Ar near-eye display system based on coupling of resin waveguide and volume holographic optical element

Abstract

The application discloses an AR near-eye display system based on coupling of a resin waveguide and a volume holographic optical element, and belongs to the technical field of augmented reality near-eye display. In view of the problems of the existing AR display system, such as large weight of glass waveguide, high mass production cost, low light efficiency, serious crosstalk and easy delamination of resin and volume holographic layer, the application adopts a resin waveguide module formed by injection molding of cyclic olefin copolymer or polymethyl methacrylate, and forms a chemical bonding interface on the surface of the resin waveguide module through an in-situ co-curing process, and records a liquid crystal type volume holographic grating as a light control module; the light control module comprises three in-coupling volume holographic gratings corresponding to red light, green light and blue light respectively, grating periods of the three gratings satisfy corresponding Bragg conditions respectively, and polarization-independent diffraction is realized by optimizing a liquid crystal pre-tilt angle. The system is mainly used for light path integration and mass production manufacturing of augmented reality glasses or head-mounted near-eye display equipment.

Description

Technical Field

[0001] This invention relates to the field of augmented reality near-eye display technology. More specifically, this invention relates to an AR near-eye display system based on the coupling of a resin waveguide and a volume holographic optical element. Background Technology

[0002] In the field of augmented reality near-eye display technology, miniaturization of optical paths, maximization of optical efficiency, and controllable mass production costs have always been major challenges facing the industry. Existing technologies have several shortcomings in the combination of waveguide materials and optical coupling elements used to transmit image light, limiting further development of AR display devices in terms of lightweight design, image quality, and large-scale production.

[0003] In terms of waveguide substrates, traditional solutions often use optical glass, such as BK7. These materials have a high density, typically reaching 2.5 g / cm³. 3 The above factors result in a relatively large weight for a single lens, making it difficult to meet the lightweight requirements for prolonged wear. Furthermore, the manufacturing process of glass waveguides is complex, requiring cold processing steps such as grinding and polishing, leading to low material utilization and hindering mass production through efficient methods like injection molding, resulting in high manufacturing costs per unit. In addition, while the pure volume holographic waveguide solution utilizes the optical properties of volume holography, the photosensitive polymer material it relies on has low mechanical strength, making it unsuitable as a standalone light carrier. In practical applications, it is susceptible to mechanical stress, limiting the reliability and structural stability of the device.

[0004] In terms of optical coupling elements, surface-embossed gratings are formed into periodic structures through etching, but their diffraction efficiency is usually low and they lack Bragg selectivity, which makes it easy for light of different angles or wavelengths to generate crosstalk, resulting in obvious stray light and affecting the purity of the displayed image. Although the pure volume holographic waveguide solution has Bragg selectivity, its fabrication process relies on thick-layer exposure, resulting in high replication costs, and the material itself is difficult to support the waveguide structure independently, often requiring composite use with other substrates.

[0005] When combining resin-based waveguides with volume holographic optical control elements, the interfacial bonding between the two becomes a critical challenge. The coefficients of thermal expansion of resin materials (such as polymethyl methacrylate) and volume holographic materials differ significantly, leading to thermal stress at the interface under varying temperatures. Traditional bonding processes often use UV-curing adhesives, but due to the mismatch in thermal expansion coefficients, delamination easily occurs at the interface, affecting product lifespan and optical stability. The root cause of this problem lies in the inherent differences in the thermodynamic properties of the two materials and the difficulty of forming sufficiently strong chemical bonds with existing bonding processes. Physical adhesion alone cannot withstand the temperature cycling and mechanical stresses of long-term use.

[0006] In multi-wavelength displays, due to the Bragg wavelength selectivity of volume holographic elements, if the grating parameters are not optimized for each wavelength of the three primary color light sources (red, green, and blue), the diffraction efficiency of different wavelengths will vary significantly, leading to an imbalance in overall light efficiency and causing color casts in the image. This problem is particularly prominent when using multi-channel information displays, as it is difficult to guarantee the brightness consistency between channels.

[0007] Regarding polarization characteristics, most volume holographic elements are quite sensitive to the polarization state of the incident light, and there is a significant difference in diffraction efficiency between s-polarized light and p-polarized light. If the polarization response is not specifically designed, a considerable proportion of the light energy in the system will be lost due to polarization mismatch, further reducing the overall optical efficiency.

[0008] In addressing these issues, the industry has attempted various solutions. For instance, improving the adhesive formulation to alleviate stress caused by differences in thermal expansion coefficients has proven insufficient to fundamentally resolve delamination. Adjusting the thickness of the volume holographic material and the exposure process has improved multi-wavelength optical efficiency, but this has increased replication costs and process complexity. Introducing additional polarization conversion elements to reduce polarization sensitivity has increased system size and optical path complexity. These attempts all involve trade-offs between material selection, process complexity, optical performance, and mass production feasibility, making it difficult to simultaneously meet the multiple requirements of lightweight design, high optical efficiency, high reliability, and low cost. Summary of the Invention

[0009] One object of the present invention is to solve at least the above-mentioned problems and to provide at least the advantages that will be described later.

[0010] Another objective of this invention is to provide an AR near-eye display system based on the coupling of resin waveguides and volume holographic optical elements. This system aims to solve the problems of weight and cost caused by the high density of existing glass waveguides and their inability to be mass-produced through injection molding, the interface delamination problem caused by the difference in thermal expansion coefficients between the resin waveguide and the volume holographic layer, the problem of light efficiency imbalance and color distortion caused by the lack of optimization of the wavelength selectivity of the volume holographic element when multiple wavelengths are coupled, and the problem of light efficiency loss caused by the sensitivity of the volume holographic element to polarization state.

[0011] To achieve these objectives and other advantages of the present invention, an AR near-eye display system based on the coupling of a resin waveguide and a volume holographic optical element is provided, comprising: The resin waveguide module, injection molded from cyclic olefin copolymer or polymethyl methacrylate, is used to transmit image light. The resin waveguide module has a thickness of 0.8~1.2mm, a refractive index of 1.50~1.55, and a density of 1.05~1.15g / cm³. 3 ; A volume holographic optical control module includes at least one input volume holographic grating and one output volume holographic grating. The volume holographic grating is a liquid crystal volume holographic grating and is recorded on the surface of a resin waveguide module. A chemical bonding interface is formed between the volume holographic optical control module and the resin waveguide module through an in-situ co-curing process. The in-situ co-curing process is as follows: a liquid crystal volume holographic material is coated on the surface of the resin waveguide module, a volume holographic grating is formed by coherent laser interference exposure, and then a thermal curing treatment is performed to form a chemical bond between the volume holographic material and the resin waveguide module. The volume holographic light control module includes three coupled volume holographic gratings corresponding to red, green, and blue light, respectively, with grating periods satisfying the following: , , ; Where λ R =635nm, λ G =532nm, λ B =450nm, θ i The angle between the incident light and the grating surface ranges from 17.5° to 20.5°. The polarization response of the volume holographic light control module achieves polarization-independent diffraction by optimizing the liquid crystal pretilt angle.

[0012] Preferably, in the AR near-eye display system based on the coupling of resin waveguide and volume holographic optical element, the coupled volume holographic grating records N Bragg gratings at different angles, where N≥5, and each angle Bragg grating corresponds to a different position on the exit pupil plane; the diffraction efficiency distribution η(θ) of each angle Bragg grating... j The objective function is determined through optimization. ; Where σ L (η) is the standard deviation of luminance within the exit pupil plane, λ reg R(η) is the regularization coefficient, and R(η) is the smoothness constraint term of the diffraction efficiency distribution. Luminance standard deviation σ L Calculated using the following formula: ; Where M is the number of sampling points within the exit pupil plane, and L k Let μ be the brightness value of the k-th sampling point. L Let M be the average brightness of the M sampling points.

[0013] Preferably, in the AR near-eye display system based on the coupling of resin waveguides and volume holographic optical elements, the spatial frequency K of the Bragg grating at each angle is... j satisfy: ; Among them Λ jLet λ be the period of the j-th angle grating, and λ be the wavelength of the incident light; the period Λ of each angle grating j In Λ min To Λ max Variation within the range, Λ min =λ / (2sinθ max ), Λ max =λ / (2·sinθ min ).

