Method for manufacturing volume holographic grating, volume holographic grating and head-mounted device

Abstract

The application relates to a preparation method of a volume holographic grating, a grating structure and a head-mounted device. The preparation method of the volume holographic grating comprises the following steps: providing a substrate, the substrate having a first surface and a second surface arranged oppositely; forming a holographic material layer on the first surface of the substrate; making incident light incident on the holographic material layer through an exposure adjusting element, and making reference light incident on the second surface of the substrate, so that the incident light and the reference light are subjected to interference exposure on the holographic material layer to form a grating structure on the holographic material layer; wherein the exposure adjusting element is configured to make the exit angles of the incident light emitted from different positions of the exposure adjusting element along a first direction different, so that the grating period of the grating structure is gradually changed. The uniformity of imaging brightness can be effectively improved, and the viewing experience is improved.

Description

Technical Field

[0001] This application relates to the field of display technology, and in particular to a method for fabricating a volume holographic grating, the volume holographic grating, and a head-mounted device. Background Technology

[0002] Augmented reality (AR), also known as augmented reality or mixed reality, is a technology that overlays virtual objects onto the real environment and allows for interaction. By projecting images of virtual objects and the real environment into the user's eyes, it provides a user experience that blends the virtual and the real.

[0003] AR glasses consist of an optical engine and a waveguide system. Incident light is directed from the optical engine to the coupling grating of the waveguide system, transmitted through the waveguide, and finally projected into the user's eye through the output grating of the waveguide system. However, traditional AR glasses suffer from uneven image brightness. Summary of the Invention

[0004] Therefore, it is necessary to provide a method for fabricating a volume holographic grating, a volume holographic grating, and a head-mounted device to address the problem of uneven imaging brightness in traditional AR glasses.

[0005] According to a first aspect of this application, a method for fabricating a volume holographic grating is provided, comprising:

[0006] A substrate is provided, the substrate having a first surface and a second surface disposed opposite to each other;

[0007] A holographic material layer is formed on the first surface of the substrate;

[0008] Incident light is incident on the holographic material layer through an exposure adjustment element, and reference light is incident on the second surface of the substrate, so that the incident light and the reference light interfere with each other on the holographic material layer to form a grating structure on the holographic material layer.

[0009] The exposure adjustment element is configured to make the exit angle of the incident light emitted from different positions along the first direction different, thereby making the grating period of the grating structure gradually change.

[0010] In one embodiment, the exposure adjustment element includes a plurality of liquid crystal layers disposed along the first direction, wherein the mass fraction of liquid crystal in at least three of the liquid crystal layers increases along the first direction, and / or the voltage applied to at least three of the liquid crystal layers decreases.

[0011] In one embodiment, the exposure adjustment element includes a first region, a second region, and a third region sequentially disposed along the first direction, wherein the mass fraction of the liquid crystal in the liquid crystal layer of the first region, the liquid crystal layer of the second region, and the liquid crystal layer of the third region increases sequentially; and / or

[0012] The voltages applied to the liquid crystal layer in the first region, the liquid crystal layer in the second region, and the liquid crystal layer in the third region decrease sequentially.

[0013] In one embodiment, the mass fraction of the liquid crystal in at least three liquid crystal layers sequentially disposed along the first direction increases sequentially; and / or

[0014] The voltage applied to at least three liquid crystal layers arranged sequentially along the first direction decreases sequentially.

[0015] In one embodiment, the method of causing incident light to pass through an exposure adjustment element and onto the holographic material layer, and causing reference light to pass onto the second surface of the substrate, so that the incident light and the reference light interfere with each other on the holographic material layer, and before forming a grating structure on the holographic material layer, the method of fabricating the volume holographic grating further includes:

[0016] Determine whether the exposure pattern formed by the incident light incident on the holographic material layer through the exposure adjustment element meets the preset requirements. If so, execute the step of causing the incident light to pass through the exposure adjustment element and be incident on the holographic material layer, and causing the reference light to be incident on the second surface of the substrate, so that the incident light and the reference light interfere with each other on the holographic material layer to form a grating structure on the holographic material layer.

[0017] In one embodiment, it is determined whether the exposure pattern formed by the incident light incident on the holographic material layer through the exposure adjustment element meets the preset requirements. If not, the voltage applied to at least one of the liquid crystal layers is adjusted until the exposure pattern formed by the incident light incident on the holographic material layer through the exposure adjustment element meets the preset requirements.

[0018] In one embodiment, determining whether the exposure pattern formed by the incident light incident on the holographic material layer through the exposure adjustment element meets a preset requirement specifically includes:

[0019] A first light-blocking screen is placed between the exposure adjustment element and the holographic material layer so that the incident light can be projected onto the first light-blocking screen through the exposure adjustment element.

[0020] Based on the pattern projected onto the first light-blocking screen, it is determined whether the exposure pattern formed by the incident light incident on the holographic material layer through the exposure adjustment element meets the preset requirements.

[0021] In one embodiment, determining whether the exposure pattern formed by the incident light incident on the holographic material layer through the exposure adjustment element meets a preset requirement based on the pattern projected onto the first light-blocking screen specifically includes:

[0022] The pattern projected onto the first light-blocking screen is photographed to obtain the photographed pattern;

[0023] Based on the comparison between the captured pattern and the preset pattern, it is determined whether the exposure pattern formed by the incident light incident on the holographic material layer through the exposure adjustment element meets the preset requirements.

