Volume polarization grating and preparation method thereof, optical waveguide and display device

Abstract

The application relates to the technical field of optical elements, in particular to a volume polarization grating and a preparation method thereof, an optical waveguide and a display device, which comprises the following steps: step 100: obtaining a liquid crystal cell; step 200: irradiating a photoalignment agent coating layer on the liquid crystal cell with light of a first wavelength to induce patterned orientation; and step 300: irradiating a premix in the liquid crystal cell with light of a second wavelength to make reactive mesogenic monomers polymerize and solidify, thereby forming a volume polarization grating. The application realizes time sequence decoupling and synergistic optimization of "orientation writing-structure locking" in a single processing flow, realizes process simplification and time sequence decoupling, has comprehensive advantages such as a more complete structure and more stable performance, and can effectively solve technical problems in existing PVG patterning processing, such as complex flow, mutual interference between orientation and solidification, and limited efficiency and consistency.

Description

Technical Field

[0001] This application relates to the field of optical element technology, and in particular to a volume polarization grating and its fabrication method, an optical waveguide, and a display device. Background Technology

[0002] A volume polarization grating is a three-dimensional polarization holographic grating based on liquid crystal materials. Its core structure is a nanoscale three-dimensional grating formed by the self-assembly of liquid crystal molecules under the influence of an optical or electric field. It utilizes the optical anisotropy of liquid crystals (such as differences in birefringence) to achieve precise control of light. It can be applied to input / output and exit pupil expansion gratings for XR / AR near-eye display waveguides, beam steering and polarization splitting / conversion devices, and the rapid fabrication of liquid crystal holographic / diffractive optical elements.

[0003] In the fabrication technology of bulk polarization gratings, a step-by-step process is generally adopted: "first, expose and pattern the substrate photoaligning agent coating - assemble the liquid crystal cell - inject the reactive mesocrystalline system - then cure under ultraviolet light". However, in the process of realizing this application, the applicant discovered that the existing technology has problems with limited product consistency and yield. Summary of the Invention

[0004] This application discloses a volume polarization grating and its fabrication method, an optical waveguide, and a display device, in order to solve the technical problems of limited product consistency and yield in related technologies.

[0005] To solve the above problems, this application adopts the following technical solution: In a first aspect, this application provides a method for fabricating a volume polarization grating, comprising the following steps: Step 100: Obtain a liquid crystal cell containing a premix, the premix comprising a reactive mesocrystalline monomer and a photoinitiator. The liquid crystal cell includes a lower substrate and an upper substrate. At least one of the inner side of the lower substrate and the inner side of the upper substrate is provided with a photoalignment agent coating. The photoalignment agent responds to light of a first wavelength, and the photoinitiator responds to light of a second wavelength. The first wavelength and the second wavelength are different wavelengths. Step 200: Irradiate the photo-alignment agent coating on the liquid crystal cell with light of the first wavelength to induce it to produce a patterned alignment; Step 300: Irradiate the premix in the liquid crystal cell with light of a second wavelength to polymerize and solidify the reactive mesocrystalline monomers, forming a bulk polarization grating.

[0006] Secondly, this application provides a volume polarization grating, which is prepared by the above-described preparation method.

[0007] Thirdly, this application provides an optical waveguide including the aforementioned volume polarization grating.

[0008] Fourthly, this application provides a display device including the aforementioned optical waveguide.

[0009] The technical solution adopted in this application can achieve the following beneficial effects: This application first completes the assembly and filling of the liquid crystal cell, and then performs polarization writing and orientation under the illumination of the first wavelength light. It can switch the second wavelength light in situ and perform polymerization and curing under the illumination of the second wavelength light. It achieves temporal decoupling and synergistic optimization of "orientation writing-structure locking" within a single processing flow. It realizes the comprehensive advantages of process simplification, temporal decoupling, more complete structure and more stable performance. It can effectively solve the technical problems of complex process, mutual interference between orientation and curing, and limited efficiency and consistency in the existing PVG patterning processing. Attached Figure Description

[0010] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0011] Figure 1 This is a simplified process flow diagram of the preparation method of this application.

[0012] Figure 2 This is a process flow diagram of the preparation method in Example 1 of this application.

[0013] Figure 3 This is a graph showing the diffraction efficiency test results of the sample in Experiment Example 1 of this application.

