Polarization volume holographic grating and preparation method therefor, and display device

Abstract

The present application provides a polarization volume holographic grating and a preparation method therefor, and a display device. The preparation method comprises: filling a first liquid crystal cell with a first liquid crystal mixture; performing an ultraviolet curing treatment on the first liquid crystal cell, so as to form a polymer template; removing an inert nematic phase liquid crystal in the polymer template to obtain a second liquid crystal cell; adding a second liquid crystal mixture into the second liquid crystal cell; and performing an ultraviolet curing treatment on the second liquid crystal cell, so as to prepare a polarization volume holographic grating.

Description

Polarizing holographic gratings and their fabrication methods, and display devices

[0001] This application claims priority to Chinese Patent Application No. 202411975262X, filed on December 30, 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] However, traditional cholesteric liquid crystal films suffer from a narrow reflectance bandwidth, limiting their application over a wide spectral range. Related technologies typically employ multilayer coating to increase the reflectance bandwidth. This method is a conventional approach for fabricating polarimetric holographic gratings, but it is complex, requiring multiple coating processes, resulting in low efficiency. Furthermore, the increased number of coating steps significantly impacts yield, hindering large-scale production. Summary of the Invention

[0005] This application provides a polarizing holographic grating and its fabrication method, as well as a display device, aiming to fabricate a polarizing holographic grating with a wide reflection bandwidth and adjustable grating thickness and polarization direction.

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

[0007] A first liquid crystal mixture is prepared and filled into a first liquid crystal cell. The first liquid crystal mixture includes at least an inert nematic liquid crystal, a first photopolymerizable liquid crystal, and a first chiral agent.

[0008] The first liquid crystal cell is subjected to ultraviolet curing treatment to cause the first photopolymer liquid crystal to undergo a photopolymerization reaction to form a polymer template;

[0009] The inert nematic liquid crystal within the polymer template is removed to obtain a second liquid crystal cell;

[0010] A second liquid crystal mixture is prepared and added to a second liquid crystal cell. The second liquid crystal mixture includes at least a second photopolymerizable liquid crystal and a second chiral agent. The type of the first photopolymerizable liquid crystal is different from the type of the second photopolymerizable liquid crystal, and the proportion of the first chiral agent is different from the proportion of the second chiral agent.

[0011] The second liquid crystal cell is subjected to ultraviolet curing treatment to cause the second photopolymer liquid crystal to undergo a photopolymerization reaction, thereby obtaining a polarizing holographic grating.

[0012] 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.

[0013] 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.

[0014] This application discloses a polarizer holographic grating and its fabrication method, as well as a display device. The method involves preparing a first liquid crystal mixture and filling it into a first liquid crystal cell. The first liquid crystal mixture includes at least an inert nematic liquid crystal, a first photopolymerizable liquid crystal, and a first chiral agent. The first liquid crystal cell is then subjected to ultraviolet curing to induce photopolymerization of the first photopolymerizable liquid crystal, forming a polymer template. The inert nematic liquid crystal within the polymer template is removed to obtain a second liquid crystal cell. A second liquid crystal mixture is then prepared and added into the second liquid crystal cell. The second liquid crystal mixture includes at least a second photopolymerizable liquid crystal and a second chiral agent. The types of the first and second photopolymerizable liquid crystals are different. The ratio of the agent is different from that of the second chiral agent; the second liquid crystal cell is subjected to ultraviolet curing treatment to cause the second photopolymer liquid crystal to undergo photopolymerization reaction, thus obtaining a polarizing holographic grating. Due to the presence of inert nematic liquid crystal in the polymer template, the inert nematic liquid crystal that does not react can be replaced with polymers of different center wavelengths. After secondary and multiple fillings, not only can the grating thickness and polarization direction be adjusted, but the polymer template can also achieve a gradient change in refractive index and pitch, thereby making the obtained polarizing holographic grating have a wider wavelength response range (usually one pitch corresponds to one wavelength), and widening the reflection bandwidth of the polarizing holographic grating. That is, a polarizing holographic grating with a wide reflection bandwidth is prepared. Attached Figure Description

[0015] 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.

