Diffraction optical waveguide and near-to-eye display equipment

Abstract

The invention provides a diffraction optical waveguide and a near-to-eye display device. The diffraction optical waveguide comprises a waveguide substrate, a coupling-out grating and an air gap. The air gap is clamped between the first total internal reflection surface and the second total internal reflection surface, and certain intervals are respectively formed between the air gap and the first total internal reflection surface and between the air gap and the second total internal reflection surface; in a direction away from the coupling-in grating, an end portion of the air gap facing away from the coupling-in grating is located between opposite ends of the coupling-out grating. According to the diffraction optical waveguide, the air gap is arranged between the first total internal reflection surface and the second total internal reflection surface, and when light is transmitted to the air gap, part of the light passes through the space between the air gap and the second total internal reflection surface and enters the coupling-out grating at the side, away from the coupling-in grating, of the air gap; the attenuation speed of color light with high diffraction efficiency can be slowed down, so that the color uniformity of a coupled-out image of the diffraction optical waveguide is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of near-eye display, in particular to a diffractive optical waveguide and a near-eye display device. BACKGROUND

[0002] The diffractive waveguide is extremely sensitive to wavelength, which results in different diffraction efficiencies of different colors of light for the diffractive waveguide, and finally results in poor color uniformity of the full-color AR (Augmented Reality) device based on the diffractive waveguide. After the image is transmitted and coupled out through the diffractive optical waveguide, the proportion of RGB colors will change, thereby affecting the visual effect. SUMMARY

[0003] The present application provides a diffractive optical waveguide and a near-eye display device, aiming to improve the color uniformity of the coupled-out image of the diffractive optical waveguide.

[0004] In a first aspect, the present application provides a diffractive optical waveguide, comprising: a waveguide substrate, a coupling-out grating, and an air gap; wherein: The waveguide substrate has opposite first and second total internal reflection surfaces, the coupling-out grating is arranged on the side of the waveguide substrate close to the first total internal reflection surface, and the air gap is arranged between the first and second total internal reflection surfaces and has a certain interval with the first and second total internal reflection surfaces respectively; The side of the air gap close to the coupling-out grating is a first reflection surface, and the side of the air gap close to the second total internal reflection surface is a second reflection surface, the first and second reflection surfaces, the first total internal reflection surface, and the second total internal reflection surface are parallel in pairs; The diffractive optical waveguide further comprises a coupling-in grating, and in the direction away from the coupling-in grating, the end of the air gap away from the coupling-in grating is located between the opposite two ends of the coupling-out grating.

[0005] The diffractive optical waveguide in the above technical solution sets the air gap between the first and second total internal reflection surfaces, when the light propagates to the air gap, part of the light passes between the air gap and the second total internal reflection surface and is incident to the coupling-out grating on the side of the air gap away from the coupling-in grating, which can slow down the attenuation speed of the light of the color with higher diffraction efficiency, thereby improving the color uniformity of the coupled-out image of the diffractive optical waveguide.

[0006] In a possible implementation, the number of air gaps is at least one; When the number of air gaps is two or more, the at least two air gaps are arranged in the direction perpendicular to the first total internal reflection surface.

[0007] In a possible implementation, the number of the air gaps is greater than or equal to two; In a possible implementation, the number of the air gaps is greater than or equal to two; In a possible implementation, the number of the air gaps is greater than or equal to two;

[0008] In a possible implementation, each of the air gaps satisfies:

[0009] wherein p is an integer greater than 0, all the air gaps are sequentially arranged as the first air gap, the second air gap, …, and the pth air gap in a direction away from the first total internal reflection surface, is the red light out-coupling light intensity of the out-coupling grating corresponding to the end point of the pth air gap away from the in-coupling grating, is the blue light out-coupling light intensity of the out-coupling grating corresponding to the end point of the pth air gap away from the in-coupling grating, is the initial red light intensity, is the initial blue light intensity, p is the distance between the pth air gap and the second total internal reflection surface, p is the length of the air gap in the first direction, H0 is the thickness of the waveguide substrate in a direction perpendicular to the first total internal reflection surface, r is the diffraction efficiency of the red light passing through the out-coupling grating, b is the diffraction efficiency of the blue light passing through the out-coupling grating, r is the red light wavelength, b is the blue light wavelength, w is the refractive index of the waveguide substrate, and T is the grating period of the out-coupling grating.

[0010] In a possible implementation, the number of the air gaps is greater than or equal to two; In a possible implementation, the number of the air gaps is greater than or equal to two; In a possible implementation, the number of the air gaps is greater than or equal to two;

[0011] In a possible implementation, each of the air gaps satisfies:

[0012] wherein: p is an integer greater than 0, all air gaps are arranged in order as the 1st, 2nd, …, pth air gaps along a direction away from the first total internal reflection surface, is a red light out-coupling light intensity of the out-coupling grating corresponding to an end point of the pth air gap away from the in-coupling grating, is a blue light out-coupling light intensity of the out-coupling grating corresponding to the end point of the pth air gap away from the in-coupling grating, is an initial light intensity of the red light, is an initial light intensity of the blue light, p is a distance between the pth air gap and the second total internal reflection surface, p is a length of the air gap in the first direction, H0 is a thickness of the waveguide substrate in a direction perpendicular to the first total internal reflection surface, r is a diffraction efficiency of the red light passing through the out-coupling grating, b is a diffraction efficiency of the blue light passing through the out-coupling grating, r is a wavelength of the red light, b is a wavelength of the blue light, w is a refractive index of the waveguide substrate, and T is a grating period of the out-coupling grating.

