Polarizing body holographic grating, preparation method thereof and display equipment

Abstract

The invention provides a polarization body holographic grating, a preparation method thereof and display equipment, and relates to the technical field of grating preparation. The preparation method comprises the following steps: preparing a first liquid crystal mixture, and filling a first liquid crystal box with the first liquid crystal mixture; ultraviolet curing treatment is carried out on the first liquid crystal box, so that the first photopolymerization liquid crystal is subjected to photopolymerization reaction, and a polymer template is formed; removing the inert nematic liquid crystal in the polymer template to obtain a second liquid crystal box; a second liquid crystal mixture is prepared and added into the second liquid crystal box, and the second liquid crystal mixture at least comprises a second photopolymerization liquid crystal and a second chiral agent; and carrying out ultraviolet curing treatment on the second liquid crystal box, so that the second photopolymerization liquid crystal is subjected to photopolymerization reaction, and the polarizer holographic grating is prepared. The invention aims to realize preparation of the polarization body holographic grating with wide reflection bandwidth and adjustable grating thickness and polarized light rotation direction.

Description

Technical Field

[0001] The present application relates to the technical field of grating preparation, and in particular to a polarization holographic grating and a preparation method and a display device thereof. Background Art

[0002] Cholesteric liquid crystal has a layered structure, and the molecular axis direction of each layer is slightly offset from the molecular axis direction of the adjacent layer, and the liquid crystal forms a spiral structure as a whole. Due to its unique spiral structure and excellent optical properties, it has broad application prospects in various fields such as optical devices (such as polarization holographic gratings).

[0003] However, the traditional cholesteric liquid crystal film has the problem of narrow reflection bandwidth, which limits its application in a wide spectral range. In the related art, the reflection bandwidth is generally increased by multi-layer coating method, which is a conventional method for preparing polarization holographic gratings. However, this method is complex and requires multiple coatings, which is inefficient. In addition, the increase in the number of processes has a significant impact on the yield rate, which is not conducive to large-scale production. Summary of the invention

[0004] The present application provides a polarization volume holographic grating and a preparation method and a display device thereof, aiming to realize the preparation of a polarization volume holographic grating with a wide reflection bandwidth and adjustable grating thickness and polarization rotation direction.

[0005] To achieve the above object, the present application provides a method for preparing a polarization volume holographic grating, the preparation method comprising:

[0006] Prepare a first liquid crystal mixture, and fill the first liquid crystal mixture into a first liquid crystal box, wherein the first liquid crystal mixture at least includes an inert nematic liquid crystal, a first photopolymerizable liquid crystal, and a first chiral agent;

[0007] Performing UV curing treatment on the first liquid crystal box to cause the first photopolymerizable liquid crystal to undergo photopolymerization reaction to form a polymer template;

[0008] removing the inert nematic liquid crystal in the polymer template to obtain a second liquid crystal cell;

[0009] Preparing a second liquid crystal mixture and adding the second liquid crystal mixture into the second liquid crystal box, wherein the second liquid crystal mixture at least includes 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 ratio of the first chiral agent is different from the ratio of the second chiral agent;

[0010] The second liquid crystal box is subjected to ultraviolet curing treatment to make the second photopolymerizable liquid crystal undergo photopolymerization reaction to obtain a polarizing body holographic grating.

[0011] In addition, to achieve the above-mentioned purpose, the present application also provides a polarization volume holographic grating, and the polarization volume holographic grating is manufactured by adopting the preparation method of the polarization volume holographic grating as mentioned above.

[0012] In addition, to achieve the above-mentioned purpose, the present application also provides a display device, which includes an optical waveguide, and the grating in the optical waveguide is the polarization holographic grating as described above.

