Diffractive optical structure, optical system and head-mounted display device

Abstract

The embodiment of the present application discloses a kind of diffractive optical structures, optical systems and head-mounted display device;Among them, the diffractive optical structure includes light transmission layer, which is at least one layer of light transmission film with refractive index greater than 1.9;The diffractive optical structure includes coupling-in region and coupling-out region, the coupling-in region is arranged on the surface or inside the light transmission layer, for the light of image source is coupled into the light transmission layer;The coupling-out region is arranged on the surface or inside the light transmission layer, for the light from the coupling-in region is coupled out from the light transmission layer;The diffractive optical structure further includes carrier sheet, the light transmission layer is arranged on the carrier sheet, and the refractive index of the carrier sheet is lower than the refractive index of the light transmission layer, the carrier sheet is used to carry the light transmission layer and only transmits ambient light.

Description

Technical Field

[0001] This application belongs to the field of augmented reality (AR) technology, specifically, it relates to a diffractive optical structure, an optical system, and a head-mounted display device. Background Technology

[0002] With the continuous development of display technology and computing power, virtual reality (VR), augmented reality (AR), and mixed reality (MR) technologies are becoming increasingly mature. These technologies use specific optical systems to transmit image light emitted from a light source to the user's eyes, providing an immersive visual experience. In head-mounted display devices such as AR and MR glasses, optical waveguide technology has become an important technical solution due to its advantages such as thinness, transparency, and wide display angle.

[0003] However, traditional optical waveguide technology often relies on high-refractive-index substrate materials to achieve total internal reflection of light. These materials are typically dense and heavy, limiting the portability and comfort of optical display devices. Furthermore, the manufacturing of high-refractive-index substrate materials is complex and costly, making it difficult to meet the market's demand for a combination of high performance and lightweight design. Summary of the Invention

[0004] The purpose of this application is to provide a new technical solution for a diffractive optical structure, an optical system, and a head-mounted display device.

[0005] According to a first aspect of this application, embodiments of this application provide a diffractive optical structure, the diffractive optical structure comprising:

[0006] The light-transmitting layer is at least one light-transmitting thin film with a refractive index greater than 1.9;

[0007] The coupling region is disposed on the surface or inside the light-transmitting layer and is used to couple the light from the image source into the light-transmitting layer.

[0008] The coupling region is disposed on the surface or inside the light-transmitting layer and is used to couple light from the coupling region out of the light-transmitting layer;

[0009] A carrier sheet, wherein the light-transmitting layer is disposed on the carrier sheet, and the refractive index of the carrier sheet is lower than that of the light-transmitting layer, the carrier sheet is used to support the light-transmitting layer and transmits only ambient light.

[0010] Optionally, the thickness of the light-transmitting layer is on the order of micrometers to millimeters.

[0011] Optionally, the light-transmitting layer is an adhesive layer, which includes a nanoimprint adhesive layer or a photoresist layer.

[0012] Optionally, the light-transmitting film is a holographic polymer layer, a metal oxide deposition layer, or a liquid crystal layer.

[0013] Optionally, the light-transmitting layer includes an upper surface and a lower surface opposite each other, and the upper surface and / or the lower surface of the light-transmitting layer are curved.

[0014] Optionally, the refractive index of the carrier sheet is less than 1.6.

[0015] Optionally, the carrier sheet is made of resin.

[0016] Optionally, the material of the carrier sheet includes polymethyl methacrylate (PMMA), polystyrene (PS), polycarbonate (PC), or polyethylene (PE).

[0017] Optionally, an air gap is provided between the substrate and the light-transmitting layer.

[0018] Optionally, the coupling region may be configured as one or more, and the coupling region may be provided with a coupling grating;

[0019] The coupling region is configured as one or more, and the coupling region is provided with a coupling grating.

[0020] Optionally, the diffractive optical structure further includes a turning region, which is disposed on the surface or inside the light-transmitting layer;

[0021] The transition region is set as one or more, and the transition region is provided with a transition grating;

[0022] The turning region is located between the coupling-in region and the coupling-out region, and is used to turn the direction of the light rays coupled into the coupling-in region and transmit them to the coupling-out region.

[0023] According to a second aspect of this application, an embodiment of this application provides an optical system, the optical system comprising:

[0024] Image source; and

[0025] As described in the first aspect, the light emitted from the image source can be incident on the coupling region of the diffraction optical structure.

[0026] According to a third aspect of this application, embodiments of this application provide a head-mounted display device, the head-mounted display device comprising:

[0027] The outer casing; and

[0028] The optical system as described in the second aspect is disposed within the housing.

[0029] One beneficial effect of the embodiments of this application is that:

[0030] The diffractive optical structure provided in this application innovatively expands the functionality of its components, abandoning the imaging light transmission function of the traditional waveguide substrate. Instead, it uses a high-refractive-index transparent film (such as one with a refractive index greater than 1.9) as the core light-transmitting layer. This high-refractive-index light-transmitting layer supports efficient total internal reflection propagation of light within the layer, thereby improving optical performance. In this application, the refractive index of the carrier sheet is significantly lower than that of the light-transmitting layer. This means that the carrier sheet no longer serves the function of imaging light transmission, but only as a mechanical support and for transmitting ambient light. Therefore, lightweight materials can be used, and it can be designed to be thinner, significantly reducing the overall weight. The diffractive optical structure provided in this application achieves the dual advantages of high performance and lightweight design through the use of a high-refractive-index light-transmitting layer, a lightweight carrier sheet, and a flexible coupling-in / coupling-out design.

[0031] The light-transmitting layer in this application serves as the primary channel for light transmission, ensuring that the diffractive optical structure maintains a large field of view (FOV) and significantly improving optical performance, including luminous efficacy, uniformity, modulation transfer function (MTF), and color reproduction. Because the light-transmitting layer uses lightweight materials, and the substrate primarily bears the load in the presence of a base, eliminating the need for high-refractive-index materials, the weight of the entire optical diffraction structure is greatly reduced, thus significantly improving the product's comfort and portability.