[0016] Figure 1 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 2 is a schematic diagram of the molecular structure of LC1 provided in an embodiment of this application;

[0018] Figure 3 is a schematic diagram of the molecular structure of S811 / R811 provided in an embodiment of this application;

[0019] Figure 4 is a schematic diagram of the molecular structure of CD1 provided in an embodiment of this application;

[0020] Figure 5 is a schematic flowchart of the steps of another method for fabricating a polarizer holographic grating provided in the embodiments of this application. Detailed Implementation

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] Cholesteric liquid crystal films, due to their unique helical structure and excellent optical properties, have broad application prospects in optical displays and holographic gratings. However, traditional cholesteric liquid crystal films suffer from narrow reflection bandwidth, limiting their application over a wide spectral range. Therefore, how to prepare cholesteric liquid crystal films with wide reflection bandwidth has become an important research direction in this field. The idea of ​​increasing the reflection bandwidth of cholesteric liquid crystal films is to change the pitch of the liquid crystal in the film. When the pitch value changes from a fixed value to multiple values ​​within a specific range, the response range to incident wavelength light becomes wider, thereby broadening its reflection bandwidth.

[0026] In related technologies, there are two main methods for broadening the reflection bandwidth of polarizing holographic gratings:

[0027] (I) Multilayer Coating Method: Another layer of cholesteric liquid crystal with different pitches is coated on an existing cholesteric liquid crystal film, thereby increasing the pitch richness of the film. This method can add one or more pitches to the film, thereby increasing the reflection bandwidth. However, this method is complex, requires multiple coatings, has low efficiency, and the increased number of processes has an adverse effect on the yield of polarizing holographic gratings, which is not conducive to large-scale production.

[0028] (II) Light Intensity-Induced Gradient Pitch Variation: In cholesteric liquid crystal films, the reaction rate is faster on the side closer to UV curing than on the other side, causing the polymerizable cholesteric liquid crystals in the vertical direction to continuously polymerize towards the illuminated side. The pitch is smaller in the region closer to the light and larger in the region farther away. The gradient pitch variation will bring about an expansion of the reflective bandwidth of the film. However, this method usually requires the preparation of a polarizing holographic grating with a large thickness. In films with a thickness of micro / nanoscale, the difference in light intensity is limited, so the pitch variation range is limited. In addition, the uneven degree of polymerization caused by the inconsistent light intensity of cholesteric liquid crystals is not conducive to the uniformity and repeatability of polarizing holographic gratings.

[0029] To address the aforementioned issues, embodiments of this application provide a polarizing holographic grating and its fabrication method, as well as a display device, for fabricating a polarizing holographic grating with a wide reflection bandwidth and adjustable grating thickness and polarization direction.

[0030] Please refer to Figure 1, 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.

[0031] As shown in Figure 1, the fabrication method of the polarizing holographic grating specifically includes steps S101 to S105.

[0032] S101. Prepare a first liquid crystal mixture and fill the first liquid crystal mixture into a first liquid crystal cell. The first liquid crystal mixture includes at least an inert nematic liquid crystal, a first photopolymerizable liquid crystal, and a first chiral agent.

[0033] The first liquid crystal mixture comprises at least an inert nematic liquid crystal, a first photopolymerizable liquid crystal, and a first chiral agent. The inert nematic liquid crystal can be a nematic liquid crystal that does not undergo photopolymerization under ultraviolet light treatment. The first photopolymerizable liquid crystal can be a photopolymerizable liquid crystal with a specific center wavelength, which can be determined based on the response bandwidth of the polarization holographic grating to be prepared, such as a blue center wavelength, a red center wavelength, a green center wavelength, etc., without specific limitations. The first chiral agent can be any chiral agent, and its corresponding proportion can be determined based on the response bandwidth of the polarization holographic grating to be prepared, and its corresponding type can be determined based on the polarization direction of the polarization holographic grating to be prepared. The first liquid crystal cell is formed by assembling an alignment layer and a substrate after exposure, and is used to fill the first liquid crystal mixture.

[0034] 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). Before polymerization, the photopolymerizable liquid crystal is periodically and orderly arranged along the alignment layer, followed by photopolymerization, to fabricate a polarizing holographic grating (PVG). In the embodiments of this application, the photopolymerizable liquid crystal can be a nematic liquid crystal such as LC1 that can react with a free radical initiator. The structure of LC1 is shown in Figure 2.

[0035] It should be noted that the first photopolymerizable liquid crystal, the second photopolymerizable liquid crystal, and the third photopolymerizable liquid crystal in this article can all be LC1 nematic liquid crystals, and the types of the first photopolymerizable liquid crystal, the second photopolymerizable liquid crystal, and the third photopolymerizable liquid crystal can be the same or different.

