Holographic polymer dispersed liquid crystal grating and preparation method thereof

Abstract

The invention discloses a holographic polymer dispersed liquid crystal grating, which is obtained by carrying out holographic recording treatment on a mixture comprising liquid crystal and polymer, and comprises the following components in percentage by mass: 20 to 60 percent of liquid crystal and 40 to 80 percent of polymer, wherein the liquid crystal comprises a first liquid crystal compound which has a chiral structure and cannot be polymerized; the polymer comprises a photopolymerization compound and a photoinitiator composition, the photoinitiator composition comprises an initiator and a photosensitizer, and the initiator can initiate a polymer reaction under illumination. A chiral structure is introduced into non-polymerizable liquid crystal molecules, so that traditional liquid crystal molecules can be spirally arranged, the diffraction efficiency on S light is improved, and the high diffraction efficiency on the S light and P light is achieved at the same time. The invention further discloses a preparation method of the holographic polymer dispersed liquid crystal grating. The holographic polymer dispersed liquid crystal grating which has high diffraction efficiency on S light and P light at the same time can be prepared.

Description

Technical Field

[0001] This invention belongs to the field of liquid crystal technology, specifically relating to a holographic polymer-dispersed liquid crystal grating and its preparation method. Background Technology

[0002] Polymer / liquid crystal composites integrate the excellent mechanical properties and processability of polymers with the superior external field response of liquid crystal molecules, thus attracting much attention. Holographic polymer / liquid crystal composites are a class of structurally ordered composite materials with holographic functions, mainly classified into holographic polymer-dispersed liquid crystals (HPDLC), holographic polymer-stabilized liquid crystals (HPSLC), and polymer-liquid crystal-polymer layers (POLICRYPS).

[0003] In the current process of fabricating gratings using holographic polymer-dispersed liquid crystals (HPDLC), the liquid crystal is aligned along the vector direction of the grating, meaning the refractive index of the polymer and the n-axis of the liquid crystal are related. e This results in a significant difference in Δn. Liquid crystal molecules are typically aligned parallel to the grating vector direction, leading to high diffraction efficiency only for P-beams and very low diffraction efficiency for S-beams. Other types of liquid crystal molecules are aligned perpendicular to the grating vector direction, resulting in high diffraction efficiency only for S-beams and very low diffraction efficiency for P-beams. Therefore, existing gratings fabricated from holographic polymer-dispersed liquid crystals can only achieve appropriate diffraction efficiency for either P-beams or S-beams, and cannot simultaneously achieve high diffraction efficiency for both P-beams and S-beams. Summary of the Invention

[0004] The purpose of this invention is to provide a holographic polymer-dispersed liquid crystal grating and its preparation method, so as to provide a grating with high diffraction efficiency for both S-rays and P-rays.

[0005] The present invention achieves the above-mentioned objectives through the following technical solutions.

[0006] In a first aspect, the present invention provides a holographic polymer-dispersed liquid crystal grating, which is obtained by holographic recording processing of a mixture including liquid crystal and polymer, comprising, by mass percentage: 20%-60% liquid crystal and 40%-80% polymer; wherein, the liquid crystal comprises a first type of liquid crystal compound having a chiral structure and being non-polymerizable; the polymer comprises a photopolymerizable compound and a photoinitiator composition, the photoinitiator composition comprising an initiator and a photosensitizer, wherein the initiator is capable of initiating a polymer reaction under light irradiation.

[0007] The holographic polymer-dispersed liquid crystal grating provided by this invention comprises 20%-60% liquid crystal and 40%-80% polymer, with a reasonable mass ratio of liquid crystal to polymer. The liquid crystal and polymer can generate a holographic grating with a periodic arrangement of polymer-rich and liquid crystal-rich phases. In traditional HPDLC, the liquid crystal exists in a uniform layered structure in the dark regions (liquid crystal-rich regions) of the interference fringes. Between adjacent polymer layers, there are polymer filaments formed due to incomplete diffusion. These polymer filaments cause the long axes of the rod-shaped liquid crystal molecules to align along the grating vector direction during diffusion, and after grating formation, they have a certain anchoring effect on the liquid crystal molecules. Due to the birefringence of liquid crystals, the diffraction efficiency of HPDLC gratings for P-rays is much higher than that for S-rays. To improve the diffraction efficiency for S-rays, the liquid crystal molecules need to be arranged randomly or helically. Introducing a chiral structure into the non-polymerizable liquid crystal molecules can cause the traditional liquid crystal molecules to be arranged helically, thereby improving the diffraction efficiency for S-rays, thus achieving high diffraction efficiency for both S-rays and P-rays simultaneously.