[0014] Preferably, in the AR near-eye display system based on the coupling of resin waveguide and volume holographic optical element, the volume holographic light control module further includes a gradient thickness grating layer. The gradient thickness grating layer is disposed on the surface of the resin waveguide module. The gradient thickness grating layer is formed by inkjet printing of liquid crystal solutions of different concentrations, wherein the high concentration liquid crystal solution corresponds to the region with high diffraction efficiency and the low concentration liquid crystal solution corresponds to the region with low diffraction efficiency. The thickness of the gradient thickness grating layer is 50~500nm.

[0015] Preferably, the AR near-eye display system based on the coupling of resin waveguide and volume holographic optical element includes the following steps in the preparation of the gradient thickness grating layer: preparing a liquid crystal solution with a mass fraction of 2-14%; coating an alignment dye solution onto the surface of the resin waveguide module to form an alignment film; printing liquid crystal solutions of different concentrations onto the surface of the alignment film according to a preset pattern by inkjet printing, wherein the preset pattern is determined according to a diffraction efficiency simulation model; and forming a gradient thickness grating structure after drying and curing.

[0016] Preferably, in the AR near-eye display system based on the coupling of resin waveguide and volume holographic optical element, the thickness distribution h(x,y) of the gradient thickness grating layer and the diffraction efficiency distribution η(θ) of the Bragg grating at each angle are... j The following joint optimization model was used to determine: ; Where η target For the target diffraction efficiency distribution, h target Let α and β represent the target thickness distribution, and α and β be the weighting coefficients.

[0017] Preferably, the AR near-eye display system based on the coupling of resin waveguide and volume holographic optical element includes a resin waveguide module comprising a first waveguide and a second waveguide; the volume holographic optical control module further includes a folded volume holographic grating disposed between the first waveguide and the second waveguide.

[0018] Preferably, in the AR near-eye display system based on the coupling of resin waveguide and volume holographic optical element, the Bragg diffraction condition of the folded volume holographic grating satisfies: ; Among them Λ foldFor the period of the folded holographic grating, i fold Let be the angle between the incident light and the grating surface. l The incident light wavelength is denoted by 1; a folded holographic grating is disposed between the first waveguide and the second waveguide to couple the image light from the first waveguide to the second waveguide.

[0019] Preferably, the AR near-eye display system based on the coupling of resin waveguide and volume holographic optical element comprises a liquid crystal-type volume holographic material including a liquid crystal material, a photoinitiator system, a chiral agent, and a mixed solvent; the liquid crystal material is RM257, the mass fraction of the photoinitiator system is 1-2%, the mass fraction of the chiral agent is 0.01-0.05%, and the mixed solvent is a mixture of PGMEA, cyclohexanone, and butyrolactone, with a mass fraction of 83-85%; the liquid crystal material, photoinitiator, chiral agent, and mixed solvent are mixed under light-protected conditions and then filtered through a filter membrane with a pore size of 0.22 micrometers. The photoinitiator system is a compound photoinitiator system, which includes a mixture of camphorquinone and diacylphosphine oxide, or a compound system including a titanocene photoinitiator and isopropylthioxanone photosensitizer.

[0020] Preferably, in the AR near-eye display system based on the coupling of resin waveguide and volume holographic optical element, the surface of the resin waveguide module is further provided with an alignment dye layer. The alignment dye layer is used to induce the directional alignment of liquid crystal molecules in the liquid crystal volume holographic material. The material of the alignment dye layer is any one of BY, SD1, or polyimide. The alignment dye layer is prepared by mixing the alignment dye, auxiliary agent, and DMF at a mass fraction ratio of 0.5~1% under light-protected conditions, filtering the mixture through a filter membrane with a pore size of 0.22 micrometers, and coating it onto the surface of the resin waveguide module to form an alignment film.

[0021] The present invention has at least the following beneficial effects: First, this invention uses a resin waveguide module injection-molded from cyclic olefin copolymers or polymethyl methacrylate, which reduces the density of the waveguide material compared to traditional glass waveguides, thus reducing the overall weight of the AR display system. Furthermore, an in-situ co-curing process is used to directly form a volume holographic grating on the surface of the resin waveguide module, creating a chemically bonded interface between the volume holographic material and the resin waveguide, instead of using traditional UV-curing adhesives. This fundamentally alleviates the interfacial thermal stress caused by the difference in thermal expansion coefficients between the resin and the volume holographic material, reducing the risk of interface delamination under varying temperature conditions. Separate volume holographic gratings are set for red, green, and blue light, with each grating period satisfying the Bragg condition for its corresponding wavelength. This improves the consistency of diffraction efficiency during multi-wavelength coupling and reduces color effect differences and color cast issues caused by the wavelength selectivity of the volume hologram. Meanwhile, by optimizing the liquid crystal pretilt angle of the liquid crystal-type volume holographic material, the diffraction efficiency of the volume holographic grating for s-polarized light and p-polarized light tends to be consistent, which can reduce the influence of the polarization state of the incident light on the system's optical efficiency and help improve the overall light energy utilization rate.

[0022] Secondly, this invention records multiple Bragg gratings at different angles within a coupled-body holographic grating. Each angle grating corresponds to a different position on the exit pupil plane. The diffraction efficiency distribution is optimized using an objective function, with the standard deviation of brightness within the exit pupil plane as the optimization target, and a smoothness constraint term is introduced. This optimization method ensures that the diffraction efficiency of each angle grating maintains a smooth transition while satisfying overall brightness uniformity. This helps avoid additional brightness unevenness or stray light introduced by abrupt changes in local diffraction efficiency, thereby improving the stability and uniformity of image brightness observed by the observer within the eye-tracking range.

[0023] Third, this invention incorporates a gradient-thickness grating layer within the volume holographic light control module. By inkjet printing liquid crystal solutions of varying concentrations, a gradient structure with a thickness ranging from 50 to 500 nm is formed. High-concentration regions correspond to high diffraction efficiency, while low-concentration regions correspond to low diffraction efficiency. This structure allows for precise local control of the diffraction efficiency distribution within the exit pupil plane, compensating for brightness differences caused by waveguide transmission loss or uneven grating diffraction efficiency. Furthermore, the thickness distribution of the gradient-thickness grating layer is collaboratively designed with the diffraction efficiency distribution of Bragg gratings at various angles through a joint optimization model. This facilitates optimal matching of diffraction efficiency and thickness distribution at the system level, improving the overall coordination between exit pupil uniformity and grating diffraction efficiency.

[0024] Fourth, this invention employs a dual-waveguide structure comprising a first waveguide and a second waveguide, with a folded volumetric holographic grating positioned between them. The image light's direction is folded from the first waveguide to the second waveguide through Bragg diffraction of the volumetric holographic grating. This structure can change the propagation direction of the image light while maintaining waveguide transmission efficiency, providing greater design freedom for the spatial layout of AR near-eye display systems. The Bragg diffraction condition of the folded volumetric holographic grating is set according to the incident light wavelength and angle. The angular selectivity of the volumetric holographic element can reduce the coupling of light from non-designed angles, which helps reduce stray light interference during the optical path folding process. Simultaneously, it avoids introducing additional prisms or reflectors, maintaining a lightweight and thin overall system structure.

[0025] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to embodiments, so that those skilled in the art can implement it based on the description.

[0027] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0028] It should be noted that, unless otherwise specified, the experimental methods described in the following implementation plan are all conventional methods, and the reagents and materials described are all commercially available unless otherwise specified.

[0029] This invention provides an AR near-eye display system based on the coupling of a resin waveguide and a volume holographic optical element, comprising: The resin waveguide module, injection molded from cyclic olefin copolymer or polymethyl methacrylate, is used to transmit image light. The resin waveguide module has a thickness of 0.8~1.2mm, a refractive index of 1.50~1.55, and a density of 1.05~1.15g / cm³. 3Cyclic olefin copolymers possess low hygroscopicity, high light transmittance, and good dimensional stability, with a density of approximately 1.02 to 1.05 g / cm³. Polymethyl methacrylate (PMMA) is a common optical plastic with a density of approximately 1.19 g / cm³. Both have significantly lower densities than traditional optical glass, forming the basis for lightweight design. Injection molding can efficiently manufacture waveguide sheets with complex shapes, and the mold precision can be controlled within ±5 micrometers during molding. The thickness of this resin waveguide module can be selected from any value within the range of 0.8 mm to 1.2 mm, such as 0.8 mm, 1.0 mm, or 1.2 mm; its refractive index can be selected from any value within the range of 1.50 to 1.55, such as 1.50, 1.53, or 1.55; and its density is from 1.05 g / cm³ to 1.15 g / cm³, such as 1.05 g / cm³, 1.10 g / cm³, or 1.15 g / cm³. After molding, the flatness of the waveguide surface can be optimized through a hot-pressing process. The hot-pressing temperature can be selected from 100 degrees Celsius to 140 degrees Celsius, for example, 120 degrees Celsius, and the hot-pressing time can be selected from 5 seconds to 15 seconds, for example, 10 seconds, so that the surface roughness Ra value of the waveguide is no greater than 0.1 micrometers. This resin waveguide module serves as the main light transmission layer in the system, and its assembly position is located between the light source module and the volume holographic optical control module. After the image light is emitted from the light source module, it is coupled into the resin waveguide module through the coupled-in volume holographic grating and propagates inside the waveguide in a total internal reflection manner until it reaches the coupled-out volume holographic grating.

