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

Abstract

Embodiments of the present application provide a diffraction optical structure, a method for expanding FOV, an optical system, and an intelligent head-mounted device; wherein, the diffraction optical structure includes a substrate and a coupling-in part and a coupling-out part arranged on the substrate; the coupling-in part is used to couple the incident infrared light into the substrate and cause the infrared light to be transmitted by total reflection in the substrate; the coupling-out part includes a coupling-out grating and a nonlinear frequency multiplier stacked on the coupling-out grating, the coupling-out part couples out the infrared light through the coupling-out grating, and converts the infrared light into light in the visible light band through the nonlinear frequency multiplier; the substrate 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 with a thickness of 1 mm for infrared light is ≤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, as an important optical element, are widely used 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 portion, for coupling the incident infrared light into the substrate, and causing the infrared light to be totally reflected and transmitted in the substrate;

[0006] An outcoupling part, comprising an outcoupling grating and a nonlinear frequency multiplier stacked on the outcoupling grating, wherein the outcoupling part couples out infrared light through the outcoupling 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 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 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 ≥800 nm.

[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, which can convert 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 a 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 for a diffractive optical structure, wherein the diffractive optical structure element includes a substrate and an incoupling portion and an outcoupling portion disposed on the substrate, the outcoupling portion including an outcoupling grating and a nonlinear frequency multiplier stacked on the outcoupling grating, the method for expanding FOV comprising:

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

[0016] coupling the infrared light into the substrate through the coupling portion, and causing the infrared light to be transmitted through total reflection within the substrate;

[0017] When the infrared light is transmitted to the outcoupling part, the infrared light is coupled out by the outcoupling grating, and the infrared light is converted into light in the visible light band by 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] The diffractive optical structure as described in the first aspect.

[0021] In a fourth aspect, the present application provides a 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 present invention provides a novel diffractive optical structure that significantly expands the field of view (FOV) while maintaining high-quality image output. By utilizing infrared wavelengths for light transmission, a substrate material with a high refractive index and low absorption rate, and nonlinear frequency doubling conversion technology, the diffractive optical structure addresses the problem of a small field of view (FOV) in existing diffractive waveguide solutions. This significantly expands the FOV while improving light transmission efficiency, which in turn enhances image brightness and clarity, 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 this specification, illustrate embodiments of the specification and, together with the description, serve to explain the principles of the specification.

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

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

[0029] Figure 3 Figure 2 shows 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 provided in the embodiment of the present application under infrared light;

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

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

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

[0034] Figure 8 This is a curve showing the change in absorptivity of the Ge substrate under infrared light provided in an embodiment of the present application;

[0035] Figure 9 This is the second diagram of the effective transmission space 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 arrangements 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 disclosure, 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 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 like 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 describes in detail the diffraction optical structure, method for expanding FOV, optical system and 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 diffraction 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 for infrared light is ≤0.03%.

[0045] The diffractive optical structure provided in the embodiments 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 increase the field of view (FOV) of the optical display device, providing users with a more immersive visual experience.

[0046] The diffractive optical structure provided in the embodiments of the present application is, for example, a diffractive optical waveguide device (also known as a diffractive optical waveguide plate).

[0047] In traditional diffractive optical structures, such as diffractive waveguide devices, incident visible light is transmitted through total internal reflection within the waveguide substrate. This transmission process is limited by two key angles:

[0048] First, there is an upper limit on the angle at which light can propagate within a waveguide substrate, namely 90°. This means that when light propagates within the waveguide substrate, the angle between it and the waveguide substrate plane must not exceed 90°. Otherwise, the light will escape from the waveguide substrate and cannot continue to propagate within 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 internal 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 waveguide substrate. Conversely, 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 diffraction 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 mainly consists of the following parts:

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

[0054] Coupling section 2: This section is responsible for coupling the incident infrared light into the diffractive optical structure substrate 1 and utilizing the principle of total internal reflection to cause the infrared light to be transmitted within the substrate 1 by total internal reflection. The use of total internal reflection can minimize light loss during transmission and improve transmission efficiency.

[0055] The outcoupling portion includes an outcoupling grating 3 and a nonlinear frequency multiplier 4. The nonlinear frequency multiplier 4 is disposed on the outcoupling grating 3 and is used to convert the infrared light transmitted from the substrate 1 into light in the visible light band during outcoupling. This conversion process achieves nonlinear frequency doubling conversion from infrared light to visible light, thus meeting the visible light requirement in applications.

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

[0057] In this application, the infrared light is converted to visible light by a specially configured nonlinear frequency multiplier 4 at the outcoupling grating 3. This conversion occurs after the light is outcoupled, thus maintaining the angular relationship of the light. The converted visible light maintains the transmission angle of the infrared light (i.e., the light from the infrared waveguide), ensuring that the field of view (FOV) is not compressed. In short, the visible light coupled out by the outcoupling portion 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). The large field of view can provide users with a more immersive visual experience.

