Polarizing body holographic grating, preparation method thereof and display equipment

Abstract

The invention relates to the technical field of grating preparation, and provides a polarization body holographic grating, a preparation method thereof and display equipment, and the method comprises the steps: selecting a plurality of parts of phase liquid crystals with different or same phase states, adding an additive and a photosensitizer, and mixing to form a liquid crystal mixture; coating a substrate with an orientation layer with the liquid crystal mixture to form an initial liquid crystal film; the additive contained in the initial liquid crystal thin film is volatilized, the molecular movement of the multiple parts of phase liquid crystals is affected in the additive volatilization process, and a cholesteric liquid crystal thin film with the screw pitch gradually changing in a gradient mode is formed; and carrying out ultraviolet curing treatment on the cholesteric liquid crystal film under the action of the photosensitizer to obtain the polarization holographic grating. According to the embodiment of the invention, the polarization body holographic grating with a wide reflection bandwidth is prepared.

Description

Technical Field

[0001] 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

[0002] 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 its unique helical structure and excellent optical properties, it has broad application prospects in various fields such as optical displays and optical devices (e.g., polarization holographic gratings). However, for polarization holographic gratings, the bandwidth of the cholesteric liquid crystal's reflection is limited by the birefringence of its molecules, resulting in insufficient bandwidth. Summary of the Invention

[0003] This application provides a polarizing holographic grating, its fabrication method, and a display device, aiming to achieve the fabrication of a polarizing holographic grating with a wide reflection bandwidth.

[0004] To achieve the above objectives, this application provides a method for fabricating a polarizing holographic grating, the method comprising:

[0005] Multiple liquid crystals of different or the same phase are selected and additives and photosensitizers are added to form a liquid crystal mixture;

[0006] The liquid crystal mixture is coated onto a substrate having an alignment layer to form an initial liquid crystal film;

[0007] The additives contained in the initial liquid crystal film are volatilized, and the volatilization process affects the molecular motion of multiple phase liquid crystals, forming a cholesteric liquid crystal film with a gradually changing pitch gradient.

[0008] The cholesteric liquid crystal film was subjected to ultraviolet curing treatment under the action of the photosensitizer to obtain a polarizing holographic grating.

[0009] In addition, to achieve the above objectives, this application also provides a polarizing holographic grating, which is prepared by the polarizing holographic grating preparation method described above.

[0010] 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.

[0011] This application discloses a polarizing holographic grating and its fabrication method and display device. By selecting multiple liquid crystal phases of different or identical phases and adding additives and photosensitizers, a liquid crystal mixture is formed. This mixture is then coated onto a substrate with an alignment layer to form an initial liquid crystal film. The additives in the initial liquid crystal film are then volatilized. During the volatilization process, the molecular motion of the liquid crystal phase is affected, forming a cholesteric liquid crystal film with a gradually changing pitch gradient. The cholesteric liquid crystal film is then subjected to ultraviolet curing under the action of a photosensitizer to obtain a polarizing holographic grating. Because the molecular motion of the liquid crystal phase during additive volatilization causes the pitch of the cholesteric phase in the film to change from a uniform state to a gradient-distributed multi-pitch state, the film's wavelength response range is broadened (typically one pitch corresponds to one wavelength), thus widening the reflection bandwidth of the polarizing holographic grating. In other words, a polarizing holographic grating with a wide reflection bandwidth is fabricated. Attached Figure Description

[0012] 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.

[0013] Figure 1 This is a schematic flowchart illustrating the steps of a method for fabricating a polarizing holographic grating according to an embodiment of this application;

[0014] Figure 2 This is a schematic diagram of the molecular structure of RM-1;

[0015] Figure 3 This is a schematic diagram of the molecular structure of RM-2;

[0016] Figure 4 This is a schematic diagram of the molecular structure of photoinitiator 1173;

[0017] Figure 5 This is a schematic diagram of the molecular structure of the photoinitiator TPO;

[0018] Figure 6 This is a schematic diagram of the molecular structure of photoinitiator 184;

[0019] Figure 7 This is a schematic diagram of the molecular structure of photoinitiator 907;

[0020] Figure 8 This is a schematic flowchart illustrating the steps of selecting multiple different phase liquid crystals and adding additives and photosensitizers to form a liquid crystal mixture, as provided in an embodiment of this application.

