Two-dimensional holographic grating exposure device and industrial production method

Abstract

A two-dimensional holographic grating exposure apparatus and industrial production method are disclosed. The apparatus consists of a front-end beam splitting and collimating optical path and a rear-end exposure module. In the front-end beam splitting and collimating optical path, the light emitted by the laser (121) is modulated by a power modulator (111), passes through an electronic shutter (131), and is split into a first sub-beam (151), a second sub-beam (152), and a third sub-beam (153) by a beam splitting unit (14). These three beams are deflected, polarized, expanded, and collimated before reaching the first, second, and third apertures, which limit the size and shape of their light spots. The three beams after passing through the apertures are introduced into the rear-end exposure module. The first and third beams pass through the first and second coupling prisms, the substrate material, and the base material, and then intersect with the second beam, which also passes through the substrate material, at the holographic material. The interference of the three beams forms a two-dimensional grating. This apparatus can simultaneously perform two-dimensional grating exposure, simplifying the two-dimensional grating exposure process and improving the efficiency of two-dimensional grating fabrication.

Description

Technical Field

[0001] This invention relates to a two-dimensional holographic grating exposure device and industrial production method, belonging to the field of holographic grating exposure technology. Background Technology

[0002] Holographic gratings, as diffractive optical elements fabricated using the principle of interference, are widely used due to their low cost, mass production capability, and high diffraction efficiency when the Bragg condition is met. They are particularly prevalent in Augmented Reality (AR) and Virtual Reality (VR) fields, such as in volume holographic diffractive waveguides, where they serve as light coupling, coupling-out, and deflection elements. However, most holographic gratings in existing volume holographic waveguides are still one-dimensional. A spatial combination of two one-dimensional gratings is typically required to achieve the effect of a two-dimensional grating, which undoubtedly increases the system's size. Given the consumer electronics industry's demand for compact and lightweight AR / VR display devices, reducing size while maintaining or optimizing existing product performance parameters has become a pressing challenge. Replacing two one-dimensional gratings with a single two-dimensional grating is an effective method for reducing system size.

[0003] The fabrication of two-dimensional gratings requires recording two interference light fields in holographic materials. Some researchers have used a two-exposure method to record two one-dimensional gratings sequentially, and then superimposed the two one-dimensional gratings to form a two-dimensional grating. This method is inefficient, and due to the photosensitive nature of holographic materials, the activity of the material decreases after the first exposure, affecting the grating formation in the second exposure, and ultimately affecting the performance of the two-dimensional grating, thus limiting its practical use. Summary of the Invention

[0004] The purpose of this invention is to realize the fabrication of two-dimensional gratings through a single exposure and to provide an industrial production method for two-dimensional holographic gratings, applicable to the field of volume holographic diffraction waveguides, and to provide a two-dimensional holographic grating exposure apparatus and industrial production method.

[0005] The technical solution implemented by the present invention is as follows: a two-dimensional holographic grating exposure device, comprising a front-end beam-splitting collimating optical path and a rear-end exposure module.

[0006] The front-end beam splitting and collimating optical path includes a light source and its power modulator, an electronic shutter, and a beam splitting unit; the beam splitting unit is used to split the main beam into a first sub-beam, a second sub-beam, and a third sub-beam; the first sub-beam, the second sub-beam, and the third sub-beam propagate along the first optical path, the second optical path, and the third optical path, respectively.

[0007] The first optical path includes a first turning unit, a first polarization unit, a first beam expander unit, a first collimation unit, and a first aperture; the second optical path includes a second polarization unit, a second beam expander unit, a second collimation unit, and a second aperture; the third optical path includes a second turning unit, a third polarization unit, a third beam expander unit, a third collimation unit, and a third aperture.

[0008] The interference of the first sub-beam and the second sub-beam forms an interference pattern in the first direction, and the interference of the second sub-beam and the third sub-beam forms an interference pattern in the second direction. The interference patterns in the two directions are superimposed to form a two-dimensional interference pattern. The second sub-beam serves as a multiplexed beam, and the device achieves a two-dimensional interference pattern using only three beams of light.