[0008] Furthermore, the first type of liquid crystal compound includes one or more of general formula I compounds and / or general formula II compounds;

[0009] The compound of general formula I is:

[0010]

[0011] R2 is selected from alkyl or alkoxy groups having 4-12 carbon atoms and one or more chiral centers. Y2 is any one of -F, -OCF3, and -CN; X3 and X4 are selected independently or simultaneously from one of H, F, and Cl. Selected from Any one of them; m2 represents 1, 2 or 3.

[0012] The compound of general formula II is:

[0013]

[0014] R3 and R4 are selected from alkyl groups having 1-7 carbon atoms; Y3 is any one of -F, -OCF3, and -CN; X5 and X6 are selected independently or simultaneously from one of H, F, and Cl. Selected from

[0015] Any one of them; m3 represents 1, 2, or 3; G is selected from

[0016] Furthermore, the compound of general formula I can be at least one of the following compounds;

[0017]

[0018]

[0019] Furthermore, the compound of general formula II may be at least one of the following compounds;

[0020]

[0021] Furthermore, the liquid crystal also includes a non-polymerizable second type of liquid crystal compound; by mass percentage, the holographic polymer-dispersed liquid crystal grating comprises: 10%-50% of the first type of liquid crystal compound; 10%-50% of the second type of liquid crystal compound; and 40%-80% of the polymer.

[0022] Furthermore, the second type of liquid crystal compound includes one or more compounds of general formula III;

[0023] The compound of general formula III is:

[0024]

[0025] Wherein, R1 is selected from alkyl or alkoxy groups having 2-12 carbon atoms; Y1 is any one of -F, -OCF3, and -CN; X1 and X2 are selected independently or simultaneously from one of H, F, and Cl. Selected from Any one of them; m1 represents 1, 2 or 3.

[0026] Furthermore, the compound of general formula III may be at least one of the following compounds;

[0027]

[0028]

[0029] Furthermore, the liquid crystal also includes one or more chiral additives.

[0030] Further, by mass percentage: the liquid crystal is 20%-60%; the photopolymer compound is 30%-70%; the photoinitiator composition is 0.1%-10%; wherein, in the photoinitiator composition, the weight ratio of the initiator to the photosensitizer is 1 / 1 to 50 / 1.

[0031] Furthermore, the photopolymer compound employs at least one 3-18 functional group acrylic acid monomer and at least one chain extender monomer.

[0032] Secondly, the present invention provides a method for preparing a holographic polymer-dispersed liquid crystal grating, comprising the following steps:

[0033] Step 1: Mix the liquid crystal and polymer from the first aspect above evenly to obtain a mixture;

[0034] Step 2: Inject the mixture from Step 1 into the liquid crystal cell and seal it to form a grating cell;

[0035] Step 3: Expose the grating cell with two coherent laser beams, and then cure it to obtain a holographic polymer-dispersed liquid crystal grating.

[0036] The method for fabricating a holographic polymer-dispersed liquid crystal grating provided by this invention utilizes the principle of polymerization-induced phase separation under coherent laser light. The photoinitiator system absorbs photons, generating active centers. Polymer monomers diffuse into the coherent bright region and undergo polymerization to form polymer polymers. Liquid crystal diffuses into the coherent dark region and undergoes phase separation. After exposure and curing, a holographic grating with periodically arranged polymer and liquid crystal is formed. This invention, by selecting a chiral, non-polymerizable liquid crystal and a polymer comprising a photopolymerizable compound and a photoinitiator composition, can prepare a holographic polymer-dispersed liquid crystal grating exhibiting high diffraction efficiency for both S- and P-beams. Detailed Implementation

[0037] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0038] <First Embodiment>

[0039] This invention provides a holographic polymer-dispersed liquid crystal grating, which is obtained by holographic recording processing of a mixture including liquid crystal and polymer. By mass percentage, it includes 20%-60% liquid crystal and 40%-80% polymer. The liquid crystal includes a first-class liquid crystal compound having a chiral structure and being non-polymerizable. The polymer includes a photopolymerizable compound and a photoinitiator composition. The photoinitiator composition includes an initiator and a photosensitizer. The initiator can initiate a polymer reaction under light irradiation.

