Polarization volume holographic grating, preparation method and exposure system thereof

Abstract

The application provides a polarization volume holographic grating, a preparation method of the polarization volume holographic grating and an exposure system, and the polarization volume holographic grating comprises a substrate layer, a two-dimensional orientation layer and a liquid crystal layer; the two-dimensional orientation layer is arranged on the surface of the substrate layer, the orientation direction of the two-dimensional orientation layer periodically changes in a first preset direction and periodically changes in a second preset direction perpendicular to the first preset direction, so that the two-dimensional orientation layer forms first and second equal phase lines with an included angle greater than zero; the liquid crystal layer is arranged on the surface of the two-dimensional orientation layer away from the substrate layer, the arrangement direction of the liquid crystal molecules in the liquid crystal layer corresponds to the orientation direction of the two-dimensional orientation layer, so that the liquid crystal layer forms a first equal phase surface corresponding to the first equal phase line and a second equal phase surface corresponding to the second equal phase line. The application orients the liquid crystal layer through the two-dimensional orientation layer, so that the polarization volume holographic grating has the diffraction characteristics of a two-dimensional grating, and the preparation of a single-layer two-dimensional polarization volume holographic grating is realized.

Description

Technical Field

[0001] This application relates to the field of gratings, and more particularly to a polarizing holographic grating, a method for fabricating the polarizing holographic grating, and an exposure system. Background Technology

[0002] A polarizing holographic grating is a polarization-selective holographic optical element. In near-eye display scenarios, a polarizing holographic grating is placed in an optical waveguide so that signal light can be coupled into the waveguide through the polarizing holographic grating, propagated within the waveguide, and then coupled out through another polarizing holographic grating, thus realizing signal light transmission. However, the polarizing holographic gratings in related technologies are limited by the fabrication methods, and the fabricated polarizing holographic gratings only have an equiphase surface in one direction, that is, the fabricated polarizing holographic gratings are one-dimensional. Therefore, in related technologies, if a two-dimensional polarizing holographic grating is required, multiple one-dimensional polarizing holographic gratings must be stacked to achieve the diffraction effect of the two-dimensional polarizing holographic grating. It can be seen that the related technologies have problems such as complicated fabrication processes and low yield of two-dimensional polarizing holographic gratings, and there is currently no method for directly fabricating two-dimensional polarizing holographic gratings. Summary of the Invention

[0003] This application provides a polarizing holographic grating, a method for fabricating the polarizing holographic grating, and an exposure system, aiming to provide a polarizing holographic grating with at least two grating period directions, thereby realizing the fabrication of a single-layer two-dimensional polarizing holographic grating.

[0004] In a first aspect, this application provides a polarizing holographic grating, the polarizing holographic grating comprising:

[0005] basal layer;

[0006] A two-dimensional orientation layer is disposed on the surface of the substrate layer. The orientation direction of the two-dimensional orientation layer changes periodically in a first preset direction and in a second preset direction perpendicular to the first preset direction, such that the two-dimensional orientation layer forms a first equiphase line and a second equiphase line, and the angle between the first equiphase line and the second equiphase line is greater than zero.

[0007] A liquid crystal layer is disposed on the surface of the two-dimensional alignment layer away from the substrate layer. The liquid crystal molecules in the liquid crystal layer are arranged in a direction corresponding to the alignment direction of the two-dimensional alignment layer, such that the liquid crystal layer forms a first equiphase surface corresponding to the first equiphase line and a second equiphase surface corresponding to the second equiphase line.

[0008] Secondly, this application also provides a method for fabricating a polarizing holographic grating, the method comprising:

[0009] A substrate layer is provided, and an orientation layer to be exposed is coated on the surface of the substrate layer;

[0010] A mask is provided such that it blocks a portion of the surface of the orientation layer to be exposed that faces away from the substrate layer.