[0036] Chiral agents can twist liquid crystal materials in a certain direction and increase the stability of liquid crystal display devices.

[0037] 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.

[0038] 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 3, and the structure of CD1 is shown in Figure 4.

[0039] It should be noted that the first chiral agent, second chiral agent, and third chiral agent mentioned in this article can all be the aforementioned chiral agents, and the types of the first chiral agent, second chiral agent, and third chiral agent can be the same or different. In the embodiments of this application, since it is necessary to broaden the reflection bandwidth of the polarizing holographic grating, and different chiral agent ratios correspond to different pitches, and different pitches correspond to different wavelengths, the ratios of the first chiral agent, second chiral agent, and third photochiral agent are different.

[0040] The main function of a liquid crystal cell is to control the passage of light to achieve display functionality. The liquid crystal cell uses an electric field to control the alignment of liquid crystal molecules, thereby regulating the transmission, reflection, or scattering of light to display images.

[0041] In some embodiments, before filling the first liquid crystal mixture into the first liquid crystal cell, a photosensitive alignment solution is coated on the substrate to obtain an alignment layer; the alignment layer is exposed to obtain a periodically aligned cholesteric liquid crystal film; a gap layer material is provided, and the substrate on which the cholesteric liquid crystal film is formed is encapsulated using the gap layer material to form a first liquid crystal cell with a gap layer.

[0042] Among them, the photosensitive orientation solution can be an orientation layer solution made of photosensitive orientation material.

[0043] 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.

[0044] For example, a commonly used photoalignment layer material can be coated onto a substrate, and the coated alignment layer can be exposed under a designed light field pattern. At this time, the molecular orientation of the alignment layer is patterned. The exposed alignment layer and the substrate are assembled, and a PET material of a specific thickness is used as a gap layer to encapsulate and form a first liquid crystal cell, and the thickness of the first liquid crystal cell is controlled.

[0045] For example, the photo-alignment material can be Nissan PIRB051, Brilliant Yellow, or SD-1; the substrate can be glass, resin, silicon carbide, or other substrates; the coating method can be any one of spin coating, inkjet printing, or blade coating; the exposure method can be any one of linear polarization exposure or polarization interference exposure. In some embodiments, polarization interference exposure is generally used.

[0046] For example, a photosensitive alignment material SD-1 was selected, and a photosensitive alignment solution with a mass fraction of 1.5 wt% was prepared using DMF as a solvent. After cleaning the glass substrate with ultraviolet ozone, the photosensitive alignment solution was spin-coated onto the substrate at a rotation speed of 3000 r / s to obtain the coated alignment layer. The layer was then exposed under a polarization interference square with a period of 1 μm and an exposure dose of 2 J / cm. 2 A periodically oriented SD-1 thin film was obtained; it was encapsulated using two substrates and the exposed alignment layer, and a gap layer was prepared using PET material to form a first liquid crystal cell with a thickness of 2 μm.

[0047] In some embodiments, based on a preset gap layer thickness, a substrate with a cholesteric liquid crystal film is encapsulated using a gap layer material to form a first liquid crystal cell with a gap layer. The thickness of the gap layer is determined by the fabrication thickness of the polarizer holographic grating.

[0048] 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.

[0049] For example, a glass substrate with upper and lower layers is encapsulated using PET material to form a first liquid crystal cell with a gap layer. The thickness of the gap layer is 2 μm, and the thickness of the first liquid crystal cell is also 2 μm. The thickness of the final polarizer holographic grating is also 2 μm.

[0050] In some embodiments, based on a preset type of first photopolymerizable liquid crystal and a first chiral agent, a corresponding first photopolymerizable liquid crystal and a first chiral agent are selected; a first liquid crystal mixture is prepared based on the ratio of the first chiral agent; wherein, the type of first photopolymerizable liquid crystal and the ratio of the first chiral agent are determined by the response bandwidth of the polarizing holographic grating, and the type of first chiral agent is determined by the polarization direction of the polarizing holographic grating. Therefore, a corresponding first photopolymerizable liquid crystal and a first chiral agent can be selected according to the response bandwidth and polarization direction of the polarizing holographic grating.

[0051] Since different types of photopolymerizable liquid crystals correspond to different center wavelengths, the type of the first photopolymerizable liquid crystal can be determined based on the response bandwidth of the polarizing holographic grating. Since different chiral agent ratios correspond to different pitches, and different pitches correspond to different wavelengths, the ratio of the first chiral agent can be determined based on the response bandwidth of the polarizing holographic grating. Since different types of chiral agents correspond to different polarization directions, the type of the first chiral agent, i.e., left-handed or right-handed, can be determined based on the polarization direction of the polarizing holographic grating.