[0014] Figure 4 This is a graph showing the spectral selectivity test results of the sample in Test Example 2 of this application. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be described in detail below. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0016] The terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and not to describe a specific order or sequence. It should be understood that such use of data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class and the number of objects is not limited; for example, a first object can be one or more. Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0017] In related technologies, a photoalignment material (such as SD-1 sulfonate azo dye or azo dye alignment agent) is typically spin-coated onto a glass / ITO substrate. A periodic alignment pattern is first formed on the substrate surface using polarization holographic interference, mask exposure, or scanning direct writing. Subsequently, the two substrates are assembled into a liquid crystal cell, and a liquid crystal mixture containing reactive mesocrystalline monomers (RM system) and a UV photoinitiator is infused via capillary action. Alignment self-assembly is achieved under a specific temperature program. Finally, UV irradiation is used to polymerize and cure the monomers, resulting in a cured bulk grating structure. The core characteristic of this route is that the "alignment writing" and "polymerization curing" processes are separated in time, typically corresponding to two or more independent steps. The existing technology uses a step-by-step process that requires alignment writing, liquid crystal cell assembly, potting, temperature-controlled alignment and final curing to be completed at different stages. The process chain is long and highly sensitive to cleanliness, alignment, time intervals and environmental stability. Fluctuations in any link (such as alignment layer aging, substrate contamination, potting bubbles, temperature program deviation) may cause uneven grating domain structure or scattering defects, thereby reducing batch consistency and mass production yield.

[0018] In related technologies, there are also methods that use the same ultraviolet band for orientation layer exposure and monomer curing exposure, or to complete orientation writing and curing separately at different work stations. In the single-band scheme, orientation layer exposure and polymerization curing may overlap in the spectrum, which may lead to "polymerization locking before orientation writing is completed" or "polymerization process affecting orientation rearrangement", thereby limiting the consistency of orientation fidelity and diffraction efficiency.

[0019] To this end, this application provides a volume polarization grating and its preparation method, optical waveguide and display device, which can realize a method with controllable timing and spectral separation of patterned orientation writing and in-situ polymerization curing in the same process, avoid mutual interference between orientation and curing, reduce process steps and alignment / cleaning sensitivity, improve the fidelity of patterned orientation, consistency of diffraction efficiency and reliability of mass production, and reduce the risk of material aging caused by ultraviolet curing.

[0020] The method for fabricating a volume polarization grating proposed in this application includes the steps of acquiring a liquid crystal cell, writing patterning alignment, and curing. Each step is described in detail below.

[0021] A method for fabricating a volume polarization grating, such as Figure 1 As shown, it includes the following steps: Step 100: Obtain a liquid crystal cell containing a premix, the premix comprising a reactive mesocrystalline monomer and a photoinitiator. The liquid crystal cell includes a lower substrate and an upper substrate. At least one of the inner side of the lower substrate and the inner side of the upper substrate is provided with a photoalignment agent coating. The photoalignment agent responds to light of a first wavelength, and the photoinitiator responds to light of a second wavelength. The first wavelength and the second wavelength are different wavelengths. In some embodiments, the photoalignment agent coating is obtained by spin coating. Specifically, spin coating can be performed on a substrate. Before spin coating, the ITO substrate can be ultrasonically cleaned sequentially in isopropanol, anhydrous ethanol, and deionized water for 10 to 15 minutes each, preferably 12 minutes each in this embodiment. After removal, the substrate is dried with nitrogen. Further, the substrate is then subjected to plasma treatment for 5 to 15 minutes, preferably 10 minutes in this embodiment.

[0022] In some specific embodiments, during spin coating, the spin coating speed is controlled at 2000 rpm to 4000 rpm, the spin coating time is 30 s to 60 s, and after spin coating, the coating is dried at 90°C to 100°C for 3 min to 10 min to form a uniform and stable photoalignment agent coating. In this embodiment, it is preferable to control the spin coating speed at 3000 rpm, the spin coating time at 40 s, and after spin coating, to dry at 95°C for 5 min to form a uniform and stable photoalignment agent coating. In some embodiments, the photoaligning agent is SD-1, whose chemical structural formula is shown in formula (1) below. (1) The photo-aligning agent SD-1 has good photoresponse characteristics and stability, and is used to achieve patterned alignment in response to light of a first wavelength.

[0023] In some embodiments, at most one of the inner sides of the lower substrate and the upper substrate is provided with a single alignment layer, thereby reducing the process of coating the photoalignment agent layer, reducing process complexity and material costs, while still maintaining sufficient boundary anchoring strength, so that the patterned alignment can be stably propagated in the bulk phase, which is suitable for large-area devices. Further, the single alignment layer is a rubbing-aligned PI layer or a uniform photoalignment layer; the rubbing-aligned PI layer is a prior art technology, specifically it can be formed by dehydrating a polyamic acid (PA) solution on the substrate surface into a polyimide (PI) film under a cyclization reaction, and then rubbing the PI film surface with a cloth or brush along a specific direction to form uniform grooves, giving it an alignment function, which will not be elaborated here. The uniform photoalignment layer is a prior art technology, specifically it can be a polymer film (such as polyimide, photoreactive polymer) formed on the substrate surface, in which the molecules (or photoreactive groups) are neatly arranged along a predetermined direction (such as the rubbing direction, the polarization direction), providing a uniform alignment reference for the liquid crystal molecules, ensuring that the liquid crystal layer achieves a uniform optical response (such as consistent transmittance, contrast), which will not be elaborated here.

