Diffractive optical structure and near-to-eye display equipment

Abstract

The embodiment of the utility model discloses a diffractive optical structure and a near-to-eye display device. The diffractive optical structure comprises a substrate, a coupling-in grating and a coupling-out grating; the substrate is provided with two opposite surfaces and is used for totally reflecting light rays coupled into the substrate and propagating; the coupling-in grating is arranged on the first surface of the two opposite surfaces of the substrate and used for coupling light into the substrate, the coupling-in grating comprises a plurality of grating ridges arranged at intervals, and any grating ridge comprises a first side edge part and a second side edge part which are obliquely arranged in the height direction of the grating ridge; the extension lines of the first side edge part and the second side edge part intersect and form a set included angle, when light emitted by an image source enters the coupled grating, a deposition layer is arranged on the surface of one side, directly facing the image source, of the grating ridge, the deposition layer covers the first side edge part and the top of the grating ridge, and the refractive index of the deposition layer is larger than that of the grating ridge; the out-coupling grating is arranged on any surface of the substrate and used for coupling out the light which comes from the in-coupling grating and is transmitted in the substrate.

Description

Technical Field

[0001] This application belongs to the field of optical diffraction element technology, specifically, this application relates to a diffractive optical structure and a near-eye display device. Background Technology

[0002] With the rapid development of AR technology, optical display devices are constantly evolving towards lighter weight and smaller size. Among them, single-layer waveguide technology is one of the important means to achieve this goal. The key challenge is how to efficiently couple a wide range of wavelengths (such as RGB three primary colors) into a single coupling region. Although traditional tilted grating structures can achieve high diffraction efficiency at specific angles and wavelengths, due to the limitation of the Bragg effect, their coupling bandwidth is often narrow, which means it is difficult to cover a wide range of RGB wavelengths at the same time. This leads to a decrease in overall coupling efficiency. Utility Model Content

[0003] The purpose of this application is to provide a new technical solution for a diffractive optical structure and a near-eye display device.

[0004] According to a first aspect of this application, embodiments of this application provide a diffractive optical structure, the diffractive optical structure comprising:

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

[0006] A coupling grating is disposed on the first surface of two opposing surfaces of the substrate for coupling light into the substrate;

[0007] A coupling grating is disposed on any surface of the substrate and is used to couple light rays from the coupling grating and propagating within the substrate out of the substrate;

[0008] The coupled grating includes a plurality of spaced grating ridges. Each grating ridge includes a first side portion and a second side portion that are inclined along its height direction. The extensions of the first side portion and the second side portion intersect and form a set angle θ, and the set angle θ is 6°≤θ≤20°. When light emitted from the image source is incident on the coupled grating, a deposition layer is provided on the side surface of the grating ridge that directly faces the image source. The deposition layer covers the first side portion and the top of the grating ridge, and the refractive index n3 of the deposition layer is greater than the refractive index n1 of the grating ridge.

[0009] Optionally, the top of the grating ridge is parallel to the first surface, and the vertical distance from any point on the top of the grating ridge to the first surface is the height h of the grating ridge, and 150nm≤h≤400nm;

[0010] The width of the grating ridge at its height h / 2 is DC, and DC < 0.7 mm.

[0011] Optionally, the set included angle θ is 10°≤θ≤20°.

[0012] Optionally, the plurality of grating ridges are arranged at intervals along the same direction on the first surface; wherein any of the grating ridges is inclined relative to the first surface of the substrate, forming an asymmetrical inclined structure.

[0013] Optionally, a grating groove is formed between any two adjacent grating ridges, and the grating groove is filled with a filling material; wherein the refractive index of the grating ridge is n1, the refractive index of the filling material is n2, and there is a set refractive index difference between n1 and n2.

[0014] Optionally, the refractive index difference between the refractive index n1 of the grating ridge and the refractive index n2 of the filling material is set to: |n1-n2|≥0.6.