[0009] The first direction and the second direction refer to the direction of the interference pattern, that is, the direction of the fringe of the generated holographic grating. The first direction and the second direction are intended to distinguish the direction of the interference pattern. Different directions mean different dimensions, and are not limited to orthogonal two-dimensional gratings that are parallel to the X-axis and Y-axis respectively.

[0010] The back-end exposure module includes a first coupling prism, a second coupling prism, a substrate material, a base material, a holographic material, and a light-absorbing element. The first coupling prism is used to couple in a first sub-beam; the second coupling prism is used to couple in a third sub-beam. The substrate material is located above the coupling prism, the base material is located above the substrate material, the holographic material is located above the base material, and the light-absorbing element is located above the holographic material. After the first and third sub-beams pass through the coupling prism, the substrate material, and the base material, they intersect with the second sub-beam, which passes through the substrate material and the base material, at the holographic material, and together they interfere to form a two-dimensional grating.

[0011] The back-end exposure module uses a method of stacking prisms and substrate materials. Prisms are used because when applying holographic gratings to waveguide displays, prism coupling is necessary to ensure that one of the beams of light meets the total internal reflection transmission condition. For two-dimensional gratings, two prisms are required to couple both the first and third sub-beams. The substrate material is used to allow the light coupled from the prisms to continue propagating a distance along its original direction, so that the three beams of light overlap at the holographic material to be exposed on the substrate, thus avoiding mutual interference between the substrate and the prisms.

[0012] The light source includes at least one laser, and if there is more than one laser, at least one beam combiner is required; the electronic shutter is located at the output end of the laser, and the beam splitting unit is located at the output end of the electronic shutter;

[0013] The beam splitting unit is a combiner with three reflective surfaces. Each reflective surface needs to be coated to control the reflectivity, so that the three sub-beams split by the beam splitter have equal or approximately equal energy.

[0014] The first and second turning units each contain at least one reflector, so that the first optical path, the second optical path, and the third optical path maintain an appropriate distance from each other and do not interfere with each other.

[0015] The first, second, and third optical paths each contain a polarization unit, a beam expander, a collimation unit, and an aperture, which are placed in a sequential order.

[0016] The polarization unit is a quarter-wave plate or a half-wave plate, an optical element used to adjust the polarization state and intensity of the light beam;

[0017] The beam expander is a spatial filter used to extend the beam diameter;

[0018] The collimation unit is a convex lens or an off-axis parabolic lens, used to obtain collimated parallel light;

[0019] The aperture is used to limit the size and shape of the light spot of the beam so that the light spots of the first sub-beam, the second sub-beam, and the third sub-beam propagating to the surface of the holographic material exactly overlap.

[0020] Within the back-end exposure module, the refractive indices of the first coupling prism, the second coupling prism, the substrate material, the base material, and the holographic material are the same or very close.

[0021] The first coupling prism couples into the first sub-beam passing through the first aperture, and the second coupling prism couples into the third sub-beam passing through the third aperture; the first sub-beam and the third sub-beam have different propagation directions, and their propagation directions do not change after being coupled into the prism.

[0022] The substrate material is in optical contact with the first and second coupling prisms to ensure that the propagation direction of the first and third sub-beams exiting from the coupling prisms and incident on the substrate material does not change; refractive index matching oil is filled between the contact surfaces of the first and second coupling prisms and the substrate material to ensure optical contact between the coupling prisms and the substrate material.

[0023] The substrate material is in optical contact with the substrate material to ensure that the propagation direction of the first sub-beam, the second sub-beam, and the third sub-beam emitted from the substrate material and incident on the substrate material does not change; refractive index matching oil is filled between the contact surfaces of the first and second coupling prisms and the substrate material to ensure optical contact between the coupling prisms and the substrate material.

[0024] The back-end exposure module is used to receive the first sub-beam, the second sub-beam, and the third sub-beam after passing through the first aperture, the second aperture, and the third aperture; the first sub-beam and the third sub-beam, after passing through the coupling prism, the substrate material, and the base material, intersect with the second sub-beam, which passes through the substrate material and the base material, at the holographic material, and together interfere to form a two-dimensional grating; the two-dimensional grating is on the base material.