[0011] The orientation layer to be exposed is irradiated with an exposure beam to expose the areas on the surface of the orientation layer that are not blocked by the mask, thereby obtaining a two-dimensional orientation layer;

[0012] During the process of the exposure beam irradiating the orientation layer to be exposed, the mask is translated along a first preset direction and the orientation layer to be exposed reciprocates in a second preset direction, or the orientation layer to be exposed is translated in the opposite direction of the first preset direction and reciprocates in the second preset direction, so that the orientation direction of the two-dimensional orientation layer exhibits periodic changes in both the first preset direction and the second preset direction, thereby forming a first equiphase line and a second equiphase line in the two-dimensional orientation layer.

[0013] The mask is removed, and liquid crystal is coated on the surface of the two-dimensional alignment layer opposite to the substrate layer to obtain the polarizing holographic grating.

[0014] Thirdly, this application also provides an exposure system, the exposure system comprising at least:

[0015] An exposure light source, wherein the exposure light source is used to provide an exposure beam that illuminates the orientation layer to be exposed;

[0016] A clamping mechanism is used to clamp a mask and move it along a first preset direction during the exposure of the orientation layer to be exposed by the exposure light source. The mask is used to cover part of the surface of the orientation layer to be exposed.

[0017] A carrying platform is used to carry a substrate layer and the orientation layer to be exposed on the substrate layer, and during the exposure of the orientation layer to be exposed by the exposure light source, it is used to carry the orientation layer to be exposed to reciprocate in a second preset direction.

[0018] This application provides a polarizing holographic grating, a method for fabricating a polarizing holographic grating, and an exposure system. The liquid crystal layer in the polarizing holographic grating of this application forms equiphase surfaces in two different directions, so that the polarizing holographic grating has Bragg diffraction effect in both different directions. This gives the polarizing grating the diffraction characteristics of a two-dimensional grating. Therefore, in scenarios where a two-dimensional grating needs to be set, only this polarizing holographic grating needs to be set to meet the requirements of using a two-dimensional grating, without the need to stack two one-dimensional gratings to simulate the effect of a two-dimensional grating. This realizes the fabrication of a single-layer two-dimensional polarizing holographic grating. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram showing the orientation direction distribution of the orientation layer in a polarizing holographic grating in related technologies;

[0021] Figure 2 This is a partial schematic diagram of a polarizing holographic grating in related technologies;

[0022] Figure 3 This is a schematic diagram of the structure of a polarizing holographic grating in related technologies;

[0023] Figure 4 A schematic diagram of the structure of a polarizer holographic grating provided in one embodiment of this application;

[0024] Figure 5 A schematic projection of a two-dimensional orientation layer along the substrate direction provided in an embodiment of this application;

[0025] Figure 6 A flowchart illustrating a method for fabricating a polarizing holographic grating according to an embodiment of this application;

[0026] Figure 7 This is a schematic diagram of the exposure process for an orientation layer to be exposed, provided in an embodiment of this application.

[0027] Figure 8 This is a schematic block diagram of the structure of an exposure system provided in an embodiment of this application.

[0028] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0029] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0030] The flowchart shown in the attached diagram is for illustrative purposes only and does not necessarily include all content and operations / steps, nor does it necessarily have to be performed in the order described. For example, some operations / steps can be broken down, combined, or partially merged, so the actual execution order may change depending on the actual situation.

[0031] Please see Figure 1 , Figure 2 and Figure 3 , Figure 1 This is a schematic diagram showing the orientation direction distribution of the orientation layer in a polarizing holographic grating in related technologies. Figure 2 This is a partial schematic diagram of a polarizing holographic grating in related technologies. Figure 3 This is a schematic diagram of the structure of a polarizing holographic grating in related technologies.

