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

Abstract

The embodiment of the utility model provides a diffractive optical structure, an optical system and an intelligent head-mounted device. Wherein the diffractive optical structure comprises a substrate, a coupling-in grating, a coupling-out grating and a first volume holographic grating; the substrate is provided with two opposite surfaces and is used for totally reflecting light rays which are propagated and coupled into the substrate; the coupling-in grating and the coupling-out grating are both arranged on the surface of the same side of the substrate, the coupling-in grating is used for coupling light into the substrate, and the coupling-out grating is used for coupling out light transmitted in the substrate; the first volume holographic grating is arranged on the surface of the other side of the substrate, and the position of the first volume holographic grating is opposite to that of the coupling-in grating; wherein the first volume holographic grating is configured to be used for adjusting the propagation direction of light rays with specific wavelengths, so that when the light rays are projected to the coupling grating, the total reflection angle of the light rays with the specific wavelengths in the substrate can be close to the total reflection angles of light rays with other wavelengths.

Description

Technical Field

[0001] This application relates to the field of optical equipment technology, and more specifically, to a diffractive optical structure, an optical system, and a smart head-mounted device. Background Technology

[0002] In existing full-color waveguide display technologies, a multi-layered design strategy is often adopted to achieve the desired display effect, dividing and distributing the spectral bandwidth to different waveguide layers. However, this approach inevitably increases the complexity of the waveguide structure, and due to the inherent thickness limitations of low-refractive-index materials (such as resin waveguides), this multi-layered structure appears bulky in practical applications, making it difficult to gain widespread market acceptance. Given these circumstances, how to achieve full-color waveguide displays with a large field of view (FOV) using low-refractive-index materials while ensuring overall bandwidth is limited has become a pressing technical challenge for the industry. Utility Model Content

[0003] The purpose of this application is to provide a new technical solution for a diffractive optical structure, an optical system, and a smart head-mounted device.

[0004] Firstly, this application provides a diffractive optical structure. The diffractive optical structure includes:

[0005] The substrate has two opposing surfaces for total internal reflection of light coupled into it;

[0006] Both the insertion grating and the output grating are disposed on the same side surface of the substrate. The insertion grating is used to couple light into the substrate, and the output grating is used to couple light propagating in the substrate out.

[0007] A first-body holographic grating is disposed on the other side surface of the substrate and is positioned opposite to the coupling grating;

[0008] The first volume holographic grating is configured to adjust the propagation direction of a specific wavelength of light so that when it is projected onto the coupling grating, the total internal reflection angle of the specific wavelength of light in the substrate is close to that of other wavelengths of light.

[0009] Optionally, the diffractive optical structure further includes a second volume holographic grating, which is disposed on the same side surface of the substrate together with the first volume holographic grating and is positioned opposite the coupling grating. The second volume holographic grating is configured to readjust the propagation direction of the specific wavelength light that has propagated through the substrate and is about to be coupled out through the coupling grating, so that the specific wavelength light can be coupled out with other wavelength light at similar exit angles within a predetermined target area.

[0010] Optionally, the coupling grating is a reflective coupling structure, and the coupling out grating is a reflective coupling out structure.

[0011] Optionally, a narrowband filter element is added to one side of the substrate where the coupling grating and the coupling grating are located. The narrowband filter element is configured to block blue light from the external environment from passing through.

[0012] Optionally, the first volume holographic grating and the second volume holographic grating are used to deflect the specific wavelength of light emitted by the optomechanism of the peripheral device, wherein the specific wavelength of light is blue light or red light emitted by the optomechanism.

[0013] Optionally, the narrowband filter element is a narrowband filter film, which is disposed on a cover plate. The cover plate is a transparent glass plate, and the cover plate is connected to the substrate by means of edge bonding with frame adhesive.

[0014] Optionally, the narrowband filter element is a narrowband filter sheet, which covers the surface of the substrate.

[0015] Optionally, the specific wavelength light is blue light. When blue light is incident on the first volume holographic grating at a specific incident angle, its propagation angle will be deflected, thereby changing its +1st order diffraction angle. However, due to the wavelength selectivity of the first volume holographic grating, the propagation angles of green and red light will not be deflected, and their original +1st order diffraction angles will remain unchanged. The +1st order diffraction angle of blue light is between that of green light and red light.

