Chiral nematic liquid crystal grating based on asymmetric orientation template and preparation method thereof

Abstract

The application discloses a chiral nematic liquid crystal grating based on an asymmetric orientation template and a preparation method, relates to the field of liquid crystal diffraction optical devices and near-eye display (XR / AR) optical waveguide coupling grating manufacturing technology. The preparation method comprises the following steps: step S10: providing a first substrate and a second substrate and preparing an orientation layer; step S20: forming an asymmetric grating orientation template; step S30: assembling a liquid crystal box; step S40: filling a reactive mesogen mixture; step S50: inducing by temperature reduction and curing under ultraviolet light to form a stable chiral nematic liquid crystal grating. The application adopts an asymmetric orientation template, avoids the high-precision registration requirement of double-sided patterning orientation on period and phase and the risk of orientation disorder, effectively suppresses defects such as dislocation and domain boundary, improves the structural integrity of the grating and the stability of the diffraction efficiency, and simultaneously reduces the equipment and process requirements, improves the yield and consistency in mass production.

Description

Technical Field

[0001] This application relates to the field of manufacturing technology of liquid crystal diffractive optical devices and optical waveguide coupling gratings for near-eye displays (XR / AR), and particularly to a chiral nematic phase grating based on an asymmetric orientation template and its fabrication method. Background Technology

[0002] The mainstream fabrication method for chiral nematic (or reactive mesocrystalline) gratings (such as polarization volume gratings PVG and cholesteric liquid crystal gratings CLC) employs a "double-sided anchoring" technique involving double-substrate double-sided optical patterning and orientation. This involves constructing periodically rotating orientation boundary conditions on the inner surfaces of the upper and lower substrates to induce a periodic orientation structure in the liquid crystal (or reactive mesocrystalline) phase. While this approach provides strong interface constraints to support the high diffraction efficiency required for the grating, it suffers from significant technical drawbacks in practical industrial applications, specifically: First, double-sided patterning orientation is extremely sensitive to registration accuracy and process consistency. Existing double-sided orientation of PVG / CLC volume gratings is mostly achieved through polarization holography or optical patterning processes, requiring strict matching of the orientation patterns of the upper and lower substrates in key dimensions such as periodic parameters, phase distribution, azimuth angle, and rotation direction. However, in large-area processes, minute disturbances such as exposure uniformity deviations, substrate micro-warping, and bonding alignment misalignments can easily cause volume orientation mismatches, leading to local periodic structural distortion and unstable diffraction efficiency.

[0003] Secondly, the lengthy and complex process chain poses a severe challenge to mass production yield and cost control. The double-sided exposure and double-sided patterning process design not only increases equipment investment and process steps, but also places more stringent requirements on the cleanliness of the production environment and the batch stability of materials. During industrial scale-up, problems such as narrowing process window, declining yield, and fluctuations in product consistency become prominent, becoming the core bottleneck restricting large-scale production.

[0004] Furthermore, bulk defects and scattering centers are prone to form, severely affecting the integrity of the periodic structure and optical performance. When there is slight incompatibility in the bilateral orientation boundary conditions, or when local stress is generated during the manufacturing process (such as curing shrinkage or film thickness fluctuations), the elastic energy of the liquid crystal is prone to accumulate, which can induce structural defects such as misalignment and domain boundaries, leading to increased stray light, reduced effective grating depth, and fluctuations in diffraction efficiency. Related research and practice have clearly confirmed that the matching of the orientation template and the integrity of the bulk structure are the key factors determining the grating diffraction efficiency and stray light suppression capability.

[0005] Finally, the devices exhibit poor tolerance to thickness tolerance and environmental disturbances, limiting long-term stability and batch-to-batch consistency. In core applications such as near-eye displays and waveguide coupling, PVGs must meet performance requirements of near 100% diffraction efficiency and large diffraction angles. However, their bulk periodic structure is extremely sensitive to film thickness fluctuations, interface anchoring strength, and material aging. The double-sided strongly constrained system is more prone to local orientation setbacks when faced with thickness deviations or external environmental disturbances (such as temperature changes, humidity fluctuations, and mechanical stress), leading to optical performance drift over time and making it difficult to meet the stringent requirements of long-term stability and batch-to-batch consistency in practical applications. Summary of the Invention

[0006] This application discloses a chiral nematic phase grating based on an asymmetric orientation template and its fabrication method, in order to solve the technical problems in related technologies, such as high difficulty in double-sided patterned orientation registration, complex process, easy generation of orientation defects leading to grating structure distortion, diffraction efficiency fluctuation, poor device stability and mass production consistency.

[0007] To solve the above problems, this application adopts the following technical solution: In a first aspect, embodiments of this application provide a method for fabricating a chiral nematic phase grating based on an asymmetric orientation template, characterized by comprising the following steps: Step S10: Provide a first substrate and a second substrate, and prepare alignment layers on the opposite surfaces of the first substrate and the second substrate respectively; Step S20: The alignment layer of the first substrate is uniformly aligned to give it a uniform non-periodic planar orientation; the alignment layer of the second substrate is patterned to give it a spatially periodic orientation distribution; thereby forming an asymmetric orientation boundary condition between the first and second substrates, which constitutes an asymmetric grating alignment template. Step S30: The first substrate and the second substrate are aligned and assembled with the alignment layers facing each other, and sealed with sealant to form a liquid crystal cell with a receiving space and an injection port; Step S40: At a temperature higher than the clearing point of the reactive mesocrystalline mixture, a reactive mesocrystalline mixture containing a chiral dopant, a polymerizable mesocrystalline monomer, a photoinitiator, and a fluorescent dye is poured into the liquid crystal cell; Step S50: After the infusion is completed, the body phase orientation structure is formed by cooling, and then ultraviolet light curing is performed to form a stable chiral nematic phase grating.

[0008] In a second aspect, embodiments of this application provide a chiral nematic bulk grating, which is prepared by the fabrication method described in the first aspect; the bulk grating includes a first substrate, a second substrate, and a liquid crystal polymer network layer disposed opposite to each other; The first substrate has a uniform non-periodic planar alignment layer on its inner side, and the second substrate has a spatially periodic alignment layer on its inner side. The liquid crystal polymer network layer forms a three-dimensional periodic volume grating structure under asymmetric alignment boundary conditions.

