Preparation method of waveguide structure and reflecting film

Abstract

The invention provides a preparation method of a waveguide structure and a reflecting film, and relates to the technical field of diffraction optical waveguides, the waveguide structure comprises an optical waveguide, the optical waveguide at least comprises an entrance pupil region and an exit pupil region, the entrance pupil region and the exit pupil region are respectively provided with an entrance pupil grating and an exit pupil grating, and the exit pupil region is provided with a first reflecting film. The reflectivity of the first reflecting film corresponding to different areas of the exit pupil grating is different, the reflectivity of the first reflecting film in the same area of the exit pupil grating is r, the diffraction efficiency of the exit pupil grating is d, r + d = a, and a is a fixed value. The first reflecting film is a regional reflecting film, and the reflectivity of the first reflecting film is designed according to the diffraction efficiency of different regions of the exit pupil grating, so that emergent light is mainly concentrated in the eye direction of a user, light leakage in the other direction is reduced, image brightness uniformity is improved, privacy is improved, light output in the eye direction is ensured, and the image quality is improved. Energy leakage towards a non-target direction is effectively inhibited; the coupling-out energy distribution state is improved, and the overall brightness and the brightness uniformity of the display image are improved.

Description

Technical Field

[0001] This application relates to the technical field of diffractive optical waveguides, and particularly relates to a preparation method for a waveguide structure and a reflective film. Background Art

[0002] As a commonly used optical display technology in augmented reality (AR) and mixed reality (MR) devices, diffractive optical waveguides have the advantages of being thin, light, and having a large field of view. Its core principle is to couple the light emitted by the display screen into the waveguide through a diffraction grating and couple it out at the exit pupil, so as to transmit the image to the user's eyes.

[0003] However, there are generally two main problems in existing diffractive optical waveguides in practical applications:

[0004] First, due to the characteristics of diffraction in two directions, transmission and reflection, part of the light will be coupled out in two opposite directions in the exit pupil area. One direction is the expected direction received by the user's eyes, while the other direction points to the external space, enabling non-users to also observe the image content from the opposite side, resulting in light leakage. This phenomenon not only causes waste of light energy but also may disclose the content that the user is watching, presenting a certain privacy and security risk.

[0005] Secondly, the diffraction efficiencies in different areas of the exit pupil are different, which leads to different brightnesses of the coupled-out images in different areas, making the overall brightness of the image uneven, with some areas being too bright and some areas being too dark.

[0006] To improve the above problems, the industry mainly compensates by optimizing the grating structure, adjusting the coupled-out distribution, or introducing a homogenization algorithm at present, but there are still deficiencies such as complex design, high energy consumption, or limited compensation effect. Summary of the Invention

[0007] The purpose of the embodiments of this application is to provide a preparation method for a waveguide structure and a reflective film, which has a simple structure, is easy to manufacture, and can effectively improve image uniformity and suppress light leakage.

[0008] On the one hand, an embodiment of this application provides a waveguide structure, including an optical waveguide. The optical waveguide at least includes an entrance pupil area and an exit pupil area. The entrance pupil area and the exit pupil area respectively have an entrance pupil grating and an exit pupil grating. A first reflective film is provided on the exit pupil area. The reflectivity of the first reflective film in different areas corresponding to the exit pupil grating is different. In the same area of the exit pupil grating, the reflectivity of the first reflective film is r, and the diffraction efficiency of the exit pupil grating is d, and r + d = a, where a is a fixed value.

[0009] Optionally, the value range of a is 0.8 to 1.2.

[0010] Optionally, a second reflective film is provided on the entrance pupil grating in the entrance pupil region. The reflectivity of different regions on the second reflective film is equal, and the reflectivity of the second reflective film is ≥90%.

[0011] Optionally, the entrance pupil grating in the entrance pupil region is two-layered, and the grating directions of the two layers of entrance pupil gratings are symmetrically arranged.

[0012] Optionally, the second reflective film and the entrance pupil grating are attached or spaced apart.

[0013] Optionally, it further includes an expanding pupil region. The expanding pupil region has an expanding pupil grating, and a reflective film is provided on the expanding pupil grating in the expanding pupil region. The reflective film is the first reflective film or the second reflective film.