[0032] Other features and advantages of this application will become clear from the following detailed description of exemplary embodiments with reference to the accompanying drawings. Attached Figure Description

[0033] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments of the present application and, together with their description, serve to explain the principles of the present application.

[0034] Figure 1 This is a schematic diagram of the structure and optical path of the diffractive optical structure provided in the embodiments of this application;

[0035] Figure 2 This is one of the schematic diagrams of the structure and optical path of a traditional diffractive waveguide;

[0036] Figure 3 This is the second schematic diagram of the structure and optical path of a traditional diffractive waveguide.

[0037] Explanation of reference numerals in the attached figures:

[0038] 1. Coupling-in region; 2. Coupling-out region; 3. Light transmission layer; 4. Carrier sheet; 5. Cover layer; 6. Traditional adhesive layer. Detailed Implementation

[0039] Various exemplary embodiments of the present application will now be described in detail with reference to the accompanying drawings. It should be noted that, unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the present application.

[0040] The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the scope of this application and its application or use.

[0041] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and equipment should be considered part of the specification.

[0042] In all the examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0043] It should be noted that similar labels and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be discussed further in subsequent figures.

[0044] The diffractive optical structure, optical system, and head-mounted display device provided in the embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0045] According to one embodiment of this application, a diffractive optical structure is provided, see [link to relevant documentation]. Figure 1 The diffractive optical structure includes a light-transmitting layer 3, which is at least one transparent thin film with a refractive index greater than 1.9. The diffractive optical structure also includes a coupling-in region 1 and a coupling-out region 2. The coupling-in region 1 is disposed on the surface or inside the light-transmitting layer 3 and is used to couple light from the image source into the light-transmitting layer 3. The coupling-out region 2 is disposed on the surface or inside the light-transmitting layer 3 and is used to couple light from the coupling-in region 1 out of the light-transmitting layer 3. The diffractive optical structure also includes a carrier sheet 4, on which the light-transmitting layer 3 is disposed, and the refractive index of the carrier sheet 4 is lower than that of the light-transmitting layer 3. The carrier sheet 4 is used to support the light-transmitting layer 3 and transmits only ambient light.

[0046] The image source emits imaging light rays. The light transmission layer 3 is specifically used to transmit imaging light rays. The image source is, for example, an optical engine.

[0047] The carrier sheet 4 does not transmit imaging light; it is translucent and can transmit ambient light.

[0048] It should be noted that all the refractive index values ​​mentioned in this application are based on tests under visible light, and more specifically, tests at 589nm (i.e., green light).

[0049] The core of the diffractive optical structure provided in this application embodiment lies in the introduction of a light-transmitting layer 3. As the core optical component of the diffractive optical structure, the light-transmitting layer 3 consists of at least one light-transmitting thin film. A key characteristic of these thin films is their high refractive index; for example, the refractive index is designed to be greater than 1.9, or even greater than 2, or even 2.2, ensuring that light can achieve efficient total internal reflection propagation within the light-transmitting layer 3.

[0050] In other words, a significant innovation in the diffractive optical structure provided in the application embodiments lies in the introduction of a light-transmitting layer 3. This design replaces the high-density, high-refractive-index waveguide substrate typically used in traditional optical waveguides as the core channel for light transmission (such as...). Figure 2 and Figure 3 (The traditional structure shown is used for comparison). Through this design, light can be transmitted efficiently and stably within the newly designed light-transmitting layer 3.

[0051] This application's design ensures optimized transmission path and improved optical efficiency for imaging light, and fundamentally solves the weight burden problem caused by the use of high-density, high-refractive-index waveguide substrates in traditional diffractive waveguide designs. By eliminating these heavy materials, the diffractive optical structure provided by this application achieves significant weight reduction, offering a lighter and more comfortable wearing experience for head-mounted display devices such as augmented reality (AR) and mixed reality (MR). Overall, this application's design significantly reduces the overall weight of the diffractive optical structure while maintaining or even improving optical performance, opening a new path for the lightweight development of head-mounted display devices.

[0052] The diffractive optical structure provided in the embodiments of this application is described below.

[0053] Light-transmitting layer 3: This is at least one light-transmitting thin film with a refractive index greater than 2. The high refractive index ensures that imaging light can undergo total internal reflection within the light-transmitting layer 3, thereby effectively transmitting light.

[0054] Coupled-in region 1: It is disposed on the surface or inside the light transmission layer 3 and is responsible for efficiently coupling external light into the light transmission layer.

[0055] In this application, the coupling region 1 can be a diffraction element such as a surface relief grating, a volume holographic grating, a metasurface, or a photonic crystal, to ensure that the imaging light emitted from the optomechanical system can enter the light transmission layer 3 at the expected angle.

[0056] Coupled-out region 2: It is disposed on the surface or inside the light transmission layer 3 and is used to couple light out from the light transmission layer 3 and transmit it to the user's eyes.

[0057] In this application, similar to the coupling-in region 1, the coupling-out region 2 also utilizes diffraction elements to effectively control light, ensuring that the user can see a clear image.

[0058] Support plate 4: Its refractive index is lower than that of the light transmission layer 3. In this application, the support plate 4 serves only as a mechanical support and does not participate in the transmission of imaging light.

[0059] In this application, the carrier sheet 4 can use ultra-light and ultra-thin lens materials, such as polymethyl methacrylate (PMMA), whose low refractive index characteristics allow the imaging light emitted from the optical engine to be mainly transmitted within the newly designed light transmission layer 3, thereby achieving a lightweight design.

[0060] The diffractive optical structure provided in this application has the following main technical advantages:

[0061] (1) The high refractive index light transmission layer 3 ensures efficient transmission of imaging light within the layer, reduces light loss, and improves optical performance, such as brightness, uniformity, and color performance. The combination of the coupling-in and coupling-out design enables the imaging light emitted from the optical engine to accurately enter and leave the light transmission layer 3, further improving light utilization and overall performance.