[0009] The technical solutions adopted in the embodiments of this application can achieve the following beneficial effects: (1) The method for fabricating chiral nematic phase gratings based on asymmetric orientation templates provided in this application adopts an asymmetric design of “single-sided patterning + uniform orientation on the opposite side”. It provides structural guidance only through the periodic orientation of a single substrate, and uses a stable and uniform orientation on the other side as a global reference boundary. This fundamentally avoids the high-precision registration requirements of period, phase and azimuth angle for double-sided patterning, eliminates the risk of volume phase orientation disorder caused by “pattern-pattern” registration deviation, and greatly improves the process repeatability, batch consistency and large-scale production yield of large-area fabrication.

[0010] (2) The chiral nematic bulk grating fabrication method based on asymmetric orientation template provided in this application adopts global stable anchoring provided by the uniform orientation side, which provides a clear reference and elastic stress release channel for the orientation evolution of bulk liquid crystal molecules. Compared with the elastic frustration that is easily generated by double-sided strong constraint, this application can effectively suppress the generation of structural defects such as dislocations and domain boundaries, reduce the interference of scattering centers and stray light, and significantly improve the integrity, uniformity and diffraction efficiency stability of the bulk grating periodic structure.

[0011] (3) The method for fabricating a chiral nematic phase grating based on an asymmetric orientation template provided in this application can effectively disperse local stress concentration by using asymmetric boundary constraints (uniform anchoring + patterned guidance), reduce the sensitivity of the device to external disturbances, avoid periodic structure drift or regional failure, significantly improve the structural stability and optical performance reliability of the volume grating during long-term use, and extend the service life of the device.

[0012] (4) The method for fabricating chiral nematic phase gratings based on asymmetric orientation templates provided in this application eliminates key steps such as patterned exposure and alignment of one side of the substrate, significantly reducing equipment investment and process control complexity, reducing key failure points such as uneven exposure, bonding offset, and double-sided orientation incompatibility, significantly broadening the manufacturable window, and reducing energy consumption and material loss in the production process, thereby achieving effective control of manufacturing costs.

[0013] (5) The chiral nematic phase grating fabrication method based on asymmetric orientation template provided in this application can be used as a functional interface for device integration on the uniform orientation side, adapting to the requirements of polarization management, bonding layer design and interface coupling with waveguide, while the patterned side focuses on the realization of grating modulation function, making the device structure division of labor clearer and more reasonable, providing convenience for system-level design, consistency control and integrated assembly in application scenarios such as waveguide coupling and exit pupil expansion, and improving the application adaptability of the device. Attached Figure Description

[0014] 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.

[0015] Figure 1 The figures show the experimental results of the spectral selectivity of the chiral nematic phase gratings prepared in Examples 1-3. Detailed Implementation

[0016] 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.

[0017] 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.

[0018] In related technologies, the mainstream fabrication methods for chiral nematic bulk gratings (such as polarization volume gratings and cholesteric liquid crystal gratings) all employ double-sided patterning alignment technology. This requires the construction of patterned alignment layers with strictly matched periods, phases, and azimuth angles on the inner surfaces of the upper and lower substrates to induce the formation of a periodic structure in the liquid crystal bulk phase. This technology demands extremely high registration accuracy for the double-sided alignment patterns. In large-area processes, it is highly susceptible to bulk phase alignment mismatches caused by disturbances such as exposure uniformity deviations, substrate micro-warping, or bonding misalignment, leading to periodic structure distortion and diffraction efficiency fluctuations. Furthermore, the lengthy process chain of double-sided exposure and double-sided patterning significantly increases equipment investment and process complexity, imposing stringent requirements on the cleanliness of the production environment and material stability, resulting in a narrowed process window and low mass production yield. In addition, the strong double-sided constraint system easily accumulates elastic stress, inducing structural defects such as dislocations and domain boundaries, making the device less resistant to thickness tolerances and environmental disturbances, and difficult to meet the needs of large-scale production and long-term stable applications.

[0019] To address this, this application proposes a chiral nematic bulk grating based on an asymmetric orientation template and its fabrication method. The core inventive concept lies in breaking away from the traditional paradigm of bifacial symmetrical orientation and adopting an asymmetric design of "single-sided patterned guidance + uniform anchoring on the opposite side": a patterned orientation layer with spatially periodic variations is constructed only on one side of the substrate to provide core guidance for the formation of the bulk grating's periodic structure; the other side of the substrate is only provided with a uniform, non-periodic planar orientation layer, serving as a global reference boundary and stress release channel for the orientation evolution of bulk liquid crystal molecules. This design fundamentally avoids the high-precision registration requirements of bifacial patterned orientation in terms of period, phase, and azimuth angle, eliminating the risk of bulk orientation disorder caused by bifacial pattern mismatch. Simultaneously, the stable anchoring provided by the uniform orientation side provides a clear orientation reference and elastic stress release path for the self-assembly of liquid crystal molecules, effectively suppressing the generation of structural defects such as dislocations and domain boundaries. While ensuring excellent optical performance, it significantly improves the process repeatability, batch-to-batch consistency, and long-term device stability of large-area fabrication, providing a practical technical path for the industrial application of chiral nematic bulk gratings.

[0020] The following is a detailed description of a chiral nematic phase grating based on an asymmetric orientation template and its fabrication method proposed in this application.

[0021] In a first aspect, this application provides a method for fabricating a chiral nematic phase grating based on an asymmetric orientation template, comprising the following steps: Step S10: Provide a first substrate and a second substrate, and prepare alignment layers on the opposite surfaces of the first substrate and the second substrate respectively; Step S20: The alignment layer of the first substrate is uniformly aligned to give it a uniform non-periodic planar orientation; the alignment layer of the second substrate is patterned to give it a spatially periodic orientation distribution; thereby forming an asymmetric orientation boundary condition between the first and second substrates, which constitutes an asymmetric grating alignment template. Step S30: The first substrate and the second substrate are aligned and assembled with the alignment layers facing each other, and sealed with sealant to form a liquid crystal cell with a receiving space and an injection port; Step S40: At a temperature higher than the clearing point of the reactive mesocrystalline mixture, a reactive mesocrystalline mixture containing a chiral dopant, a polymerizable mesocrystalline monomer, a photoinitiator, and a fluorescent dye is poured into the liquid crystal cell; Step S50: After the infusion is completed, the orientation structure of the bulk phase is formed by cooling orientation induction, and then ultraviolet light curing is performed to form a stable chiral nematic bulk grating.

[0022] In some embodiments, in step S20, the patterning orientation process employs polarization holographic interference exposure, scanning direct writing exposure, or mask-assisted exposure, with an exposure time of 2 seconds to 20 minutes.

