Augmented reality based lens

Abstract

The application discloses a lens based on augmented reality and belongs to the technical field of augmented reality near-eye display, and mainly solves the problems of system thickness, large assembly error and damaged optical performance caused by the fact that the waveguide display and the refractive correction function are realized in a separated body in the prior art. The lens directly constructs a low-refractive layer, a high-refractive waveguide layer and a diffraction grating structure on a refractive lens, realizes single-chip integrated design by controlling the total reflection transmission of light in the waveguide layer and the diffraction of the light grating, and then the light enters the human eye through each layer. The lens is mainly used in augmented reality equipment, can provide virtual image display and has vision correction function at the same time, and is suitable for user groups who need to wear correction lenses.

Description

Technical Field

[0001] This invention relates to the field of augmented reality near-eye display technology, and more specifically to an augmented reality-based lens. Background Technology

[0002] In the field of augmented reality near-eye displays, waveguide technology has become the mainstream solution due to its ability to achieve thinness and transparency. However, existing waveguide display systems still face several technical challenges when targeting users requiring vision correction.

[0003] The current common solution involves mounting an additional corrective lens with refractive power in addition to the independent planar waveguide element. This split architecture significantly increases the overall thickness of the optical system, contradicting the trend towards thinner and lighter consumer electronics. More importantly, this structure introduces an additional optical interface, which not only increases light energy loss but also generates stray light, reducing image contrast. From an optical design perspective, the two independent optical elements need to maintain strict alignment of their optical axes; however, in actual assembly and use, slight displacement or tilt is unavoidable, leading to positional deviations or image quality degradation in the virtual image.

[0004] The primary cause of these problems is that current technology treats display function and vision correction function as two separate optical systems. The manufacturing process of planar waveguide components is based on mature flat-panel optics technology, while refractive lenses follow traditional spectacle lens manufacturing standards. These two systems inherently differ in material systems, optical design, and manufacturing processes. This design paradigm presents a fundamental challenge to system integration: fusing the two requires precise optical thin-film deposition and nanoscale photolithography on curved substrates, placing extremely high demands on existing manufacturing technologies.

[0005] Fabricating optical waveguide structures on curved substrates presents numerous technical challenges. First, controlling the uniformity of thin-film deposition on curved surfaces is challenging, potentially leading to uneven waveguide layer thickness or inconsistent refractive index distribution, affecting light transmission characteristics. Second, nanoscale photolithography on non-planar substrates presents significant issues with depth-of-focus limitations and pattern distortion correction, making it difficult to guarantee the geometric accuracy and diffraction efficiency of the grating structure. Furthermore, the thermomechanical mismatch between organic resin materials and inorganic optical thin-film materials generates interfacial stress during temperature changes, impacting the long-term reliability of the device.

[0006] These technical challenges make it difficult for existing augmented reality near-eye display devices to simultaneously meet the demands for thinness, high performance, and vision correction. Especially with the trend towards larger field of view and smaller size, the limitations of traditional split-type solutions are becoming increasingly apparent. Therefore, new technological approaches are needed to address the key technical bottlenecks in the integration of curved optical systems. Summary of the Invention

[0007] One object of the present invention is to solve at least the above-mentioned problems and / or defects, and to provide at least the advantages described below.

[0008] One objective of this invention is to solve the technical problem of integrating augmented reality display functionality with refractive correction functionality.

[0009] One objective of this invention is to solve the problem of selecting refractive lenses that serve as waveguide substrates.

[0010] One objective of this invention is to solve the problem of the integration process between the low refractive index layer and the refractive lens substrate.

[0011] One objective of this invention is to solve the technical problem of efficient coupling and output of light from a waveguide.

[0012] One objective of this invention is to solve the technical problem that diffraction grating structures are easily damaged.

[0013] One objective of this invention is to solve the optical aberration problem caused by the curved surface of refractive lenses and the multilayer film structure.

[0014] One objective of this invention is to solve the technical problem of inaccurate performance prediction of complex optical systems.

[0015] One objective of this invention is to solve the technical problems of harsh total reflection conditions and small system tolerances within waveguides.

[0016] One objective of this invention is to solve the technical problem of stress arising between the resin substrate and the inorganic thin film layer due to the mismatch in the coefficients of thermal expansion.

[0017] One objective of this invention is to solve the technical problem that the effect of a single uniform stress transition layer is limited.

[0018] One object of the present invention is to provide an augmented reality-based lens, comprising:

[0019] Refractory lenses have a refractive power used to correct vision;

[0020] A low refractive index layer is formed on one side surface of the refractive lens;

[0021] A high-refractive-index waveguide layer is formed on top of the low-refractive-index layer, wherein the refractive index of the high-refractive-index waveguide layer is greater than the refractive index of the low-refractive-index layer; and

[0022] A diffraction grating structure is formed on the outer surface of the high-refractive-index waveguide layer;

[0023] The high-refractive-index waveguide layer is configured to receive and transmit light carrying image information via total internal reflection. The incident angle of the light at the interface between the high-refractive-index waveguide layer and the low-refractive-index layer is greater than the critical angle of total internal reflection, so that the light is confined to propagate within the high-refractive-index waveguide layer.

[0024] The diffraction grating structure is configured to diffract the light out of the high refractive index waveguide layer, so that it passes through the low refractive index layer and the refractive lens in sequence before entering the human eye.

[0025] Preferably, in the augmented reality-based lens, the refractive lens is a plano-concave lens or a plano-convex lens; the refractive lens is made of glass or optical resin material.

[0026] Preferably, in the augmented reality-based lens, the low refractive index layer is a coating layer or an adhesive layer.

[0027] Preferably, in the augmented reality-based lens, the diffraction grating structure is a surface relief grating or a volume holographic grating.

[0028] Preferably, the augmented reality-based lens further includes a protective layer formed on the diffraction grating structure; the protective layer is a low-refractive-index thin film or protective glass.

[0029] Preferably, in the augmented reality-based lens, the diffraction grating structure is a non-uniform, aberration-corrected grating.

[0030] The local grating period Λ(x,y) and local grating orientation φ(x,y) of the aberration-corrected grating are functions of the position coordinates (x,y) on the grating plane.

[0031] The functions Λ(x,y) and φ(x,y) are determined by reverse optimization design using ray tracing software. The optimization objective is to minimize the deviation between the wavefront phase formed at the pupil of the human eye and the ideal spherical wave of the light rays emitted from the diffraction grating structure and passing through the low refractive index layer and the refractive lens in sequence.

[0032] Preferably, in the augmented reality-based lens, the parameters of the high-refractive-index waveguide layer and the diffraction grating structure are determined through a co-simulation process; the co-simulation process sequentially couples the rigorous coupled-wave analysis module and the non-sequential ray tracing software.

[0033] The rigorous coupled-wave analysis module is used to establish a local diffraction efficiency database of the diffraction grating structure, which contains the grating diffraction efficiency under different incident angles, polarization states and wavelengths.

[0034] The non-sequential ray tracing software calls the diffraction efficiency database to trace the complete optical path from the entrance pupil of the optomechanical system to the exit pupil of the human eye. The complete optical path includes multiple total internal reflections of light in the high refractive index waveguide layer, local diffraction events at the diffraction grating structure, and the transmission process through the low refractive index layer and the refractive lens.

[0035] The optimization objective of the co-simulation process is to maximize the luminous flux and uniformity at the exit pupil of the human eye.

[0036] Preferably, in the augmented reality-based lens, the refractive index n1 of the low-refractive-index layer and the refractive index n2 of the high-refractive-index waveguide layer satisfy the following condition: n2-n1≥0.3; the low-refractive-index layer is composed of a cured magnesium fluoride or silicon dioxide coating layer, and the refractive index n1 is between 1.38 and 1.46 at a wavelength of 550nm; the high-refractive-index waveguide layer is composed of a cured strontium titanate or zinc sulfide coating layer, and the refractive index n2 is between 2.2 and 2.5 at a wavelength of 550nm.