[0062] (2) In this application, the carrier sheet 4 does not serve the function of transmitting imaging light, but only as a support structure and transmitting ambient light. Therefore, lightweight materials can be used and it can be designed to be thinner, which can significantly reduce the weight of the entire diffractive optical structure.

[0063] In summary, the diffractive optical structure provided in this application innovatively expands the functionality of its components, abandoning the imaging light transmission function of the traditional waveguide substrate. Instead, it employs a high-refractive-index transparent film (e.g., with a refractive index greater than 1.9) as the core light-transmitting layer. This high-refractive-index light-transmitting layer supports efficient total internal reflection propagation of light within the layer, thereby improving optical performance. In this application, the refractive index of the carrier sheet is significantly lower than that of the light-transmitting layer. This means that the carrier sheet no longer serves the function of imaging light transmission but only acts as a mechanical support and transmits ambient light. Therefore, lightweight materials can be selected and the structure can be designed to be thinner, significantly reducing the overall weight. The diffractive optical structure provided in this application achieves the dual advantages of high performance and lightweight design through the use of a high-refractive-index light-transmitting layer, a lightweight carrier sheet, and a flexible coupling-in / coupling-out design.

[0064] The light-transmitting layer in this application serves as the primary channel for light transmission, ensuring that the diffractive optical structure maintains a large field of view (FOV) and significantly improving optical performance, including luminous efficacy, uniformity, modulation transfer function (MTF), and color reproduction. Because the light-transmitting layer uses lightweight materials, and the substrate primarily bears the load in the presence of a base, eliminating the need for high-refractive-index materials, the weight of the entire optical diffraction structure is greatly reduced, thus significantly improving the product's comfort and portability.

[0065] The diffractive optical structure provided in this application embodiment is designed to eliminate the need for traditional high refractive index and high density substrates, achieving a balance between lightweight and high performance.

[0066] The diffractive optical structure of this application embodiment achieves a significant reduction in overall weight while maintaining high performance through a high-refractive-index light-transmitting layer 3, a lightweight carrier sheet 4, and a flexible coupling-in and coupling-out design, bringing a revolutionary optical solution to wearable devices such as AR / MR glasses.

[0067] In some examples of this application, the thickness of the light-transmitting layer 3 is on the order of micrometers to millimeters.

[0068] The thickness range from micrometers to millimeters ensures that the light-transmitting layer 3 can effectively support total internal reflection propagation of light within it. This thickness range allows imaging light to maintain high transmission efficiency within the light-transmitting layer 3, which helps to improve overall optical performance.

[0069] In this application, the thickness range of the light-transmitting layer 3 is designed to achieve a balance between high performance and lightweight design. Specifically, traditionally, in order to obtain a large field of view (FOV) and better optical performance, optical waveguides often require the use of waveguide substrate materials with high refractive index but high density, and may require multi-layer structures, which leads to an increase in the overall weight of the optical waveguide. However, by designing the thickness of the light-transmitting layer 3 to be on the micrometer to millimeter scale and using a high refractive index transparent film as the light-transmitting layer, high performance can be maintained while eliminating the dependence on heavy waveguide substrate materials, thereby achieving lightweight design of the optical waveguide.

[0070] In this application, the light-transmitting layer 3 serves as the transmission channel for imaging light, and its refractive index directly affects the transmission efficiency and angular range of the imaging light. By employing a high-refractive-index material (such as a titanium oxide deposition layer with a refractive index of approximately 2.55), efficient transmission of imaging light and a large field of view (FOV) can be achieved within a thickness ranging from micrometers to millimeters. This represents an improvement in optical performance compared to traditional thick waveguide substrate materials.

[0071] Furthermore, thicknesses ranging from micrometers to millimeters are easily achievable with existing manufacturing processes, which facilitates mass production and cost control. At the same time, a well-designed thickness also improves product yield and stability.

[0072] In some examples of this application, the light-transmitting layer 3 is an adhesive layer, which includes a nanoimprint adhesive layer or a photoresist layer.

[0073] Both nanoimprint retardants and photoresists possess excellent pattern replication capabilities, enabling precise transfer of pre-defined grating patterns onto waveguide substrates. This is particularly important for fabricating diffraction gratings with complex micro / nano structures. This application utilizes the nanoimprint retardant layer or photoresist layer in the fabrication of the diffraction grating as the light-transmitting layer 3 to transmit imaging light. Compared to traditional high-refractive-index waveguide substrate materials (such as glass or high-density resin), these retardant materials can have lower densities, thus significantly reducing the overall weight of the diffraction optical structure. Simultaneously, by selecting high-refractive-index retardant materials, the optical performance of the diffraction optical structure can be maintained or even improved, such as field of view (FOV), luminous efficiency, and uniformity, thereby achieving a perfect combination of lightweight and high performance.

[0074] Furthermore, nanoimprinted resist layers and photoresist layers offer flexibility in material selection. Resist materials with different refractive indices and physical properties can be chosen based on specific application requirements to optimize the overall performance of the diffractive optical structure.

[0075] In some examples of this application, the light-transmitting film is a holographic polymer layer, a metal oxide deposition layer, or a liquid crystal layer.

[0076] Based on the examples above and the example provided in this application, this application employs a variety of transparent films in the selection of materials for the transparent film, including but not limited to various forms of adhesive layers, holographic polymer layers with advanced optical properties, and metal oxide deposition layers and liquid crystal layers with high refractive indices.

[0077] It is worth mentioning that the holographic polymer layer, the metal oxide deposition layer (such as the titanium oxide deposition layer), and the liquid crystal layer can all provide high refractive indices. Specifically, taking the titanium oxide deposition layer as an example, its refractive index can reach between 2.5 and 2.7. Such a high refractive index not only meets the requirement of total internal reflection of light within the light transmission layer, but also further increases the field of view (FOV) of the diffractive optical structure, thereby improving the upper limit of optical performance.

[0078] It should be noted that the material of the light-transmitting film in the light-transmitting layer 3 of this application is related to the grating type of the coupling region 1 and the coupling region 2. The following two examples illustrate this.