[0023] The polarization holographic interference exposure uses two or more beams of polarized light to form a spatially varying polarization field on the substrate surface, so that the orientation easy axis of the optical alignment layer is arranged periodically in space, which is suitable for the preparation of large-area, periodically uniform alignment patterns. The scanning direct writing exposure uses a scanning exposure system with polarization control function to write the orientation azimuth distribution point by point or line by line on the substrate surface, which can realize complex local periodic modulation, phase encoding and non-uniform periodic structure design. The mask-assisted exposure achieves selective modulation of the exposure area through a mask or spatial light modulator (SLM), which helps optimize the transition of the alignment region boundary and reduce exposure crosstalk between adjacent regions. It is understood that using polarization holographic interference exposure, scanning direct-write exposure, or mask-assisted exposure to perform patterned alignment processing can form a micro-area alignment structure with controllable azimuth angle on the surface of the first substrate, allowing liquid crystal molecules to achieve partitioned alignment according to a preset pattern. This is beneficial for meeting the complex functional requirements of devices such as multi-domain structures and multi-viewpoint control.

[0024] In some embodiments, in step S20, the patterning orientation process employs polarized holographic interference exposure, using two beams of coherent ultraviolet polarized light (with the same wavelength of 365nm to 405nm and a total light intensity of 1mW / cm²). 2 ~500mW / cm 2 The light is incident in an orthogonally linearly polarized manner, with an exposure time of 2 seconds to 20 minutes. An example is: Two coherent ultraviolet polarized beams with a wavelength of 365 nm were used, with a total light intensity of 15 mW / cm². 2 The exposure time is 10 minutes; Two coherent ultraviolet polarized beams with a wavelength of 365 nm were used, with a total light intensity of 500 mW / cm². 2 The exposure time is 2 seconds; Two coherent ultraviolet polarized beams with a wavelength of 365 nm were used, with a total light intensity of 100 mW / cm². 2 The exposure time is 30 seconds; Two coherent ultraviolet polarized beams with a wavelength of 385 nm were used, with a total light intensity of 50 mW / cm². 2 The exposure time is 2 minutes; Two coherent ultraviolet polarized beams with a wavelength of 405 nm were used, with a total light intensity of 200 mW / cm². 2 The exposure time is 5 seconds. Those skilled in the art can make conventional adjustments within the above-mentioned wavelength, total light intensity, and exposure time range according to the photosensitivity of the orientation material, the required grating period, and the diffraction efficiency requirements, and can achieve the desired patterned orientation effect.

[0025] In some embodiments, in step S20, the uniform orientation process involves placing the first substrate under a linearly polarized ultraviolet light source with a wavelength of 365 nm to 405 nm and a light intensity of 1 mW / cm². 2 ~500mW / cm 2 Exposure is performed at a fixed polarization azimuth angle, with an exposure time ranging from 2 seconds to 20 minutes. An example is: An ultraviolet single-polarized light source with a wavelength of 365 nm and a light intensity of 15 mW / cm² is used. 2 The exposure time is 10 minutes; An ultraviolet single-polarized light source with a wavelength of 365 nm and a light intensity of 500 mW / cm² is used. 2 The exposure time is 2 seconds; A single-polarized ultraviolet light source with a wavelength of 365 nm and a light intensity of 100 mW / cm² is used. 2 The exposure time is 30 seconds; An ultraviolet single-polarized light source with a wavelength of 385 nm and a light intensity of 50 mW / cm² was used. 2 The exposure time is 2 minutes; An ultraviolet single-polarized light source with a wavelength of 405 nm and a light intensity of 200 mW / cm² was used. 2 The exposure time is 5 seconds. Those skilled in the art can make conventional adjustments within the above wavelength, light intensity, and exposure time range according to the photosensitivity of the actual orientation material and the required orientation quality, and can achieve the desired uniform orientation effect.

[0026] It is understandable that using a linearly polarized ultraviolet light source to perform uniform orientation treatment with a fixed polarization azimuth angle can form an orientation layer with a uniform orientation direction on the surface of the first substrate, so that the liquid crystal molecules are neatly arranged in a single direction, which is beneficial to improving the overall optical uniformity and working stability of the device.

[0027] In some embodiments, in step S20, the uniform orientation process is performed using a friction orientation method, whereby the orientation layer on the first substrate is subjected to unidirectional friction to obtain a uniform, non-periodic planar orientation. As a specific implementation of this friction orientation method, the photo-orientation layer on the first substrate can be replaced with a polyimide friction orientation layer, and the polyimide layer can be unidirectionally rubbed and oriented using a friction cloth.

[0028] In some embodiments, in step S40, the mass ratio of each component in the reactive mesocrystalline mixture is: Chiral dopant: polymerizable mesocrystalline monomer: photoinitiator: fluorescent dye = (2~2.5): (89~104): (0.1~1.0): (0.1~1.0). It is understood that under the above mass ratio, the reactive mesocrystalline mixture possesses suitable helical twisting ability, good polymerizable crosslinking characteristics, and fluorescence response performance. The components have good compatibility, resulting in uniform orientation and stable structure after film formation, which is beneficial for ensuring the optical performance and luminous efficiency of the device. It also facilitates coating and curing processes. It should be noted that the preparation of the reactive mesocrystalline mixture must be carried out under light-protected conditions; after weighing, each component must be transferred sequentially to a light-protected brown bottle to avoid prepolymerization or component performance drift caused by ambient light.

[0029] In some embodiments, the mixture is further homogenized after preparation: the container containing the mixture is transferred to a glove box with a nitrogen gas integral of ≥95%, heated at a constant temperature of 90°C and continuously stirred until the mixture forms a uniform, clear and transparent isotropic liquid; this ensures that all components are fully dissolved and uniformly dispersed, avoiding problems such as orientation domains, phase separation or uneven solidification caused by local uneven concentration.

[0030] In some embodiments, the filling process is as follows: the liquid crystal cell is placed in a glove box and preheated at 90°C to reduce the viscosity of the mixture and improve the filling stability; then, the homogenized reactive mesocrystalline mixture is injected into the liquid crystal cell using capillary action. During the filling process, air bubbles should be avoided. If necessary, slow spotting, vacuum degassing, or slight heating while filling can be used to reduce the risk of residual air bubbles.

[0031] In some embodiments, in step S40, the polymerizable mesocrystalline monomer is selected from at least two of RM82, RM23, and RM105. It is understood that using at least two of RM82, RM23, and RM105 as polymerizable mesocrystalline monomers can adjust the mesocrystalline phase range, rheological properties, and crosslinking density, improving the flatness, mechanical strength, and weather resistance of the alignment layer, which is beneficial for achieving stable and uniform liquid crystal alignment and excellent optical performance. Of course, the polymerizable mesocrystalline monomer is not limited to the types disclosed in this application; other polymerizable mesocrystalline monomers can also be used, as long as they can achieve ordered arrangement under the action of the alignment layer and can undergo polymerization and crosslinking under ultraviolet light to lock the alignment structure, all are applicable to this application.