[0032] A polarizing holographic grating is a polarization-selective holographic optical element that records the polarization information of two interfering beams, including right-circularly polarized (RCP) and left-circularly polarized (LCP). Specifically, in related technologies, the polarizing holographic grating uses two circularly polarized beams with opposite polarization states to simultaneously expose the alignment layer 121 on the polarizing grating. This causes the material molecules in the alignment layer 121 to align in an orderly manner according to the polarization direction of the light field resulting from the superposition of the two polarized beams at their respective positions, resulting in the alignment direction of the alignment layer 121 as shown in the image. Figure 1 As shown, it can be seen that, due to limitations in the preparation method, Figure 1 The orientation direction of the alignment layer 121 shown changes periodically in the X-axis direction but not in the Y-axis direction. This causes the liquid crystal molecules to deflect under the orientation of the alignment layer 121 after it is coated with liquid crystal. The deflection state is as follows: Figure 2 As shown, it should be understood that the liquid crystal molecules near the alignment layer 121 will strictly align according to the alignment direction of the alignment layer 121, but along the direction away from the alignment layer 121, the control force of the alignment layer 121 on the liquid crystal molecules weakens, and the liquid crystal molecules will rotate, thus forming a periodicity in the Z-axis direction; the fabricated polarizing holographic grating is as follows. Figure 3As shown, the equiphase surface of the liquid crystal layer 13 in the polarizing holographic grating indicates that the polarizing holographic grating has no periodicity in the direction parallel to the equiphase surface. Therefore, the polarizing holographic grating has only one grating period direction, which is a one-dimensional polarizing holographic grating. Thus, if the diffraction effect of a two-dimensional polarizing holographic grating is to be achieved, two one-dimensional polarizing holographic gratings need to be stacked to simulate the diffraction effect of the two-dimensional grating. This results in problems such as complex fabrication process, high cost, and low yield of finished products.

[0033] The orientation direction of the polarizing holographic grating alignment layer 121 provided in this application changes periodically in two different directions, thus forming two equiphase surfaces in the liquid crystal layer 13 of the polarizing holographic grating in different directions. This enables the polarizing holographic grating to possess the diffraction characteristics of a two-dimensional grating, realizing the fabrication of a single-layer two-dimensional polarizing holographic grating. This solves the problem that two one-dimensional polarizing holographic gratings need to be stacked when achieving the diffraction effect of a two-dimensional grating using a polarizing holographic grating, thereby solving the problems of complex process, high cost and low yield in the fabrication of two-dimensional polarizing holographic gratings.

[0034] The following detailed description of some embodiments of this application is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0035] Please refer to Figure 4 , Figure 4 This is a schematic diagram of the structure of a polarizer holographic grating provided in one embodiment of this application.

[0036] like Figure 4As shown, the polarizer holographic grating includes a substrate layer 11, a two-dimensional alignment layer 122, and a liquid crystal layer 13. The two-dimensional alignment layer 122 is disposed on the surface of the substrate layer 11. The alignment direction of the two-dimensional alignment layer 122 changes periodically in a first preset direction and also periodically in a second preset direction, forming a first equiphase line and a second equiphase line, with the angle between the first and second equiphase lines being greater than zero. The liquid crystal layer 13 is disposed on the surface of the two-dimensional alignment layer 122 away from the substrate layer 11. During the fabrication of the polarizer holographic grating, the liquid crystal molecules in the liquid crystal layer 13 are deflected under the alignment effect of the two-dimensional alignment layer 122, causing the alignment direction of the liquid crystal molecules to correspond to the alignment direction of the two-dimensional alignment layer 122. In specific implementation, the alignment direction of the liquid crystal molecules near the two-dimensional alignment layer 122 corresponds to the alignment direction of the liquid crystal molecules in the two-dimensional alignment layer 122. The orientation directions are exactly the same. However, along the direction away from the contact plane between the two-dimensional alignment layer 122 and the liquid crystal layer 13, the force exerted by the two-dimensional alignment layer 122 on the liquid crystal molecules gradually weakens. Due to the physical properties of the liquid crystal molecules themselves, the liquid crystal molecules will continue to rotate in this direction, thus forming a periodicity in this direction as well. This results in the final equiphase surface not being perpendicular to the plane where the alignment layer 121 is located. Furthermore, since the thickness of the liquid crystal layer 13 is greater than the thickness of the two-dimensional alignment layer 122, a first equiphase surface corresponding to the first equiphase line and a second equiphase surface corresponding to the second equiphase line can be formed in the liquid crystal layer 13 of the polarizer holographic grating. It should be understood that the angle between the first equiphase surface and the second equiphase surface is determined by the angle between the first equiphase line and the second equiphase line and the pitch of the liquid crystal molecules in the Z direction.