[0025] The holographic material is provided with a protective layer, and a light-absorbing element is attached to the protective layer. The light-absorbing element is in optical contact with the protective layer of the holographic material. A refractive index matching oil is filled between the light-absorbing element and the protective layer of the holographic material to ensure optical contact between the light-absorbing element and the protective layer of the holographic material. The absorption spectrum of the light-absorbing glass includes at least the spectrum of the light source.

[0026] This invention discloses an industrial production method for two-dimensional holographic gratings, which consists of five steps: holographic box fabrication, holographic box alignment and installation, automatic exposure program startup, holographic box removal, and post-processing.

[0027] The holographic box fabrication involves coating the substrate material with holographic material to ensure uniform coverage, followed by a protective layer. The holographic box is then positioned and installed on the substrate material, with a coherent light beam illuminating the area to be exposed. An automatic exposure program is initiated, starting the shutter control program and automatically exposing the holographic box according to the designed sequence to form a two-dimensional grating. After the exposure program completes, the holographic box with the formed two-dimensional grating is removed from the substrate material. Post-processing involves UV curing to ensure all unreacted holographic material reacts, thus stabilizing the two-dimensional grating.

[0028] The beneficial effects of this invention are as follows: This invention provides a two-dimensional holographic grating exposure device, including a front-end beam-splitting and collimating optical path and a back-end exposure module. The front-end beam-splitting and collimating optical path includes a light source and its power modulator, an electronic shutter, and a beam-splitting unit. The back-end exposure module is used to receive the first, second, and third sub-beams after passing through the first, second, and third apertures; the first and third sub-beams, after passing through a coupling prism, a substrate material, and a base material, intersect with the second sub-beam, which has passed through the substrate material and the base material, at the holographic material, and together interfere to form a two-dimensional grating. This device realizes the fabrication of a two-dimensional grating in a single exposure.

[0029] The present invention employs a beam splitting unit with a combiner having three reflective surfaces. Each reflective surface needs to be coated to control the reflectivity, so that the energy of the three sub-beams split by the beam splitter is equal or approximately equal.

[0030] This invention utilizes a beam splitter to divide the light emitted by a laser into three sub-beams. The first and second sub-beams interfere to form an interference pattern in a first direction, while the second and third sub-beams interfere to form an interference pattern in a second direction. The interference patterns in the two directions are superimposed to form a two-dimensional interference pattern. This invention uses the second sub-beam as a multiplexed beam, achieving a two-dimensional interference pattern with only three beams, one less than the four beams used in traditional techniques. This simplifies the optical path, reduces the number of components, and lowers costs.

[0031] Furthermore, based on the aforementioned two-dimensional holographic grating exposure apparatus, an industrial production method for two-dimensional holographic gratings is proposed. This method comprises five steps: holographic box fabrication, holographic box alignment and installation, automatic exposure program initiation, holographic box removal, and post-processing. Using the aforementioned two-dimensional holographic grating exposure apparatus and industrial production method improves the production efficiency and product performance of two-dimensional holographic gratings. The fabricated two-dimensional gratings can be applied in the field of volume holographic diffraction waveguides, effectively reducing system size. Attached Figure Description

[0032] Figure 1 This application provides a schematic diagram of the structure of the front-end beam-splitting and collimating optical path of a two-dimensional holographic grating exposure device.

[0033] Figure 2a This is a schematic diagram of the front view structure of the rear exposure module of the two-dimensional holographic grating exposure device of the present invention;

[0034] Figure 2b This is a schematic diagram of the rear exposure module structure of the two-dimensional holographic grating exposure device of the present invention.

[0035] Figure 2c This is a schematic diagram of the left-side structure of the rear exposure module of the two-dimensional holographic grating exposure device of the present invention;

[0036] Figure 2d This is a schematic diagram of the right-side structure of the rear exposure module of the two-dimensional holographic grating exposure device of the present invention;

[0037] Figure 3a This is an isometric side view of the rear exposure module of the two-dimensional holographic grating exposure device of the present invention;

[0038] Figure 3b This is a schematic diagram of the front sight frame structure of the rear exposure module of the two-dimensional holographic grating exposure device of the present invention;

[0039] Figure 3c This is a schematic diagram of the right-side frame structure of the rear exposure module of the two-dimensional holographic grating exposure device of the present invention;

[0040] Figure 4 This is a schematic diagram of the front-end beam-splitting and collimating optical path structure of the two-dimensional holographic grating exposure device of the present invention;

[0041] Figure 5 This is a schematic diagram of the industrial production method of the two-dimensional holographic grating exposure device of the present invention;

[0042] Figure 6a This is a schematic diagram of a commonly used two-dimensional pupil expander holographic diffraction waveguide structure.