[0013] The present application discloses a polarization body holographic grating and a preparation method thereof, and a display device, wherein a first liquid crystal mixture is prepared and filled into a first liquid crystal box, wherein the first liquid crystal mixture at least includes an inert nematic phase liquid crystal, a first photopolymerizable liquid crystal, and a first chiral agent; the first liquid crystal box is subjected to ultraviolet curing treatment to make the first photopolymerizable liquid crystal undergo a photopolymerization reaction to form a polymer template; the inert nematic phase liquid crystal in the polymer template is removed to obtain a second liquid crystal box; a second liquid crystal mixture is prepared and added into the second liquid crystal box, wherein the second liquid crystal mixture at least includes a second photopolymerizable liquid crystal and a second chiral agent, wherein the type of the first photopolymerizable liquid crystal is different from the type of the second photopolymerizable liquid crystal, and the first chiral agent is The ratio of the first photopolymerizable agent is different from that of the second chiral agent; the second liquid crystal box is subjected to ultraviolet curing treatment to make the second photopolymerizable liquid crystal undergo photopolymerization reaction to obtain a polarizer holographic grating; due to the presence of the inert nematic phase liquid crystal in the polymer template, the inert nematic phase liquid crystal that does not react can be replaced by polymers with different central wavelengths; after secondary and multiple fillings, not only the grating thickness and the handedness of polarized light can be adjusted, but also the polymer template can achieve a gradient refractive index and pitch, thereby making the prepared polarizer holographic grating have a wider response range to wavelength (usually one pitch corresponds to one wavelength), broadening the reflection bandwidth of the polarizer holographic grating, that is, a polarizer holographic grating with a wide reflection bandwidth is prepared. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0015] Figure 1 It is a schematic flow chart of the steps of a method for preparing a polarization holographic grating provided in an embodiment of the present application;

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

[0017] Figure 3is a schematic diagram of the molecular structure of S811 / R811 provided in an embodiment of the present application;

[0018] Figure 4 is a schematic diagram of the molecular structure of CD1 provided in an embodiment of the present application;

[0019] Figure 5 It is a schematic flow chart of the steps of another method for preparing a polarization holographic grating provided in an embodiment of the present application. DETAILED DESCRIPTION

[0020] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0021] The flowcharts shown in the accompanying drawings are only examples and do not necessarily include all the contents and operations / steps, nor must they be executed in the order described. For example, some operations / steps may also be decomposed, combined or partially merged, so the actual execution order may change according to actual conditions.

[0022] It should be understood that the terms used in this application specification are only for the purpose of describing specific embodiments and are not intended to limit the application. As used in this application specification and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0023] It should also be understood that the term “and / or” used in the specification and appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0024] Cholesteric liquid crystal films have broad application prospects in the fields of optical display and holographic grating due to their unique spiral structure and excellent optical properties. However, traditional cholesteric liquid crystal films have the problem of narrow reflection bandwidth, which limits their application in 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 value of the pitch changes from a fixed value to multiple values ​​within a specific range, the light response range to the incident wavelength becomes wider, thereby broadening its reflection bandwidth.

[0025] In the related art, there are two main methods for broadening the reflection bandwidth of the polarization holographic grating:

[0026] (I) Multilayer coating method: another layer of cholesteric liquid crystal with other pitches is coated on the existing cholesteric liquid crystal film, thereby increasing the pitch richness of the film. This method can increase one or more pitches in the film, thereby increasing the reflection bandwidth, but the process of this method is complicated, requires multiple coatings, and has low efficiency. In addition, the increase in the number of processes has an adverse effect on the yield of the polarization holographic grating, which is not conducive to large-scale production.

[0027] (ii) Gradient pitch variation induced by light intensity: In cholesteric liquid crystal films, the reaction speed of the side close to UV curing is faster than that of the other side, causing the polymerizable cholesteric liquid crystal in the vertical direction to continuously polymerize toward the illuminated side. The pitch is smaller in areas closer to the light, and larger in areas farther away. The gradient pitch variation will lead to an expansion of the reflection bandwidth of the film. However, this method usually requires the preparation of a thicker polarizer holographic grating. In films with micro / nanometer thickness, the difference in light intensity is limited, so the range of pitch variation is limited. In addition, the uneven degree of polymerization of cholesteric liquid crystal due to inconsistent light intensity is not conducive to the uniformity and repeatability of the polarizer holographic grating.

[0028] To solve the above problems, the embodiments of the present application provide a polarization holographic grating and a preparation method and a display device thereof, which are used to prepare a polarization holographic grating with a wide reflection bandwidth and adjustable grating thickness and polarization direction.

[0029] See also Figure 1 , Figure 1 The present invention is a flowchart of a method for preparing a polarization holographic grating provided in an embodiment of the present invention. The polarization holographic grating can be applied to display devices, wherein the display devices include but are not limited to AR (Augmented Reality) glasses, VR (Virtual Reality) glasses and other near-eye display devices, HUD (head-up display), etc.

[0030] like Figure 1 As shown, the method for preparing the polarization volume holographic grating specifically includes steps S101 to S105.

[0031] S101, preparing a first liquid crystal mixture, and filling the first liquid crystal mixture into a first liquid crystal box, wherein the first liquid crystal mixture at least includes an inert nematic liquid crystal, a first photopolymerizable liquid crystal, and a first chiral agent.

