31 and at least two stepped surfaces 32 oppositely arranged with respect to the base surface 31; each stepped surface 32 is parallel to the base surface 31, and in the direction away from the input coupling grating 1, the vertical distance between the stepped surface 32 and the base surface 31 gradually decreases. From the above, the waveguide substrate 3 has two opposite side surfaces, and the light can repeatedly reflect between the two side surfaces. Here, the base surface 31 is one side surface of the waveguide substrate 3, and the stepped surface 32 is a part of the other side surface of the waveguide substrate 3. That is, when the light repeatedly reflects within the waveguide substrate 3, when the light reaches the stepped surface 32, the light will repeatedly reflect between the stepped surface 32 and the base surface 31.

[0046] These stepped surfaces 32 correspond to the output coupling gratings 2 one by one. When specifically fixing the output coupling gratings 2, each output coupling grating 2 can be arranged on a stepped surface 32; or, each output coupling grating 2 is arranged on the base surface 31 and opposite to a stepped surface 32.

[0047] Here, the output grating 2 is disposed on the base surface 31 and opposite to a stepped surface 32, specifically: each stepped surface 32 has a corresponding area on the base surface 31 opposite to the stepped surface 32, and each output grating 2 is disposed within a corresponding area.

[0048] Whether the output grating 2 is disposed on the stepped surface 32 or on the base surface 31, the step difference of the stepped surface 32 will cause the thickness of the waveguide substrate 3 carrying different output gratings 2 to be different, that is, it can achieve the purpose of changing the number of times the light contacts the output grating 2 per unit distance by changing the thickness of the waveguide substrate 3, thereby improving the brightness uniformity of the light in the output region of the diffractive optical waveguide.

[0049] As an optional implementation manner, when specifically setting the output grating 2, each output grating 2 is disposed on a stepped surface 32. In this setting manner, the step difference of the stepped surface 32 can be used to naturally position each output grating 2, improve the positioning accuracy of the output grating 2, and reduce the assembly difficulty of the output grating 2.

[0050] Refer to Figure 2 , Figure 2 which is a schematic diagram of the dimensions of the output grating and the waveguide substrate in the embodiment of the present application.

[0051] As an optional implementation manner, the width of the output grating 2 and the drop between the stepped surfaces 32 can follow a certain rule. For ease of understanding, it is assumed that there are n output gratings 2 in the output grating group. Correspondingly, the waveguide substrate 3 has n stepped surfaces 32, and each stepped surface 32 corresponds to an output grating 2. These output gratings 2 and stepped surfaces 32 are sequentially named in the direction away from the input grating 1, that is, the output grating 2 closest to the input grating 1 is the first output grating, the corresponding stepped surface 32 is the first stepped surface, the output grating 2 farthest from the input grating 1 is the nth output grating, and the corresponding stepped surface 32 is the nth stepped surface.

[0052] In the direction away from the input grating, the distance between the nth stepped surface and the base surface satisfies:

[0053]

[0054] The width of the nth stepped surface in the direction away from the input grating satisfies:

[0055]

[0056] wherein, L0 is the thickness of the waveguide substrate at the input grating, h0 is the width of each output grating, Ln is the height between the nth stepped surface and the base surface in the direction away from the input grating, hn is the width of the nth stepped surface in the direction away from the input grating, a is the total number of stepped surfaces; n is a positive integer less than or equal to a.

[0057] Through calculation verification and simulation verification, by setting the width of the output grating and the height difference between the stepped surfaces to satisfy the above formula relationship, the brightness of the output light in the entire output region can be made to be at a relatively uniform level, thereby improving the imaging quality of the output light and further enhancing the user experience.

[0058] As an alternative implementation, when specifically setting the output grating 2, for at least one output grating 2, in the direction away from the input grating 1, the output efficiency of the output grating 2 gradually increases. Specifically, to change the output efficiency of the same output grating 2, it can be achieved by controlling various ways such as the change of the grating period, duty cycle, depth, etc. Along the direction away from the input grating 1, as the light propagates in the direction away from the input grating 1, the intensity of the light irradiating the same output grating 2 will gradually decrease. By setting the output efficiency of the output grating 2 to gradually increase, it can at least offset the gradual attenuation of the light intensity to a certain extent, thereby improving the brightness uniformity of the output light on the same output grating 2 and further enhancing the imaging effect of the output light.