[0030] A volume holographic optical control module includes at least one input volume holographic grating and one output volume holographic grating. The volume holographic grating is a liquid crystal-type volume holographic grating, recorded on the surface of a resin waveguide module. A chemical bonding interface is formed between the volume holographic optical control module and the resin waveguide module through an in-situ co-curing process. The in-situ co-curing process involves coating a liquid crystal-type volume holographic material onto the surface of the resin waveguide module, forming a volume holographic grating through coherent laser interference exposure, and then subjecting it to thermal curing to achieve chemical bonding between the volume holographic material and the resin waveguide module. The coating thickness of the liquid crystal-type volume holographic material on the surface of the resin waveguide module can be selected from 20 micrometers to... The material is initially 50 micrometers in diameter. A volume holographic grating is then formed through coherent laser interference exposure. The exposure light source can be a laser with a wavelength of 325 nm, 532 nm, or 633 nm, such as a helium-neon laser or an argon-ion laser. The exposure power can be selected from 5 mW / cm² to 15 mW / cm², for example, 10 mW / cm². After exposure, a thermosetting process is performed. The thermosetting temperature can be selected from 80°C to 120°C, for example, 100°C, and the thermosetting time can be selected from 30 minutes to 90 minutes, for example, 60 minutes, to chemically bond the volume holographic material to the resin waveguide module. The coupled volume holographic grating in the volume holographic optical control module is assembled on the light-emitting side of the light source module, used to diffract the image light into the resin waveguide module. The coupled volume holographic grating is assembled on the side of the resin waveguide module facing the human eye, used to diffract the image light within the waveguide and output it to the human eye.

[0031] The volume holographic light control module includes three coupled volume holographic gratings corresponding to red, green, and blue light, respectively, with grating periods satisfying the following: , , ; Where λ R =635nm, λ G =532nm, λ B =450nm, θ i The angle between the incident light and the grating surface is denoted by Λ, which ranges from 17.5° to 20.5°; the grating period Λ corresponding to the red light is... R The grating period Λ corresponding to green light can be selected from 925 nanometers to approximately 1045 nanometers. G The grating period Λ corresponding to blue light can be selected from 775 nanometers to approximately 876 nanometers. B The wavelength can be selected from 655 nm to approximately 740 nm. Taking red light (635 nm) as an example, a helium-neon laser is used as the light source. The laser beam is split into two beams by a beam splitter. After passing through a reflector, a beam expander, and a collimating lens, interference fringes are formed on the surface of the waveguide coated with material at an angle of approximately 17.7° to 20.1°. The period Λ of the interference fringes is determined by the formula λ = 2Λsinθ, from which Λ can be calculated.R Approximately 925 nanometers. By controlling the exposure time and power (e.g., 10 milliwatts per square centimeter, exposure time 10 seconds), a volume holographic grating corresponding to red light was recorded in the material. Similarly, by changing the exposure wavelength and interference angle, the corresponding green light (532 nanometers, Λ) was recorded. G (≈775 nanometers) and blue light (450 nanometers, Λ) B These three gratings (approximately 655 nanometers) can be spatially separated or superimposed to a certain extent.

[0032] The polarization response of the volume holographic optical control module achieves polarization-independent diffraction by optimizing the liquid crystal pretilt angle. The pretilt angle can be selected from 40 to 50 degrees, for example, 45 degrees, to make the diffraction efficiencies of s-polarized light and p-polarized light more consistent. The liquid crystal-type volume holographic material can include liquid crystal material, photoinitiator, chiral agent, and mixed solvent. The liquid crystal material can be RM257, the photoinitiator can be selected from 1% to 2% by mass, the chiral agent can be selected from 0.01% to 0.05% by mass, and the mixed solvent can be a mixture of propylene glycol methyl ether acetate, cyclohexanone, and butyrolactone, with a mass fraction of 83% to 85%. A feasible ratio is: RM257 14% by mass, photoinitiator 1.5%, chiral agent 0.03%, and mixed solvent 84.47%. After mixing and stirring all components under light-shielded conditions for 30 minutes, the mixture is filtered through a PTFE membrane with a pore size of 0.22 micrometers to remove impurities and obtain a uniform coating solution. An alignment dye layer can also be deposited on the surface of the resin waveguide module. This alignment dye layer is used to induce the directional alignment of liquid crystal molecules in the liquid crystal holographic material. The material of the alignment dye layer can be any of BY, SD1, or polyimide. The alignment dye layer can be prepared by mixing the alignment dye, additives, and DMF at a mass fraction ratio of 0.5% to 1% under light-shielded conditions, filtering through a 0.22-micrometer pore size filter, and coating it onto the surface of the resin waveguide module to form an alignment film. By controlling the polarization state during exposure and subsequent heat treatment conditions, the liquid crystal molecules form a specific orientation within the grating (e.g., a pretilt angle of 45°), thereby making the diffraction efficiencies of s-polarized light and p-polarized light in the grating tend to be consistent.

[0033] The above technical solution systematically solves the problems of weight and cost, delamination between resin and bulk holographic layer, imbalance of multi-wavelength light effect and color deviation, and light effect loss caused by polarization sensitivity in existing AR near-eye display systems by selecting resin waveguide materials and molding processes, constructing in-situ co-curing interfaces, matching the Bragg conditions of the three wavelengths respectively, and optimizing the polarization of the liquid crystal pretilt angle. It achieves a lightweight, highly reliable, color-balanced, and light-efficiency-enhanced AR near-eye display system.

[0034] In another technical solution, the AR near-eye display system based on the coupling of resin waveguide and volume holographic optical element has N Bragg gratings at different angles recorded on the coupled volume holographic grating, where N≥5, and N can be an integer between 5 and 20, such as 5, 10, or 20. Each angle Bragg grating corresponds to a different position on the exit pupil surface. That is, when the incident light reaches the coupled grating at different angles, it will be diffracted by the corresponding angle Bragg grating and output to a specific area on the exit pupil surface. This design expands the beam that originally propagated in a single direction within the waveguide into a beam covering a larger exit pupil area, and the exit pupil size can be expanded to 10 mm by 10 mm. The diffraction efficiency distribution η(θ) of each angle Bragg grating is shown. j The objective function is determined through optimization. ; Where σ L (η) is the standard deviation of luminance within the exit pupil plane, λ reg R(η) is the regularization coefficient, and R(η) is the smoothness constraint term of the diffraction efficiency distribution. Luminance standard deviation σ L Calculated using the following formula: ; Where M is the number of sampling points within the exit pupil plane, and L k Let μ be the brightness value of the k-th sampling point. L Let M be the average brightness of the M sampling points. In actual optimization, the number of sampling points M can be chosen from 100 to 400, for example, 100, 200, or 400 sampling points, evenly distributed within the exit pupil plane. The regularization coefficient λ... reg It can be any value in the range of 0.01 to 0.1, such as 0.01, 0.05, or 0.1, to balance the relationship between brightness uniformity and the smoothness of diffraction efficiency distribution. The smoothness constraint term R(η) can be defined as the sum of the squares of the differences in diffraction efficiencies between adjacent angle gratings, i.e.: ; By solving for the minimum value of this objective function, an optimized diffraction efficiency distribution η(θ) can be obtained. jThis optimization aims to minimize the brightness difference among sampling points within the exit pupil plane while avoiding drastic jumps in diffraction efficiency between adjacent angles. This optimization can be performed using numerical optimization algorithms, such as gradient descent or genetic algorithms. In practical implementation, a model of the waveguide and grating can be pre-built using optical simulation software (such as Zemax or RSoft), with the initial diffraction efficiency distribution input, and the brightness standard deviation iteratively calculated until the objective function converges.