[0013] In a possible implementation, each of the air gaps satisfies: a = [r, g, b]; wherein: m is an integer greater than or equal to 1, is a light intensity of the red light after m times of out-coupling, is a light intensity of the green light after m times of out-coupling, is a light intensity of the blue light after m times of out-coupling, g is a wavelength of the blue light, is an initial light intensity of the green light, is a brightness uniformity of the out-coupled light.

[0014] In a possible implementation, along a direction perpendicular to the first total internal reflection surface, a thickness of the air gap is greater than a skin depth of the total internal reflection light in the waveguide substrate, and is less than or equal to 2 microns.

[0015] In a possible implementation, the waveguide substrate includes at least two substrate pieces, and the at least two substrate pieces are arranged in a stack along a direction perpendicular to the first total internal reflection surface. At least one of the substrate pieces has a groove near a side surface of an adjacent substrate piece, and the groove and the adjacent substrate piece enclose the air gap.

[0016] In a second aspect, the present application provides a near-eye display device, comprising a device body, and the diffractive optical waveguide as described above arranged on the device body.

[0017] The diffractive optical waveguide in the near-eye display device described above, by arranging the air gap between the first total internal reflection surface and the second total internal reflection surface, when the light propagates to the air gap, part of the light passes between the air gap and the second total internal reflection surface and is incident to the out-coupling grating on the side of the air gap away from the in-coupling grating, which can slow down the decay rate of light of a color with higher diffraction efficiency, thereby improving the color uniformity of the out-coupled image of the diffractive optical waveguide. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments will be briefly introduced as follows, the drawings herein are incorporated into the specification and form a part of the specification, which show the embodiments consistent with the present application, and are used to illustrate the technical solutions of the present application together with the specification. It should be understood that the following drawings only show certain embodiments of the present application, and therefore should not be regarded as a limitation on the scope, and for those skilled in the art, other related drawings can also be obtained without creative labor.

[0019] Figure 1 A schematic diagram for red light and blue light propagation in the diffractive optical waveguide; Figure 2 A schematic diagram of the diffractive optical waveguide provided by the present application as a whole; Figure 3 A schematic diagram of light attenuation of different colors when no air gap is arranged in the waveguide substrate; Figure 4 A schematic diagram of light attenuation of different colors when one air gap is arranged in the diffractive optical waveguide provided by the present application; Figure 5 One of the schematic diagrams of air gap arrangement in the embodiments of the present application; Figure 6 The second schematic diagram of air gap arrangement in the embodiments of the present application; Figure 7 A schematic diagram of light attenuation of different colors when two air gaps are arranged in the diffractive optical waveguide provided by the present application; Figure 8 One of the schematic diagrams of air gap formation in the embodiments of the present application; Figure 9 The second schematic diagram of air gap formation in the embodiments of the present application. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of the present application more clear, the present application will be further described in detail below with reference to the drawings.

[0021] It should be noted that the technical terms or scientific terms used in the one or more embodiments of the present disclosure should be understood as the general meaning understood by the person skilled in the art to which the present disclosure belongs, unless otherwise defined. The terms "first", "second", and the like used in the one or more embodiments of the present disclosure do not represent any order, quantity, or importance, but are only used to distinguish different components. The terms "include", "contain", and the like mean that the elements or objects before the terms encompass the elements or objects listed after the terms and their equivalents, and do not exclude other elements or objects. The terms "connect" or "connected" and the like are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. The terms "up", "down", "left", "right", and the like are only used to represent relative positional relationships, and when the absolute positions of the described objects change, the relative positional relationships can also change accordingly.

[0022] To facilitate the understanding of the diffraction optical waveguide provided by the embodiments of the present application, the application scenario thereof is first described. The diffraction optical waveguide provided by the embodiments of the present application can be applied to a near-eye display device, and in particular, can be applied to devices such as AR glasses.

[0023] The diffraction waveguide is extremely sensitive to wavelength. One of the reasons why the diffraction waveguide is sensitive to wavelength is that the propagation angles of RGB three-color light in the diffraction optical waveguide are different. This will cause the diffraction waveguide to have different diffraction efficiencies for different colors of light, and ultimately cause the full-color AR (Augmented Reality) device based on the diffraction waveguide to exhibit poor color uniformity. After the image is transmitted and coupled out through the diffraction optical waveguide, the proportion of RGB colors will change, thereby affecting the visual effect.