[0032] Wherein, the first liquid crystal mixture at least includes an inert nematic phase liquid crystal, a first photopolymerizable liquid crystal and a first chiral agent, the inert nematic phase liquid crystal can be a nematic phase liquid crystal that does not undergo photopolymerization reaction under ultraviolet light treatment, the first photopolymerizable liquid crystal can be a photopolymerizable liquid crystal of a specific central wavelength, the specific central wavelength can be determined according to the response bandwidth of the polarizer holographic grating to be prepared, for example, it can be a blue central wavelength, a red central wavelength, a green central wavelength, etc., which is not specifically limited here. The first chiral agent can be any chiral agent, the corresponding proportion of which can be determined according to the response bandwidth of the polarizer holographic grating to be prepared, and the corresponding type of which can be determined according to the polarization direction of the polarizer holographic grating to be prepared. The first liquid crystal box is formed by assembling the exposed orientation layer and the substrate, and is used to fill the first liquid crystal mixture.

[0033] Photopolymerizable liquid crystal is a liquid crystal material formed by photopolymerization. The molecular structure of photopolymerizable liquid crystal has a liquid crystal core and has reactive functional groups at the ends. These functional groups can form a polymer network through photopolymerization to become a liquid crystal polymer (LCP). Before polymerization, the photopolymerizable liquid crystal is periodically and orderly arranged along the orientation layer, and then photopolymerization occurs to prepare a polarizer holographic grating (PVG). In the embodiment of the present application, the photopolymerizable liquid crystal can be a nematic phase liquid crystal such as LC1 that can react with a free radical initiator. The structure of LC1 is as follows: Figure 2 shown.

[0034] It should be noted that the first photopolymerized liquid crystal, the second photopolymerized liquid crystal and the third photopolymerized liquid crystal in this article can all be LC1 nematic liquid crystals, and the types of the first photopolymerized liquid crystal, the second photopolymerized liquid crystal and the third photopolymerized liquid crystal can be the same or different.

[0035] Chiral agents can twist liquid crystal materials in a certain direction and increase the stability of liquid crystal display devices.

[0036] Chiral agents can induce phase transitions in liquid crystal materials, such as from nematic phase to cholesteric phase or chiral nematic phase. In TN (twisted nematic) display mode, chiral agents can twist the orientation of liquid crystal molecules by 90° and inhibit the formation of disclination; in STN (super twisted nematic) display mode, it can achieve the required higher twist angle (180°~270°); in reflective cholesteric liquid crystal display, chiral agents can form the required short pitch.

[0037] Exemplary chiral agents include but are not limited to R5011, S5011, R1011, S1011, R811, S811, CD1, etc. The structure of S811 / R811 is as follows Figure 3 As shown, the structure of CD1 is Figure 4 shown.

[0038] It should be noted that the first chiral agent, the second chiral agent and the third chiral agent in this article can all be the above-mentioned chiral agents, and the types of the first chiral agent, the second chiral agent and the third chiral agent can be the same or different. In the embodiment of the present application, since it is necessary to broaden the reflection bandwidth of the polarizer holographic grating, different chiral agent ratios correspond to different pitches, and different pitches correspond to different wavelengths, therefore, the ratios of the first chiral agent, the second chiral agent and the third chiral agent are different.

[0039] The main function of the liquid crystal box is to control the passage of light and realize the display function. The liquid crystal box controls the arrangement of liquid crystal molecules through the electric field, thereby adjusting the transmission, reflection or scattering of light to realize the display of images.

[0040] In some embodiments, before filling the first liquid crystal mixture into the first liquid crystal box, a photosensitive orientation solution is coated on the substrate to obtain an orientation layer; the orientation layer is exposed to light to obtain a periodically oriented cholesteric liquid crystal film; a gap layer material is provided, and the substrate formed with the cholesteric liquid crystal film is encapsulated using the gap layer material to form a first liquid crystal box having a gap layer.

[0041] The photosensitive alignment solution may be an alignment layer solution made of a photosensitive alignment material.

[0042] Exemplarily, the gap layer material can be polyethylene terephthalate (PET), which is a thermoplastic polyester produced by a condensation reaction of terephthalic acid and ethylene glycol. It has a highly crystalline structure, a smooth and glossy surface, good creep resistance, fatigue resistance and friction resistance, and is one of the toughest materials among thermoplastics.

[0043] For example, a commonly used photo-alignment layer material can be coated on 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 box and control the thickness of the first liquid crystal box.