[0059] As an alternative implementation, when specifically setting the waveguide substrate 3, the waveguide substrate 3 further includes a stepped surface 33. The stepped surface 33 is used to connect two adjacent stepped surfaces 32, and the stepped surface 33 is an extinction surface. The waveguide substrate 3 provided in the present application forms stepped surfaces 32 parallel to the base surface 31 by using its own thickness difference. At the thickness transition of the waveguide substrate 3, the adjacent two stepped surfaces 32 are connected by the stepped surface 33, that is, each adjacent two stepped surfaces 32 are connected by a stepped surface 33. Optionally, each stepped surface 33 can be set to be perpendicular to the base surface 31. With this setting, there is no gap between two adjacent stepped surfaces 32 in the direction away from the input grating 1, so that the output grating 2 can be tightly connected, avoiding the appearance of bright-dark stripes in the output region.

[0060] For the stepped surface 33, no output grating 2 is provided on the stepped surface 33. When light irradiates the stepped surface 33, if the stepped surface 33 is a transparent surface, the light will be reflected and refracted on the stepped surface 33 to form stray light, which will interfere with the light normally output through the output grating 2 and may interfere with the normal imaging of the output light. By setting the stepped surface 33 as an extinction surface, the influence of stray light on imaging can be reduced, thereby improving the imaging quality of the output light.

[0061] It should be noted that the specific method for treating the stepped surface 33 as an extinction surface is not limited here. In some possible implementation manners, it can be achieved by coating the stepped surface 33, sandblasting the surface, etc.

[0062] During the process that the light is repeatedly reflected in the waveguide substrate 3 and gradually propagates away from the coupling grating 1, after the light irradiates the step surface 32 near the coupling grating 1 in the direction from the base surface 31 to the step surface 32, part of the light will be reflected towards the base surface 31 and propagate away from the coupling grating 1 at the same time. At this time, part of the light will be blocked by the step surface 32 that has undergone extinction treatment, and this part of the blocked light will not be able to reach the next step surface 32 for coupling out. Therefore, it will appear as a black line in the coupling-out area. If the number of black lines is too large or too wide, it will affect the imaging effect of the coupled-out light.

[0063] As an alternative implementation manner, when specifically setting the step surface 32, the number of step surfaces 32 is less than or equal to 5. Specifically, the number of step surfaces 32 can be two, three, four, or five. By controlling the number of step surfaces 32 within a certain range, the number of displayed black lines caused by the light blocking of the step surface 32 can be reduced, thereby reducing the influence of the black lines on imaging.

[0064] As an alternative implementation manner, when specifically setting the step surface 32, the vertical distance between any step surface 32 and the base surface 31 is not less than 1 / 3 of the thickness of the waveguide substrate 3 where the coupling grating 1 is located. Here, the vertical distance between the step surface 32 and the base surface 31 is the thickness of the waveguide substrate 3 at the step surface 32. By controlling the thickness of the waveguide substrate 3 at the step surface 32 to be not less than 1 / 3 of the thickness of the waveguide substrate 3 where the coupling grating 1 is located, the thickness difference between two adjacent step surfaces 32 can be reduced, that is, the width of the stepped surface 33 between two adjacent step surfaces 32 can be reduced, and further the light-blocking area of the stepped surface 33 can be reduced, thereby reducing the width of the displayed black lines caused by the light blocking of the stepped surface 33 and achieving the purpose of improving the imaging effect of the coupled-out light.

[0065] Of course, in addition to setting the stepped surface 33 as an extinction surface, the generation of stray light can also be suppressed by other means. In another possible implementation manner, the stepped surface 33 can be set as a total reflection surface. Refer to Figure 3 , Figure 3 which is a schematic diagram of the stepped surface being a total reflection surface in the embodiment of the present application. As Figure 2 shown, after setting the stepped surface 33 as a total reflection surface, the light irradiating the stepped surface 33 will be irradiated back to the base surface 31. This part of the light can still be repeatedly reflected in the waveguide substrate 3 after irradiating the base surface 31, but it changes from gradually propagating away from the coupling grating 2 to gradually propagating close to the coupling grating 2. When these lights irradiate the coupling grating 2 again, the angle between the light and the coupling grating 2 does not change, and still part of the light can be coupled out and imaged.