[0024] Reference Figure 1 , Figure 1 For the propagation diagrams of red light and blue light in the diffraction optical waveguide, in general, the light rays coupled into the diffraction optical waveguide at the same incident angle have the smallest propagation angle when propagating in the waveguide, and the red light has the largest propagation angle. This will cause the blue light to contact the coupling-out grating the most times when coupling out, and the red light the least times, which will cause the blue light to more easily couple out more energy in the front part of the coupling-out grating, and the red light to more easily couple out more energy in the rear part of the coupling-out grating. This characteristic makes it difficult to reconcile the color uniformity.

[0025] Based on this, the present application provides a diffraction optical waveguide, which aims to improve the color uniformity of the coupled-out image of the diffraction optical waveguide. The diffraction optical waveguide provided by the embodiments of the present application will be specifically introduced below with reference to the accompanying drawings.

[0026] Reference Figure 2 , Figure 2A schematic diagram of the diffraction optical waveguide provided by the present application is shown in FIG. 1. For convenience of description, in FIG. 1, the direction perpendicular to the first total internal reflection surface 11 is represented by the X direction, and the direction away from the coupling-out waveguide is represented by the Y direction. Figure 2

[0027] As shown in FIG. 1, the diffraction optical waveguide provided by the present application includes a coupling-in grating (not shown in the figure), a waveguide substrate 1, and a coupling-out grating 2, which is disposed on the waveguide substrate 1. Specifically, the waveguide substrate 1 has opposite first and second total internal reflection surfaces 11 and 12, and the coupling-out grating 2 is disposed on the side of the waveguide substrate 1 close to the first total internal reflection surface 11. After light is coupled into the waveguide substrate 1 by the coupling-in grating of the diffraction optical waveguide, the light repeatedly reflects between the first and second total internal reflection surfaces 11 and 12 and propagates in the direction of the coupling-out grating 2. After the light is incident on the coupling-out grating 2 from the waveguide substrate 1, part of the light is coupled out of the diffraction optical waveguide by the coupling-out grating 2 and forms an image, and part of the light is reflected and propagates in the direction of the second total internal reflection surface 12. Figure 2 Figure 2

[0028] The diffraction optical waveguide provided by the embodiments of the present application further includes an air gap 3, which is sandwiched between the first and second total internal reflection surfaces 11 and 12 and has a certain spacing from both the first and second total internal reflection surfaces. Specifically, the air gap 3 is a hollow space sandwiched between the first and second total internal reflection surfaces 11 and 12. At the position of the air gap 3, the air gap 3 separates the waveguide substrate 1, so that when light propagates to the air gap 3, part of the light repeatedly reflects between the air gap 3 and the first total internal reflection surface 11, and part of the light repeatedly reflects between the air gap 3 and the second total internal reflection surface 12. For convenience of description, the side of the air gap 3 close to the coupling-out grating 2 is a first reflection surface 31, and the side of the air gap 3 close to the second total internal reflection surface 12 is a second reflection surface 32. The first and second reflection surfaces 31 and 32 have similar properties to the total internal reflection surfaces of the waveguide substrate 1, and can totally reflect the light that satisfies the total internal reflection condition in the waveguide substrate 1, so that the light is totally reflected by the first and second reflection surfaces 31 and 32 when it is incident on the first and second reflection surfaces 31 and 32.

[0029] When the air gap 3 is specifically disposed, in the direction away from the coupling-in grating, the end of the air gap 3 away from the coupling-in grating is located between the opposite two ends of the coupling-out grating 2. By thus disposing the air gap 3, when different colors of totally internally reflected light propagates to the air gap 3 in the waveguide substrate 1, the air gap 3 separates the light, part of which passes between the air gap 3 and the first total internal reflection surface 11, and part of which passes between the air gap 3 and the second total internal reflection surface 12. Figure 2 ​​​The light path indicated by the solid line with the middle arrow, the light between the air gap 3 and the first total internal reflection surface 11, will repeatedly reflect and propagate between the first reflection surface 31 and the first total internal reflection surface 11. During the reflection process, part of the light will be incident to the out-coupling grating 2, so that part of the light is coupled out from the out-coupling grating 2 and imaged. Each time the light is incident to the out-coupling grating 2, part of the light is coupled out. The light gradually attenuates during the propagation process away from the in-coupling grating. The light between the air gap 3 and the second total internal reflection surface 12 will repeatedly reflect and propagate between the second reflection surface 32 and the second total internal reflection surface 12. During the propagation process, the light does not pass through the out-coupling grating 2, and it can be approximately considered that the light does not attenuate during the propagation process away from the in-coupling grating.

[0030] Reference is made to Figure 3 and Figure 4 , Figure 3 FIG. 4 is a schematic diagram of the attenuation of light of different colors when no air gap 3 is provided in the waveguide substrate 1. Figure 4 FIG. 5 is a schematic diagram of the attenuation of light of different colors when the diffractive optical waveguide provided by the present application is provided with an air gap 3. Figure 3 and Figure 4 FIG. 6 schematically shows the attenuation process of red, green and blue light; wherein the horizontal coordinate distance refers to the distance between a point on the out-coupling grating 2 away from the in-coupling grating and the end of the out-coupling grating 2 close to the in-coupling grating, that is, the distance of the light passing through the out-coupling grating 2 away from the in-coupling grating; the vertical coordinate is the light intensity of the out-coupled light.