[0040] A holographic polymer-dispersed liquid crystal grating is constructed using a first-class liquid crystal compound with a chiral structure and a polymer. Compared to gratings in existing technologies, the first-class liquid crystal compound, due to its chiral structure and non-polymerizable nature, allows the liquid crystal molecules to arrange themselves in a helical, disordered manner under the influence of the chiral structure. Specifically, the n-axis of the liquid crystal molecules... e The grating can be oriented in any direction, thus improving the diffraction efficiency for S-beams, achieving high diffraction efficiency for both S-beams and P-beams simultaneously. Furthermore, achieving high diffraction efficiency for both S-beams and P-beams simultaneously reduces losses in the light source waveguide. The chiral structure here can be either certain branches of the liquid crystal molecule having one or more chiral centers, or certain branches of the liquid crystal molecule having chiral groups.

[0041] In a preferred embodiment, the liquid crystal percentage can be 20%, 30%, 40%, 50%, or 60%, and the polymer percentage can be 40%, 50%, 60%, 70%, or 80%. The holographic polymer-dispersed liquid crystal grating provided by this invention, by controlling the percentages of liquid crystal and polymer, can precisely control the composition of the holographic polymer-dispersed liquid crystal grating and adjust its light transmittance and diffraction efficiency for S- and P-beams.

[0042] As a further improvement to the embodiments of the present invention, the first type of liquid crystal compound includes one or more of general formula I compounds and / or general formula II compounds.

[0043] The compound of general formula I is:

[0044]

[0045] Wherein, R2 is selected from alkyl or alkoxy groups having 4-12 carbon atoms and one or more chiral centers; Y2 is any one of -F, -OCF3, and -CN; X3 and X4 are selected independently or simultaneously from one of H, F, and Cl. Selected from Any one of them; m2 represents 1, 2 or 3.

[0046] The compound of general formula II is:

[0047]

[0048] R3 and R4 are selected from alkyl groups having 1-7 carbon atoms; Y3 is any one of -F, -OCF3, and -CN; X5 and X6 are selected independently or simultaneously from one of H, F, and Cl. Selected from

[0049] Any one of them; m3 represents 1, 2, or 3; G is selected from

[0050] As a further improvement to the embodiments of the present invention, the compound of general formula I can be at least one of the following compounds;

[0051]

[0052] It should be noted that the above compounds are only a part of the examples of compounds of general formula I and should not be construed as limiting the compounds of general formula I.

[0053] As a further improvement to the embodiments of the present invention, the compound of general formula II may be at least one of the following compounds;

[0054]

[0055] It should be noted that the above compounds are only a part of the examples of compounds of general formula II and should not be construed as limiting the compounds of general formula II.

[0056] As a further improvement of this invention, the liquid crystal further includes a non-polymerizable second type of liquid crystal compound; the holographic polymer-dispersed liquid crystal grating comprises, by mass percentage: 10%-50% of the first type of liquid crystal compound; 10%-50% of the second type of liquid crystal compound; and 40%-80% of the polymer. In a preferred embodiment, the proportion of the first type of liquid crystal compound can be 10%, 20%, 30%, 40%, or 50%, the proportion of the second type of liquid crystal compound can be 10%, 20%, 30%, 40%, or 50%, and the proportion of the polymer can be 40%, 50%, 60%, 70%, or 80%. The holographic polymer-dispersed liquid crystal grating provided by this invention, by controlling the proportions of the first type of liquid crystal compound, the second type of liquid crystal compound, and the polymer, can precisely control the composition of the holographic polymer-dispersed liquid crystal grating and adjust its light transmittance and diffraction efficiency for S- and P-beams.

[0057] As a further improvement to the embodiments of the present invention, the second type of liquid crystal compound includes one or more of the compounds of general formula III.

[0058] Compound of general formula III is:

[0059]

[0060] Wherein, R1 is selected from alkyl or alkoxy groups having 2-12 carbon atoms; Y1 is any one of -F, -OCF3, and -CN; X1 and X2 are selected independently or simultaneously from one of H, F, and Cl. Selected from Any one of them; m1 represents 1, 2 or 3.

