Diffractive light guide and display products with uniform exit pupil brightness

Abstract

The present invention belongs to the technical field of optical waveguides, and discloses a diffraction optical waveguide and display product with uniform exit pupil brightness. The diffraction optical waveguide includes a waveguide layer, an in-coupling grating and an out-coupling grating, the waveguide layer has a first surface and a second surface opposite to each other, the in-coupling grating is located on the first surface, the second surface or between the first surface and the second surface, and the out-coupling grating is located on the first surface, the second surface or between the first surface and the second surface. In particular, the diffraction optical waveguide also includes a beam splitting layer, which is located between the first surface and the second surface and has only a semi-reflective and semi-transparent effect on the propagating light. The propagating light is the light that is reflected and propagated back and forth between the first surface and the second surface. The semi-reflective and semi-transparent effect of the beam splitting layer on the propagating light improves the uniformity of the exit pupil brightness of the diffraction optical waveguide, and even if the diffraction efficiency of the out-coupling grating is constant in space, the uniformity of the exit pupil brightness of the diffraction optical waveguide can be improved.

Description

Technical Field

[0001] The present invention belongs to the field of optical waveguide technology, and specifically relates to a diffraction optical waveguide and display product with uniform exit pupil brightness. Background Art

[0002] With the continuous development of the information age, people have higher and higher requirements for the performance of near-eye display systems in production and life, especially in terms of image clarity, field of view, comfort and portability. To meet these growing demands, various new display technologies have emerged, among which the display system using holographic waveguide technology is currently a hot research topic in the field of augmented reality (AR).

[0003] Holographic diffraction waveguide is an optical technology that uses coupling gratings, waveguide materials and coupling gratings to achieve a large exit pupil and a large field of view. This technology combines the diffraction characteristics of the grating in the holographic recording material and the total reflection characteristics of the light beam at the boundary of the waveguide medium. Compared with traditional optical systems, holographic diffraction waveguides have smaller volume and lighter weight. They are widely used in portable / head-mounted display terminals, and have achieved certain results in augmented reality and virtual reality display helmets in recent years.

[0004] In the holographic waveguide display structure, the transmission and diffraction process of the light beam is the key to achieving high-quality image display. When the light beam passes through the coupling-in grating, it enters the waveguide through diffraction and undergoes total reflection on the inner surface of the waveguide material. This total reflection process ensures that the light beam can be transmitted over a long distance inside the waveguide while avoiding the loss of light energy. When the light beam reaches the coupling-out grating, part of the light will be emitted from the waveguide through diffraction and form a visible image in the air; while the other part of the light will pass through the coupling-out grating and continue to undergo total reflection on the inner surface of the waveguide material. When it reaches the coupling-out grating again, part of the light will still be diffracted while the other part will continue to propagate through total reflection, and the cycle will repeat.

[0005] The number of times the light beam is diffracted by the outcoupling grating depends on the size of the outcoupling grating and the size of the incident angle. Due to total reflection, as the number of diffraction increases, the intensity of the light incident on the outcoupling grating decreases successively. If the diffraction efficiency of the outcoupling grating is constant, the diffracted light will be uneven, such as Figure 1 shown. Utility Model Content

[0006] The present solution aims to overcome at least one defect in the prior art and provide a diffraction light waveguide with uniform exit pupil brightness.

[0007] In order to solve the above technical problems, the following technical solutions are adopted:

[0008] In the first aspect, a diffraction light waveguide with uniform exit pupil brightness is proposed. The diffraction light waveguide includes a waveguide layer, an in-coupling grating and an out-coupling grating, the waveguide layer has a first surface and a second surface opposite to each other, the in-coupling grating is located on the first surface, the second surface or between the first surface and the second surface, and the out-coupling grating is located on the first surface, the second surface or between the first surface and the second surface. In particular, the diffraction light waveguide also includes a beam splitting layer, which is located between the first surface and the second surface and has a semi-reflective and semi-transmissive effect only on the propagating light, and has only a transmissive effect on other light. The propagating light is the light that is reflected and propagated back and forth between the first surface and the second surface.