[0031] Taking blue light and red light as examples, as Figure 3 schematically shown, the blue light attenuates faster during the propagation process away from the in-coupling grating, while the red light attenuates slower. When no air gap 3 is provided in the waveguide substrate 1, the farther the light is incident to the in-coupling grating, the greater the light intensity difference between the blue light and the red light of the out-coupled light. This color difference will make the color of the out-coupled image uneven, affecting the viewing experience. After the air gap 3 is provided in the waveguide substrate 1, as Figure 4 schematically shown, the air gap 3 separates the light, and only the light between the air gap 3 and the first total internal reflection surface 11 is coupled out on the side of the out-coupling grating 2 close to the in-coupling grating. At this time, only part of the light gradually attenuates. After the light passes through the air gap 3, the light between the air gap 3 and the second total internal reflection surface 12, which is approximately non-attenuated light, is incident to the out-coupling grating 2, supplementing the energy of the attenuated blue light and red light. It is not difficult to understand that the attenuation of the light passing through the out-coupling grating 2 is exponential attenuation, while the supplement of the energy of the blue light and the red light after passing through the air gap 3 is multiple supplement. After such energy supplement, the proportion difference between the light intensity of the blue light and the red light is reduced, which can improve the proportion difference of the light intensity of the red light and the blue light in the same out-coupled area, thereby improving the color uniformity of the waveguide out-coupled image.

[0032] It is worth mentioning that, here deviates from the direction of the coupling-in grating, that is, the direction of the light propagating gradually toward the coupling-out grating 2 by the coupling-in grating in the process of repeatedly performing total internal reflection of the light in the waveguide substrate 1.

[0033] In addition, when the air gap 3 is specifically arranged, the first reflection surface 31, the second reflection surface 32, the first total internal reflection surface 11, and the second total internal reflection surface 12 are parallel in pairs. In this way, when the total internal reflection light satisfying the total internal reflection condition in the waveguide substrate 1 is irradiated to the first reflection surface 31 and the second reflection surface 32, the reflection of the light through the first reflection surface 31 and the second reflection surface 32 does not change the incident angle of the light incident to the first total internal reflection surface 11 and the second total internal reflection surface 12 again, so that the risk of affecting the normal field coupling-out of the light from the coupling-out grating 2 due to the reflection of the first reflection surface 31 and the second reflection surface 32 can be reduced.

[0034] In summary, the diffractive optical waveguide provided by the present application can slow down the decay speed of the light of the color with higher diffraction efficiency when the light propagates to the air gap 3, so that the color uniformity of the coupled-out image of the diffractive optical waveguide is improved.

[0035] Reference is made to Figure 5 and Figure 6 , Figure 5 Fig. 1 is a schematic diagram of the arrangement of the air gap 3 in an embodiment of the present application, Figure 6 Fig. 2 is a schematic diagram of the arrangement of the air gap 3 in another embodiment of the present application.

[0036] As an optional implementation, when the air gap 3 is specifically arranged, the number of the air gap 3 is at least one, that is, the number of the air gap 3 can be one, two, three, four, five, or more. When the number of the air gap 3 is two or more, at least two air gaps 3 are arranged in a direction perpendicular to the first total internal reflection surface 11. When two or more air gaps 3 are specifically arranged, the end of the two or more air gaps 3 close to the coupling-in grating can be arranged in alignment as shown in Figure 5 , the end of the two or more air gaps 3 away from the coupling-in grating can be arranged in sequence in a direction away from the first total internal reflection surface 11, and the length of the air gap 3 gradually increases; or as shown in Figure 6 , the air gap 3 closest to the first total internal reflection surface 11 is aligned with the end of the coupling-out grating 2 close to the coupling-in grating, and then arranged in alignment from head to tail in the direction of the second total internal reflection surface 12; of course, in addition to Figure 5 or Figure 6In other possible embodiments, two or more air gaps 3 can be arranged in a partially overlapping staggered manner, etc.

[0037] When the number of air gaps 3 is one, one air gap 3 separates the light into two parts, and when two air gaps 3 are arranged, the two air gaps 3 separate the light into three parts, and so on. The more air gaps 3, the more parts the air gaps 3 can separate the light into. The more parts the light is separated into, the more levels of energy the light is separated into, and the less different the light intensity proportions of different lights can be, thereby further improving the color uniformity of the out-coupled image of the diffractive optical waveguide.

[0038] As an optional embodiment, the number of air gaps 3 is greater than or equal to two. In a specific arrangement of these air gaps 3, along the direction away from the in-coupling grating, the end point of each air gap 3 on the side close to the in-coupling grating is aligned with the end point of the out-coupling grating 2 on the side close to the in-coupling grating; and for any two air gaps 3, along the direction perpendicular to the first total internal reflection surface 11, the length of the air gap 3 away from the first total internal reflection surface 11 is greater than the length of the air gap 3 close to the first total internal reflection surface 11. That is, the end of all air gaps 3 close to the in-coupling grating is aligned with the end point of the out-coupling grating on the side close to the in-coupling grating, and the lengths of all air gaps 3 arranged along the direction away from the first total internal reflection surface 11 increase in turn.