[0024] In some embodiments, during the assembly of the liquid crystal cell, after applying a photoaligning agent layer to the lower substrate and / or the upper substrate, encapsulant is applied around the periphery of one of the lower and upper substrates to form a sealing frame and retain a filling port. The filling port is used to fill the premix. The lower substrate and the upper substrate are then bonded together. The thickness of the liquid crystal cell is controlled to be 10μm~20μm. In this embodiment, the thickness of the liquid crystal cell is preferably 15μm to ensure that the liquid crystal molecules have sufficient space for self-assembly. It is preferable to use a thickness measurement system to measure at multiple points and take the average value as the final thickness.

[0025] In some specific embodiments, the encapsulating adhesive includes 0.1wt% to 1.0wt% silica spacer powder by weight. In this embodiment, it is preferred that the encapsulating adhesive includes 0.5wt% silica spacer powder by weight to prevent deformation of the liquid crystal cell during the potting process. The silica spacer powder added to the encapsulating adhesive serves as a spacer medium, and its core function is to precisely control the spacing between the two substrates, ensuring uniform and stable liquid crystal cell thickness. Simultaneously, the silica spacer powder possesses good mechanical stability and chemical inertness, which can enhance the robustness of the encapsulation structure and prevent deformation of the liquid crystal cell during subsequent temperature control and curing processes.

[0026] In some embodiments, the reactive mesocrystalline monomer includes at least two of RM257, RM23, and RM105; the photoinitiator includes at least one of Irgacure 784, Irgacure 819 (phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide), Irgacure 651 (2,2-dimethoxy-2-phenylacetophenone (benzoin dimethyl ether)), Irgacure 2959 (2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone), and Irgacure 369 (2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone); the premix further includes a first chiral agent and a second chiral agent, wherein the first chiral agent and the second chiral agent have opposite chirality, the first chiral agent being R5011 or S5011, and the second chiral agent being R5011 or S5011. The chemical structural formula of RM257 is shown in formula (2) below. (2) The chemical structural formula of RM23 is shown in formula (3) below. (3) The chemical structural formula of RM105 is shown in formula (4) below. (4) The chemical structural formulas of R5011 and S5011 are shown in formula (5) below (without distinguishing between different chiralities). (5) The chemical structural formula of Irgacure784 is shown in formula (6) below. (6) The reactive mesocrystalline monomer includes at least two of RM257, RM23, and RM105. Specifically, the reactive mesocrystalline monomer can also be a combination of any two of RM257, RM23, and RM105, such as using RM257 and RM23 as a reactive mesocrystalline monomer, or using RM23 and RM105 as a reactive mesocrystalline monomer; the reactive mesocrystalline monomer can also be a combination of RM257, RM23, and RM105.

[0027] In some specific embodiments, the reactive mesocrystalline monomers include RM257, RM23 and RM105, and the mass ratio of the three is RM257:RM23:RM105 = (20~30):(20~30):(45~55).

[0028] Specifically, the premix includes RM257, RM23, RM105, R5011, S5011 and Irgacure784, and the mass ratio of the six is ​​RM257:RM23:RM105:R5011:S5011:Irgacure784 = (20~30):(20~30):(45~55):(1~3):(0.1~0.8):(0.5~1.0); the preferred mass ratio in this embodiment is RM257:RM23:RM105:R5011:S5011:Irgacure784 = 24.4:24.4:47.9:2.2:0.3:0.8.

[0029] Specifically, when preparing the premix, the reactive mesocrystalline monomer, the first chiral agent, the second chiral agent and the photoinitiator are added to a brown bottle, placed on a nitrogen glove box heating table, and heated and magnetically stirred at 70°C to 90°C. In this embodiment, it is preferred to heat and magnetically stir at 80°C until the mixture is a homogeneous and clear liquid, thus obtaining the premix.