[0044] Exemplarily, the photo-orientation material may be Nissan PIRB051, Brilliant Yellow or SD-1, the substrate may be glass, resin, silicon carbide or other substrates, the coating method may be any one of spin coating, inkjet printing and scraping; the exposure form may be any one of linear polarized light exposure and polarized interference exposure, preferably, polarized interference exposure is generally used.

[0045] 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 the glass substrate was cleaned with ultraviolet ozone, the photosensitive alignment solution was spin-coated on the substrate at a rotation speed of 3000 r / s to obtain a coated alignment layer, which was exposed under a polarization interference square with a period of 1 um, and the exposure dose was 2 J / cm 2 , obtaining a periodically oriented SD-1 film; using two substrates and the exposed orientation layer for packaging, and using PET material to prepare a gap layer, forming a first liquid crystal box with a thickness of 2um.

[0046] In some embodiments, based on the preset thickness of the gap layer, the substrate formed with the cholesteric liquid crystal film is packaged with the gap layer material to form a first liquid crystal cell having the gap layer, wherein the thickness of the gap layer is determined by the prepared thickness of the polarizer holographic grating.

[0047] For example, the thickness of the gap layer can be determined according to the required thickness of the polarization 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 box having the gap layer can be formed.

[0048] Exemplarily, a glass substrate having an upper and lower interlayer is encapsulated using PET material to form a first liquid crystal box having a gap layer, and the thickness of the gap layer is 2um, and the thickness of the first liquid crystal box is also 2um, and the thickness of the finally obtained polarization holographic grating is also 2um.

[0049] In some embodiments, based on the preset type of the first photopolymerizable liquid crystal and the type of the first chiral agent, the corresponding first photopolymerizable liquid crystal and the first chiral agent are selected; based on the ratio of the first chiral agent, the first liquid crystal mixture is prepared; wherein the type of the first photopolymerizable liquid crystal and the ratio of the first chiral agent are determined by the response bandwidth of the polarization volume holographic grating, and the type of the first chiral agent is determined by the polarization rotation direction of the polarization volume holographic grating. Thus, the corresponding first photopolymerizable liquid crystal and the first chiral agent can be selected according to the response bandwidth and polarization rotation direction of the polarization volume holographic grating.

[0050] Since different types of photopolymerized liquid crystals correspond to different central wavelengths, the type of the first photopolymerized liquid crystal can be determined based on the response bandwidth of the polarizer 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 polarizer 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 polarizer holographic grating.

[0051] For example, in terms of mass percentage, the mass of the inert nematic liquid crystal in the first liquid crystal mixture can range from 20-70%; the mass of the first photopolymerizable liquid crystal in the first liquid crystal mixture can range from 1-20%; and the mass of the chiral agent in the first liquid crystal mixture can range from 10-80%.

[0052] Exemplarily, taking the central wavelength of the first photopolymerized liquid crystal as the blue central wavelength as an example, in terms of mass percentage (wt%), the inert nematic phase liquid crystal SLC-6830A (53.0wt%), the first chiral agent CD1 (10.0wt%), the first chiral agent S811 (32.0wt%), and the first photopolymerized liquid crystal LC1 (5.0wt%) can be selected and blended to obtain the first liquid crystal mixture.

[0053] S102, performing ultraviolet curing treatment on the first liquid crystal box to cause the first photopolymerizable liquid crystal to undergo photopolymerization reaction to form a polymer template.

[0054] Since the first liquid crystal box is filled with the first liquid crystal mixture, and the first photopolymerizable liquid crystal in the first liquid crystal mixture can undergo photopolymerization reaction under the action of ultraviolet light and a chiral agent, thereby forming a polymer network with a specific central wavelength, while the inert nematic phase liquid crystal in the first liquid crystal mixture does not react under the action of ultraviolet light, so the inert nematic phase liquid crystal remains in an unreacted flow state, and therefore the polymer template includes a polymer network with a specific central wavelength and an inert nematic phase liquid crystal in a flow state.

[0055] Exemplarily, the assembled first liquid crystal box can be exposed to ultraviolet light with a wavelength of 365nm for 30 minutes, so that the first photopolymerized liquid crystal in the first liquid crystal box reacts to form a polymer network with a specific central wavelength. At this time, the thickness of the formed polymer template is the thickness of the gap layer.

[0056] For example, the assembled first 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 / cm 2 The irradiation time was 15 min, thereby obtaining a polymer template with a specific central wavelength.

