Polarization volume grating and preparation method therefor, and display device

Abstract

The present application provides a polarization volume grating and a preparation method therefor, and a display device. The preparation method comprises: mixing a photo-alignment liquid crystal, a photo-polymerized liquid crystal, a chiral agent, a radical initiator, and an ionic initiator to obtain a liquid crystal mixture; using the liquid crystal mixture to prepare a blended liquid crystal layer on a substrate; performing exposure treatment on the blended liquid crystal layer to prepare a periodically aligned cholesteric liquid crystal thin film; and performing curing treatment on the cholesteric liquid crystal thin film to obtain a polarization volume grating.

Description

Polarizing holographic gratings and their fabrication methods, and display devices

[0001] This application claims priority to Chinese Patent Application No. 2024119966563, filed on December 31, 2024, entitled "Polarizing Holographic Grating and its Preparation Method and Display Device", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of grating fabrication technology, and in particular to a polarizing holographic grating, its fabrication method, and a display device thereof. Background Technology

[0003] Cholesteric liquid crystals possess a layered structure, with the molecular axes of each layer slightly offset from those of adjacent layers, forming a helical structure overall. Due to their unique helical structure and excellent optical properties, they have broad application prospects in various fields such as optical devices (e.g., polarizer holographic gratings).

[0004] In related technologies, polarization holographic gratings are generally prepared by surface orientation. This method is a conventional method for preparing polarization holographic gratings. However, this method is complex, requires multiple coating processes, and has low efficiency. Moreover, for thick-film polarization holographic gratings, the increase in the number of coating processes has an adverse effect on the yield and is not conducive to large-scale production. Summary of the Invention

[0005] This application provides a polarizing holographic grating and its fabrication method and display device. The fabrication method has the characteristics of fewer fabrication steps and simpler process, which is conducive to obtaining gratings with a high yield. In addition, the method requires a low exposure dose, which is conducive to saving production capacity and promoting the mass production of polarizing holographic gratings (PVG).

[0006] To achieve the above objectives, this application provides a method for fabricating a polarizing holographic grating, the method comprising:

[0007] A liquid crystal mixture is prepared by mixing photo-aligned liquid crystal, photopolymerizable liquid crystal, chiral agent, free radical initiator and ionic initiator;

[0008] A substrate is provided, and a blended liquid crystal layer is formed on the substrate using the liquid crystal mixture;

[0009] The blended liquid crystal layer is exposed to induce photopolymerization of the photo-oriented liquid crystal in the blended liquid crystal layer, thereby obtaining a periodically oriented cholesteric liquid crystal film.

[0010] The cholesteric liquid crystal film is subjected to ultraviolet curing treatment to induce photopolymerization of the photopolymerizable liquid crystal in the cholesteric liquid crystal film, thereby obtaining a polarizing holographic grating.

[0011] In addition, to achieve the above objectives, this application also provides a polarizing volume holographic grating, which is prepared by the polarizing volume holographic grating preparation method described above.

[0012] In addition, to achieve the above objectives, this application also provides a display device, the display device including an optical waveguide, wherein the grating in the optical waveguide is a polarizing holographic grating as described above.

[0013] This application discloses a polarizing holographic grating, its fabrication method, and a display device. The method involves mixing photo-aligned liquid crystal, photopolymerizable liquid crystal, a chiral agent, a free radical initiator, and an ionic initiator to obtain a liquid crystal mixture. A substrate is provided, and a blended liquid crystal layer is fabricated on the substrate using the liquid crystal mixture. The blended liquid crystal layer is exposed to induce photopolymerization of the photo-aligned liquid crystal, resulting in a periodically oriented cholesteric liquid crystal film. The cholesteric liquid crystal film is then subjected to ultraviolet curing to induce photopolymerization of the photopolymerizable liquid crystal, thus obtaining the polarizing holographic grating. This allows for rapid fabrication of polarizing holographic gratings through polarization interference exposure and ultraviolet curing, requiring only a single coating process. This avoids the impact of lengthy processes on grating yield. Furthermore, the exposure process requires only weak blue light and a small exposure dose to achieve grating fabrication. Simultaneously, polarizing holographic gratings with thicknesses of micrometers and above can be fabricated. The molecular design is simple, and the raw materials are readily available, facilitating the rapid production of polarizing holographic gratings and their derivative devices. Attached Figure Description

[0014] 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.