[0016] Optionally, the specific wavelength light is red light. When red light is incident on the first volume holographic grating at a specific incident angle, its propagation angle will be deflected, thereby changing its +1st order diffraction angle. However, due to the wavelength selectivity of the first volume holographic grating, the propagation angles of green and blue light will not be deflected, and their original +1st order diffraction angles will remain unchanged. The +1st order diffraction angle of the red light is between the +1st order diffraction angles of the green light and the blue light.

[0017] Secondly, this application provides an optical system. The optical system includes:

[0018] Optical mechanism; and

[0019] The diffractive optical structure as described in the first aspect;

[0020] The optical engine is located on the side of the substrate where the first volumetric holographic grating is disposed, and the light emitted by the optical engine can be projected onto the first volumetric holographic grating.

[0021] Thirdly, this application provides a smart head-mounted device, the smart head-mounted device comprising:

[0022] The outer casing; and

[0023] The optical system as described in the second aspect.

[0024] The beneficial effects of this application are as follows:

[0025] This application provides a diffractive optical structure that introduces a volume holographic grating on the opposite side of the coupling grating. This design effectively overcomes the technical bottleneck of low-refractive-index materials in achieving large field-of-view (FOV) full-color waveguide displays, enabling the use of low-refractive-index materials, such as resin, to achieve a FOV display effect of 30° or even larger. Simultaneously, this diffractive optical structure optimizes color uniformity, ensuring that the total internal reflection angles of B / G / R light within the substrate tend to be consistent, thereby significantly improving the overall quality of the display effect. Furthermore, compared to traditional multilayer structures, the diffractive optical structure of this application is simpler, reducing manufacturing difficulty and cost, and enhancing practicality. In summary, this application provides a new solution for the development and application of full-color waveguide display technology.

[0026] Other features and advantages of this specification will become clear from the following detailed description of exemplary embodiments with reference to the accompanying drawings. Attached Figure Description

[0027] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments of this specification and, together with their description, serve to explain the principles of this specification.

[0028] Figure 1 This is one of the structural schematic diagrams of the diffraction optical structure provided in the embodiments of this application;

[0029] Figure 2 This is the second schematic diagram of the diffractive optical structure provided in the embodiments of this application;

[0030] Figure 3 This is one of the structural schematic diagrams of the optical system provided in the embodiments of this application;

[0031] Figure 4 This is a second schematic diagram of the optical system provided in an embodiment of this application.

[0032] Explanation of reference numerals in the attached figures:

[0033] 10. Substrate; 20. Coupled-in grating; 30. Coupled-out grating; 40. First-volume holographic grating; 50. Second-volume holographic grating; 60. Narrowband filter element; 70. Optomechanical system; 01. Human eye. Detailed Implementation

[0034] 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.

[0035] 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.

[0036] Technologies and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such technologies and equipment should be considered part of the specification.

[0037] 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.

[0038] 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.

[0039] The diffractive optical structure, optical system, and smart head-mounted device provided in the embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0040] 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 substrate 10, a coupling grating 20, an output grating 30, and a first volume holographic grating 40. The substrate 10 has two opposing surfaces for total internal reflection of light coupled into it. The coupling grating 20 and the output grating 30 are both disposed on the same side surface of the substrate 10. The coupling grating 20 couples light into the substrate 10, and the output grating 30 couples light out of the substrate 10. The first volume holographic grating 40 is disposed on the other side surface of the substrate 10, and is positioned opposite the coupling grating 20. The first volume holographic grating 40 is configured to adjust the propagation direction of a specific wavelength of light, so that when projected onto the coupling grating 20, the total internal reflection angle of that specific wavelength of light within the substrate 10 is close to the total internal reflection angle of other wavelengths of light.

[0041] This application provides a novel design for a diffractive optical structure, which mainly includes the following parts.

[0042] The diffractive optical structure provided in this application includes a substrate 10, which has two opposing surfaces and is used for total internal reflection to propagate light coupled therein.

[0043] The substrate 10 here can be made of a low-refractive-index material, such as a resin material with a refractive index of 1.6 or 1.7. In the optical design of this application, the use of a low-refractive-index substrate helps to achieve a larger field of view (FOV) display.

