Diffractive optical structure, method for expanding FOV, optical system and intelligent head-mounted device

Abstract

The embodiment of the invention provides a diffractive optical structure, a method for expanding FOV, an optical system and intelligent head-mounted equipment. The diffractive optical structure comprises a substrate, a coupling-in part and a coupling-out part, wherein the coupling-in part and the coupling-out part are arranged on the substrate. The coupling part is used for coupling incident infrared light into the substrate and enabling the infrared light to be transmitted in the substrate in a total reflection manner; the coupling-out part comprises a coupling-out grating and a nonlinear frequency multiplier stacked on the coupling-out grating, and the coupling-out part couples out infrared light through the coupling-out grating and converts the infrared light into light in a visible light band through the nonlinear frequency multiplier; the substrate is made of a material with a high refractive index and a low absorption characteristic in an infrared band, the high refractive index n meets the condition that n is larger than or equal to 3, and in the infrared band, the absorption rate k of the substrate with the thickness of 1 mm to infrared light is smaller than or equal to 0.03%.

Description

Technical Field

[0001] The embodiments of the present application relate to the field of optical display technology. More specifically, the embodiments of the present application relate to a diffraction optical structure, a method for expanding FOV, an optical system and an intelligent head-mounted device. Background Art

[0002] In virtual reality (VR) and augmented reality (AR) technologies, diffraction waveguide devices are widely used as an important optical element to guide image light to the user's eyes. However, existing diffraction waveguide solutions generally have the problem of small FOV, especially compared with geometric waveguide solutions. This is mainly because when light is coupled into the diffraction waveguide device in a diffraction manner, the propagation angle of the RGB wavelength will be dispersed due to the diffraction equation, thereby squeezing the transmittable space of the substrate. In theory, a substrate with a higher refractive index is required to further expand the FOV that the waveguide can transmit, but in the visible light band, the refractive index of glass is currently only about 2.1 at most, which limits the further improvement of FOV. Summary of the invention

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

[0004] In a first aspect, the present application provides a diffractive optical structure. The diffractive optical structure includes a substrate and:

[0005] A coupling part, used for coupling the incident infrared light into the substrate, and making the infrared light be transmitted by total reflection in the substrate;

[0006] The coupling-out part comprises a coupling-out grating and a nonlinear frequency multiplier stacked on the coupling-out grating, wherein the coupling-out part couples out infrared light through the coupling-out grating and converts the infrared light into light in the visible light band through the nonlinear frequency multiplier;

[0007] The substrate is made of a material with high refractive index and low absorption characteristics in the infrared band, wherein the high refractive index n satisfies the condition of n≥3, and in the infrared band, the absorption rate k of the substrate with a thickness of 1 mm to infrared light is ≤0.03%.

[0008] Optionally, the substrate is made of silicon Si or germanium Ge.

[0009] Optionally, the wavelength λ of the incident infrared light is ≥800nm.

[0010] Optionally, when the central wavelength of the incident infrared light is less than 1500nm, the substrate is made of silicon Si, the diffraction optical structure is configured to transmit infrared light with a FOV ≥ 110°, and the nonlinear frequency multiplier is a nonlinear doubled frequency optical crystal capable of converting the infrared light into RGB color light.

[0011] Optionally, when the central wavelengths of the incident infrared light are 920nm, 1050nm, and 1270nm respectively, in the outcoupling part, the nonlinear doubled frequency optical crystal can convert the infrared light with the three specific central wavelengths into light in the visible light band with central wavelengths of 460nm, 525nm, and 635nm respectively.

[0012] Optionally, when the central wavelength of the incident infrared light is ≥1500nm, the material of the substrate is germanium Ge, the diffraction optical structure is configured to transmit infrared light with FOV≥180°, and the nonlinear frequency multiplier is a nonlinear quadruple frequency optical crystal, which can convert the infrared light into RGB color light.

[0013] Optionally, when the central wavelengths of the incident infrared light are 1840nm, 2100nm, and 2540nm, respectively, in the outcoupling part, the nonlinear quadrupled frequency optical crystal can convert the infrared light with the three specific central wavelengths into light in the visible light band with central wavelengths of 460nm, 525nm, and 635nm, respectively.

[0014] In a second aspect, the present application provides a method for expanding FOV, which is used for a diffractive optical structure, wherein the diffractive optical structure element includes a substrate and an in-coupling part and an out-coupling part arranged on the substrate, wherein the out-coupling part includes an out-coupling grating and a nonlinear frequency multiplier stacked on the out-coupling grating, and the method for expanding FOV includes:

[0015] generating infrared light and projecting it to the coupling portion;

[0016] The infrared light is coupled into the substrate through the coupling-in portion, and the infrared light is transmitted through total reflection in the substrate;

[0017] When the infrared light is transmitted to the outcoupling part, the infrared light is coupled out through the outcoupling grating, and the infrared light is converted into light in the visible light band through the nonlinear frequency multiplier.

[0018] In a third aspect, the present application provides an optical system, comprising:

[0019] a light source for generating infrared light; and

[0020] A diffractive optical structure as described in the first aspect.

[0021] In a fourth aspect, the present application provides a smart head-mounted device, the smart head-mounted device comprising:

[0022] An optical system as described in the third aspect.