[0052] For example, by mass percentage, the inert nematic liquid crystal may contain 20-70% of the first liquid crystal mixture; the first photopolymerizable liquid crystal may contain 1-20% of the first liquid crystal mixture; and the chiral agent may contain 10-80% of the first liquid crystal mixture.

[0053] For example, taking the center wavelength of the first photopolymerizable liquid crystal as the blue center wavelength as an example, the first liquid crystal mixture can be prepared by blending inert nematic liquid crystal SLC-6830A (53.0 wt%), first chiral agent CD1 (10.0 wt%), first chiral agent S811 (32.0 wt%), and first photopolymerizable liquid crystal LC1 (5.0 wt%) in terms of mass percentage (wt%).

[0054] S102. The first liquid crystal cell is subjected to ultraviolet curing treatment to cause the first photopolymer liquid crystal to undergo a photopolymerization reaction and form a polymer template.

[0055] Since the first liquid crystal cell is filled with a first liquid crystal mixture, and the first photopolymerizable liquid crystal in the first liquid crystal mixture can undergo photopolymerization under the action of ultraviolet light and chiral agent to form a polymer network with a specific center wavelength, while the inert nematic liquid crystal in the first liquid crystal mixture will not react under the action of ultraviolet light, so the inert nematic liquid crystal is still in an unreacted flow state. Therefore, the polymer template includes a polymer network with a specific center wavelength and an inert nematic liquid crystal in a flow state.

[0056] For example, the assembled first liquid crystal cell can be irradiated under ultraviolet light with a wavelength of 365nm for 30 minutes, thereby causing the first photopolymerizable liquid crystal in the first liquid crystal cell to react and form a polymer network with a specific center wavelength. At this time, the thickness of the polymer template formed is the thickness of the interstitial layer.

[0057] For example, the assembled first liquid crystal cell can be irradiated under a UV-LED lamp at a temperature of 30°C and an intensity of 0.65 mW / cm². 2 The irradiation time is 15 minutes, thereby obtaining a polymer template with a specific center wavelength.

[0058] It should be noted that the irradiation time, irradiation intensity, and irradiation temperature can be optimized according to the actual situation.

[0059] S103. Remove the inert nematic liquid crystal from the polymer template to obtain the second liquid crystal cell.

[0060] Because the polymer template includes a polymer network with a specific center wavelength and an inert nematic liquid crystal in a flowing state, the polymer network is relatively stable and difficult to be washed away, while the inert nematic liquid crystal in a flowing state is relatively unstable and easy to be washed away.

[0061] In some embodiments, the polymer template is cleaned to remove the inert nematic liquid crystal within it; the cleaned polymer template is then dried to obtain a second liquid crystal cell. This process removes unreacted inert nematic liquid crystal, providing conditions for subsequent filling with a second liquid crystal mixture with different center wavelengths.

[0062] For example, the polymer template can be immersed in a cyclohexane solution for 24-72 hours, and then immersed in a tetrahydrofuran solution for 10-30 minutes to remove unreacted inert nematic liquid crystal from the polymer template. Finally, it can be dried in a vacuum environment at 50-70°C for 3 hours to remove solvents such as cyclohexane solution and tetrahydrofuran solution, thereby obtaining the second liquid crystal cell.

[0063] The second liquid crystal cell is formed by removing the inert nematic liquid crystal from the polymer template, which facilitates the subsequent filling of the second liquid crystal mixture with the empty spaces after cleaning.

[0064] S104. Prepare a second liquid crystal mixture and add the second liquid crystal mixture into a second liquid crystal cell. The second liquid crystal mixture includes at least a second photopolymerizable liquid crystal and a second chiral agent. The type of the first photopolymerizable liquid crystal is different from the type of the second photopolymerizable liquid crystal, and the proportion of the first chiral agent is different from the proportion of the second chiral agent.

[0065] To broaden the reflection bandwidth of the polarizer holographic grating, a second liquid crystal mixture with a different center wavelength than the first liquid crystal mixture needs to be added to the second liquid crystal cell. For example, if the center wavelength of the first liquid crystal mixture is blue, the center wavelength of the second liquid crystal mixture could be green. This allows the subsequently fabricated polarizer holographic grating to simultaneously reflect green and blue light, thus achieving a multi-reflection bandwidth. Because the center wavelengths of the first and second liquid crystal mixtures are different, the types of the first and second photopolymerizable liquid crystals are different, and the proportions of the first and second chiral agents are also different.