[0015] Figure 1 is a schematic diagram of the fabrication process of a polarizing holographic grating provided by related technologies;

[0016] Figure 2 is a schematic flowchart of the steps of a method for fabricating a polarizing holographic grating according to an embodiment of this application;

[0017] Figure 3 is a schematic diagram of the molecular structure of a photo-aligned liquid crystal RM1 provided in an embodiment of this application;

[0018] Figure 4 is a schematic diagram of the molecular structure of a photopolymerizable liquid crystal LC1 provided in an embodiment of this application;

[0019] Figure 5 is a schematic diagram of the molecular structure of a chiral agent S811 / R811 provided in an embodiment of this application;

[0020] Figure 6 is a schematic diagram of the molecular structure of a chiral agent CD1 provided in an embodiment of this application;

[0021] Figure 7 is a schematic diagram of the molecular structure of a free radical initiator Radical Initiator 1 provided in an embodiment of this application;

[0022] Figure 8 is a schematic diagram of the molecular structure of an ionic initiator Cation Initiator 1 provided in an embodiment of this application;

[0023] Figure 9 is a schematic diagram of the fabrication process of a polarizer holographic grating provided in an embodiment of this application. Detailed Implementation

[0024] 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.

[0025] 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.

[0026] 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.

[0027] It should also be understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0028] Cholesteric liquid crystal thin films, due to their unique helical structure and excellent optical properties, have broad application prospects in optical displays, photonic devices, and holographic gratings. Polarization holographic gratings utilize periodically ordered cholesteric liquid crystals for light manipulation and can be used in photodetectors, diffractive waveguide displays, and other applications, offering unique advantages. In the fabrication of polarization holographic gratings (PVGs), the arrangement of liquid crystal molecules in the thin film is controlled, typically by light-driven specific orientation materials to achieve periodic arrangement, which significantly affects the optical properties of the thin film, such as transmittance and haze.

[0029] In related technologies, there are two main methods for fabricating polarizing holographic gratings using photo-aligned liquid crystals:

[0030] (I) Surface Alignment Method: As shown in Figure 1, a layer of photoalignment material, typically on the nanometer scale, is first coated on the substrate. Exposure is performed using a polarization interference light source. Subsequently, cholesteric liquid crystal is coated onto the photoaligned film. The liquid crystal molecules can further polymerize under a second exposure, generating a liquid crystal film with a specific orientation. This method is a relatively conventional method for preparing polarization holographic gratings. However, this method is complex, requires multiple coating processes, and has low efficiency. Furthermore, for thick-film polarization holographic gratings, the increased number of coating processes negatively impacts the yield, hindering large-scale production.

[0031] (II) Bulk Orientation Method: This method involves designing and synthesizing photoresponsive cholesteric liquid crystal molecular fragments, performing bulk exposure using a polarization interference light source, and inducing photopolymerization reactions in the main chain or side chains of the liquid crystal molecules, resulting in local alignment parallel to the polarization direction of the light source. The film is then heated to above the clearing point and cooled for setting. Although this method requires only one exposure to prepare a polarization-based holographic grating, it typically requires high exposure intensity to initiate photopolymerization throughout the entire film system. Furthermore, the thickness of the prepared film is limited, making it unsuitable for preparing thick-film polarization-based holographic gratings. Additionally, the specific liquid crystal molecule synthesis steps are cumbersome, hindering rapid industrial application.

[0032] To address the aforementioned issues, this application provides a polarizing holographic grating, its fabrication method, and a display device, which reduces the number of fabrication steps, simplifies the fabrication process, increases the yield, and requires less exposure dose.

[0033] Please refer to Figure 2, which is a schematic flowchart of a method for fabricating a polarizing holographic grating according to an embodiment of this application. This polarizing holographic grating can be applied to display devices, including but not limited to near-eye display devices such as AR (Augmented Reality) glasses and VR (Virtual Reality) glasses, and HUD (head-up display) devices.

[0034] As shown in Figure 2, the fabrication method of the polarizing holographic grating specifically includes steps S101 to S104.

[0035] S101. A liquid crystal mixture is prepared by mixing photo-aligned liquid crystal, photopolymerizable liquid crystal, chiral agent, free radical initiator and ionic initiator.