[0023] The beneficial effects of this application are:

[0024] The embodiment of the present application provides a new diffractive optical structure, which can significantly expand the FOV while maintaining high-quality image output. The diffractive optical structure provided in the embodiment of the present application solves the problem of small field of view FOV in the existing diffractive waveguide solution by using infrared band for light transmission, high refractive index and low absorption rate substrate material and nonlinear frequency doubling conversion technology, significantly expands the FOV, and improves the light transmission efficiency, which is conducive to enhancing the brightness and clarity of the image, thereby improving the user's visual experience.

[0025] Other features and advantages of the present specification will become apparent from the following detailed description of exemplary embodiments of the present specification with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the specification and, together with the description, serve to explain the principles of the specification.

[0027] Figure 1 A schematic diagram of the structure of a diffractive optical structure provided in an embodiment of the present application;

[0028] Figure 2 One of the effective transmission space diagrams of a traditional single-layer waveguide substrate in K space;

[0029] Figure 3 The second diagram of the effective transmission space of a traditional single-layer waveguide substrate in K space;

[0030] Figure 4 The refractive index change curve of the Si substrate under infrared light provided in the embodiment of the present application;

[0031] Figure 5 This is a curve showing the change in absorptivity of the Si substrate under infrared light provided in the embodiment of the present application;

[0032] Figure 6 One of the spatial diagrams of the effective transmission of the basis of the present application in K space;

[0033] Figure 7 The refractive index variation curve of the Ge substrate under infrared light provided in the embodiment of the present application;

[0034] Figure 8 The absorption rate variation curve of the Ge substrate under infrared light provided in the embodiment of the present application;

[0035] Fig. 9 This is the second spatial diagram of the effective transmission of the basis of this application in K space.

[0036] Description of reference numerals:

[0037] 1. Substrate; 2. Coupling part; 3. Out-coupling grating; 4. Nonlinear frequency multiplier. DETAILED DESCRIPTION

[0038] 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 of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present application.

[0039] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the present application, its application, or uses.

[0040] Techniques and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the techniques and equipment should be considered part of the specification.

[0041] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0042] It should be noted that like reference numerals and letters refer to similar items in the following figures, and therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0043] The following is a detailed description of the diffractive optical structure, the method for expanding FOV, the optical system and the smart head-mounted device provided in the embodiments of the present application in conjunction with the accompanying drawings.

[0044] According to one embodiment of the present application, a diffractive optical structure is provided. Figure 1The diffractive optical structure includes a substrate 1 and a coupling-in part 2 and a coupling-out part arranged on the substrate 1; wherein the coupling-in part 2 is used to couple the incident infrared light into the substrate 1, and make the infrared light be transmitted by total reflection in the substrate 1; the coupling-out part includes a coupling-out grating 3 and a nonlinear frequency multiplier 4 stacked on the coupling-out grating 3, the coupling-out part couples out the infrared light through the coupling-out grating 3, and converts the infrared light into light in the visible light band through the nonlinear frequency multiplier 4; the substrate 1 is made of a material with a high refractive index and low absorption characteristics in the infrared band, wherein the high refractive index n satisfies the condition of n≥3, and in the infrared band, the absorption rate k of the substrate 1 with a thickness of 1 mm to infrared light is ≤0.03%.

[0045] The diffractive optical structure provided in the embodiment of the present application has wide applicability in VR (virtual reality) optical display devices or AR (augmented reality) optical display devices. The diffractive optical structure of the present application can significantly improve the field of view FOV of the optical display device, bringing a more immersive visual experience to the user.

[0046] The diffractive optical structure provided in the embodiment of the present application is, for example, a diffractive optical waveguide device (also called a diffractive optical waveguide sheet).

[0047] In traditional diffractive optical structures, taking diffractive optical waveguide devices as an example, incident visible light is transmitted through total reflection inside its waveguide substrate. This transmission process is limited by two key angles:

[0048] First, there is an upper limit to the angle at which light can be transmitted in the waveguide substrate, which is 90°. This means that when light is transmitted inside the waveguide substrate, the angle between it and the waveguide substrate plane does not exceed 90°, otherwise the light will escape from the waveguide substrate and cannot continue to be transmitted in the waveguide substrate.

[0049] Secondly, there is a lower limit to the angle of light transmission, namely the critical angle of total reflection theta. The value of this critical angle is not fixed, but depends on two key factors: the refractive index n of the waveguide substrate material and the sub and the refractive index n of the medium surrounding the waveguide substrate sup According to Snell's law and the principle of total reflection, when light passes through the waveguide substrate with a higher refractive index n sub Towards a medium with a lower refractive index n sup When the incident angle is greater than or equal to the critical angle theta, the light will be totally reflected at the interface between the waveguide substrate and the medium and continue to propagate along the inside of the waveguide substrate. On the contrary, if the incident angle is less than the critical angle theta, the light will be partially or completely refracted into the surrounding medium and no longer propagate along the waveguide substrate.

[0050] In traditional diffraction optical structures, the total reflection transmission process of light in the waveguide substrate is constrained by the upper limit of 90° and the lower limit of the total reflection critical angle theta determined by the refractive index of the substrate and the surrounding medium.

[0051] The diffractive optical structure provided in the embodiment of the present application effectively overcomes the limitations of traditional near-eye optical display devices in terms of FOV, thereby greatly enhancing the user's visual experience, allowing the user to enjoy a more realistic and three-dimensional visual effect.