[0037] Preferably, in the augmented reality-based lens, a stress transition layer is provided between the refractive lens and the low-refractive-index layer; the coefficient of thermal expansion of the refractive lens is α. sub The coefficient of thermal expansion of the stress transition layer is α. trans And the coefficient of thermal expansion of the low refractive index layer is α low Satisfy the following relationship: α low <α trans <α sub , wherein, the α sub Between 7.0×10 -5 / K to 9.0×10 -5 Between / K; the α low Between 0.5×10 -6 / K to 5.5×10 -6 Between / K; the α trans Between 5.0×10 -6 / K to 5.0×10 -5 Between / K.

[0038] Preferably, in the augmented reality-based lens, the stress transition layer is a periodic multilayer structure composed of alternating layers of silicon monoxide and silicon nitride; in the periodic multilayer structure, the initial layer adjacent to the refractive lens is a silicon monoxide layer, and the terminating layer adjacent to the low refractive index layer is a silicon nitride layer; the total thickness of the periodic multilayer structure is 50 nanometers to 200 nanometers, and it consists of 5 to 20 sub-layer cycles; wherein, the thickness of a single sub-layer cycle decreases gradually from the initial layer to the terminating layer, the thickness of the first sub-layer cycle adjacent to the refractive lens is 15 nanometers to 5 nanometers, and the thickness of the last sub-layer cycle adjacent to the low refractive index layer is 5 nanometers to 1 nanometer.

[0039] The present invention has at least the following beneficial effects:

[0040] The beneficial effects of this invention lie in achieving a monolithic integration of augmented reality display and refractive correction functions. By directly constructing the waveguide structure onto the refractive lens, the overall thickness and weight of the optical system are significantly reduced. This integrated design eliminates the optical axis alignment error problem inherent in split structures, while also reducing stray light from redundant optical interfaces, thus improving image contrast and optical efficiency. This approach provides a new technological path for developing lightweight augmented reality glasses.

[0041] This invention provides a regular and predictable optical surface by using plano-concave or plano-convex lenses as waveguide substrates, creating favorable conditions for the uniform deposition of subsequent functional thin films and the fabrication of precision grating structures. This lens selection ensures the necessary refractive correction capability while reducing the technological difficulty of constructing optical waveguide structures on curved surfaces, thereby improving manufacturing yield and cost-effectiveness.

[0042] This invention achieves an ultra-thin, low-refractive-index layer through coating or bonding processes, significantly reducing the overall thickness of the system. The adhesive layer in the bonding process also acts as a stress buffer, improving the bonding reliability between different material layers. This approach overcomes the thickness limitations of traditional independent substrates, making it possible to achieve thinner and lighter devices.

[0043] This invention provides a reliable technical path for light coupling output by offering two optional solutions: surface relief gratings and volume holographic gratings. Each of these grating technologies has its own advantages and can be selected according to different performance requirements and process conditions, thus improving the adaptability and practicality of the technical solution.

[0044] This invention effectively prevents physical damage or contamination of the diffraction grating during use by setting a protective layer outside the grating structure, ensuring the long-term stability of its optical performance. This protective measure extends the lifespan of the device and improves product reliability.

[0045] This invention utilizes a non-uniform aberration-correcting grating to actively compensate for optical aberrations introduced by the curvature of refractive lenses and multilayer film structures. This reverse optimization design method ensures that virtual images maintain clear imaging quality even after traversing complex optical paths, thus enhancing the user experience.

[0046] This invention achieves accurate prediction of the performance of complex optical systems by establishing a joint simulation process combining rigorous coupled-wave analysis and non-sequential ray tracing. This high-precision simulation method provides a reliable basis for optimized design, shortens the development cycle, and improves product performance.

[0047] This invention significantly reduces the critical angle requirement for total internal reflection by employing a material combination with a refractive index difference greater than 0.3, thus relaxing the tolerances for the incident angle of light and the system assembly precision. This design improves the robustness and production yield of the system, which is beneficial for large-scale commercial production.

[0048] This invention achieves a gradient transition of thermal stress between different material layers by setting a stress transition layer with a moderate coefficient of thermal expansion, thus avoiding stress concentration. This design improves the bonding strength between film layers and enhances the reliability of the device under temperature variation environments.

[0049] This invention employs a periodic gradient multilayer structure as a stress transition layer, utilizing multiple interfaces to effectively disperse and absorb thermal stress, thereby blocking crack propagation paths. This innovative structure further enhances stress management, ensuring the stability of the device during long-term use.

[0050] 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. Attached Figure Description

[0051] Figure 1 This is a schematic diagram of the structure of the augmented reality-based lens provided by the present invention.

[0052] Figure 2 This is a schematic diagram illustrating the working principle of the augmented reality-based lens provided for this invention. Detailed Implementation

[0053] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0054] like Figure 1 and Figure 2As shown, the present invention provides an augmented reality-based lens, comprising: a refractive lens 1 having a refractive power for correcting vision; a low refractive index layer 2 formed on one side surface of the refractive lens; a high refractive index waveguide layer 3 formed on the low refractive index layer, wherein the refractive index of the high refractive index waveguide layer 3 is greater than that of the low refractive index layer; and a diffraction grating structure 4 formed on the outer surface of the high refractive index waveguide layer 3; wherein the high refractive index waveguide layer 3 is configured to receive and transmit light carrying image information via total internal reflection, wherein the incident angle of the light at the interface between the high refractive index waveguide layer and the low refractive index layer is greater than the critical angle of total internal reflection, so that the light is confined to propagate within the high refractive index waveguide layer 3; wherein the diffraction grating structure 4 is configured to diffract the light out of the high refractive index waveguide layer 3, so that it passes sequentially through the low refractive index layer 2 and the refractive lens 1 before entering the human eye.

[0055] This invention uses a plano-concave or plano-convex refractive lens as a substrate, onto which a low-refractive-index film or adhesive is first deposited. Then, a high-refractive-index substrate is placed outside the film or adhesive as a light transmission medium. Finally, a diffraction grating (such as a surface relief grating or a volume holographic grating) is placed on the outermost layer as a light-deflecting grating. In this way, virtual light is transmitted within the high-refractive-index substrate film layer and does not enter the outer layer of the low-refractive-index film or adhesive, achieving lossless light propagation.

[0056] Figure 2 Local region A in the middle corresponds to Figure 1 Local region A in the middle. Figure 2 The dashed line represents the direction of the virtual ray. At the interface between the high-refractive base and the low-refractive lens, the incident angle θ of the virtual ray is greater than arcsin(n1 / n2). Therefore, the ray will not enter the low-refractive lens and will propagate to the right without loss. During its propagation to the right, when the ray encounters a diffraction grating, the grating diffracts the virtual ray towards the eye, passing through the low-refractive lens and the refractive lens before entering the eye.

[0057] This invention has the following advantages: 1. By directly fabricating the waveguide on the refractive lens, the overall thickness of AR glasses is reduced. 2. The original solution had a thicker substrate, requiring a relatively large exit pupil size for the optical engine. This invention reduces the exit pupil size requirement, allowing the optical engine to be smaller, lighter, and more suitable for the shape of glasses. 3. With a refractive lens on the outer side, and virtual light not propagating towards the refractive lens side, the refractive lens can replace a protective glass. Only a protective glass needs to be added to the outer side of the grating. 4. If a low-reflection film is also coated on the outer side of the grating, a protective lens is not needed on the outer side of the grating, achieving the function of thin and light AR refractive lens glasses. Because the film layers are relatively small, the overall thickness of the lens is basically the same as that of a regular refractive lens.