[0057] It should be noted that the irradiation time, irradiation intensity and irradiation temperature can be optimized according to actual conditions.

[0058] S103, removing the inert nematic liquid crystal in the polymer template to obtain a second liquid crystal cell.

[0059] Since the polymer template includes a polymer network with a specific central wavelength and an inert nematic liquid crystal in a fluid state, the polymer network is relatively stable and difficult to be washed away, while the inert nematic liquid crystal in a fluid state is relatively unstable and easy to be washed away.

[0060] In some embodiments, the polymer template is cleaned to remove the inert nematic liquid crystal in the polymer template, and the cleaned polymer template is dried to obtain a second liquid crystal box, thereby removing the unreacted inert nematic liquid crystal and providing conditions for subsequent filling of a second liquid crystal mixture with a different central wavelength.

[0061] 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 in the polymer template, and finally dried in a vacuum environment at 50-70° C. for 3 hours to remove solvents such as the cyclohexane solution and the tetrahydrofuran solution, thereby preparing a second liquid crystal box.

[0062] The second liquid crystal box is formed by removing the inert nematic liquid crystal in the polymer template, so that the vacant space after cleaning can be used to fill the second liquid crystal mixture.

[0063] S104, prepare a second liquid crystal mixture, and add the second liquid crystal mixture into a second liquid crystal box, the second liquid crystal mixture at least includes 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 ratio of the first chiral agent is different from the ratio of the second chiral agent.

[0064] Since the reflection bandwidth of the polarizer holographic grating needs to be broadened, a second liquid crystal mixture having a different central wavelength from the first liquid crystal mixture needs to be added to the second liquid crystal box. For example, the central wavelength of the first liquid crystal mixture is the blue central wavelength, and the central wavelength of the second liquid crystal mixture can be the green central wavelength, so that the subsequently prepared polarizer holographic grating can simultaneously reflect green and blue light, thereby achieving a multi-reflection bandwidth. Since the central wavelengths of the first liquid crystal mixture and the second liquid crystal mixture are different, the type of the first photopolymerized liquid crystal is different from the type of the second photopolymerized liquid crystal, and the ratio of the first chiral agent is also different from the ratio of the second chiral agent.

[0065] In some embodiments, based on the preset type of second photopolymerizable liquid crystal and the type of second chiral agent, corresponding second photopolymerizable liquid crystal and 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 polarizer holographic grating, and the type of the second chiral agent is determined by the polarization direction of the polarizer holographic grating.

[0066] Since different types of photopolymerized liquid crystals correspond to different central wavelengths, the type of the second photopolymerized liquid crystal can be determined based on the response bandwidth of the polarizer 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 polarizer 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 polarizer holographic grating.

[0067] It should be noted that the central wavelength of the second liquid crystal mixture is different from the central wavelength of the first liquid crystal mixture.

[0068] In some embodiments, the second liquid crystal mixture may further include inert nematic liquid crystals, which is helpful for subsequently broadening the response bandwidth of the polarization volume holographic grating as needed.

[0069] For example, in terms of mass percentage, the mass of the inert nematic phase liquid crystal in the second liquid crystal mixture can range from 30-80%; the mass of the second photopolymerizable liquid crystal in the second liquid crystal mixture can range from 1-30%; and the mass of the chiral agent in the second liquid crystal mixture can range from 10-80%.

[0070] Exemplarily, taking the central wavelength of the second photopolymerized liquid crystal as the green central wavelength as an example, in terms of mass percentage (wt%), the inert nematic phase liquid crystal SLC-1717 (62.3wt%), the second chiral agent S811 (22.7wt%), and the first photopolymerized liquid crystal LC1 (15.0wt%) can be selected and blended to obtain the second liquid crystal mixture.

[0071] For example, the second liquid crystal mixture may be added into the second liquid crystal cell by utilizing capillary action.

[0072] In some embodiments, the second liquid crystal mixture may further include a third photopolymerized liquid crystal and a third chiral agent, wherein the type of the third photopolymerized liquid crystal is different from the types of the first photopolymerized liquid crystal and the second photopolymerized liquid crystal, and the proportion of the third chiral agent is different from the proportion of the first chiral agent and the second chiral agent.

[0073] In the implementation of the present 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, there are two corresponding central wavelengths in the second liquid crystal mixture in the present implementation. For example, the second liquid crystal mixture has a green central wavelength and a red central wavelength.