[0061] As a further improvement to the embodiments of the present invention, the compound of general formula III may be at least one of the following compounds;

[0062]

[0063]

[0064] As a further improvement of this invention, the liquid crystal further includes one or more chiral additives. The addition of chiral additives can suppress the alignment of liquid crystal molecules along the grating pointing vector or along the grating grooves, thereby improving the diffraction efficiency of S / P light. In a preferred embodiment, the mass ratio of the chiral additive to the liquid crystal molecules ranges from 1 / 100 to 1 / 1.

[0065] As a further improvement of the embodiments of the present invention, the chiral additive includes at least one of: R / S5011, R / S811, R / S1011, R / S2011, chiral disohydrated hexitol, chiral disohydrated sorbitol, chiral disohydrated mannitol, chiral disohydrated idoleol, and derivatives. Preferably, it has a high HTP value and good compatibility with liquid crystal molecules, reducing the addition of chiral additives and the risk of low-temperature precipitation, and ensuring the temperature range of the liquid crystal phase; chiral disohydrated sorbitol is preferred.

[0066] As a further improvement of the embodiments of the present invention, the liquid crystal is 20%-60% by mass percentage; the photopolymer compound is 30%-70%; and the photoinitiator composition is 0.1%-10%. In the photoinitiator composition, in order to control the degree of phase separation, the weight ratio of the initiator to the photosensitizer is 1 / 1 to 50 / 1.

[0067] As a further improvement of this invention, the initiator includes triethylamine, triethanolamine, diisopropyl N,N-dicarboxylate-2,6-dioxane, N-phenylglycine, aromatic diazonium salts, aromatic sulfonium salts, aromatic iodonium salts, metallocene-based compounds, aromatic phosphonium salts, etc. The light sensitivity of the prepolymer material depends on the photosensitive dye and its concentration; the higher the concentration, the more sensitive it is to light. In most cases, the solubility of the photosensitizer limits its concentration; photosensitizers include Bengal rose red, Bengal rose red ester, Bengal rose red sodium salt, eosin, eosin sodium salt, camphorquinone, fluorescein diacetate, methylene blue, initiator 784, etc.

[0068] As a further improvement to the embodiments of the present invention, the photopolymerizable compound, by mass percentage, employs at least one 3-18 functional group acrylic monomer and at least one chain extender monomer. In a preferred embodiment, a low-viscosity, high-functionality monomer is preferred, with a viscosity of 100-400 cps and a functionality of 4-10. For example, a prepolymer with suitable functionality and viscosity is selected by combining a 5-functional group acrylate with di, tri, and tetraacrylates; such as ethylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol tri, tetra, penta, and hexaacrylates, and Changxing 6361-100; based on the optimal diffraction efficiency, the average functionality of the prepolymer is between 1 and 5. The photopolymerizable compound preferably employs Changxing 6361-100 and dipentaerythritol hexaacrylate.

[0069] As a further improvement of this invention, the chain extender can increase the solubility of the prepolymer material and the polymerization reaction rate. The chain extender is generally a small-molecule vinyl monomer, which, compared to multifunctional acrylates, is less susceptible to steric hindrance and reacts more readily with multifunctional acrylic acid. The chain extender monomer includes at least one of acrylonitrile, acrylic acid, acrylamide, hydroxyethyl methacrylate, dimethylallylamine, ethylidene urea ethoxylate, dimethacrylamide, and N-vinyl-2-pyrrolidone. The chain extender monomer helps dissolve the solid initiator, reduces the size of the liquid crystal droplets, and improves diffraction efficiency.

[0070] The liquid crystal provided in the embodiments of the present invention will be specifically described below through several sub-examples.

[0071] Table 1 shows the composition and proportions of the liquid crystals in each sub-example (by mass percentage):

[0072] Table 1

[0073] Compound Code Sub-example 1 Sub-example 2 Sub-example 3 Sub-example 4 Sub-example 5 Sub-example 6 I-2 5 5 7 5 I-3 20 20 20 5 I-4 20 15 15 10 10 I-6 10 10 10 5 5 I-8 15 20 5 20 10 10 I-9 10 10 10 10 10 I-10 15 15 15 5 5 Ⅱ-1 2 2 5 2 1 Ⅱ-2 3 3 10 2 1 Ⅲ-4 20 15 20 Ⅲ-6 10 5 5 Ⅲ-8 15 Ⅲ-9 5 Ⅲ-11 15 10 15 Ⅲ-12 10 10 10 Ⅲ-14 5 5 5 R5011 3 1 3

[0074] It should be noted that the components of the liquid crystal compositions in each sub-example use the example compounds from the compounds of general formula I, general formula II, and general formula III described above, and are represented by the codes to the right of the example compounds to simplify the table examples. For example, sub-example 1 uses example compounds I-2, I-3, I-4, I-6, I-8, I-9, and I-10 from general formula I, and example compounds II-1 and II-2 from general formula II. Of course, the above sub-examples do not illustrate all embodiments, nor do they use all example compounds or other compounds from general formula I, general formula II, and general formula III besides the example compounds. The above six sub-examples are only some examples of liquid crystals in this invention and should not be construed as limiting the liquid crystals in this invention.