[0014] On the other hand, an embodiment of the present application provides a method for preparing a reflective film for preparing the first reflective film in the above waveguide structure. The first reflective film is a holographic reflective film, including: controlling the laser beam emitted by the laser. The beam is expanded, collimated, and shaped by a diaphragm and then incident on the photosensitive film. The beam transmitted through the photosensitive film is reflected by a mirror back to the photosensitive film to form the holographic reflective film on the photosensitive film.

[0015] Optionally, it further includes a mask. The mask is provided between the beam expander-collimator and the diaphragm, and the mask is used to control the exposure intensity of different regions on the holographic reflective film.

[0016] Optionally, the photosensitive film is provided on glass. The shape of the glass is the same as that of the optical waveguide, and the optical waveguide and the glass are adhesively provided.

[0017] Optionally, the photosensitive film is provided on a PET coil so that the holographic reflective film is formed on the PET coil, and the PET coil is provided in the exit pupil region.

[0018] The waveguide structure and the method for preparing a reflective film provided by the embodiments of the present application, by providing the first reflective film in the exit pupil region, the first reflective film is a sub-region reflective film, and its reflectivity is designed according to the diffraction efficiency of different regions of the exit pupil grating, so that the emitted light is mainly concentrated in the direction of the user's eyes, reducing the light leakage in the other direction, improving the image brightness uniformity and enhancing the privacy. While ensuring the light output in the direction of the human eye, it effectively suppresses the energy leakage to non-target directions; it can also improve the state of the coupled-out energy distribution, enhancing the overall brightness and brightness uniformity of the displayed image. And such a waveguide structure is simple in structure and easy to manufacture. Description of the Drawings

[0019] To more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required for use in the embodiments of the present application. It should be understood that the following drawings only show certain embodiments of the present application and should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0020] Figure 1 is one of the schematic diagrams of the waveguide structure provided by the embodiments of the present application;

[0021] Figure 2 is another schematic diagram of the waveguide structure provided by the embodiments of the present application;

[0022] Figure 3 is still another schematic diagram of the waveguide structure provided by the embodiments of the present application;

[0023] Figure 4 is one of the schematic diagrams of the double-layer entrance pupil grating structure of the waveguide structure provided by the embodiments of the present application;

[0024] Figure 5 is another schematic diagram of the double-layer entrance pupil grating structure of the waveguide structure provided by the embodiments of the present application;

[0025] Figure 6 is the optical path diagram for preparing the first reflective film in the waveguide structure provided by the embodiments of the present application;

[0026] Figure 7 is the refractive index modulation - reflection efficiency curve diagram of the waveguide structure provided by the embodiments of the present application;

[0027] Figure 8 is the curve diagram of the reflection efficiency of the waveguide structure varying with the exposure dose provided by the embodiments of the present application.

[0028] Icon: 10 - optical waveguide; 11 - entrance pupil region; 111 - first entrance pupil grating; 112 - second entrance pupil grating; 12 - exit pupil region; 21 - first reflective film; 22 - second reflective film; 31 - optical machine; 40 - laser; 41 - beam expander collimator; 42 - aperture stop; 43 - aperture; 44 - shaper; 45 - photosensitive film; 46 - mirror; In - incident light ray. Detailed implementation manners

[0029] The following will clearly and completely describe the technical solutions in the embodiments of the present application in conjunction with the drawings in the embodiments of the present application.

[0030] In the description of the present application, it should be noted that the orientation or positional relationship indicated by terms such as "inner" and "outer" is based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of this application is customarily placed during use. This is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present application. In addition, terms such as "first" and "second" are only used for distinguishing descriptions and cannot be construed as indicating or implying relative importance.

[0031] It should also be noted that unless otherwise clearly specified and defined, the terms "set" and "connect" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific circumstances.

[0032] The following two core problems exist in the current diffractive optical waveguide technology:

[0033] Light leakage problem in non-target directions: In the existing diffractive optical waveguide system, the grating structure in the exit pupil region couples out light in both transmission and reflection directions simultaneously. Although one of the directions is the target light output direction designed for the user's eyes, the light in the other direction may also be received by external observers, resulting in image leakage. This phenomenon not only reduces the overall energy utilization efficiency of the system but also may pose a risk of user privacy exposure.