[0066] In some embodiments, based on the preset type of the second photopolymerizable liquid crystal and the type of the second chiral agent, a corresponding second photopolymerizable liquid crystal and a second chiral agent are selected; based on the ratio of the second chiral agent, a second liquid crystal mixture is prepared; wherein, the type of the second photopolymerizable liquid crystal and the ratio of the second chiral agent are determined by the response bandwidth of the polarizing holographic grating, and the type of the second chiral agent is determined by the polarization direction of the polarizing holographic grating.

[0067] Since different types of photopolymerizable liquid crystals correspond to different center wavelengths, the type of the second photopolymerizable liquid crystal can be determined based on the response bandwidth of the polarizing holographic grating. Since different chiral agent ratios correspond to different pitches, and different pitches correspond to different wavelengths, the ratio of the second chiral agent can be determined based on the response bandwidth of the polarizing holographic grating. Since different types of chiral agents correspond to different polarization directions, the type of the second chiral agent, i.e., left-handed or right-handed, can be determined based on the polarization direction of the polarizing holographic grating.

[0068] It should be noted that the center wavelength of the second liquid crystal mixture is different from that of the first liquid crystal mixture.

[0069] In some embodiments, the second liquid crystal mixture may further include an inert nematic liquid crystal. This facilitates further widening of the response bandwidth of the polarizer holographic grating as needed.

[0070] For example, by mass percentage, the inert nematic liquid crystal may contain 30-80% of the second liquid crystal mixture; the second photopolymerizable liquid crystal may contain 1-30% of the second liquid crystal mixture; and the chiral agent may contain 10-80% of the second liquid crystal mixture.

[0071] For example, taking the center wavelength of the second photopolymerizable liquid crystal as the green center wavelength as an example, the second liquid crystal mixture can be prepared by blending inert nematic liquid crystal SLC-1717 (62.3 wt%), second chiral agent S811 (22.7 wt%), and first photopolymerizable liquid crystal LC1 (15.0 wt%) in terms of mass percentage (wt%).

[0072] For example, a second liquid crystal mixture can be added into the second liquid crystal cell using capillary action.

[0073] In some embodiments, the second liquid crystal mixture may further include a third photopolymerizable liquid crystal and a third chiral agent, wherein the type of the third photopolymerizable liquid crystal is different from the types of the first and second photopolymerizable liquid crystals, and the proportion of the third chiral agent is different from the proportion of the first and second chiral agents.

[0074] In this application, since the second liquid crystal mixture includes a second photopolymerizable liquid crystal and a third photopolymerizable liquid crystal, and the second photopolymerizable liquid crystal and the third photopolymerizable liquid crystal are of different types, the second liquid crystal mixture in this application corresponds to two center wavelengths, such as a green center wavelength and a red center wavelength.

[0075] For example, taking a polymerizable cholesteric liquid crystal formulation comprising a green center wavelength and a red center wavelength in a second liquid crystal mixture as an example, the mass ratio of the polymerizable cholesteric liquid crystal formulation with the green center wavelength and the red center wavelength can be 1:1, wherein the mass ratio of the components of the formulation corresponding to the green center wavelength is: SLC-1717 (62.3 wt%), S811 (22.7 wt%), LC1 (15.0 wt%); and the mass ratio of the formulation corresponding to the red center wavelength is SLC1717 (77.0 wt%), CD1 (10.0 wt%), S811 (15.0 wt%), LC1 (5.0 wt%).

[0076] S105. The second liquid crystal cell is subjected to ultraviolet curing treatment to cause the second photopolymer liquid crystal to undergo photopolymerization reaction, thereby obtaining a polarizing holographic grating.

[0077] Since the second liquid crystal cell is filled with a second liquid crystal mixture, and the second photopolymerizable liquid crystal in the second liquid crystal mixture can undergo photopolymerization under the action of ultraviolet light and chiral agent to form a polymer network with a specific center wavelength, even if the second liquid crystal mixture contains inert nematic liquid crystal, the inert nematic liquid crystal will not react under the action of ultraviolet light.

[0078] For example, the second liquid crystal cell can be irradiated under UV light with a wavelength of 365nm for 30 minutes, thereby causing the photopolymer liquid crystal in the first liquid crystal cell to react and form a polymer network of a specific wavelength, namely a polarizing holographic grating. The thickness of the formed polarizing holographic grating is the thickness of the gap layer.