[0075] Table 2 shows the composition and proportions (by weight) of the holographic polymer-dispersed liquid crystal grating in the sub-examples:

[0076] Table 2

[0077]

[0078] In this embodiment, the photopolymerization compound includes Changxing 6361-100 and dipentaerythritol hexaacrylate; the chain extender monomers are N-vinyl-2-pyrrolidone and hydroxyethyl methacrylate; the photosensitizer is Bengal rose red and the initiator is 784, with the initiator being N-phenylglycine and diphenyliodonium salt. The liquid crystal and polymer are mixed in a 30 / 70 ratio. In the comparative example, the liquid crystal is the commercially available E7 formulation, and the other components are the same as in sub-examples 7 to 12.

[0079] The raw materials prepared according to the proportions of sub-examples 7 to 12 and the comparative example were placed in sample bottles and mixed evenly by magnetic stirring at 20°C for 60 minutes. Then, the mixture was poured into a 7µm liquid crystal cell and exposed to a coherent laser with a wavelength of 532nm and an intensity of 3.5mW / cm2 for 45s. The grating was then bleached with 365nm ultraviolet light, and finally, a holographic polymer-dispersed liquid crystal grating was prepared.

[0080] Table 3 shows the S-ray diffraction efficiency and P-ray diffraction efficiency of sub-examples 7 to 12 and the comparative example. Wherein, S-ray diffraction efficiency = S-ray diffraction intensity / total intensity; P-ray diffraction efficiency = P-ray diffraction intensity / total intensity.

[0081] Table 3

[0082]

[0083] Compared with the comparative example, any of the sub-examples 7 to 12 provided by the present invention, under the same polymer initiation system, exhibits a chiral structure in the liquid crystals of sub-examples 7 to 12. This chiral structure can be an alkyl or alkoxy group with one or more chiral centers in a compound of general formula I, or a G (chiral group) in general formula II. Introducing a chiral structure into the non-polymerizable liquid crystal molecule allows the conventional liquid crystal molecules to arrange themselves in a helical pattern, thereby improving the diffraction efficiency for S-rays and achieving high diffraction efficiency for both S-rays and P-rays simultaneously. For example, sub-example 7 has a diffraction efficiency of 79.51% for S-rays and 91.55% for P-rays. In contrast, the comparative example has a diffraction efficiency of 9.84% for S-rays and 90.57% for P-rays. Therefore, the holographic polymer-dispersed liquid crystal grating provided by the present invention shows a significant improvement in diffraction efficiency for both S-rays and P-rays compared to the comparative example.

[0084] <Second Embodiment>

[0085] This embodiment provides a method for preparing a holographic polymer-dispersed liquid crystal grating, including the following steps:

[0086] Step 1: Mix the liquid crystal and polymer from the first embodiment above evenly to obtain a mixture;

[0087] Step 2: Inject the mixture from Step 1 into the liquid crystal cell and seal it to form a grating cell;

[0088] Step 3: Expose the grating cell with two coherent laser beams, and then cure it to obtain a holographic polymer-dispersed liquid crystal grating.

[0089] The method for fabricating a holographic polymer-dispersed liquid crystal grating provided in this embodiment utilizes the principle of polymerization-induced phase separation under coherent laser light. The photoinitiator system absorbs photons, generating active centers. Polymer monomers diffuse into the coherent bright region and undergo polymerization to form polymer polymers. Liquid crystal diffuses into the coherent dark region and undergoes phase separation. After exposure and curing, a holographic grating with periodically arranged polymer and liquid crystal is formed. This invention, by selecting a chiral, non-polymerizable first-class liquid crystal compound and a polymer comprising a photopolymerizable compound and a photoinitiator composition, can prepare a holographic polymer-dispersed liquid crystal grating exhibiting high diffraction efficiency for both S-rays and P-rays.