[0015] Optionally, the filling material in the grating groove is air. When the grating groove is an air groove, the refractive index n1 of the grating ridge satisfies: |n1-1|≥0.6.

[0016] Optionally, the coupled grating is a transmission grating.

[0017] Optionally, the deposited layer is a titanium oxide layer.

[0018] Optionally, the sum of the grating vectors of the coupled-in grating and the coupled-out grating is zero.

[0019] According to a second aspect of this application, embodiments of this application provide a near-eye display device, the near-eye display device comprising:

[0020] Image source; and

[0021] As described in the first aspect, the light emitted from the image source can be incident on the coupling grating of the diffraction optical structure.

[0022] One beneficial effect of the embodiments of this application is that:

[0023] The diffraction optical structure provided in this application embodiment features a novel design for the coupling grating. The two sides of each grating ridge are tilted along the height direction. The key is that the extended lines of these two sides intersect at a single point, forming a predetermined angle θ, ranging from 6° to 20°. This asymmetric tilted grating design, while breaking the Bragg effect relied upon by traditional tilted gratings, brings significant advantages:

[0024] First, it can broaden the coupling bandwidth of the coupling grating to a certain extent, so that in a single-layer diffractive optical structure, only a single coupling grating can efficiently cover the three wavelengths of light: R, G, and B. This characteristic is crucial for realizing lightweight and miniaturized optical display devices.

[0025] Secondly, although it sacrifices a certain degree of peak diffraction efficiency at specific wavelengths, this design maintains a high overall coupling efficiency by reasonably controlling the difference in tilt angles on both sides of the grating ridge. In particular, for the red light band, this design improves the coupling efficiency and makes up for the deficiency of insufficient coupling efficiency of traditional tilted gratings in the red light band.

[0026] Furthermore, by adjusting the value of θ, the diffraction performance of the coupling grating can be optimized to meet the needs of different application scenarios. For example, in applications where red light band performance needs to be emphasized, the included angle θ can be appropriately increased to broaden the coupling bandwidth of red light.

[0027] Other features and advantages of this application will become clear from the following detailed description of exemplary embodiments with reference to the accompanying drawings. Attached Figure Description

[0028] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments of the present application and, together with their description, serve to explain the principles of the present application.

[0029] Figure 1 One of the structural diagrams of the coupling grating of the diffraction optical structure provided in the embodiments of this application;

[0030] Figure 2 for Figure 1 The diagram shows the coupling efficiency distribution of the coupling grating with respect to three different wavelength bands.

[0031] Figure 3 A second structural diagram of the coupling grating for the diffraction optical structure provided in the embodiments of this application;

[0032] Figure 4 for Figure 3 The diagram shows the coupling efficiency distribution of the coupling grating with respect to three different wavelength bands.

[0033] Figure 5 The third structural diagram of the coupling grating for the diffraction optical structure provided in the embodiments of this application;

[0034] Figure 6 The fourth structural diagram of the coupling grating of the diffraction optical structure provided in the embodiments of this application;

[0035] Figure 7 for Figure 6The diagram shows the coupling efficiency distribution of the coupling grating with respect to three different wavelength bands.

[0036] Figure 8 The structure and optical path diagram of a traditional diffractive waveguide (when the coupling grating is a tilted grating);

[0037] Figure 9 The diffraction efficiency distribution of a conventional tilting grating with respect to wavelength and incident angle is shown.

[0038] Figure 10 The structure and optical path diagram of the diffractive optical structure provided in the embodiments of this application are shown.

[0039] Explanation of reference numerals in the attached figures:

[0040] 1. Coupled grating; 11. Grating ridge; 111. First side; 112. Second side; 113. Top; 12. Grating groove; 13. Deposition layer; 2. Coupled grating; 3. Substrate; 31. First surface; 01. Light ray. Detailed Implementation

[0041] Various exemplary embodiments of the present application will now be described in detail with reference to the accompanying drawings. It should be noted that, unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the present application.

[0042] The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the scope of this application and its application or use.