[0044] The diffraction optical structure provided in this application embodiment includes a coupling grating 20, see [link to relevant documentation]. Figure 1 The coupling grating 20 is disposed on one side surface of the substrate 10, for example, on the side opposite to the optomechanism of the peripheral device. The coupling grating 20 is responsible for directing light—for example, light originating from the optomechanism 70 (see [reference])—into the optical path. Figure 3 It is efficiently coupled into the interior of the substrate 10. This design not only ensures the smooth introduction of incident light, but also lays the foundation for subsequent light propagation and display.

[0045] The diffraction optical structure provided in this application embodiment includes a coupling grating 30. Please continue to refer to... Figure 1 The coupling-out grating 30 and the coupling-in grating 20 are located on the same surface of the substrate 10. The coupling-out grating 30 is used to couple out light propagating within the substrate 10. The coupling-out grating 30 ensures that light can exit from the substrate 10 in a predetermined direction and angle for user observation. Please refer to... Figure 1 The light emitted through the coupling grating 30 can enter the human eye 01.

[0046] The diffractive optical structure provided in this application embodiment also incorporates the design of at least one volume holographic grating, wherein... Figure 1 The first volume holographic grating 40 shown in the image is representative. This first volume holographic grating 40 is disposed on the other surface of the substrate 10, and is arranged symmetrically with the coupling grating 20 in the thickness direction of the substrate 10. The first volume holographic grating 40, with its unique volume holographic technology characteristics, possesses the dual advantages of wavelength selectivity and angle selectivity. In this application, it is configured to modulate a specific wavelength in the incident light, changing its propagation direction. This specific wavelength of light can be, for example, blue light (B light) or red light (R light), thereby meeting diverse optical design requirements.

[0047] The diffractive optical structure provided in this application embodiment enables full-color display with a large field of view (FOV). Specifically, by combining a substrate 10 with a low refractive index and a volume holographic grating, the diffractive optical structure provided in this application embodiment solves the problem that the bandwidth of a low refractive index substrate cannot encompass the entire field of view of a large RGB three-color FOV. The introduction of the volume holographic grating can adjust the propagation direction of specific wavelength light, so that when it is projected onto the coupling grating 20, the total internal reflection angle of that specific wavelength light within the substrate 10 is close to the total internal reflection angle of other wavelength light. In this way, even with low refractive index materials, full-color display with a large FOV can be achieved.

[0048] It should be noted that the total internal reflection angle of the specific wavelength light in the substrate 10 can be close to that of the total internal reflection angle of other wavelength light. This can mean that the total internal reflection angle of the specific wavelength light in the substrate 10 is between the total internal reflection angles of the other two wavelength light.

[0049] Inside the substrate 10, the B / G / R rays have similar total internal reflection angles, resulting in a convergent emission trend when they reach the coupling grating 30. This means they are coupled out at approximately the same positions on the coupling grating 30. This characteristic effectively avoids the uneven distribution that can occur when different wavelengths of light are coupled out, such as an overly concentrated blue light and relatively sparse red light. This design significantly improves color uniformity, ensuring a consistent and uniform display, which is crucial for enhancing overall display quality and user experience.

[0050] In the embodiments of this application, the volume holographic grating exhibits the ability to control the transmission angle of light of specific wavelengths, such as red or blue light. This design endows the diffractive optical structure with great flexibility, allowing it to be customized according to different display requirements and application scenarios. By controlling the propagation direction of light of specific wavelengths, this diffractive optical structure can optimize the display effect and meet diverse usage needs.

[0051] The diffractive optical structure provided in this application introduces a volume holographic grating on the opposite side of the coupling grating 20. This design effectively overcomes the technical bottleneck of low-refractive-index materials in achieving large FOV full-color waveguide displays, enabling the use of low-refractive-index materials, such as resin, to achieve a FOV display effect of 30 degrees or even larger. Simultaneously, the diffractive optical structure optimizes color uniformity, ensuring that the total reflection angles of B / G / R light within the substrate 10 tend to be consistent, thereby significantly improving the overall quality of the display effect. Furthermore, compared to traditional multi-layer structures, the diffractive optical structure of this application is a single-layer structure, which is simple in structure, reduces manufacturing difficulty and cost, and enhances practicality. In summary, this application provides a new solution for the development and application of full-color waveguide display technology.