[0030] In some embodiments, after preheating the liquid crystal cell to 75°C~85°C (preferably 78°C in this embodiment), the premix is ​​injected into the liquid crystal cell through the injection port. After injection, the injection port is sealed to prevent leakage and backflow of air bubbles. Specifically, the premix can be injected into the liquid crystal cell through the injection port using capillary action, or it can be injected into the liquid crystal cell through the injection port using pressurized injection.

[0031] In some embodiments, after the premix is ​​poured into the liquid crystal cell, the liquid crystal cell is first cooled and stabilized at 50°C to 60°C, and then left to stand for 15 to 25 minutes to achieve initial alignment balance and reduce flow marks. Preferably, in this embodiment, after the premix is ​​poured into the liquid crystal cell, the liquid crystal cell is first cooled and stabilized at 55°C, and then left to stand for 18 minutes to achieve initial alignment balance and reduce flow marks.

[0032] Step 200: Irradiate the photo-alignment agent coating on the liquid crystal cell with light of the first wavelength to induce patterned alignment.

[0033] In some embodiments, patterning orientation is achieved by polarization holographic interference, DMD / SLM direct writing, or mask exposure. Polarization holography is suitable for large-area, high-throughput periodic structures; DMD direct writing is suitable for complex phase / non-uniform periodic patterns; mask exposure lowers the equipment threshold and provides more stable processes.

[0034] In some embodiments, in step S200, the exposure time is controlled to be 5 min to 20 min, and the liquid crystal cell temperature is maintained at 50°C to 60°C during the exposure period to ensure the stability of the orientation writing. In this embodiment, the exposure time is preferably controlled to be 10 min, and the liquid crystal cell temperature is maintained at 55°C during the exposure period.

[0035] In some embodiments, after completing the writing patterning orientation, the liquid crystal cell temperature is maintained at 50°C~60°C for 3 to 10 minutes to promote further propagation of the bulk orientation and elimination of defects, thereby further stabilizing the orientation of the liquid crystal molecules. Preferably, in this embodiment, after completing the writing patterning orientation, the liquid crystal cell temperature is maintained at 55°C for 4 minutes to promote further propagation of the bulk orientation and elimination of defects, thereby further stabilizing the orientation of the liquid crystal molecules.

[0036] Step 300: Irradiate the premix in the liquid crystal cell with light of a second wavelength to polymerize and solidify the reactive mesocrystalline monomers, forming a bulk polarization grating.

[0037] In some embodiments, steps S200 and S300 are controlled to be performed at the same workstation, thereby reducing the risks of contamination, aging and alignment errors caused by multiple workstations, multiple handling and intermediate waiting, thereby improving batch consistency and manufacturing stability, and making it more suitable for large-area and large-scale preparation.

[0038] In some specific embodiments, in step S300, the light intensity of the second wavelength is controlled to be 10 mW / cm². 2 ~20mW / cm 2 The curing time is 5 to 10 minutes to allow the reactive mesocrystalline monomers to fully polymerize and solidify. In this embodiment, the light intensity of the second wavelength is preferably controlled at 15 mW / cm². 2 The curing time is 8 minutes to allow the reactive mesocrystalline monomers to fully polymerize and cure.

[0039] In some specific embodiments, the first wavelength is 360nm~370nm and the second wavelength is 470nm~500nm to achieve spectral separability and avoid interference between orientation writing and polymerization curing. In this embodiment, the first wavelength is preferably 365nm and the second wavelength is 488nm to achieve spectral separability and avoid interference between orientation writing and polymerization curing.

[0040] Step S400 involves UV curing the liquid crystal cell for 3 to 10 minutes, followed by annealing at 40°C to 50°C for 20 to 30 minutes to release curing stress, reduce scattering, and improve structural stability. In this embodiment, it is preferable to UV cure the liquid crystal cell for 5 minutes, followed by annealing at 45°C for 35 minutes to release curing stress, reduce scattering, and improve structural stability.

[0041] The volume polarization grating proposed in this application is prepared by the above-described preparation method.

[0042] The optical waveguide proposed in this application includes the aforementioned volume polarization grating.

[0043] The display device proposed in this application includes the aforementioned optical waveguide. Example 1

[0044] This embodiment describes a method for fabricating a volume polarization grating, such as... Figure 2 As shown, it includes the following steps: (1) The ITO substrate was ultrasonically cleaned in isopropanol, anhydrous ethanol and deionized water in sequence for 12 min each (the ultrasonic cleaning time for each solvent was 12 min); after removal, it was dried with nitrogen; then the substrate was subjected to plasma treatment for 10 min; then SD-1 was spin-coated on the inner surface of the two substrates. During the spin-coating process, the spin-coating speed was controlled at 3000 rpm and the spin-coating time was 40 s; after spin-coating, it was pre-baked at 95°C on a hot plate for 5 min.