[0035] In the above technical solution, by recording multiple Bragg gratings at different angles in the coupled-body holographic grating, and using an optimization method with the standard deviation of brightness within the exit pupil plane as the objective function to determine the diffraction efficiency distribution of each angle grating, the diffraction efficiency of each angle grating can maintain a smooth transition while satisfying the overall brightness uniformity. This design avoids additional brightness unevenness or stray light introduced by abrupt changes in local diffraction efficiency, ensuring that the image brightness observed by the observer at different exit pupil positions remains highly consistent during eye movement, effectively improving exit pupil uniformity. Simultaneously, the introduction of regularization coefficients and smoothness constraints makes the optimization results more consistent with the diffraction efficiency distribution achievable in actual processes, reducing the fabrication difficulty caused by drastic changes in diffraction efficiency. This technical solution combines resin waveguides, in-situ co-curing, three-wavelength coupled gratings, and polarization-independent design to jointly construct a lightweight, highly reliable, color-balanced, brightness-uniform, and luminous-efficiency enhanced AR near-eye display system.

[0036] In another technical solution, the AR near-eye display system based on the coupling of resin waveguides and volume holographic optical elements has a spatial frequency K of Bragg gratings at each angle. j (spatial frequency K) j This represents the phase change of a grating per unit length, typically expressed in radians per micrometer or nanometer, and satisfies the following: ; This formula shows that different incident angles θ j Corresponding to different spatial frequencies K j That is, corresponding to different grating periods Λ j In practical design, the spatial frequency or period corresponding to each angle grating can be calculated based on the required exit pupil extension angle range.

[0037] Among them Λ j Let θ be the period of the j-th angular grating. j Let λ be the angle between the incident light and the grating surface corresponding to the j-th angle grating, and λ be the wavelength of the incident light; the period Λ of each angle grating is... j In Λ min To Λ max Variation within the range, Λ min =λ / (2sinθ max ), Λmax =λ / (2sinθ min ). θ and θ max These are the minimum and maximum values ​​of the angle between the incident light and the grating surface, respectively, and their values ​​correspond to the angular range of the exit pupil expansion.

[0038] For example, when the incident light wavelength λ is 532 nanometers (green light) and the incident angle range is set to 15 degrees to 30 degrees, θ min =15 degrees, θ max =30 degrees. According to the formula, Λ max =532 / (2×sin15°)=532 / (2×0.2588)≈1028 nanometers, Λ min =532 / (2×sin30°)=532 / (2×0.5)=532 nanometers. That is, within this incident angle range, the grating period needs to vary between 532 nanometers and 1028 nanometers. For red light (635 nanometers) and blue light (450 nanometers), their respective period ranges can be calculated similarly. For example, for red light within the same incident angle range, Λ min =635 / (2×0.5)=635 nanometers, Λ max =635 / (2×0.2588)≈1227 nanometers; blue light is Λ min =450 / (2×0.5) = 450 nanometers, Λ max =450 / (2×0.2588)≈869 nm. By setting the grating period at different angles within the above range, it can be ensured that the Bragg condition is satisfied for each angle grating, thereby achieving effective diffraction of light at different incident angles.

[0039] In actual fabrication, holographic interferometry can be used to record gratings at various angles according to the required period range. For example, for green light (532 nm), to record a grating with a period of 800 nm, the corresponding incident angle θ can be calculated using Bragg's formula: θ = arcsin(λ / (2Λ)) = arcsin(532 / (2×800)) = arcsin(0.3325) ≈ 19.4 degrees. By adjusting the angle between the two laser beams in the interferometry exposure, making half of the angle equal to the incident angle, the grating with the required period can be recorded in the volume holographic material. For gratings with multiple angles, multiple exposures can be used, changing the angle between the two laser beams in each exposure to record gratings with different periods in the same region of the material. The time or energy of each exposure can be appropriately allocated to control the diffraction efficiency of each grating angle and meet the requirements of optimized diffraction efficiency distribution.

[0040] The aforementioned technical solution, by clarifying the mathematical relationship between the spatial frequency and period of Bragg gratings at each angle and defining the boundary conditions for the period variation with the incident angle, provides a clear computational basis for the design of angle-multiplexed volumetric holographic gratings. This constraint ensures that each grating operates within the Bragg diffraction region, avoiding a decrease in diffraction efficiency or an increase in crosstalk under non-Bragg conditions. Furthermore, the method for determining the period range is applicable to independent designs for different wavelengths (red, green, and blue light) and is compatible with three-wavelength coupled gratings. This technical solution, combined with resin waveguides, in-situ co-curing interfaces, three-wavelength coupled gratings, and angle-multiplexed exit pupil expansion and diffraction efficiency optimization, collectively constructs a structurally clear and parameter-controllable AR near-eye display system.

[0041] In another technical solution, the AR near-eye display system based on the coupling of resin waveguide and volume holographic optical element further includes a gradient thickness grating layer in the volume holographic light control module. The gradient thickness grating layer is disposed on the surface of the resin waveguide module and is stacked with the aforementioned volume holographic grating layer formed by interference exposure. The gradient thickness grating layer is formed by inkjet printing of liquid crystal solutions of different concentrations, wherein the high concentration liquid crystal solution corresponds to the region with high diffraction efficiency and the low concentration liquid crystal solution corresponds to the region with low diffraction efficiency. The thickness of the gradient thickness grating layer is 50~500nm.

[0042] The gradient-thickness grating layer and the volume holographic grating are stacked with the gradient layer at the bottom and the volume holographic layer on top. This structure has the advantages of good process compatibility and high optical coordination efficiency. The specific fabrication process is as follows: Step 1: Inkjet printing gradient thickness grating layer On the clean surface of the resin waveguide module, an alignment dye solution (e.g., a DMF solution of SD1, mass fraction 0.5-1%) is first coated and dried to form an alignment film. Then, liquid crystal solutions of different mass fractions are prepared (e.g., RM257 system liquid crystal solutions with mass fractions of 2%, 6%, 10%, and 14%, containing photoinitiators and chiral agents). Based on the preset pattern determined by the diffraction efficiency simulation model, liquid crystal solutions of different concentrations are printed onto corresponding areas on the alignment film surface using an inkjet printer: high-concentration liquid crystal solutions are printed on areas requiring high diffraction efficiency (e.g., the exit pupil center), and low-concentration liquid crystal solutions are printed on areas requiring low diffraction efficiency (e.g., the exit pupil edge). After printing, the surface is preheated at 80°C for 30 seconds to evaporate the solvent, followed by UV curing to form a gradient thickness grating layer with a thickness of 50-500 nm.

[0043] Step 2: Coating the holographic material On the surface of the cured gradient thickness grating layer, a liquid crystal-type volume holographic material (e.g., 14 wt% RM257 liquid crystal, 1.5 wt% photoinitiator, 0.03 wt% chiral agent, and 84.47 wt% mixed solvent) is coated using spin coating or slot coating methods, with the coating thickness controlled between 20 and 50 μm. Since the gradient thickness grating layer is completely cured and extremely thin (≤500 nm), its surface smoothness is good and does not affect the uniform coating of the volume holographic material.

[0044] Step 3: Interference Exposure Recording Holographic Grating The coated sample is placed in the holographic exposure optical path, and a coherent laser (e.g., wavelength 532nm) is used for two-beam interference exposure. An angle-multiplexed Bragg grating (which can contain multiple gratings at different angles, corresponding to the exit pupil expansion) is recorded in the volume holographic material layer. Since the scattering and absorption of the exposure light by the gradient thickness grating layer are negligible, the interference fringes can be clearly recorded in the volume holographic material layer.

[0045] Step 4: Thermal curing to form chemical bonds After exposure, a thermal curing process (e.g., 100℃ × 60 minutes) is performed to form cross-layer chemical bonds between the volume holographic material, the gradient thickness grating layer, and the resin waveguide surface, achieving integrated manufacturing.

[0046] Synergistic mechanism of the two gratings Volume holographic gratings provide Bragg selectivity for angle and wavelength, achieving high diffraction efficiency (≥85%), low crosstalk (≤-35dB), and exit pupil expansion (10mm×10mm). Gradient-thickness grating layers finely control diffraction efficiency at the subwavelength scale through their spatially varying thickness (i.e., varying duty cycle or optical path difference), compensating for local brightness differences caused by waveguide transmission loss, light source inhomogeneity, or inherent efficiency fluctuations of the volume holographic grating.