[0052] See some examples in this application. Figure 1 The diffractive optical structure further includes a second volume holographic grating 50, which is disposed on the same side surface of the substrate 10 together with the first volume holographic grating 40 and is positioned opposite the coupling grating 30. The second volume holographic grating 50 is configured to readjust the propagation direction of the specific wavelength light that propagates through the substrate 10 and is about to be coupled out through the coupling grating 30, so that the specific wavelength light and other wavelength light can be coupled out at similar exit angles within a predetermined target area.

[0053] In this example of the application, the design of the diffractive optical structure has been further optimized. Specifically, in addition to the first volume holographic grating 40 mentioned above, a second volume holographic grating 50 is also introduced, see [link to relevant documentation]. Figure 1 The second volume holographic grating 50 and the first volume holographic grating 40 are located on the same side surface of the substrate 10, and the position of the second volume holographic grating 50 is arranged opposite to that of the coupling grating 30.

[0054] The introduction of the second volume holographic grating 50 serves to readjust the propagation direction of specific wavelength light, such as blue or red light, that has propagated through the substrate 10 and is about to be coupled out through the coupling grating 30. The purpose of this adjustment is to ensure that the light of that specific wavelength can be coupled out at a similar exit angle to other wavelength light (such as green light) within a predetermined target area.

[0055] It is worth noting that the second volume holographic grating 50 is functionally consistent with the first volume holographic grating 40, meaning they possess the same operating characteristics and adjustment capabilities. Specifically, when the first volume holographic grating 40 is designed to adjust the propagation direction of blue light (B-light), the second volume holographic grating 50 also undertakes the task of adjusting the blue light. This synergy ensures the consistency and efficiency of the entire diffractive optical structure in processing specific wavelengths of light.

[0056] In this example of the application, a second volume holographic grating 50 is introduced to optimize the color uniformity of the displayed image. The main function of this design is to readjust the propagation direction of specific wavelengths of light transmitted in the substrate 10. Through this adjustment process, when different wavelengths of light reach the coupling grating 30 and are coupled out, they can maintain a more consistent emission angle. This consistency effectively avoids the problem of uneven color distribution, which is one of the key factors in improving display quality. The significant improvement in color uniformity directly leads to an enhanced visual effect, making the displayed image clearer. It can be said that the introduction of the second volume holographic grating 50 not only enriches the functional characteristics of the diffractive optical structure but also significantly improves its performance in practical applications, bringing users a superior visual experience.

[0057] In some examples of this application, the substrate 10 is a resin material.

[0058] First, resin materials, as a low-refractive-index substrate material, have a relatively large critical angle for total internal reflection. This characteristic is crucial for achieving full-color waveguide displays with a large field of view (FOV). In traditional waveguide display technology, low-refractive-index materials often struggle to achieve full-color displays with a large FOV because the bandwidth of the low-refractive-index substrate cannot encompass the entire field of view of a large RGB (red, green, and blue) FOV.

[0059] However, by employing the volume holographic grating method proposed in this application, the low refractive index of the resin material can be utilized to allow blue light (B light), which has a smaller +1st order diffraction angle, to enter total internal reflection, while red light (R light) remains in a more energy-efficient band. This allows for the use of a smaller refractive index (such as 1.6 or 1.7 for the resin material) to achieve a larger field of view (FOV) for full-color display.

[0060] Secondly, using resin materials as a substrate offers advantages such as low processing costs, light weight, and high plasticity. These advantages make resin substrates more flexible and economical in the manufacturing process of waveguide display devices. For example, resin materials can be easily used to manufacture complex waveguide structures through processes such as injection molding, thereby meeting diverse design requirements. At the same time, the lighter weight also helps to reduce the burden on the entire optical system and improve wearing comfort.

[0061] In this example of the application, the choice of resin material as the substrate 10 is based on several technical considerations and brings significant technical benefits. This design choice not only helps to achieve a large FOV full-color waveguide display, but also improves the economy, flexibility, and wearing comfort of the entire display system.