[0024] In one embodiment, determining whether the exposure pattern formed by the incident light incident on the holographic material layer through the exposure adjustment element meets a preset requirement further includes:

[0025] The second light-blocking screen is disposed on the second surface of the substrate away from the first surface, and the first light-blocking screen and the second light-blocking screen are symmetrically arranged with regard to the whole formed by the substrate and the holographic material layer, so that the reference light can be incident on the second light-blocking screen.

[0026] In one embodiment, the method for fabricating the volume holographic grating further includes:

[0027] Determine whether the thickness of the grating structure has reached a preset value; if so, then perform a curing process on the holographic material layer.

[0028] If not, the holographic material layer is removed, and then the process of forming a holographic material layer on the first surface of the substrate is performed again.

[0029] According to a second aspect of this application, a volume holographic grating is provided, the grating structure being prepared by the volume holographic grating preparation method described in any of the above embodiments.

[0030] According to a third aspect of this application, a head-mounted device is provided, including the aforementioned volume holographic grating.

[0031] The aforementioned method for fabricating a volume holographic grating, the volume holographic grating itself, and the head-mounted device can utilize an exposure adjustment element to change the exit angle of the incident light, resulting in different exit angles of the incident light emitted from different positions along the first direction from the exposure adjustment element. This, in turn, causes the grating period of the grating structure to exhibit a gradual change. Thus, this grating structure can be applied to the coupling grating and coupling grating of a waveguide system. Taking the application of the grating structure to the coupling grating as an example, during the transmission of light (light emitted by the optomechanical system) through the waveguide of the waveguide system, the light first... The light is transmitted to a point on the coupling grating with a larger grating period and diffracted there, where the light intensity is high and the light can be diffracted out. Then, it continues to be transmitted through the waveguide to a point on the coupling grating with a smaller grating period and diffracted there, where the light intensity is low and more light can be diffracted out. This makes the light intensity coupled out at different positions along the longitudinal direction of the coupling grating roughly uniform, which can effectively improve the uniformity of image brightness and thus improve the viewing experience. Attached Figure Description

[0032] Figure 1 A schematic diagram of a fabrication apparatus for fabricating a grating structure is shown in one embodiment of this application.

[0033] Figure 2 A schematic flowchart of a method for fabricating a volume holographic grating according to an embodiment of this application is shown.

[0034] Figure 3 This diagram illustrates the principle of interference exposure of incident light and reference light on a holographic material layer according to an embodiment of this application.

[0035] Figure 4 A schematic diagram of the structure of an exposure adjustment element according to an embodiment of this application is shown.

[0036] Figure 5 A schematic diagram of the structure of an exposure adjustment element according to an embodiment of this application is shown (when voltage is applied).

[0037] Figure 6 This diagram illustrates the principle of how an exposure adjustment element according to an embodiment of the present application changes the exit angle of incident light.

[0038] Figure 7 A schematic diagram of the structure of a grating obtained by a method for fabricating a volume holographic grating according to an embodiment of this application is shown.

[0039] Figure 8 A schematic diagram of the exposure adjustment element according to another embodiment of this application is shown (when voltage is applied).

[0040] Figure 9A schematic diagram is shown showing the principle that the exit angle of incident light changes when a voltage is applied to the exposure adjustment element of an embodiment of this application.

[0041] Figure 10 This diagram illustrates the principle of interference exposure of incident light and reference light on a holographic material layer according to another embodiment of this application.

[0042] Figure 11 A schematic diagram of the structure of a grating structure obtained by a method for fabricating a volume holographic grating according to another embodiment of this application is shown.

[0043] Figure 12 A schematic diagram of the fabrication apparatus for fabricating a volume holographic grating is shown in one embodiment of this application (with a first light-blocking screen, a CCD camera, and a second light-blocking screen set).

[0044] Figure 13 A schematic diagram of the structure of a head-mounted device according to an embodiment of this application is shown.

[0045] Reference numerals: 210, substrate; 211, second surface; 220, holographic material layer; 221, grating structure; 230, exposure adjustment element; 2301, first region; 2302, second region; 2303, third region; 231, liquid crystal layer; 2311, liquid crystal; 2312, polymer matrix; 240, first light-blocking screen; 250, CCD camera; 260, second light-blocking screen; 271, laser source; 272, shutter; 273, beam splitter; 281, first reflector; 282, first filter; 283, first collimator Device; 284, First aperture; 291, Second reflector; 292, Second filter; 293, Second collimator; 294, Second aperture; 311, Incident light; 312, Reference light; 410, Optomechanical; 420, Coupled-in grating; 430, Coupled-out grating; 440, Waveguide; Step S110; Step S111; Step S120; Step S1201; Step S121; Step S1211; Step S1212; Step S12121; Step S12122; Step S130; Step S140; Step S150. Detailed Implementation

[0046] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0047] In the description of this application, it should be understood that if terms such as "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" appear, these terms indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0048] Furthermore, where the terms "first" and "second" appear, these terms are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, where the term "multiple" appears, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0049] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0050] In this application, unless otherwise expressly specified and limited, the use of descriptions such as "above" or "below" the second feature indicates that the first and second features are in direct contact or indirect contact via an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. Similarly, "below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0051] It should be noted that if an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. If an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. If so, the terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used in this application are for illustrative purposes only and do not represent the only possible implementation.