[0021] Figure 9This is a schematic diagram showing the distribution of various components in an initial liquid crystal film provided in an embodiment of this application;

[0022] Figure 10 This is a schematic diagram showing the distribution of various components in a cholesteric liquid crystal film provided in an embodiment of this application. Detailed Implementation

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] Please see Figure 1 , Figure 1 This is a schematic flowchart illustrating a method for fabricating a polarizing holographic grating according to an embodiment of this application. The 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.

[0029] like Figure 1 As shown, the fabrication method of the polarizing holographic grating specifically includes steps S101 to S104.

[0030] S101. Select multiple liquid crystals of different or the same phase, add additives and photosensitizers, and mix them to form a liquid crystal mixture.

[0031] To fabricate a polarizer holographic grating, two or more liquid crystal phases with specific molecular structures are first selected, and then these two or more liquid crystal phases of different or the same phase are mixed. The types of liquid crystal phases include, but are not limited to, cholesteric liquid crystals and nematic liquid crystals. The selected liquid crystal phases can be of the same phase, such as all being cholesteric liquid crystals, or they can be of multiple different phases, such as some being cholesteric liquid crystals and some being nematic liquid crystals.

[0032] For example, the selected liquid crystal phases include RM-1 and RM-2. RM-1 has the chemical name 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene, and its chemical formula is C. 33 H 32 O 10 , structure as Figure 2 As shown. RM-2's chemical name is 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-cyanobenzene, and its chemical formula is C. 33 H 29 O 10 , structure as Figure 3 As shown.

[0033] Two or more liquid crystals of different or the same phase are mixed, and then appropriate additives, photosensitizers, and other components are added to form a liquid crystal mixture. The additives include, but are not limited to, chloronaphthalene additive 1-CN, and the photosensitizers include, but are not limited to, photoinitiator 1173, photoinitiator TPO, photoinitiator 184, and photoinitiator 907.

[0034] Among them, photoinitiator 1173 has the chemical name 2-hydroxy-2-methyl-1-phenyl-1-propanone, with the chemical formula C6H5COC(CH3)2OH, and its structure is as follows. Figure 4 As shown.

[0035] The photoinitiator TPO has the chemical name 2,4,6-trimethylbenzoyl-diphenylphosphine oxide and its chemical formula is C. 22 H 21 O2P, structure as follows Figure 5 As shown.

[0036] Photoinitiator 184 has the chemical name 1-hydroxycyclohexylphenyl ketone and its chemical formula is C. 13 H 16 O2, structure as follows Figure 6 As shown.

[0037] Photoinitiator 907 has the chemical name 2-methyl-1-[4-(methylthio)phenyl]-2-(4-morpholinyl)-1-propanone, and its chemical formula is C0. 13 H 17 NO2S, structure as follows Figure 7 As shown.

[0038] In some embodiments, such as Figure 8 As shown, step S101 may include sub-steps S1011 to S1013.

[0039] S1011. Select a first phase liquid crystal and a second phase liquid crystal, and mix the first phase liquid crystal and the second phase liquid crystal to form a phase liquid crystal mixture;

[0040] S1012. Add a chiral agent and a photosensitizer to the liquid crystal mixture, and dissolve them in a solvent. After thorough stirring, a blend solution is formed.

[0041] S1013. Add additives to the blend solution and let it stand to form the liquid crystal mixture.

[0042] For example, the first phase of liquid crystal is as follows: Figure 2 The RM-1 shown has a second phase liquid crystal as shown in the figure. Figure 3 The RM-2 shown is formed by mixing RM-1 and RM-2 to form a phase liquid crystal mixture.

[0043] For example, mixing the first phase liquid crystal and the second phase liquid crystal to form a phase liquid crystal mixture includes: mixing the first phase liquid crystal and the second phase liquid crystal in a preset ratio to form the phase liquid crystal mixture.