[0043] Figure 6b This is a schematic diagram of the structure of a two-dimensional grating fabricated by the two-dimensional holographic grating exposure device of the present invention applied to a volume holographic diffraction waveguide. Detailed Implementation

[0044] This embodiment provides a two-dimensional holographic grating exposure device and an industrial production method, wherein the two-dimensional holographic grating exposure device includes a front-end beam-splitting collimating optical path and a rear-end exposure module.

[0045] like Figure 1 As shown, the front-end beam splitting and collimating optical path 10 of the device in this embodiment includes a power modulator 111, a light source 121, an electronic shutter 131, a beam splitting unit 14, first bending units 161 and 162, second bending units 163 and 164, a first polarization unit 171, a second polarization unit 172, a third polarization unit 173, a first beam expander unit 181, a second beam expander unit 182, a third beam expander unit 183, a first collimating unit 191, a second collimating unit 192, a third collimating unit 193, a first aperture 201, a second aperture 202, and a third aperture 203.

[0046] In this embodiment, the power modulation device 111 is used to modulate the output power of the light source. The electronic shutter 131 is located at the output end of the light source 121. When the shutter 131 is opened, the light is transmitted backward. The beam splitting unit 14 splits the light transmitted from the shutter 131 into a first sub-beam 151, a second sub-beam 152, and a third sub-beam 153. The first sub-beam 151 is deflected by the first deflection units 161 and 162 and incident towards the first polarization unit 171. After polarization and intensity modulation by the polarization unit 171, it exits to the first beam expander unit 181, expands the beam diameter, and is then collimated by the first collimation unit 191 before reaching the first aperture stop 201, which limits the size and shape of the beam spot. The second sub-beam 152 is incident towards the second polarization unit 172 and, after polarization and intensity modulation by the second polarization unit 172, exits to the second beam expander unit 181. 82. After the beam diameter is expanded, it is collimated by the second collimating unit 192, and then reaches the second aperture 202, which limits the size and shape of the beam spot. The third sub-beam 153 is deflected by the third turning units 163 and 164 and is incident on the third polarization unit 173. After polarization and intensity modulation by the polarization unit 173, it is emitted to the third beam expanding unit 183, and after the beam diameter is expanded, it is collimated by the third collimating unit 193, and then reaches the third aperture 203, which limits the size and shape of the beam spot.

[0047] In this embodiment, the power modulation device 111 is used to modulate the output power of the light source so that the light intensity incident on the holographic material matches the photosensitive characteristics of the holographic material.

[0048] The beam splitting unit 14 in this embodiment includes a first beam splitter 141, a second beam splitter 142, and a first reflector 143; wherein the surfaces of the first beam splitter 141, the second beam splitter 142, and the first reflector 143 need to be coated to ensure that the light energy emitted by the light source 121 is uniformly divided into three equal parts, so that the light intensities of the first sub-beam 151, the second sub-beam 152, and the third sub-beam 153 that are finally incident on the holographic material are as equal as possible.

[0049] In this embodiment, the first turning unit may be a combination of reflectors including reflectors 161 and 162, and the second turning unit may be a combination of reflectors including reflectors 163 and 164.

[0050] In this embodiment, the first polarization unit 171, the second polarization unit 172, and the third polarization unit 173 can be a half-wave plate or a quarter-wave plate, or a combination of both. The purpose is to adjust the polarization state of the first sub-beam 151, the second sub-beam 152, and the third sub-beam 153 to ensure that the first sub-beam 151, the second sub-beam 152, and the third sub-beam 153 that are finally incident on the holographic material have the same polarization state. Therefore, the polarization unit here has the function of polarization compensation.

[0051] In this embodiment, the first beam expander 181, the second beam expander 182, and the third beam expander 183 can be spatial filters.