[0079] Example 1: Application of metal oxide deposition layers in grating structures:

[0080] For cases where surface relief gratings or volume holographic gratings are required for coupling region 1 and coupling region 2, this application introduces a metal oxide deposition layer (such as a titanium oxide deposition layer) as part of the light-transmitting layer 3. This material not only possesses a high refractive index, which is beneficial for total internal reflection transmission of light, but also ensures the fineness and consistency of the grating structure through precise control of the deposition process. Furthermore, the addition of the metal oxide deposition layer enhances the durability and environmental stability of the light-transmitting layer, providing a longer service life for the diffractive optical structure.

[0081] Example 2: Advantages of dynamic control of liquid crystal layers:

[0082] To achieve dynamic tunability of the grating structure in coupling region 1 and coupling region 2, this application can also employ a liquid crystal layer as the light-transmitting layer 3. The liquid crystal layer not only possesses excellent optical properties but also, through its unique electro-optic effect, allows for dynamic adjustment of its refractive index and transmission characteristics by applying voltage. This design enables the diffractive optical structure to control the transmission path and distribution of light in real time according to actual needs, providing richer interactive experiences and greater adaptability for augmented reality (AR) and mixed reality (MR) applications.

[0083] In terms of material selection, this application employs a variety of light-transmitting films, including but not limited to various forms of adhesive layers, holographic polymer layers with advanced optical properties, and metal oxide deposition layers and liquid crystal layers with high refractive indices. It is worth noting that these materials not only provide excellent optical transparency but also possess high refractive indices. For example, when the light-transmitting layer 3 is a titanium oxide deposition layer, its refractive index can reach as high as 2.5 to 2.7. This characteristic greatly expands the flexibility and performance ceiling of optical design, fully meeting the total internal reflection requirements in light transmission scenarios, thus laying the foundation for the diffractive optical structure in high-performance optical applications.

[0084] In some examples of this application, the light-transmitting layer 3 includes an upper surface and a lower surface opposite each other, and the upper surface and / or the lower surface of the light-transmitting layer 3 are curved.

[0085] Optionally, the light-transmitting layer 3 of this application can be a planar thin layer, or it can have a shape with a curved upper surface and / or lower surface. This application does not impose specific restrictions on this.

[0086] In other words, the light transmission layer 3 is not limited to a planar thin layer, but can also be designed as a curved shape to meet the needs of different application scenarios (such as vision correction, ergonomic design, etc.).

[0087] In this example of the application, the light-transmitting layer 3 is designed to have opposing upper and lower surfaces, and these surfaces can be curved. This design brings several technical advantages, as follows:

[0088] (1) It can adapt to the curvature of the human eye and improve wearing comfort. Since the human eye mask has a certain curvature, the upper or lower surface of the light transmission layer 3 is designed as a curved shape, which can better fit the contour of the eyeball, reduce the pressure and discomfort when wearing, and thus improve the user's wearing comfort.

[0089] (2) It can appropriately expand the field of view (FOV). The curved light transmission layer 3 can guide light more effectively, so that the light can better match the visual characteristics of the human eye during transmission. By reasonably designing the curvature of the surface, the field of view can be expanded, enhancing immersion and interactive experience.

[0090] The diffractive optical structure provided in the embodiments of this application is described in [reference]. Figure 1 In addition to the core light-transmitting layer 3, it also has a carrier plate 4. The light-transmitting layer 3 is disposed on the carrier plate 4. The carrier plate 4 is used to provide a stable support platform for the light-transmitting layer 3 without affecting the transmission of ambient light.

[0091] It should be noted that, see Figure 2 and Figure 3 Traditional waveguide substrates not only serve as supporting structures but also directly participate in the transmission of imaging rays emitted from the optomechanical system, acting as the primary medium for total internal reflection of imaging rays. Their refractive index directly determines the range of light propagation angles and the field of view (FOV).

[0092] In this application, see Figure 1 The imaging light is mainly transmitted in the light transmission layer 3, while the main function of the carrier sheet 4 is to support the light transmission layer 3 and allow ambient light to pass through.

[0093] To achieve a wide field of view and excellent optical performance, traditional waveguide substrates require high-refractive-index materials, such as high-refractive-index glass or crystals. These materials often have high density, resulting in a relatively heavy overall weight for the optical waveguide. Furthermore, to maintain sufficient optical thickness and structural strength, traditional waveguide substrates typically have a large thickness, which also increases the overall weight of the optical waveguide.

[0094] Since the carrier plate 4 of this application no longer undertakes the function of transmitting imaging light, it can be made of materials with lower density and lighter weight, such as resin materials (e.g., PMMA, PS, PC, etc.). These materials not only reduce the overall weight of the diffraction optical structure but also maintain good mechanical and processing properties. Furthermore, since the carrier plate 4 of this application does not participate in the transmission of imaging light, it can be made thinner and lighter, reducing the weight of the diffraction optical structure and improving wearing comfort.

[0095] In some examples of this application, the refractive index of the carrier sheet 4 is less than 1.6.

[0096] When the refractive index of the carrier plate 4 is less than 1.6, it forms a significant difference from the refractive index of the light-transmitting layer 3 (which reaches 1.9 or even greater than 2 or 2.2). This design achieves effective control of the light transmission path in the diffractive optical structure. Specifically, since the refractive index of the carrier plate 4 is much lower than that of the light-transmitting layer 3, when the imaging light is emitted from the optomechanical system, it is mainly confined to the high-refractive-index light-transmitting layer 3 for transmission, rather than penetrating into the low-refractive-index carrier plate 4.

[0097] This design in this application offers several key technical advantages:

[0098] By adjusting the refractive index and thickness of the light-transmitting layer 3, the transmission path and angle of the imaging light can be precisely controlled, thereby achieving a larger field of view (FOV) and a more uniform light intensity distribution, enhancing the user's visual experience.