[0032] The structural formula of the RM82 is shown in equation (1) below: (1); The structural formula of the RM23 is shown in equation (2) below: (2); The structural formula of the RM105 is shown in equation (3) below: (3); In some embodiments, in step S40, the polymerizable mesocrystalline monomer comprises RM82, RM23, and RM105, and the mass ratio of the three is: RM82:RM23:RM105 = (22-27):(22-27):(45-50). It is understandable that the RM82, RM23, and RM105 compound system with the above mass ratio allows the mesocrystalline mixture to exhibit a stable liquid crystal phase within a suitable temperature range, possessing both suitable fluidity and crosslinking activity. The polymer network formed after curing has a regular orientation and dense structure, which is beneficial for improving the optical uniformity and mechanical stability of the film.

[0033] In some embodiments, in step S40, the fluorescent dye is selected from laser dyes.

[0034] In some embodiments, in step S40, the laser dye is selected from at least one of DCM, DCJ, DCJT, DCJTB, rhodamine-based, coumarin-based, and BODIPY-based laser dyes. It is understood that the selected laser dyes all exhibit excellent compatibility with other raw materials in the reactive mesocrystalline mixture, have a wide tunable emission wavelength range, can adapt to the emission wavelength requirements of different application scenarios, and possess good photothermal stability.

[0035] In some embodiments, in step S40, the photoinitiator is selected from at least one of 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).

[0036] In some embodiments, in step S40, the chiral dopant is selected from R5011 or S5011. Of course, the selection of the chiral dopant is not limited to the chiral dopant disclosed in this application; other chiral dopant may also be used. The chemical structural formulas of R5011 and S5011 are both shown in formula (4) below (without distinguishing between different chiralities): (4); For example, the reactive mesocrystalline mixture comprises RM82, RM23, RM105, R5011, DCM, and Irgacure819, and the mass ratio of each component is: RM82:RM23:RM105:R5011:DCM:Irgacure819=24.4:24.4:47.9:2.2:0.3:0.8.

[0037] In some embodiments, in step S50, the cooling orientation is achieved by cooling to 40°C to 60°C at a rate of 0.1°C / min to 1°C / min to induce the formation of a bulk orientation structure. It is understood that a slow cooling rate of 0.1°C / min to 1°C / min to 40°C to 60°C provides sufficient molecular relaxation and alignment time for the reactive mesocrystalline mixture, promoting the orderly arrangement of molecules within the system, stabilizing the formation of a bulk orientation structure, and ensuring the orientation uniformity and structural regularity of the grating device.

[0038] In some embodiments, in step S50, the ultraviolet curing is performed at a temperature of 40°C to 60°C using ultraviolet light with a wavelength of 365nm to 405nm at a concentration of 1mW / cm². 2 ~500mW / cm 2 Irradiate with light of high intensity for 2 seconds to 10 minutes. Example: Using ultraviolet light with a wavelength of 385nm at 1mW / cm 2 Irradiate with light intensity for 10 minutes; Using ultraviolet light with a wavelength of 385nm at 500mW / cm 2 Irradiate with light intensity for 2 seconds; Using ultraviolet light with a wavelength of 365nm at 300mW / cm2 Irradiation with light intensity for 30 seconds; those skilled in the art can make conventional adjustments within the above-mentioned temperature, wavelength, light intensity, and time range according to the composition of the reactive mesocrystalline mixture and the required degree of cross-linking, all of which can cause the reactive mesocrystalline mixture to undergo polymerization and cross-linking, and lock the bulk phase orientation structure to form a grating device. It is understood that the above-mentioned ultraviolet curing conditions can cause the reactive mesocrystalline mixture to undergo rapid and sufficient polymerization and cross-linking without destroying the already formed orientation structure, effectively locking the bulk phase micro-orientation, and ultimately obtaining a grating device with stable structure and reliable optical performance.

[0039] In some embodiments, step S10, before the alignment layer is prepared, further includes surface pretreatment of the first substrate and the second substrate. The surface pretreatment includes surface cleaning and surface activation of the first and second substrates. It is understood that surface cleaning and activation of the first and second substrates before alignment layer preparation can remove impurities and contaminants from the substrate surfaces, improve surface energy and wettability, which is beneficial for the uniform formation and firm adhesion of the subsequent alignment layer, thereby improving the overall stability and lifespan of the device.

[0040] In some embodiments, the surface pretreatment is as follows: two ITO glass substrates are selected as the first substrate and the second substrate, and are placed in isopropanol, anhydrous ethanol and deionized water for ultrasonic cleaning respectively. The ultrasonic time for each solvent is 10 to 20 minutes (preferably 15 minutes for each solvent). After cleaning, nitrogen gas is blown or clean hot air is used for drying to remove organic contaminants, particulate impurities and adsorbed water film on the substrate surface, so as to ensure the cleanliness of the substrate surface and reduce the risk of pinholes, shrinkage cavities or local desorption in the subsequent alignment layer.

[0041] In some embodiments, the surface activation treatment is: to perform plasma treatment on the cleaned ITO glass substrate for 5 to 15 minutes (preferably 10 minutes) to improve the surface energy and wettability of the ITO glass substrate, improve the spreadability and film uniformity of the photoalignment agent, and help improve the alignment anchoring consistency and the overall stability of the device.

[0042] In some embodiments, in step S10, the preparation of the alignment layer includes: spin-coating a photoalignment agent (e.g., SD-1 or bright yellow) onto the surfaces of the first and second substrates respectively, with a spin-coating speed of 2500 rpm to 3500 rpm and a spin-coating time of 30 s to 60 s (preferably with a spin-coating speed of 3000 rpm and a spin-coating time of 40 s); after spin-coating, pre-baking the substrates on a hot stage at 80°C to 100°C for 4 to 6 minutes (preferably pre-baking on a hot stage at 90°C for 5 minutes) to fully remove the solvent in the photoalignment agent, and finally obtaining a photoalignment layer with uniform thickness and dense structure, providing a stable substrate for subsequent alignment processing and ordered molecular arrangement, and ensuring the consistency and reliability of the optical performance of the device. The photoalignment agent SD-1 has the following structural formula (5): (5).