[0079] It should be noted that the thickness of each component in the polarizing holographic grating is determined according to the mass percentage of the added liquid crystal mixture formula, and the orientation of each thin film in the polarizing holographic grating is jointly determined by the alignment layer and the corresponding liquid crystal mixture.

[0080] For example, taking the first liquid crystal mixture corresponding to the blue center wavelength and the second liquid crystal mixture corresponding to the green center wavelength as an example, the second liquid crystal cell can be placed under a UV-LED lamp for irradiation at a temperature of 30°C and an irradiation intensity of 0.65mW / cm². 2 The irradiation time was 15 minutes, thus obtaining a polarizing holographic grating with green and blue light reflection characteristics, with corresponding reflection bandwidths of 468nm and 537nm, respectively.

[0081] For example, taking the first liquid crystal mixture corresponding to the blue center wavelength and the second liquid crystal mixture corresponding to the green and red center wavelengths as examples, the second liquid crystal cell can be placed under a UV-LED lamp for irradiation at a temperature of 30°C and an irradiation intensity of 0.65 mW / cm². 2 The irradiation time was 15 minutes, thus obtaining a polarizing holographic grating with red, green and blue light reflection characteristics, with corresponding reflection bandwidths of 705nm, 468nm and 537nm respectively.

[0082] It should be noted that the irradiation time, irradiation intensity, and irradiation temperature can be optimized according to the actual situation.

[0083] In the above embodiments, a first liquid crystal mixture is prepared and filled into a first liquid crystal cell. The first liquid crystal mixture includes at least an inert nematic liquid crystal, a first photopolymerizable liquid crystal, and a first chiral agent. The first liquid crystal cell is subjected to ultraviolet curing treatment to cause the first photopolymerizable liquid crystal to undergo a photopolymerization reaction to form a polymer template. The inert nematic liquid crystal in the polymer template is removed to obtain a second liquid crystal cell. A second liquid crystal mixture is prepared and added into the second liquid crystal cell. The second liquid crystal mixture includes at least a second photopolymerizable liquid crystal and a second chiral agent. The types of the first and second photopolymerizable liquid crystals are different, and the proportions of the first and second chiral agents are different. Different proportions; the second liquid crystal cell is subjected to ultraviolet curing treatment to cause the second photopolymer liquid crystal to undergo photopolymerization reaction, and a polarizing holographic grating is obtained. Due to the presence of inert nematic liquid crystal in the polymer template, the inert nematic liquid crystal that does not react can be replaced with polymers of different center wavelengths. After secondary and multiple fillings, not only can the grating thickness and polarization direction be adjusted, but the polymer template can also achieve a gradient change in refractive index and pitch, thereby making the obtained polarizing holographic grating have a wider wavelength response range (usually one pitch corresponds to one wavelength), and widening the reflection bandwidth of the polarizing holographic grating. That is, a polarizing holographic grating with multiple reflection bandwidths is prepared.

[0084] As shown in Figure 5, the polarization holographic grating of the present invention will be described below with reference to specific embodiments.

[0085] Example 1: Fabrication of a polarizing holographic grating with blue / green dual-reflection bandwidth

[0086] (1) Select photosensitive alignment material SD-1, prepare a photosensitive alignment solution with a mass fraction of 1.5wt% using DMF as solvent, clean the glass substrate with ultraviolet ozone, spin coat the photosensitive alignment solution onto the substrate at a speed of 3000r / s, and obtain the coated alignment layer.

[0087] (2) Exposure was performed under a polarization interference square with a period of 1 μm, and the exposure dose was 2 J / cm. 2 SD-1 thin films with periodic orientation were obtained.

[0088] (3) Two substrates are used for encapsulation, with PET material as the gap layer and a thickness of 2um. At the same time, the liquid crystal cell is filled with a cholesteric liquid crystal formula with a blue center wavelength. The mass ratio of the components in the formula is: SLC-6830A (53.0wt%), CD1 (10.0wt%), S811 (32.0wt%), LC1 (5.0wt%).

[0089] (4) Place the liquid crystal cell under a UV-LED lamp for irradiation at a temperature of 30℃ and an intensity of 0.65mW / cm².2 The irradiation time was 15 minutes, and a blue polymer template was obtained.