[0047] In the above technical solution, the thickness of the gradient thickness grating layer can be selected to be any value within the range of 50 nanometers to 500 nanometers, such as 50 nanometers, 200 nanometers, or 500 nanometers. This gradient thickness grating layer is bonded to the surface of the resin waveguide module, and a stable bond is formed through a subsequent curing process. This can compensate for brightness differences caused by waveguide transmission loss or uneven grating diffraction efficiency, and improve color uniformity.

[0048] In another technical solution, the AR near-eye display system based on the coupling of resin waveguide and volume holographic optical element includes the following steps for preparing the gradient thickness grating layer: preparing a liquid crystal solution with a mass fraction of 2-14%; coating an alignment dye solution onto the surface of the resin waveguide module to form an alignment film; printing liquid crystal solutions of different concentrations onto the surface of the alignment film according to a preset pattern using inkjet printing, wherein the preset pattern is determined based on a diffraction efficiency simulation model; and forming a gradient thickness grating structure after drying and curing.

[0049] The fabrication of gradient thickness grating layers includes the following steps: The first step is to prepare liquid crystal solutions with different mass fractions. The liquid crystal material, photoinitiator, chiral agent, and mixed solvent are weighed and mixed in a specific ratio under light-protected conditions. The liquid crystal material can be RM257, the photoinitiator can have a mass fraction of 1% to 2%, the chiral agent can have a mass fraction of 0.01% to 0.05%, and the mixed solvent can be a mixture of propylene glycol methyl ether acetate, cyclohexanone, and butyrolactone, with a mass fraction of 83% to 85%. The mass fraction of the liquid crystal can be selected from multiple gradient values ​​within the range of 2% to 14%, for example, 2%, 4%, 6%, 8%, 10%, and 14%. After mixing and stirring all components under light-protected conditions for 30 minutes, the mixture is filtered using a 0.22-micron PTFE filter membrane to obtain liquid crystal solutions of different concentrations. The filtered solutions are then sealed with aluminum foil and stored at room temperature for later use.

[0050] The second step is to prepare the orientation dye solution. Weigh the orientation dye, auxiliaries, and DMF at a mass fraction ratio of 0.5% to 1% under light-protected conditions, mix for 30 minutes, and then filter using a 0.22-micron pore size polytetrafluoroethylene (PTFE) membrane to obtain the orientation dye solution. The orientation dye can be selected from any of BY, SD1, or polyimide.

[0051] The third step involves coating the surface of the resin waveguide module with an alignment dye solution to form an alignment film. This alignment film is used to induce the directional alignment of liquid crystal molecules in the liquid crystal holographic material.

[0052] The fourth step involves inkjet printing liquid crystal solutions of varying concentrations onto the alignment film surface according to a pre-defined pattern. This pre-defined pattern is determined based on a diffraction efficiency simulation model; specifically, according to the target diffraction efficiency distribution, high-concentration ink is used to print areas with high diffraction efficiency, while low-concentration ink is used to print areas with low diffraction efficiency. During inkjet printing, the number of printing layers can be controlled as needed; for example, multiple layers can be printed to increase the thickness of high-concentration areas, while a single layer can be used to print low-concentration areas.

[0053] The fifth step is drying and curing. First, preheat at 80 degrees Celsius for 30 seconds to evaporate the solvent, then perform UV curing to form a gradient thickness grating structure. UV curing can be performed using a mercury lamp or an LED UV light source, and the curing wavelength can be selected as 365 nanometers.

[0054] The above technical solution can form a gradient thickness grating layer with a thickness varying from 50 nanometers to 500 nanometers on the surface of a resin waveguide module, enabling precise control of diffraction efficiency in different regions. This fabrication method is compatible with in-situ co-curing processes, allowing for the completion of steps such as alignment layer coating, inkjet printing of gradient thickness layers, and holographic interference exposure recording holographic gratings on the same waveguide substrate, achieving integrated manufacturing.

[0055] In another technical solution, the AR near-eye display system based on the coupling of resin waveguide and volume holographic optical element has a thickness distribution h(x,y) of gradient thickness grating layer and a diffraction efficiency distribution η(θ) of Bragg grating at each angle. j The following joint optimization model was used to determine: ; Where h(x,y) represents the thickness of the gradient thickness grating layer at position (x,y) on the surface of the resin waveguide module, in nanometers; η(θ) j ) represents the diffraction efficiency of the Bragg grating at the j-th angle, with a value ranging from 0 to 1; η target The target diffraction efficiency distribution, i.e., the curve of the desired diffraction efficiency as a function of angle or position; h target η represents the target thickness distribution, i.e., the curve showing the desired thickness changing with position; α and β are weighting coefficients used to balance the relative importance of diffraction efficiency optimization and thickness distribution optimization. In practical applications, η... target It can be determined based on optical design specifications, such as the diffraction efficiency values ​​of gratings at various angles corresponding to achieving a brightness uniformity of over 90% within the exit pupil plane. target The thickness can be determined based on process capabilities; for example, inkjet printing can achieve thicknesses ranging from 50 nanometers to 500 nanometers, and thickness variations between adjacent regions should be smooth to avoid scattering. α and β are weighting coefficients used to balance the relative importance of the constraints of diffraction efficiency distribution approaching the target and thickness distribution approaching the target with the primary objective of minimizing the brightness standard deviation. The weighting coefficients α and β can be chosen as any value within the range of 0.01 to 10, for example, α=0.1, β=0.1, or adjusted according to actual needs.

[0056] σ L (η,h) is the standard deviation of luminance within the exit pupil plane, and its calculation formula is: M represents the number of sampling points within the exit pupil plane, and L represents... k Let μ be the brightness value of the k-th sampling point. L The average brightness of M sampling points, .

[0057] The above objective function Given a single diffraction efficiency distribution η, this technical solution optimizes the uniformity of the exit pupil brightness. The joint optimization model further introduces the thickness distribution h as an independent optimization variable, and directly includes σ in the objective function. L The (η,h) term indicates that the standard deviation of luminance depends on both η and h. Additionally, by adding... and Two regularization terms ensure that the optimization result, while pursuing brightness uniformity, does not deviate from the preset target diffraction efficiency distribution and the target thickness distribution achievable by the process. During the solution process, numerical optimization algorithms, such as gradient descent or genetic algorithms, can be used to iteratively update η and h until the objective function converges. The optimization process must satisfy the thickness boundary constraint, i.e., 50 nm ≤ h(x,y) ≤ 500 nm, and the diffraction efficiency boundary constraint, 0 ≤ η(θ). j )≤1.

[0058] In the above technical solution, a joint optimization model is established, using the thickness distribution of the gradient thickness grating layer and the diffraction efficiency distribution of Bragg gratings at various angles as variables for simultaneous optimization. The primary objective is to minimize the standard deviation of brightness within the exit pupil plane, supplemented by regularization constraints on diffraction efficiency and thickness distribution. This model ensures a balance between brightness uniformity, diffraction efficiency target matching, and process feasibility, forming a progressive relationship with the aforementioned optimization framework—providing the optimization basis when only diffraction efficiency is considered. This technical solution then introduces thickness distribution as an additional degree of freedom for adjustment, achieving more refined collaborative optimization. The aforementioned resin waveguide, in-situ co-curing interface, three-wavelength coupling grating, and angle multiplexing grating design are compatible, jointly constructing a fully optimized AR near-eye display system from optical design to process implementation.

[0059] In another technical solution, the AR near-eye display system based on the coupling of resin waveguides and volume holographic optical elements includes a resin waveguide module comprising a first waveguide and a second waveguide. The first and second waveguides can be prepared by injection molding using cyclic olefin copolymers or polymethyl methacrylate materials, respectively. The thickness, refractive index, and other parameters of the two waveguides can be the same as those of the resin waveguide module, for example, a thickness of 0.8 to 1.2 mm and a refractive index of 1.50 to 1.55. The volume holographic optical control module also includes a folded volume holographic grating, which is disposed between the first and second waveguides to couple image light from the first waveguide to the second waveguide.

[0060] In the above technical solution, during actual assembly, the first waveguide can handle horizontal light transmission, and its length can be selected to be approximately 30 mm; the second waveguide can handle vertical light transmission, and its length can be selected to be approximately 20 mm; the folded-body holographic grating is located at the junction of the first and second waveguides, achieving a 90-degree fold in the optical path through Bragg diffraction, thereby reducing the size of the front frame of the AR glasses. This folded-body holographic grating is also a liquid crystal volumetric holographic grating, which can be recorded on the surface of the first or second waveguide using the same in-situ co-curing process as described above, and forms an optical connection with the other waveguide. By setting the first waveguide, the second waveguide, and the folded-body holographic grating, the propagation direction of image light can be changed while maintaining waveguide transmission efficiency, providing greater design freedom for the spatial layout of the AR near-eye display system.