[0052] The diffractive optical structure provided in the embodiment of the present application is mainly composed of the following parts:

[0053] Substrate 1: As a medium for light transmission, the selection of the substrate 1 is very important. In this application, materials with high refractive index and low absorption in the infrared band, such as silicon Si, germanium Ge, etc., are selected to ensure that infrared light can be efficiently transmitted in the substrate 1 with a large FOV.

[0054] Coupling part 2: This part is responsible for coupling the incident infrared light into the substrate 1 of the diffractive optical structure, and using the total reflection principle to make the infrared light fully reflected and transmitted in the substrate 1. The use of total reflection can minimize the loss of light during transmission and improve transmission efficiency.

[0055] The outcoupling part includes an outcoupling grating 3 and a nonlinear frequency multiplier 4: the nonlinear frequency multiplier 4 is arranged on the outcoupling grating 3, and is used to convert the infrared light transmitted in the substrate 1 into light in the visible light band when outcoupling. This conversion process realizes the nonlinear frequency doubling conversion from infrared light to visible light, thereby meeting the demand for visible light in the application.

[0056] In the present application, in the out-coupling part, the nonlinear frequency multiplier 4 can be disposed on the out-coupling grating 3 by means of a frame glue.

[0057] In the present application, the light in the infrared band is converted into the light in the visible band by the specially arranged nonlinear frequency multiplier 4 at the coupling-out grating 3, that is, this conversion process occurs after the light is coupled out, so the angle relationship of the light will not be changed, that is, the light in the visible band after conversion still maintains the transmission angle of the infrared light (that is, the light of the infrared waveguide), ensuring that the field of view FOV will not be compressed. In short, the light in the visible band coupled out by the coupling-out part has the same FOV as the infrared light coupled into the substrate 1.

[0058] Due to the use of infrared band transmission and the substrate 1 for transmitting infrared light, the diffractive optical structure of the embodiment of the present application can achieve a field of view FOV of up to 110° or even 180°. This large field of view characteristic is of great significance for improving the user experience of VR / AR optical display devices. The diffractive optical structure provided in the embodiment of the present application can significantly expand the field of view (FOV). A large field of view can provide users with a more immersive visual experience.

[0059] The embodiment of the present application provides a new diffractive optical structure, which can significantly expand the FOV while maintaining high-quality image output. Specifically, the diffractive optical structure provided in the embodiment of the present application solves the problem of small field of view FOV in the existing diffractive waveguide solution by using infrared band for light transmission, high refractive index and low absorption rate substrate material and nonlinear frequency doubling conversion technology, significantly expands the FOV, and improves the light transmission efficiency, which is conducive to enhancing the brightness and clarity of the image, thereby improving the user's visual experience.

[0060] The diffractive optical structure provided in the embodiment of the present application realizes a VR / AR optical display device with a large field of view by adopting infrared band transmission and nonlinear frequency doubling conversion and other technical means, while keeping the angle relationship of the light in the visible light band after conversion uncompressed. These technical effects jointly improve the overall performance and practicality of the diffractive optical structure, and provide strong support for its application in the VR / AR field.

[0061] The diffractive optical structure provided in the embodiment of the present application has a substrate 1 specially designed for transmitting light in the infrared band. Based on this, the substrate 1 is designed to be made of a material with a high refractive index and low absorption characteristics in the infrared band, wherein the high refractive index n satisfies the condition of n≥3, and in the infrared band, the absorption rate k of the substrate 1 with a thickness of 1 mm to infrared light is ≤0.03%.

[0062] The substrate 1 is made of a material with a high refractive index in the infrared band, and the refractive index n satisfies the condition of n≥3. The use of high refractive index materials can significantly expand the transmission angle range of light in the substrate 1 of the diffractive optical structure, thereby achieving a larger field of view FOV. This is crucial to improving the visual experience of AR / VR optical display devices.

[0063] In the infrared band, the absorption rate k of the substrate 1 with a thickness of 1 mm to infrared light is ≤ 0.03%, which means that the material of the substrate 1 of the present application absorbs very little infrared light, which is almost negligible. This low absorption rate of infrared light can ensure that the loss of infrared light is reduced during the transmission of the substrate 1, thereby improving the transmission efficiency. The low absorption rate also helps to maintain the intensity and brightness of the light, thereby ensuring the quality of the final displayed image.

[0064] The design of the substrate 1 of the present application: On the one hand, the use of high refractive index materials makes the incident infrared light have a larger transmission angle range inside the substrate, which can support a larger FOV and improve the user's visual experience. On the other hand, the low absorption rate ensures that the energy loss of infrared light during transmission is very small, which improves the optical efficiency of the entire diffractive optical structure. Overall, this design not only optimizes the optical performance of the diffractive optical structure, but also improves its energy utilization efficiency.

[0065] See also Figure 2 , Figure 2 The effective transmission spatial distribution of a conventional single-layer waveguide substrate in K space is shown, where K space is used to describe the spatial frequency domain of an optical imaging system. Taking the case of a 1.7 refractive index substrate and air as the surrounding medium as an example, the critical angle is about 36°. Figure 2 The 36° circle in the inner ring represents the boundary of the transmission space.