[0090] (5) The blue polymer template was immersed in cyclohexane solution for 48 h and then in tetrahydrofuran for 20 min to remove unreacted liquid crystal components from the polymer template. It was then dried under vacuum at 60 °C for 3 h to remove the solvent. A polymerizable cholesteric phase liquid crystal formulation with a green central wavelength was added via capillary action. The composition of the formulation was: SLC-1717 (62.3 wt%), S811 (22.7 wt%), and LC1 (15.0 wt%).

[0091] (6) Place the liquid crystal cell under a UV-LED lamp again for irradiation at a temperature of 30℃ and an intensity of 0.65mW / cm². 2 The irradiation time was 15 min, and a polarized holographic grating with blue / green light reflection characteristics was obtained, with reflection bandwidths of 468 nm and 537 nm, respectively.

[0092] Example 2: Fabrication of a polarizing holographic grating with red / blue / green three-reflection bandwidth

[0093] (1) Select photosensitive alignment material SD-1, prepare a photosensitive alignment solution with a mass fraction of 1.5wt% using DMF as solvent, clean the glass substrate with ultraviolet ozone, spin coat the photosensitive alignment solution onto the substrate at a speed of 3000r / s, and obtain the coated alignment layer.

[0094] (2) Exposure was performed under a polarization interference square with a period of 1 μm, and the exposure dose was 2 J / cm. 2 SD-1 thin films with periodic orientation were obtained.

[0095] (3) Two substrates are used for encapsulation, with PET material as the gap layer and a thickness of 2um. At the same time, the liquid crystal cell is filled with a cholesteric liquid crystal formula with a blue center wavelength. The mass ratio of the components in the formula is: SLC-6830A (53.0wt%), CD1 (10.0wt%), S811 (32.0wt%), LC1 (5.0wt%).

[0096] (4) Place the liquid crystal cell under a UV-LED lamp for irradiation at a temperature of 30℃ and an intensity of 0.65mW / cm². 2 The irradiation time was 15 minutes, and a blue polymer template was obtained.

[0097] (5) The blue polymer template was immersed in cyclohexane solution for 48 h and then in tetrahydrofuran for 20 min to remove unreacted liquid crystal components from the polymer template. It was then dried under vacuum at 60 °C for 3 h to remove the solvent. Polymerizable cholesteric liquid crystal formulations with green and red center wavelengths were added via capillary action at a mass ratio of 1:1. The mass ratio of the formulation components corresponding to the green center wavelength was: SLC-1717 (62.3 wt%), S811 (22.7 wt%), and LC1 (15.0 wt%); the mass ratio of the formulation components corresponding to the red center wavelength was: SLC1717 (77.0 wt%), CD1 (10.0 wt%), S811 (15.0 wt%), and LC1 (5.0 wt%).

[0098] (6) Place the liquid crystal cell under a UV-LED lamp again for irradiation at a temperature of 30℃ and an intensity of 0.65mW / cm². 2 The irradiation time was 15 min, and a polarizing holographic grating with red / blue / green light reflection characteristics was obtained, with reflection bandwidths of 705 nm, 468 nm and 537 nm, respectively.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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 first liquid crystal mixture is prepared and filled into a first liquid crystal cell. The first liquid crystal mixture includes at least an inert nematic liquid crystal, a first photopolymerizable liquid crystal, and a first chiral agent. The first liquid crystal cell is subjected to ultraviolet curing treatment to cause the first photopolymer liquid crystal to undergo a photopolymerization reaction to form a polymer template; The inert nematic liquid crystal within the polymer template is removed to obtain a second liquid crystal cell; A second liquid crystal mixture is prepared and added to a second liquid crystal cell. The second liquid crystal mixture includes at least a second photopolymerizable liquid crystal and a second chiral agent. The type of the first photopolymerizable liquid crystal is different from the type of the second photopolymerizable liquid crystal, and the proportion of the first chiral agent is different from the proportion of the second chiral agent. The second liquid crystal cell is subjected to ultraviolet curing treatment to cause the second photopolymer liquid crystal to undergo a photopolymerization reaction, thereby obtaining a polarizing holographic grating.

2. The preparation method according to claim 1, wherein, Before filling the first liquid crystal mixture into the first liquid crystal cell, the method further includes: An alignment layer is prepared by coating a photosensitive alignment solution onto a substrate. The alignment layer is exposed to obtain a periodically aligned cholesteric liquid crystal film. A spacer layer material is provided, and the spacer layer material is used to encapsulate a substrate on which the cholesteric liquid crystal film is formed, thereby forming a first liquid crystal cell with a spacer layer.