[0043] In some implementations, to ensure process repeatability, the alignment agent solution can be filtered with a 0.22μm PTFE filter membrane before spin coating, and the photoalignment agent solution can be stored away from light. The spin coating process is carried out in a dust-free and dry environment to reduce the impact of particulate impurities and moisture on the film quality of the photoalignment layer, and improve the uniformity of the alignment layer and the stability of the process.

[0044] In some embodiments, step S30 includes encapsulating two substrates with an encapsulating adhesive to form a liquid crystal cell. The encapsulating adhesive contains a spacer medium, which is silica space powder. It is understood that adding silica space powder as a spacer medium to the encapsulating adhesive allows for precise control of the spacing between the two substrates, ensuring uniform and stable liquid crystal cell thickness, and providing reliable assurance for the bandwidth, diffraction efficiency, and optical uniformity of the bulk grating. Simultaneously, silica space powder possesses good mechanical stability and chemical inertness, which helps improve the strength of the encapsulation structure and prevents deformation or thickness shift of the liquid crystal cell during subsequent cooling alignment, UV curing, and other processes, providing structural support for the stable formation of the bulk alignment structure.

[0045] In some embodiments, the particle size of the silica space powder is 10μm to 14μm (preferably 12μm); the mass percentage content of the silica space powder in the encapsulating adhesive is 0.3% to 1% (preferably 0.5%).

[0046] In some embodiments, after the liquid crystal cell is assembled, the thickness of the liquid crystal cell is measured and verified: a spectral thickness measurement system is used to detect the thickness at multiple points of the liquid crystal cell, and the average value of the multi-point measurement is taken as the actual thickness of the liquid crystal cell to ensure that the thickness of the liquid crystal cell is consistent with the design value, thereby ensuring the stable and reliable performance of the volume grating.

[0047] Secondly, this application provides a chiral nematic bulk grating, which is prepared by the above-described method; the bulk grating includes a first substrate, a second substrate, and a liquid crystal polymer network layer disposed opposite to each other; The first substrate has a uniform non-periodic planar alignment layer on its inner side, and the second substrate has a spatially periodic alignment layer on its inner side. The liquid crystal polymer network layer forms a three-dimensional periodic volume grating structure under asymmetric alignment boundary conditions.

[0048] The following is in conjunction with the appendix Figure 1 This application provides a detailed description of a chiral nematic phase grating based on an asymmetric orientation template and its fabrication method through specific embodiments and application scenarios. Example 1:

[0049] This application provides a method for fabricating a chiral nematic phase grating based on an asymmetric orientation template, comprising the following steps: Step S10: Substrate Processing Step S101: Surface cleaning treatment. Select two ITO glass substrates as the first substrate and the second substrate, and place them in isopropanol, anhydrous ethanol and deionized water for ultrasonic cleaning in sequence. The ultrasonic time for each solvent is 15 minutes. After cleaning, use nitrogen to blow dry to avoid water stains. Step S102: Surface activation treatment, the first and second substrates after surface cleaning are subjected to plasma treatment for 10 minutes; Step S103: Prepare an alignment layer. An alignment layer is prepared on the opposite surfaces of the first substrate and the second substrate. The alignment layer uses photoalignment agent SD-1 and is formed by spin coating. The spin coating parameters are 3000 rpm and 40 seconds. After spin coating, it is pre-baked at 90°C for 5 minutes. Before spin coating, the photoaligning agent SD-1 was filtered (using a 0.22μm PTFE membrane) and stored away from light; the spin coating environment required to be dust-free and dry was to reduce the impact of particles and moisture on the alignment layer. Step S20: Orientation Processing Step S201: Perform a uniform orientation process on the orientation layer of the first substrate to give it a uniform, non-periodic planar orientation. The specific operation is as follows: The first substrate was horizontally fixed on a dust-free, shockproof exposure stage to isolate it from stray ambient light; a single-polarized ultraviolet light source (wavelength 365 nm, light intensity 15 mW / cm²) was used. 2 The polarization azimuth angle is set to 0°, and the first substrate alignment layer surface is perpendicularly incident and continuously and uniformly exposed for 10 minutes. During the entire exposure process, the first substrate has no displacement and no temperature fluctuation, so that the alignment layer forms a uniform planar easy-alignment axis that is continuous throughout the entire domain and has no spatial variation.

[0050] Step S202: Pattern the orientation layer of the second substrate to give it a spatially periodic orientation distribution. The specific operation is as follows: The second substrate was fixed to the same source anti-vibration interference optical path platform, and two coherent ultraviolet polarized beams (both wavelength 365nm, total intensity 15 mW / cm²) were used. 2 Orthogonally linearly polarized incident light is used; the angle between the two coherent beams is adjusted to form stable sinusoidal periodic polarized interference fringes on the surface of the alignment layer, the spatial period of which is determined by the angle between the two coherent beams; utilizing the polarization sensitivity of the optical alignment material, the easy alignment axis of the alignment layer is induced to change cyclically with the interference polarization state in a micrometer-scale spatial period, and the exposure steady state lasts for 10 minutes; the alignment period can be precisely controlled by finely adjusting the optical path angle to adapt to the needs of different band volume gratings.

[0051] This creates asymmetric orientation boundary conditions between the first and second substrates, forming an asymmetric grating orientation template. Step S30: Assemble the LCD cell The first and second substrates, after being processed in step S20 above, are aligned and assembled with their alignment layers facing each other. A sealing frame is formed around the substrates using UV-curable encapsulant. A spacer medium (silica space powder with a particle size of 12μm) is added to the encapsulant to control the cell thickness, wherein the weight percentage of the silica space powder is 0.5wt%. The encapsulant is used to seal and form a liquid crystal cell with a receiving space and a filling port. After assembly, the cell thickness of the liquid crystal cell is measured at multiple points and the average value is taken as the final thickness to ensure batch-to-batch consistency.

[0052] Step S40: Injection of reactive mesocrystalline mixture Step S401: Prepare a reactive mesocrystalline mixture, wherein the mass ratio of each component in the reactive mesocrystalline mixture is: Chiral dopant: polymerizable mesocrystalline monomer: photoinitiator: fluorescent dye = 2.2: 96.7: 0.8: 0.3; Among them, the polymerizable mesocrystalline monomers include RM82, RM23 and RM105, and the mass ratio of the three is RM82:RM23:RM105=24.4:24.4:47.9; The chiral dopant used is R5011; The fluorescent dye used is DCM; The photoinitiator used was Irgacure 819.