[0062] The substrate 10 in this application is a resin substrate with a refractive index of, for example, 1.6 or 1.7.

[0063] Of course, the substrate 10 of the diffractive optical structure of this application may be made of resin materials, or other materials with low refractive index, and this application does not limit this.

[0064] See some examples in this application. Figure 1 The coupling grating 20 is a reflective coupling structure, and the coupling grating 30 is a reflective coupling structure.

[0065] In this example of the application, the coupling grating 20 is designed as a reflective coupling structure, and the coupling grating 30 is designed as a reflective coupling structure. The advantages of this design are analyzed below from the perspectives of light utilization efficiency and simplicity of manufacturing process.

[0066] The reflective coupling-in and coupling-out structures help improve light utilization efficiency. Through the reflective design, light can be coupled and guided more efficiently when entering and leaving the substrate 10, reducing light loss and scattering, thereby improving the optical performance of the entire waveguide display device.

[0067] In this design, the coupling grating 20 and the coupling grating 30 are disposed on two separate surfaces of the substrate 10, respectively, along with the volume holographic gratings (such as the first volume holographic grating 40 and the second volume holographic grating 50). From a manufacturing process perspective, this design offers the following significant advantages:

[0068] The design of separating the volume holographic grating and the reflective coupling-in and coupling-out gratings on opposite sides of the substrate avoids mutual interference during processing. This separate design allows each layer to be processed and tested independently, reducing processing difficulty and cost. Since the reflective grating and the volume holographic grating can be processed separately, they can be produced in parallel, shortening the overall manufacturing cycle.

[0069] It is worth noting that although a reflective coupling-in structure and a reflective coupling-out structure are used in the example of this application, in other embodiments, it is also possible to directly set volume holographic gratings on the coupling-in grating 20 and the coupling-out grating 30, in which case the coupling-in grating 20 and the coupling-out grating 30 become transmissive. This design choice also has its unique advantages, such as better control over the direction and angle of light propagation, achieving more precise light coupling and separation.

[0070] However, the design of transmissive gratings also requires attention to some issues. For example, directly fabricating volume holographic gratings on the input and output gratings is not only technically challenging but can also lead to high costs. Therefore, in specific applications, a trade-off and selection process must be made based on actual needs and technical conditions.

[0071] See some examples in this application. Figure 2 A narrowband filter element 60 is added to one side of the substrate 10 where the coupling grating 20 and the coupling grating 30 are located. The narrowband filter element 60 is configured to block blue light from passing through the external environment.

[0072] In this example of the application, see Figure 2 A unique design feature is the addition of a narrowband filter element 60 on the side of the substrate 10 where the coupling grating 20 and the output grating 30 are located. The core purpose of this design is to block specific wavelengths of light, such as blue light, from passing through, thereby further optimizing the performance of the diffractive optical structure.

[0073] In waveguide display technology, especially in applications using low-refractive-index substrates to achieve large field-of-view (FOV) full-color displays, the impact of ambient light on display performance cannot be ignored. In particular, the blue light band, if not effectively processed, can interfere with the display image, causing color distortion or degrading the display quality. Therefore, it is necessary to adopt an effective method to shield or reduce the interference of ambient blue light on waveguide display devices.

[0074] The narrowband filter element 60 proposed in this example is designed and disposed on one side of the substrate 10, adjacent to the coupling grating 20 and the coupling grating 30. The narrowband filter element 60 has high wavelength selectivity, capable of blocking the transmission of specific wavelengths of blue light (e.g., 440nm to 460nm). This design not only effectively reduces the interference of external blue light on the display effect but also maintains the normal transmission of other necessary light, thereby ensuring the clarity and color purity of the displayed image.

[0075] By introducing the narrowband filter element 60, the diffractive optical structure in this application example achieves a significant improvement in display performance. Specifically, the use of the narrowband filter element 60 makes the displayed image clearer and the colors purer, bringing users a more immersive visual experience.

[0076] See some examples in this application. Figure 3 The first volume holographic grating 40 and the second volume holographic grating 50 are used to deflect the specific wavelength light emitted by the optical engine of the peripheral device, wherein the specific wavelength light is blue light or red light emitted by the optical engine.