[0052] Research has revealed that the uneven brightness in traditional AR glasses stems from the following: Incident light is transmitted through a coupling grating to the waveguide of the waveguide system. As the light propagates within the waveguide, its energy is gradually lost. When the light emitted by the optical engine reaches the output grating, a portion of it is diffracted by the output grating and exits the waveguide to reach the eye. The other portion continues to propagate within the waveguide, further diffracted by the output grating, and exits the waveguide to reach the eye. Thus, the intensity of the light diffracted by the output grating gradually decreases, leading to uneven brightness in traditional AR glasses and consequently affecting the viewing experience.

[0053] To address the issue of uneven image brightness in traditional AR glasses, this application presents a method for fabricating a volume holographic grating. The grating period of the formed grating structure exhibits a gradual change, which can improve the problem of uneven image brightness and enhance the viewing experience.

[0054] Figure 1 This invention illustrates a schematic diagram of a fabrication apparatus for volume holographic gratings according to an embodiment of this application. Figure 2 A schematic flowchart of a method for fabricating a volume holographic grating according to an embodiment of this application is shown.

[0055] Please see Figure 1 and Figure 2 and in conjunction with reference Figure 3 The method for fabricating a volume holographic grating according to an embodiment of this application includes the following steps:

[0056] S110, a substrate 210 is provided, the substrate 210 having a first surface and a second surface 211 disposed opposite to each other.

[0057] S120. A holographic material layer 220 is formed on the first surface of the substrate 210. The holographic material layer 220 is a coating that can react to form a grating structure 221 when the incident light 311 and the reference light 312 are exposed by interference. The material of the holographic material layer 220 includes, but is not limited to, photopolymers and photorefractive crystals.

[0058] S130, incident light 311 is incident on holographic material layer 220 through exposure adjustment element 230, and reference light 312 is incident on second surface 211 of substrate 210, so that incident light 311 and reference light 312 interfere and expose on holographic material layer 220, and grating structure 221 is formed on holographic material layer 220.

[0059] The exposure adjustment element 230 is configured to make the exit angle of the incident light 311 emitted from different positions along the first direction F1 of the exposure adjustment element 230 different, thereby gradually changing the grating period of the grating structure 221. Thus, the exposure adjustment element 230 can be used to change the exit angle of the incident light 311, making the exit angle of the incident light 311 emitted from different positions along the first direction F1 of the exposure adjustment element 230 different, thereby making the grating period of the grating structure 221 gradually change. Therefore, the grating structure 221 can be applied to the coupling grating 420 and the coupling grating 430 of the waveguide system. Taking the application of the grating structure 221 to the coupling grating 430 as an example, the light (light emitted by the optomechanical system 410)... During transmission through waveguide 440 of the waveguide system, light first travels to a location with a larger grating period on the coupling grating 430 and is diffracted there. At this point, the light intensity is high, and the light can be diffracted out through this location. Then, it continues to travel through waveguide 440 to a location with a smaller grating period on the coupling grating 430 and is diffracted there. At this point, the light intensity is low, and more light can be diffracted out through this location. This makes the light intensity coupled out at different positions along the longitudinal direction of the coupling grating 430 approximately uniform, which can effectively improve the uniformity of image brightness and thus improve the viewing experience (the principle of the coupling grating 420 improving the uniformity of image brightness is similar and will not be elaborated here).

[0060] Optionally, the fabrication apparatus for the grating structure 221 further includes a laser source 271, a shutter 272, and a beam splitter 273. The light emitted from the laser source 271 is transmitted to the beam splitter 273 via the shutter 272, and is split into incident light 311 and reference light 312 by the beam splitter 273. The fabrication apparatus for the grating structure 221 further includes a first reflector 281, a first filter 282, a first collimator 283, a first aperture 284, a second reflector 291, a second filter 292, a second collimator 293, and a second aperture 294. The incident light 311 is reflected by the first reflector 281 to the first filter 282, and then transmitted to the first collimator via the first filter 282. The incident light 311 is collimated by the first collimator 283 and then collimated by the first aperture 284. Finally, it is transmitted to the exposure adjustment element 230 through the first aperture 284. After the exposure adjustment element 230 adjusts the exit direction of the incident light 311, it is transmitted to the holographic material layer 220. The reference light 312 is transmitted to the second collimator 293 through the second filter 292 and then collimated by the second collimator 293 and then transmitted to the second reflector 291 through the second aperture 294. Finally, it can be reflected by the second reflector 291 onto the second surface 211 of the substrate 210 so that it can interfere with the incident light 311 transmitted to the holographic material layer 220 for exposure.

[0061] In some embodiments, please refer to Figure 4 and Figure 5 The exposure adjustment element 230 includes a plurality of liquid crystal layers 231 disposed along the first direction F1, and the mass fraction of liquid crystal 2311 in at least three liquid crystal layers 231 increases along the first direction F1.