[0058] This invention provides a specific implementation of an augmented reality-based lens. The core of this lens lies in directly fabricating an optical waveguide structure onto the refractive lens substrate, achieving functional monolithic integration.

[0059] First, a refractive lens is provided as a supporting substrate. This lens is a plano-concave lens molded from polycarbonate material, with a refractive power of -450 degrees, used to correct myopia. One optical surface of the lens is planar, and the other is a concave spherical surface. Next, a low-refractive-index layer is deposited using physical vapor deposition. This layer is made of silicon dioxide with a refractive index of approximately 1.46 and a physical thickness controlled at 200 nanometers, requiring uniform thickness and a smooth surface. Above the low-refractive-index layer, the core high-refractive-index waveguide layer of this invention is deposited using radio frequency magnetron sputtering. This layer is made of zinc sulfide with a refractive index of approximately 2.35 and a physical thickness of 150 nanometers. A refractive index difference greater than 0.8 is formed between this waveguide layer and the underlying silicon dioxide layer, ensuring the conditions required for total internal reflection transmission of light within the waveguide layer. Finally, a surface relief grating structure is fabricated on the outer surface of the high-refractive-index waveguide layer using nanoimprint lithography. This grating is a non-uniform aberration correction grating, whose period and local orientation are functions of position. Its specific pattern distribution is determined by optical design software using an inverse optimization algorithm. The optimization goal is to compensate for the optical distortion caused by the curved surface of the lower refractive lens and the multilayer film structure on the virtual optical path, ensuring that light ultimately converges to the pupil of the human eye with good quality.

[0060] During operation, a beam of light emitted from the miniature image source enters the lens from its edge. After being deflected by the inclination grating structure in that area, it enters the high-refractive-index waveguide layer. Due to total internal reflection, the beam is confined within the waveguide layer and propagates forward. When the beam reaches the outclination grating region directly in front of the eye, it is diffracted by the grating and changes direction, detaching from the waveguide layer. The outgoing beam then passes sequentially through the low-refractive-index layer and the lens substrate, ultimately carrying virtual image information into the eye. Through this monolithically integrated lens, the user can simultaneously perceive a clear view of the real world and the superimposed virtual image.

[0061] Existing technologies primarily employ a split-type integrated approach. This approach first manufactures a single, flat augmented reality waveguide lens, which itself does not possess refractive correction capabilities. Then, an additional refractive lens is fitted for users requiring vision correction. Finally, a mechanical structure mounts the refractive lens onto the side of the waveguide lens closest to the eye, assembling them into a complete pair of glasses. In contrast, the main differences of this invention are: firstly, the fundamental structure is different. Existing technologies involve mechanically stacking two independent lenses, resulting in a split structure. This invention, however, directly fabricates the waveguide's optical structure onto the surface of the refractive lens, forming a monolithic integrated structure. Secondly, the functions and effects differ. The two-piece structure of existing technologies inevitably leads to a significant increase in overall thickness and weight, affecting wearing comfort, and multiple optical surfaces introduce more stray light reflection, reducing image contrast. This invention, being a monolithic integration, significantly reduces the overall thickness and weight of the lens, resulting in a simpler optical path, less stray light, and superior image quality. In summary, this invention effectively overcomes the shortcomings of existing split-type technologies, such as bulkiness and impaired optical performance, through a monolithic integration solution, providing a lighter, thinner, and more optically superior augmented reality refractive lens solution that is more suitable for everyday wear.

[0062] In a preferred embodiment, the refractive lens in the augmented reality-based lens is a plano-concave lens or a plano-convex lens; the refractive lens is made of glass or optical resin material.

[0063] In existing technologies, refractive lenses can be of any type, and their design is independent of the optical performance of the waveguide sheet; the two are optically independent components. This invention, however, uses a plano-concave or plano-convex lens as the substrate. The plano-concave or plano-convex configuration provides a relatively simple, regular, symmetrical surface, which, compared to other complex aspherical surfaces, greatly reduces the difficulty and cost of achieving uniform coating and fabricating precision grating structures on it, while ensuring that the virtual optical path has predictable and compensable aberration characteristics.

[0064] In summary, by using plano-concave or plano-convex lenses as the integrated substrate, this invention integrates refractive correction and waveguide display functions, effectively overcoming the inherent defects of existing split technologies such as bulkiness, small alignment tolerance, and complex manufacturing, and providing a more stable, thinner, and mass-producible technical solution.

[0065] In a preferred embodiment, the low refractive index layer in the augmented reality-based lens is a coating layer or an adhesive layer.

[0066] This embodiment employs two process paths to achieve the low refractive index layer.

[0067] The first approach employs a coating process, specifically electron beam evaporation in physical vapor deposition. The lens substrate is placed in a high-vacuum chamber, using high-purity magnesium fluoride as the evaporation source. By precisely controlling the power and scanning path of the electron beam, the magnesium fluoride material is heated and sublimated. Its vapor then condenses and deposits uniformly onto the surface of the rotating refractive lens, ultimately forming a dense, smooth, and uniformly thick magnesium fluoride thin film. This film layer is directly bonded to the resin substrate, serving as the lower cladding layer for the subsequent high-refractive-index waveguide layer.

[0068] The second approach employs an adhesive bonding process. First, a thin silica film is sputtered onto a separate planar optical substrate to create a low-refractive-index layer. Then, an optical-grade UV-curable adhesive is coated onto the surface of this silica film. Next, the silica film coated with adhesive is aligned and bonded to the target surface of the refractive lens. Air bubbles are removed and the adhesive layer is evenly distributed by rolling. Finally, UV light is irradiated from one side of the transparent refractive lens to fully cure the adhesive, thus firmly bonding the entire low-refractive-index layer to the lens. The cured adhesive layer also becomes part of the low-refractive-index structure.

[0069] After successfully fabricating the low-refractive-index layer, the subsequent processes are the same regardless of which path is used. That is, a high-refractive-index waveguide layer is deposited on top of the low-refractive-index layer using a sputtering process, and finally a grating structure is fabricated on the surface of the waveguide layer using nanoimprint lithography, thereby completing the fabrication of the entire integrated lens.

[0070] The low-refractive-index layer provided by this invention is no longer a separate, heavy substrate, but an ultra-thin functional layer directly attached to the refractive lens through coating or bonding processes. This transformation solves two technical problems: First, the thickness problem. The thickness of the coated or bonded thin film layer is typically on the order of hundreds of nanometers to several micrometers. Compared with the millimeter-scale traditional substrates, this greatly reduces the overall volume and weight of the structure, laying the foundation for achieving thinner and lighter eyeglasses. Second, the stress matching problem, especially in the bonding process. The optical adhesive layer in the middle has a certain degree of flexibility and can act as a stress buffer, effectively absorbing the stress caused by the mismatch in the coefficients of thermal expansion between the refractive lens substrate and the rigid inorganic thin film layer. This improves the long-term reliability of the entire multilayer structure under temperature changes and avoids the risk of film cracking or detachment.

[0071] Therefore, by defining the low refractive index layer as an ultrathin functional layer that can be achieved through coating or bonding processes, rather than a mechanical substrate, the present invention successfully integrates the waveguide structure with the refractive lens both physically and optically, overcoming the limitations of traditional solutions in terms of size and reliability.

[0072] In a preferred embodiment, the diffraction grating structure in the augmented reality-based lens is a surface relief grating or a volume holographic grating.