[0037] It should be noted that within the space of the liquid crystal layer 13, there exist two equiphase surfaces with different orientations: a first equiphase surface and a second equiphase surface. This causes the polarizing holographic grating to exhibit Bragg diffraction in both different directions. Therefore, the liquid crystal layer 13, possessing two polarizing holographic gratings with different orientations, can achieve the same diffraction effect as a two-dimensional grating. It should be understood that an equiphase surface refers to the surface formed in space by liquid crystal molecules with all rotation angles or molecular orientations being exactly the same.

[0038] Please see Figure 5 , Figure 5 This is a schematic projection of the two-dimensional orientation layer 122 along the direction of the base layer 11, provided in an embodiment of this application.

[0039] In some embodiments, in the projection of the two-dimensional orientation layer 122 along the direction of the base layer 11, the lines connecting the position points with the same orientation direction are serrated.

[0040] For example, the projection of the two-dimensional alignment layer 122 along the direction of the base layer 11, Figure 5The double-headed arrows in the diagram indicate the polarization direction of the exposed light field or the orientation direction at that location. The lines connecting points with the same orientation direction are zigzag-shaped. It should be understood that the lines connecting points with the same orientation direction are equiphase lines. That is, there are at least two equiphase lines with different directions, which makes the lines connecting points with the same orientation direction appear zigzag-shaped.

[0041] In some embodiments, the first preset direction is the X-axis direction of the preset coordinate system, the second preset direction is the Y-axis direction of the preset coordinate system, and the origin of the preset coordinate system is any point on the plane where the base layer 11 is located.

[0042] For example, the origin of the preset coordinate system is any point on the plane where the substrate layer 11 is located. Therefore, the XY plane of the preset coordinate system is the plane where the substrate layer 11 is located. Specifically, in the projection of the two-dimensional alignment layer 122 on the XY plane, the alignment direction of the two-dimensional alignment layer 122 exhibits periodic changes along the X-axis and along the Y-axis, thereby enabling the two-dimensional alignment layer 122 to form a first equiphase line and a second equiphase line. This, in turn, enables the liquid crystal layer 13 on the surface of the two-dimensional alignment layer 122 to form a first equiphase surface corresponding to the first equiphase line and a second equiphase surface corresponding to the second equiphase line, so that the polarizer holographic grating has the diffraction characteristics of a two-dimensional grating.

[0043] In the specific implementation process, the base layer 11 can be rectangular or circular, and the shape of the base layer is not limited here.

[0044] In some embodiments, the substrate layer 11 comprises resin or glass; the two-dimensional alignment layer 122 comprises one of polyimide, organic azo compound, and acrylate polymer; and the liquid crystal layer 13 comprises cholesteric liquid crystal.

[0045] In specific implementation, the substrate 11 can be prepared using resin or glass, and the two-dimensional alignment layer 122 can be prepared using one of polyimide, organic azo compound, and acrylate polymer; this application does not limit the application. The liquid crystal coated on the two-dimensional alignment layer 122 is a cholesteric liquid crystal. The cholesteric liquid crystal molecules near the two-dimensional alignment layer 122 are strictly aligned according to the alignment direction of the two-dimensional alignment layer 122. However, along the direction away from the contact plane between the two-dimensional alignment layer 122 and the liquid crystal layer 13, due to the inherent properties of the cholesteric liquid crystal molecules, they continuously rotate, thus forming a periodicity in this direction. Consequently, the first and second equiphase planes formed in the liquid crystal layer 13 are not perpendicular to the plane where the two-dimensional alignment layer 122 is located. The cholesteric liquid crystal can be, for example, a chiral liquid crystal or a non-chiral liquid crystal with added chiral compounds; this application also does not limit the application.

[0046] The polarization holographic grating provided in the above embodiments has the diffraction characteristics of a two-dimensional grating, thereby avoiding the need to stack two one-dimensional polarization holographic gratings to simulate the diffraction effect of a two-dimensional grating in scenarios where a two-dimensional grating needs to be set, and realizing the fabrication of a single-layer two-dimensional polarization holographic grating.