[0062] The liquid crystal layer 231 may be made of liquid crystal 2311 and polymer matrix 2312. For example, the liquid crystal layer 231 may be made of polymer dispersed liquid crystal (PDLC), which includes an organic solid polymer matrix and liquid crystal 2311 dispersed in micron-sized droplets within the organic solid polymer matrix.

[0063] The mass fraction of liquid crystal 2311 in liquid crystal layer 231 refers to the mass fraction of liquid crystal 2311 in liquid crystal layer 231. For example, if the material of liquid crystal layer 231 includes liquid crystal 2311 and polymer matrix 2312, the mass fraction of liquid crystal 2311 in liquid crystal layer 231 refers to the mass fraction of liquid crystal 2311 in the sum of the mass of liquid crystal 2311 and the mass of polymer matrix 2312.

[0064] Along the first direction F1, the mass fraction of liquid crystal 2311 in at least three liquid crystal layers 231 increases sequentially. This can be achieved by sequentially setting at least three liquid crystal layers 231 along the first direction F1 with increasing mass fraction, or by sequentially setting at least four liquid crystal layers 231 along the first direction F1 with increasing mass fraction. For example,... Figure 4 In the illustrated embodiment, the mass fraction of liquid crystal 2311 in the nine liquid crystal layers 231 arranged sequentially along the first direction F1 increases sequentially; alternatively, the mass fraction of liquid crystal 2311 in at least three regions of the liquid crystal layers 231 increases sequentially along the first direction F1, for example, as... Figure 5 In the illustrated embodiment, the mass fraction of liquid crystal 2311 in the liquid crystal layer 231 of the first region 2301, the liquid crystal layer 231 of the second region 2302, and the liquid crystal layer 231 of the third region 2303 increases sequentially.

[0065] Please see Figure 3 and in conjunction with reference Figure 6 Since the mass fraction of the liquid crystal 2311 in the liquid crystal layer 231 directly affects the emission angle of the incident light 311 emitted from the corresponding liquid crystal layer 231, and the higher the mass fraction of the liquid crystal 2311 in the liquid crystal layer 231, the smaller the emission angle of the incident light 311 emitted from the liquid crystal layer 231, the exposure adjustment element 230 can be used to make the grating at the corresponding position of the grating structure 221 more sparse, thereby making the grating period at the corresponding position of the grating structure 221 larger; conversely, the lower the mass fraction of the liquid crystal 2311 in the liquid crystal layer 231, the higher the grating at the corresponding position of the grating structure 221, thereby making the grating period at the corresponding position of the grating structure 221 smaller. Thus, a grating structure 221 with a gradually changing grating period can be formed (see [reference]). Figure 7 ).

[0066] In other embodiments, a decreasing voltage is applied to at least three liquid crystal layers 231 along a first direction F1.

[0067] Along the first direction F1, the voltage applied to at least three liquid crystal layers 231 decreases sequentially. This can be achieved by sequentially decreasing the voltage applied to at least three liquid crystal layers 231 arranged sequentially along the first direction F1, or by sequentially decreasing the voltage applied to at least four liquid crystal layers 231 arranged sequentially along the first direction F1. For example,... Figure 8In the illustrated embodiment, the voltage applied to the nine liquid crystal layers 231 arranged sequentially along the first direction F1 decreases sequentially, i.e., V9, V8, V7... and V1 decrease sequentially; alternatively, the voltage applied to the liquid crystal layers 231 in at least three regions along the first direction F1 decreases sequentially, for example, the voltage applied to the liquid crystal layer 231 in the first region 2301, the liquid crystal layer 231 in the second region 2302, and the liquid crystal layer 231 in the third region 2303 decreases sequentially. Figure 5 In the sequence, V3, V2, and V1 decrease in that order.

[0068] The electric field strength generated by the voltage applied to the liquid crystal layer 231 is 2.5-12.5V / μm. For example, the electric field strengths generated by the voltage applied to the nine liquid crystal layers 231 arranged sequentially along the first direction F1 are 12.5V / μm, 10.9V / μm, 9.8V / μm, 8.4V / μm, 6.8V / μm, 5.4V / μm, 4.5V / μm, 3.5V / μm and 2.5V / μm, respectively. For another example, the electric field strengths generated by the voltage applied to the liquid crystal layer 231 in the first region 2301, the liquid crystal layer 231 in the second region 2302 and the liquid crystal layer 231 in the third region 2303 are 12.5V / μm, 6.8V / μm and 4.5V / μm, respectively.

[0069] like Figure 9 As shown, by adjusting the voltage applied to the liquid crystal layer 231, the emission angle of the incident light 311 emitted from the liquid crystal layer 231 can be changed, so that the emission angle of the incident light 311 emitted from different positions of the exposure adjustment element 230 along the first direction F1 is different, and a grating structure 221 with a gradually changing grating period can also be formed.

[0070] In some embodiments, the exposure adjustment element 230 includes a plurality of liquid crystal layers 231 disposed along a first direction F1, wherein the mass fraction of liquid crystal 2311 in at least three liquid crystal layers 231 increases along the first direction F1, and the voltage applied to at least three liquid crystal layers 231 decreases.