[0036] Photo-aligned liquid crystals are liquid crystal materials whose molecular alignment can be controlled by light. They exhibit photoresponsive properties and can undergo photochemical reactions under specific light fields, thus achieving a periodically ordered arrangement. Furthermore, the ordered structure of photo-aligned liquid crystals can alter the orientation vectors of other liquid crystal molecules in the film, resulting in a periodically ordered arrangement of liquid crystal molecules throughout the entire film. In the embodiments of this application, the photo-aligned liquid crystal can be a nematic liquid crystal such as RM1, which can react with free radical initiators. The structure of RM1 is shown in Figure 3.

[0037] For example, photo-oriented liquid crystals may contain reactive functional groups such as acrylate groups, which can react with free radical initiators to obtain periodically oriented cholesteric liquid crystal films.

[0038] Photopolymerizable liquid crystals are liquid crystal materials formed through photopolymerization. The molecular structure of photopolymerizable liquid crystals has a liquid crystal core and reactive functional groups at its ends. These functional groups can form a polymer network through photopolymerization, thus becoming a liquid crystal polymer (LCP), i.e., a polarizer holographic grating. In the embodiments of this application, the photopolymerizable liquid crystal can be a nematic liquid crystal such as LC1 that can react with ionic initiators. The structure of LC1 is shown in Figure 4.

[0039] Chiral agents can twist liquid crystal materials in a certain direction and increase the stability of liquid crystal display devices.

[0040] Chiral agents can induce phase transitions in liquid crystal materials, such as from a nematic phase to a cholesteric phase or a chiral nematic phase. In TN (twisted nematic) display mode, chiral agents can twist the orientation of liquid crystal molecules by 90° and suppress the formation of dislocations; in STN (super-twisted nematic) display mode, it can achieve the required higher twist angle (180°–270°); in reflective cholesteric liquid crystal displays, chiral agents can form the required short pitch.

[0041] For example, chiral agents include, but are not limited to, R5011, S5011, R1011, S1011, R811, S811, CD1, etc. The structure of S811 / R811 is shown in Figure 5, and the structure of CD1 is shown in Figure 6.

[0042] The free radical initiator can be one or more of peroxide initiators, azo initiators, and redox initiators. For example, the free radical initiator can be Radical Initiator 1, the structure of which is shown in Figure 7.

[0043] For example, peroxide initiators may include cumene hydroperoxide, benzoyl peroxide, tert-butyl hydroperoxide, etc. These initiators decompose to generate free radicals under heating or light conditions, and typically have a high decomposition rate, classifying them as highly reactive initiators.

[0044] For example, azo initiators may include azobisisobutyronitrile (AIBN), azobisisoheptanenitrile, etc. These initiators decompose at lower temperatures to form free radicals, are generally relatively stable, have a low decomposition rate, and are classified as low-activity initiators.

[0045] For example, redox initiators may include hydrogen peroxide-ferrous salt, persulfate-sulfite, etc. These initiators generate primary free radicals through redox reactions, have low decomposition activation energies, and can initiate polymerization reactions at lower temperatures.

[0046] Ionic initiators can be cationic initiators. After absorbing light energy, the molecules of a cationic initiator undergo photolysis, producing a superacid (superprotic acid), which then initiates the polymerization of the cationic oligomer and the reactive diluent. For example, the ionic initiator can be Cation Initiator 1, the structure of which is shown in Figure 8.

[0047] For example, cationic initiators may include onium salt initiators, organometallic initiators, and organosilane initiators.

[0048] For example, onium salt initiators may include diazonium salts, diaryliodoonium salts, triarylthionium salts, alkylthionium salts, etc.

[0049] For example, organometallic initiators may include iron aromatic salts, sulfonyloxy ketones, and triarylsiloxanes.

[0050] For example, organosilane initiators may include triarylsiloxanes, etc.

[0051] Specifically, a liquid crystal mixture can be prepared by uniformly mixing photo-aligned liquid crystal, photopolymerizable liquid crystal, chiral agent, free radical initiator and ionic initiator.

[0052] In some embodiments, the total mass percentage of the photo-aligned liquid crystal and the free radical initiator in the liquid crystal mixture is less than or equal to 40%; and / or, the mass percentage of the chiral agent in the liquid crystal mixture is less than or equal to 20%; and / or, the mass percentage of the free radical initiator in the mixture of the photo-aligned liquid crystal and the free radical initiator is less than or equal to 20%; and / or, the mass percentage of the ionic initiator in the mixture of the photopolymerizable liquid crystal and the ionic initiator is less than or equal to 20%.