[0066] exist Figure 2 In the figure, multiple concentric rings represent different spatial frequency ranges from the inside to the outside, and the outermost 90° ring marks the maximum transmission angle. These rings together define the annular zone of the effective transmission space. It is worth noting that Figure 2 The rectangular boxes marked with b = 460nm (blue light), g = 525nm (green light), and r = 635nm (red light) in the figure represent the transmission range of light of different wavelengths in K space. For an image with a 30° field of view FOV, it cannot be completely placed in this ring consisting of a 36° inner ring and a 90° outer ring. This means that part of the image with a 30° FOV exceeds the range of the effective transmission space, which may cause image distortion or ineffective transmission.

[0067] That is to say, through Figure 2 It shows that in K space, light of different wavelengths has a specific transmission range, which is defined by the critical angle and the inner and outer rings. The image with a 30° FOV may not be effectively transmitted because it exceeds this transmission range.

[0068] As the field of view FOV increases further, the refractive index of the existing glass system can no longer support it. Figure 3It can be observed that the optical imaging system parameters corresponding to different wavelengths (such as b = 460nm blue light, g = 525nm green light, r = 635nm red light) have a significant impact on the overall performance. When the field of view requirements increase, traditional glass materials may not provide enough refractive index to meet the design requirements, thus affecting the overall performance of the optical imaging system.

[0069] Although high refractive index materials, such as LiNbO3 and SiC, can meet this challenge, their high cost requires a trade-off between material performance and cost control in applications. Therefore, while pursuing a larger field of view, it is necessary to find the right balance between material selection and economy to ensure that the system's performance and cost-effectiveness meet expectations.

[0070] Based on this, this application proposes to use an infrared band with a wavelength exceeding 800nm ​​and select corresponding high-refractive index materials to effectively solve the problem of insufficient refractive index in traditional glass systems when increasing the field of view FOV. The solution of this application not only breaks through the limitations of existing technologies, but also fully considers the optimal balance between material performance and cost-effectiveness, aiming to achieve more efficient and economical optical performance improvement.

[0071] In some examples of the present application, the substrate 1 is made of silicon Si or germanium Ge.

[0072] Although high refractive index materials may be expensive in the visible light band, in the infrared band, some materials such as silicon Si, germanium Ge, etc. can achieve the required refractive index. Therefore, the present application can effectively reduce the production cost of the entire diffractive optical structure by selecting these relatively low-cost materials as the substrate 1 of the diffractive optical structure.

[0073] In this example of the present application, it is pointed out that the material of the substrate 1 is silicon Si or germanium Ge. The selection of these two materials is based on their high refractive index and low absorption characteristics in the infrared band.

[0074] Silicon Si and germanium Ge have excellent optical properties in the infrared band. First, their high refractive index (n ≥ 3) can significantly expand the total reflection transmission angle range of light inside the substrate 1, thereby supporting a larger field of view FOV. This feature is crucial for virtual display devices, augmented reality devices, etc., because it can provide a wider field of view and enhance the user's immersion and experience.

[0075] Secondly, the absorption rate of silicon Si and germanium Ge in the infrared band is very low. In the example of this application, the absorption rate k of the infrared light of the substrate 1 with a thickness of 1 mm is ≤ 0.03%, which means that the energy loss of the light during transmission is very small. The low absorption rate not only helps to maintain the brightness of the optical system, but also improves the optical efficiency and energy utilization efficiency of the entire diffractive optical structure.

[0076] In general, the selection of silicon Si or germanium Ge as the material of the substrate 1 in this application can significantly improve the optical performance of near-eye display devices (such as VR / AR devices). The high refractive index and low absorption rate characteristics of these two materials enable the diffractive optical structure to support a larger FOV while maintaining high optical efficiency and energy utilization efficiency.

[0077] In some examples of the present application, the wavelength λ of the incident infrared light is ≥ 800 nm.

[0078] First, from the perspective of the optical properties of the material, when the wavelength λ of the infrared light projected onto the diffractive optical structure reaches or exceeds 800nm, the high refractive index characteristics of silicon Si and germanium Ge as substrate materials in the infrared band can be fully utilized. The refractive index of these substrate materials in the infrared band is n≥3, which is much higher than the refractive index of glass in the visible light band (up to about 2.1). The high refractive index means that the total reflection transmission angle range of the light inside the substrate 1 is larger, thereby supporting a large field of view FOV, such as a 110° FOV or even a 180° FOV.

[0079] Secondly, from the principle of diffraction waveguide technology, when light is coupled into the substrate through the coupling part in a diffraction manner, the propagation angle of the traditional RGB wavelength will be dispersed due to the diffraction equation, squeezing the transmittable space of the substrate. In the infrared band, especially when the wavelength λ≥800nm, the diffraction effect has a relatively small impact on the propagation angle of light, which makes the transmission of infrared light inside the special substrate more stable, reducing the possibility of energy loss and image distortion.

[0080] In addition, the selection of infrared light with a wavelength λ≥800nm ​​also takes into account the conversion efficiency of the nonlinear frequency multiplier 4. In the example of the present application, the nonlinear frequency multiplier 4 is used to convert light in the infrared band into light in the visible light band. When infrared light with a longer wavelength undergoes nonlinear frequency multiplication conversion, it is easier to meet the phase matching condition, thereby improving the conversion efficiency.