[0061] In another technical solution, the AR near-eye display system based on the coupling of resin waveguide and volume holographic optical element satisfies the Bragg diffraction condition of the folded volume holographic grating: ; Among them Λ fold For the period of the folded holographic grating, i fold Let be the angle between the incident light and the grating surface. l The incident light wavelength is denoted by 1; a folded holographic grating is disposed between the first waveguide and the second waveguide to couple the image light from the first waveguide to the second waveguide.

[0062] The above formula is derived from Bragg's equation for volume holographic gratings: 2Λsinθ=λ (taking the diffraction order m=1). In optical path folding applications, the folding volume holographic grating is placed between the first and second waveguides. Its function is to diffract the image light from the first waveguide into the second waveguide and change its propagation direction. For example, when a 90-degree optical path fold is required, the angle θ between the incident light and the grating surface can be set. fold The angle is 45 degrees. For image light of different wavelengths (e.g., red light 635 nm, green light 532 nm, blue light 450 nm), corresponding folded-body holographic grating periods can be designed. Taking green light (532 nm) as an example, when θ... fold At 45 degrees, Λ fold =532 / (2·sin45°)=532 / (2×0.7071)≈376 nm. In actual fabrication, the period of the folded volume holographic grating can be calculated using the above formula based on the required folding angle and incident light wavelength, and the grating can be recorded using the same holographic interference exposure method as described above. This folded volume holographic grating can reduce the coupling of light from non-designed angles by utilizing the angular selectivity of the volume holographic element, which is beneficial for reducing stray light interference during the optical path folding process, while avoiding the introduction of additional prisms or mirrors, thus maintaining the overall thin and light structure of the system.

[0063] In another technical solution, the AR near-eye display system based on the coupling of resin waveguide and volume holographic optical element comprises a liquid crystal-type volume holographic material including a liquid crystal material, a photoinitiator system, a chiral agent, and a mixed solvent. The liquid crystal material is RM257, and the total mass fraction of the photoinitiator system is 1-2%. The photoinitiator system can be a mixture of 0.5-1% camphorquinone (CQ) and 0.5-1% bis(hydroxyphosphine oxide) (BAPO), or a system combining a blue light-sensitive titanoceramsite photoinitiator (such as Irgacure 784) and a green / red light-sensitive photosensitizer (such as isopropylthioxanthone ITX). The chiral agent has a mass fraction of 0.01-0.05%, and the mixed solvent is a mixture of PGMEA, cyclohexanone, and butyrolactone, with a mass fraction of 83-85%. The liquid crystal material, photoinitiator, chiral agent, and mixed solvent are mixed under light-protected conditions and then filtered through a filter membrane with a pore size of 0.22 micrometers.

[0064] The above technical solution further describes the specific composition of the liquid crystal holographic material. The liquid crystal holographic material includes liquid crystal material, photoinitiator system, chiral agent, and mixed solvent. The liquid crystal material can be RM257, and the total mass fraction of the photoinitiator system is 1-2%. The photoinitiator system can be a mixture of camphorquinone (CQ) and bis(BAPO) with a mass fraction of 0.5-1%, or a combination of a blue light-sensitive titanoceramic photoinitiator (such as Irgacure 784) and a green / red light-sensitive photosensitizer (such as isopropylthioxanthone ITX). The mass fraction of the chiral agent can be selected from 0.01% to 0.05%, for example, 0.03%. The mixed solvent is a mixture of propylene glycol methyl ether acetate, cyclohexanone, and butyrolactone, and the mass fraction of the mixed solvent can be selected from 83% to 85%, for example, 84.47%. In the mixed solvent, the volume ratio of propylene glycol methyl ether acetate, cyclohexanone, and butyrolactone can be selected as 6:2:2. For example, when preparing 100 ml of mixed solvent, take 60 ml of propylene glycol methyl ether acetate, 20 ml of cyclohexanone, and 20 ml of butyrolactone, mix them thoroughly, and then use. At this ratio, the mixed solvent has good solubility and a moderate evaporation rate, suitable for spin coating or slot coating processes. The sum of the mass fractions of the above components is 100%. During preparation, the liquid crystal material, photoinitiator, chiral agent, and mixed solvent are weighed according to the proportions under light-protected conditions, mixed and stirred for 30 minutes, and then filtered using a 0.22-micron pore size filter membrane to obtain a uniform coating solution. This coating solution can be directly used in an in-situ co-curing process, coated onto the surface of a resin waveguide module, and after interference exposure and thermal curing, forms a liquid crystal holographic grating.

[0065] It should be noted that, due to the large wavelength range of red light (635nm), green light (532nm), and blue light (450nm), a single photoinitiator is unlikely to respond efficiently to all three wavelengths simultaneously. Therefore, the liquid crystal-type volume holographic material of this invention employs a complex photoinitiator system: for example, camphorquinone (CQ, absorption peak approximately 470nm) can effectively respond to blue light and some green light, while bis(acylphosphine oxide) (BAPO, absorption peak 370~420nm) can be sensitized for red light recording via energy transfer after blue light excitation; alternatively, a titanoceramsite photoinitiator (such as Irgacure 784, absorption peak up to 532nm) combined with an isopropylthioxanthone (ITX) photosensitizer can achieve effective response to all three wavelengths. Through stepwise or simultaneous exposure, volume holographic gratings of corresponding wavelengths can be recorded separately.

[0066] In another technical solution, the AR near-eye display system based on the coupling of resin waveguide and volume holographic optical element further includes an alignment dye layer on the surface of the resin waveguide module. This alignment dye layer is used to induce the directional alignment of liquid crystal molecules in the liquid crystal-type volume holographic material. The material of the alignment dye layer is any one of BY, SD1, or polyimide. The alignment dye layer is prepared by mixing the alignment dye, additives, and DMF at a mass fraction ratio of 0.5-1% under light-protected conditions, filtering the mixture through a 0.22-micron pore size filter, and coating it onto the surface of the resin waveguide module to form an alignment film. The alignment dye layer and the resin waveguide module are firmly bonded by chemical bonding (e.g., the active groups in the alignment dye molecules react with the carboxyl groups, hydroxyl groups, and other polar groups on the resin surface to form covalent bonds or strong hydrogen bonds). Subsequently, during the thermosetting process, the residual functional groups of the coated liquid crystal-type volume holographic material further cross-link with the active sites on the surface of the alignment dye layer, forming chemical bonds. Thus, the volume holographic optical control module and the resin waveguide module achieve integrated co-curing connection through a cross-layer chemical bonding network of "resin-orientation layer-volume holographic material", rather than a simple physical bonding.

[0067] The above technical solution further describes the alignment dye layer disposed on the surface of the resin waveguide module. This alignment dye layer is used to induce the directional alignment of liquid crystal molecules in the liquid crystal holographic material. The material of the alignment dye layer can be any one of BY, SD1, or polyimide. The alignment dye layer is prepared by mixing the alignment dye, additives, and DMF at a mass fraction ratio of 0.5% to 1% under light-protected conditions, for example, 0.8%. After stirring for 30 minutes, the mixture is filtered through a 0.22-micron pore size filter to obtain an alignment dye solution. This solution is then coated onto the surface of the resin waveguide module to form an alignment film. This alignment film is located between the resin waveguide module and the liquid crystal holographic material, guiding the liquid crystal molecules to align in a preset direction during exposure and thermal curing. This, combined with the aforementioned liquid crystal pretilt angle optimization, achieves polarization-independent diffraction.

[0068] Test case The technical effects of the present invention are systematically verified through multiple comparative examples and experimental cases. All samples used the same light source (635nm red light, 532nm green light, 450nm blue light, 5mW / channel) and testing environment, with only the waveguide structure, bonding method and grating design being changed.

[0069] I. Sample Preparation Comparative Example 1 (Traditional bonding process) Waveguide: COC resin waveguide, 1.0mm thick, 1.53 refractive index.

[0070] Volume holographic grating: A liquid crystal volume holographic grating (green light 532nm, period 778nm, thickness 30μm) is independently fabricated on a glass substrate and then peeled off for later use.

[0071] Bonding: Apply the UV-curable adhesive NOA61 to the waveguide surface, bond the grating film, and UV cure for 5 minutes.