[0059] The present invention provides a novel diffractive optical structure that significantly expands the field of view (FOV) while maintaining high-quality image output. Specifically, the diffractive optical structure provided by the present invention addresses the problem of a small field of view (FOV) in existing diffractive waveguide solutions by utilizing infrared wavelengths for light transmission, a substrate material with a high refractive index and low absorption rate, and nonlinear frequency doubling conversion technology. This significantly expands the FOV while improving light transmission efficiency, which in turn enhances image brightness and clarity, thereby improving the user's visual experience.

[0060] The diffractive optical structure provided in the embodiments of this application utilizes infrared transmission and nonlinear frequency conversion techniques to achieve a wide field of view VR / AR optical display device while maintaining the angular relationship of the converted visible light without compression. These technical effects collectively enhance the overall performance and practicality of the diffractive optical structure, providing strong support for its application in the VR / AR field.

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

[0062] The substrate 1 is made of a material with a high refractive index in the infrared band, with a refractive index n satisfying the condition n ≥ 3. The use of a high refractive index material significantly expands the angular range of light propagation within the diffractive optical structure's substrate 1, thereby achieving a larger field of view (FOV). This is crucial for enhancing the visual experience of AR / VR optical display devices.

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

[0064] The design of substrate 1 in this application: On the one hand, the use of high-refractive-index materials allows incident infrared light to travel over a wider range of angles within the substrate, thereby supporting a larger field of view (FOV) and enhancing the user's visual experience. On the other hand, the low absorption rate ensures minimal energy loss during infrared light transmission, improving 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 a substrate with a refractive index of 1.7 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 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) 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 within this annulus formed by the 36° inner ring and the 90° outer ring. This means that the image with a 30° FOV partially exceeds the effective transmission range, 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, 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 for blue light, g = 525nm for green light, and r = 635nm for red light) have a significant impact on overall performance. When the field of view requirements increase, traditional glass materials may not provide sufficient 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 means that a trade-off between material performance and cost control is necessary in applications. Therefore, while pursuing a larger field of view, a proper balance must be found between material selection and economic efficiency to ensure that the system's performance and cost-effectiveness meet expectations.

[0070] Based on this, this application proposes using infrared wavelengths exceeding 800nm ​​and selecting corresponding high-refractive-index materials to effectively address the insufficient refractive index of traditional glass systems when increasing the field of view (FOV). This solution not only overcomes 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 improvements.

[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, some materials such as silicon (Si) and germanium (Ge) can achieve the required refractive index in the infrared band. 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. These two materials are selected based on their high refractive index and low absorption properties in the infrared band.

[0074] Silicon (Si) and germanium (Ge) exhibit excellent optical properties in the infrared band. Their high refractive index (n ≥ 3) significantly expands the angle range of total internal reflection (TIR) ​​within the substrate 1, enabling a wider field of view (FOV). This characteristic is crucial for devices such as virtual displays and augmented reality, as it provides a wider field of view and enhances user immersion and experience.

[0075] Secondly, silicon (Si) and germanium (Ge) have very low absorption rates in the infrared band. In the example presented in this application, the absorption rate k of infrared light for a 1mm-thick substrate 1 is ≤ 0.03%, which means that energy loss during light transmission is very minimal. This low absorption rate not only helps maintain the brightness of the optical system but also improves the optical efficiency and energy utilization of the entire diffractive optical structure.

[0076] Overall, the choice of silicon (Si) or germanium (Ge) as the material for 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 properties of these two materials enable diffractive optical structures to support a larger FOV while maintaining high optical and energy efficiency.

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

[0078] First of all, from the perspective of material optical properties, when the wavelength λ of the infrared light projected onto the diffractive optical structure reaches or exceeds 800nm, silicon Si and germanium Ge, etc., as substrate materials, can give full play to their high refractive index characteristics in the infrared band. The refractive index n of these substrate materials in the infrared band is ≥ 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 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, based on the principles of diffraction waveguide technology, when light is diffracted through the coupling element and injected into the substrate, the propagation angles of traditional RGB wavelengths are dispersed due to the diffraction equation, squeezing the substrate's available transmission space. However, in the infrared band, especially for wavelengths λ ≥ 800nm, the diffraction effect has a relatively small impact on the light propagation angle. This results in more stable infrared light transmission within the specially designed substrate, reducing energy loss and image distortion.