[0034] Image brightness non-uniformity problem: Since the imaging process of the optical waveguide depends on the gradual coupling out of light in the exit pupil region, the diffraction efficiencies of different regions in the exit pupil are inconsistent, resulting in differences in light intensity in different regions of the exit pupil, and ultimately causing unevenness in the brightness distribution of the displayed image, which affects the visual experience.

[0035] In view of this, to solve the above problems, please refer to Figure 1 As shown, the embodiment of the present application provides a waveguide structure, which can be applied to a near-eye display system based on a diffractive optical waveguide 10, and is particularly applicable to application scenarios such as augmented reality (AR), mixed reality (MR), and other applications that require head-mounted display devices; it includes: an optical waveguide 10, the optical waveguide 10 at least includes an entrance pupil region 11 and an exit pupil region 12, the entrance pupil region 11 and the exit pupil region 12 respectively have an entrance pupil grating and an exit pupil grating, a first reflective film 21 is provided on the exit pupil region 12, and the reflectivities of the first reflective film 21 corresponding to different regions of the exit pupil grating are different. In the same region of the exit pupil grating, the reflectivity of the first reflective film 21 is r, the diffraction efficiency of the exit pupil grating is d, and r + d = a, where a is a fixed value.

[0036] An entrance pupil region 11 and an exit pupil region 12 are formed on the optical waveguide 10. The optical waveguide 10 serves as the core optical transmission medium, usually a flat transparent material (such as glass or high refractive index plastic), with multiple diffraction grating structures embedded or attached to its surface, which are used to conduct multiple total internal reflection guiding propagations on the image light and sequentially couple it out in the exit pupil region 12.

[0037] The entrance pupil region 11 includes a coupling structure (such as a diffraction grating or a wedge prism, etc.) for coupling the image light of the display source into the optical waveguide 10. In this application, the coupling structure of the entrance pupil region 11 is an entrance pupil grating.

[0038] The entrance pupil region 11 generally corresponds to the display source module, and the display source module is generally a microdisplay device, such as Micro-LED, OLED, or LCoS, etc., which is used to generate the image content to be displayed. The image light is coupled into the optical waveguide 10 through the entrance pupil grating in the entrance pupil region 11 and propagates.

[0039] The exit pupil region 12 is the region where the optical waveguide 10 finally outputs the image light to the human eye. A first reflective film 21 is provided on the surface of the exit pupil region 12. The reflectivities of different regions of the first reflective film 21 corresponding to the exit pupil grating are different. That is to say, the first reflective film 21 is a sub-region reflective film, and its reflectivity is designed according to the diffraction efficiency of different regions of the exit pupil grating, so that the outgoing light is mainly concentrated in the direction of the user's eyes, reducing the light leakage in the other direction, improving the image brightness uniformity and enhancing the privacy. Through the configuration of the first reflective film 21, the imaging quality can be effectively improved in the above system, the user experience can be enhanced, and the application ability of the device in the high-end display field can be expanded.

[0040] In this application, within the same region of the exit pupil grating, the reflectivity of the first reflective film 21 is r, the diffraction efficiency of the exit pupil grating is d, and r + d = a, where a is a fixed value. The value range of a is 0.8 to 1.2.

[0041] Furthermore, a second reflective film 22 is provided on the entrance pupil grating in the entrance pupil region 11. The second reflective film 22 has the same reflectivity, that is, the reflectivities of different regions on the second reflective film 22 are equal, and the reflectivity of the second reflective film 22 ≥ 90%. The second reflective film 22 can be used to reflect some of the image light that is not effectively coupled in, so that it is redirected inside the optical waveguide 10, thereby enhancing the light flux entering the system.

[0042] A pupil expansion region may also be provided on the optical waveguide 10. A pupil expansion grating is provided in the pupil expansion region. After the image light coupled into the optical waveguide 10 passes through the entrance pupil region 11 and the pupil expansion region, it is coupled out by the exit pupil region 12. The pupil expansion region is used to enlarge the exit pupil range of the system to support free viewing by the user within a certain range. In this application, a reflective film is provided in the pupil expansion region. The reflective film may be the first reflective film 21 to suppress the leakage of ineffective light and improve the energy utilization efficiency of the system. The reflective film in the pupil expansion region may also be the second reflective film 22, which can also enhance the light flux.