[0071] On the one hand, by setting the mass fraction of the liquid crystal 2311 in the liquid crystal layer 231, the emission angle of the incident light 311 emitted from the liquid crystal layer 231 can be changed. On the other hand, by adjusting the voltage applied to the liquid crystal layer 231, the emission angle of the incident light 311 emitted from the liquid crystal layer 231 can also be changed, so that the emission angle of the incident light 311 emitted from different positions of the exposure adjustment element 230 along the first direction F1 is different, and a grating structure 221 with a gradually changing grating period can also be formed.

[0072] In some embodiments, please refer to Figure 5The exposure adjustment element 230 includes a first region 2301, a second region 2302 and a third region 2303 arranged sequentially along the first direction F1, wherein the mass fraction of liquid crystal 2311 in the liquid crystal layer 231 of the first region 2301, the liquid crystal layer 231 of the second region 2302 and the liquid crystal layer 231 of the third region 2303 increases sequentially.

[0073] The mass fraction of liquid crystal 2311 in liquid crystal layer 231 is 30%-60%.

[0074] The mass fraction of liquid crystal 2311 in the liquid crystal layer 231 of the first region 2301 can be 30%-40%, the mass fraction of liquid crystal 2311 in the liquid crystal layer 231 of the second region 2302 can be 40%-50%, and the mass fraction of liquid crystal 2311 in the liquid crystal layer 231 of the third region 2303 can be 50%-60%. For example, the mass fraction of liquid crystal 2311 in the liquid crystal layer 231 of the first region 2301 is 32%, the mass fraction of liquid crystal 2311 in the liquid crystal layer 231 of the second region 2302 is 45.5%, and the mass fraction of liquid crystal 2311 in the liquid crystal layer 231 of the third region 2303 is 52%.

[0075] In this way, the grating period at the position corresponding to the third region 2303 on the grating structure 221 is maximized, the grating period at the position corresponding to the second region 2302 on the grating structure 221 is next, and the grating period at the position corresponding to the first region 2301 on the grating structure 221 is minimized (please refer to...). Figure 5 , Figure 10 and Figure 11 (To understand), the light with higher intensity (the light emitted by the optical engine 410) is diffracted through the part of the coupling grating 430 with a larger grating period, so that the light can be diffracted out through this part. The light with lower intensity (the light emitted by the optical engine 410) is diffracted through the part of the coupling grating 430 with a smaller grating period, so that more light can be diffracted out through this part, which can improve the uniformity of the image brightness.

[0076] In other embodiments, please refer to Figure 4 , Figure 7 and Figure 8 The mass fraction of liquid crystal 2311 in at least three liquid crystal layers 231 arranged sequentially along the first direction F1 increases sequentially.

[0077] In this way, a grating structure 221 with a gradually changing grating period can be formed. For example, there are nine liquid crystal layers 231, and the mass fractions of liquid crystal 2311 in the nine liquid crystal layers 231 are 32%, 34%, 37%, 40%, 42%, 44%, 46%, 48%, and 52%, respectively. The grating period of the formed grating structure 221 gradually decreases, and gradually decreases in the range of 0.82μm-0.43μm.

[0078] In some embodiments, the mass fraction of liquid crystal 2311 of at least three liquid crystal layers 231 arranged sequentially along the first direction F1 increases sequentially, and the voltage applied to the at least three liquid crystal layers 231 arranged sequentially along the first direction F1 decreases sequentially.

[0079] For example, in this embodiment (corresponding to Embodiment 1 in Table 1), the mass fractions of liquid crystal 2311 in the nine liquid crystal layers 231 arranged sequentially along the first direction F1 are 32%, 34%, 37%, 40%, 42%, 44%, 46%, 48%, and 52%, respectively. The electric field strengths generated by the voltage applied to the nine liquid crystal layers 231 arranged sequentially along the first direction F1 are 12.5V / μm, 10.9V / μm, 9.8V / μm, 8.4V / μm, 6.8V / μm, 5.4V / μm, 4.5V / μm, 3.5V / μm, and 2.5V / μm, respectively.

[0080] Table 1 below provides a comparison of the optical parameters of the comparative example and this embodiment (corresponding to Embodiment 1 in Table 1). In the comparative example, the grating period of the grating is constant at 0.82 μm. As can be seen from Table 1 below, compared with the comparative example, in this embodiment (corresponding to Embodiment 1 in Table 1), the grating period of the grating structure 221 prepared by the volume holographic grating preparation method of this application shows a gradual trend in the range of 0.82 μm-0.43 μm, which can effectively improve the uniformity of imaging brightness, diffraction efficiency, contrast and clarity of the head-mounted device, improve light leakage, and thus improve the viewing experience.

[0081] Table 1. Comparison of optical parameters for comparative examples, Example 1, and Example 2.

[0082]

[0083]

[0084] In some other embodiments, the mass fraction of liquid crystal 2311 in the liquid crystal layer 231 of the first region 2301, the liquid crystal layer 231 of the second region 2302, and the liquid crystal layer 231 of the third region 2303 increases sequentially, and the voltage applied to the liquid crystal layer 231 of the first region 2301, the liquid crystal layer 231 of the second region 2302, and the liquid crystal layer 231 of the third region 2303 decreases sequentially.