[0044] The preset ratio can be flexibly set according to the actual situation. For example, the preset ratio is set to 1:1. Of course, the preset ratio can also be set to other values. No specific restrictions are made in this application.

[0045] For example, RM-1 and RM-2 are mixed in a preset ratio of 1:1 by mass to form a phase liquid crystal mixture.

[0046] Next, chiral agents, photosensitizers, and other chemical reagents are added to the cholesteric liquid crystal mixture. The chiral agents include, but are not limited to, R5011, S5011, R1011, S1011, R811, and S811. The chiral agents are added to form a cholesteric liquid crystal. The photosensitizer can be any one or more of photoinitiator 1173, photoinitiator TPO, photoinitiator 184, and photoinitiator 907. The photosensitizer is added for subsequent ultraviolet curing.

[0047] In some embodiments, adding a chiral agent and a photosensitizer to the phase liquid crystal mixture includes: adding a chiral agent of a first preset proportion and a photosensitizer of a second preset proportion, wherein the first preset proportion is greater than the second preset proportion.

[0048] The first and second preset percentages can be flexibly set according to actual conditions. For example, the first and second preset percentages represent mass percentages (wt%). Setting the first preset percentage to 1 wt% and the second preset percentage to 0.05 wt% means the first preset percentage is greater than the second preset percentage, i.e., the proportion of the chiral agent is greater than the proportion of the photosensitizer. Of course, the first and second preset percentages can also be set to other values, and this application does not impose specific restrictions.

[0049] For example, 1 wt% of chiral agent R5011 and 0.05 wt% of photoinitiator 1173 are added to the phase liquid crystal mixture.

[0050] The phase-liquid crystal mixture is then dissolved in a solvent, including but not limited to toluene. For example, the phase-liquid crystal mixture is dissolved in toluene at a specific temperature (e.g., 60°C).

[0051] After thorough stirring, a blended solution is formed.

[0052] An additive is then added to the blend solution; for example, chloronaphthalene additive 1-CN is added. After standing, a liquid crystal mixture is obtained. The additive is added to adjust the vertical distribution of the multiple phases of liquid crystal during the subsequent film formation process of the liquid crystal mixture.

[0053] In some embodiments, adding an additive to the blend solution and allowing it to stand to form the liquid crystal mixture includes: adding an additive of a third preset proportion by mass to the blend solution and allowing it to stand to form the liquid crystal mixture, wherein the third preset proportion is greater than the first preset proportion.

[0054] The third preset percentage can be flexibly set according to the actual situation. For example, the third preset percentage is set to 5wt%, which is greater than the first preset percentage. Of course, the third preset percentage can also be set to other values, and this application does not impose specific restrictions.

[0055] For example, using chloronaphthalene additive 1-CN, 5 wt% of chloronaphthalene additive 1-CN is added to the blend solution, and after standing, a liquid crystal mixture is obtained.

[0056] S102. The liquid crystal mixture is coated onto a substrate having an alignment layer to form an initial liquid crystal film.

[0057] The function of the alignment layer is to align the director of the liquid crystal along a specific direction. Using a substrate with an alignment layer, the outer side of the substrate is coated with the alignment layer. A liquid crystal mixture is then coated onto the alignment layer to form an initial liquid crystal film, for example, forming a film like... Figure 9 The initial liquid crystal film shown.

[0058] For example, an azo alignment layer is used as the alignment layer. It is exposed under circularly polarized light interference to generate a horizontal periodic alignment structure, resulting in a periodically aligned azo alignment layer.

[0059] In some embodiments, coating the liquid crystal mixture onto a substrate having an alignment layer to form an initial liquid crystal film includes:

[0060] The liquid crystal mixture is coated onto the substrate having the alignment layer using a selected coating method, and the orientation vectors of multiple phase liquid crystals are aligned in a specific direction through the alignment layer to form the initial liquid crystal film. The coating method includes at least one of spin coating, blade coating, and inkjet printing.

[0061] For example, a liquid crystal mixture is coated onto a substrate with an alignment layer by means of spin coating, blade coating, inkjet printing, etc. The alignment layer aligns the directional vectors of RM-1 and RM-2 in a specific direction to form an initial liquid crystal film.