[0090] As a further improvement of this embodiment of the invention, during the exposure process in step 3, the polymer diffuses from the coherent dark region to the coherent bright region, and the liquid crystal diffuses from the coherent bright region to the coherent dark region. The liquid crystal diffusion time is less than the liquid crystal nucleation time, and the liquid crystal nucleation time is less than the system gelation time. When this condition is met, the phase separation structure is ordered, and the liquid crystal-rich phase is continuous, which enables the grating to have better diffraction efficiency, thereby improving the performance of the grating.

[0091] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and its improved concept, should be covered within the scope of protection of the present invention.

Claims

1. A holographic polymer dispersed liquid crystal grating, characterized by, The holographic polymer-dispersed liquid crystal grating is obtained by holographic recording of a mixture including liquid crystal and polymer, comprising 20%-60% liquid crystal and 40%-80% polymer by mass percentage. The liquid crystal includes a first type of liquid crystal compound having a chiral structure and being non-polymerizable; The polymer includes a photopolymerizable compound and a photoinitiator composition, the photoinitiator composition including an initiator and a photosensitizer, the initiator being able to initiate a polymer reaction under light irradiation.

2. The holographic polymer dispersed liquid crystal grating of claim 1, wherein, The first type of liquid crystal compounds includes one or more of general formula I compounds and / or general formula II compounds; The compound of general formula I is: R2 is selected from alkyl or alkoxy groups having 4-12 carbon atoms and one or more chiral centers; Y2 is any one of -F, -OCF3, and -CN; X3 and X4 are selected independently or simultaneously from one of H, F, and Cl; selected from the group consisting of any one of the group consisting of m2 represents 1, 2, or 3; The compound of general formula II is: Among them, R3 and R4 are selected from alkyl groups having 1-7 carbon atoms; Y3 can be any one of -F, -OCF3, or -CN; X5 and X6 are selected independently or simultaneously from one of H, F, and Cl; selected from the group consisting of any one of the group consisting of m3 represents 1, 2, or 3; G is selected from 3. The holographic polymer-dispersed liquid crystal grating according to claim 2, wherein the compound of general formula I may be at least one of the following compounds; 4. The holographic polymer-dispersed liquid crystal grating according to claim 2, wherein the compound of general formula II may be at least one of the following compounds; 5. The holographic polymer dispersed liquid crystal grating according to any one of claims 1 to 4, wherein The liquid crystal also includes a type II liquid crystal compound that is not polymerizable; The holographic polymer-dispersed liquid crystal grating comprises, by weight percentage: The first type of liquid crystal compound is 10%-50%; The second type of liquid crystal compound is 10%-50%; The polymer comprises 40%-80%.

6. The holographic polymer dispersed liquid crystal grating of claim 5, wherein, The second type of liquid crystal compounds includes one or more of the compounds of general formula III; The compound of general formula III is: R1 is selected from alkyl or alkoxy groups having 2-12 carbon atoms; Y1 can be any one of -F, -OCF3, or -CN; X1 and X2 are selected independently or simultaneously from one of H, F, and Cl; Selected from Any one of them; m1 represents 1, 2, or 3.

7. The holographic polymer-dispersed liquid crystal grating according to claim 6, wherein the compound of general formula III may be at least one of the following compounds; 8. The holographic polymer-dispersed liquid crystal grating according to any one of claims 1 to 4, characterized in that, The liquid crystal also includes one or more chiral additives.

9. The holographic polymer-dispersed liquid crystal grating according to claim 1, characterized in that, By weight percentage: The liquid crystal content is 20%-60%; The photopolymer compound is 30%-70%; The photoinitiator composition is 0.1%-10%; In the photoinitiator composition, the weight ratio of the initiator to the photosensitizer is 1 / 1 to 50 / 1.

10. The holographic polymer-dispersed liquid crystal grating according to claim 9, characterized in that, The photopolymer compound uses at least one 3-18 functional group acrylic acid monomer and at least one chain extender monomer.

11. A method for preparing a holographic polymer-dispersed liquid crystal grating, characterized in that, Includes the following steps: Step 1: Mix the liquid crystal and the polymer according to any one of claims 1 to 10 uniformly to obtain a mixture; Step 2: Inject the mixture from Step 1 into the liquid crystal cell and seal it to form a grating cell; Step 3: Expose the grating cell with two coherent laser beams, and then cure it to obtain a holographic polymer-dispersed liquid crystal grating.

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