[0073] In this embodiment, the lens is manufactured after the high-refractive-index waveguide layer is deposited. This embodiment provides two different grating fabrication schemes. The first scheme uses surface relief grating technology. A layer of electron beam photoresist is spin-coated onto the surface of the high-refractive-index waveguide layer, and then exposed using an electron beam direct writing device. The electron beam scans according to a pre-designed non-uniform grating pattern, which is precisely calculated to compensate for aberrations generated by the refractive lens. After exposure, development is performed to remove the photoresist in the exposed area, forming a mask for the grating structure. Then, a reactive ion etching process is used, using the photoresist as a mask, to precisely transfer the pattern into the underlying zinc sulfide waveguide layer, forming a relief structure with a specific depth and shape. Finally, the remaining photoresist is removed, completing the fabrication of the surface relief grating.

[0074] The second approach employs volume holographic grating technology. First, a photosensitive polymer film is spin-coated onto the waveguide layer surface as the recording medium. Two coherent laser beams are used to perform interference exposure on the photosensitive polymer layer; the interference of the two beams forms alternating bright and dark fringes. By precisely controlling the incident angle and phase of the two beams, the desired grating structure with the required period and orientation can be recorded. After exposure, heat treatment and other processes are performed to fix the grating pattern, forming a volume holographic grating. This type of grating achieves its diffraction function by altering the refractive index distribution within the material.

[0075] This invention provides two technical approaches: surface relief gratings and volume holographic gratings, particularly enabling the creation of aberration-correcting gratings for non-uniformity. Surface relief gratings, using electron beam direct writing technology, can flexibly fabricate gratings with arbitrarily complex patterns, allowing for independent design of the period and orientation of each local region, thus accurately compensating for aberrations introduced by the curvature of refractive lenses. Volume holographic gratings, through interference recording, can form high-quality diffraction wavefronts with high diffraction efficiency. Both approaches effectively solve the technical challenge of achieving high-quality imaging on complex optical surfaces.

[0076] In a preferred embodiment, the augmented reality-based lens further includes a protective layer formed on the diffraction grating structure; the protective layer is a low-refractive-index thin film or protective glass.

[0077] In this embodiment, the lens is manufactured after the diffraction grating structure is fabricated. This embodiment provides two different protective layer implementation schemes. The first scheme uses a low-refractive-index thin film as the protective layer. A silicon dioxide thin film is deposited on the surface of the high-refractive-index waveguide layer on which the diffraction grating is fabricated using plasma-enhanced chemical vapor deposition. During the deposition process, parameters such as the proportion of reactive gases, chamber pressure, and temperature are precisely controlled to ensure that the silicon dioxide thin film can uniformly cover the surface contour of the grating structure, completely fill the recessed area of ​​the grating, and form a smooth protective layer on the surface. The refractive index of this silicon dioxide thin film is approximately 1.46, which is lower than the refractive index of the waveguide layer and will not affect the total internal reflection transmission within the waveguide layer. The film thickness is controlled between 500 nanometers and 1 micrometer, providing sufficient mechanical protection without significantly affecting optical performance.

[0078] The second approach uses protective glass as the protective layer. First, a sheet of ultra-thin tempered glass, with a thickness of 0.1 to 0.3 millimeters, is selected. Optical adhesive is applied to one surface of the glass sheet and the surface of the grating structure of the lens, respectively, and then the two are precisely aligned and bonded together. An air bubble is eliminated through a rolling process, ensuring even distribution of the adhesive layer. Finally, the adhesive is fully cured by ultraviolet light irradiation or thermal curing, permanently bonding the protective glass to the grating structure. The outer surface of the protective glass can be treated with anti-reflective coatings and oleophobic / hydrophobic coatings to enhance optical performance and stain resistance.

[0079] The grating structure is directly exposed to the elements, making it susceptible to physical damage during cleaning, wiping, or daily use, leading to decreased diffraction efficiency or deterioration of optical performance. This invention designs two targeted protection schemes for the fragile diffraction grating structure. The low-refractive-index thin-film scheme achieves in-situ protection of the grating structure by directly growing a robust inorganic thin film on the grating surface. This protective layer is extremely thin and highly integrated with the optical system, without adding extra volume. The protective glass scheme provides stronger mechanical protection, particularly suitable for applications with higher durability requirements. Both protection schemes ensure that the refractive index of the protective layer is lower than that of the waveguide layer, preventing disruption of total internal reflection conditions within the waveguide, while effectively preventing damage to the grating structure from the external environment, significantly improving product reliability and lifespan. This protective layer design solves the structural durability problem faced by augmented reality lenses in practical use.

[0080] In a preferred embodiment, in the augmented reality-based lens, the diffraction grating structure is a non-uniform, aberration-corrected grating; the local grating period Λ(x,y) and local grating orientation φ(x,y) of the aberration-corrected grating are functions of the position coordinates (x,y) on the grating plane; the functions Λ(x,y) and φ(x,y) are determined by reverse optimization design using ray tracing software, and the optimization objective is to minimize the deviation between the wavefront phase formed at the pupil of the human eye and the ideal spherical wave of the light rays emitted from the diffraction grating structure and passing sequentially through the low-refractive-index layer and the refractive lens.

[0081] In this embodiment, the lens is fabricated after the high-refractive-index waveguide layer is deposited, followed by grating fabrication. First, a precision electron beam lithography system is used to expose the waveguide layer surface. The electron beam scans according to a pre-calculated non-uniform pattern, generated through an inverse optimization algorithm. During optimization, optical design software establishes a complete optical path including the refractive lens surface, multilayer film structure, and a human eye model. Ray tracing calculations determine the required grating period and orientation at each location, ensuring that the light diffracted from that point accurately converges to the pupil of the human eye after passing through the entire optical system. After exposure, development is performed to form a photoresist mask with a continuously varying period. Subsequently, a reactive ion etching process is used to transfer the non-uniform pattern to the underlying waveguide layer. During etching, the etching depth and sidewall angle are monitored in real time to ensure that the grating groove shape in each local area meets the design requirements. The resulting grating structure has different periods and orientations at different locations; these parameter variations are smooth and continuous, accurately compensating for wavefront distortion introduced by the refractive lens surface and multilayer film structure.

[0082] For example, lens design is carried out in three stages.

[0083] Designing a lens to correct high astigmatism, where the refractive power includes myopia and it is also a toric lens, introduces numerous, unique, and non-rotationally symmetric advanced aberrations (such as oblique astigmatism). Traditional uniform gratings would cause severe distortion and blurring of the virtual image, rendering them unusable.

[0084] Phase 1: System Modeling and Initial Analysis (using Zemax OpticStudio)

[0085] A complete optical system model is built in Zemax, including: a micro projector (optical engine), an entrance pupil, a refractive lens substrate with a specific toric curvature, a low refractive index layer, a high refractive index waveguide layer, and an initially set uniform grating.

[0086] Ray tracing is performed to analyze the image quality of the virtual image on the user's retina. The software generates dot plots, modulation transfer function (MTF) curves, and wavefront diagrams, quantifying the severe astigmatism and coma present in the image. This stage clarifies the root cause of the problem.

[0087] Phase 2: Reverse Optimization and Raster Design (using Zemax and a custom MATLAB algorithm)

[0088] Inverse optimization target setting: The optimization target is to minimize the deviation (i.e., wavefront error) between the wavefront phase formed at the pupil of the human eye and the ideal spherical wave after the light rays exit from the grating and pass through the entire lens system.

[0089] The optimization process is as follows: Zemax, through its Damped Least Squares (DLS) optimization engine, begins by attempting to adjust the local period Λ(x,y) and local orientation φ(x,y) of the grating. These variables are defined as position functions on the grating surface. Due to the complexity of aberrations, the DLS algorithm may get stuck in local optima. In this case, the system's performance parameters (such as the wavefront error Zernike coefficients) are exported to MATLAB. In MATLAB, a global optimization algorithm (such as a genetic algorithm) is invoked to explore a wider range of grating parameters to find a better initial solution. The better solution found by the genetic algorithm is then re-imported into Zemax, and the DLS algorithm is used again for refined local optimization, ultimately obtaining the globally optimal non-uniform grating design parameters.