[0009] This solution improves the brightness uniformity of the exit pupil of the diffraction waveguide through the semi-reflective and semi-transparent effect of the beam splitter. Compared with the back-and-forth reflection and propagation between the two surfaces of the waveguide layer, the reflection effect of the beam splitter allows the propagating light to be reflected and propagated back and forth between the waveguide layer surface with a smaller spacing and the beam splitter layer, the propagation step is reduced, the number of times the coupled grating is diffracted increases, and the coupling density of the propagating light is improved. Compared with the second reflection layer which only has a reflective effect on the propagating light, the transmission effect of the beam splitting layer also allows the propagating light passing through the beam splitting layer to be reflected by the surface of the waveguide layer and then be interspersed between the propagating light reflected by the beam splitting layer. The density of the propagating light increases, the number of times it is diffracted by the out-coupling grating increases, and the out-coupling density also increases accordingly. More importantly, the transmission effect of the beam splitting layer makes it possible for only a part of the propagating light to contact the out-coupling grating at an early stage, thereby reducing the out-coupling light intensity and brightness at an early stage, while the other part will contact the out-coupling grating at a later stage, thereby increasing the out-coupling light intensity and brightness at a later stage, thereby reducing the light intensity difference and brightness difference between the early stage and the later stage. Even if the diffraction efficiency of the out-coupling grating is constant in space, the brightness uniformity of the exit pupil of the diffraction light waveguide can be improved.

[0010] The reflectivity of the beam splitting layer to the propagating light is 31-69%, preferably 41-59%, and the transmittance is 31-69%, preferably 41-59%. When irradiated by the propagating light, a part of the propagating light can be reflected back and another part of the propagating light can be transmitted, thereby splitting the propagating light into two beams to achieve beam splitting.

[0011] The beam splitter can have a semi-reflective and semi-transmissive effect only on the light propagating at a large angle, and almost only a transmissive effect on the light propagating at a small angle. In other words, the propagating light includes a first propagating light and a second propagating light, the incident angle of the first propagating light is greater than the incident angle of the second propagating light, and the beam splitter has a semi-reflective and semi-transmissive effect only on the first propagating light. Specifically, the reflectivity of the beam splitter to the first propagating light is 31 to 69%, preferably 41 to 59%, and the transmittance is 31 to 69%, preferably 41 to 59%, and the transmittance to the second propagating light is more than 80%, preferably more than 90%.

[0012] The beam splitting layer can use a reflective volume holographic grating. The reflectivity and transmittance of the reflective volume holographic grating can be kept constant in space or vary with space. Specifically, the reflectivity and transmittance of the reflective volume holographic grating that vary with space increases along the propagation direction of the light, and decreases along the propagation direction of the light, which is conducive to making the exit pupil brightness of the diffraction light waveguide more uniform.

[0013] The beam splitting layer can also use a semi-transparent and semi-reflective film. The semi-transparent and semi-reflective film can be made of multiple layers of films with different refractive indices, and the film materials can be silicon dioxide (SiO2), titanium dioxide (TiO2), zinc sulfide (ZnS), etc. The reflectivity of the semi-transparent and semi-reflective film can be adjusted by optically designing the combination of films with different refractive indices.

[0014] The coupling-in grating can be a volume holographic grating, and the coupling-out grating can also be a volume holographic grating, which can be a transmission volume holographic grating or a reflection volume holographic grating. When both the coupling-in grating and the coupling-out grating are volume holographic gratings, the coupling-in grating and the coupling-out grating can be located on the same grating layer or on different grating layers. The diffraction efficiency of the volume holographic grating used as the coupling-out grating can be increased along the propagation direction of the light, which is conducive to making the exit pupil brightness of the diffraction optical waveguide more uniform.

[0015] In a second aspect, a display product is provided, which includes a projection optical machine and a diffraction optical waveguide, wherein the diffraction optical waveguide is the diffraction optical waveguide with uniform exit pupil brightness provided in the first aspect.

[0016] This solution improves the uniformity of the exit pupil brightness of the display product by using a diffraction light waveguide with a beam splitter layer, and reduces or even avoids the phenomenon of uneven diffraction light. Compared with the propagation of back and forth reflection between the two surfaces of the waveguide layer, the reflection effect of the beam splitter layer allows the propagating light to be reflected and propagated back and forth between the waveguide layer surface with a smaller spacing and the beam splitter layer, the propagation step is reduced, the number of diffraction by the out-coupled grating is increased, and the out-coupling density of the propagating light is improved. Compared with the second reflection layer that only has a reflective effect on the propagating light, the transmission effect of the beam splitter layer allows only part of the propagating light to contact the out-coupled grating at an early stage, reducing the early out-coupled light intensity and brightness, while the other part will contact the out-coupled grating at a later stage, increasing the later out-coupled light intensity and brightness, thereby reducing the early and late light intensity differences and brightness differences. Even if the diffraction efficiency of the out-coupled grating is constant in space, the uniformity of the exit pupil brightness of the diffraction light waveguide can be improved.