[0039] In this way, P air gaps 3 separate the space between the first total internal reflection surface 11 and the second total internal reflection surface 12 into P+1 channels, and the light is separated into P+1 parts and propagates in the P+1 channels when it reaches the position of the air gap 3; the light between the first air gap 3 and the first total internal reflection surface 11 is gradually out-coupled through the out-coupling grating 2; after the light propagates to the end of the first air gap 3 away from the in-coupling grating, the light between the first air gap 3 and the second air gap 3 is supplemented to the remaining light between the first air gap 3 and the first total internal reflection surface 11; and so on, after the light propagates to the end of each air gap 3 away from the in-coupling grating, the light below the air gap 3 is supplemented.

[0040] Optionally, in the arrangement in which the end point of each air gap 3 on the side close to the in-coupling grating is aligned with the end point of the out-coupling grating 2 on the side close to the in-coupling grating, each air gap 3 can satisfy Formula One: ; wherein p is an integer greater than 0, all air gaps 3 are arranged in turn as the first air gap, the second air gap, …, the pth air gap 3 along the direction away from the first total internal reflection surface 11, is the red out-coupled light intensity of the out-coupling grating 2 corresponding to the end point of the pth air gap 3 on the side away from the in-coupling grating, the blue light out-coupling light intensity of the corresponding out-coupling grating 2 at the end point of the pth air gap 3 away from the in-coupling grating, the red light initial light intensity, the blue light initial light intensity, Hp is the distance between the pth air gap 3 and the second total internal reflection surface 12, sp is the length of the air gap 3 in the first direction, H0 is the thickness of the waveguide substrate 1 in the direction perpendicular to the first total internal reflection surface 11, ηr is the diffraction efficiency of the red light through the out-coupling grating 2, ηb is the diffraction efficiency of the blue light through the out-coupling grating 2, λr is the red light wavelength, λb is the blue light wavelength, nw is the refractive index of the waveguide substrate 1, and T is the grating period of the out-coupling grating 2.

[0041] According to the optical principle, the red, green and blue light out-coupling period lengths are respectively: a = [r, g, b]; When the light ray reaches the out-coupling grating 2 for the mth time, the light ray with the wavelength λa is located at the position of away from the end of the out-coupling grating 2 close to the in-coupling grating, and at this time, the light intensity of the out-coupling light ray is: a = [r, g, b]; When the light ray is transmitted for a distance s, the out-coupling times of the point s closest to the point s behind the point s are Therefore, the light intensity of the out-coupling light ray can be expressed as: a = [r, g, b]; For the 1st air gap 3a pointing from the first total internal reflection surface 11 to the second total internal reflection surface 12, the initial light intensity of the light ray between the 1st air gap 3a and the first total internal reflection surface 11 is: a = [r, g, b]; Therefore, the light intensity of the out-coupling light ray of the corresponding out-coupling grating 2 at the end point of the 1st air gap 3a away from the in-coupling grating is:

[0042] It is worth noting that here is the light intensity of the last light out-coupled between the first air gap 3a and the first total internal reflection surface 11. Since the light reflection has a certain period, microscopically, the last light out-coupled is incident to the out-coupling grating 2 at the end point of the first air gap 3a on the side away from the in-coupling grating. However, since the period of light reflection is much smaller than the length of the out-coupling grating 2, for the convenience of calculation, the light intensity of the last light out-coupled between the first air gap 3a and the first total internal reflection surface 11 is directly approximated to the light out-coupling intensity of the out-coupling grating 2 at the end point of the first air gap 3a on the side away from the in-coupling grating. Similarly, for the convenience of calculation, the approximation condition is continued when calculating other air gaps 3.

[0043] After the light passes through the first air gap 3a, the light between the first air gap 3a and the second air gap 3b is supplemented and participates in the out-coupling. The light intensity of the supplemented light is , so the light out-coupling intensity of the out-coupling grating 2 at the end point of the second air gap 3b on the side away from the in-coupling grating is: a = [r, g, b]; Similarly, the light out-coupling intensity of the out-coupling grating 2 at the end point of the pth air gap 3 on the side away from the in-coupling grating is:

[0044] For the out-coupling light waveguide, if the out-coupling light intensity of the red light and the blue light with the largest wavelength difference among the three colors of light is equal at the end point of the last air gap 3 on the side away from the in-coupling grating, the corresponding out-coupling grating 2, a better color uniformity effect can be obtained, that is, by adjusting the number, length of the air gap 3 and the initial light intensity of the three colors of light, the light intensity of the out-coupled light can satisfy formula one, and the color uniformity of the out-coupled image of the diffraction light waveguide can be further improved.

[0045] As an optional implementation, when the air gap 3 is specifically arranged, the number of the air gap 3 is greater than or equal to two, and as shown in Figure 6 , the end point of the air gap 3 adjacent to the first total internal reflection surface 11 on the side close to the in-coupling grating is aligned with the end point of the out-coupling grating 2 on the side close to the in-coupling grating in the direction away from the in-coupling grating; in the direction of the first total internal reflection surface 11 pointing to the second total internal reflection surface 12, the end point of each air gap 3 on the side close to the in-coupling grating is aligned with the end point of the last air gap 3 on the side close to the in-coupling grating.