[0099] Since the carrier plate 4 does not need to have high refractive index characteristics, it can be made of lightweight materials, such as resin materials, thereby significantly reducing the overall weight of the diffraction optical structure and improving wearing comfort.

[0100] In some examples of this application, the carrier sheet 4 is made of resin material.

[0101] Resin materials generally have a low refractive index, and some resin materials can even have a refractive index below 1.5, which can create a large refractive index difference with the light transmission layer 3.

[0102] When the carrier sheet 4 is made of resin material, especially resin material with a refractive index lower than 1.5, the refractive index difference between it and the high-refractive-index light-transmitting layer 3 can be further increased. This design brings more significant technical advantages:

[0103] (1) Due to the greater difference in refractive index, the total internal reflection condition of the imaging light in the light transmission layer 3 is more stringent, and the light is more effectively confined in the light transmission layer 3, reducing the possibility of the imaging light leaking into the carrier sheet 4, thereby improving the light transmission efficiency.

[0104] (2) Improved field of view (FOV): A larger difference in refractive index allows for the design of a wider light transmission angle, which may result in a larger field of view, providing users with a wider field of view.

[0105] Resin materials have a lower density than traditional waveguide substrate materials such as glass, which can reduce the weight of the entire diffractive optical structure.

[0106] In some examples of this application, the material of the carrier sheet 4 includes polymethyl methacrylate (PMMA), polystyrene (PS), polycarbonate (PC), or polyethylene (PE).

[0107] In this example of the application, the material of the carrier sheet 4 can be, for example, PMMA, PS, PE, or PC. These resin materials have a low refractive index and also possess good weather resistance and chemical stability, enabling them to resist wear, corrosion, and aging during daily use. This ensures the long-term stability and reliability of the diffractive optical structure in complex and changing operating environments.

[0108] In some examples of this application, an air gap is provided between the carrier sheet 4 and the light-transmitting layer 3.

[0109] In some examples of this application, when the diffractive optical structure design includes a carrier sheet 4, an air gap is designed between the carrier sheet 4 and the light-transmitting layer 3. For example, this air gap is generally required to be greater than several wavelengths, i.e., at least 1 micrometer.

[0110] According to this example of the application, providing a certain air gap between the light-transmitting layer 3 and the carrier sheet 4 is beneficial to improving optical performance. This is because:

[0111] The refractive index of air itself is only about 1, and the difference between the refractive index of air and light transmission layer 3 is more significant, which expands the upper limit of optical properties such as FOV and uniformity.

[0112] The air gap effectively isolates the carrier sheet 4 from the interference of light transmission in the light-transmitting layer 3. Since the carrier sheet 4 no longer directly participates in light transmission, the air layer between it and the light-transmitting layer 3 becomes a clear optical interface, reducing optical losses that may be caused by the refractive index and absorption characteristics of the substrate material.

[0113] The presence of air gaps helps reduce light reflection and scattering at the interface between the carrier sheet 4 and the light-transmitting layer 3, increasing light transmittance and thus enhancing the clarity and brightness of the display. This is particularly important for improving the visual effects of optical display devices such as AR / MR glasses.

[0114] The air gap isolates the thermal and mechanical stresses between the carrier plate 4 and the light transmission layer 3 to a certain extent, which helps to prevent structural damage or performance degradation caused by stress concentration, thereby improving the stability and reliability of the entire diffractive optical structure.

[0115] In some examples of this application, the coupling-in region 1 is set to one or more, and the coupling-in region 1 is provided with a coupling-in grating; the coupling-out region 2 is set to one or more, and the coupling-out region 2 is provided with a coupling-out grating.

[0116] In a specific example, the light-transmitting layer 3 of the diffractive optical structure can be provided with multiple coupling-in regions 1 and coupling-out regions 2, and corresponding coupling-in gratings and coupling-out gratings can be arranged in each region. This design can increase the selection of the coupling path of light from the light source to the user's eyes. This means that light can enter the light-transmitting layer 3 from multiple entrances and exit from multiple exits, thereby improving the utilization efficiency of light.

[0117] Furthermore, the design of multiple coupling-in and coupling-out regions helps to expand the field of view of the diffractive optical structure.

[0118] For example, each coupling region 1 can couple light into the light transmission layer 3 from different angles, while each coupling region 2 can couple light out from different positions, thus forming a wider field of view.

[0119] Furthermore, the design of multiple input and output regions helps improve the optical uniformity of the diffractive optical structure. By setting input and output gratings at different locations, the distribution of light in the light transmission layer 3 can be made more uniform, reducing visual discomfort caused by excessively high or low local light intensity. At the same time, by adjusting the grating parameters of each input and output region, the diffraction efficiency and distribution uniformity of light can be further optimized, improving the overall display quality.

[0120] The design in this example enables the diffractive optical structure to be more widely used in various augmented reality (AR) and mixed reality (MR) devices. Whether it is smart glasses, helmet displays, or other forms of head-mounted displays, specific optical performance requirements and application scenarios can be met by adjusting the layout and parameters of coupling region 1 and coupling region 2.

[0121] In some examples of this application, the diffractive optical structure further includes a turning region, which is disposed on the surface or inside the light-transmitting layer 3; the turning region is configured as one or more, and the turning region is provided with a turning grating; the turning region is located between the coupling-in region 1 and the coupling-out region 2, and is used to turn the direction of the light coupled into the coupling-in region 1 and transmit it to the coupling-out region 2.

[0122] The presence of the diffraction grating allows for more flexible and diverse light transmission paths within the light transmission layer 3. By designing the diffraction parameters of the diffraction grating, the propagation direction and angle of light can be effectively controlled, reducing light loss during transmission and improving light transmission efficiency.

[0123] The design of the transition region and the transition grating enables the diffractive optical structure to achieve a wider field of view within a limited physical space. By rationally arranging the position and angle of the transition grating, light rays from the coupling region 1 can be directed to different coupling regions 2, thereby expanding the user's field of view.