[0017] Compared with the prior art, this solution has the following beneficial effects: this solution improves the uniformity of the exit pupil brightness of the diffraction light waveguide through the semi-reflective and semi-transmissive effect of the beam splitting layer. Even if the diffraction efficiency of the out-coupling grating is constant in space, the uniformity of the exit pupil brightness of the diffraction light waveguide can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings are for illustrative purposes only and should not be construed as limitations on the present invention. In order to better illustrate the present invention, some parts of the drawings may be omitted, enlarged, or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0019] Figure 1 It is a schematic diagram of the structure and optical path of the existing diffraction optical waveguide.

[0020] Figure 2 The diagram is a schematic diagram of the structure and optical path of a diffraction optical waveguide with a second reflection layer.

[0021] Figure 3 It is a schematic diagram of the structure and optical path of a diffraction optical waveguide with a beam splitting layer (the coupling-in grating is located between the first surface and the second surface, and the coupling-out grating is located on the first surface).

[0022] Figure 4 The present invention is a schematic diagram of the structure and optical path of a diffraction optical waveguide (the coupling-in grating is located between the first surface and the second surface, and the coupling-out grating is located on the second surface) provided with a beam splitting layer.

[0023] Figure 5 It is a schematic diagram of the structure and optical path of a diffraction optical waveguide (the coupling-in grating and the coupling-out grating are both located between the first surface and the second surface) provided with a beam splitting layer.

[0024] Figure 6 It is a schematic diagram of the structure and optical path of a diffraction optical waveguide with a beam splitting layer (the coupling-in grating is located on the first surface, and the coupling-out grating is located between the first surface and the second surface).

[0025] Figure 7 It is a schematic diagram of the structure and optical path of a diffraction optical waveguide (the coupling-in grating is located on the second surface, and the coupling-out grating is located between the first surface and the second surface) with a beam splitting layer.

[0026] Figure 8 It is a schematic diagram of the structure and optical path of a diffraction optical waveguide in which the beam splitting layer only half reflects and half transmits light at a large angle.

[0027] Fig. 9 is a graph of the reflectivity of a reflective volume holographic grating acting as a beam splitter.

[0028] Fig.10 It is a reflectivity curve of the semi-transparent and semi-reflective film acting as a beam splitter.

[0029] Fig.11 It is a schematic diagram showing the structure and optical path of the product.

[0030] Explanation of the reference numerals: waveguide layer 110 , first surface 111 , second surface 112 , coupling-in grating 121 , coupling-out grating 122 , beam splitting layer 130 , second reflection layer 140 , projection optical machine 200 , human eye E. DETAILED DESCRIPTION

[0031] In order to enable those skilled in the art to better understand the present solution, the present solution is further described in detail below in conjunction with specific embodiments.

[0032] Figures 3 to 7 The following diagram shows possible diffraction optical waveguides to realize the transmission and expansion functions of light beams. Figures 3 to 7 As shown, the diffraction optical waveguide includes a waveguide layer 110, an incoupling grating 121, an outcoupling grating 122 and a beam splitting layer 130. The waveguide layer 110, the incoupling grating 121, the outcoupling grating 122 and the beam splitting layer 130 are all layered structures. The waveguide layer 110 has two opposite surfaces, namely a first surface 111 and a second surface 112. The incoupling grating 121 can be disposed on the surface or inside of the waveguide layer 110, and can be specifically disposed on the first surface 111 (e.g., Figure 6 ), and may also be disposed on the second surface 112 of the waveguide layer 110 (eg Figure 7 ), and may also be disposed between the first surface 111 and the second surface 112 of the waveguide layer 110 (eg Figure 3 , 4 , 5). The outcoupling grating 122 can also be disposed on the surface or inside of the waveguide layer 110, and can be specifically disposed on the first surface 111 of the waveguide layer 110 (eg Figure 3 ), and may also be disposed on the second surface 112 of the waveguide layer 110 (eg Figure 4 ), and may also be disposed between the first surface 111 and the second surface 112 of the waveguide layer 110 (eg Figure 5 , 6 , 7). The beam splitting layer 130 is disposed between the first surface 111 and the second surface 112 of the waveguide layer 110.