[0046] In this way, the P air gaps 3 also divide the space between the first total internal reflection surface 11 and the second total internal reflection surface 12 into P+1 channels, but the light is first divided into two parts when reaching the position of the first air gap 3, one part propagates between the first air gap 3 and the first total internal reflection surface 11, and the other part propagates between the first air gap 3 and the second total internal reflection surface 12; when the light passes through the end point of the first air gap 3 on the side away from the coupling-in grating, the light between the first air gap 3 and the second total internal reflection surface 12 is again divided into two parts, one part is supplemented to the remaining light between the first air gap 3 and the first total internal reflection surface 11, and the other part propagates between the second air gap 3 and the second total internal reflection surface 12; and so on, so that the light is supplemented by the light below the air gap 3 after propagating to the end of the air gap 3 away from the coupling-in grating.

[0047] Optionally, in the arrangement mode in which the end point of each air gap 3 on the side close to the coupling-in grating is aligned with the end point of the previous air gap 3 on the side close to the coupling-in grating, each air gap 3 can be arranged to satisfy formula two:

[0048] Wherein: p is an integer greater than 0, all air gaps 3 are arranged in the first, second, …, and pth air gaps 3 in the direction away from the first total internal reflection surface 11, The red light coupling-out light intensity of the coupling-out grating 2 corresponding to the end point of the pth air gap 3 on the side away from the coupling-in grating, The blue light coupling-out light intensity of the coupling-out grating 2 corresponding to the end point of the pth air gap 3 on the side away from the coupling-in grating, The initial red light intensity, The initial blue light intensity, p The distance between the pth air gap 3 and the second total internal reflection surface 12, p The length of the air gap 3 in the first direction, H0 is the thickness of the waveguide substrate 1 in the direction perpendicular to the first total internal reflection surface 11, r The diffraction efficiency of red light passing through the coupling-out grating 2, b The diffraction efficiency of blue light passing through the coupling-out grating 2, r The wavelength of red light, b The wavelength of blue light, w The refractive index of the waveguide substrate 1, and T is the grating period of the coupling-out grating 2.

[0049] Referring to the derivation process of formula one described above, the difference between the two air gap 3 arrangement modes is that, in the arrangement mode in which the end point of each air gap 3 on the side close to the coupling-in grating is aligned with the end point of the previous air gap 3 on the side close to the coupling-in grating, the energy supplemented after each air gap 3 ends is and the transmission distance of each air gap 3 is s p The two differences are brought into the derivation process of formula one, and formula two is obtained. By adjusting the number, length of air gap 3 and the initial light intensity of three-color light, the light intensity of the out-coupled light can meet formula two, and the color uniformity of the out-coupled image of the diffractive optical waveguide can be further improved.

[0050] As an optional implementation, when the air gap 3 is specifically set, each air gap 3 can also be set to meet formula three: a = [r, g, b]; wherein m is an integer greater than or equal to 1, is the light intensity of red light after m times of out-coupling, is the light intensity of green light after m times of out-coupling, is the light intensity of blue light after m times of out-coupling, λ g is the wavelength of blue light, is the initial light intensity of green light, is the brightness uniformity of the out-coupled light.

[0051] Referring to the derivation process of formula one, the light intensity of three-color light after m times of out-coupling is

[0052] In the light intensity formula, satisfies: a = [r, g, b]; In specific implementation, the numerical value of color uniformity can be set according to actual needs, for example, it can be set to 85%, 90%, 95%, etc. By setting the air gap 3 to meet formula three, the overall brightness uniformity of the out-coupled image of the diffractive optical waveguide can be improved, and thus the display effect of the diffractive optical waveguide can be further improved.

[0053] For reference Figure 3 , Figure 4 and Figure 7 , Figure 7The attenuation of different color light rays is shown in the diffraction optical waveguide provided in the present application with two air gaps 3. As a specific example, in a simulation experiment, the red light wavelength is 625 nm, the green light wavelength is 550 nm, the blue light center wavelength is 450 nm, the red light, green light, and blue light coupling-out efficiency is set to 5%, the energy of the red light, green light, and blue light entering the coupling-in grating is the same, the grating period is 370 nm, the waveguide thickness is 0.7 mm, the incident light is 0°, and the total length of the coupling-out grating 2 is 24 mm. It should be noted that the coupling-out efficiency of the red light, green light, and blue light here refers to the energy of different color light rays coupled out each time when the light rays are incident to the coupling-out grating 2, which is a microscopic concept, and should be distinguished from the macroscopic concept of the diffraction efficiency of different color light described above.