[0081] In summary, the design of the wavelength λ of the incident infrared light ≥ 800nmnm can make full use of the high refractive index characteristics of the material of the substrate 1 in the infrared band, expand the total reflection transmission angle range of the light inside the substrate 1, and support a larger FOV. At the same time, this design also helps to reduce the impact of the diffraction effect on the propagation angle of the light, improve the stability of light transmission and image quality. In addition, it can also improve the efficiency of the nonlinear frequency doubling converter, so that the entire diffraction optical structure can achieve more efficient energy utilization while maintaining high optical performance.

[0082] In some examples of the present application, when the central wavelength of the incident infrared light is less than 1500nm, the material of the substrate 1 is silicon Si, the diffraction optical structure is configured to transmit infrared light with a FOV ≥ 110°, and the nonlinear frequency multiplier 4 is a nonlinear doubled frequency optical crystal, which can convert the infrared light into RGB color light.

[0083] In this example of the present application, when the central wavelength of the incident infrared light is less than 1500nm, the diffractive optical structure is designed to support light transmission with a larger field of view FOV. For example, the diffraction angle and direction of the light can be effectively controlled to ensure that the FOV reaches or exceeds 110°.

[0084] In this example of the present application, the wavelength of infrared light can be converted into the wavelength of visible light by using a nonlinear double frequency optical crystal. After the wavelength conversion, the light in the visible light band can maintain high brightness and contrast, thereby improving the quality of the image. In addition, the nonlinear double frequency process itself has little effect on the phase and polarization state of the light, which helps to maintain the original characteristics of the image.

[0085] In addition, through nonlinear double frequency optical crystals, color restoration of light from infrared light to visible light band can be achieved. These are crucial for the application of near-eye display devices, because the accuracy of color restoration directly affects the immersion and realism of the user experience.

[0086] In some examples of this application, see Figure 6 When the central wavelengths of the incident infrared light are 920nm, 1050nm, and 1270nm respectively, in the outcoupling part, the nonlinear doubled frequency optical crystal can convert the infrared light with the three specific central wavelengths into light in the visible light band with central wavelengths of 460nm, 525nm, and 635nm respectively.

[0087] In this example of the present application, the wavelength conversion function and technical effect of the nonlinear double frequency optical crystal are described when the wavelengths of the incident infrared light are 920nm, 1050nm, and 1270nm respectively.

[0088] In this example of the present application, three specific infrared light wavelengths of r1 = 920 nm, r2 = 1050 nm, and r3 = 1270 nm are selected. These wavelengths are all within the infrared band and are suitable for the substrate material used, such as silicon Si, and the high refractive index characteristics.

[0089] In this example of the present application, the coupling-out portion includes a coupling-out grating 3 and a nonlinear double frequency optical crystal covering the coupling-out grating 3, and the nonlinear double frequency optical crystal can convert 920nm, 1050nm, and 1270nm infrared light into 460nm, 525nm, and 635nm visible light, respectively. The wavelength of light here refers to the central wavelength.

[0090] It should be noted that the light emitted by the outcoupling part is the light in the visible light band after conversion, and the light in the visible light band after conversion can be further used or displayed after being coupled out.

[0091] In this example of the present application, the nonlinear frequency doubling optical crystal is able to accurately achieve wavelength conversion, ensuring that the wavelength of the output light matches the expected wavelength. This is critical for color accuracy and color reproduction, especially in applications such as augmented reality.

[0092] By adopting infrared band and high refractive index substrate materials and combining nonlinear double frequency technology, the diffraction optical structure provided in the embodiment of the present application can support a larger FOV.

[0093] In this example of the present application, when the center lengths of the incident infrared light are 920nm, 1050nm, and 1270nm, respectively, the diffractive optical structure can transmit infrared light with a sufficiently large FOV, such as infrared light with a FOV of 110°, and convert it into color light in the visible light band, such as RGB light, thereby providing a larger field of view. By providing a larger field of view and high-quality images, the user's visual experience and sense of immersion can be enhanced. The converted light in the visible light band has higher brightness and contrast, which helps to improve image quality.

[0094] See also Figure 4 and Figure 5 The data of silicon Si material shown in the figure shows that in the infrared band, silicon Si material exhibits excellent performance: that is, there is no obvious absorption phenomenon, see Figure 5 , and its refractive index can reach above 3, see Figure 4 , which makes it possible to expand the field of view FOV.

[0095] Specifically, at specific wavelength points in the infrared band, such as r1=920nm, r2=1050nm and r3=1270nm, by using Si material as the substrate 1 and combining with the diffraction waveguide technology, a field of view angle FOV of up to 110° can be achieved, and the field of view angle can be completely contained in the annulus defined by the critical angle, see Figure 6 , thus ensuring effective transmission and high-quality display of images.

[0096] In this example of the present application, a nonlinear double frequency optical crystal is used at the outcoupling grating 3 of the outcoupling part. The function of this optical crystal is to convert a specific wavelength in the infrared band into a wavelength in the visible light band. Specifically, see Figure 6 , which converts infrared light with central wavelengths of 920nm, 1050nm and 1270nm into visible light of 460nm (blue), 525nm (green) and 635nm (red) respectively. This conversion process not only maintains the color reproduction and clarity of the image, but also greatly broadens the application scope of diffraction waveguide technology in the field of augmented reality.