3. The preparation method according to claim 2, wherein, The method of encapsulating a substrate on which the cholesteric liquid crystal film is formed using the spacer layer material to form a first liquid crystal cell with a spacer 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; Based on the thickness of the gap layer, the substrate on which the cholesteric liquid crystal film is formed is encapsulated using the gap layer material to form a first liquid crystal cell with a gap layer.

4. The preparation method according to claim 1, wherein, The preparation of the first liquid crystal mixture includes: Based on the preset type of first photopolymerizable liquid crystal and type of first chiral agent, the corresponding first photopolymerizable liquid crystal and first chiral agent are selected; A first liquid crystal mixture is prepared based on the proportion of the first chiral agent.

5. The preparation method according to claim 4, wherein, Before selecting the corresponding first photopolymerizable liquid crystal and first chiral agent based on the preset type of first photopolymerizable liquid crystal and type of first chiral agent, the method further includes: The type of the first photopolymer liquid crystal and the proportion of the first chiral agent are determined based on the response bandwidth of the polarizing holographic grating. The type of the first chiral agent is determined based on the polarization direction of the polarizing light in the polarizing holographic grating.

6. The preparation method according to claim 1, wherein, The process of removing the inert nematic liquid crystal from the polymer template to obtain a second liquid crystal cell includes: The polymer template is cleaned to remove the inert nematic liquid crystal within it. The cleaned polymer template is dried to obtain a second liquid crystal cell.

7. The preparation method according to claim 6, wherein, The step of cleaning the polymer template to remove the inert nematic liquid crystal within the polymer template includes: The polymer template is first immersed in a cyclohexane solution, and then immersed in a tetrahydrofuran solution to remove the inert nematic liquid crystal within the polymer template.

8. The preparation method according to claim 1, wherein, The preparation of the second liquid crystal mixture includes: Based on the preset types of the second photopolymerizable liquid crystal and the second chiral agent, the corresponding second photopolymerizable liquid crystal and second chiral agent are selected. A second liquid crystal mixture was prepared based on the proportion of the second chiral agent.

9. The preparation method according to claim 8, wherein, Before selecting the corresponding second photopolymerizable liquid crystal and second chiral agent based on the preset type of the second photopolymerizable liquid crystal and second chiral agent, the method further includes: The type of the second photopolymerizable liquid crystal and the proportion of the second chiral agent are determined based on the response bandwidth of the polarizing holographic grating. The type of the second chiral agent is determined based on the polarization direction of the polarizing holographic grating.

10. The preparation method according to claim 1, wherein, The step of adding the second liquid crystal mixture into the second liquid crystal cell includes: The second liquid crystal mixture is added into the second liquid crystal cell using capillary action.

11. The preparation method according to claim 1, wherein, The second liquid crystal mixture further includes a third photopolymerizable liquid crystal and a third chiral agent, wherein the type of the third photopolymerizable liquid crystal is different from the types of the first and second photopolymerizable liquid crystals, and the proportion of the third chiral agent is different from the proportion of the first and second chiral agents.

12. The preparation method according to claim 11, wherein, The second liquid crystal mixture has two corresponding center wavelengths.

13. The preparation method according to claim 1, wherein, The first liquid crystal mixture is a photopolymerizable liquid crystal with a blue center wavelength, a red center wavelength, or a green center wavelength.

14. The preparation method according to claim 1, wherein, The first chiral agent and the second chiral agent are at least one of R5011, S5011, R1011, S1011, R811, S811, and CD1.

15. The preparation method according to claim 1, wherein, By mass percentage, the inert nematic liquid crystal accounts for 20-70% of the content in the first liquid crystal mixture; the first photopolymerizable liquid crystal accounts for 1-20% of the content in the first liquid crystal mixture; and the first chiral agent accounts for 10-80% of the content in the first liquid crystal mixture.

16. The preparation method according to claim 1, wherein, The center wavelength of the second liquid crystal mixture is different from that of the first liquid crystal mixture.

17. The preparation method according to claim 1, wherein, The second liquid crystal mixture also includes inert nematic liquid crystal.

18. The preparation method according to claim 17, wherein, The inert nematic liquid crystal accounts for 30-80% of the content in the second liquid crystal mixture by mass percentage; the second photopolymerizable liquid crystal accounts for 1-30% of the content in the second liquid crystal mixture; and the second chiral agent accounts for 10-80% of the content in the second liquid crystal mixture.

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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