[0043] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and equipment should be considered part of the specification.

[0044] In all the examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0045] It should be noted that similar labels and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be discussed further in subsequent figures.

[0046] The diffractive optical structure and near-eye display device provided in the embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0047] According to one embodiment of this application, a diffractive optical structure is provided, see [link to relevant documentation]. Figure 1The diffractive optical structure includes a substrate 3, a coupling grating 1, and an output grating 2. The substrate 3 has two opposing surfaces for total internal reflection of light coupled into it. The coupling grating 1 is disposed on the first surface 31 of the two opposing surfaces of the substrate 3 to couple light into the substrate 3. The coupling grating 1 includes a plurality of spaced-apart grating ridges 11. Each grating ridge 11 includes a first side portion 111 and a second side portion 112 inclined along its height direction. The extensions of the first side portion 111 and the second side portion 112 intersect to form a set angle θ, wherein the set angle θ is 6°≤θ≤20°. See [reference needed]. Figure 3 When light emitted from the image source is incident on the coupling grating 1, a deposition layer 13 is provided on the side surface of the grating ridge 11 that directly faces the image source. The deposition layer 13 covers the first side edge 111 and the top 113 of the grating ridge 11, and the refractive index n3 of the deposition layer 13 is greater than the refractive index n1 of the grating ridge 11. The coupling grating 2 is disposed on any surface of the substrate 3 and is used to couple the light from the coupling grating 1 that propagates within the substrate 3 out of the substrate 3.

[0048] The diffractive optical structure proposed in this application mainly includes a substrate 3, a coupling grating 1, and a coupling grating 2; wherein, both the coupling grating 1 and the coupling grating 2 are disposed on the substrate 3. The optical solution provided in this application embodiment has a new design for the coupling grating 1, aiming to ensure the coupling efficiency of the coupling grating 1 while further expanding the coupling bandwidth of the coupling grating 1.

[0049] The main components of the diffractive optical structure are described in detail below.

[0050] See Figure 1 The substrate 3 is a single-layer sheet structure with a certain thickness. Specifically, the substrate 3 has two opposing surfaces, namely a first surface 31 and a second surface (the second surface is opposite to the first surface 31). The substrate 3 is used for total internal reflection to propagate light coupled into the substrate 3 from the coupling grating 1.

[0051] See Figure 1The coupling grating 1 is disposed on the first surface 31 of the two opposing surfaces of the substrate 3, and its main function is to couple light into the substrate 3. Notably, the coupling grating 1 employs a novel asymmetric structural design: the angles between the two sides of any grating ridge 11 of the coupling grating 1—namely, the first side 111 and the second side 112—and the first surface 31 of the substrate 3 are different; that is, the first side 111 and the second side 112 are designed to be non-parallel. Based on this design, the extensions of the first side 111 and the second side 112 intersect at a point, forming a set angle θ, which ranges from 6° to 20°. This special design of the coupling grating 1 in this application, while breaking the Bragg effect of traditional tilted gratings, brings significant advantages, which will be explained in detail below.

[0052] Specifically, the design of the coupling grating 1 in this application can bring at least the following technical effects:

[0053] (1) Increase coupling bandwidth: See Figure 1 By designing the two sides (i.e., the first side 111 and the second side 112) of each grating ridge 1 in the coupling grating 1 to be inclined and non-parallel, this structural design breaks the Bragg effect of traditional inclined gratings, while allowing the coupling grating to achieve efficient coupling over a wider wavelength range. For example, among the R, G, and B wavelengths, it significantly broadens the coupling bandwidth of the red light band (R light), thereby effectively solving the problem that traditional inclined gratings cannot cover a wide wavelength range.

[0054] (2) Maintaining high coupling efficiency: The design of the coupling grating 1, by reasonably controlling the difference in tilt angle between the two sides of the grating ridge 11, sacrifices the peak diffraction efficiency at a specific wavelength to a certain extent, but in return, achieves an effective improvement in the overall coupling efficiency. This design ensures that the coupling grating 1 has a significant improvement in diffraction efficiency in bands with low diffraction efficiency, such as the red light band (R light), thereby ensuring the stability and high efficiency of the overall coupling efficiency of the diffractive optical structure.