[0097] See also Figures 4 to 6 It can be seen that after using Si material as substrate 1 and configuring a nonlinear double frequency optical crystal at the outcoupling grating 3, the overall performance of the diffraction optical structure is significantly improved. In particular, in terms of expanding the field of view, the technical solution proposed in this application shows obvious advantages.

[0098] In some examples of the present application, when the central wavelength of the incident infrared light is ≥1500nm, the material of the substrate 1 is germanium Ge, the diffraction optical structure is configured to transmit infrared light with FOV≥180°, and the nonlinear frequency multiplier 4 is a nonlinear quadruple frequency optical crystal, which can convert the infrared light into RGB color light.

[0099] In this example of the present application, the wavelength of the incident infrared light is ≥ 1500 nm. These long-wavelength infrared lights have a high refractive index in a specific base material such as germanium Ge and are not easily absorbed.

[0100] The diffractive optical structure provided in this example of the present application is configured to transmit infrared light with a FOV ≥ 180°. In other words, the diffractive optical structure is designed to ensure that long-wavelength infrared light is transmitted in the substrate 1 in a total reflection manner and can support a field of view FOV that exceeds the traditional limit.

[0101] In this example of the present application, the nonlinear frequency multiplier uses a nonlinear quadrupled frequency optical crystal, which has the ability to convert long-wavelength infrared light into light in the visible light band, and the conversion ratio is four times the frequency, that is, the wavelength of the infrared light is divided by 4 to obtain the wavelength of the visible light band.

[0102] Nonlinear quadrupled frequency optical crystals can convert long-wavelength infrared light into light in the visible light band. The converted light can cover multiple colors (such as RGB) within the visible light range of the human eye, thereby achieving colorful image display.

[0103] Through the design of the diffractive optical structure, the entire diffractive optical structure can transmit infrared light with a FOV ≥ 180°. This is of great significance in applications such as augmented reality, because a wider field of view can provide richer visual information and a more realistic sense of immersion.

[0104] In this example of the present application, a material with high refractive index and low absorption characteristics such as germanium Ge is selected as the substrate to ensure effective transmission of infrared light in the substrate 1. At the same time, the use of nonlinear quadruple frequency optical crystals also optimizes the efficiency and quality of wavelength conversion.

[0105] In summary, when the wavelength of the incident infrared light is ≥1500nm, the diffractive optical structure can transmit infrared light with a FOV ≥180° and convert it into light in the visible light band through the combination of the diffractive optical structure and the nonlinear quadruple frequency optical crystal. This technology not only realizes the display of ultra-large field of view FOV, but also optimizes the efficiency and quality of wavelength conversion.

[0106] In some examples of this application, see Fig. 9 When the central wavelengths of the incident infrared light are 1840nm, 2100nm, and 2540nm respectively, in the outcoupling part, the nonlinear quadrupled frequency optical crystal can convert the infrared light with the three specific central wavelengths into light in the visible light band with central wavelengths of 460nm, 525nm, and 635nm respectively.

[0107] In this example of the present application, three specific infrared light wavelengths are selected: 1840nm, 2100nm, and 2540nm. These wavelengths have a higher refractive index in substrate materials such as Ge and are not easily absorbed, and are suitable for achieving long-distance, low-loss infrared light transmission.

[0108] In this example of the present application, a nonlinear quadruple frequency optical crystal is used. The crystal has a nonlinear optical effect and can convert long-wavelength infrared light into short-wavelength visible light.

[0109] In this example of the present application, the nonlinear quadrupled frequency optical crystal can convert infrared light of 1840nm, 2100nm, and 2540nm into RGB light of visible light bands with central wavelengths of 460nm, 525nm, and 635nm, respectively. The conversion ratio is quadrupled frequency, that is, the wavelength of the infrared light is divided by 4 to obtain the wavelength of the visible light band. The converted visible light band can, for example, enter the field of view of an observer or a receiver.

[0110] The nonlinear quadrupled frequency optical crystal achieves precise wavelength conversion, converting infrared light of a specific wavelength into light within the visible light band. This enables the diffractive optical structure to produce visible light with a specific color to meet the needs of different application scenarios. Through the nonlinear quadrupled frequency process, the energy of the infrared light is effectively converted into energy in the visible light band. The converted visible light band covers a variety of colors (blue, green, and red) within the visible light range of the human eye, which enables the device to present colorful images and pictures, improving the quality of the visual experience.

[0111] In this example of the present application, a solution is proposed, that is, germanium Ge is used as the material of the substrate 1. This choice is based on the excellent performance of germanium Ge in the infrared band above 1500nm: see Figure 8 , it will not produce obvious absorption phenomenon, and its refractive index can be as high as 4 or above, see Figure 7 This performance makes Germanium Ge an ideal choice for achieving a larger field of view (FOV).

[0112] Specifically, when germanium Ge is used as the substrate 1, the diffractive optical structure can operate stably in the infrared band exceeding 1500nm, and due to the high refractive index characteristics of germanium Ge, the field of view FOV of the entire diffractive optical structure can be further expanded. Fig. 9 It can be seen that at specific wavelengths such as 1840nm, 2100nm and 2540nm, the diffractive optical structure using germanium Ge as the substrate 1 can achieve a field of view FOV coverage of up to 180°, which almost achieves full space coverage and brings a revolutionary breakthrough in augmented reality technology.