[0090] Phase 3: Verification and Iteration

[0091] The optimized non-uniform grating parameters were substituted into the Zemax model for final ray tracing verification. The MTF curve was checked to ensure it was close to the diffraction limit and the wavefront error was effectively suppressed to below λ / 4 (Marechal criterion), ensuring the virtual image was clear and distortion-free.

[0092] Uniform periodic gratings maintain a fixed grating period and constant orientation throughout their entire effective area. This design cannot compensate for aberrations caused by complex optical surfaces, resulting in distortion and blurring of virtual images. This invention employs a non-uniform aberration-correcting grating design, where the grating parameters for each local region are precisely optimized. Through a reverse optical design method, the grating itself possesses wavefront correction capabilities, actively compensating for aberrations in the optical system and significantly improving the visual quality of augmented reality displays.

[0093] In a preferred embodiment, in the augmented reality-based lens, the parameters of the high-refractive-index waveguide layer and the diffraction grating structure are determined through a co-simulation process. The co-simulation process sequentially couples a rigorous coupled-wave analysis module with non-sequential ray tracing software. The rigorous coupled-wave analysis module establishes a local diffraction efficiency database for the diffraction grating structure, containing the grating diffraction efficiency under different incident angles, polarization states, and wavelengths. The non-sequential ray tracing software calls the diffraction efficiency database to trace the complete optical path from the entrance pupil of the optomechanical system to the exit pupil of the human eye. This complete optical path includes multiple total internal reflections of light within the high-refractive-index waveguide layer, local diffraction events at the diffraction grating structure, and the transmission process through the low-refractive-index layer and the refractive lens. The optimization objective of the co-simulation process is to maximize the luminous flux and uniformity at the exit pupil of the human eye.

[0094] In this embodiment, the lens design process employs an advanced co-simulation method. First, a complete optical system model is established in professional optical design software, including the optomechanical exit pupil position, the coupling region, the curved structure of the refractive lens, the multilayer film interface, and the position of the human eye's pupil. Then, a rigorous coupled-wave analysis module is activated to perform refined modeling of the designed diffraction grating structure. This module calculates precise diffraction efficiency data for the grating under different incident angles, polarization states, and wavelengths, generating a database containing millions of records. After the database is established, non-sequential ray tracing software is launched and parameters are correlated. The software emits millions of rays with different angles, polarizations, and wavelengths from the optomechanical exit pupil position, tracing the multiple total internal reflection propagation processes of these rays within the waveguide layer. When the rays interact with the grating structure, the software queries the pre-established diffraction efficiency database in real time, obtaining accurate diffraction behavior parameters based on the specific incident conditions of the rays, rather than using an idealized simplified model. After diffraction, the rays continue to be traced through the low-refractive-index layer and the curved surface of the refractive lens, ultimately statistically analyzing the light energy distribution reaching the human eye's exit pupil. Based on the initial tracing results, the optimization algorithm automatically adjusts the grating parameters and system structure, repeats the above co-simulation process, and after multiple iterations of optimization, finally obtains the optimal design scheme that can simultaneously achieve high light flux and good uniformity.

[0095] For example, designing a lens in three stages.

[0096] When designing an AR lens with a wide field of view, light rays from the edge perspective will be incident on the decoupling grating at extremely high angles. Traditional design methods cannot accurately predict the different effects of such large-angle incident light on the diffraction efficiency of RGB (red, green, and blue) light, resulting in severe color separation (e.g., yellowing or bluish tinge at the edges) and uneven brightness in the final product at the edge of the field of view.

[0097] Step 1: Use the RCWA module to create a "real" raster database

[0098] Designers first use rigorous coupled-wave analysis (RCWA) software such as Lumerical FDTD or VirtualLab Fusion to precisely model the three-dimensional shape (tooth shape, groove depth, sidewall angles) of the designed surface relief grating. The software simulates a beam of light incident on the grating at various angles ranging from 0 to 70 degrees, with S-polarization and P-polarization, and at three wavelengths: red (630 nm), green (532 nm), and blue (465 nm). For each combination (angle + polarization + wavelength), the software calculates a precise diffraction efficiency value. For example, "55-degree incident angle, P-polarization, green light, diffraction efficiency towards the human eye is 37.5%." This process generates a massive database containing tens or even hundreds of thousands of records. This database fully reflects the real, non-ideal physical behavior of the grating.

[0099] Step 2: Perform "realistic" ray tracing in non-sequential software

[0100] Designers import the aforementioned database into the non-sequence mode of Zemax OpticStudio or ANSYS SPEOS.

[0101] In the non-sequential model, millions of rays are emitted from the optical engine. Each ray carries unique properties: position, direction, wavelength, and polarization state. When a simulated "green light, P-polarized, at a 55-degree angle" strikes a region of the grating, the ray tracing engine doesn't calculate it using a simple average efficiency formula. Instead, it automatically queries the RCWA database generated in the first step to determine precisely that this ray has a 37.5% probability of being diffracted towards the human eye; the remaining energy may continue to propagate or be wasted. The software meticulously records all rays that successfully enter the human eye and statistically analyzes their position, energy, and color on the retina.

[0102] Step 3: Analysis and Optimization

[0103] After tracing is complete, the software can generate a color uniformity analysis map and a relative illumination map across the entire field of view. Designers will clearly see that at the edge viewpoints, due to the differences in diffraction efficiency of different colors of light, there is a significant color shift (for example, red light has high efficiency, while blue light has low efficiency, resulting in a reddish tint at the edges). Subsequently, designers will return to the grating design, adjust the grating tooth profile parameters (such as modulating the tooth depth or duty cycle), and then repeat steps one and two.

[0104] After multiple iterative cycles of "RCWA library construction - non-sequence tracing - analysis", an optimal grating design was finally found, which makes the diffraction efficiency curves of RGB light match as much as possible in all viewing angles, thereby fundamentally eliminating color shift at the edge of the field of view and achieving high uniformity of color and brightness throughout the entire field of view.

[0105] Simplified optical simulation methods typically use sequential ray tracing software combined with ideal diffraction models for design. This approach simplifies the diffraction behavior of gratings to an idealized model with a fixed efficiency, failing to accurately reflect the efficiency variations and polarization dependence of actual gratings under different incident conditions. Furthermore, simplified models cannot handle multiple reflections and diffraction coupling effects of light in complex curved surface systems, leading to significant deviations between design results and actual performance. This invention establishes a joint simulation process combining rigorous coupled-wave analysis and non-sequential ray tracing. Rigorous coupled-wave analysis accurately calculates the true diffraction characteristics of the grating, while non-sequential ray tracing precisely simulates the actual propagation path of light in complex optical systems. This combination achieves high-precision simulation of the entire process from optomechanical to human eye. This joint simulation method effectively solves the technical challenge of traditional simplified models failing to accurately predict system optical performance, significantly improving design accuracy and reliability, and ensuring that the final product achieves the expected optical performance indicators.

[0106] In a preferred embodiment, in the augmented reality-based lens, the refractive index n1 of the low-refractive-index layer and the refractive index n2 of the high-refractive-index waveguide layer satisfy: n2-n1≥0.3; the low-refractive-index layer is composed of a cured magnesium fluoride or silicon dioxide coating layer, and the refractive index n1 is between 1.38 and 1.46 at a wavelength of 550nm; the high-refractive-index waveguide layer is composed of a cured strontium titanate or zinc sulfide coating layer, and the refractive index n2 is between 2.2 and 2.5 at a wavelength of 550nm.