[0053] After weighing, transfer each component sequentially to a light-proof brown bottle to avoid prepolymerization or performance drift caused by ambient light. Mix the components in a nitrogen glove box and heat and stir to homogenize. The nitrogen gas volume in the glove box should be greater than 95%, and the mixture should be heated at a constant temperature of 90°C with continuous stirring until the reactive mesocrystalline mixture presents a uniform, clear, and transparent isotropic liquid state.

[0054] Step S402: Pouring and Curing. The liquid crystal cell is placed in a glove box and preheated at 90°C to reduce the viscosity of the reactive mesocrystalline mixture and improve pouring stability. Then, the uniformly stirred reactive mesocrystalline mixture is injected into the liquid crystal cell using capillary action. Air bubbles should be avoided during pouring; if necessary, slow spotting, vacuum degassing, or gentle heating while pouring can be used to reduce the risk of residual air bubbles.

[0055] Step S50: Cooling orientation induction and UV curing Step S501: Cooling orientation induction. After the infusion is completed, the temperature of the liquid crystal cell is reduced to 50°C at a cooling rate of 0.4°C / min. During this process, the reactive mesocrystalline mixture undergoes orientation rearrangement and bulk structure self-organization under the constraint of "uniform anchoring boundary of the first substrate + patterned anchoring boundary of the second substrate", forming a stable spatial periodic orientation structure, i.e. the precursor structure of the PVG bulk grating. Step S502: UV curing. The liquid crystal cell that has undergone orientation induction is placed in a UV light source at 50°C and a wavelength of 385nm, with a UV intensity of 10mW / cm². 2 The light intensity is irradiated for 5 minutes to cure the reactive mesocrystalline system, causing it to polymerize and crosslink, and locking the bulk phase orientation structure to form a stable chiral nematic grating. Example 2:

[0056] The difference between this embodiment and Embodiment 1 is that: In step S103: the first substrate orientation layer material is polyimide (PI), which is formed by spin coating with spin coating parameters of 3000 rpm and 40 s. After spin coating, it is pre-baked at 90°C for 5 minutes. In step S201: The alignment layer of the first substrate undergoes a uniform alignment treatment to achieve a uniform, non-periodic planar alignment. In this embodiment, the alignment layer of the first substrate achieves uniform alignment through unidirectional rubbing to simplify the exposure equipment, replacing the SD-1 photoalignment layer with a common polyimide (PI) rubbing alignment layer. The specific operation is as follows: The friction cloth is made of rayon velvet, the friction roller rotates at 1200 rpm, the substrate conveying speed is 1 meter / minute, and the friction depth is 0.3 mm. It should be noted that these parameters are merely examples, and those skilled in the art can make routine adjustments based on the alignment film material and equipment conditions. Furthermore, the uniform, aperiodic planar alignment obtained through friction alignment allows for a pretilt angle of approximately 0–2°, which has no substantial impact on the diffraction efficiency and polarization selectivity of the chiral nematic grating, and is equivalent to the optical alignment effect of Example 1. Compared to the optical alignment of Example 1, the friction alignment equipment is simpler and the process is more mature, completing the alignment process within seconds, which is beneficial for improving production cycle time, but it requires higher cleanliness. The other steps are the same as in Example 1, and a stable chiral nematic phase grating is finally obtained. Example 3:

[0057] The difference between this embodiment and Embodiment 1 is that: In step S202: The alignment layer of the second substrate is patterned to achieve a spatially periodic alignment distribution. In this embodiment, the polarization holographic interferometry exposure in Example 1 is replaced with scanning direct-write exposure. The specific operation is as follows: The polarization holographic interference exposure of the SD-1 optical alignment layer of the second substrate was replaced with scanning direct writing exposure. Scanning direct writing exposure uses a pulsed laser with a wavelength of 365 nm, a laser power of 50 mW, a focused spot diameter of 2 μm, a scanning speed of 10 mm / s, and linear polarization perpendicular to the scanning direction. Based on the required grating period, the corresponding scanning path spacing is set to 1.5 μm, forming a spatially periodic alignment distribution on the substrate. Compared with the polarization holographic interference exposure in Example 1, scanning direct writing exposure eliminates the need for masks or complex optical paths, allowing direct programming control of the alignment pattern to achieve grating structures with arbitrary periods and arbitrary orientation angles, significantly improving the freedom of pattern design. The rest is the same as in Example 1, and a stable chiral nematic phase grating is finally obtained. Example 4:

[0058] The difference between this embodiment and Embodiment 1 is that: In step S202: The alignment layer of the second substrate is patterned to achieve a spatially periodic orientation distribution. In this embodiment, the polarization holographic interference exposure in Example 1 is replaced with mask-assisted exposure. The specific operation is as follows: The polarization holographic interference exposure of the SD-1 optical alignment layer of the second substrate is replaced with mask-assisted exposure. Specifically, a quartz substrate chromium mask is used, on which a pattern with the required period and duty cycle is formed (e.g., a wire grid structure with a period of 1.5 μm and a duty cycle of 1:1, but those skilled in the art can flexibly design according to the target grating period, which is not limited to the technical parameters of this invention). The exposure light source is a 365 nm ultraviolet LED lamp with a power density of 20 mW / cm². 2 The exposure time was 2 minutes, and the cumulative exposure dose was 2.4 J / cm². 2 During exposure, the mask is in close contact with the substrate to ensure pattern transfer accuracy. Compared with the polarization holographic interference exposure in Example 1, the mask-assisted exposure equipment has lower cost, a wider process window, is suitable for mass production, and does not require a complex optical path alignment system. The rest is the same as in Example 1, and a stable chiral nematic phase grating is finally obtained. Example 5:

[0059] The difference between this embodiment and Embodiment 1 is that in step S401, when preparing the reactive mesocrystalline mixture, the mass ratio of each component is: Chiral dopant: polymerizable mesocrystalline monomer: photoinitiator: fluorescent dye = 2:89:0.1:0.5.

[0060] The polymerizable mesocrystalline monomers include RM82, RM23, and RM105, and the mass ratio of the three is as follows: RM82:RM23:RM105 = 22:22:45; Replace R5011 with S5011; Replace the photoinitiator with Irgacure 651; The rest is the same as in Example 1, and a stable chiral nematic phase grating is finally obtained. Example 6:

[0061] The difference between this embodiment and Embodiment 1 is that in step S401, when preparing the reactive mesocrystalline mixture, the mass ratio of each component is: Chiral dopant: polymerizable mesocrystalline monomer: photoinitiator: fluorescent dye = 2.5: 104: 0.5: 1.0.