[0047] Please see Figure 6 , Figure 6 This is a flowchart illustrating a method for fabricating a polarizing holographic grating according to an embodiment of this application.

[0048] This application also provides a method for preparing a polarizing holographic grating to obtain the polarizing holographic grating described in the preceding embodiments.

[0049] It should be understood that in related technologies, the polarization holographic gratings produced by the fabrication method described above are one-dimensional gratings, which limits the application scenarios of polarization holographic gratings. However, the fabrication method of polarization holographic gratings provided in this application can directly produce polarization holographic gratings with diffraction characteristics of two-dimensional gratings.

[0050] like Figure 6 As shown, the method for fabricating a polarizing holographic grating includes steps S101 to S104.

[0051] Step S101: Provide a substrate layer and coat the surface of the substrate layer with an orientation layer to be exposed.

[0052] For example, a substrate layer is provided to coat an orientation layer to be exposed on its surface for exposure. The substrate layer may be made of resin or glass, and this application does not limit the material or method of preparation of the substrate layer.

[0053] Step S102: Provide a mask, and make the mask block part of the surface of the orientation layer to be exposed away from the substrate layer.

[0054] For example, the mask is opaque, so during the exposure process, the area of ​​the surface of the orientation layer to be exposed that is blocked by the mask can be avoided from being exposed, thereby allowing the area to be exposed on the orientation layer to be adjusted by controlling the area blocked by the mask.

[0055] In some embodiments, the mask is an opaque flat plate, or the mask has a light-transmitting structure, which includes a slit or a through hole.

[0056] In specific implementation, if the mask is a single opaque flat plate, the edge of the mask can be used to block the orientation layer to be exposed. Specifically, the exposure beam shines on the edge of the mask, allowing part of the exposure beam to reach the orientation layer to be exposed, while the rest is blocked by the mask, thus achieving the effect of exposing the orientation layer to be exposed using the edge of the mask. Alternatively, if the mask has a light-transmitting structure, the light-transmitting structure can be used to expose the orientation layer to be exposed. Specifically, the exposure beam shines on the mask, and part of the exposure beam passes through the light-transmitting structure on the mask to reach the orientation layer to be exposed, thereby achieving the exposure of the orientation layer to be exposed. The light-transmitting structure includes, but is not limited to, slits or through holes. This application does not limit the specific light-transmitting structure.

[0057] Step S103: Irradiate the orientation layer to be exposed using an exposure beam to expose the areas on the surface of the orientation layer that are not blocked by the mask, thereby obtaining a two-dimensional orientation layer; wherein, during the process of the exposure beam irradiating the orientation layer to be exposed, the mask translates along a first preset direction and the orientation layer to be exposed reciprocates along a second preset direction, or the orientation layer to be exposed translates in the opposite direction of the first preset direction and reciprocates along the second preset direction, so that the orientation direction of the two-dimensional orientation layer exhibits periodic changes in both the first preset direction and the second preset direction, thereby forming a first equiphase line and a second equiphase line in the two-dimensional orientation layer.

[0058] For example, an exposure beam and a mask are used to expose the alignment layer to be exposed in order to prepare a two-dimensional alignment layer. Specifically, the mask is moved to adjust the area blocked by the mask, and the exposure beam is used to complete the exposure of the alignment layer to be exposed.

[0059] Please see Figure 7 , Figure 7 This is a schematic diagram of the exposure process of the orientation layer to be exposed, provided in an embodiment of this application.

[0060] For ease of description, the following embodiments use an opaque flat plate as an example.