[0052] In this embodiment, the first collimation unit 191, the second collimation unit 192, and the third collimation unit 193 can be a convex lens, a Fourier transform lens, or a concave parabolic lens.

[0053] In this embodiment, the first aperture 201, the second aperture 202, and the third aperture 203 do not necessarily have the same size and shape, but it is required that by limiting the shape and size of the first aperture 201, the second aperture 202, and the third aperture 203, the light spot size and shape of the first sub-beam 151, the second sub-beam 152, and the third sub-beam 153 that finally converge onto the holographic material plane are the same.

[0054] like Figures 2a-2d As shown, Figure 2a This is a front view structural diagram of the back-end exposure module 20. Figure 2b This is a rear-view structural diagram of the back-end exposure module 20. Figure 2c This is a left-side view of the back-end exposure module 20. Figure 2d This is a right-side structural diagram of the back-end exposure module 20.

[0055] The back-end exposure module 20 in this embodiment includes a first coupling prism 211, a second coupling prism 212, a substrate material 22, a base material 23, a holographic material 24, and a light-absorbing element 25. Through observation... Figures 2a-2d The relative positions of each component in the back-end exposure module can be easily obtained. The first coupling prism 211 and the second coupling prism 212 are both located below the substrate material 22, and each has a right-angled surface that is in close contact with the lower surface of the substrate material 22. The substrate material 23 is located above the substrate material 22 and is in close contact with the substrate material 22. The holographic material 24 is located on the substrate material 23. The light-absorbing element 25 is attached to the holographic material 24.

[0056] like Figure 3a The diagram shown is an isometric side view of the back-end exposure module 20. Light rays 151 passing through the first aperture 201, 152 passing through the second aperture, and 153 passing through the third aperture are respectively introduced into the back-end exposure module along different paths by a reflector (not shown). Figure 3b The diagram shows the front-view frame structure of the back-end exposure module 20. The first sub-beam 151 enters from the inclined surface of the first coupling prism 211, passes through the coupling prism 211, substrate material 22, base material 23, and reaches the holographic material 24. The second sub-beam 152 directly passes through the substrate material 22 and base material 23 and reaches the holographic material 24. The first sub-beam 151 and the second sub-beam 152 intersect at the holographic material 24, interfering to form a one-dimensional grating. Figure 3c The diagram shows the right-side scaffold structure of the back-end exposure module 20. The second sub-beam 152 is directly transmitted through the substrate material 22, the base material 23, and reaches the holographic material 24. The third sub-beam 153 is incident from the inclined surface of the second coupling prism 212, and is transmitted through the coupling prism 212, the substrate material 22, the base material 23, and reaches the holographic material 24. The second sub-beam 152 and the third sub-beam 153 intersect at the holographic material 24, and interfere to form a one-dimensional grating. The pairwise interference of the three beams occurs simultaneously, so the two one-dimensional gratings can be superimposed to generate a two-dimensional grating in one step.

[0057] like Figure 3b As shown, the first sub-beam 151 and the second sub-beam 152 interfere at the holographic material 24, generating holographic grating fringes parallel to the x-axis; as Figure 3c As shown, the second sub-beam 152 and the third sub-beam 153 interfere at the holographic material 24, and the resulting holographic grating fringes are parallel to the y-axis; the fringes of the two gratings are orthogonal, forming a two-dimensional grating.

[0058] In this embodiment, the first sub-beam 151 is incident perpendicularly from the inclined surface of the first coupling prism 211, the second sub-beam 152 is incident perpendicularly from the lower surface of the substrate material 22, and the third sub-beam 153 is incident perpendicularly from the inclined surface of the second coupling prism 212.

[0059] The base angle of the first coupling prism 211 and the second coupling prism 212 in this embodiment can be varied according to actual needs.

[0060] In this embodiment, the positions of the first coupling prism 211 and the second coupling prism 212 on the bottom surface of the substrate material 22 can be translated or rotated as needed.

[0061] In this embodiment, the first coupling prism 211, the second coupling prism 212, the substrate material 22, the base material 23, and the holographic material 24 are all transparent materials, and their refractive indices must be the same, but slight differences are allowed.