[0045] (2) Apply encapsulant around a substrate to form a sealing frame and retain a filling port. The filling port is used to fill the premix. The encapsulant includes 0.5 wt% silica spacer powder. The two substrates are bonded together to complete the assembly of the liquid crystal cell. The thickness of the liquid crystal cell is controlled to be 15 μm. The thickness is measured at multiple points using a thickness measurement system and the average value is taken as the final thickness.

[0046] (3) Add the reactive mesocrystalline monomer, the first chiral agent, the second chiral agent and the photoinitiator to a brown bottle, place it on a nitrogen glove box heating table, heat it under a nitrogen protective atmosphere at 80°C and stir it magnetically until the mixture is a homogeneous and clear liquid to obtain a premix. The premix includes RM257, RM23, RM105, R5011, S5011 and Irgacure784, and the mass ratio of RM257:RM23:RM105:R5011:S5011:Irgacure784 is 24.4:24.4:47.9:2.2:0.3:0.8.

[0047] Specifically, in preparing the premix: the reactive mesocrystalline monomers used are RM257, RM23, and RM105; the primary chiral agent is R5011; the secondary chiral agent is S5011; and the photoinitiator is Irgacure784. RM257, RM23, RM105, R5011, S5011, and Irgacure784 are added to a brown bottle in a mass ratio of RM257:RM23:RM105:R5011:S5011:Irgacure784 = 24.4:24.4:47.9:2.2:0.3:0.8. The brown bottle is placed on a heating table inside a nitrogen glove box, heated under a nitrogen protective atmosphere at 80°C, and magnetically stirred until the mixture becomes a homogeneous and clear liquid, thus obtaining the premix.

[0048] (4) After preheating the liquid crystal cell to 78°C, the premix is ​​injected into the liquid crystal cell through the injection port using capillary action. After injection, the injection port is sealed to avoid leakage and backflow of air bubbles.

[0049] (5) After the premix is ​​poured into the liquid crystal cell, the liquid crystal cell is cooled down and stabilized at 55°C, and left to stand for 18 minutes to complete the initial orientation balance and reduce flow marks.

[0050] (6) Polarization holographic interference is used to expose the liquid crystal cell under the illumination of light of the first wavelength to write the patterned orientation. The exposure time is controlled to be 10 min. During the exposure, the temperature of the liquid crystal cell is kept at 55°C. The first wavelength is 365 nm.

[0051] (7) After completing the writing patterning orientation, keep the liquid crystal cell temperature at 55°C for 5 minutes to promote further propagation of the bulk orientation and elimination of defects.

[0052] (8) At the same workstation, switch to the second wavelength of light to irradiate the liquid crystal cell, excite the photoinitiator and trigger polymerization and curing, and control the light intensity of the second wavelength to 15mW / cm. 2 The curing time is 8 minutes, and the second wavelength is 488 nm.

[0053] (9) The liquid crystal cell is cured with ultraviolet light for 5 min and then annealed at 45°C for 35 min to release curing stress, reduce scattering and improve structural stability.

[0054] This embodiment completes patterning orientation writing and solidification locking directly after the liquid crystal cell is assembled and filled, reducing the risks of contamination, aging and alignment errors caused by multiple workstations, multiple handling and intermediate waiting, thereby improving batch consistency and manufacturing stability, significantly simplifying the process flow, reducing process chain sensitivity, improving yield and consistency, and making it more suitable for large-area and large-scale preparation.

[0055] Furthermore, compared to existing single-band or spectral overlapping systems, where polymerization may start before the orientation is fully established, potentially leading to problems such as orientation not being fully propagated before locking, increased domain boundaries, and distortion of the periodic structure, this embodiment first completes the SD-1 patterned orientation writing with light of the first wavelength, and then switches to light of the second wavelength to trigger polymerization, ensuring a clear timing sequence of "orientation first, then locking," thereby improving the bulk orientation fidelity and the integrity of the periodic structure, achieving "timing decoupling" between orientation writing and polymerization solidification, and avoiding orientation defects caused by premature locking.

[0056] Meanwhile, in this embodiment, since the orientation pattern is established in situ within the cell and quickly locked under optimized timing, the bulk periodic orientation modulation is more complete and the defect density is lower. This can effectively reduce scattering caused by domain structure, phase error and micro inhomogeneity, thereby improving the diffraction efficiency, in-plane uniformity and low stray light performance of the PVG that the display system is concerned with, and improving diffraction efficiency and in-plane uniformity while reducing scattering and stray light.