[0033] The waveguide layer 110 is used to realize the back and forth reflection propagation of the light beam. The waveguide layer 110 generally has a total reflection critical angle θ c , the absolute value of the incident angle exceeds the critical angle of total reflection θ c When the light irradiates the first surface 111 or the second surface 112 of the waveguide layer 110 in the waveguide layer 110, it can be completely reflected back by the first surface 111 or the second surface 112 of the waveguide layer 110, so as to propagate along the extension direction of the waveguide layer 110 in the form of back and forth reflection in the waveguide layer 110. This propagation can be called total reflection propagation. A first reflection layer (not shown) can also be attached to the first surface 111 and the second surface 112 of the waveguide layer 110. The first reflection layer has a high reflection critical angle θr (0<θ r <θ c ), the absolute value of the incident angle exceeds the high reflection critical angle θ r When the light irradiates the first reflection layer attached to the first surface 111 or the second surface 112 of the waveguide layer 110 in the waveguide layer 110, most of it (more than 80%) can be reflected back by the first reflection layer, and can also propagate along the extension direction of the waveguide layer 110 in the form of back and forth reflection in the waveguide layer 110. This propagation can be called high reflection propagation. Regardless of total reflection propagation (reflectivity 100%) or high reflection propagation (reflectivity more than 80%), the light propagating along the extension direction of the waveguide layer 110 in the form of back and forth reflection in the waveguide layer 110 can be called propagation light.

[0034] The coupling grating 121 is used to achieve the coupling of the light beam. When the light beam is emitted to the diffraction light waveguide, the absolute value of its incident angle is usually less than the total reflection critical angle θ of the waveguide layer 110. c , even smaller than the high reflection critical angle θ of the first reflection layer r , and cannot be reflected back and forth in the waveguide layer 110. The coupling grating 121 can diffract the light and change its incident angle, so that the absolute value of the incident angle of the light exceeds the critical angle θ of total reflection of the waveguide layer 110 c Or the high reflection critical angle θ of the first reflection layer r , so it can be reflected and propagated back and forth in the waveguide layer 110, thereby achieving the coupling of the light beam.

[0035] The outcoupling grating 122 is used to realize the outcoupling of the light beam. When the light beam is reflected back and forth in the waveguide layer 110, the absolute value of its incident angle exceeds the critical angle θ of total reflection of the waveguide layer 110. c Or the high reflection critical angle θ of the first reflection layer r When the light is irradiated to the surface of the waveguide layer 110 or the first reflective layer in the waveguide layer 110, it will be reflected back into the waveguide layer 110 and cannot be emitted out of the waveguide layer 110. The outcoupling grating 122 can diffract the light and change its incident angle, so that the absolute value of the incident angle of the light is less than the critical angle θ of total reflection of the waveguide layer 110. c Or the high reflection critical angle θ of the first reflection layer r , so it can be emitted out of the waveguide layer 110, thereby achieving the outcoupling of the light beam.

[0036] The diffraction efficiency of the outcoupling grating 122 is usually not 100%. Each time the light beam passes through the outcoupling grating 122, a portion of the light beam will be diffracted by the outcoupling grating 122 and coupled out of the waveguide layer 110, and another portion of the light beam will pass through the outcoupling grating 122 and continue to be reflected and propagated back and forth in the waveguide layer 110. The number of times the light beam is diffracted by the outcoupling grating 122 depends on the size of the outcoupling grating 122 and the size of the incident angle. As the number of diffraction increases, the intensity of the light incident on the outcoupling grating 122 decreases successively. If the diffraction efficiency of the outcoupling grating 122 is constant, the phenomenon of uneven diffracted light will occur, such as Figure 1 As shown. Figures 1 to 7 In the diffraction optical waveguide shown, the diffraction efficiency of the outcoupling grating 122 is 50%. It should be noted that Figures 1 to 7 This is only an example and cannot be used as a limitation on the diffraction efficiency of the out-coupling grating 122 .