[0072] Features: Physically bonded with an adhesive layer interface; no gradient thickness layer; single waveguide; single-angle coupling grating (no angle multiplexing).

[0073] Comparative Example 2 (Optimized bonding process) Waveguide: Same as Comparative Example 1.

[0074] Surface treatment: Plasma activation treatment.

[0075] Adhesive: Low thermal expansion coefficient optical adhesive (Δα≈8×10) -6 / K).

[0076] The rest: Same as in comparison 1.

[0077] Features: The physical bonding process is optimized, but an adhesive layer is still present; otherwise, it is the same as Comparative Example 1.

[0078] Comparative Example 3 (only in-situ co-curing, no gradient layer, no angle reuse) Waveguide: Same as Comparative Example 1.

[0079] Fabrication: In-situ co-curing process (see Experiment Example 1) was used to directly record a volumetric holographic grating (green light 532nm, period 778nm) on the waveguide surface without setting a gradient thickness grating layer; the coupling grating was single-angle.

[0080] Features: chemically bonded interface, no adhesive layer; however, there is no gradient thickness control and no angle reuse for exit pupil expansion.

[0081] Comparative Example 4 (with gradient layer, but no angle reuse, no joint optimization) Waveguide: Same as Comparative Example 1.

[0082] Fabrication: Gradient-thickness grating layers (concentration 2% / 6% / 10% / 14%, pre-set pattern based on experience) were first inkjet-printed on the waveguide surface, followed by in-situ co-curing of a bulk holographic grating (single angle). A joint optimization model was not used to determine the thickness distribution.

[0083] Features: It has gradient layers but is not jointly optimized; there is no angle reuse.

[0084] Experimental Example 1 (Basic Scheme of this Invention: In-situ Co-curing + Gradient Layer + Three-wavelength Coupling) Waveguide: COC resin waveguide, 1.0mm thick, 1.53 refractive index.

[0085] Orientation layer: coated with SD1 orientation dye (0.8wt% DMF solution, 2μm filter) and spin-coated to form a film.

[0086] Gradient thickness grating layers: Prepare RM257 liquid crystal solutions with mass fractions of 2%, 6%, 10%, and 14% (containing 1.5% photoinitiator, 0.03% chiral agent, and solvent PGMEA:cyclohexanone:GBL = 6:2:2). Determine the printing pattern based on the diffraction efficiency simulation model (print 3 layers at 14% in the central high diffraction region and 1 layer at 2% in the edge low diffraction region). After inkjet printing, preheat at 80℃ for 30 seconds, then UV cure, with a thickness of 50~500nm.

[0087] Holographic material coating: same basic formulation (RM257 14%, photoinitiator 1.5%, chiral agent 0.03%, solvent 84.47%), slit coating thickness 30μm.

[0088] Holographic exposure: using red light (635nm, angle 2θ) respectively R =2×20°), green light (532nm, 2θ) G =2×20°), blue light (450nm, 2θ) B Three interferometric exposures were performed (2×20°) to record three coupled-volume holographic gratings with periods Λ... R ≈925nm, Λ G ≈778nm, Λ B ≈655nm. The liquid crystal pretilt angle is set to 45° via exposure polarization control.

[0089] Heat curing: Heat curing at 100℃ for 60 minutes to form chemical bonds.

[0090] The coupled-out grating is a single-angle grating (without angle multiplexing) with a period of 778nm.

[0091] Waveguide structure: Single waveguide.

[0092] Experimental Example 2 (Angle Reuse + Joint Optimization Scheme of the Invention) Differences from Experimental Example 1: Coupled-out gratings: Using angle multiplexing technology, five Bragg gratings at different angles are recorded in the coupling region, corresponding to the incident angle θ. j =15°, 20°, 25°, 30°, 35° (green light 532nm). Spatial frequency K of the grating at each angle. j =2π / Λ j Λ j =532 / (2·sinθ j ), calculated to obtain Λ 15° ≈1028nm, Λ 20° ≈778nm, Λ 25° ≈629nm, Λ 30° ≈532nm, Λ 35° ≈464nm. Periodic range Λ min ~Λ max =464~1028nm.

[0093] Diffraction efficiency optimization: Diffraction efficiency η(θ) of gratings at various angles j The objective function is determined through optimization, with the standard deviation of the luminance within the exit pupil plane, σ, as the criterion. L The objective is to minimize this value, with a smoothness constraint term R(η). The sampling points on the exit pupil surface are M=200, and the regularization coefficient is λ. reg =0.05. Optimized η(θ) j The distribution is as follows: 15°→0.25, 20°→0.35, 25°→0.30, 30°→0.20, 35°→0.10 (normalized).

[0094] Joint optimization of gradient thickness layers: The thickness distribution h(x,y) of the gradient thickness grating layer and η(θ_j) mentioned above are determined through a joint optimization model, with the objective function being min[σ]. L (η,h)+α·||η-η target || 2 +β·||hh target || 2 ], with α=0.1 and β=0.1. After optimization, the thickness is approximately 450nm in the central region and approximately 80nm in the edge region.

[0095] The rest: Same as in Experiment 1.

[0096] Experimental Example 3 (Dual Waveguide + Folding Grating Scheme of the Invention) The difference from Example 2 is as follows: Waveguides: Two COC waveguides are used. The first waveguide is 30mm long (for horizontal light transmission) and the second waveguide is 20mm long (for vertical light transmission). Both are 1.0mm thick.

[0097] Folded-fold holographic grating: Located between the first and second waveguides, designed for 90° optical path folding. Incident light wavelength λ = 532 nm, incident angle θ_fold = 45°, according to Bragg's condition Λ fold =λ / (2·sinθ fold =532 / (2·sin45°) = 376nm. The wavelength is recorded at the end of the first waveguide through holographic interference exposure and then thermally cured to form a chemical bond.

[0098] The rest: coupling in, gradient layer, angle reuse coupling out are the same as in Experiment Example 2.

[0099] Features: Enables optical path folding, reducing the size of the system's front frame.

[0100] II. Performance Testing Methods Interface delamination rate: After high temperature and high humidity (85℃ / 85%RH, 500h) and thermal shock (-40℃↔85℃, 200 cycles), the delamination area was observed under an optical microscope and the percentage of delamination area was statistically analyzed.

[0101] Diffraction efficiency retention rate: The ratio of the absolute diffraction efficiency of the green light (532nm) coupled into the grating before and after the test.

[0102] Exit pupil uniformity: 200 sampling points are evenly distributed within the exit pupil surface (10mm × 10mm), the luminance L_k is measured, and U = 1 - σ is calculated. L / μ L .

[0103] RGB lighting effect differences: Measure the relative diffraction efficiency of the red, green, and blue channels, and calculate Δη=(η max -η min ) / η max ×100%.

[0104] Optical path deflection efficiency (Experimental Example 3): Measure the ratio of the optical power input to the first waveguide to the optical power coupled out from the second waveguide.

[0105] Front frame dimensions: Measure the maximum horizontal × vertical dimensions of the AR display module.

[0106] III. Test Results Table 1 Interface reliability and diffraction efficiency stability Table 2 Optical performance and color uniformity Table 3 Comparison of Angle Reuse and Joint Optimization Effects (Internal Parameter Scan of Experiment Example 2) Note: Unoptimized scheme: The diffraction efficiency of the grating is equal at all angles (0.20), and the thickness of the gradient thickness grating layer is uniform (250nm).

[0107] Only optimize η(θ) j Solution: Maintain uniform gradient layer thickness (250 nm) and optimize only the diffraction efficiency distribution at each angle.

[0108] Joint optimization scheme: Simultaneously optimize the diffraction efficiency distribution at each angle and the spatial thickness distribution of the gradient thickness grating layer, and add thickness smoothing constraints (α=0.1, β=0.1) to the objective function.

[0109] Exit pupil uniformity U=1-σ L / μ L , σ L The standard deviation of the brightness of 200 sampling points on the exit pupil surface, μ L This represents the average brightness.

[0110] RGB lighting effect difference Δη=(η max -η min ) / η max ×100%, with test wavelengths of 635nm, 532nm, and 450nm.

[0111] IV. Data Analysis 1. Interface reliability (Comparative Examples 1-3 vs Experimental Examples 1-3) Comparative Example 1 (traditional bonding) showed a delamination rate of 18-22% after environmental testing, and a diffraction efficiency retention rate of only about 35%, which could not meet the requirements for long-term use of AR glasses.

[0112] Although Comparative Example 2 (optimized bonding) showed improvement, the delamination rate was still 9-11%, and the retention rate was about 70%, so there was still a risk to reliability.