[0085] For example, in this embodiment (corresponding to Embodiment 2 in Table 1), the mass fraction of liquid crystal 2311 in the liquid crystal layer 231 of the first region 2301 is 32%, the mass fraction of liquid crystal 2311 in the liquid crystal layer 231 of the second region 2302 is 45.5%, and the mass fraction of liquid crystal 2311 in the liquid crystal layer 231 of the third region 2303 is 52%. The electric field strengths generated by the voltages applied to the liquid crystal layer 231 of the first region 2301, the liquid crystal layer 231 of the second region 2302, and the liquid crystal layer 231 of the third region 2303 are 12.5V / μm, 6.8V / μm, and 4.5V / μm, respectively.

[0086] As can be seen from Table 1 above, compared with the comparative example, in this embodiment (corresponding to embodiment 2 in Table 1), the grating period of the grating structure 221 prepared by the volume holographic grating preparation method of this application is gradually varied. The grating periods corresponding to the first region 2301, the second region 2302, and the third region 2303 on the grating structure 221 are 0.43μm, 0.55μm, and 0.82μm, respectively. The grating structure 221 of this application can effectively improve the uniformity of imaging brightness, diffraction efficiency, contrast, and clarity of the head-mounted device, thereby improving the viewing experience.

[0087] In some embodiments, please refer again Figure 2 The incident light 311 is incident on the holographic material layer 220 through the exposure adjustment element 230, and the reference light 312 is incident on the second surface 211 of the substrate 210, so that the incident light 311 and the reference light 312 interfere with each other on the holographic material layer 220. Before step S130, which forms the grating structure 221 on the holographic material layer 220, the method for fabricating the volume holographic grating further includes:

[0088] S121. Determine whether the exposure pattern formed by the incident light 311 incident on the holographic material layer 220 through the exposure adjustment element 230 meets the preset requirements. If so, proceed to step S130.

[0089] Therefore, before using incident light 311 and reference light 312 for interference exposure, it is possible to check whether the exposure pattern to be formed meets the preset requirements, so as to form a preset exposure pattern on the holographic material layer 220 and thus obtain a grating structure 221 with a gradually changing grating period.

[0090] Please refer to it again. Figure 2S1201 If the exposure pattern formed by the incident light 311 incident on the holographic material layer 220 through the exposure adjustment element 230 does not meet the preset requirements, the voltage applied to at least one liquid crystal layer 231 is adjusted until the exposure pattern formed by the incident light 311 incident on the holographic material layer 220 through the exposure adjustment element 230 meets the preset requirements.

[0091] Before interference exposure using incident light 311 and reference light 312, if it is found that the exposure pattern to be formed does not meet the preset requirements, the voltage applied to at least one liquid crystal layer 231 can be adjusted until the exposure pattern to be formed meets the preset requirements again, thereby forming the preset exposure pattern on the holographic material layer 220, and thus obtaining the grating structure 221 with a gradually changing grating period.

[0092] Optionally, step S1201 can be performed after step S120. In this embodiment, after step S120, the formed exposure adjustment element 230 includes a plurality of liquid crystal layers 231 disposed along the first direction F1. Along the first direction F1, the mass fraction of liquid crystal 2311 in at least three liquid crystal layers 231 increases. In step S1201, the voltage applied to at least three liquid crystal layers 231 decreases. If it is found that the exposure pattern to be formed does not meet the preset requirements, the voltage applied to at least one liquid crystal layer 231 can be adjusted until the exposure pattern to be formed meets the preset requirements again. In this way, the reliability of the volume holographic grating fabrication method can be improved.

[0093] In this embodiment, determining whether the exposure pattern formed by the incident light 311 incident on the holographic material layer 220 through the exposure adjustment element 230 meets the preset requirements specifically includes:

[0094] S1211, The first light-blocking screen 240 is positioned between the exposure adjustment element 230 and the holographic material layer 220 (e.g., ...). Figure 12 (as shown), so that the incident light 311 can be projected onto the first light-blocking screen 240 through the exposure adjustment element 230.

[0095] S1212. Based on the pattern projected onto the first light-blocking screen 240, determine whether the exposure pattern formed by the incident light 311 incident on the holographic material layer 220 through the exposure adjustment element 230 meets the preset requirements.

[0096] The pattern projected onto the first light-blocking screen 240 can be compared with a preset pattern. If the difference between the pattern projected onto the first light-blocking screen 240 and the preset pattern is small, it indicates that the exposure pattern formed by the incident light 311 incident on the holographic material layer 220 by the exposure adjustment element 230 meets the preset requirements. If the difference between the pattern projected onto the first light-blocking screen 240 and the preset pattern is large, it indicates that the exposure pattern formed by the incident light 311 incident on the holographic material layer 220 by the exposure adjustment element 230 does not meet the preset requirements. In this way, it is possible to check whether the exposure pattern to be formed meets the preset requirements before using the incident light 311 and the reference light 312 for interference exposure.

[0097] In this embodiment, step S1212, which determines whether the exposure pattern formed by the incident light 311 incident on the holographic material layer 220 through the exposure adjustment element 230 meets the preset requirements based on the pattern projected on the first light-blocking screen 240, specifically includes:

[0098] S12121. Take a picture of the pattern projected onto the first light-blocking screen 240 to obtain the picture. A CCD camera 250 can be used to take a picture of the pattern projected onto the first light-blocking screen 240 to obtain the picture.