[0074] Exemplarily, taking the polymerizable cholesteric liquid crystal formula including a green center wavelength and a red center wavelength in the second liquid crystal mixture as an example, the mass ratio of the polymerizable cholesteric liquid crystal formula with a green center wavelength and a red center wavelength can be 1:1, wherein the mass ratio of the components of the formula corresponding to the green center wavelength is: SLC-1717 (62.3wt%), S811 (22.7wt%), LC1 (15.0wt%); the mass ratio of the formula corresponding to the red center wavelength is SLC1717 (77.0wt%), CD1 (10.0wt%), S811 (15.0wt%), LC1 (5.0wt%).

[0075] S105, performing ultraviolet curing treatment on the second liquid crystal box to make the second photopolymerizable liquid crystal undergo photopolymerization reaction to obtain a polarization body holographic grating.

[0076] Since the second liquid crystal box is filled with the 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 a chiral agent, thereby forming a polymer network with a specific central wavelength, even if the second liquid crystal mixture contains an inert nematic phase liquid crystal, the inert nematic phase liquid crystal will not react under the action of ultraviolet light.

[0077] Exemplarily, the second liquid crystal box can be exposed to UV light with a wavelength of 365nm for 30 minutes, so that the photopolymerized liquid crystal in the first liquid crystal box reacts to form a polymer network of a specific wavelength, namely a polarizer holographic grating, and the thickness of the formed polarizer holographic grating is the thickness of the gap layer.

[0078] It should be noted that the thickness of each component in the polarizer holographic grating is determined according to the mass percentage of the added liquid crystal mixture formula, and the alignment of each film in the polarizer holographic grating is determined by the orientation layer and the corresponding liquid crystal mixture.

[0079] For example, taking the first liquid crystal mixture corresponding to the blue central wavelength and the second liquid crystal mixture corresponding to the green central wavelength as an example, the second liquid crystal box can be placed under a UV-LED lamp with an irradiation temperature of 30°C and an irradiation intensity of 0.65 mW / cm 2 , the irradiation time is 15min, thereby obtaining a polarization holographic grating with green and blue light reflection characteristics, and the corresponding reflection bandwidths are 468nm and 537nm respectively.

[0080] For example, taking the first liquid crystal mixture corresponding to the blue central wavelength and the second liquid crystal mixture corresponding to the green central wavelength and the red central wavelength as an example, the second liquid crystal box can be placed under a UV-LED lamp with an irradiation temperature of 30°C and an irradiation intensity of 0.65 mW / cm 2, the irradiation time is 15min, thereby obtaining a polarization holographic grating with red, green and blue light reflection characteristics, and the corresponding reflection bandwidths are 705nm, 468nm and 537nm respectively.

[0081] It should be noted that the irradiation time, irradiation intensity and irradiation temperature can be optimized according to actual conditions.

[0082] In the above embodiment, a first liquid crystal mixture is prepared and filled into a first liquid crystal box, the first liquid crystal mixture at least comprising an inert nematic phase liquid crystal, a first photopolymerizable liquid crystal and a first chiral agent; the first liquid crystal box is subjected to UV curing treatment to cause the first photopolymerizable liquid crystal to undergo a photopolymerization reaction to form a polymer template; the inert nematic phase liquid crystal in the polymer template is removed to obtain a second liquid crystal box; a second liquid crystal mixture is prepared and added into the second liquid crystal box, the second liquid crystal mixture at least comprising 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 ratio of the first chiral agent to the second chiral agent is 2.5. The ratios are different; the second liquid crystal box is subjected to UV curing treatment to make the second photopolymerizable liquid crystal undergo photopolymerization reaction to obtain a polarizer holographic grating. Due to the presence of the inert nematic phase liquid crystal in the polymer template, the inert nematic phase liquid crystal that does not react can be replaced by polymers with different central wavelengths. After secondary and multiple fillings, not only the grating thickness and the handedness of polarized light can be adjusted, but also the polymer template can achieve a gradient refractive index and pitch, thereby making the prepared polarizer holographic grating have a wider wavelength response range (usually one pitch corresponds to one wavelength), broadening the reflection bandwidth of the polarizer holographic grating, that is, a polarizer holographic grating with multiple reflection bandwidths is prepared.

[0083] like Figure 5 As shown, the polarization volume holographic grating of the present invention is described below in conjunction with specific embodiments.

[0084] Example 1: Preparation of polarization volume holographic grating with blue / green dual reflection bandwidth

[0085] (1) Select photosensitive alignment material SD-1, use DMF as solvent to prepare a photosensitive alignment solution with a mass fraction of 1.5 wt%, use ultraviolet ozone to clean the glass substrate, and then spin-coat the photosensitive alignment solution on the substrate at a rotation speed of 3000 r / s to obtain a coated alignment layer.