[0061] like Figure 7 As shown, before exposure begins, the mask completely blocks the area of ​​the orientation layer to be exposed, preventing the exposure beam from reaching the layer. After exposure begins, the mask translates along a first preset direction (X-axis, as shown in the figure) at a speed of V2, gradually exposing the area of ​​the orientation layer to be exposed to the exposure spot corresponding to the exposure beam. Simultaneously, the orientation layer translates along a second preset direction (Y-axis, as shown in the figure) at a speed of V1. This exposure process is as follows: Figure 7As shown in Figure ac, as the orientation layer to be exposed and the mask are translated, a set of oblique first equiphase lines are formed on the surface of the orientation layer to be exposed. The direction of the first equiphase lines is related to V1 and V2. After the mask and the orientation layer to be exposed have moved a certain distance, they enter a state similar to... Figure 7 As shown in the figure, the exposure process involves the orientation layer to be exposed translating along the -Y axis at a speed of V1', while the mask continues to translate along the X axis. Similarly, with the translation of the orientation layer and the mask, another set of second isophase lines with different directions is formed on the surface of the orientation layer to be exposed. After a certain displacement, the orientation layer to be exposed again translates along the Y axis, and this process is repeated until the orientation layer to be exposed is fully exposed. It should be understood that the orientation layer to be exposed reciprocates along the Y axis, while the mask translates along the X axis throughout, thus exposing the first and second isophase lines with different directions on the orientation layer to be exposed, resulting in a two-dimensional orientation layer. The arrangement of orientation directions in the two-dimensional orientation layer can be referenced... Figure 5 The corresponding embodiments are not described here.

[0062] In some embodiments, the mask is translated along a first preset direction on the surface of the orientation layer to be exposed, including: the relative displacement between the mask and the orientation layer to be exposed in the second preset direction is zero, and the mask is translated at a constant speed or at a variable speed along the first preset direction.

[0063] It should be understood that during the movement of the mask and the orientation layer to be exposed, there is no relative displacement between them in the Y-axis direction, so that oblique equiphase lines can be exposed on the orientation layer to be exposed; and the mask can be translated at a uniform speed or at a variable speed in the X-axis direction, which is not limited in this application. It should be noted that the orientation layer to be exposed moves at a uniform speed during the translation in one direction, but the corresponding moving speeds of the orientation layer in the two directions can be different, which can be set according to actual design requirements, and this application does not limit it.

[0064] In other embodiments, the positions of the exposure light source and the mask are fixed, and the mask partially blocks the exposure beam, allowing the remaining portion of the exposure beam to expose the alignment layer not blocked by the mask. In specific implementations, the alignment layer moves at a constant speed in a direction opposite to the first preset direction, while simultaneously reciprocating in a second preset direction. Therefore, during the process of the alignment layer moving from being blocked by the mask to being exposed, the newly moved alignment layer from under the mask can be exposed by the same exposure spot, avoiding uneven exposure of the alignment layer due to uneven exposure spots, ensuring exposure consistency and alignment stability throughout the alignment layer; furthermore, the mask does not need to be moved during exposure, making the entire exposure system more stable and reducing exposure errors.

[0065] Step S104: Remove the mask and coat the surface of the two-dimensional alignment layer away from the substrate layer with liquid crystal to obtain the polarizer holographic grating.

[0066] For example, after exposure is completed, the mask is removed, and liquid crystal is coated on the surface of the two-dimensional alignment layer away from the substrate layer. The liquid crystal is deflected under the alignment effect of the two-dimensional alignment layer to form a liquid crystal layer, thereby completing the fabrication of a single-layer two-dimensional polarizing holographic grating.

[0067] In some embodiments, coating the surface of the two-dimensional alignment layer away from the substrate layer with liquid crystal to obtain the polarizing holographic grating includes: after coating the surface of the two-dimensional alignment layer away from the substrate layer with liquid crystal, aligning and curing the liquid crystal to form a liquid crystal layer to obtain the polarizing holographic grating; wherein the alignment direction of the liquid crystal in the liquid crystal layer corresponds to the alignment direction of the two-dimensional alignment layer, such that the liquid crystal layer forms a first equiphase surface corresponding to the first equiphase line and a second equiphase surface corresponding to the second equiphase line.