[0057] In addition, this embodiment achieves spectral function separation through wavelength switching, so that the orientation writing stage is mainly dominated by the SD-1 response and the curing stage is mainly dominated by the visible light initiation system, reducing crosstalk between the two, thereby expanding the available process window, improving tolerance to exposure dose fluctuations, slight differences in cell thickness and temperature control disturbances, enhancing engineering reproducibility, improving process window and parameter tolerance, and reducing the stringent dependence on temperature program and exposure dose.

[0058] Furthermore, this embodiment uses a visible light excitation initiation system for curing, which reduces the dependence on high-energy ultraviolet irradiation of the alignment layer and functional materials. This helps to reduce the risk of yellowing, increased absorption, and interface performance degradation, thereby improving the device transmittance and long-term stability, meeting the requirements of near-eye displays for high transmittance, low scattering, and durability, reducing the risk of ultraviolet-related material aging, and improving the long-term reliability of the device (especially suitable for XR waveguides).

[0059] In summary, this application achieves a comprehensive advantage through the key technical feature of "one-step exposure curing (first polarization writing orientation, then wavelength switching in-situ polymerization)" which is different from existing technologies. This feature simplifies the process, decouples the timing sequence, and provides more complete structure and more stable performance. It can effectively solve the technical problems in existing PVG patterning processes, such as complex processes, mutual interference between orientation and curing, and limited efficiency and consistency. Example 2

[0060] This embodiment describes a method for preparing a volume polarization grating, which differs from Embodiment 1 in that: for the two substrates constituting the liquid crystal cell, an SD-1 photoalignment agent coating is applied to one substrate (during spin coating, the spin coating speed is controlled at 3000 rpm and the spin coating time is 40 s; after spin coating, it is pre-baked at 95°C on a hot plate for 5 min), and a rubbing alignment PI layer is set on the other substrate.

[0061] The remaining steps are the same as in Example 1, and will not be repeated here.

[0062] In this embodiment, by reducing one SD-1 coating and pre-baking step, the process complexity and material cost are reduced; at the same time, sufficient boundary anchoring strength is still maintained, so that the patterned orientation can be stably propagated in the bulk phase, which is suitable for large-area devices. Example 3

[0063] The method for preparing a volume polarization grating in this embodiment differs from that in Embodiment 1 in that: for the two substrates constituting the liquid crystal cell, an SD-1 photoalignment agent coating is applied to one substrate (during the spin coating process, the spin coating speed is controlled at 3000 rpm and the spin coating time is 40 s; after spin coating, it is pre-baked at 95°C on a hot stage for 5 min), and a uniform photoalignment layer is set on the other substrate.

[0064] In this embodiment, by reducing one SD-1 coating and pre-baking step, the process complexity and material cost are reduced; at the same time, sufficient boundary anchoring strength is still maintained, so that the patterned orientation can be stably propagated in the bulk phase, which is suitable for large-area devices. Example 4

[0065] This embodiment provides a method for fabricating a volume polarization grating, which differs from Embodiment 1 in that: the liquid crystal cell is polarized and exposed under light of the first wavelength by direct writing with a DMD to write the patterned orientation.

[0066] The remaining steps are the same as in Example 1, and will not be repeated here.

[0067] In this embodiment, the liquid crystal cell is polarized and exposed by direct writing of DMD under the illumination of light of the first wavelength. DMD (Digital Micromirror Device) direct writing is a maskless photolithography technology. It dynamically generates patterns through the micromirror array of DMD chip and directly projects them onto the photo-alignment material or liquid crystal layer to achieve exposure. It has advantages such as high-speed dynamic pattern switching, maskless cost, and non-contact processing, and is suitable for complex phase / non-uniform periodic patterns. Example 5

[0068] This embodiment provides a method for fabricating a volume polarization grating, which differs from Embodiment 1 in that: the liquid crystal cell is polarized and exposed under light of the first wavelength by direct writing using SLM to write the patterned orientation.

[0069] The remaining steps are the same as in Example 1, and will not be repeated here.

[0070] In this embodiment, the liquid crystal cell is polarized and exposed by direct writing using SLM under illumination with light of the first wavelength. SLM (spatial light modulator, such as liquid crystal SLM or digital micromirror SLM) direct writing is a dynamic light field control technology. Through the phase / amplitude modulation at the pixel level of SLM, an exposure light field with arbitrary polarization state or phase distribution is generated. It has advantages such as high resolution, precise polarization control, and dynamic adjustability. It is suitable for complex phase / non-uniform periodic patterns and can be used for high-precision PVG and functional light field control. Example 6

[0071] This embodiment provides a method for fabricating a volume polarization grating, which differs from Embodiment 1 in that: the liquid crystal cell is polarized by exposure under light of a first wavelength through mask exposure in order to write patterned orientation.