[0062] In this embodiment, optical contact is maintained between the first coupling prism 211 and the substrate material 22, and between the second coupling prism 212 and the substrate material 22, such as by applying a refractive index matching liquid between the contact interfaces.

[0063] In this embodiment, the thickness and shape of the substrate material glass can be adjusted as needed, serving as a degree of freedom to ensure that the three sub-beams intersect exactly at the holographic material 24.

[0064] In this embodiment, the substrate material 22 and the substrate 23 are kept in optical contact, such as by applying a refractive index matching liquid between the contact interfaces.

[0065] In this embodiment, the holographic material 24 has a protective layer on its surface, and the protective layer maintains optical contact with the light-absorbing element 25, such as by coating a refractive index matching liquid between the contact interfaces.

[0066] In this embodiment, the absorption spectrum of the light-absorbing element 25 should at least include the spectrum of the light source 121.

[0067] The light source in this embodiment includes at least one laser and a beam combiner; wherein each laser is located at each input end of the beam combiner, and a beam splitting unit is located at the output end of the beam combiner.

[0068] like Figure 4 As shown, in this embodiment, at least one laser includes a red laser 121, a blue laser 122, and a green laser 123, and the beam combiner is a beam combining prism 301. The beam combining prism 301 has a first incident surface, a second incident surface, a third incident surface, and an exit surface; the red laser 121 is disposed on the first incident surface of the beam combining prism 301, the green laser 123 is disposed on the second incident surface of the beam combining prism 301, and the blue laser 122 is disposed on the third incident surface of the beam combining prism 301.

[0069] In this embodiment, the beam-combining prism 301 is an X-prism, composed of four right-angle prisms bonded together. The diagonal faces of the X-prism have mutually orthogonal first and second dichroic films. The first dichroic film reflects red light and transmits green and blue light; the second dichroic film reflects blue light and transmits red and green light. Thus, as... Figure 4As shown, the beam combiner prism 301 can combine the red light emitted by the red laser 121, the green light emitted by the green laser 123, and the blue light emitted by the blue laser 122 into a single laser beam output. In practical applications, the arrangement of the lasers and the structure of the beam combiner prism 301 can be set according to actual needs. The beam combiner can also be other suitable spectral beam combining devices, and there is no need to be limited to the limitations of this embodiment.

[0070] In this embodiment, the holographic grating exposure uses a color-combining laser light source, so the two-dimensional grating generated by the exposure can be applied to the diffraction of red, green and blue light.

[0071] This embodiment provides an industrial production method for two-dimensional holographic gratings, such as... Figure 5 As shown.

[0072] The production apparatus of the method consists of the apparatus described above. The industrial production method of the two-dimensional holographic grating is completed by five steps: holographic box fabrication S1, holographic box alignment and installation S2, automatic exposure program start-up S3, holographic box removal S4, and post-processing S5.

[0073] In this embodiment, the holographic box fabrication S1 can be carried out by coating or other methods to make the holographic material 24 evenly distributed on the surface of the substrate material 23. The surface of the holographic material 24 is covered with a protective layer, and the substrate material 23, the holographic material 24 and the protective layer together form a holographic box.

[0074] In this embodiment, the holographic box alignment and mounting S2 involves placing the fabricated holographic box on the substrate material 22 and ensuring that the coherent light beam illuminates the area of ​​the holographic box to be exposed. Specifically, a refractive index oil is first coated onto the upper surface of the substrate material 22. Then, the holographic box is placed in a positioning fixture (not shown) on the upper surface of the substrate material 22, and a refractive index oil is coated onto the surface of the holographic box. Finally, a light-absorbing glass 25 is placed over the upper surface of the holographic box. The purpose of the positioning fixture is to ensure that after the holographic box is fixed, the coherent light precisely illuminates the area of ​​the holographic box to be exposed.

[0075] In this embodiment, the automatic exposure program is started by S3, which can start the shutter control program and automatically expose according to the design program to form a two-dimensional grating. Specifically, the shutter control program can automatically control the opening and closing state of the shutter, thereby controlling the exposure time.

[0076] In this embodiment, the holographic cell removal S4 requires removing the holographic cell, which has formed a two-dimensional grating, from the substrate material after the exposure process has finished.