[0062] The polymerizable mesocrystalline monomers include RM82, RM23, and RM105, and the mass ratio of the three is as follows: RM82:RM23:RM105 = 27:27:50; Replace the photoinitiator with Irgacure 2959; The rest is the same as in Example 1, and a stable chiral nematic phase grating is finally obtained. Example 7:

[0063] The difference between this embodiment and Embodiment 1 is that: Step S201: Perform a uniform orientation process on the orientation layer of the first substrate to give it a uniform, non-periodic planar orientation. The specific operation is as follows: The first substrate was horizontally fixed on a dust-free, shockproof exposure stage to isolate it from stray ambient light; a single-polarized ultraviolet light source (wavelength 365 nm, light intensity 500 mW / cm²) was used. 2 The polarization azimuth angle is set to 0°, and the first substrate alignment layer surface is perpendicularly incident and continuously and uniformly exposed for 2 seconds. During the entire exposure process, the first substrate has no displacement and no temperature fluctuation, so that the alignment layer forms a uniform plane easy-alignment axis that is continuous throughout the entire domain and has no spatial variation. Step S202: Pattern the orientation layer of the second substrate to give it a spatially periodic orientation distribution. The specific operation is as follows: The second substrate was fixed to the same source anti-vibration interference optical path platform, and two beams of coherent ultraviolet polarized light (both wavelength 365nm, total light intensity 500 mW / cm²) were used. 2 Orthogonally linearly polarized incident light; adjusting the angle between the two coherent beams to form stable sinusoidal periodic polarized interference fringes on the surface of the alignment layer, the spatial period of which is determined by the angle between the two coherent beams; utilizing the polarization sensitivity of the optical alignment material, inducing the easy alignment axis of the alignment layer to change cyclically with the interference polarization state at the micrometer level, with the exposure steady state lasting for 5 seconds; the alignment period can be precisely controlled by finely adjusting the optical path angle to adapt to the needs of different band volume gratings; The rest is the same as in Example 1, and a stable chiral nematic phase grating is finally obtained. Example 8:

[0064] The difference between this embodiment and Embodiment 1 is that: Step S501: Cooling orientation induction. After the infusion is completed, the temperature of the liquid crystal cell is reduced to 60°C at a cooling rate of 0.1°C / min. During this process, the reactive mesocrystalline mixture undergoes orientation rearrangement and bulk structure self-organization under the constraint of "uniform anchoring boundary of the first substrate + patterned anchoring boundary of the second substrate", forming a stable spatial periodic orientation structure. Step S502: UV curing. The liquid crystal cell that has undergone orientation induction is placed in a UV light source with a temperature of 60℃ and a wavelength of 385nm, at a concentration of 1mW / cm². 2 The reactive mesocrystalline system is cured by irradiation with light intensity for 10 minutes, which causes polymerization and cross-linking and locks the bulk phase orientation structure. The rest is the same as in Example 1, and a stable chiral nematic phase grating is finally obtained. Example 9:

[0065] The difference between this embodiment and Embodiment 1 is that: Step S501: Cooling orientation induction. After the infusion is completed, the temperature of the liquid crystal cell is reduced to 40°C at a cooling rate of 1°C / min. During this process, the reactive mesocrystalline mixture undergoes orientation rearrangement and bulk structure self-organization under the constraint of "uniform anchoring boundary of the first substrate + patterned anchoring boundary of the second substrate", forming a stable spatial periodic orientation structure. Step S502: UV curing. The liquid crystal cell that has undergone orientation induction is placed in a UV light source with a temperature of 40℃ and a wavelength of 385nm, at a power of 500mW / cm². 2 The light intensity is irradiated for 2 seconds to cure the reactive mesocrystalline system, causing it to polymerize and cross-link and lock the bulk phase orientation structure. The rest is the same as in Example 1, and a stable chiral nematic phase grating is finally obtained.

[0066] II. Experimental Example: 1. First-order diffraction efficiency test Using the chiral nematic phase gratings prepared in Examples 1-6 as experimental samples, diffraction efficiency characterization experiments were carried out to test their diffraction efficiency.

[0067] 1.1 Experimental Methods: This experiment uses a laser light source as the incident light, and a continuous laser with a wavelength of 532 nm is selected as the preferred light source. Environmental parameters are strictly controlled throughout the test, keeping the ambient temperature constant at 25℃ and the relative humidity within the range of 40% to 60%, to eliminate the interference of environmental factors on the test results.

[0068] Specific test steps: After beam expansion and collimation, the laser emitted by the laser is incident perpendicularly (or incident at a preset small angle) onto the test surface of the chiral nematic phase grating sample. The incident light intensity I0 and the first-order diffraction light intensity I1 are measured using a power meter. The first-order diffraction efficiency η is calculated according to the following formula (Ⅰ): (I); In formula (Ⅰ), I0 is the incident light intensity, and I1 is the first-order diffraction light intensity. To ensure the accuracy and repeatability of the test data, each sample was tested in parallel three times. After removing outlier data, the average value was taken as the final first-order diffraction efficiency test result for that sample.

[0069] 1.2 Experimental Results: Tests showed that the chiral nematic phase gratings prepared in Examples 1-6 all exhibited obvious diffraction phenomena, and the first-order diffraction efficiency was relatively high. The test results of the first-order diffraction efficiency are detailed in Table 1. Table 1 Results of First-Order Diffraction Efficiency Test As shown in Table 1, the first-order diffraction efficiencies of Examples 1 to 6 range from 62.1% to 83.4%, all at a relatively high level. Among them, Examples 4 (83.4%) and 5 (80.1%) exhibit the best diffraction efficiencies, indicating that their bulk periodicity modulation capability is more significant. The diffraction efficiencies of Examples 1 to 6 show some process dependence, but overall they can meet the application requirements, indicating that the orientation treatment and photopolymerization process adopted in this application have good compatibility and adjustability.

[0070] The above results show that the chiral nematic phase grating constructed in this application has good bulk phase periodic modulation capability and high optical energy utilization efficiency, which can meet the application requirements of beam separation, wavefront modulation and optical information processing.

[0071] Although specific first-order diffraction efficiency data are not provided for Examples 7-9, testing using the same method confirmed that they all exhibited obvious diffraction phenomena essentially consistent with Examples 1-6, and the first-order diffraction efficiency was within the same order of magnitude (not less than 60%), with no failures or significant degradation caused by process deviations. This demonstrates that the technical solution of this application has good consistency and repeatability under different embodiment conditions.

[0072] 2. Spectral selectivity test Using the chiral nematic phase gratings prepared in Examples 1-3 as experimental samples, their spectral selectivity characteristics were further tested to explore the wavelength modulation and screening performance of the samples.