[0080] Furthermore, the selection of infrared light with a wavelength λ ≥ 800 nm also takes into account the conversion efficiency of nonlinear frequency multiplier 4. In the example of this application, nonlinear frequency multiplier 4 is used to convert infrared light into visible light. Longer wavelength infrared light can more easily meet phase matching requirements during nonlinear frequency multiplication, thereby improving conversion efficiency.

[0081] In summary, the design of an incident infrared light wavelength λ ≥ 800nm ​​fully utilizes the high refractive index of substrate 1 in the infrared band, expanding the angle range of total internal reflection transmission of light within substrate 1 and supporting a larger field of view (FOV). This design also helps reduce the impact of diffraction effects on the propagation angle of light, improving the stability of light transmission and image quality. Furthermore, it improves the efficiency of the nonlinear frequency doubling converter, enabling the entire diffractive optical structure to 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 1500 nm, 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, a nonlinear frequency doubling optical crystal is used to convert the wavelength of infrared light to that of visible light. After wavelength conversion, the visible light maintains high brightness and contrast, thereby improving image quality. Furthermore, the nonlinear frequency doubling process itself has minimal effect on the phase and polarization state of the light, helping to preserve the original characteristics of the image.

[0085] Furthermore, through nonlinear frequency doubling optical crystals, color restoration can be achieved from infrared to visible light. This is crucial for near-eye display applications, as the accuracy of color restoration directly affects the immersive and realistic 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 frequency doubling optical crystal are described when the wavelengths of the incident infrared light are 920 nm, 1050 nm, and 1270 nm, respectively.

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

[0089] In this example of the present application, the outcoupling portion includes an outcoupling grating 3 and a nonlinear frequency-doubled optical crystal disposed on the outcoupling grating 3. The nonlinear frequency-doubled optical crystal can convert 920nm, 1050nm, and 1270nm infrared light into 460nm, 525nm, and 635nm visible light, respectively. The wavelength of the light here refers to the center wavelength.

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

[0091] In this example, the nonlinear frequency-doubled optical crystal can precisely convert wavelengths, ensuring the output light has the desired wavelength. This is crucial for color accuracy and reproduction, especially in applications such as augmented reality.

[0092] By adopting infrared band and high refractive index substrate materials, combined with 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, for example, 110°, and convert it into colored light in the visible light band, such as RGB light, thereby providing a wider field of view. By providing a wider field of view and high-quality images, the user's visual experience and sense of immersion can be enhanced. The converted visible light band has higher brightness and contrast, which helps 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 wavelengths in the infrared band, such as r1 = 920 nm, r2 = 1050 nm, and r3 = 1270 nm, using Si material as the substrate 1 and combining it with diffraction waveguide technology, a field of view (FOV) of up to 110° can be achieved, and this field of view can be completely contained within 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 This process converts infrared light with central wavelengths of 920nm, 1050nm, and 1270nm into visible light at 460nm (blue), 525nm (green), and 635nm (red), respectively. This conversion process not only maintains image color reproduction and clarity, but also significantly expands the application range of diffraction waveguide technology in augmented reality.

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

[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 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.

[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 certain substrate materials 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 by total internal reflection within the substrate 1, and can support a field of view (FOV) that exceeds conventional limits.

[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 visible light. The converted light can cover multiple colors within the visible light range of the human eye (such as RGB), thus achieving rich color image display.

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

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

[0105] In summary, when incident infrared light has a wavelength ≥1500nm, the diffractive optical structure, combined with a nonlinear quadrupled frequency optical crystal, can transmit infrared light with a FOV ≥180° and convert it into visible light. This technology not only enables displays with an ultra-large field of view (FOV) but also optimizes the efficiency and quality of wavelength conversion.

[0106] In some examples of this application, see Figure 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 high refractive index and are not easily absorbed in substrate materials such as Ge, making them suitable for 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, a nonlinear quadrupled frequency optical crystal can convert infrared light at wavelengths of 1840 nm, 2100 nm, and 2540 nm into RGB light in the visible light band with center wavelengths of 460 nm, 525 nm, and 635 nm, respectively. The conversion ratio is quadrupled frequency, meaning 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 receiver.

[0110] The nonlinear quadrupling optical crystal achieves precise wavelength conversion, converting infrared light of a specific wavelength into light within the visible light band. This enables the diffraction optical structure to produce visible light with a specific color to meet the needs of different application scenarios. Through the nonlinear quadrupling 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 within the visible light range of the human eye (blue, green, red), 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, using germanium Ge as the material of substrate 1. This choice is based on the excellent performance of germanium Ge in the infrared band above 1500nm: see Figure 8 , it does 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. Figure 9 It can be seen that at specific wavelengths such as 1840nm, 2100nm and 2540nm, the diffraction 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] Furthermore, similar to Si materials, when using germanium (Ge) as the substrate 1, this application employs a nonlinear quadrupled frequency optical crystal at the outcoupling grating 3. This crystal converts specific wavelengths in the infrared band into wavelengths in the visible light band, thereby ensuring image color reproduction and clarity. Through this conversion process, the technical solution proposed in this application not only significantly expands the field of view, but also maintains high-quality image display, opening up new avenues 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 an incoupling portion 2 and an outcoupling portion disposed on the substrate 1. The outcoupling portion includes an outcoupling grating 3 and a nonlinear frequency multiplier 4 stacked on the outcoupling grating 3. The method for expanding the FOV includes the following steps S100 to S300:

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

[0116] Step S200, coupling the infrared light into the substrate 1 through the coupling portion 2, and causing the infrared light to be transmitted by total reflection within 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 step S100 described above, infrared light of a specific wavelength is first generated. The wavelength of this infrared light is selected based on the refractive index and absorption properties of the substrate 1 material to ensure that the incident infrared light is effectively transmitted within the substrate 1 without excessive absorption. The incident infrared light is then projected onto the coupling-in portion 2 of the diffractive optical structure, preparing to enter the substrate 1 for total internal reflection transmission.

[0119] According to the above step S200: the coupling portion 2 is designed to efficiently couple externally 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 a 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 outcoupling part of the diffraction optical structure, it will be coupled out through the outcoupling 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 present invention provides a method for expanding the field of view (FOV) of a diffractive optical structure. By using infrared light and transmitting it through total internal reflection in a high-refractive-index substrate 1, the method can achieve a larger FOV than traditional diffractive waveguide solutions. This is particularly suitable for applications requiring 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. This not only allows the device to produce color images visible to the human eye, but also improves energy utilization because most of the input infrared light can be effectively converted into visible light.

[0124] Although high-refractive-index substrate materials (such as LiNbO3 and SiC) can be expensive, the present invention's method for expanding FOV reduces overall costs by using infrared wavelengths and corresponding materials such as Si and Ge. These materials have a higher refractive index in the infrared band and are less susceptible to absorption, allowing the use of more affordable 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 FOV expansion method provided by the embodiments of this application achieves an expanded field of view, efficient wavelength conversion, reduced material costs, and an enhanced visual experience by combining infrared light, a substrate with a high refractive index and low absorptivity, total internal reflection transmission, and nonlinear frequency doubling technology. These technical effects make the method of this 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, comprising 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 embodiments of the present application, the light source is designed to generate infrared light. The wavelength of this infrared light is selected based on the refractive index and absorption properties of the substrate material in the diffractive optical structure. By precisely selecting the wavelength of the infrared light, it is possible to ensure that the light is effectively transmitted through the substrate 1 without excessive absorption.

[0129] As described above, the diffraction optical structure includes a substrate 1, a coupling-in part 2, and an outcoupling part (which includes an outcoupling grating 3 and a nonlinear frequency multiplier 4). These components 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 outcoupling 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 embodiments of the present application can achieve efficient infrared-to-visible light conversion. The infrared light generated by the light source is precisely coupled into the substrate 1 of the diffractive optical structure and transmitted through total internal reflection, reducing energy loss. Then, in the outcoupling portion, 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 a high-refractive-index substrate material and the transmission characteristics of infrared light to achieve a larger FOV than traditional diffraction waveguide solutions. This gives the optical system a significant advantage in application scenarios that require a wide field of view. In addition, although high-refractive-index substrate materials can be costly, the optical system of the present application reduces overall costs 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, which 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 diffraction optical structure and optical system, and therefore has at least 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 for illustration only and are not intended to limit the scope of the present application. It should be understood by those skilled in the art that the above examples 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 base (1) and: A coupling portion (2) is used to couple incident infrared light into the substrate (1) and 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, wherein: The material of the substrate (1) is silicon Si or germanium Ge.

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

4. The diffractive optical structure according to claim 1, wherein: When the central wavelength of the incident infrared light is less than 1500 nm, the substrate (1) is made of silicon (Si), the diffraction optical structure is configured to transmit infrared light with a FOV of ≥110°, and the nonlinear frequency multiplier (4) is a nonlinear doubled 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, wherein: 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 capable of converting 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 diffraction optical structural element comprises a substrate (1), an incoupling portion (2) and an outcoupling portion arranged on the substrate (1), the outcoupling portion comprising an outcoupling grating (3) and a nonlinear frequency multiplier (4) stacked on the outcoupling grating (3), and the method for expanding FOV comprises: generating infrared light and projecting it onto the coupling portion (2); The infrared light is coupled into the substrate (1) through the coupling portion (2), and the infrared light is transmitted by total reflection within 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 The diffractive optical structure according to any one of claims 1 to 7.

10. A smart head-mounted device, characterized in that: include: The optical system according to claim 9.

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