[0053] For example, by controlling the total mass of the photo-oriented liquid crystal and the free radical initiator in the liquid crystal mixture to be less than or equal to 40%, the cholesteric liquid crystal film produced can be made to have better performance.

[0054] For example, the total mass of photo-oriented liquid crystal and free radical initiator in the liquid crystal mixture can be 5%, 10%, 20%, 28%, 30%, 35%, 40%, etc.

[0055] For example, by controlling the chiral agent to have a content of less than or equal to 20% in the liquid crystal mixture, the pitch of the liquid crystal material can be controlled, thereby controlling the phase transition of the liquid crystal material and avoiding the production of liquid crystals that do not meet the pitch requirements.

[0056] For example, the chiral agent can be present in the liquid crystal mixture at a concentration of 3%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, etc.

[0057] For example, the content of the free radical initiator in the mixture of photo-aligned liquid crystal and free radical initiator is controlled to be less than or equal to 20%, thereby enabling the photo-aligned liquid crystal and free radical initiator to react sufficiently to obtain a periodically oriented cholesteric liquid crystal film.

[0058] For example, the content of the free radical initiator in the mixture of photo-aligned liquid crystal and free radical initiator can be 3%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, etc.

[0059] For example, the content of the ionic initiator in the mixture of photopolymerizable liquid crystal and ionic initiator is controlled to be less than or equal to 20%, thereby enabling the photopolymerizable liquid crystal and ionic initiator to react fully to form a liquid crystal polymer network, i.e., a polarizer holographic grating.

[0060] For example, the content of ionic initiators in the mixture of photopolymerizable liquid crystal and ionic initiators can be 3%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, etc.

[0061] For example, by mass percentage (wt%), a liquid crystal mixture can be prepared by blending photo-oriented liquid crystal component RM1 (30wt%), free radical initiator Radical Initiator 1 (3wt%), R5011 (3wt%), photopolymerizable liquid crystal LC1 (60wt%), and ionic initiator Cation Initiator 1 (4wt%).

[0062] S102. A substrate is provided, and a blended liquid crystal layer is formed on the substrate using a liquid crystal mixture.

[0063] The blended liquid crystal layer can be a thin film formed on a substrate by a liquid crystal mixture.

[0064] For example, the substrate can be glass, resin, silicon carbide, etc., without specific limitations.

[0065] In some embodiments, before forming a blended liquid crystal layer on a substrate using a liquid crystal mixture, a liquid crystal mixture solution is prepared using the liquid crystal mixture and an organic solvent; the liquid crystal mixture solution is then coated onto the substrate using a selected coating method to form a blended liquid crystal layer. This allows the formation of a blended liquid crystal layer of the appropriate thickness.

[0066] Specifically, the coating method includes at least one of spin coating, blade coating, and inkjet printing.

[0067] For example, a liquid crystal mixture is dissolved in an organic solvent and stirred evenly to obtain a liquid crystal mixture solution. The liquid crystal mixture solution is then coated onto a substrate with an alignment layer by spin coating, doctor blade coating, inkjet printing, or other methods to form a blended liquid crystal layer.

[0068] For example, using xylene as the organic solvent, a 20wt% liquid crystal mixture solution is prepared by mixing xylene and liquid crystal, and then spin-coated onto a glass substrate at a speed of 3000 rpm / s to obtain a blended liquid crystal layer with a thickness of about 500 nm.

[0069] It should be noted that, although blended liquid crystal layers of any thickness can be prepared in this embodiment, due to the characteristics of the spin coating process, the method of this embodiment is generally used to prepare thinner blended liquid crystal layers.

[0070] In some embodiments, a spacer layer material is provided, and a substrate is encapsulated using the spacer layer material to form a liquid crystal cell with a spacer layer; a liquid crystal mixture is then filled into the liquid crystal cell to form a blended liquid crystal layer. This allows the fabrication of a blended liquid crystal layer of the appropriate thickness.

[0071] The main function of the liquid crystal cell is to control the passage of light to achieve the display function. The liquid crystal cell controls the arrangement of liquid crystal molecules through an electric field, thereby adjusting the transmission, reflection, or scattering of light to achieve image display.

[0072] For example, the interstitial layer material can be polyethylene terephthalate (PET), a thermoplastic polyester produced by polycondensation of terephthalic acid and ethylene glycol. It has a highly crystalline structure, a smooth and glossy surface, and good creep resistance, fatigue resistance, and abrasion resistance. It is one of the toughest thermoplastic materials.