[0037] The beam splitting layer 130 has only a semi-reflective and semi-transmissive effect on the propagating light. When irradiated by the propagating light, it can reflect a part of the propagating light back and let the other part of the propagating light pass through, thereby splitting the propagating light into two beams to achieve beam splitting. The reflectivity of the beam splitting layer 130 for the propagating light is 31-69%, preferably 41-59%, and the transmittance is 31-69%, preferably 41-59%. For example, in Figures 3 to 7 In the diffraction waveguide shown, the reflectivity and transmittance of the beam splitting layer 130 to the propagating light are both 50%. Figures 3 to 7 This is only an example and cannot be used as a limitation on the reflectivity and transmittance of the beam splitting layer 130. The beam splitting layer 130 has almost only a transmission effect on other light (with a transmittance of more than 80%), where other light refers to light other than the propagating light, including coupled light, etc., to ensure that the coupled light can be emitted outside the waveguide layer 110 to achieve light output.

[0038] refer to Figure 1 It can be seen that if the beam splitting layer 130 is removed, the propagating light will be reflected back and forth between the two surfaces of the waveguide layer 110, the propagation step distance is large, the number of diffracted times by the out-coupled grating 122 is small, the out-coupling density of the propagating light is small, and the light intensity difference between the first two out-coupled light beams reaches 25%, and the brightness uniformity is poor. Figure 2 It can be seen that if the beam splitting layer 130 is replaced by a second reflection layer 140 (with a reflectivity of more than 70%) that has only a reflective effect on the propagating light, the propagating light will be reflected and propagated back and forth between the surface of the waveguide layer 110 and the beam splitting layer 130. Although the propagation step is reduced, the number of diffracted times by the out-coupled grating 122 increases, and the out-coupling density of the propagating light increases, the light intensity difference between the first two out-coupled light beams (red dotted line and orange dotted line) is still 25%, and the light intensity difference between the first and last out-coupled light beams (red dotted line and green dotted line) reaches 43.75%, and the brightness uniformity is poor.

[0039] refer to Figure 3 It can be seen that the reflection effect of the beam splitter 130 allows the propagating light to reflect and propagate back and forth between the surface of the waveguide layer 110 with a smaller spacing and the beam splitter 130, the propagation step is reduced, the number of diffracted times by the out-coupling grating 122 is increased, and the out-coupling density of the propagating light is improved. At the same time, the transmission effect of the beam splitter 130 also allows the part of the propagating light transmitted by the beam splitter 130 (red solid line) to be interspersed between the parts reflected by the beam splitter 130 (orange dotted line and green dotted line) after being reflected by the surface of the waveguide layer 110, thereby increasing the density of the propagating light and further improving the out-coupling density of the propagating light. More importantly, the transmission effect of the beam splitting layer 130 ensures that only a part of the propagated light is propagated to the front of the outcoupling grating 122 and coupled out by the outcoupling grating 122. The light intensity of the first few outcoupling light beams is relatively weakened, and the light intensity difference is reduced to less than 12.5%. The other part of the propagated light will be propagated to the rear of the outcoupling grating 122, superimposed with the propagated light that has passed the front of the outcoupling grating 122 but has not been coupled out, and is coupled out by the outcoupling grating 122. The light intensity of the last few outcoupling light beams is relatively enhanced, and the light intensity difference between the first and the last outcoupling light beams (yellow dotted line and purple dotted line) is only 10.94%, and the brightness uniformity is significantly improved.

[0040] In summary, compared with the propagation by reflection back and forth between the two surfaces of the waveguide layer 110, the reflection effect of the beam splitting layer 130 allows the propagating light to be reflected back and forth between the surface of the waveguide layer 110 and the beam splitting layer 130 with a smaller spacing, the propagation step is reduced, the number of diffracted times by the out-coupling grating 122 is increased, and the out-coupling density of the propagating light is improved. Compared with the second reflection layer 140 which has only a reflective effect on the propagating light, the transmission effect of the beam splitting layer 130 also allows the propagating light passing through the beam splitting layer 130 to be reflected by the surface of the waveguide layer 110 and then be interspersed between the propagating light reflected by the beam splitting layer 130. The density of the propagating light increases, the number of times it is diffracted by the outcoupling grating 122 increases, and the outcoupling density also increases accordingly. More importantly, the transmission effect of the beam splitting layer 130 allows only a part of the propagating light to contact the outcoupling grating 122 at an early stage, thereby reducing the outcoupling light intensity and brightness at an early stage, while the other part will contact the outcoupling grating 122 at a later stage, thereby increasing the outcoupling light intensity and brightness at a later stage, thereby reducing the light intensity difference and brightness difference between the early stage and the later stage. Even if the diffraction efficiency of the outcoupling grating 122 is constant in space, the uniformity of the exit pupil brightness of the diffraction light waveguide can be improved.