[0068] For example, after coating the surface of the two-dimensional alignment layer away from the substrate layer with liquid crystal, the liquid crystal is oriented and cured to form a liquid crystal layer, thereby completing the fabrication of a polarizing holographic grating. It should be understood that the alignment direction of the liquid crystal is deflected under the action of the two-dimensional alignment layer. Specifically, the alignment direction of the liquid crystal near the two-dimensional alignment layer is the same as the alignment direction in the two-dimensional alignment layer. However, along the direction away from the two-dimensional alignment layer, although the force exerted by the two-dimensional alignment layer on the liquid crystal gradually decreases, due to the properties of the liquid crystal itself, the alignment direction of the liquid crystal will continue to rotate in the direction away from the two-dimensional alignment layer. This causes the alignment direction of the liquid crystal in this direction to also exhibit periodic changes, thereby forming a first equiphase surface and a second equiphase surface in the liquid crystal layer. This allows the fabricated polarizing holographic grating to possess the diffraction characteristics of a two-dimensional grating, thereby realizing the fabrication of a single-layer two-dimensional polarizing holographic grating.

[0069] In the specific implementation process, the coated liquid crystal is a cholesteric liquid crystal.

[0070] In some embodiments, the exposure beam includes a first exposure beam and a second exposure beam, wherein the polarization direction of the first exposure beam is opposite to that of the second exposure beam.

[0071] In a specific implementation, the first exposure beam and the second exposure beam simultaneously irradiate the area to be exposed in the orientation layer from different directions to expose the area to be exposed. The first exposure beam is left-handed circularly polarized light, the second exposure beam is right-handed circularly polarized light, and the first exposure beam and the second exposure beam are beams from the same source.

[0072] The method for fabricating polarization holographic gratings provided in the above embodiments solves the problem that exposure methods in related technologies cannot fabricate two-dimensional polarization holographic gratings.

[0073] Please see Figure 8 , Figure 8 This is a schematic block diagram of the structure of an exposure system provided in an embodiment of this application.

[0074] like Figure 8 As shown, the exposure system includes an exposure light source 100, a clamping mechanism 200, and a platform 300. The exposure light source 100 provides an exposure beam to the orientation layer to be exposed, thus exposing the orientation layer. The clamping mechanism 200 clamps a mask, and during the exposure of the orientation layer, the clamping mask moves along a first preset direction. The platform 300 supports a substrate layer and the orientation layer to be exposed, allowing the exposure beam from the exposure light source 100 to irradiate the orientation layer placed on the platform 300 for exposure. During exposure, the platform reciprocates in a second preset direction, causing the orientation layer to also reciprocate in the second preset direction. Combined with the clamping mechanism 200 clamping the mask and moving it along the first preset direction, two sets of equiphase lines with different directions can be exposed on the orientation layer to be exposed, thereby obtaining a two-dimensional orientation layer.

[0075] It should be noted that after the exposure system completes the exposure of the alignment layer to be exposed, liquid crystal coating and other processes can be continued through other equipment, or liquid crystal coating and other processes can be continued on the exposure system itself, without any restrictions.

[0076] In another embodiment, if the exposure process of the orientation layer to be exposed is a translation in the opposite direction of the first preset direction and a reciprocating motion in the second preset direction, then the exposure system does not need to be equipped with a clamping mechanism. It only needs to enable the carrier platform to translate in the first preset direction and reciprocate in the second preset direction. Those skilled in the art can set the exposure system according to the actual exposure requirements, and this application does not limit it.

[0077] It should be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the scope of the application. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0078] It should also be understood that the term "and / or" as used in this specification and the appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes such combinations. It should be noted that, herein, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or system that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or system. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or system that includes that element.