[0099] S12122. Based on the comparison between the captured pattern and the preset pattern, determine whether the exposure pattern formed by the incident light 311 incident on the holographic material layer 220 through the exposure adjustment element 230 meets the preset requirements.

[0100] The CCD camera 250 includes an image capture module and an analysis and processing module. The image capture module is used to capture a pattern projected onto the first light-blocking screen 240 to obtain an image capture pattern. The analysis and processing module is used to compare the image capture pattern with a preset pattern to obtain a comparison result between the image capture pattern and the preset pattern. Based on the comparison result between the image capture pattern and the preset pattern, it determines whether the exposure pattern formed by the incident light 311 incident on the holographic material layer 220 through the exposure adjustment element 230 meets the preset requirements.

[0101] If the difference between the captured pattern and the preset pattern is small, it indicates that the exposure pattern formed by the incident light 311 incident on the holographic material layer 220 by the exposure adjustment element 230 meets the preset requirements. If the difference between the captured pattern and the preset pattern is large, it indicates that the exposure pattern formed by the incident light 311 incident on the holographic material layer 220 by the exposure adjustment element 230 does not meet the preset requirements.

[0102] In this embodiment, determining whether the exposure pattern formed by the incident light 311 incident on the holographic material layer 220 through the exposure adjustment element 230 meets the preset requirements further includes:

[0103] The second light barrier 260 is disposed on the side of the second surface 211 of the substrate 210 away from the first surface, and the first light barrier 240 and the second light barrier 260 are symmetrically arranged with regard to the whole formed by the substrate 210 and the holographic material layer 220, so that the reference light 312 can be incident on the second light barrier 260.

[0104] In this way, the reference light 312 can be blocked by the second light barrier 260 before the second surface 211 of the substrate 210. When it is found that the exposure pattern formed by the incident light 311 incident on the holographic material layer 220 through the exposure adjustment element 230 meets the preset requirements, the first light barrier 240 and the second light barrier 260 can be removed at the same time. This allows the reference light beam 312 to be incident on the second surface 211 of the substrate 210, while the incident light 311 can be incident on the holographic material layer 220. This allows the reference light beam 312 and the incident light 311 to better interfere with each other during exposure, thereby improving the reliability of the grating structure 221.

[0105] In this embodiment, incident light 311 is incident on the holographic material layer 220 through exposure adjustment element 230, and reference light 312 is incident on the second surface 211 of substrate 210, so that incident light 311 and reference light 312 interfere with each other on the holographic material layer 220. The step S130 of forming grating structure 221 on holographic material layer 220 specifically includes:

[0106] Simultaneously, the first light-blocking screen 240 and the second light-blocking screen 260 are removed so that the reference beam 312 and the incident light 311 can interfere with each other for exposure, so as to form a grating structure 221 on the holographic material layer 220.

[0107] In some embodiments, please refer again Figure 3 The fabrication methods for volume holographic gratings also include:

[0108] S140. Determine whether the thickness of the grating structure 221 has reached the preset value.

[0109] S150, If so, then the holographic material layer 220 is cured.

[0110] S111. If not, remove the holographic material layer 220 and then form the holographic material layer 220 on the first surface of the substrate 210. In the step of removing the holographic material layer 220, the substrate 210 may be cleaned to remove the holographic material layer 220.

[0111] First, check if the thickness of the grating structure 221 meets the requirements. If it does, then the holographic material layer 220 is cured by baking. If not, the substrate 210 needs to be cleaned before re-forming the holographic material layer 220 on the first surface of the substrate 210 to re-fabricate the grating structure 221. This improves the reliability of the volume holographic grating fabrication method.

[0112] The volume holographic grating provided in one embodiment of this application is prepared by the volume holographic grating preparation method of any of the above embodiments.

[0113] Please see Figure 13 One embodiment of this application provides a head-mounted device including the volume holographic grating described above. The volume holographic grating includes a substrate 210 and a grating structure 221.

[0114] The head-mounted device includes an input grating 420 and an output grating 430. Both the input grating 420 and the output grating 430 include the aforementioned volume holographic grating. The grating period gradient of the grating structure 221 of the input grating 420 and the output grating 430 is the same. The head-mounted device includes an optomechanical system 410 and a waveguide 440.

[0115] The grating period of the grating structure 221 of the volume holographic grating prepared by the method of this application shows a gradual trend in the range of 0.82μm-0.43μm.

[0116] Thus, during the transmission of light emitted from the optical engine 410 through the waveguide 440, the light first travels to a location on the grating structure 221 with a larger grating period (e.g., 0.82 μm), where the light intensity is higher and the light can be diffracted out. Then, it travels through the waveguide 440 to a location on the grating structure 221 with a smaller grating period (e.g., 0.55 μm or 0.43 μm), where the light intensity is lower and more light can be diffracted out. In this way, the light intensity coupled out of the coupling grating 430 at different positions along its longitudinal direction can be made to be roughly consistent. The grating structure 221 of this application can be used to improve the uniformity of image brightness, diffraction efficiency, contrast and sharpness, thereby improving the viewing experience.