[0113] Comparative Example 3 and all experimental cases (using in-situ co-curing process) showed a delamination rate of ≤0.5% and a retention rate of ≥95%. This demonstrates that the chemical bonding interface formed by in-situ co-curing fundamentally solves the delamination problem caused by the mismatch in thermal expansion coefficients between the resin and the bulk holographic material, which is a fundamental breakthrough that cannot be achieved by traditional bonding methods.

[0114] 2. Color uniformity (Comparative Examples 1-4 vs. Experimental Example 1) Compared to the three non-gradient thickness layers, the RGB lighting effects of the 1-3 samples differ by as much as 28-32%, resulting in severe color cast.

[0115] Although Comparative Example 4 has a gradient layer, it is not jointly optimized, and the difference is reduced to 12%, which is a limited improvement.

[0116] Experiment 1 uses a gradient-thickness grating layer and optimizes it according to the simulation model, reducing the difference to 6% and improving it by about 70% (compared to Comparative Example 3). This demonstrates that a gradient-thickness layer can achieve dynamic balance of diffraction efficiency across three wavelengths.

[0117] 3. Exit pupil uniformity (Experimental Example 2 vs. others) Experimental Example 2 employed an angle-multiplexed coupling grating and optimized the diffraction efficiency distribution at each angle using an objective function, achieving an exit pupil uniformity U=92%, significantly higher than the unoptimized scheme (≤78%). The joint optimization model (simultaneously optimizing diffraction efficiency and gradient thickness distribution) further reduced the brightness standard deviation to 0.08 and increased U to 92%, outperforming the scheme that only optimized diffraction efficiency (86%). This verifies that the optimization method of this invention has significant synergistic effects.

[0118] 4. Double waveguide folding (Experimental Example 3) Experiment 3 achieved a 90° optical path fold while maintaining high reliability (delamination rate ≤0.5%), high uniformity (91%), and low chromatic aberration (5%). The fold efficiency was 87%, and the front frame size was reduced from 60×40mm to 50×30mm (area reduction of 37.5%). This demonstrates that the dual-waveguide + folding grating structure can effectively reduce the system size without affecting the core optical performance.

[0119] The number of devices and processing scale described herein are for the purpose of simplifying the description of the invention. Applications, modifications, and variations of the invention will be readily apparent to those skilled in the art.

[0120] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details.

Claims

1. An AR near-eye display system based on the coupling of resin waveguides and volume holographic optical elements, characterized in that, include: Resin waveguide modules, injection molded from cyclic olefin copolymers or polymethyl methacrylate, are used to transmit image light. The resin waveguide modules have a thickness of 0.8-1.2 mm, a refractive index of 1.50-1.55, and a density of 1.05-1.15 g / cm³. 3 ; A volume holographic optical control module includes at least one input volume holographic grating and one output volume holographic grating. The volume holographic grating is a liquid crystal volume holographic grating and is recorded on the surface of a resin waveguide module. A chemical bonding interface is formed between the volume holographic optical control module and the resin waveguide module through an in-situ co-curing process. The in-situ co-curing process is as follows: a liquid crystal volume holographic material is coated on the surface of the resin waveguide module, a volume holographic grating is formed by coherent laser interference exposure, and then a thermal curing treatment is performed to form a chemical bond between the volume holographic material and the resin waveguide module. The volume holographic light control module includes three coupled volume holographic gratings corresponding to red, green, and blue light, respectively, with grating periods satisfying the following: ， ， ； Where λ R =635nm, λ G =532nm, λ B =450nm, θ i The angle between the incident light and the grating surface is 17.5-20.5°. The polarization response of the volume holographic light control module achieves polarization-independent diffraction by optimizing the liquid crystal pretilt angle.

2. The AR near-eye display system based on the coupling of resin waveguide and volume holographic optical element as described in claim 1, characterized in that, The coupled-volume holographic grating records N Bragg gratings at different angles, where N≥5, and each angle Bragg grating corresponds to a different position on the exit pupil plane; the diffraction efficiency distribution η(θ) of each angle Bragg grating... j The objective function is determined through optimization. ； Where σ L (η) is the standard deviation of luminance within the exit pupil plane, λ reg R(η) is the regularization coefficient, and R(η) is the smoothness constraint term of the diffraction efficiency distribution. Luminance standard deviation σ L Calculated using the following formula: ； Where M is the number of sampling points within the exit pupil plane, and L k Let μ be the brightness value of the k-th sampling point. L Let M be the average brightness of the M sampling points.

3. The AR near-eye display system based on the coupling of resin waveguide and volume holographic optical element as described in claim 2, characterized in that, Spatial frequency K of Bragg gratings at various angles j satisfy: ； Among them Λ j Let λ be the period of the j-th angle grating, and λ be the wavelength of the incident light; the period Λ of each angle grating j In Λ min To Λ max Variation within the range, Λ min =λ / (2sinθ max ), Λ max =λ / (2sinθ min ).

4. The AR near-eye display system based on the coupling of resin waveguide and volume holographic optical element as described in claim 2, characterized in that, The volume holographic light control module also includes a gradient thickness grating layer, which is disposed on the surface of the resin waveguide module. The gradient thickness grating layer is formed by inkjet printing of liquid crystal solutions of different concentrations. The high concentration liquid crystal solution corresponds to the region with high diffraction efficiency, and the low concentration liquid crystal solution corresponds to the region with low diffraction efficiency. The thickness of the gradient thickness grating layer is 50~500nm.

5. The AR near-eye display system based on the coupling of resin waveguide and volume holographic optical element as described in claim 4, characterized in that, The preparation of the gradient thickness grating layer includes: preparing a liquid crystal solution with a mass fraction of 2-14%; coating an alignment dye solution onto the surface of a resin waveguide module to form an alignment film; printing liquid crystal solutions of different concentrations onto the surface of the alignment film according to a preset pattern by inkjet printing. The preset pattern is determined based on a diffraction efficiency simulation model. After drying and curing, a gradient thickness grating structure is formed.

6. The AR near-eye display system based on the coupling of resin waveguide and volume holographic optical element as described in claim 4, characterized in that, The thickness distribution h(x,y) of the gradient thickness grating layer and the diffraction efficiency distribution η(θ) of the Bragg grating at each angle. j The following joint optimization model was used to determine: ； Where η target For the target diffraction efficiency distribution, h target Let α and β represent the target thickness distribution, and α and β be the weighting coefficients.

7. The AR near-eye display system based on the coupling of resin waveguide and volume holographic optical element as described in claim 1, characterized in that, The resin waveguide module includes a first waveguide and a second waveguide; the volume holographic optical control module also includes a folded volume holographic grating, which is disposed between the first waveguide and the second waveguide.

8. The AR near-eye display system based on the coupling of resin waveguide and volume holographic optical element as described in claim 7, characterized in that, The Bragg diffraction condition of a folded holographic grating is satisfied as follows: ； Among them Λ fold For the period of the folded holographic grating, θ fold Let be the angle between the incident light and the grating surface. λ The incident light wavelength is denoted by 1; a folded holographic grating is disposed between the first waveguide and the second waveguide to couple the image light from the first waveguide to the second waveguide.

9. The AR near-eye display system based on the coupling of resin waveguide and volume holographic optical element as described in claim 1, characterized in that, The liquid crystal holographic material comprises liquid crystal material, photoinitiator system, chiral agent, and mixed solvent; the liquid crystal material is RM257, the mass fraction of the photoinitiator system is 1-2%, the mass fraction of the chiral agent is 0.01-0.05%, and the mixed solvent is a mixture of PGMEA, cyclohexanone, and butyrolactone, with a mass fraction of 83-85%; the liquid crystal material, photoinitiator, chiral agent, and mixed solvent are mixed under light-protected conditions and then filtered through a filter membrane with a pore size of 0.22 micrometers.

10. The AR near-eye display system based on the coupling of resin waveguide and volume holographic optical element as described in claim 1, characterized in that, The surface of the resin waveguide module is also provided with an alignment dye layer, which is used to induce the directional alignment of liquid crystal molecules in the liquid crystal holographic material. The material of the alignment dye layer is any one of BY, SD1 or polyimide. The alignment dye layer is prepared by mixing the alignment dye, auxiliary agent and DMF at a mass fraction ratio of 0.5-1% under light-protected conditions, filtering through a filter membrane with a pore size of 0.22 micrometers, and coating it on the surface of the resin waveguide module to form an alignment film.

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