[0086] (2) Exposure was performed 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 film was obtained.

[0087] (3) Two substrates are used for packaging, with PET material as the gap layer with a thickness of 2um. At the same time, the liquid crystal box is filled with a cholesteric liquid crystal formula with a blue central wavelength. The mass ratio of the components of the formula is: SLC-6830A (53.0wt%), CD1 (10.0wt%), S811 (32.0wt%), and LC1 (5.0wt%).

[0088] (4) Place the liquid crystal box under UV-LED light at a temperature of 30°C and an intensity of 0.65 mW / cm 2 , the irradiation time was 15 min, and a blue polymer template was obtained.

[0089] (5) Immerse the blue polymer template in a cyclohexane solution for 48 hours and in tetrahydrofuran for 20 minutes to remove unreacted liquid crystal and other components in the polymer template, and dry it in a vacuum environment at 60°C for 3 hours to remove the solvent. A polymerizable cholesteric liquid crystal formula with a green central wavelength is added by capillary action, and the mass ratio of the components of the formula is: SLC-1717 (62.3wt%), S811 (22.7wt%), LC1 (15.0wt%).

[0090] (6) Place the liquid crystal box under the UV-LED lamp again, the irradiation temperature is 30°C, and the irradiation intensity is 0.65mW / cm 2 , the irradiation time is 15min, and a polarized holographic grating with blue / green light reflection characteristics is obtained, and its reflection bandwidth is 468nm and 537nm respectively.

[0091] Example 2: Preparation of polarization volume holographic grating with red / blue / green triple reflection bandwidth

[0092] (1) Select photosensitive alignment material SD-1, use DMF as solvent to prepare a photosensitive alignment solution with a mass fraction of 1.5 wt%, use ultraviolet ozone to clean the glass substrate, and then spin-coat the photosensitive alignment solution on the substrate at a rotation speed of 3000 r / s to obtain a coated alignment layer.

[0093] (2) Exposure was performed 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 film was obtained.

[0094] (3) Two substrates are used for packaging, with PET material as the gap layer with a thickness of 2um. At the same time, the liquid crystal box is filled with a cholesteric liquid crystal formula with a blue central wavelength. The mass ratio of the components of the formula is: SLC-6830A (53.0wt%), CD1 (10.0wt%), S811 (32.0wt%), and LC1 (5.0wt%).

[0095] (4) Place the liquid crystal box under UV-LED light at a temperature of 30°C and an intensity of 0.65 mW / cm 2 , the irradiation time was 15 min, and a blue polymer template was obtained.

[0096] (5) Immerse the blue polymer template in a cyclohexane solution for 48 hours and in tetrahydrofuran for 20 minutes to remove unreacted liquid crystal components in the polymer template, and dry it in a vacuum environment at 60°C for 3 hours to remove the solvent. Add the polymerizable cholesteric liquid crystal formula of green and red center wavelengths by capillary action, and the added mass ratio is 1:1, wherein the mass ratio of the formula components corresponding to the green center wavelength is: SLC-1717 (62.3wt%), S811 (22.7wt%), LC1 (15.0wt%); the mass ratio of the formula components corresponding to the red center wavelength is SLC1717 (77.0wt%), CD1 (10.0wt%), S811 (15.0wt%), LC1 (5.0wt%).

[0097] (6) Place the liquid crystal box under the UV-LED lamp again, the irradiation temperature is 30°C, and the irradiation intensity is 0.65mW / cm 2 , the irradiation time is 15min, and a polarized holographic grating with red / blue / green light reflection characteristics is obtained, and its reflection bandwidths are 705nm, 468nm and 537nm respectively.

[0098] The embodiment of the present application also provides a polarization volume holographic grating, which is prepared by the method for preparing the polarization volume holographic grating in the above embodiment. Therefore, the polarization volume holographic grating can achieve the beneficial effects that can be achieved by the method for preparing the polarization volume holographic grating provided in the embodiment of the present application, which are detailed in the previous embodiment and will not be repeated here.

[0099] In an embodiment of the present application, a display device is further provided, the display device includes an optical waveguide, wherein the grating in the optical waveguide can be the polarization volume holographic grating in the above embodiment. Therefore, the display device can achieve the beneficial effects that can be achieved by the method for preparing the polarization volume holographic grating provided in the embodiment of the present application, as detailed in the previous embodiment, which will not be repeated here.