[0124] Especially in applications of curved waveguides, the angular grating can further adjust the direction of light transmission to adapt to the shape of the curved surface and the user's field of vision needs, providing a more immersive visual experience.

[0125] In some examples of this application, the coupling grating, the coupling out grating, and the transition grating include surface relief gratings, volume holographic gratings, metasurfaces, or photonic crystals.

[0126] In other words, the diffractive optical structure provided in this application embodiment can have an input grating that is a surface relief grating, a volume holographic grating, a metasurface, or a photonic crystal, and an output grating that is also a surface relief grating, a volume holographic grating, a metasurface, or a photonic crystal. When the diffractive optical structure is further designed to include a transition grating, the transition grating can also be selected from a surface relief grating, a volume holographic grating, a metasurface, or a photonic crystal.

[0127] The grating types in this example all exhibit high diffraction efficiency, enabling efficient coupling of incident light into and out of the light-transmitting layer 3. In particular, metasurfaces and photonic crystals, through meticulous structural design, can achieve excellent optical behavior, thereby further enhancing diffraction efficiency.

[0128] Different types of gratings have different optical properties, such as angle sensitivity and polarization dependence. By selecting the appropriate grating type, the performance of diffractive optical structures in different application scenarios can be optimized, such as increasing the field of view and improving color uniformity.

[0129] Different types of gratings are suitable for different manufacturing processes. For example, surface relief gratings are suitable for nanoimprint lithography, while volume holographic gratings are suitable for holographic recording technology. This compatibility makes the production process of diffractive optical structures more flexible and diverse, allowing for the selection of appropriate manufacturing processes based on existing production conditions.

[0130] The diffractive optical structure provided in the embodiments of this application is, for example, a diffractive waveguide.

[0131] Optionally, in the diffractive optical structure provided in this application embodiment, a coating or layer can also be provided as a cover layer 5 on one side of the light transmission layer 3 where the coupling-in region 1 and the coupling-out region 2 are provided, see [link to relevant documentation]. Figure 1 .

[0132] See Figure 1 The coating or layer 5 serves to protect the underlying input and output gratings from environmental factors such as dust, moisture, chemicals, and mechanical damage. This helps improve the durability and lifespan of the diffractive optical structure.

[0133] Furthermore, by selecting appropriate materials and technologies, the covering layer 5 can further enhance the performance of the diffractive optical structure. For example, an antireflective coating can reduce light reflection loss at the interface and improve light transmittance; an antireflective coating can reduce stray light and improve image clarity and contrast; and a multilayer film structure can achieve specific spectral modulation to meet more complex optical design requirements.

[0134] The capping layer 5 must first be transparent to ensure that it does not block or scatter incident or emitted light. Common transparent materials include inorganic materials such as silicon dioxide (SiO2), silicon nitride (Si3N4), and titanium dioxide (TiO2), as well as low refractive index materials such as magnesium fluoride (MgF2) and calcium fluoride (CaF2). These materials have good optical properties and chemical stability.

[0135] Depending on specific needs, materials with specific functionalities can also be selected as the covering layer 5.

[0136] The material of the covering layer 5 can be selected as needed, and this application does not impose any restrictions on it.

[0137] The diffractive optical structure provided in this application features high performance and lightweight design. The key to achieving this technical effect stems from a novel application of the "residual adhesive problem" in traditional optical waveguides. Traditional optical waveguides typically use transparent media such as glass or resin as the carrier sheet 4, see [link to relevant documentation]. Figure 2 A conventional adhesive layer 6, such as an imprinting adhesive, is coated onto its surface, and a grating structure is then fabricated on the imprinting adhesive. In a conventional optical waveguide, the total internal reflection condition of light determines the field of view (FOV) of the optical waveguide, and the size of the FOV is directly limited by the refractive index of the carrier sheet 4 of the conventional optical waveguide.

[0138] Specifically, the FOV of a traditional optical waveguide is mainly determined by the refractive index n of its carrier plate 4, and the angle during transmission. θ The range is as follows: .

[0139] Meanwhile, within the effective field of view (FOV), the optical performance of the waveguide (such as luminous efficacy, uniformity, MTF, and color performance) is also closely related to the refractive index of the substrate. Generally speaking, the higher the refractive index of the waveguide substrate, the greater the potential for achieving FOV and optical performance (such as luminous efficacy, uniformity, MTF, and color performance).

[0140] In actual manufacturing processes, the problem of "residual adhesive" is often encountered. This is because during the manufacturing of optical waveguides, a thin layer of imprinted adhesive remains on the non-grating area of ​​the waveguide substrate surface. As a result, light undergoes total internal reflection at the interface between the waveguide carrier 4 and air, but at the interface between the carrier 4 and the conventional adhesive layer 6 (the refractive index of the conventional adhesive layer 6 is comparable to or even higher than that of the carrier 4), the light enters the conventional adhesive layer 6, is reflected, and then returns to the carrier 4. See [link to documentation]. Figure 3 .

[0141] Typically, the imprinting adhesive layer 6 remaining on the substrate of an optical waveguide is very thin, on the order of hundreds of nanometers, and will not disrupt the normal operation of the optical waveguide. However, since the refractive index of the traditional adhesive layer 6 is different from that of the carrier sheet 4, it has a certain impact on the optical performance of the optical waveguide.

[0142] Regarding the "residual adhesive problem" that is traditionally considered a defect, if the thickness of this traditional adhesive layer 6 can be increased to the micrometer or even millimeter level, then light may be transmitted mainly in the thickened traditional adhesive layer 6, rather than just acting as a reflective medium between interfaces.

[0143] Furthermore, if the refractive index of this conventional adhesive layer 6 is significantly higher than that of the substrate material, and the refractive index of the substrate is designed to be relatively low, then light may simultaneously undergo total internal reflection at both the interfaces between the conventional adhesive layer 6 and air, and between the conventional adhesive layer 6 and the carrier sheet 4, thus transmitting entirely within the conventional adhesive layer 6, and the angular range during the transmission process is: .