[0107] The physical basis for transmitting images via optical waveguides is total internal reflection. For light to travel in a zigzag pattern within the waveguide layer without leakage, a core condition must be met: the angle of incidence θ at the interface between the waveguide layer (n2) and the cladding (n1) must be greater than the critical angle for total internal reflection θ. c .

[0108] The critical angle for total internal reflection is determined by a simple formula: θ c =arcsin(n1 / n2)

[0109] This formula clearly shows that the ratio of n2 to n1 determines the size of the critical angle.

[0110] When n2 and n1 are very close (i.e., the difference in refractive index is small), the ratio n1 / n2 ≈ 1, so θ c≈arcsin(1)=90°. This means that the light must propagate at an angle almost parallel to the interface (incident angle close to 90°) for total internal reflection to occur. This is impossible in practical applications because the incident angle is a range when the optomechanically coupled light enters the waveguide, and it is difficult to be so precise. Any tiny deviation will cause the incident angle θ<θ c The light cannot be completely reflected; instead, most of it is refracted into the low-refractive-index layer, resulting in a huge loss of light energy and making the image dark and unclear.

[0111] When n2 is much larger than n1 (i.e., the refractive index difference is large, satisfying n2-n1≥0.3), the ratio n1 / n2 will become very small, so θ c =arcsin(a very small number), the result is θ. c The angle is also very small. For example: n2 = 2.35 (ZnS), n1 = 1.38 (MgF2), then n1 / n2 ≈ 0.587, θ c ≈arcsin(0.587)≈36°. This means that total internal reflection can occur as long as the incident angle of light at the interface is greater than 36°. This condition is extremely easy to satisfy. Optical light incident on the mechanism can easily propagate in the waveguide at angles of 40°, 50°, 60° or even larger, and all these rays can be firmly "locked" within the waveguide layer to achieve lossless or low-loss transmission.

[0112] Therefore, setting a large refractive index difference can significantly reduce the critical angle θ for total internal reflection. c This greatly relaxes the requirements for the angle of light transmission, ensuring that total internal reflection can occur stably and reliably.

[0113] A large refractive index difference can reduce the precision requirements for optomechanical-waveguide alignment. A large refractive index difference and a small critical angle mean that the allowable range (tolerance) of the incident angle becomes wider when the optomechanical system couples light into the waveguide. Even if there is a slight deviation in the installation position of the optomechanical system, causing a variation in the angle of incident light, this range will almost always fall within a range greater than θ. c Within this range, the system can still function normally. If the refractive index difference is very small, θ c The angle tolerance of the optical engine is very narrow, and the assembly difficulty and cost increase exponentially.

[0114] A large refractive index difference allows for a wider field of view (FOV). The larger the FOV of augmented reality glasses, the more immersive the experience. A larger FOV means a greater range of angles over which light propagates within the waveguide. For light rays over a large angle range to satisfy the condition of total internal reflection, a certain θ must be required. c Small enough. A large refractive index difference is precisely what allows for a small θ. c This is a prerequisite for achieving a large field of view.

[0115] A large refractive index difference can improve manufacturing yield. In actual coating processes, there are slight batch variations and uniformity fluctuations in the refractive index and thickness of the thin film. A large refractive index difference (n2-n1≥0.3) provides a strong "buffer" or "safety redundancy." Even if the measured values ​​of n1 or n2 drift slightly, the large difference can still ensure that θ c If the refractive index difference is kept stable at a very small value, the system performance will not be fatally affected. Conversely, if the refractive index difference is already very small (e.g., 0.1), then any tiny fluctuation in the manufacturing process may cause the critical angle to increase sharply, causing the design that was working normally to suddenly fail, directly leading to a sharp drop in yield.

[0116] In summary, setting the refractive index difference between the low-refractive-index layer and the high-refractive-index waveguide layer to n2-n1≥0.3 can significantly reduce the critical angle of total internal reflection, enabling light to transmit stably and with low loss within the waveguide over a wider angular range. This also endows the system with strong robustness, reduces the stringent requirements on optomechanical alignment accuracy, supports a larger field of view, and mitigates the risks associated with manufacturing process fluctuations, ultimately achieving the goals of high performance, high yield, and mass production.

[0117] This invention selects magnesium fluoride (MgF2) or silicon dioxide (SiO2) as the low refractive index layer. Magnesium fluoride (MgF2) has one of the lowest refractive indices among common optical coating materials, with a refractive index of 1.38 at the standard visible light reference wavelength of 550 nm. It is used to achieve a large refractive index difference (n2-n1≥0.3), minimizing the critical angle for total internal reflection. Silicon dioxide (SiO2) has a slightly higher refractive index of approximately 1.46, but this is still far lower than that of the waveguide layer, and its performance is extremely stable, making it a reliable and versatile choice. Both materials can form hard, dense films. As a "protective layer," they are directly attached to the relatively soft resin lens, effectively resisting scratches and wear from daily wiping. They possess excellent chemical stability, are resistant to water and acid / alkali corrosion, and can withstand environmental conditions such as humidity and sweat, ensuring long-term product reliability. MgF2 and SiO2 are the most fundamental and mature materials in the optical coating industry. Their deposition processes (such as electron beam evaporation and sputtering) are widely mastered, with known parameters that are easy to control, enabling the production of high-quality, uniform thin films. Through appropriate processing (such as ion source-assisted deposition), they can form a strong bond with the resin substrate and the overlying waveguide layer, preventing delamination.

[0118] This invention selects strontium titanate (SrTiO3) or zinc sulfide (ZnS) as the high refractive index waveguide layer. SrTiO3 is an ultra-high refractive index material with a refractive index greater than 2.3 at the standard visible light reference wavelength of 550 nm, which can be used to achieve ultra-large refractive index differences. Zinc sulfide (ZnS) also has a high refractive index, with a refractive index of approximately 2.35 at the standard visible light reference wavelength of 550 nm, and is a commonly used high refractive index material in traditional infrared and visible light fields. Light undergoes dozens or even hundreds of reflections in the waveguide layer, and any tiny absorption will be amplified, leading to a sharp decrease in image brightness. Therefore, low absorption loss is crucial. SrTiO3 and ZnS have good transparency throughout the visible light band (400-700 nm), ensuring efficient transmission of red, green, and blue light and avoiding color shifts or darkening of the image. At the same time, a rough film layer can cause severe light scattering, which can also cause image blurring and darkening. Both materials can be deposited using standard thermal evaporation (ZnS) or sputtering (SrTiO3) processes, forming dense, smooth, low-scattering thin films under certain process conditions, achieving low transport losses. Pairing these two materials can produce synergistic effects. The refractive index difference of the MgF2 / ZnS combination is approximately 0.97, while the difference is even greater for the MgF2 / SrTiO3 combination. This provides the system with significant design margins and performance redundancy. The thermomechanical properties of MgF2 / SiO2 and ZnS / SrTiO3 are relatively similar, reducing stress within the multilayer film and improving structural stability. These materials can be deposited sequentially in the same vacuum deposition equipment by changing the target or evaporation source, simplifying the manufacturing process and facilitating large-scale production.

[0119] In summary, the combination of MgF2 / SiO2 and ZnS / SrTiO3 can achieve a large and stable refractive index difference (n2-n1≥0.3), possessing properties such as low absorption, high transparency, high hardness, and high stability. This combination is suitable for large-scale, high-precision optical coating processes, enabling the fabrication of high-quality functional thin films that maintain stable performance during long-term use and resist environmental aging and physical wear.

[0120] In one embodiment, the lens manufacturing process begins with preparing a polycarbonate lens substrate with a refractive power of -400 degrees. A low-refractive-index layer is deposited on the lens substrate using plasma-assisted electron beam evaporation. High-purity magnesium fluoride is selected as the evaporation source, and a dense magnesium fluoride thin film with a thickness of 180 nanometers and a refractive index of 1.38 is grown under vacuum conditions by precisely controlling the electron beam current and substrate temperature. This thin film exhibits excellent optical uniformity and surface smoothness.