[0117] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0118] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for fabricating a volume holographic grating, characterized in that, include: A substrate is provided, the substrate having a first surface and a second surface disposed opposite to each other; A holographic material layer is formed on the first surface of the substrate; Incident light is incident on the holographic material layer through an exposure adjustment element, and reference light is incident on the second surface of the substrate, so that the incident light and the reference light interfere with each other on the holographic material layer to form a grating structure on the holographic material layer. The exposure adjustment element is configured to make the exit angle of the incident light emitted from different positions along the first direction different, thereby making the grating period of the grating structure gradually change. The exposure adjustment element includes a plurality of liquid crystal layers disposed along the first direction, wherein the mass fraction of liquid crystal in at least three of the liquid crystal layers increases along the first direction; the material of the liquid crystal layer includes liquid crystal and polymer matrix, and the mass fraction of liquid crystal in the liquid crystal layer refers to the mass fraction of the liquid crystal relative to the sum of the mass of the liquid crystal and the mass of the polymer matrix; and / or, the voltage applied to at least three of the liquid crystal layers decreases.

2. The method for fabricating a volume holographic grating according to claim 1, characterized in that, The holographic material layer is made of photopolymers and photorefractive crystals.

3. The method for fabricating a volume holographic grating according to claim 2, characterized in that, The exposure adjustment element includes a first region, a second region, and a third region arranged sequentially along the first direction, wherein the mass fraction of the liquid crystal in the liquid crystal layer of the first region, the liquid crystal layer of the second region, and the liquid crystal layer of the third region increases sequentially. and / or The voltages applied to the liquid crystal layer in the first region, the liquid crystal layer in the second region, and the liquid crystal layer in the third region decrease sequentially.

4. The method for fabricating a volume holographic grating according to claim 2, characterized in that, Along the first direction, the mass fraction of the liquid crystal in at least three liquid crystal layers arranged sequentially increases sequentially; and / or The voltage applied to at least three liquid crystal layers arranged sequentially along the first direction decreases sequentially.

5. The method for fabricating a volume holographic grating according to claim 2, characterized in that, The method for fabricating the volume holographic grating, which involves passing incident light through an exposure adjustment element onto the holographic material layer and incident reference light onto the second surface of the substrate, to cause interference exposure between the incident light and the reference light on the holographic material layer, further includes the following steps before forming a grating structure on the holographic material layer: Determine whether the exposure pattern formed by the incident light incident on the holographic material layer through the exposure adjustment element meets the preset requirements. If so, execute the step of causing the incident light to pass through the exposure adjustment element and be incident on the holographic material layer, and causing the reference light to be incident on the second surface of the substrate, so that the incident light and the reference light interfere with each other on the holographic material layer to form a grating structure on the holographic material layer.

6. The method for fabricating a volume holographic grating according to claim 5, characterized in that, Determine whether the exposure pattern formed by the incident light incident on the holographic material layer through the exposure adjustment element meets the preset requirements. If not, adjust the voltage applied to at least one of the liquid crystal layers until the exposure pattern formed by the incident light incident on the holographic material layer through the exposure adjustment element meets the preset requirements.

7. The method for fabricating a volume holographic grating according to claim 5, characterized in that, The determination of whether the exposure pattern formed by the incident light incident on the holographic material layer through the exposure adjustment element meets the preset requirements specifically includes: A first light-blocking screen is placed between the exposure adjustment element and the holographic material layer so that the incident light can be projected onto the first light-blocking screen through the exposure adjustment element. Based on the pattern projected onto the first light-blocking screen, it is determined whether the exposure pattern formed by the incident light incident on the holographic material layer through the exposure adjustment element meets the preset requirements.

8. The method for fabricating a volume holographic grating according to claim 7, characterized in that, The step of determining whether the exposure pattern formed by the incident light incident on the holographic material layer through the exposure adjustment element meets the preset requirements based on the pattern projected on the first light-blocking screen specifically includes: The pattern projected onto the first light-blocking screen is photographed to obtain the photographed pattern; Based on the comparison between the captured pattern and the preset pattern, it is determined whether the exposure pattern formed by the incident light incident on the holographic material layer through the exposure adjustment element meets the preset requirements.

9. The method for fabricating a volume holographic grating according to claim 7, characterized in that, The determination of whether the exposure pattern formed by the incident light incident on the holographic material layer through the exposure adjustment element meets the preset requirements further includes: The second light-blocking screen is disposed on the second surface of the substrate away from the first surface, and the first light-blocking screen and the second light-blocking screen are symmetrically arranged with regard to the whole formed by the substrate and the holographic material layer, so that the reference light can be incident on the second light-blocking screen.

10. The method for fabricating a volume holographic grating according to any one of claims 1-9, characterized in that, The method for fabricating the volume holographic grating further includes: Determine whether the thickness of the grating structure has reached a preset value; if so, then perform a curing process on the holographic material layer. If not, the holographic material layer is removed, and then the process of forming a holographic material layer on the first surface of the substrate is performed again.

11. A volume holographic grating, characterized in that, The volume holographic grating is prepared by the method for preparing a volume holographic grating according to any one of claims 1-10.

12. A head-mounted device, characterized in that, Includes the volume holographic grating as described in claim 11.

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