[0100] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or system including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or system. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or system including the element.

[0101] The above description is only a specific implementation mode of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or substitutions within the technical scope disclosed in the present application, and these modifications or substitutions should be included in the protection scope of the present application.

Claims

1. A method for preparing a polarization holographic grating, characterized in that: The preparation method comprises: Prepare a first liquid crystal mixture, and fill the first liquid crystal mixture into a first liquid crystal box, wherein the first liquid crystal mixture at least includes an inert nematic liquid crystal, a first photopolymerizable liquid crystal, and a first chiral agent; Performing UV curing treatment on the first liquid crystal box to cause the first photopolymerizable liquid crystal to undergo photopolymerization reaction to form a polymer template; removing the inert nematic liquid crystal in the polymer template to obtain a second liquid crystal cell; Preparing a second liquid crystal mixture and adding the second liquid crystal mixture into the second liquid crystal box, wherein the second liquid crystal mixture at least includes 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 ratio of the first chiral agent is different from the ratio of the second chiral agent; The second liquid crystal box is subjected to ultraviolet curing treatment to make the second photopolymerizable liquid crystal undergo photopolymerization reaction to obtain a polarizing body holographic grating.

2. The preparation method according to claim 1, characterized in that: Before filling the first liquid crystal mixture into the first liquid crystal box, the method further includes: coating a photosensitive alignment solution on a substrate to prepare an alignment layer; Expose the alignment layer to obtain a periodically oriented cholesteric liquid crystal film; A gap layer material is provided, and the substrate formed with the cholesteric liquid crystal film is packaged using the gap layer material to form a first liquid crystal box with a gap layer.

3. The preparation method according to claim 2, characterized in that: The method of packaging the substrate formed with the cholesteric liquid crystal film by using the gap layer material to form a first liquid crystal box having a gap layer comprises: Based on the preset thickness of the gap layer, the substrate formed with the cholesteric liquid crystal film is encapsulated by using the gap layer material to form a first liquid crystal box with the gap layer. Wherein, the thickness of the gap layer is determined by the preparation thickness of the polarization holographic grating.

4. The preparation method according to claim 1, characterized in that: The step of preparing the first liquid crystal mixture comprises: Based on the preset types of the first photopolymerizable liquid crystal and the first chiral agent, selecting the corresponding first photopolymerizable liquid crystal and the first chiral agent; Based on the ratio of the first chiral agent, preparing a first liquid crystal mixture; The type of the first photopolymerizable liquid crystal and the ratio of the first chiral agent are determined by the response bandwidth of the polarizer holographic grating, and the type of the first chiral agent is determined by the polarization rotation direction of the polarizer holographic grating.

5. The preparation method according to claim 1, characterized in that: The step of removing the inert nematic liquid crystal in the polymer template to obtain a second liquid crystal cell comprises: Performing a cleaning treatment on the polymer template to clean out the inert nematic liquid crystal in the polymer template; The cleaned polymer template is dried to obtain a second liquid crystal box.

6. The preparation method according to claim 1, characterized in that: The step of preparing the second liquid crystal mixture comprises: Based on the preset type of the second photopolymerizable liquid crystal and the type of the second chiral agent, selecting the corresponding second photopolymerizable liquid crystal and the second chiral agent; Based on the ratio of the second chiral agent, preparing a second liquid crystal mixture; The type of the second photopolymerizable liquid crystal and the ratio of the second chiral agent are determined by the response bandwidth of the polarizer holographic grating, and the type of the second chiral agent is determined by the polarization rotation direction of the polarizer holographic grating.

7. The preparation method according to claim 1, characterized in that: The step of adding the second liquid crystal mixture into the second liquid crystal cell comprises: The second liquid crystal mixture is added into the second liquid crystal cell by using capillary action.

8. The preparation method according to claim 1, characterized in that: The second liquid crystal mixture also 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 photopolymerizable liquid crystal and the second photopolymerizable liquid crystal, and the proportion of the third chiral agent is different from the proportion of the first chiral agent and the second chiral agent.

9. The preparation method according to any one of claims 1 to 8, characterized in that: The second liquid crystal mixture further includes an inert nematic liquid crystal.

10. A polarization holographic grating, characterized in that: The polarization volume holographic grating is manufactured by the method for manufacturing a polarization volume holographic grating as claimed in any one of claims 1 to 9.

11. A display device, characterized in that: The display device comprises an optical waveguide, wherein the grating in the optical waveguide is the polarization volume holographic grating as claimed in claim 10.

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