[0113] In addition, similar to Si material, when germanium Ge is used as the substrate 1, a nonlinear quadrupled frequency optical crystal is configured at the outcoupling grating 3. The function of this crystal is to convert a specific wavelength in the infrared band into a wavelength in the visible light band, thereby ensuring the color reproduction and clarity of the image. Through this conversion process, the technical solution proposed in this application not only achieves a significant expansion of the field of view, but also maintains high-quality display of the image, opening up a new path for the development of augmented reality technology.

[0114] According to one embodiment of the present application, a method for expanding FOV is provided for a diffractive optical structure, see Figure 1 The diffractive optical structure element includes a substrate 1 and a coupling-in portion 2 and a coupling-out portion arranged on the substrate 1, the coupling-out portion includes a coupling-out grating 3 and a nonlinear frequency multiplier 4 stacked on the coupling-out grating 3, and the method for expanding FOV includes the following steps S100 to S300:

[0115] Step S100, generating infrared light and projecting it to the coupling part 2;

[0116] Step S200, coupling the infrared light into the substrate 1 through the coupling-in portion 2, and causing the infrared light to be transmitted by total reflection in the substrate 1;

[0117] Step S300: When the infrared light is transmitted to the outcoupling part, the infrared light is coupled out through the outcoupling grating 3, and the infrared light is converted into light in the visible light band through the nonlinear frequency multiplier 4.

[0118] According to the above step S100, in this step, infrared light with a specific wavelength is first generated. The wavelength of these infrared lights is selected based on the refractive index and absorption characteristics of the material of the substrate 1 to ensure that the incident infrared light can be effectively transmitted in the substrate 1 without being excessively absorbed. The incident infrared light is then projected onto the coupling-in portion 2 of the diffractive optical structure, ready to enter the substrate 1 for total reflection transmission.

[0119] According to the above step S200: the coupling part 2 is designed to efficiently couple external incident infrared light into the substrate 1. This involves optical design and material selection to ensure that the incident infrared light can enter the substrate 1 at a suitable angle, thereby triggering the total reflection condition.

[0120] Once entering the substrate, the incident infrared light will be transmitted by total reflection within the substrate 1. This step utilizes the principle of total reflection, allowing the infrared light to be transmitted over a longer distance within the substrate 1 with less loss.

[0121] According to the above-mentioned step S300: when the infrared light is transmitted to the coupling-out part of the diffraction optical structure, it will be coupled out through the coupling-out grating 3, and at the same time it will encounter the nonlinear frequency multiplier 4. This nonlinear frequency multiplier 4 has special nonlinear optical properties and can convert the infrared light into light in the visible light band (RGB light).

[0122] The method for expanding FOV provided in the embodiment of the present application is used for a diffractive optical structure. By using infrared light and performing total reflection transmission in a high refractive index substrate 1, the method for expanding FOV can achieve a larger FOV than the traditional diffractive waveguide solution. This is particularly suitable for application scenarios that require a wide field of view, such as augmented reality (AR) devices.

[0123] The nonlinear frequency multiplier 4 can convert the wavelength of the incident infrared light into a wavelength in the visible light band, which not only allows the device to produce color images visible to the human eye, but also improves the energy utilization rate, because most of the input infrared light can be effectively converted into visible light.

[0124] Although high-refractive-index substrate materials (such as LiNbO3, SiC) may be costly, the method of expanding FOV in the present application reduces the overall cost by using infrared bands and corresponding materials such as Si and Ge. These materials have a higher refractive index in the infrared band and are not easily absorbed, allowing the use of more economical materials to achieve high-performance diffractive optical structures.

[0125] Since it can produce colorful light in the visible light band and has a larger FOV, the method of expanding the FOV of the present application can provide a more immersive and realistic visual experience in augmented reality (AR), virtual reality (VR) and other optical display applications.

[0126] In summary, the method for expanding FOV provided in the embodiment of the present application achieves an extended field of view, efficient wavelength conversion, reduced material cost, and enhanced visual experience by combining infrared light, a substrate with a high refractive index and low absorptivity, total reflection transmission, and nonlinear frequency doubling technology. These technical effects make the method of the present application have broad application prospects in the field of optical display technology.

[0127] According to one embodiment of the present application, an optical system is provided, which includes a light source and the diffraction optical structure as described above, wherein the light source is used to generate infrared light.

[0128] In the optical system provided in the embodiment of the present application, the light source is designed to generate infrared light. The wavelength of these infrared light rays is selected based on the refractive index and absorption characteristics of the substrate material in the diffractive optical structure. By accurately selecting the wavelength of the infrared light, it can be ensured that the light is effectively transmitted in the substrate 1 without being excessively absorbed.

[0129] As described above, the diffraction optical structure includes a substrate 1, a coupling-in part 2, and a coupling-out part (which includes a coupling-out grating 3 and a nonlinear frequency multiplier 4). These elements work together to couple the infrared light generated by the light source into the substrate 1, transmit it through total reflection, and then convert it into light in the visible light band at the coupling-out grating 3 through the nonlinear frequency multiplier 4.