[0073] Specifically, the thickness of the gap layer is determined by the fabrication thickness of the polarizing holographic grating.

[0074] For example, the thickness of the gap layer can be determined according to the required thickness of the polarizer holographic grating to be prepared, so that a gap layer of a specific thickness can be prepared according to actual needs, and a liquid crystal cell with the gap layer can be formed.

[0075] For example, a glass substrate with upper and lower interlayers is encapsulated using PET material to form a liquid crystal cell with a gap layer and a thickness of 10 μm. A liquid crystal mixture is then filled into the assembled liquid crystal cell, and a blended liquid crystal layer is formed at the upper and lower interlayers of the glass substrate. The thickness of the liquid crystal cell is also 10 μm, and the thickness of the final polarizer holographic grating is also 10 μm.

[0076] It should be noted that, although blended liquid crystal layers of any thickness can be prepared in this embodiment, due to the characteristics of the liquid crystal cell, the method of this embodiment is generally used to prepare thicker blended liquid crystal layers.

[0077] S103. Expose the blended liquid crystal layer to induce photopolymerization of the photo-oriented liquid crystal in the blended liquid crystal layer, thereby obtaining a periodically oriented cholesteric liquid crystal film.

[0078] For example, by exposing the blended liquid crystal layer, the photo-aligned liquid crystal in the blended liquid crystal layer can undergo a photopolymerization reaction, thereby aligning the director of the liquid crystal along a specific direction, thus forming a periodically oriented cholesteric liquid crystal film.

[0079] In some embodiments, the blended liquid crystal layer is exposed under a designed light field pattern to pattern and fix the molecular orientation of the photo-oriented liquid crystal in the blended liquid crystal layer, so that the liquid crystal molecules present a specific periodic arrangement, thereby obtaining a periodically oriented cholesteric liquid crystal film.

[0080] For example, exposure can be performed under a polarization interference light field with a period of 1 μm, at which time the photo-aligned liquid crystal RM1 in the blended liquid crystal layer will undergo a photopolymerization reaction, thereby obtaining a periodically oriented cholesteric liquid crystal film.

[0081] In the embodiments of this application, the photo-aligned liquid crystal is used to undergo photopolymerization under visible light, while the photopolymerizable liquid crystal does not undergo photopolymerization under visible light. Therefore, by controlling the light wavelength, the photo-aligned liquid crystal in the blended liquid crystal layer can undergo photopolymerization, and the photopolymerizable liquid crystal will not undergo photopolymerization under visible light, thereby obtaining a periodically oriented cholesteric liquid crystal film.

[0082] In some embodiments, the exposure parameters corresponding to the exposure processing include the light wavelength and the exposure dose, wherein the light wavelength is 400-500 nm and the exposure dose is 0.3-5 J / cm. 2 Therefore, periodically oriented cholesteric liquid crystal films can be rapidly prepared using only weak blue light polarization interference exposure.

[0083] In related technologies, taking the fabrication of polarization holographic gratings via bulk alignment as an example, a high exposure intensity is generally required to initiate photopolymerization within the entire thin film system. Furthermore, the thicker the polarization holographic grating, the stronger the required exposure intensity; the exposure dose typically needs to be greater than 10 J / cm². 2 If the exposure intensity does not reach the corresponding intensity, the photopolymerization effect of the photo-aligned liquid crystal will be worse, which will lead to a decrease in the yield of the polarization holographic grating. Therefore, the bulk alignment method is not conducive to the preparation of thick-film polarization holographic gratings.

[0084] As shown in Figure 9, in this embodiment of the application, since the blended liquid crystal layer contains photo-aligned liquid crystal, only the bottom layer needs to be exposed. The photo-aligned liquid crystal in the bottom layer will undergo photopolymerization reaction according to the periodic light field distribution. Then, by utilizing the free radical polymerization transfer characteristics of the photo-aligned liquid crystal, the orientation (director) of the liquid crystal is periodically transferred and arranged. All the photo-aligned liquid crystals in the blended liquid crystal layer undergo photopolymerization reaction, thereby obtaining a periodically oriented cholesteric liquid crystal film.

[0085] For example, the light wavelength is typically controlled at 400-500nm, and the exposure dose is controlled at 0.3-5J / cm². 2 This means that periodically oriented cholesteric liquid crystal films can be rapidly prepared using relatively weak blue light polarization interference exposure.