[0072] The remaining steps are the same as in Example 1, and will not be repeated here.

[0073] In this embodiment, the liquid crystal cell is polarized by using mask exposure under the illumination of light of the first wavelength. The pattern is projected onto the photo-alignment material through a physical mask (such as a quartz mask) to achieve batch replication. It has advantages such as low cost, high consistency and high production efficiency, and is suitable for large-scale mass production and consumer-grade AR products. Example 7

[0074] The method for preparing a volume polarization grating in this embodiment differs from that in Embodiment 1 in that step (7) is omitted.

[0075] The remaining steps are the same as in Example 1, and will not be repeated here.

[0076] In this embodiment, by omitting step (7), the process time is further shortened and the production line cycle time is increased; it is suitable for situations where the orientation propagation speed is fast, the box thickness is thin, or the system viscosity is low. Example 8

[0077] The method for preparing a volume polarization grating in this embodiment differs from that in Embodiment 1 in that step (9) is omitted.

[0078] The remaining steps are the same as in Example 1, and will not be repeated here.

[0079] In this embodiment, step (9) is omitted to reduce the number of processes and shorten the processing cycle; it is suitable for scenarios where the sensitivity to residual stress is low or post-processing is replaced by the system assembly process. Example 9

[0080] The method for preparing a volume polarization grating in this embodiment differs from that in Embodiment 1 in that: in step (3), the premix comprises RM257:RM23:RM105:R5011:S5011:Irgacure819, and the mass ratio of each component is RM257:RM23:RM105:R5011:S5011:Irgacure819=20:30:45:1:0.1:1.0.

[0081] The remaining steps are the same as in Example 1, and will not be repeated here. Example 10

[0082] The method for preparing a volume polarization grating in this embodiment differs from that in Embodiment 1 in that: in step (3), the premix comprises RM257:RM23:RM105:R5011:S5011:Irgacure651, and the mass ratio of each component is RM257:RM23:RM105:R5011:S5011:Irgacure651=30:24:55:3:0.5:0.8; in step (9), the liquid crystal cell is cured with ultraviolet light for 3 min, and then annealed at 50°C for 20 min.

[0083] The remaining steps are the same as in Example 1, and will not be repeated here. Example 11

[0084] The method for preparing a volume polarization grating in this embodiment differs from that in Embodiment 1 in that: in step (3), the premix comprises RM257:RM23:RM105:R5011:S5011:Irgacure2959, and the mass ratio of each component is RM257:RM23:RM105:R5011:S5011:Irgacure2959=26:20:48:2:0.8:0.5; in step (9), the liquid crystal cell is cured with ultraviolet light for 10 min, and then annealed at 40°C for 30 min.

[0085] The remaining steps are the same as in Example 1, and will not be repeated here.

[0086] Experimental Example 1 Volume polarization gratings with periods of 460 nm, 550 nm, and 665 nm were prepared as samples using the preparation method of Example 1. The samples were fixed on a rotating platform, and a monochromatic laser was incident perpendicularly on the sample surface. After sample modulation, the incident light intensity I0 and the first-order diffraction light intensity I1 were measured using a power meter, and based on... Calculate the first-order diffraction efficiency. Each sample should be tested at least three times, and the average value should be taken as the final result. The test results are as follows: Figure 3 As shown.

[0087] from Figure 3As can be seen, the volume polarization gratings prepared by the method in Example 1 all exhibit significant diffraction phenomena. The first-order diffraction efficiency of the 550nm period volume polarization grating (green light period) reaches 87.2%, demonstrating the optimal process maturity and material matching for green light gratings. The first-order diffraction efficiency of the 665nm period volume polarization grating (red light period) is 83.7%, falling within the high-performance range. This is attributed to the greater process tolerance of the longer wavelength period and the easier achievement of uniformity in bulk refractive index modulation. The first-order diffraction efficiency of the 460nm period volume polarization grating (blue light period) is 78.0%, exceeding the application threshold of 75%. In summary, the method in Example 1 facilitates the formation of regular and stable periodic orientation structures within the material, thereby improving the diffraction performance of the volume polarization grating.

[0088] Experimental Example 2 Using the preparation method of Example 1, volume polarization gratings with periods of 460 nm, 550 nm, and 665 nm were prepared as samples. A broadband light source was collimated and irradiated onto the sample surface. Transmission or reflection spectra were collected within a preset wavelength range, and parameters such as the center peak position, peak intensity, and full width at half maximum (FWHM) were recorded. The test results are as follows: Figure 4 As shown.