[0043] In summary, the entrance pupil region 11 generally needs to be set corresponding to the optical engine 31. The light emitted by the optical engine 31 is coupled into the optical waveguide 10 from the entrance pupil region 11. At this time, since the entrance pupil region 11 also couples light into the optical waveguide 10 by grating diffraction, there will also be light loss on the other side. Therefore, the second reflective film 22 can also be provided at the place corresponding to the entrance pupil region 11 to reflect the leaked light into the optical waveguide 10, which can ultimately improve the brightness of the image. The second reflective film 22 provided in the entrance pupil region 11 does not directly participate in imaging, so the reflectivity of the second reflective film 22 does not need to be set in zones. The higher the overall reflectivity of the second reflective film 22, the better, and some possible secondary diffraction problems can also be reduced accordingly.

[0044] There may also be a certain amount of light leakage in the pupil expansion region. Therefore, a reflective film can also be provided in the pupil expansion region. The reflective film in the pupil expansion region can be the second reflective film 22 with the same reflectivity in the whole region, or the first reflective film 21 with the reflectivity set in zones according to the diffraction efficiency of pupil expansion. This application does not make a limitation.

[0045] The first reflective film 21 is provided on the exit pupil region 12. The reflectivity of the first reflective film 21 needs to be set according to the diffraction efficiency of different regions on the exit pupil. For example, if the exit pupil region 12 is divided into n regions, the first reflective film 21 is also correspondingly divided into n regions. The reflectivity r of the first reflective film 21 in the same region and the grating diffraction efficiency d of this region (here the diffraction efficiency refers to the proportion of the energy diffracted into the human eye in the total energy obtained by this region) need to satisfy: r1 + d1 = r2 + d2 = r3 + d3 =... = a, where a is a constant, and the value range of a is 0.8 to 1.2. In this way, the energy obtained by different regions of the entire exit pupil is relatively close, thereby improving the uniformity of the image, and since the first reflective film 21 recovers and utilizes the originally wasted energy, the image brightness is also improved.

[0046] The waveguide structure of the present application optimizes the light energy management structure in the exit pupil region 12, effectively suppressing the energy leakage in non-target directions while ensuring the light output in the human eye direction, improving the coupled-out energy distribution state, enhancing the overall brightness and brightness uniformity of the displayed image, and taking into account the light energy utilization rates of the entrance pupil region 11 and the pupil expansion region, further improving the system efficiency and display effect.

[0047] Specifically, in the example of the present application, as Figure 2 shown, reflective films are provided on both the entrance pupil region 11 and the exit pupil region 12 of the optical waveguide 10. The entrance pupil region 11 corresponds to the light engine 31. The light engine 31 emits light. Some of the light is directly coupled into the optical waveguide 10 through the entrance pupil region 11 for total reflection propagation, and some of the light is transmitted through the entrance pupil region 11, reflected by the second reflective film 22 on the entrance pupil region 11, and then hits the entrance pupil region 11 again and is coupled into the optical waveguide 10 for propagation. The blue light in the figure represents this process.

[0048] The light coupled into the optical waveguide 10 reaches the exit pupil region 12 after multiple total reflection propagations. Some of the light is coupled out through the exit pupil region 12 into the human eye, and some of the light is coupled out and propagated in the direction opposite to the human eye. The yellow part of the light represents the light reflected by the first reflective film 21 towards the human eye, and after touching the first reflective film 21, it is reflected towards the human eye for propagation.

[0049] Among them, the partitioning of the first reflective film 21 in the exit pupil region 12 corresponds to the exit pupil partitioning. Exemplarily, the exit pupil is divided into three regions a, b, and c from near the entrance pupil to far from the entrance pupil. The diffraction efficiencies of the three regions are 60%, 70%, and 80% respectively, and it is set that r + d = 1. Assuming that the energy obtained by each region itself is 100 parts, then after diffraction in the three regions, region a obtains 60 parts of energy, region b obtains 70 parts of energy, and region c obtains 80 parts of energy. At this time, the picture uniformity is 60 / 80 = 0.75; then according to the above conditions, the reflectivities of the first reflective film 21 in the three regions should be set to: 40%, 30%, and 20%. After the energy reflected back by the first reflective film 21 is superimposed, region a obtains 60 + 40 * 0.4 = 76 parts of energy, and so on, region b obtains 79 parts of energy, and region c obtains 84 parts of energy. At this time, the picture uniformity is 76 / 84 = 0.9; the uniformity of the partitioned first reflective film 21 set in the present application is increased by 20% compared with the non-partitioned reflective film, and the average brightness of the picture is increased from the original (60 + 70 + 80) / 3 = 70 to (76 + 79 + 84) / 3 = 79.6, an increase of 13%. In addition, the coupling efficiency of the entrance pupil region 11 itself is only about 30% or so. After using the first reflective film 21 to recover the light leakage, the coupling efficiency of the entrance pupil region 11 can be increased to more than 60%, which means that the overall brightness of the picture can be doubled.