[0077] In this example of the application, the first volume holographic grating 40 and the second volume holographic grating 50 are described as modulating the light emitted by the optomechanism 70 of the peripheral device, such as blue light or red light emitted by the optomechanism 70. The wavelength range of the blue light or red light emitted by the optomechanism is relatively narrow.

[0078] See some examples in this application. Figure 2 The narrowband filter element 60 is a narrowband filter film, which is disposed on a cover plate. The cover plate is a transparent glass plate, and the cover plate is connected to the substrate 10 by means of edge bonding with frame glue.

[0079] In this example of the application, the narrowband filter element 60 is designed as a narrowband filter film and is disposed on a transparent glass cover. This cover not only protects the diffractive optical structure but also provides a platform for mounting the narrowband filter film. The narrowband filter film and the cover are tightly bonded together using adhesives or specific processes to ensure their stability and optical performance. Simultaneously, the cover is firmly connected to the substrate 10 via edge bonding with frame adhesive, forming a complete and sealed diffractive optical structure unit.

[0080] Furthermore, the cover plate, as a protective structure for the entire diffractive optical structure, effectively prevents dust, moisture, and other contaminants from damaging the coupling grating 20 and coupling grating 30 on its surface. Simultaneously, the edge-bonding connection method provides additional stability and durability. The narrow-band filter film can precisely block the transmission of blue light in specific wavelengths, thereby optimizing the display effect and reducing color distortion.

[0081] Furthermore, since the narrowband filter film is mounted on the cover plate, it can be replaced or maintained relatively easily when necessary without disassembling the entire diffractive optical structure.

[0082] In some examples of this application, the narrowband filter element 60 is a narrowband filter sheet that covers the surface of the substrate 10.

[0083] In this example of the application, the narrowband filter element 60 is designed as a narrowband filter sheet and directly covers the surface of the substrate 10 where the coupling grating 20 and the output grating 30 are disposed. Compared with the design where it is disposed on the cover plate, directly covering the surface of the substrate 10 with the narrowband filter sheet simplifies the overall structure and reduces manufacturing costs. The narrowband filter sheet can also accurately filter out blue light of specific wavelengths, thereby improving display effect and color uniformity.

[0084] The design in this example makes the diffractive optical structure more compact, which is beneficial for achieving high-performance display functions within a limited space.

[0085] See some examples in this application. Figure 1 The specific wavelength of light is blue light. When blue light is incident on the first volume holographic grating 40 at a specific incident angle, its propagation angle will be deflected, thereby changing its +1st order diffraction angle. However, due to the wavelength selectivity of the first volume holographic grating 40, the propagation angle of green light and red light will not be deflected, and their original +1st order diffraction angle will remain unchanged. The +1st order diffraction angle of blue light is located between the +1st order diffraction angles of green light and red light.

[0086] In this example of the application, a volume holographic grating is chosen to adjust the blue light. When blue light is incident on the first volume holographic grating 40 at a specific incident angle, its propagation direction is deflected. This deflection is based on the wavelength selectivity and incident angle selectivity of the first volume holographic grating 40, meaning that only light within a specific wavelength range, such as blue light (B light) from 440nm to 460nm, will be deflected within this angle range. At the same time, green light (G light) and red light (R light) will not have their propagation angles deflected due to the wavelength selectivity of the first volume holographic grating 40, thus maintaining their original +1st order diffraction angles.

[0087] In a specific example, see Figure 1 For blue light in the 440nm to 460nm wavelength range (this blue light is produced by...) Figure 3 The blue light emitted by the optomechanical unit 70 (not from the external environment) undergoes a specific volume holographic grating design. This design utilizes the wavelength selectivity and incident angle selectivity of the volume holographic grating, causing blue light (B light) within this narrow wavelength range to be deflected at an incident angle of -20° to 20°. Specifically, blue light (B light) originally incident at 0° is deflected to a 20° angle after passing through the first volume holographic grating 40. Subsequently, this deflected blue light passes through a reflective coupling grating and is coupled into the substrate 10 for total internal reflection propagation. At this point, the +1st order diffraction angle of the blue light (B light) becomes 60°.