[0086] For example, when preparing a blended liquid crystal layer using a spin-coating process, exposure can be performed under a polarization interference light field with a period of 1 μm, a wavelength of 457 nm, and an exposure dose of 0.3 J / cm. 2 The exposure time was 5 minutes. Since the blended liquid crystal layer prepared by spin coating is generally thin, the exposure dose was controlled at 0.3 J / cm². 2 That is, or greater than 0.3 J / cm 2 At this point, the photo-aligned liquid crystal RM1 in the blended liquid crystal layer will undergo a photopolymerization reaction, thereby obtaining a periodically oriented cholesteric liquid crystal film.

[0087] For example, when preparing a blended liquid crystal layer using a liquid crystal cell, exposure can be performed under a polarization interference light field with a period of 1 μm, a wavelength of 457 nm, and an exposure dose of 0.5 J / cm. 2 The exposure time was 5 minutes. Since the blended liquid crystal layer prepared using a liquid crystal cell is generally quite thick, the exposure dose was controlled at 0.5 J / cm². 2 That is, or greater than 0.5 J / cm 2 At this point, the photo-aligned liquid crystal RM1 in the blended liquid crystal layer will undergo a photopolymerization reaction, thereby obtaining a periodically oriented cholesteric liquid crystal film.

[0088] It should be noted that the exposure dose required for the exposure processing in the embodiments of this application is much smaller than that in the related technologies. That is, this application realizes the rapid preparation of periodically oriented cholesteric liquid crystal films using weaker blue light polarization interference exposure.

[0089] S104. The cholesteric liquid crystal film is subjected to ultraviolet curing treatment to induce photopolymerization of the photopolymerizable liquid crystal in the cholesteric liquid crystal film, thereby obtaining a polarizing holographic grating.

[0090] In this embodiment, photopolymerizable liquid crystal is used to undergo photopolymerization under ultraviolet light, while photoalignment liquid crystal does not undergo photopolymerization under ultraviolet light. Therefore, by controlling the light wavelength, the photopolymerizable liquid crystal in the cholesteric liquid crystal film can undergo photopolymerization, thereby producing a polarizing holographic grating.

[0091] In some embodiments, a cholesteric liquid crystal film is subjected to ultraviolet curing treatment based on preset ultraviolet curing parameters, so that the photopolymerizable liquid crystal in the cholesteric liquid crystal film undergoes a photopolymerization reaction to obtain a polarizing holographic grating; wherein, the ultraviolet curing parameters are determined by the preparation thickness of the polarizing holographic grating, and the ultraviolet curing parameters include irradiation intensity and irradiation time.

[0092] For example, the greater the fabrication thickness of the polarizing holographic grating, the stronger the irradiation intensity and the longer the irradiation time. Therefore, the irradiation intensity and irradiation time can generally be adjusted by the fabrication thickness of the polarizing holographic grating.

[0093] For example, if the polarizing holographic grating is relatively thin, the cholesteric liquid crystal film can be irradiated under a UV-LED lamp at a temperature of 30°C and an intensity of 0.65 mW / cm². 2 An irradiation time of 15 minutes was used to induce photopolymerization of the photopolymerizable liquid crystal in the cholesteric phase liquid crystal film, thereby producing a polarizing holographic grating.

[0094] For example, if the polarizer holographic grating is relatively thick, the cholesteric liquid crystal film can be irradiated under a UV-LED lamp at a temperature of 30°C and an intensity of 1.5 mW / cm². 2 An irradiation time of 15 minutes was used to induce photopolymerization of the photopolymerizable liquid crystal in the cholesteric phase liquid crystal film, thereby producing a polarizing holographic grating.

[0095] In the above embodiments, a liquid crystal mixture is prepared by mixing photo-aligned liquid crystal, photopolymerizable liquid crystal, chiral agent, free radical initiator, and ionic initiator; a substrate is provided, and a blended liquid crystal layer is prepared on the substrate using the liquid crystal mixture; the blended liquid crystal layer is exposed to induce photopolymerization of the photo-aligned liquid crystal in the blended liquid crystal layer, thereby preparing a periodically oriented cholesteric liquid crystal film; the cholesteric liquid crystal film is then subjected to ultraviolet curing to induce photopolymerization of the photopolymerizable liquid crystal in the cholesteric liquid crystal film, thereby preparing a polarization holographic grating. Thus, polarization holographic gratings can be rapidly prepared in a single coating step using polarization interference exposure and ultraviolet curing, avoiding the impact of lengthy process flows on grating yield. Furthermore, the exposure process requires only weak blue light and a small exposure dose to achieve grating preparation. Simultaneously, polarization holographic gratings with thicknesses of micrometers and above can also be prepared. The molecular design is simple, and the raw materials are readily available, which is beneficial for the rapid production of polarization holographic gratings and their derivative devices.