[0050] With the above settings, the brightness and uniformity of the screen are significantly improved. The setting of the first reflective film 21 in the exit pupil area 12 also has the advantage of blocking the external leakage of light, protecting the privacy of users, and ultimately enhancing the user experience.

[0051] In some other examples, such as Figure 3 shown, in order to improve the coupling efficiency of the entrance pupil area 11, the entrance pupil area 11 can also be set as a double-layer grating. The grating directions of the two layers of entrance pupil gratings are symmetrical, and the types of entrance pupil gratings are not limited. It can be a holographic grating or a surface relief grating, etc.

[0052] Taking the entrance pupil grating as a holographic grating as an example in this application, the light propagation in the entrance pupil area 11 is as Figure 4 、 Figure 5 shown.

[0053] Figure 4 In, a spacing is formed between the first reflective film 21 and the double-layer grating. The incident light In is coupled into by the second entrance pupil grating. The incident light In is incident from the left side of the optical waveguide 10 and propagates to the right side of the optical waveguide 10. The first reflective film 21 can reflect the leaked light of the first entrance pupil grating 111, and the reflected light will be mainly diffracted by the first entrance pupil grating 111 in the opposite direction (the left side of the optical waveguide 10).

[0054] Figure 5 In, the first reflective film 21 and the double-layer grating are arranged in a fitting manner. The incident light In is coupled into by the second entrance pupil grating 112. The incident light In is incident from the right side of the optical waveguide 10 and propagates to the left side of the optical waveguide 10. The first reflective film 21 can reflect the leaked light of the second entrance pupil grating 112, and the reflected light will be mainly diffracted by the second entrance pupil grating 112 in the opposite direction (the right side of the optical waveguide 10).

[0055] On this basis, the embodiment of this application also provides a preparation method of a reflective film for preparing the first reflective film 21 in the above waveguide structure. The first reflective film 21 is a holographic reflective film. The preparation and efficiency control process of the holographic reflective film can be realized by a reflective volume holographic grating. Make a zero-degree angle reflective grating, and adjust the reflection efficiency of each area by controlling the grating thickness, exposure dose, reference object ratio or baking time; the method includes:

[0056] Controlling the laser beam emitted by the laser 40, the beam is expanded, collimated, and shaped by the aperture 42 and then incident on the photosensitive film 45. The beam passing through the photosensitive film 45 is reflected by the mirror 46 again towards the photosensitive film 45 to form a holographic reflective film on the photosensitive film 45.

[0057] Such as Figure 6As shown, it is the optical path diagram for preparing the first reflective film 21. For single-beam light interference, the optical path is as follows: The laser beam of the laser 40 is expanded and collimated by the beam expander-collimator 41, shaped by the aperture 42, and then incident on the photosensitive film 45. The beam passing through the photosensitive film 45 is reflected by the mirror 46 at an angle of 180 degrees back to the photosensitive film 45 again. At this time, the grating inclination angle is 0 degrees, which is equivalent to a holographic mirror. An aperture 43 and a shaper 44 can also be arranged behind the aperture 42.

[0058] A mask for controlling the spot intensity can also be arranged between the beam expander-collimator 41 and the aperture 42 to realize the one-step preparation of the holographic reflective film, so as to control the reflection efficiency distribution of each region of the holographic reflective film. The transmittance of each region of the mask should match the diffraction efficiency distribution of the middle grating and the exit pupil grating.

[0059] Figure 7 It is a refractive index modulation-reflection efficiency curve diagram. Through the refractive index modulation-reflection efficiency curve diagram, it can be shown that the reflection efficiency of the first reflective film 21 can be controlled by controlling the refractive index modulation inside the material.