[0055] (3) By adjusting the angle at which the extended lines on both sides of the grating ridge 11 intersect (i.e., ... Figure 1 The set angle θ shown can be used to optimize the coupling bandwidth and diffraction efficiency of the entire coupling grating 1 in different application scenarios. For example, for applications that require special emphasis on red light band performance, the angle can be adjusted appropriately to broaden the red light coupling bandwidth.

[0056] (4) The diffractive optical structure of this application achieves efficient coupling of R, G and B wavelengths through a single-layer substrate design, which provides strong support for the application of single-layer light guide devices (such as single-layer diffractive waveguides) in the field of augmented reality and promotes the development of lightweight AR optical solutions.

[0057] It should be noted that the Bragg effect, also known as Bragg diffraction, is a physical phenomenon in optics. It refers to the phenomenon where, when light waves strike a material with a periodic structure, such as a grating, light of a specific wavelength is strongly reflected or diffracted, forming specific diffraction peaks. This Bragg effect is particularly pronounced in traditional tilted gratings because the tilt angle and periodic structure of the grating further affect the diffraction behavior of light.

[0058] The Bragg effect of traditional tilted gratings is mainly manifested in their ability to achieve high-efficiency diffraction at specific wavelengths and incident angles, which can improve coupling efficiency when used as a coupling grating. This is because the periodic structure of the tilted grating interacts with the wavelength and incident angle of the light wave, causing the light wave satisfying the Bragg condition to be diffracted in a specific direction. However, this high-efficiency diffraction is usually accompanied by a narrow coupling bandwidth, meaning that high diffraction efficiency can only be maintained within a very small range of wavelengths and incident angles. Specifically, for certain wavelength bands of light, such as the red band in R, G, and B light, traditional tilted gratings have low coupling efficiency, resulting in a significant loss of the red band during coupling.

[0059] See Figure 8 , Figure 8 A side view of a conventional diffractive optical structure is shown, wherein the coupling grating 1 is a conventional tilted grating, and the grating ridge 11 is a symmetrical structure. Specifically, when the conventional tilted grating is used as the coupling grating 1 of this diffractive optical structure and R, G, B rays are coupled in, the coupled R, G, B rays enter the substrate 3, propagate through total internal reflection, and are then coupled out by the coupling grating 2.

[0060] exist Figure 8 Based on the diffractive optical structure shown, see [link to diagram]. Figure 9 , Figure 9 The image shows three diagrams: the leftmost diagram shows the diffraction efficiency distribution for the blue light band (B-light), the middle diagram shows the diffraction efficiency distribution for the green light band (G-light), and the rightmost diagram shows the diffraction efficiency distribution for the red light band (R-light). Figure 9 Looking at the three images shown: Figure 8 The conventional tilt grating shown in the figure, as an asymmetric diffraction element, can exhibit excellent diffraction efficiency under certain conditions due to its Bragg effect, but this advantage is accompanied by a significant limitation in coupling bandwidth.

[0061] Furthermore, when Figure 8 The conventional tilting grating shown in the figure exhibits some drawbacks when used as a coupling grating in diffractive optical structures that need to simultaneously cover the full spectrum of R, G, and B (red, green, and blue) light. For example, it has limitations in the red light band (see [reference needed]). Figure 9 (See the right side of the diagram). The coverage angle of the diffraction bandwidth of a traditional tilted grating is compared to that of the blue light band (which can...). Figure 9 (See left side of the image) and the green band (which can) Figure 9 The image (intermediate view) shows a significant reduction, meaning that the red light band is the most severely lacking among the R, G, and B bands. Regarding this, from... Figure 9 It is evident that in the red light band, the angle covered by the diffraction bandwidth is significantly smaller than that of the blue and green light bands, and the overall diffraction efficiency decreases considerably, with a peak diffraction efficiency of around 0.6. This affects the coupling efficiency of the red light band. The fundamental reason for this is that traditional tilted gratings exhibit the Bragg effect. While this ensures high diffraction efficiency (which can lead to higher coupling efficiency), the coupling bandwidth is typically narrow, resulting in incomplete coupling of the red light band.