[0077] In this embodiment, the post-processing S5 can be performed by ultraviolet curing or other methods to fully react the unreacted holographic material, thereby making the two-dimensional grating stable.

[0078] The purpose of this invention is to provide a two-dimensional holographic grating exposure device and industrial production method. The device and method can produce two-dimensional gratings in one exposure, thereby improving the production efficiency and product performance of two-dimensional holographic gratings. The produced two-dimensional gratings can be applied in the field of volume holographic diffraction waveguides, effectively reducing the system volume.

[0079] This embodiment can apply the two-dimensional holographic grating made using the above-mentioned device and production method to the field of volume holographic diffraction waveguides, using one two-dimensional grating to replace the original two one-dimensional gratings, effectively compressing the system volume.

[0080] like Figure 6a As shown, Figure 6a The current mainstream design method for diffractive waveguides requires the use of gratings to expand the pupil in two directions in order to obtain a larger observable area of ​​the image, i.e., the eye movement range. Figure 6a The coupling grating 511 in the middle waveguide 51 couples the image light into the waveguide, first through the deflection grating 512 for pupil expansion in the y-direction, then through the coupling output grating for pupil expansion in the x-direction, and finally couples it out to the human eye, thereby obtaining a larger eye movement range. For example... Figure 6b As shown, if a two-dimensional grating made by the above method is used directly, one two-dimensional grating 522 can be used to replace two one-dimensional gratings to achieve pupil expansion in two directions, thus effectively compressing the system volume.

Claims

1. A two-dimensional holographic grating exposure apparatus, characterized in that, The device includes a front-end beam-splitting and collimating optical path and a rear-end exposure module; The front-end beam-splitting collimating optical path includes a light source and its power modulator, an electronic shutter, and a beam-splitting unit; the beam-splitting unit is used to divide the main beam into a first sub-beam, a second sub-beam, and a third sub-beam; the first sub-beam, the second sub-beam, and the third sub-beam propagate along the first optical path, the second optical path, and the third optical path, respectively. The beam splitting unit is a combiner with three reflective surfaces. Each reflective surface needs to be coated to control the reflectivity, so that the three sub-beams split by the beam splitter have equal or approximately equal energy. The back-end exposure module includes a first coupling prism, a second coupling prism, a substrate material, a base material, a holographic material, and a light-absorbing element; the first coupling prism is used to couple in a first sub-beam. The second coupling prism is used to couple the third sub-beam; the substrate material is located above the coupling prism, the base material is located above the substrate material, the holographic material is located above the base material, and the light-absorbing element is located above the holographic material; after the first and third sub-beams pass through the coupling prism, the substrate material, and the base material, they intersect with the second sub-beam, which passes through the substrate material and the base material, at the holographic material, and together interfere to form a two-dimensional grating; thus realizing the fabrication of a two-dimensional grating in a single exposure. The interference of the first sub-beam and the second sub-beam forms an interference pattern in the first direction, and the interference of the second sub-beam and the third sub-beam forms an interference pattern in the second direction. The interference patterns in the two directions are superimposed to form a two-dimensional interference pattern. The second sub-beam serves as a multiplexed beam, and the device achieves a two-dimensional interference pattern using only three beams of light. The back-end exposure module uses a method of stacking prisms and substrate materials. Prisms are used because when applying holographic gratings to waveguide displays, prism coupling is necessary to ensure that one of the beams of light meets the total internal reflection transmission condition. For two-dimensional gratings, two prisms are required to couple both the first and third sub-beams. The substrate material is used to allow the light coupled from the prisms to continue propagating a distance along its original direction, so that the three beams of light overlap at the holographic material to be exposed on the substrate, thus avoiding mutual interference between the substrate and the prisms.