[0088] To illustrate this more clearly, we can use blue light (B-light) without being deflected by a volume holographic grating as a comparison. Under the same conditions (e.g., 0° incidence), if blue light (B-light) passes directly through a reflective coupling grating without being deflected by a volume holographic grating, its +1st order diffraction angle is approximately 40°. In other words, without deflection, the total internal reflection angle range of blue light (B-light) is limited, which affects the color accuracy of large FOV full-color displays.

[0089] It is worth noting that the simultaneously incident green light (G light) and red light (R light) are not affected by deflection due to the wavelength selectivity of the first volume holographic grating 40. Therefore, under the same conditions (0° incident), the +1st order diffraction angles of the green light (G light) and red light (R light) after passing through the reflective coupling grating are 55° and 65°, respectively, which remain unchanged.

[0090] Through the specific design in this example, the +1st order diffraction angle of blue light (B light) was adjusted, increasing it from 40° to 60°, thus creating a more balanced distribution with the +1st order diffraction angles of green light (G light) and red light (R light) (55° and 65° respectively). This adjustment not only expands the total internal reflection angle range of the RGB colors but also helps optimize color uniformity and accuracy, thereby achieving the technical goal of large FOV full-color waveguide display.

[0091] Therefore, by adjusting the +1st order diffraction angle of blue light to fall between the +1st order diffraction angles of green and red light, this application solves the bandwidth limitation problem faced by low refractive index substrate materials in achieving large FOV full-color displays. This design allows for the use of materials with smaller refractive indices to achieve a larger field of view (FOV) while maintaining full-color display of RGB colors.

[0092] After refraction, the +1st order diffraction angle of blue light (B light) is closer to that of green light (G light) and red light (R light), which helps to achieve a convergent landing point in the coupling part. This avoids the situation where blue light (B light) is too dense and red light (R light) is too sparse, thus significantly optimizing color uniformity and improving display effect.

[0093] Furthermore, since green light (G light) and red light (R light) are unaffected by the first holographic grating 40 and maintain their original propagation paths and +1 order diffraction angles, their energy transmission efficiency is preserved. Meanwhile, blue light (B light), after deflection, can still enter the substrate 10 for total internal reflection transmission, ensuring the overall brightness and clarity of the display.

[0094] In addition to adjusting the blue light (B light), the red light (R light) can also be adjusted. In the RGB three-color light spectrum, blue light (B light) and red light (R light) are considered to be edge rays at the two ends of the spectrum.

[0095] In some examples of this application, the specific wavelength of light is red light. When red light is incident on the first volume holographic grating 40 at a specific incident angle, its propagation angle will be deflected, thereby changing its +1st order diffraction angle. However, due to the wavelength selectivity of the first volume holographic grating 40, the propagation angle of green and blue light will not be deflected, and the original +1st order diffraction angle will remain unchanged. The +1st order diffraction angle of the red light is located between the +1st order diffraction angles of the green light and the blue light.

[0096] When red light (R light) is incident on the first volume holographic grating 40 at a specific incident angle, its propagation path is deflected. This deflection effect is achieved based on the wavelength selectivity and angle selectivity of the volume holographic grating. Specifically, only red light within a specific wavelength range (such as red light in a specific band) will be deflected within this angle range. At the same time, green light (G light) and blue light (B light) incident simultaneously will not have their propagation angles deflected due to the wavelength selectivity of the first volume holographic grating 40, thus maintaining their original +1 order diffraction angles.

[0097] In this example of the application, by adjusting the +1st order diffraction angle of red light (R light) to lie between the +1st order diffraction angles of green light (G light) and blue light (B light), this design helps to achieve a more balanced color distribution in the optical display system. Particularly in low-refractive-index substrate materials, this adjustment can optimize the relative positions and overlap of the RGB colors, thereby improving color accuracy and uniformity.

[0098] According to another embodiment of this application, an optical system is provided, see [link to relevant documentation]. Figure 3 and Figure 4 The optical system includes an optical engine 70 and a diffractive optical structure as described above; the optical engine 70 is located on the side of the substrate 10 where the first volume holographic grating 40 is disposed, and the light emitted by the optical engine 70 can be projected onto the first volume holographic grating 40.