[0054] When no air gap 3 is provided, the red light, green light, and blue light coupling-out energy attenuation is shown in FIG. 6, and the brightness uniformity of the red light, green light, and blue light is 56.8%, 44%, and 30.8%, respectively. Figure 3

[0055] After adding an air gap 3 with a length of 10 mm and a distance of 120.25 mm from the second total internal reflection surface, the red light, green light, and blue light coupling-out energy and distance relationship is shown in FIG. 7, and the brightness uniformity of the red light, green light, and blue light is increased to 58%, 54.6%, and 48.6%, respectively. Figure 4

[0056] After adding an air gap 3 with a length of 5.5 mm and a distance of 120.32 mm from the second total internal reflection surface, and adding an air gap 3 with a length of 8 mm and a distance of 120.15 mm from the second total internal reflection surface, the red light, green light, and blue light coupling-out energy and distance relationship is shown in FIG. 8, and the color uniformity of the blue light can be improved to 54.8%. Figure 4

[0057] Therefore, the simulation implementation can verify that the color uniformity of the diffraction optical waveguide coupling-out image can be greatly improved by providing the air gap 3 in the waveguide substrate 1.

[0058] As an optional implementation, when the air gap 3 is specifically provided, the thickness of the air gap 3 in the direction perpendicular to the first total internal reflection surface 11 is greater than the skin depth of the total internal reflection light in the waveguide substrate 1, and is less than or equal to 2 microns.

[0059] ​​​Specifically, the skin depth of the light refers to the depth of the light reaching into the object from the surface of the object, and the skin depth is related to the material of the irradiated surface, the wavelength of the light, etc. The skin depth of the RGB three-color light for imaging is usually between 10 nanometers and several hundred nanometers when the light is irradiated to the first reflecting surface 31 or the second reflecting surface 32. By setting the thickness of the air gap 3 to be greater than the skin depth of the totally internally reflected light in the waveguide substrate 1, the light irradiated to the first reflecting surface 31 can be prevented from being transmitted to the second reflecting surface 32, or the light irradiated to the second reflecting surface 32 can be prevented from being transmitted to the first reflecting surface 31, when the thickness of the air gap 3 is too thin. If the thickness of the air gap 3 is too thick, the side surface of the air gap 3 connecting the first reflecting surface 31 and the second reflecting surface 32 will also reflect more light, thereby increasing the stray light in the waveguide substrate 1. By setting the thickness of the air gap 3 to be greater than the skin depth of the totally internally reflected light in the waveguide substrate 1 and less than or equal to 2 microns, the light can be prevented from penetrating the first reflecting surface 31 and the second reflecting surface 32 at the same time, and the stray light in the waveguide substrate 1 can be controlled at a low level at the same time.

[0060] Reference is made to Figure 8 and Figure 9 , Figure 8 Fig. 1 is a schematic diagram of the air gap 3 in an embodiment of the present application, Figure 9 Fig. 2 is another schematic diagram of the air gap 3 in an embodiment of the present application.

[0061] As an optional embodiment, when the diffraction optical waveguide is specifically set, the waveguide substrate 1 includes at least two substrate pieces 13, and the at least two substrate pieces 13 are stacked along a direction perpendicular to the first totally internally reflecting surface 11. The side surface of at least one substrate piece 13 close to the adjacent substrate piece 13 has a groove, and the groove and the adjacent substrate piece 13 enclose the air gap 3.

[0062] Specifically, when only one air gap 3 is arranged in the waveguide substrate 1, the waveguide substrate 1 can be made of only two substrate pieces 13. When the waveguide substrate 1 is specifically prepared, only one of the two substrate pieces 13 can be provided with a groove, or both of the two substrate pieces 13 can be provided with grooves. When two air gaps 3 are arranged in the waveguide substrate 1, three substrate pieces 13 can be used to make the waveguide substrate 1, and one air gap 3 is formed between each two substrate pieces 13. In other optional embodiments, the two substrate pieces 13 can also be arranged in a stepped shape that can engage with each other, and one air gap 3 is formed between the two pairs of stepped surfaces of the two substrate pieces 13 that are in contact with each other. By analogy, when the waveguide substrate 1 has more air gaps 3, two substrate pieces 13 or multiple substrate pieces 13 can be stacked to form all the air gaps 3.

[0063] The air gap 3 is formed by stacking two or more substrate pieces 13. This has the characteristics of simple preparation and being conducive to production.

[0064] The embodiment of the present application also provides a near-eye display device, comprising a device body and the above-mentioned diffractive optical waveguide arranged on the device body.

[0065] The diffractive optical waveguide in the above-mentioned near-eye display device can slow down the attenuation speed of light of a color with high diffraction efficiency by arranging an air gap between the first total internal reflection surface and the second total internal reflection surface, so that part of the light passes between the air gap and the second total internal reflection surface and is incident on the out-coupling grating on the side of the air gap away from the in-coupling grating, thereby improving the color uniformity of the out-coupled image of the diffractive optical waveguide.

[0066] One or more embodiments of the present specification are intended to cover all such alternatives, modifications and variations that fall within the broad scope of the appended claims. Therefore, any omission, modification, equivalent replacement, improvement, etc. made in the spirit and principle of one or more embodiments of the present specification should be included in the protection scope of the present disclosure.