[0041] like Figure 1As shown, light of different wavelengths will have different incident angles after being diffracted by the coupling-in grating 121. The larger the incident angle, the larger the propagation step, and the larger the spacing between two adjacent coupled-out light beams when the light is diffracted by the coupling-out grating 122. Too large a spacing between two adjacent coupled-out light beams will cause the coupled-out light to be too sparse, so that less light enters the human eye, thereby reducing the brightness of the field of view corresponding to the large-angle light. For propagation light with a smaller incident angle, since the spacing between two adjacent coupled-out light beams is smaller, the coupled-out light is denser, and more light enters the human eye, thereby not reducing the brightness of the field of view corresponding to the small-angle light. Therefore, the beam splitting layer 130 can only have a semi-reflective and semi-transmissive effect on light propagating at a large angle, and almost only have a transmissive effect on light propagating at a small angle. As shown in FIG. Figure 8 As shown, the propagating light includes a first propagating light with a first incident angle α1 and a second propagating light with a second incident angle α2 (α1 and α2 are both thresholds, and α1>α2), the reflectivity of the beam splitting layer 130 to the first propagating light is 31-69%, preferably 41-59%, and the transmittance is 31-69%, preferably 41-59%, and the transmittance to the second propagating light is more than 80%, preferably more than 90%.

[0042] The beam splitting layer 130 can be a reflective volume holographic grating or a semi-transparent and semi-reflective film. The reflective volume holographic grating serving as the beam splitting layer 130 can be produced by double-beam exposure. During the production process, the signal light and the reference light are emitted from both sides of the holographic photosensitive material layer to the holographic photosensitive material layer, and double-beam interference occurs. The holographic photosensitive material layer records the interference fringe distribution in the form of a refractive index change distribution, forming a reflective volume holographic grating. The reflectivity curve of the reflective volume holographic grating can be controlled by the exposure angle and diffraction efficiency of the signal light and the reference light during the exposure production by optical software design. Fig. 9 The possible reflectivity curve of the reflective volume holographic grating is described as an example. As shown in the figure, the reflective volume holographic grating has a reflectivity curve of θ1 to θ2 (θ1≤θ r <θ c <θ2 or θ r <θ1≤θ c <θ2 or θ r <θ c <θ1<θ2) is R1~R2 (31%≤R1<R2≤69%). The reflectivity and transmittance of the reflective volume holographic grating acting as the beam splitting layer 130 can be kept constant in space or can vary with space. For the reflective volume holographic grating whose reflectivity and transmittance vary with space, its reflectivity can gradually increase along the propagation direction of the propagating light in the waveguide layer 110, while its transmittance can gradually decrease along the propagation direction of the propagating light in the waveguide layer 110, so that the exit pupil brightness of the diffraction light waveguide is more uniform.

[0043] The semi-transparent and semi-reflective film serving as the beam splitting layer 130 can be formed by stacking multiple layers of films with different refractive indices, and the film materials can be selected from silicon dioxide (SiO2), titanium dioxide (TiO2), zinc sulfide (ZnS), etc. The reflectivity of the semi-transparent and semi-reflective film can be adjusted by optically designing the combination of film materials with different refractive indices. Fig.10 The reflectivity curve of the semi-transparent and semi-reflective film is described as an example. As shown in the figure, the semi-transparent and semi-reflective film has a high reflectivity when the incident angle exceeds θ3 (θ3≤θ r <θ c or θ r <θ3≤θ c or θ r <θ c The reflectivity of the propagating light of (θ3) is R3 (31%≤R3≤69%).