[0099] The optomechanical system 70 serves as a light source, emitting RGB light that is received by the first bulk holographic grating 40 and then projected onto the coupling grating 20. The first bulk holographic grating 40 deflects light of specific wavelengths, making the total internal reflection angles of the RGB light within the substrate 10 approximately equal. This not only helps optimize color uniformity but also avoids problems such as excessively dense blue light and sparse red light, thereby improving the overall display effect.

[0100] According to another embodiment of this application, a smart head-mounted device is provided, the smart head-mounted device including: a housing and the optical system as described above.

[0101] The smart head-mounted device is, for example, an AR optical display device.

[0102] The specific implementation of the smart head-mounted device in this application can refer to the various embodiments of the diffractive optical structure and optical system 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.

[0103] 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.

[0104] 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, include: The substrate (10) has two opposing surfaces for total internal reflection of light coupled into it; The insertion grating (20) and the extraction grating (30) are both disposed on the same side surface of the substrate (10). The insertion grating (20) is used to couple light into the substrate (10), and the extraction grating (30) is used to couple light propagating in the substrate (10) out. A first-body holographic grating (40) is disposed on the other side surface of the substrate (10) and is positioned opposite to the coupling grating (20); The first volume holographic grating (40) is configured to adjust the propagation direction of red or blue light so that when it is projected onto the coupling grating (20), the total internal reflection angle of the red or blue light in the substrate (10) is close to that of green light and another unadjusted color light.

2. The diffractive optical structure according to claim 1, characterized in that, The diffractive optical structure further includes a second volume holographic grating (50), which is disposed on the same side surface of the substrate (10) together with the first volume holographic grating (40) and is positioned opposite to the coupling grating (30). The second volume holographic grating (50) is configured to readjust the propagation direction of the red or blue light that propagates through the substrate (10) and is about to be coupled out through the coupling grating (30) so that the red or blue light has a similar exit angle as the green light and another unadjusted color light are coupled out from the coupling grating (30).

3. The diffractive optical structure according to claim 2, characterized in that, The coupling grating (20) is a reflective coupling structure, and the coupling grating (30) is a reflective coupling structure.

4. The diffractive optical structure according to claim 2, characterized in that, A narrowband filter element (60) is added to one side of the substrate (10) where the coupling grating (20) and the coupling grating (30) are located. The narrowband filter element (60) is configured to block blue light from passing through the external environment.

5. The diffractive optical structure according to claim 2, characterized in that, The first volume holographic grating (40) and the second volume holographic grating (50) are used to deflect red or blue light emitted by the optomechanism (70) of the peripheral device.

6. The diffractive optical structure according to claim 4, characterized in that, The narrowband filter element (60) is a narrowband filter film, which is disposed on a cover plate. The cover plate is a transparent glass plate and is connected to the substrate (10) by means of edge bonding with frame glue.

7. The diffractive optical structure according to claim 4, characterized in that, The narrowband filter element (60) is a narrowband filter sheet, which covers the surface of the substrate (10).

8. The diffractive optical structure according to claim 5, characterized in that, The first volume holographic grating (40) is configured to adjust blue light. When blue light is incident on the first volume holographic grating (40), its propagation angle will be deflected, thereby changing its +1st order diffraction angle. However, due to the wavelength selectivity of the first volume holographic grating (40), the propagation angle of green light and red light will not be deflected, and the original +1st order diffraction angle will remain unchanged. The +1st order diffraction angle of blue light is between the +1st order diffraction angles of green light and red light.

9. The diffractive optical structure according to claim 5, characterized in that, The first volume holographic grating (40) is configured to adjust the red light. When the red light is incident on the first volume holographic grating (40), its propagation angle will be deflected, thereby changing its +1st order diffraction angle. However, due to the wavelength selectivity of the first volume holographic grating (40), the propagation angle of the green and blue light will not be deflected, and the original +1st order diffraction angle will remain unchanged. The +1st order diffraction angle of the red light is between the +1st order diffraction angles of the green light and the blue light.

10. An optical system, characterized in that, include: Optical mechanism (70); and The diffractive optical structure as described in any one of claims 1-9; The optical engine (70) is located on the side of the substrate (10) where the first volume holographic grating (40) is disposed, and the light emitted by the optical engine (70) can be projected onto the first volume holographic grating (40).

11. A smart head-mounted device, characterized in that, include: shell; and The optical system as described in claim 10.

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