[0089] from Figure 4 As can be seen, the volume polarization grating prepared by the method in Example 1 exhibits obvious selective response peaks in the visible light band, with concentrated peak positions and narrow half-widths (WHMs). Specifically, the peak set of the 460nm period volume polarization grating highly matches the blue light wavelength, the 550nm period volume polarization grating peak is compatible with the green light system, and the 665nm period volume polarization grating peak is compatible with the red light application band. This proves that the actual fabricated value of the volume polarization grating period is consistent with the design value, and the spatial periodicity of the bulk structure has not deviated, which is a core prerequisite for device qualification. The 460nm period volume polarization grating has a narrow bandwidth and the strongest narrowband screening capability, making it suitable for high-spectral-purity blue light polarization control / filtering (such as blue light channels in laser displays and high-precision blue light sensing), effectively avoiding blue stray light interference. The 550nm period volume polarization grating has a moderate bandwidth, balancing peak efficiency and spectral screening accuracy. The 65nm volume polarization grating has a slightly wider bandwidth and a slightly larger optical tolerance, making it suitable for red light applications with a slightly wider incident angle (such as AR light waveguides and red laser processing).

[0090] 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 apparatus 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 apparatus. 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 apparatus that includes that element.

[0091] Furthermore, it should be noted that the scope of the methods and apparatus in the embodiments of this application is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. In addition, features described with reference to certain examples may be combined in other examples.

[0092] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A method for fabricating a volume polarization grating, characterized in that, Includes the following steps: Step 100: Obtain a liquid crystal cell containing a premix, the premix comprising a reactive mesocrystalline monomer and a photoinitiator. The liquid crystal cell includes a lower substrate and an upper substrate. At least one of the inner side of the lower substrate and the inner side of the upper substrate is provided with a photoalignment agent coating. The photoalignment agent responds to light of a first wavelength, and the photoinitiator responds to light of a second wavelength. The first wavelength and the second wavelength are different wavelengths. Step 200: Irradiate the photo-alignment agent coating on the liquid crystal cell with light of the first wavelength to induce it to generate a patterned alignment. Step 300: Irradiate the premix in the liquid crystal cell with light of a second wavelength to polymerize and solidify the reactive mesocrystalline monomers, forming a bulk polarization grating.

2. The method for fabricating a volume polarization grating according to claim 1, characterized in that, At most one of the inner sides of the lower substrate and the upper substrate is provided with a single orientation layer.

3. The method for fabricating a volume polarization grating according to claim 1, characterized in that, The premix also includes a first chiral agent and a second chiral agent, the first chiral agent and the second chiral agent having opposite chirality, and the mass ratio of each component in the premix is ​​reactive mesocrystalline monomer: first chiral agent: second chiral agent: photoinitiator = (85~115): (1~3): (0.1~0.8): (0.5~1.0).

4. The method for fabricating a volume polarization grating according to claim 3, characterized in that, The first chiral agent is R5011 or S5011, and the second chiral agent is R5011 or S5011; And / or, the reactive mesocrystalline monomer includes at least two of RM257, RM23, and RM105; And / or, the photoinitiator includes at least one of Irgacure784, Irgacure819, Irgacure651, Irgacure2959 and Irgacure369.

5. The method for fabricating a volume polarization grating according to claim 4, characterized in that, The reactive mesocrystalline monomers include RM257, RM23 and RM105, and the mass ratio of the three is RM257:RM23:RM105 = (20~30):(20~30):(45~55); Alternatively, the premix includes RM257, RM23, RM105, R5011, S5011 and Irgacure784, and the mass ratio of the six is ​​RM257:RM23:RM105:R5011:S5011:Irgacure784 = (20~30):(20~30):(45~55):(1~3):(0.1~0.8):(0.5~1.0).

6. A method for fabricating a volume polarization grating according to any one of claims 1 to 4, characterized in that, In step S200, the patterning orientation is achieved by polarization holographic interference, DMD / SLM direct writing, or mask exposure; And / or, steps S200 and S300 are performed at the same workstation; And / or, the first wavelength is 360nm~370nm, and the second wavelength is 470nm~500nm.

7. A method for fabricating a volume polarization grating according to any one of claims 1 to 4, characterized in that, It also includes step S400, in which the liquid crystal cell is subjected to ultraviolet curing treatment for 3 min to 10 min, and then annealed at 40℃ to 50℃ for 20 min to 30 min.

8. A volume polarization grating, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 7.

9. An optical waveguide, characterized in that, Includes the volume polarization grating as described in claim 8.

10. A display device, characterized in that, Includes the optical waveguide as described in claim 9.

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