[0062] S103. The additives contained in the initial liquid crystal film are volatilized, and the volatilization process affects the molecular motion of multiple phase liquid crystals to form a cholesteric liquid crystal film with a gradually changing pitch gradient.

[0063] Pitch refers to the distance between two adjacent molecular chains in a liquid crystal helical structure as their long axes change 360°. Different liquid crystal phases correspond to different pitches. When the initial liquid crystal film is left to stand for a period of time, the additives contained in the initial liquid crystal film will volatilize. Due to the volatilization of the additives, the molecules of multiple different liquid crystal phases move, such as the molecules of RM-1 and RM-2. Through molecular movement, the multiple different liquid crystal phases are distributed in layers in the vertical direction. For example, RM-2 gathers in the upper layer and RM-1 gathers in the lower layer. The pitches of the different liquid crystal phases distributed in layers are different, thus forming a cholesteric liquid crystal film with a gradually changing pitch gradient.

[0064] In some embodiments, the step of causing the additive contained in the initial liquid crystal film to volatilize, and affecting the molecular motion of multiple phase liquid crystals during the volatilization process to form a cholesteric liquid crystal film with a gradually changing pitch gradient, includes: heating the initial liquid crystal film at a target temperature for a preset time, wherein the volatilization of the additive during the heating process affects the molecular motion of multiple phase liquid crystals, thereby changing the vertical distribution of multiple phase liquid crystals in the initial liquid crystal film and forming the cholesteric liquid crystal film with a gradually changing pitch gradient.

[0065] The preset duration can be flexibly set according to the actual situation; the higher the target temperature, the shorter the preset duration. For example, for a target temperature of 100℃, the preset duration is set to 3 minutes. Of course, the preset duration can also be set to other values, and this application does not impose specific restrictions.

[0066] For example, when the initial liquid crystal film is heated at 100°C for 3 minutes, the additives in the initial liquid crystal film rapidly volatilize. Due to intermolecular interactions, RM-2 in the initial liquid crystal film moves in a gradient to the film surface, resulting in a cholesteric liquid crystal film with a gradually changing pitch gradient. For example, forming a cholesteric phase liquid crystal film as shown in the example. Figure 10 The cholesteric liquid crystal film shown has an RM-2 enriched region on the upper layer and an RM-1 enriched region on the lower layer.

[0067] S104. The cholesteric liquid crystal film is subjected to ultraviolet curing treatment under the action of the photosensitizer to obtain a polarizing holographic grating.

[0068] For example, after obtaining the cholesteric liquid crystal film, the cholesteric liquid crystal film is irradiated with an ultraviolet (UV) device, and then UV-cured under the action of a photosensitizer. The UV device includes, but is not limited to, a UV-emitting diode.

[0069] For example, a cholesteric liquid crystal film is cured under ultraviolet light irradiation with an ultraviolet light-emitting diode in the wavelength range of 100-400 nm. The liquid crystal end groups polymerize, and the gradually changing pitch is fixed, ensuring its stability and durability. This completes the fabrication of a polarizing holographic grating. Due to the gradually changing pitch, the response range to incident wavelengths widens, thereby broadening the reflection bandwidth of the polarizing holographic grating. In other words, a polarizing holographic grating with a wide reflection bandwidth is fabricated.