2. The two-dimensional holographic grating exposure apparatus according to claim 1, characterized in that, The light source includes at least one laser, and if there is more than one laser, at least one beam combiner is required; the electronic shutter is located at the output end of the laser, and the beam splitting unit is located at the output end of the electronic shutter; The first optical path includes a first turning unit, a first polarization unit, a first beam expanding unit, a first collimating unit, and a first aperture; the second optical path includes a second polarization unit, a second beam expanding unit, a second collimating unit, and a second aperture; the third optical path includes a second turning unit, a third polarization unit, a third beam expanding unit, a third collimating unit, and a third aperture. The first and second turning units each contain at least one reflector, so that the first optical path, the second optical path, and the third optical path maintain an appropriate distance from each other and do not interfere with each other. The first, second, and third optical paths each contain a polarization unit, a beam expander, a collimation unit, and an aperture, which are placed in a sequential order. The polarization unit is a quarter-wave plate or a half-wave plate, an optical element used to adjust the polarization state and intensity of the light beam; The beam expander is a spatial filter used to extend the beam diameter; The collimation unit is a convex lens or an off-axis parabolic lens, used to obtain collimated parallel light; The aperture is used to limit the size and shape of the light spot of the beam so that the light spots of the first sub-beam, the second sub-beam, and the third sub-beam propagating to the surface of the holographic material exactly overlap.

3. The two-dimensional holographic grating exposure apparatus according to claim 1, characterized in that, The Within the back-end exposure module, the refractive indices of the first coupling prism, the second coupling prism, the substrate material, the base material, and the holographic material are the same or very close.

4. The two-dimensional holographic grating exposure apparatus according to claim 1, characterized in that, The first coupling prism couples into the first sub-beam passing through the first aperture, and the second coupling prism couples into the third sub-beam passing through the third aperture; the first sub-beam and the third sub-beam have different propagation directions, and their propagation directions do not change after being coupled into the prism.

5. The two-dimensional holographic grating exposure apparatus according to claim 1, characterized in that, The substrate material is in optical contact with the first and second coupling prisms to ensure that the propagation directions of the first and third sub-beams exiting from the coupling prisms and incident on the substrate material do not change. Refractive index matching oil is filled between the contact surfaces of the first and second coupling prisms and the substrate material to ensure optical contact between the coupling prisms and the substrate material.

6. The two-dimensional holographic grating exposure apparatus according to claim 1, characterized in that, The substrate glass is in optical contact with the substrate material to ensure that the propagation directions of the first sub-beam, the second sub-beam, and the third sub-beam emitted from and incident on the substrate material do not change; refractive index matching oil is filled between the contact surfaces of the first and second coupling prisms and the substrate material to ensure optical contact between the coupling prisms and the substrate material.

7. The two-dimensional holographic grating exposure apparatus according to claim 1, characterized in that, The back-end exposure module is used to receive the first sub-beam, the second sub-beam, and the third sub-beam after passing through the first aperture, the second aperture, and the third aperture; the first sub-beam and the third sub-beam, after passing through the coupling prism, the substrate material, and the base material, intersect with the second sub-beam, which passes through the substrate material and the base material, at the holographic material, and together interfere to form a two-dimensional grating; the two-dimensional grating is on the base material.

8. The two-dimensional holographic grating exposure apparatus according to claim 1, characterized in that, The holographic material is provided with a protective layer, and a light-absorbing element is attached to the protective layer. The light-absorbing element is in optical contact with the protective layer of the holographic material. A refractive index matching oil is filled between the light-absorbing element and the protective layer of the holographic material to ensure optical contact between the light-absorbing element and the protective layer of the holographic material. The absorption spectrum of the light-absorbing glass includes at least the spectrum of the light source.

9. The industrial production method of a two-dimensional holographic grating exposure apparatus according to any one of claims 1-8, characterized in that, The method consists of five steps: holographic box fabrication, holographic box alignment and installation, automatic exposure program startup, holographic box removal, and post-processing.

10. An industrial production method for a two-dimensional holographic grating according to claim 9, characterized in that, The holographic box is fabricated by coating the holographic material evenly onto the surface of the substrate material, and the surface of the material is covered with a protective layer; the holographic box is aligned and installed by placing the fabricated holographic box on the substrate material and illuminating the area of ​​the holographic box to be exposed with a coherent light beam. The automatic exposure program is started, the shutter control program is activated, and the exposure is automatically performed according to the design program to form a two-dimensional grating; the holographic box is removed after the exposure program is completed, and the holographic box with the formed two-dimensional grating is removed from the substrate material; the post-processing uses ultraviolet curing to make all the unreacted holographic material react completely, so that the two-dimensional grating is formed and stabilized.

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