[0067] The above is merely specific implementation of the present application, but the protection scope of the present application is not limited to this, any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A diffractive optical waveguide, characterized in that, include: Waveguide substrate, coupling grating, and air gap; wherein: The waveguide substrate has a first total internal reflection surface and a second total internal reflection surface, the coupling grating is disposed on the side of the waveguide substrate close to the first total internal reflection surface, the air gap is sandwiched between the first total internal reflection surface and the second total internal reflection surface, and the air gap is spaced apart from both the first total internal reflection surface and the second total internal reflection surface. The first reflective surface is located on the side of the air gap near the coupling grating, and the second reflective surface is located on the side of the air gap near the second total internal reflective surface. The first reflective surface, the second reflective surface, the first total internal reflective surface, and the second total internal reflective surface are parallel to each other. The diffractive waveguide also includes a coupling grating, and along a direction away from the coupling grating, the end of the air gap away from the coupling grating is located between the opposite ends of the coupling grating.

2. The diffractive waveguide according to claim 1, characterized in that, The number of air gaps is at least one; When there are two or more air gaps, at least two of the air gaps are spaced apart along a direction perpendicular to the first total internal reflection surface.

3. The diffractive waveguide according to claim 1, characterized in that, The number of air gaps is greater than or equal to two; Along the direction away from the coupling grating, the end point of each air gap on the side near the coupling grating is aligned with the end point of the output grating on the side near the coupling grating; For any two air gaps, along the direction perpendicular to the first total internal reflection surface, the length of the air gap farther away from the first total internal reflection surface is greater than the length of the air gap closer to the first total internal reflection surface.

4. The diffractive waveguide according to claim 3, characterized in that, Each of the aforementioned air gaps satisfies the following: Where p is an integer greater than 0, and all air gaps are arranged sequentially along the direction away from the first total internal reflection surface as the 1st, 2nd, ..., pth air gap. Let be the red light intensity of the output grating at the endpoint of the p-th air gap on the side furthest from the input grating. Let be the blue light intensity of the output grating at the endpoint of the p-th air gap on the side furthest from the input grating. The initial intensity of red light. H represents the initial intensity of blue light. p s is the distance between the p-th air gap and the second total internal reflective surface. p H0 is the length of the air gap in the first direction, H0 is the thickness of the waveguide substrate in the direction perpendicular to the first total internal reflection surface, and η is the length of the air gap in the first direction. r η is the diffraction efficiency of red light after passing through the coupling grating. b λ represents the diffraction efficiency of blue light after passing through the coupling grating. r For red light wavelength, λ b For blue light wavelength, n w Let be the refractive index of the waveguide substrate, and T be the grating period of the coupled grating.

5. The diffractive waveguide according to claim 2, characterized in that, The number of air gaps is greater than or equal to two; Along the direction away from the coupling grating, the end point of the air gap adjacent to the first total internal reflection surface on the side closer to the coupling grating is aligned with the end point of the output grating on the side closer to the coupling grating. Arranged sequentially along the direction from the first total internal reflection surface to the second total internal reflection surface, starting from the second air gap away from the first total internal reflection surface, the end point of each air gap near the coupling grating is aligned with the end point of the previous air gap near the coupling grating.

6. The diffractive waveguide according to claim 5, characterized in that, Each of the aforementioned air gaps satisfies the following: Where p is an integer greater than 0, and all air gaps are arranged sequentially along the direction away from the first total internal reflection surface as the 1st, 2nd, ..., pth air gap. Let be the red light intensity of the output grating at the endpoint of the p-th air gap on the side furthest from the input grating. Let be the blue light intensity of the output grating at the endpoint of the p-th air gap on the side furthest from the input grating. The initial intensity of red light. H represents the initial intensity of blue light. p s is the distance between the p-th air gap and the second total internal reflective surface. p H0 is the length of the air gap in the first direction, H0 is the thickness of the waveguide substrate in the direction perpendicular to the first total internal reflection surface, and η is the length of the air gap in the first direction. r η is the diffraction efficiency of red light after passing through the coupling grating. b λ represents the diffraction efficiency of blue light after passing through the coupling grating. r For red light wavelength, λ b For blue light wavelength, n w Let be the refractive index of the waveguide substrate, and T be the grating period of the coupled grating.

7. The diffractive waveguide according to claim 4 or 6, characterized in that, Each of the aforementioned air gaps satisfies: ,a=[r,g,b]; Where: m is an integer greater than or equal to 1, Let be the intensity of the red light after m coupling cycles. Let be the intensity of the green light after m coupling cycles. Let λ be the intensity of blue light after m coupling cycles. g It is the wavelength of blue light. The initial intensity of green light. The uniformity of brightness of the coupled light.

8. The diffractive waveguide according to claim 1, characterized in that, Along the direction perpendicular to the first total internal reflection surface, the thickness of the air gap is greater than the skin depth of the total internal reflection light in the waveguide substrate, and less than or equal to 2 micrometers.

9. The diffractive waveguide according to any one of claims 1 to 8, characterized in that, The waveguide substrate includes at least two substrate sheets, which are stacked together along a direction perpendicular to the first total internal reflection surface. At least one of the substrates has a groove on a side near an adjacent substrate, the groove and the adjacent substrate forming the air gap.

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

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