[0060] Figure 8 It is a curve diagram of the reflection efficiency changing with the exposure dose. Through the least squares fitting, the formula for the reflection efficiency changing with the exposure dose can be obtained: Reflection efficiency (%) ≈ -0.0436x² + 3.189x - 23.14; where x is the exposure dose.

[0061] Under the same exposure time, the exposure intensity of each exit pupil region 12 can be controlled through the mask to control the exposure dose. The exposure dose E = exposure light intensity × exposure time.

[0062] When specifically applied to the waveguide structure, the photosensitive film 45 can be arranged on the glass, and the shape of the glass is the same as that of the optical waveguide 10. The photosensitive film 45 is attached to the transparent glass, and then exposed through the above optical path. A holographic reflective film is formed on this glass, and the shape of this glass matches the shape of the optical waveguide 10. Finally, the glass and the optical waveguide 10 are bonded, and the bonding method can use various glues.

[0063] Or, first prepare the holographic reflective film separately, and then attach the holographic reflective film to the corresponding output grating region; this method can bond the photosensitive film 45 with the PET coil. In this way, the holographic reflective film finally formed on the photosensitive film 45 is attached to the PET coil, and then the PET coil is attached to the corresponding output grating region. This method is simple and reduces the overall weight of the equipment because no additional glass is required to attach the holographic reflective film.

[0064] By arranging the first reflective film 21 in the exit pupil region 12, the light leakage on the outside can be reduced, protecting the user's privacy; and the uniformity and brightness of the display screen can be improved.

[0065] The preparation method of this reflective film includes the same structure and beneficial effects as the waveguide structure in the foregoing embodiments. The structure and beneficial effects of the waveguide structure have been described in detail in the foregoing embodiments and will not be elaborated here.

[0066] The above are only the embodiments of the present application and are not intended to limit the protection scope of the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A waveguide structure, characterized in that, Comprising: An optical waveguide, the optical waveguide at least comprising an entrance pupil region and an exit pupil region, the entrance pupil region and the exit pupil region respectively having an entrance pupil grating and an exit pupil grating, a first reflective film being provided on the exit pupil region, the reflectivity of the first reflective film being different for different regions corresponding to the exit pupil grating, the reflectivity of the first reflective film being r within the same region of the exit pupil grating, the diffraction efficiency of the exit pupil grating being d, and r + d = a, where a is a fixed value.

2. The waveguide structure according to claim 1, wherein The value range of a is 0.8 to 1.

2.

3. The waveguide structure according to claim 1, characterized in that, A second reflective film is provided on the entrance pupil grating of the entrance pupil region, the reflectivity of different regions on the second reflective film being equal, and the reflectivity of the second reflective film ≥ 90%.

4. The waveguide structure according to claim 3, characterized in that, The entrance pupil grating of the entrance pupil region is two-layered, and the grating directions of the two-layered entrance pupil gratings are symmetrically arranged.

5. The waveguide structure according to claim 4, characterized in that, The second reflective film and the entrance pupil grating are adhesively attached or have a spacing therebetween.

6. The waveguide structure according to any one of claims 1 to 5, characterized in that, It further comprises a beam expander region, the beam expander region having a beam expander grating, and a reflective film being provided on the beam expander grating of the beam expander region, the reflective film being the first reflective film or the second reflective film.

7. A method for preparing a reflective film, which is used to prepare the first reflective film in the waveguide structure according to any one of claims 1 to 6, wherein the first reflective film is a holographic reflective film, and is characterized in that, The method comprises: Controlling the laser output beam, the beam being expanded, collimated, and incident on the photosensitive film after being shaped by a diaphragm, and the beam passing through the photosensitive film is reflected back to the photosensitive film by a reflector to form the holographic reflective film on the photosensitive film.

8. The method for preparing a reflective film according to claim 7, wherein It further comprises a mask, the mask being provided between the beam expander collimator and the diaphragm, and the mask being used to control the exposure intensity of different regions on the holographic reflective film.

9. The method for preparing a reflective film according to claim 7 or 8, characterized in that, The photosensitive film is provided on glass, the shape of the glass being the same as that of the optical waveguide, and the optical waveguide and the glass are adhesively attached.

10. The method for preparing a reflective film according to claim 7 or 8, characterized in that, The photosensitive film is provided on a PET coil so that the holographic reflective film is formed on the PET coil, and the PET coil is provided on the exit pupil region.

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