[0121] After completing the fabrication of the low-refractive-index layer, the evaporation source was changed within the same vacuum chamber, and zinc sulfide was used as the high-refractive-index waveguide layer material. By adjusting the deposition rate and oxygen partial pressure, the crystallinity and optical properties of the zinc sulfide film were controlled, ultimately forming a high-quality waveguide layer with a thickness of 150 nanometers and a refractive index of 2.35. Measurements showed that the refractive index difference between the two thin films reached 0.97, far exceeding the technical requirement of 0.3.

[0122] A surface-embossed grating structure is fabricated on the waveguide layer surface using nanoimprint lithography. Due to the large refractive index difference providing ample design tolerance, the grating design does not need to pursue extreme parameters; efficient light coupling and transmission can be achieved using a relatively relaxed process window.

[0123] This invention employs a material system with an extremely large refractive index difference; the combination of magnesium fluoride and zinc sulfide produces a refractive index difference close to one. This material combination significantly reduces the critical angle for total internal reflection, allowing light to undergo total internal reflection at an angle greater than approximately 36 degrees. This characteristic relaxes the tolerance requirements for the incident angle of light, allowing for greater deviations in the position and angle of the optical engine without affecting optical performance. Simultaneously, the larger refractive index difference reduces the difficulty of grating design and improves manufacturing yield. This innovative material selection fundamentally solves the technical challenges of excessively high assembly precision requirements and low yield in augmented reality systems.

[0124] In a preferred embodiment, the augmented reality-based lens includes a stress transition layer between the refractive lens and the low-refractive-index layer; the coefficient of thermal expansion of the refractive lens is α. sub The coefficient of thermal expansion of the stress transition layer is α. trans And the coefficient of thermal expansion of the low refractive index layer is α low Satisfy the following relationship: α low <α trans <α sub , wherein, the α sub Between 7.0×10 -5 / K to 9.0×10 -5 Between / K; the α low Between 0.5×10 -6 / K to 5.5×10 -6 Between / K; the α trans Between 5.0×10 -6 / K to 5.0×10 -5 Between / K.

[0125] In one embodiment, the lens manufacturing process begins with preparing a polycarbonate refractive lens substrate. A stress transition layer is deposited on the concave surface of the lens using plasma-enhanced chemical vapor deposition (PECVD). By precisely controlling the flow rates and deposition power of reactive gases such as silane, nitrogen, and nitrous oxide, a silicon oxynitride thin film is grown on the lens surface. The coefficient of thermal expansion of this film lies between that of the polycarbonate substrate and the subsequent low-refractive-index silicon dioxide layer, forming a favorable gradient transition in the coefficient of thermal expansion.

[0126] During the deposition process, real-time spectral monitoring technology is used to precisely control the chemical composition and thickness of the thin film, ensuring that the thermal expansion coefficient of the stress transition layer remains stable at 7.0 × 10⁻⁶. -6 Approximately / K. This value is higher than that of the silicon dioxide layer (0.5 × 10⁻⁶). -6 / K, but significantly lower than the 8.0×10 of the polycarbonate substrate. -5 / K perfectly satisfies the intermediate value requirement specified in claim 9.

[0127] After the stress transition layer was prepared, a low-refractive-index silica layer and a high-refractive-index zinc sulfide waveguide layer were deposited in the same equipment. Due to the buffering effect of the stress transition layer, the entire multilayer film system exhibited good surface smoothness after deposition, with no visible warping or cracks. Subsequent grating fabrication and packaging processes proceeded smoothly based on this.

[0128] If the stress effects between film layers are ignored, directly depositing functional films on mismatched substrates may lead to film cracking or detachment during product use due to temperature changes. Choosing materials with similar coefficients of thermal expansion severely limits material selection and may sacrifice optical performance. This invention introduces a stress transition layer with a coefficient of thermal expansion strictly between that of the substrate and the functional film layer. This design creates a gradient in the coefficient of thermal expansion, allowing thermal stress between different material layers to be released progressively, rather than accumulating at a single interface. This approach allows designers to prioritize material combinations with optimal optical performance without being limited by their thermomechanical property differences, fundamentally solving the reliability and durability challenges of integrating high-performance optical films with plastic substrates.

[0129] Low refractive index layers (such as SiO2, α) low ≈0.5×10 -6 Alpha (α) is a hard, brittle inorganic material with an extremely low coefficient of thermal expansion, meaning it hardly expands or contracts with temperature changes. Refractive lenses (α...) sub ≈80×10 -6The lens substrate ( / K) is typically a resin material (such as polycarbonate) with a high coefficient of thermal expansion, meaning it expands significantly as the temperature rises and contracts noticeably as the temperature drops. Therefore, when the temperature changes (e.g., from 0°C in winter to 40°C in summer, or from indoors to outdoors), the substrate attempts to expand or contract dramatically, while the inorganic film of the low-refractive-index layer does not. This huge difference in expansion and contraction generates enormous shear stress at the interface between the two layers. This stress can cause the film to wrinkle and warp, deforming the optical surface of the lens, leading to image distortion, and even causing the film to crack and peel off.

[0130] This invention relieves this stress by introducing a stress transition layer. The coefficient of thermal expansion (CTE) is set to α. low <α trans <α sub The reasons are as follows:

[0131] (1) Achieve a gradient transition of stress and avoid sudden stress changes.

[0132] If you jump directly from a resin substrate with a CTE of 80 to a SiO2 layer with a CTE of 0.5, the CTE difference at the interface is as high as 79.5. Stress will concentrate and reach its peak at this point, easily leading to failure. Inserting a transition layer with a CTE of 5.0 to 50 creates two new interfaces. Resin / transition layer interface: CTE difference is Δα1 = |80 - α trans |;Transition layer / SiO2 interface: CTE difference is Δα2=|α trans -0.5|. By selecting α trans The value of ensures that both the differences Δα1 and Δα2 are much less than 79.5. In this way, the enormous total stress is decomposed into two smaller, tolerable stress steps, thus preventing failure at any single interface.

[0133] (2) Protective thin film layer

[0134] The low-refractive-index layer and the high-refractive-index waveguide layer are core components for achieving optical functions, and the stress acting on them must be minimized. The CTE of the transition layer is set to be closer to that of the low-refractive-index layer (i.e., α). trans The lower limit of the bias range, such as 5.0 × 10 -6 The ratio / K) allows Δα2 to become very small. This means that the low-refractive-index layer experiences almost no stress from the transition layer and is well "isolated" and protected, thus ensuring its optical performance and structural integrity.

[0135] (3) Ensure process feasibility and material selection range

[0136] α trans The range is set at 5.0 × 10 -6 / K to 5.0×10 -5 The relatively wide range of / K has significant engineering implications. The lower end of this range (~5ppm / K) is close to many inorganic oxides and nitrides (such as Si3N4, and some glasses). The upper end of this range (~50ppm / K) is close to some organic polymers or organic-inorganic hybrid materials. It is relatively easy to select materials from existing sources that meet both CTE requirements and other key performance indicators such as adhesion, transparency, plating suitability, and durability.

[0137] In a preferred embodiment, in the augmented reality-based lens, the stress transition layer is a periodic multilayer structure composed of alternating layers of silicon monoxide and silicon nitride; in the periodic multilayer structure, the initial layer adjacent to the refractive lens is a silicon monoxide layer, and the terminating layer adjacent to the low refractive index layer is a silicon nitride layer; the total thickness of the periodic multilayer structure is 50 nanometers to 200 nanometers, and it consists of 5 to 20 sub-layer cycles; wherein, the thickness of a single sub-layer cycle decreases gradually from the initial layer to the terminating layer, the thickness of the first sub-layer cycle adjacent to the refractive lens is 15 nanometers to 5 nanometers, and the thickness of the last sub-layer cycle adjacent to the low refractive index layer is 5 nanometers to 1 nanometer.