[0130] By combining the light source with the diffractive optical structure, the optical system provided by the embodiment of the present application can achieve efficient conversion from infrared to visible light. The infrared light generated by the light source is precisely coupled into the substrate 1 of the diffractive optical structure and transmitted through total reflection, reducing energy loss. Then, in the outcoupling part, the infrared light is converted into light in the visible light band through the nonlinear frequency multiplier 4 therein, achieving efficient wavelength conversion.

[0131] The optical system of the embodiment of the present application utilizes the high refractive index substrate material and the transmission characteristics of infrared light to achieve a larger FOV than the traditional diffraction waveguide solution. This gives the optical system a significant advantage in application scenarios that require a wide field of view. In addition, although the high refractive index substrate material may be expensive, the optical system of the present application reduces the overall cost by using infrared bands and corresponding materials such as Si and Ge.

[0132] According to another embodiment of the present application, a smart head-mounted device is provided, wherein the smart head-mounted device includes the optical system as described above.

[0133] The smart head mounted device provided in the embodiment of the present application can be a virtual reality optical display device or an augmented reality optical display device. In the smart head mounted device, the optical system can be set to two, one corresponding to the user's left eye and the other corresponding to the user's right eye.

[0134] The specific implementation of the intelligent head-mounted device of the embodiment of the present application can refer to the various embodiments of the above-mentioned diffractive optical structure and optical system, so it at least has all the beneficial effects brought by the technical solutions of the above-mentioned embodiments, which will not be repeated here one by one.

[0135] The above embodiments focus on 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. Considering the simplicity of the text, they will not be repeated here.

[0136] Although some specific embodiments of the present application have been described in detail by way of example, it should be understood by those skilled in the art that the above examples are only for illustration, not for limiting the scope of the present application. It should be understood by those skilled in the art that the above embodiments may be modified without departing from the scope and spirit of the present application. The scope of the present application is defined by the appended claims.

Claims

1. A diffractive optical structure, characterized in that: It comprises a substrate (1) and: A coupling portion (2) is used to couple incident infrared light into the substrate (1) and to cause the infrared light to be transmitted by total reflection in the substrate (1); An outcoupling part comprises an outcoupling grating (3) and a nonlinear frequency multiplier (4) stacked on the outcoupling grating (3), wherein the outcoupling part couples out infrared light through the outcoupling grating (3) and converts the infrared light into light in the visible light band through the nonlinear frequency multiplier (4); The substrate (1) is made of a material having a high refractive index and low absorption characteristics in the infrared band, wherein the high refractive index n satisfies the condition of n≥3, and in the infrared band, the absorption rate k of the substrate (1) with a thickness of 1 mm to infrared light is ≤0.03%.

2. The diffractive optical structure according to claim 1, characterized in that: The material of the substrate (1) is silicon Si or germanium Ge.

3. The diffractive optical structure according to claim 1, characterized in that: The wavelength λ of the incident infrared light is ≥800nm.

4. The diffractive optical structure according to claim 1, characterized in that: When the central wavelength of the incident infrared light is less than 1500nm, the material of the substrate (1) is silicon Si, the diffraction optical structure is configured to be able to transmit infrared light with a FOV of ≥110°, and the nonlinear frequency multiplier (4) is a nonlinear double frequency optical crystal capable of converting the infrared light into RGB color light.

5. The diffractive optical structure according to claim 4, characterized in that: When the central wavelengths of the incident infrared light are 920nm, 1050nm, and 1270nm respectively, in the outcoupling part, the nonlinear doubled frequency optical crystal can convert the infrared light with the three specific central wavelengths into light in the visible light band with central wavelengths of 460nm, 525nm, and 635nm respectively.

6. The diffractive optical structure according to claim 1, characterized in that: When the central wavelength of the incident infrared light is ≥1500nm, the material of the substrate (1) is germanium Ge, the diffraction optical structure is configured to be able to transmit infrared light with a FOV ≥180°, and the nonlinear frequency multiplier (4) is a nonlinear quadruple frequency optical crystal, which can convert the infrared light into RGB color light.

7. The diffractive optical structure according to claim 6, characterized in that: When the central wavelengths of the incident infrared light are 1840nm, 2100nm, and 2540nm respectively, in the outcoupling part, the nonlinear quadrupled frequency optical crystal can convert the infrared light with the three specific central wavelengths into light in the visible light band with central wavelengths of 460nm, 525nm, and 635nm respectively.

8. A method for expanding FOV for a diffractive optical structure, characterized in that: The diffractive optical structural element comprises a substrate (1) and a coupling-in portion (2) and a coupling-out portion arranged on the substrate (1); the coupling-out portion comprises a coupling-out grating (3) and a nonlinear frequency multiplier (4) stacked on the coupling-out grating (3); and the method for expanding FOV comprises: generating infrared light and projecting it to the coupling-in portion (2); The infrared light is coupled into the substrate (1) through the coupling-in portion (2), and the infrared light is transmitted by total reflection in the substrate (1); When the infrared light is transmitted to the outcoupling part, the infrared light is coupled out through the outcoupling grating (3), and the infrared light is converted into light in the visible light band through the nonlinear frequency multiplier (4).

9. An optical system, characterized in that: include: a light source for generating infrared light; and A diffractive optical structure as claimed in any one of claims 1 to 7.

10. A smart head mounted device, characterized in that: include: An optical system as claimed in claim 9.

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