[0070] In the above embodiments, multiple liquid crystal phases of different or the same phase are selected, and additives and photosensitizers are added to form a liquid crystal mixture. The liquid crystal mixture is coated on a substrate with an alignment layer to form an initial liquid crystal film. The additives contained in the initial liquid crystal film are volatilized. During the volatilization of the additives, the molecular motion of the liquid crystal phase is affected, forming a cholesteric liquid crystal film with a gradually changing pitch gradient. Then, the cholesteric liquid crystal film is subjected to ultraviolet curing treatment under the action of a photosensitizer to obtain a polarizing holographic grating. Because the molecular motion of the liquid crystal phase during the volatilization of the additives causes the pitch of the cholesteric phase in the film to change from a uniform state to a gradient-distributed multi-pitch state, the response range of the film to wavelength becomes wider (usually one pitch corresponds to one wavelength), thus broadening the reflection bandwidth of the polarizing holographic grating. That is, a polarizing holographic grating with a wide reflection bandwidth is prepared.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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 preparing a polarization holographic grating, characterized in that: The method for preparing the polarization volume holographic grating comprises: Selecting a plurality of phase liquid crystals of different or same phases, adding additives and photosensitizers, and mixing to form a liquid crystal mixture; coating the liquid crystal mixture on a substrate having an alignment layer to form an initial liquid crystal film; volatilize the additive contained in the initial liquid crystal film, and during the volatilization process of the additive, affect the molecular motion of a plurality of liquid crystals to form a cholesteric liquid crystal film with a gradual pitch gradient; The cholesteric liquid crystal film is subjected to ultraviolet curing treatment under the action of the photosensitizer to obtain a polarized holographic grating.

2. The method for preparing a polarization holographic grating according to claim 1, characterized in that: The method of selecting a plurality of liquid crystals of different or same phases, adding additives and photosensitizers, and mixing them to form a liquid crystal mixture comprises: Selecting a first phase liquid crystal and a second phase liquid crystal, and mixing the first phase liquid crystal and the second phase liquid crystal to form a phase liquid crystal mixture; Adding a chiral agent and a photosensitizer to the phase liquid crystal mixture, mixing them into a solvent to dissolve, and after sufficient stirring, forming a blended solution; Adding additives to the blended solution and allowing to stand to form the liquid crystal mixture.

3. The method for preparing a polarization holographic grating according to claim 2, characterized in that: The step of mixing the first phase liquid crystal with the second phase liquid crystal to form a phase liquid crystal mixture comprises: The first phase liquid crystal and the second phase liquid crystal are mixed according to a preset ratio to form the phase liquid crystal mixture.

4. The method for preparing a polarization holographic grating according to claim 3, characterized in that: The first phase liquid crystal is 1,4-bis-[4-(3-acryloxypropoxy)benzoyloxy]-2-methylbenzene, and the second phase liquid crystal is 1,4-bis-[4-(3-acryloxypropoxy)benzoyloxy]-2-cyanobenzene, and the preset ratio is 1:

1.

5. The method for preparing a polarization holographic grating according to claim 3, characterized in that: The step of adding a chiral agent and a photosensitizer to the phase liquid crystal mixture comprises: A chiral agent having a mass corresponding to a first preset proportion is added to the phase liquid crystal mixture, and a photosensitizer having a mass corresponding to a second preset proportion is added, wherein the first preset proportion is greater than the second preset proportion.

6. The method for preparing a polarization holographic grating according to claim 5, characterized in that: The step of adding an additive to the blended solution and allowing the mixture to stand to form the liquid crystal mixture comprises: Adding an additive of a mass corresponding to a third preset proportion to the blended solution, and allowing to stand to form the liquid crystal mixture, wherein the third preset proportion is greater than the first preset proportion.

7. The method for preparing a polarization holographic grating according to claim 1, characterized in that: The step of coating the liquid crystal mixture on a substrate having an alignment layer to form an initial liquid crystal film comprises: The liquid crystal mixture is coated on the substrate having the alignment layer by a selected coating method, and the directors of the plurality of phase liquid crystals are arranged in a specific direction by the alignment layer to form the initial liquid crystal film, wherein the coating method includes at least one of spin coating, scraper coating, and inkjet printing.

8. The method for preparing a polarization holographic grating according to claim 1, characterized in that: The step of volatilizing the additive contained in the initial liquid crystal film and influencing the molecular motion of a plurality of liquid crystal phases during the volatilization of the additive to form a cholesteric liquid crystal film with a gradual pitch change includes: The initial liquid crystal film is heated at a target temperature for a preset time. During the heating process, the additive volatilizes and affects the molecular movement of multiple phase liquid crystals, thereby changing the vertical distribution of multiple phase liquid crystals in the initial liquid crystal film, forming the cholesteric phase liquid crystal film with a gradient pitch.

9. 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 8.

10. 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 9.

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