[0144] Based on the above considerations, the design in this application not only changes the traditional optical waveguide design that uses the substrate as the main light transmission channel, but also eliminates the need for a high-refractive-index substrate material by introducing a high-refractive-index light-transmitting layer 3 as a new light transmission medium. This allows for the selection of a lighter, lower-density material as the support sheet 4 (in which case the substrate only serves a supporting function and no longer bears the light transmission function), thereby significantly reducing the weight of the entire diffractive optical structure while achieving high-performance optical characteristics. This design not only resolves the contradiction between high performance and lightweight design, but also opens up new possibilities for the application of diffractive optical structures in augmented reality (AR) and mixed reality (MR) devices.

[0145] In summary, this application proposes a novel design: extending the thickness of the traditional adhesive layer 6 (i.e., residual adhesive) to the micrometer or even millimeter level to form a completely new light transmission medium—the light-transmitting layer 3. This light-transmitting layer is not limited to traditional nanoimprint adhesive layers; it can also widely utilize various high-refractive-index optical thin-film materials, including photoresist layers, holographic polymer layers, metal oxide deposition layers, and liquid crystal layers. Through design, these light-transmitting layers 3 possess sufficient thickness and refractive index to ensure that light can propagate through total internal reflection while preventing light leakage into the substrate.

[0146] Under this structural design, the function of the support plate 4 has undergone a fundamental change. It no longer participates in the transmission of imaging light rays, but is transformed into a support plate that only has load-bearing and stabilizing mechanical properties. This change allows for the use of lighter and thinner lens materials to manufacture the support plate 4, which can significantly reduce its refractive index and material density, thereby effectively reducing the weight of the entire diffractive optical structure.

[0147] Furthermore, since the carrier plate 4 primarily serves a load-bearing function, its optical thickness is no longer a critical factor, allowing for further reduction in thickness without concerns about adverse effects on optical performance. In certain design scenarios, if the light-transmitting layer 3 already possesses sufficient strength and stability, or has been reinforced through other structural means, the carrier plate 4 may even be completely unnecessary, further simplifying the structure of the diffractive optical system and reducing costs.

[0148] In summary, this application, by introducing an innovative light-transmitting layer 3, eliminates the reliance of traditional optical waveguides on high-refractive-index substrate materials, achieving the dual goals of high performance and lightweight diffractive optical structures. This design not only broadens the range of materials available for diffractive optical structures but also enables lighter and more comfortable augmented reality (AR) and mixed reality (MR) devices.

[0149] The diffractive optical structure of this application is further described below through Examples 1 and 2.

[0150] Example 1

[0151] The diffractive optical structure provided in this embodiment 1 includes a carrier sheet 4 and a light transmission layer 3. The light transmission layer 3 is disposed on the carrier sheet 4, and the light transmission layer 3 is provided with a coupling-in grating and a coupling-out grating for transmitting light coupled into the light transmission layer 3 from the coupling-in grating to the coupling-out grating. The coupling-out grating is used to couple light out to the outside of the light transmission layer 3.

[0152] The carrier sheet 4 is made of polymethyl methacrylate (PMMA), a lightweight polymer with stable optical properties. The carrier sheet 4 has a thickness of 0.5 mm and a refractive index of 1.49, which is much lower than that of traditional high refractive index substrate materials.

[0153] The light-transmitting layer 3 is made of titanium oxide; specifically, a layer of titanium oxide (TiO2) with a thickness of 0.1 mm is deposited on the carrier sheet 4 as the light-transmitting layer 3, and its refractive index is as high as about 2.55 (it should be noted that the refractive index of titanium oxide in different crystal forms ranges from about 2.5 to 2.7).

[0154] The design in this embodiment 1 enables the imaging light emitted from the optomechanical system to propagate efficiently through total internal reflection within the light transmission layer 3, while the carrier sheet 4 mainly serves to provide structural support and transmit ambient light.

[0155] In this configuration, the minimum transmission angle of light in the light transmission layer 3 is... θ It is approximately 36°, which corresponds to a maximum field of view (FOV) of approximately 80° for monochromatic light in air.

[0156] Example 2

[0157] To further achieve the ultimate in lightweight design, the diffractive optical structure of this application may not require a support plate 4. This design can greatly reduce the overall weight of the diffractive optical structure. The high refractive index of the light transmission layer 3 (such as a titanium oxide deposition layer) ensures the effective transmission of light.

[0158] Under these conditions, the minimum transmission angle of light in the light transmission layer 3 θ This can be reduced to approximately 23°, thereby increasing the maximum FOV of monochromatic light incident in air to approximately 120°, a performance that significantly surpasses traditional high refractive index substrate solutions.

[0159] In addition, the diffractive optical structure of this application, when a carrier sheet 4 is provided, can also achieve the technical effect as in Embodiment 2 if a certain air gap is maintained between the carrier sheet 4 and the light transmission layer 3.

[0160] Compared to traditional waveguide substrates using high-refractive-index glass, even with a refractive index as high as 2.0 (significantly exceeding that of ordinary glass), this approach still exhibits limitations in practical applications. During light transmission, the minimum angle of this type of waveguide substrate is limited to approximately 30°, resulting in a maximum field of view (FOV) of only about 76° for monochromatic light in air. This performance is not only significantly inferior to the solution in Example 1, but also far behind the solution in Example 2 (which does not require a substrate) or the solution that adds an air gap between the light-transmitting layer 3 and the carrier sheet 4.

[0161] Furthermore, the high density of waveguide substrates made of high-refractive-index glass makes their weight a significant concern. For example, in Example 1, polymethyl methacrylate (PMMA) has a density approximately four times that of PMMA. This means that in the AR / MR field, where lightweight devices are prioritized, traditional high-refractive-index glass substrates struggle to find an ideal balance between optical performance and weight, presenting a clear disadvantage compared to the technical solution of this application.

[0162] The core advantage of this application lies in the fact that by transferring the waveguide function from a heavy substrate to a thin and high-refractive-index optical film, not only is the overall weight significantly reduced, but a wider field of view and superior optical performance are also achieved, opening up new avenues for the design and application of augmented reality and mixed reality devices.