[0096] As shown in Figure 9, the polarizing holographic grating of this application will be described below with reference to specific embodiments.

[0097] Example 1:

[0098] (1) Select photo-aligned liquid crystal RM1 (30wt%), free radical initiator Radical Initiator 1 (3wt%), R5011 (3wt%), photopolymerizable liquid crystal LC1 (60wt%), and ionic initiator Cation Initiator 1 (4wt%), and prepare a 20wt% solution with xylene as solvent. Spin coat the solution onto a glass substrate at a speed of 3000rpm / s to obtain a blended liquid crystal layer with a thickness of about 500nm.

[0099] (2) The blended liquid crystal layer was exposed under a polarization interference light field with a period of 1 μm, a wavelength of 457 nm, and an exposure dose of 0.5 J / cm. 2 At this point, the photo-aligned liquid crystal RM1 in the blended liquid crystal layer undergoes a photopolymerization reaction to obtain a periodically oriented cholesteric liquid crystal film.

[0100] (3) The cholesteric phase liquid crystal film was irradiated under a UV-LED lamp at a temperature of 30℃ and an intensity of 0.65mW / cm². 2 The irradiation time was 15 min, and a thin-film polarizer holographic grating (PVG) was obtained.

[0101] Example 2:

[0102] (1) Select photo-aligned liquid crystal RM1 (30wt%), free radical initiator Radical Initiator 1 (3wt%), R5011 (3wt%), photopolymerizable liquid crystal LC1 (60wt%), and ionic initiator Cation Initiator 1 (4wt%), and prepare a liquid crystal cell with a thickness of 10µm by using PET as the gap layer (10µm) and glass substrate as the upper and lower sandwich layers.

[0103] (2) The liquid crystal cell was exposed under a polarization interference light field with a period of 1 μm, a wavelength of 457 nm, and an exposure dose of 0.5 J / cm. 2 At this point, the photo-aligned liquid crystal RM1 in the blended liquid crystal layer undergoes a photopolymerization reaction to obtain a periodically oriented cholesteric liquid crystal film.

[0104] (3) The cholesteric phase liquid crystal film was irradiated under a UV-LED lamp at a temperature of 30℃ and an intensity of 1.5 mW / cm². 2 The irradiation time was 15 min, and a thick-film polarizer holographic grating (PVG) was obtained.

[0105] The embodiments of this application also provide a polarizing holographic grating, which is fabricated using the polarizing holographic grating fabrication method described in the above embodiments. Therefore, this polarizing holographic grating can achieve the beneficial effects achievable by the polarizing holographic grating fabrication method provided in the embodiments of this application, as detailed in the preceding embodiments, and will not be repeated here.

[0106] This application also provides a display device in its embodiments. The display device includes an optical waveguide, wherein the grating in the optical waveguide can be a polarizing holographic grating as described in the above embodiments. Therefore, the display device can achieve the beneficial effects that the polarizing holographic grating fabrication method provided in the embodiments of this application can achieve, as detailed in the preceding embodiments, and will not be repeated here.

[0107] It should be noted that, in this document, 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. Unless otherwise specified, 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.

[0108] The above description is merely a specific embodiment 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 scope of the technology disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application.

Claims

1. A method for fabricating a polarizing holographic grating, the method comprising: A liquid crystal mixture is prepared by mixing photo-aligned liquid crystal, photopolymerizable liquid crystal, chiral agent, free radical initiator and ionic initiator; A substrate is provided, and a blended liquid crystal layer is formed on the substrate using the liquid crystal mixture; The blended liquid crystal layer is exposed to induce photopolymerization of the photo-oriented liquid crystal in the blended liquid crystal layer, thereby obtaining a periodically oriented cholesteric liquid crystal film. The cholesteric liquid crystal film is subjected to ultraviolet curing treatment to induce photopolymerization of the photopolymerizable liquid crystal in the cholesteric liquid crystal film, thereby obtaining a polarizing holographic grating.