[0138] In this embodiment, the lens manufacturing process begins with preparing a polycarbonate refractive lens substrate. A stress transition layer is deposited on the concave surface of the lens using magnetron sputtering. Using alternating targets of silicon monoxide and silicon nitride, and by precisely controlling the sputtering power, gas atmosphere, and deposition time, a gradient multilayer structure consisting of 15 sublayer cycles is grown on the lens surface.

[0139] The deposition process begins with the first sublayer adjacent to the refractive lens, which is made of silicon-rich silica and has a deposition thickness controlled at 12 nanometers. Subsequent sublayers maintain an alternating material composition but with decreasing thickness, decreasing by approximately 0.7 nanometers in each cycle. When depositing the final layer adjacent to the low-refractive-index layer, the thickness of this silica sublayer is precisely controlled at 2 nanometers. The total thickness of the entire stress transition layer is 105 nanometers, forming a complete, smooth, gradient structure.

[0140] This periodic multilayer structure effectively disperses and releases stress through interfacial effects, and the interfaces between sublayers can block crack propagation paths. After the stress transition layer is prepared, a low-refractive-index silica layer and a high-refractive-index zinc sulfide waveguide layer are deposited. Due to the stress matching effect of the gradient multilayer structure, the entire film system exhibits excellent interfacial bonding strength and thermal stability.

[0141] Existing technologies typically employ a uniform stress-matching layer made of a single material. The design approach involves selecting a material with a thermal expansion coefficient between that of the substrate and the functional layer to achieve stress transition. While this method provides some stress buffering, limitations in material properties often restrict the range of thermal expansion coefficient adjustment. Furthermore, single-layer interfaces are prone to stress concentration under severe thermal cycling, leading to interface failure. This invention employs a periodic gradient multilayer structure as the stress transition layer. This design creates numerous internal interfaces through multiple alternating sublayers. These interfaces effectively disperse and absorb concentrated thermal stress, preventing stress accumulation at a single interface. The gradient design with decreasing thickness further achieves a smooth transition in the thermal expansion coefficient, avoiding abrupt changes in material properties. More importantly, the interfaces in the multilayer structure effectively block the propagation path of microcracks, significantly improving the mechanical reliability and durability of the film system. This innovative structure solves the technical challenge of traditional single-layer stress-matching layers failing under long-term thermal cycling conditions, providing a reliable guarantee for the long-term stability of optical devices.

[0142] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. It can be applied to various fields suitable for the present invention. Other modifications can be readily made by those skilled in the art. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and examples shown and described herein.

Claims

1. An augmented reality-based lens, characterized in that, include: Refractory lenses have a refractive power used to correct vision; A low refractive index layer is formed on one side surface of the refractive lens; A high-refractive-index waveguide layer is formed on top of the low-refractive-index layer, wherein the refractive index of the high-refractive-index waveguide layer is greater than the refractive index of the low-refractive-index layer; and A diffraction grating structure is formed on the outer surface of the high-refractive-index waveguide layer; The high-refractive-index waveguide layer is configured to receive and transmit light carrying image information via total internal reflection. The incident angle of the light at the interface between the high-refractive-index waveguide layer and the low-refractive-index layer is greater than the critical angle of total internal reflection, so that the light is confined to propagate within the high-refractive-index waveguide layer. The diffraction grating structure is configured to diffract the light out of the high refractive index waveguide layer, so that it passes through the low refractive index layer and the refractive lens in sequence before entering the human eye; The refractive index n1 of the low-refractive-index layer and the refractive index n2 of the high-refractive-index waveguide layer satisfy the following condition: n2 - n1 ≥ 0.3; the low-refractive-index layer is composed of a cured magnesium fluoride or silicon dioxide coating layer, and the refractive index n1 is between 1.38 and 1.46 at a wavelength of 550 nm; the high-refractive-index waveguide layer is composed of a cured strontium titanate or zinc sulfide coating layer, and the refractive index n2 is between 2.2 and 2.5 at a wavelength of 550 nm; A stress transition layer is provided between the refractive lens and the low-refractive-index layer; the coefficient of thermal expansion of the refractive lens is αsub, the coefficient of thermal expansion of the stress transition layer is αtrans, and the coefficient of thermal expansion of the low-refractive-index layer is αlow, satisfying the following relationship: αlow < αtrans < αsub, where αsub is between 7.0 × 10⁻⁶. -5 / K to 9.0×10 -5 / K; the α low is between 0.5 × 10 -6 / K to 5.5×10 -6 The αtrans is between / K; the αtrans is between 5.0 × 10 -6 / K to 5.0×10 -5 Between / K; The stress transition layer is a periodic multilayer structure composed of alternating layers of silicon monoxide and silicon nitride. In the periodic multilayer structure, the initial layer adjacent to the refractive lens is a silicon monoxide layer, and the terminating layer adjacent to the low refractive index layer is a silicon nitride layer. The total thickness of the periodic multilayer structure is 50 nanometers to 200 nanometers, and it consists of 5 to 20 sub-layer cycles. The thickness of a single sub-layer cycle decreases gradually from the initial layer to the terminating layer. The thickness of the first sub-layer cycle adjacent to the refractive lens is 15 nanometers to 5 nanometers, and the thickness of the last sub-layer cycle adjacent to the low refractive index layer is 5 nanometers to 1 nanometer.

2. The augmented reality-based lens according to claim 1, characterized in that, The refractive lens is a plano-concave lens or a plano-convex lens; the refractive lens is made of glass or optical resin material.

3. The augmented reality-based lens according to claim 1, characterized in that, The low refractive index layer is a coating layer or an adhesive layer.

4. The augmented reality-based lens according to claim 1, characterized in that, The diffraction grating structure is a surface relief grating or a volume holographic grating.

5. The augmented reality-based lens according to claim 1, characterized in that, It also includes a protective layer formed on the diffraction grating structure; the protective layer is a low-refractive-index thin film or protective glass.

6. The augmented reality-based lens according to claim 5, characterized in that, The diffraction grating structure is a non-uniform, aberration-corrected grating; The local grating period Λ(x,y) and local grating orientation φ(x,y) of the aberration-corrected grating are functions of the position coordinates (x,y) on the grating plane. The functions Λ(x,y) and φ(x,y) are determined by reverse optimization design using ray tracing software. The optimization objective is to minimize the deviation between the wavefront phase formed at the pupil of the human eye and the ideal spherical wave of the light rays emitted from the diffraction grating structure and passing through the low refractive index layer and the refractive lens in sequence.

7. The augmented reality-based lens according to claim 1, characterized in that, The parameters of the high-refractive-index waveguide layer and the diffraction grating structure are determined through a co-simulation process; the co-simulation process sequentially couples the rigorous coupled-wave analysis module and the non-sequential ray tracing software. The rigorous coupled-wave analysis module is used to establish a local diffraction efficiency database of the diffraction grating structure, which contains the grating diffraction efficiency under different incident angles, polarization states and wavelengths. The non-sequential ray tracing software calls the diffraction efficiency database to trace the complete optical path from the entrance pupil of the optomechanical system to the exit pupil of the human eye. The complete optical path includes multiple total internal reflections of light in the high refractive index waveguide layer, local diffraction events at the diffraction grating structure, and the transmission process through the low refractive index layer and the refractive lens. The optimization objective of the co-simulation process is to maximize the luminous flux and uniformity at the exit pupil of the human eye.

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