[0079] The sequence numbers of the embodiments in this application are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments. The above descriptions are merely specific implementations of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A polarizing holographic grating, characterized in that, The polarizer holographic grating includes: basal layer; A two-dimensional orientation layer is disposed on the surface of the substrate layer. In the projection of the two-dimensional orientation layer along the direction of the substrate layer, the lines connecting the positions with the same orientation direction are serrated. The orientation direction of the two-dimensional orientation layer changes periodically in a first preset direction and periodically in a second preset direction perpendicular to the first preset direction, such that the two-dimensional orientation layer forms a first equiphase line and a second equiphase line, and the angle between the first equiphase line and the second equiphase line is greater than zero. A liquid crystal layer is disposed on the surface of the two-dimensional alignment layer away from the substrate layer. The alignment direction of the liquid crystal molecules in the liquid crystal layer corresponds to the alignment direction of the two-dimensional alignment layer. The alignment direction of the liquid crystal molecules near the two-dimensional alignment layer is exactly the same as the alignment direction in the two-dimensional alignment layer. Along the direction away from the contact plane between the two-dimensional alignment layer and the liquid crystal layer, the liquid crystal molecules continuously rotate, so that the liquid crystal layer forms a first equiphase surface corresponding to the first equiphase line and a second equiphase surface corresponding to the second equiphase line. The first equiphase surface and the second equiphase surface are not perpendicular to the plane where the two-dimensional alignment layer is located. The angle between the first equiphase surface and the second equiphase surface is determined by the angle between the first equiphase line and the second equiphase line and the pitch of the liquid crystal molecules in the Z direction.

2. The polarizing holographic grating as described in claim 1, characterized in that, The first preset direction is the X-axis direction of the preset coordinate system, the second preset direction is the Y-axis direction of the preset coordinate system, and the origin of the preset coordinate system is any point on the plane where the base layer is located.

3. The polarizer holographic grating as described in claim 1 or 2, characterized in that, The substrate layer comprises resin or glass; the two-dimensional orientation layer comprises one of polyimide, organic azo compound, and acrylate polymer; and the liquid crystal layer comprises cholesteric liquid crystal.

4. A method for fabricating a polarizing holographic grating, characterized in that, The method for fabricating the polarizing holographic grating as described in claim 1 includes: A substrate layer is provided, and an orientation layer to be exposed is coated on the surface of the substrate layer; A mask is provided such that it blocks a portion of the surface of the orientation layer to be exposed that faces away from the substrate layer. The orientation layer to be exposed is irradiated with an exposure beam to expose the areas on the surface of the orientation layer that are not blocked by the mask, thereby obtaining a two-dimensional orientation layer; During the process of the exposure beam irradiating the orientation layer to be exposed, the mask is translated along a first preset direction and the orientation layer to be exposed reciprocates in a second preset direction, or the orientation layer to be exposed is translated in the opposite direction of the first preset direction and reciprocates in the second preset direction, so that the orientation direction of the two-dimensional orientation layer exhibits periodic changes in both the first preset direction and the second preset direction, thereby forming a first equiphase line and a second equiphase line in the two-dimensional orientation layer. The mask is removed, and liquid crystal is coated on the surface of the two-dimensional alignment layer opposite to the substrate layer to obtain the polarizing holographic grating.

5. The method for fabricating a polarizing holographic grating as described in claim 4, characterized in that, The mask is an opaque flat plate, or the mask has a light-transmitting structure, which includes a slit or a through hole.

6. The method for fabricating a polarizing holographic grating as described in claim 4, characterized in that, The mask is translated along a first preset direction on the surface of the orientation layer to be exposed, including: The relative displacement between the mask and the orientation layer to be exposed in the second preset direction is zero, and the mask is translated at a uniform speed or at a variable speed along the first preset direction.

7. The method for fabricating a polarizing holographic grating as described in claim 4, characterized in that, The exposure beam includes a first exposure beam and a second exposure beam, wherein the polarization direction of the first exposure beam is opposite to that of the second exposure beam.

8. The method for fabricating a polarizing holographic grating as described in any one of claims 4-7, characterized in that, The process of coating the surface of the two-dimensional alignment layer opposite to the substrate layer with liquid crystal to obtain the polarizer holographic grating includes: After coating the surface of the two-dimensional alignment layer away from the substrate layer with liquid crystal, the liquid crystal is oriented and cured to form a liquid crystal layer, thereby obtaining the polarizing holographic grating; The liquid crystal molecules in the liquid crystal layer are arranged in a direction that corresponds to the orientation direction of the two-dimensional alignment layer, such that the liquid crystal layer forms a first equiphase surface corresponding to the first equiphase line and a second equiphase surface corresponding to the second equiphase line.

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