2. The preparation method according to claim 1, wherein, The total mass percentage of the photo-aligned liquid crystal and the free radical initiator in the liquid crystal mixture is less than or equal to 40%.

3. The preparation method according to claim 1, wherein, The chiral agent comprises less than or equal to 20% of the liquid crystal mixture.

4. The preparation method according to claim 1, wherein, The free radical initiator is present in a content of less than or equal to 20% in the mixture of the photo-aligned liquid crystal and the free radical initiator.

5. The preparation method according to claim 1, wherein, The ionic initiator is present in a content of less than or equal to 20% in the mixture of the photopolymerizable liquid crystal and the ionic initiator.

6. The preparation method according to claim 1, wherein, Before fabricating the blended liquid crystal layer on the substrate using the liquid crystal mixture, the method further includes: A liquid crystal mixture solution is prepared using the liquid crystal mixture and an organic solvent; The process of fabricating a blended liquid crystal layer on the substrate using the liquid crystal mixture includes: The liquid crystal mixture solution is coated onto the substrate using a selected coating method to form a blended liquid crystal layer.

7. The preparation method according to claim 6, wherein, The coating method includes at least one of spin coating, blade coating, and inkjet printing.

8. The preparation method according to claim 1, wherein, The process of fabricating a blended liquid crystal layer on the substrate using the liquid crystal mixture includes: A gap layer material is provided, and the substrate is encapsulated using the gap layer material to form a liquid crystal cell with a gap layer; The liquid crystal mixture is filled into the liquid crystal cell to form a blended liquid crystal layer.

9. The preparation method according to claim 8, wherein, The provision of a gap layer material, and the encapsulation of the substrate using the gap layer material to form a liquid crystal cell with a gap layer, includes: The thickness of the gap layer of the liquid crystal cell is determined based on the fabrication thickness of the polarizing holographic grating; The gap layer material is provided according to the gap layer thickness, and the substrate is encapsulated using the gap layer material to form a liquid crystal cell with a gap layer.

10. The preparation method according to claim 8, wherein, The interstitial layer material includes polyethylene terephthalate.

11. The preparation method according to claim 1, wherein, The step of exposing the blended liquid crystal layer to induce photopolymerization of the photo-aligned liquid crystals in the blended liquid crystal layer to obtain a periodically oriented cholesteric liquid crystal film includes: The blended liquid crystal layer is exposed under a designed light field pattern to pattern and fix the molecular orientation of the photo-oriented liquid crystal in the blended liquid crystal layer, so that the liquid crystal molecules present a specific periodic arrangement, thus obtaining a periodically oriented cholesteric liquid crystal film.

12. The preparation method according to claim 1, wherein, The step of performing ultraviolet curing on the cholesteric liquid crystal film to induce photopolymerization of the photopolymerizable liquid crystal in the cholesteric liquid crystal film to obtain a polarizing holographic grating includes: Based on preset UV curing parameters, the cholesteric liquid crystal film is subjected to UV curing treatment, causing the photopolymerizable liquid crystal in the cholesteric liquid crystal film to undergo a photopolymerization reaction, thereby obtaining a polarizing holographic grating.

13. The preparation method according to claim 12, wherein, Before performing UV curing treatment on the cholesteric liquid crystal film based on preset UV curing parameters, the method further includes: The UV curing parameters are determined based on the fabrication thickness of the polarizer holographic grating.

14. The preparation method according to claim 12, wherein, The UV curing parameters include irradiation intensity and irradiation time.

15. The preparation method according to claim 1, wherein, The exposure parameters corresponding to the exposure processing include the light wavelength and the exposure dose, wherein the light wavelength is 400-500nm and the exposure dose is 0.3-5J / cm. 2 .

16. The preparation method according to claim 1, wherein, The photo-aligned liquid crystal includes reactive functional groups capable of reacting with the free radical initiator.

17. The preparation method according to claim 14, wherein, The reactive functional group is an acrylate group.

18. The preparation method according to claim 1, wherein, The chiral agent is at least one of R5011, S5011, R1011, S1011, R811, S811, and CD1.

19. A polarizing volume holographic grating, wherein the polarizing volume holographic grating is prepared by the method for preparing a polarizing volume holographic grating as described in any one of claims 1 to 18.

20. A display device comprising an optical waveguide, wherein the grating in the optical waveguide is a polarizer holographic grating as described in claim 19.

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