[0073] 2.1 Experimental Methods: A halogen tungsten lamp or xenon lamp is used as a broadband incident light source. The light emitted from the source is collimated and then incident perpendicularly onto the chiral nematic grating sample. Transmission and reflection spectra are simultaneously acquired using a fiber optic spectrometer. The preferred test wavelength range is 400–800 nm, covering the entire visible light spectrum. During the test, the ambient temperature is maintained at 25℃ and the relative humidity at 40%–60%. The transmittance and reflectance values ​​of each sample at different wavelengths are recorded, and the corresponding center-selective wavelength and full width at half maximum (FWHM) are extracted from the fitted spectral curves to evaluate the spectral selectivity.

[0074] 2.2 Experimental Results Test results are as follows Figure 1As shown. Test results indicate that the chiral nematic bulk gratings prepared in Examples 1-3 exhibit obvious selective reflection peaks or selective diffraction peaks in the visible light band, with good tunability of peak position response. The peak position can be controllably adjusted with changes in chiral agent concentration, liquid crystal ratio, and exposure parameters. Specifically, Sample 1 (465 nm period) corresponds to Example 1, Sample 2 (565 nm period) corresponds to Example 2, and Sample 3 (676 nm period) corresponds to Example 3. The center response wavelengths of the three experimental samples are all located in the range of 450–700 nm, with narrow half-widths and good spectral selectivity. These results demonstrate that the bulk grating prepared in this application possesses excellent wavelength selection capability and tunability.

[0075] 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 chiral nematic phase grating based on an asymmetric orientation template, characterized in that, Includes the following steps: Step S10: Provide a first substrate and a second substrate, and prepare alignment layers on the opposite surfaces of the first substrate and the second substrate respectively; Step S20: Perform a uniform orientation process on the orientation layer of the first substrate to give it a uniform non-periodic planar orientation; The orientation layer of the second substrate is patterned to give it a spatially periodic orientation distribution. This creates asymmetric orientation boundary conditions between the first and second substrates, forming an asymmetric grating orientation template. Step S30: The first substrate and the second substrate are aligned and assembled with the alignment layers facing each other, and sealed with sealant to form a liquid crystal cell with a receiving space and an injection port; Step S40: At a temperature higher than the clearing point of the reactive mesocrystalline mixture, a reactive mesocrystalline mixture containing a chiral dopant, a polymerizable mesocrystalline monomer, a photoinitiator, and a fluorescent dye is poured into the liquid crystal cell; Step S50: After the infusion is completed, the body phase orientation structure is formed by cooling, and then ultraviolet light curing is performed to form a stable chiral nematic phase grating.

2. The method for fabricating a chiral nematic phase grating based on an asymmetric orientation template according to claim 1, characterized in that, In step S20, the patterning orientation process employs polarization holographic interference exposure, scanning direct writing exposure, or mask-assisted exposure, and the exposure time is 2 seconds to 20 minutes. And / or, in step S20, the uniform orientation process is performed in one of the following ways: Method 1: Place the first substrate under a linearly polarized ultraviolet light source and expose it with a fixed polarization azimuth angle for 2 seconds to 20 minutes; Method 2: Use the friction orientation method to perform unidirectional friction treatment on the orientation layer on the first substrate to obtain a uniform non-periodic planar orientation.

3. The method for fabricating a chiral nematic phase grating based on an asymmetric orientation template according to claim 1, characterized in that, In step S40, the mass ratio of each component in the reactive mesocrystalline mixture is: Chiral dopant: polymerizable mesocrystalline monomer: photoinitiator: fluorescent dye = (2~2.5): (89~104): (0.1~1.0): (0.1~1.0).

4. The method for fabricating a chiral nematic phase grating based on an asymmetric orientation template according to claim 3, characterized in that, In step S40, the polymerizable mesocrystalline monomer is selected from at least two of RM82, RM23 and RM105; And / or, in step S40, the fluorescent dye is selected from laser dyes.

5. The method for fabricating a chiral nematic phase grating based on an asymmetric orientation template according to claim 4, characterized in that, In step S40, the polymerizable mesocrystalline monomer comprises RM82, RM23, and RM105, and the mass ratio of the three is: RM82:RM23:RM105=(22~27):(22~27):(45~50).

6. The method for fabricating a chiral nematic phase grating based on an asymmetric orientation template according to claim 4, characterized in that, In step S40, the laser dye is selected from at least one of DCM, DCJ, DCJT, DCJTB, rhodamine, coumarin, and BODIPY laser dyes.

7. The method for fabricating a chiral nematic phase grating based on an asymmetric orientation template according to any one of claims 1 to 6, characterized in that, In step S40, the photoinitiator is selected from at least one of Irgacure 819, Irgacure 651, Irgacure 2959 and Irgacure 369; And / or, in step S40, the chiral dopant is selected from R5011 or S5011.

8. The method for fabricating a chiral nematic phase grating based on an asymmetric orientation template according to any one of claims 1 to 6, characterized in that, In step S50, the cooling-induced bulk phase orientation structure formation is achieved by cooling to 40°C to 60°C at a rate of 0.1°C / min to 1°C / min to induce the formation of the bulk phase orientation structure. And / or, in step S50, the ultraviolet curing is performed at a temperature of 40℃~60℃, using ultraviolet light with a wavelength of 365nm~405nm at a frequency of 1mW / cm². 2 ~500mW / cm 2 Irradiation with light intensity for 2 seconds to 10 minutes causes the reactive mesocrystalline mixture to polymerize and crosslink, locking the bulk phase orientation structure to form a grating device.

9. The method for fabricating a chiral nematic phase grating based on an asymmetric orientation template according to any one of claims 1 to 6, characterized in that, In step S10, before the alignment layer is prepared, the first substrate and the second substrate are subjected to surface pretreatment, which includes surface cleaning and surface activation treatment of the first substrate and the second substrate. And / or, in step S10, the preparation of the alignment layer includes: spin-coating a photoalignment agent onto the surfaces of the first substrate and the second substrate respectively, and pre-baking after spin-coating to obtain a uniform and dense photoalignment layer.

10. A chiral nematic phase grating, characterized in that, The bulk grating is prepared by the preparation method according to any one of claims 1 to 9; the bulk grating comprises a first substrate, a second substrate, and a liquid crystal polymer network layer disposed opposite to each other; The first substrate has a uniform non-periodic planar alignment layer on its inner side, and the second substrate has a spatially periodic alignment layer on its inner side. The liquid crystal polymer network layer forms a three-dimensional periodic volume grating structure under asymmetric alignment boundary conditions.

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