[0163] According to another embodiment of this application, an optical system is provided. The optical system includes an optomechanical system and a diffractive optical structure as described above, wherein light rays emitted from the image source can be incident on a coupling region 1 on the diffractive optical structure.

[0164] By combining the optomechanical system with the diffractive optical structure, a complete optical system is formed. The cooperation between the optomechanical system and the diffractive optical structure ensures that the light emitted from the optomechanical system can be coupled into the light transmission layer 3 efficiently and accurately. Through the synergistic effect of the coupling grating, the deflection grating (which can be set as needed), and the coupling grating, the image information is accurately transmitted to the user's eyes.

[0165] The optical system provided in this application is applicable to augmented reality (AR) and mixed reality (MR) devices. By precisely controlling the transmission path and angle of light, virtual information can be superimposed on the user's field of vision, achieving a fusion of virtual and reality.

[0166] For example, in AR and MR devices, the optical system of this application can provide users with a clear and immersive visual experience, meeting the information display and interaction needs in complex scenarios.

[0167] The diffractive optical structure provided in this application achieves a balance between high performance and lightweight design through innovative design. Combining this lightweight diffractive optical structure with an optomechanical system helps reduce the weight and size of the entire optical system.

[0168] For example, in AR and MR devices, lightweight design is crucial for improving user comfort. By reducing the weight of the device, user fatigue during extended wear can be reduced, thus enhancing the user experience.

[0169] Of course, besides AR and MR devices, this optical system can also be applied to other fields requiring high-quality optical transmission. By adjusting the parameters of the optomechanical and diffractive optical structures, specific needs in different application scenarios can be met.

[0170] According to another embodiment of this application, a head-mounted display device is provided, which includes a housing and an optical system as described above, the optical system being disposed in the housing.

[0171] The head-mounted display device provided in this application utilizes the efficient transmission and high-quality display characteristics of the optical system to offer users a clear and realistic visual experience. Whether immersed in a virtual world or overlaying virtual information onto the real world, users can obtain excellent visual enjoyment and interactivity.

[0172] As mentioned earlier, the optical system used in the head-mounted display device of this application has already reduced its weight through lightweight design. Combined with the selection of materials and structural design of the housing, the entire head-mounted display device has also achieved lightweighting, greatly reducing user fatigue during prolonged wear. In addition, the choice of housing material and ergonomic design also contribute to improving wearing comfort.

[0173] The specific implementation of the optical system and head-mounted display device in this application can refer to the various embodiments of the diffractive optical structure described above. Therefore, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, and will not be described in detail here.

[0174] The above embodiments mainly describe the differences between the various embodiments. As long as the different optimization features between the various embodiments are not contradictory, they can be combined to form a better embodiment. For the sake of brevity, they will not be elaborated here.

[0175] While specific embodiments of this application have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of this application. Those skilled in the art should understand that modifications can be made to the above embodiments without departing from the scope and spirit of this application. The scope of this application is defined by the appended claims.

Claims

1. A diffractive optical structure, characterized in that, The diffractive optical structure includes: The light-transmitting layer (3) is at least one light-transmitting film with a refractive index greater than 1.9, and light propagates through total internal reflection inside the light-transmitting layer; The coupling region (1) is disposed on the surface or inside the light transmission layer (3) and is used to couple the light from the image source into the light transmission layer (3); The coupling region (2) is disposed on the surface or inside the light transmission layer (3) for coupling light from the coupling region (1) out of the light transmission layer (3); A carrier sheet (4) is provided on which the light-transmitting layer (3) is disposed, and the refractive index of the carrier sheet (4) is lower than that of the light-transmitting layer (3). The carrier sheet (4) is used to support the light-transmitting layer (3) and transmits only ambient light. The carrier sheet is made of lightweight material. The light-transparent film is an adhesive layer, which includes a nanoimprint adhesive layer or a photoresist layer. An air gap is provided between the carrier sheet (4) and the light transmission layer (3), and the air gap is ≥1 micrometer; The refractive index of the carrier sheet (4) is less than 1.6; When the imaging light is emitted from the optical engine, it is confined to the light transmission layer (3) for transmission, rather than being transmitted to the carrier plate (4). The carrier plate (4) only serves as a mechanical support and does not participate in the transmission of the imaging light.

2. The diffractive optical structure according to claim 1, characterized in that, The thickness of the light-transmitting layer (3) is in the range of micrometers to millimeters.

3. The diffractive optical structure according to claim 1, characterized in that, The light-transmitting layer (3) includes an upper surface and a lower surface opposite to each other, and the upper surface and / or the lower surface of the light-transmitting layer (3) are curved.

4. The diffractive optical structure according to claim 1, characterized in that, The carrier sheet (4) is made of resin.

5. The diffractive optical structure according to claim 4, characterized in that, The material of the carrier sheet (4) includes polymethyl methacrylate (PMMA), polystyrene (PS), polycarbonate (PC), or polyethylene (PE).

6. The diffractive optical structure according to any one of claims 1-5, characterized in that, The coupling region (1) is configured as one or more, and the coupling region (1) is provided with a coupling grating; The coupling region (2) is configured as one or more, and the coupling region (2) is provided with a coupling grating.

7. The diffractive optical structure according to claim 6, characterized in that, The diffractive optical structure further includes a transition region, which is disposed on the surface or inside the light-transmitting layer (3); The transition region is set as one or more, and the transition region is provided with a transition grating; The turning region is located between the coupling-in region (1) and the coupling-out region (2), and is used to turn the direction of the light rays coupled into the coupling-in region (1) and transmit them to the coupling-out region (2).

8. An optical system, characterized in that, include: Image source; and According to any one of claims 1-7, the light emitted from the image source can be incident on the coupling region (1) of the diffraction optical structure.

9. A head-mounted display device, characterized in that, include: shell; and The optical system as claimed in claim 8, wherein the optical system is disposed within the housing.

Images