[0066] Therefore, by setting the stepped surface 33 as a total reflection surface, the stray light generated by the stepped surface 33 can also be suppressed, thereby improving the imaging quality of the coupled light.

[0067] An embodiment of the present application further provides a near-eye display device, including a near-eye display device body and any one of the diffraction optical waveguides as described above provided on the near-eye display device body.

[0068] For the diffraction optical waveguide adopted by the above near-eye display device, when light is coupled out through different output gratings, in the area closer to the input grating, the brightness of a single beam of light is stronger, but the waveguide substrate is thicker and the number of times the light contacts the output grating is less; while in the area farther from the input grating, the brightness of a single beam of light is weaker, but the waveguide substrate is thinner and the number of times the light contacts the output grating is more; in this way, the brightness uniformity of the light in the output area of the diffraction optical waveguide can be improved by changing the thickness of the waveguide substrate.

[0069] One or more embodiments of this specification are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of one or more embodiments of this specification shall be included within the protection scope of the present disclosure.

[0070] The above is only the specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed in the present application, and all of them should be covered within the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A diffractive optical waveguide, characterized in that, Comprising: A waveguide substrate, an input grating disposed on one side surface of the waveguide substrate, and an output grating group; wherein, The output grating group includes at least two output gratings, and at least two of the output gratings are located on the same side of the waveguide substrate; In a direction away from the input grating, at least two of the output gratings are arranged in sequence and fixed on the waveguide substrate, and the thickness of the waveguide substrate carrying the output gratings gradually decreases.

2. The diffractive optical waveguide according to claim 1, wherein The waveguide substrate includes a base surface and at least two stepped surfaces oppositely disposed to the base surface; Each of the stepped surfaces is parallel to the base surface, and in a direction away from the input grating, the vertical distance between the stepped surface and the base surface gradually decreases; The stepped surfaces correspond to the output gratings one by one; Each of the output gratings is disposed on one of the stepped surfaces; alternatively, each of the output gratings is disposed on the base surface and opposite to one of the stepped surfaces.

3. The diffractive optical waveguide according to claim 2, wherein Each of the output gratings is disposed on one of the stepped surfaces.

4. The diffractive optical waveguide according to claim 2, wherein In a direction away from the input grating, the distance between the nth stepped surface and the base surface satisfies: The width of the nth stepped surface in a direction away from the input grating satisfies: Wherein, L0 is the thickness of the waveguide substrate at the input grating, h0 is the width of the output grating group in a direction away from the input grating, Ln is the vertical height between the nth stepped surface and the (n + 1)th stepped surface in a direction away from the input grating, hn is the width of the nth stepped surface in a direction away from the input grating, a is the total number of stepped surfaces; n is a positive integer less than or equal to a.

5. The diffractive optical waveguide according to claim 2, wherein For at least one of the output gratings, in a direction away from the input grating, the output efficiency of the output grating gradually increases.

6. The diffractive optical waveguide according to any one of claims 2 to 5, characterized in that, The waveguide substrate further includes a stepped surface for connecting two adjacent stepped surfaces; The stepped surface is an extinction surface.

7. The diffractive optical waveguide according to claim 6, characterized in that, The number of the stepped surfaces is less than or equal to 5.

8. The diffractive optical waveguide according to claim 6, characterized in that, The vertical distance between any one of the stepped surfaces and the base surface is not less than 1 / 3 of the thickness of the waveguide substrate at the position of the input grating.

9. The diffractive optical waveguide according to any one of claims 2 to 5, characterized in that, The waveguide substrate further includes a stepped surface for connecting two adjacent stepped surfaces; The stepped surface is a total reflection surface.

10. A near-eye display device, characterized in that, Comprising a near-eye display device body and a diffractive optical waveguide as described in any one of claims 1 to 9 disposed on the near-eye display device body.

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