[0044] In addition, the above-mentioned diffraction optical waveguide may also include a turning grating (not shown). The turning grating is used to change the propagation direction of the propagating light in the waveguide and expand the range of the light beam, thereby realizing the turning of the light beam. The coupling-in grating 121, the coupling-out grating 122 and the turning grating may all be volume holographic gratings, which may be transmission volume holographic gratings or reflection volume holographic gratings. Any two or more of the coupling-in grating 121, the coupling-out grating 122 or the turning grating, which are all volume holographic gratings, may be located on the same grating layer or on different grating layers. The diffraction efficiency of the volume holographic grating used as the coupling-out grating 122 may remain constant in space or vary with space. The diffraction efficiency of the volume holographic grating whose diffraction efficiency varies with space may gradually increase along the propagation direction of the propagating light in the waveguide layer 110, so that the exit pupil brightness of the diffraction optical waveguide is more uniform.

[0045] Fig.11 Possible display products are shown. Fig.11As shown, the display product includes a projection optical machine 200 and the above-mentioned diffraction optical waveguide provided with a beam splitting layer 130. The projection optical machine 200 is similar to a projector, and projects a light beam with a virtual image into the diffraction optical waveguide. The diffraction optical waveguide transmits and couples the light from the projection optical machine 200, and the coupled light enters the human eye to form a virtual image with uniform brightness, realizing different effects such as virtual reality (VR), augmented reality (AR), and mixed reality (MR). According to different effects, display products can be divided into different types. Among them, VR display products are the carriers of virtual reality technology, which use computer technology to generate a three-dimensional virtual world that allows the wearer to interact with it, so that the wearer has an immersive feeling. AR display products are the carriers of enhanced realization technology, which use computer technology to apply virtual information to the real world, so that the real environment and virtual objects are superimposed on the same screen or space in real time and exist simultaneously. MR display products are the carriers of mixed reality technology, combining the characteristics of VR and AR, allowing the wearer to interact with real and virtual environments.

[0046] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation methods of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all implementation methods here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. A diffraction light waveguide with uniform exit pupil brightness, comprising a waveguide layer, an in-coupling grating and an out-coupling grating, wherein the waveguide layer has a first surface and a second surface opposite to each other, the in-coupling grating is located on the first surface, the second surface or between the first surface and the second surface, and the out-coupling grating is located on the first surface, the second surface or between the first surface and the second surface; characterized in that: It also includes a beam splitting layer, which is located between the first surface and the second surface and has only a semi-reflective and semi-transmissive effect on the propagating light; the propagating light is the light that is reflected and propagated back and forth between the first surface and the second surface.

2. The diffractive optical waveguide with uniform exit pupil brightness according to claim 1, characterized in that: The reflectivity of the beam splitting layer to the propagating light is 31-69%, and the transmittance is 31-69%.

3. The diffractive optical waveguide with uniform exit pupil brightness according to claim 1, characterized in that: The propagating light comprises a first propagating light and a second propagating light, the incident angle of the first propagating light is greater than the incident angle of the second propagating light, and the beam splitting layer has a semi-transmissive and semi-reflective effect only on the first propagating light.

4. The diffractive optical waveguide with uniform exit pupil brightness according to claim 3, characterized in that: The reflectivity of the beam splitting layer to the first propagation light is 31-69%, the transmittance is 31-69%, and the transmittance to the second propagation light is more than 80%.

5. The diffractive optical waveguide with uniform exit pupil brightness according to any one of claims 1 to 4, characterized in that: The beam splitting layer is a reflective volume holographic grating.

6. The diffractive optical waveguide with uniform exit pupil brightness according to claim 5, characterized in that: The reflectivity of the reflective volume holographic grating to the propagating light increases along the propagation direction of the light, and the transmittance to the propagating light decreases along the propagation direction of the light.

7. The diffractive optical waveguide with uniform exit pupil brightness according to any one of claims 1 to 4, characterized in that: The beam splitting layer is a semi-transparent and semi-reflective membrane.

8. The diffractive optical waveguide with uniform exit pupil brightness according to claim 7, characterized in that: The semi-transparent and semi-reflective film is formed by stacking multiple layers of films with different refractive indices.

9. The diffractive optical waveguide with uniform exit pupil brightness according to any one of claims 1 to 4, characterized in that: The coupling-in grating is a volume holographic grating; and / or The outcoupling grating is a volume holographic grating, and its diffraction efficiency increases along the propagation direction of the light.

10. A display product, comprising a projection optical machine and a diffractive optical waveguide, characterized in that: The diffractive light waveguide is the diffractive light waveguide with uniform exit pupil brightness as claimed in any one of claims 1 to 9.

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