[0062] The design of the coupling grating 1 provided in this embodiment is described in [reference]. Figure 1 Without completely abandoning the high diffraction efficiency advantage brought by the Bragg effect, by adjusting the tilt angle of the two sides of each grating ridge 11 to have a certain difference (that is, the two sides are not parallel), this adjustment destroys the conditions of the Bragg effect. Thus, at the cost of a moderate sacrifice of diffraction efficiency, it effectively widens the coupling band width of the coupling grating 1, while also ensuring a high coupling efficiency.

[0063] See Figure 2 , Figure 2 The diagram shows the diffraction efficiency distribution of the coupling grating 1 provided in this application for different wavelength bands when R, G, and B light rays are coupled in: the diagram on the left is the coupling efficiency distribution of the blue light band (B light), the diagram in the middle is the coupling efficiency distribution of the green light band (G light), and the diagram on the right is the diffraction efficiency distribution of the red light band (R light).

[0064] Will Figure 2 As described above Figure 9 After comparison, it can be determined that, Figure 2 The coupling bandwidth range of the coupling grating 1 in the red band shown in the figure is compared to... Figure 9 The conventional tilting grating shown in the figure significantly widens the coupling bandwidth range in the red light band.

[0065] It is particularly worth mentioning that, although the design of the coupling grating 1 provided in this application inevitably sacrifices the peak diffraction efficiency of the red light band during the bandwidth expansion process, this loss is controlled within a small range and will not affect the overall coupling efficiency, thus ensuring the relative stability of the overall coupling efficiency.

[0066] In other words, the design in this application breaks the strict limitations of the original Bragg effect by adjusting the difference in parallelism between the two sides of the grating ridge 11 in the coupling grating 1, thereby increasing the coupling bandwidth while maintaining a certain diffraction efficiency. For example, it can effectively solve the problem of the lack of red light band when R, G, and B light are coupled. Therefore, the coupling grating 1 proposed in this application has found a balance between expanding the coupling bandwidth and maintaining the peak diffraction efficiency, providing a new design for the further development of diffractive optics technology.

[0067] It is also worth noting that, see Figure 3 When light emitted from an external image source (e.g., an optical engine) is incident on the coupled grating 1, a deposition layer 13 is disposed on the side surface of the grating ridge 11 directly facing the image source (hereinafter also referred to as the inclined sunny side of the grating ridge). That is, the deposition layer 13 covers the first side edge 111 and the top 113 of the grating ridge 11, and the refractive index n3 of the deposition layer 13 is greater than the refractive index n1 of the grating ridge 11. Further deposition of material on the inclined sunny side of the grating ridge 11, i.e., the side directly facing the light source, can further improve the diffraction efficiency; however, the refractive index of the deposition layer 13 must be designed to be greater than the refractive index of the grating ridge 11.

[0068] The material of the deposition layer 13 can be titanium oxide.

[0069] In one example, see Figure 4 When the deposition layer 13 is titanium oxide material and the grating ridge 11 is made of glue with a refractive index of 1.9, the resulting coupling grating 1 has a high diffraction efficiency distribution for R, G, and B rays.

[0070] The high refractive index (e.g., n3 > n1) of the deposition layer 13 enhances the coupling efficiency of light from the peripheral image source to the grating ridge 11. When light is incident from a low-refractive-index medium (such as air) to a high-refractive-index medium (such as the deposition layer), total internal reflection or strong refraction occurs, thereby increasing the probability that light will enter the grating ridge 11 and be effectively diffracted. The presence of the deposition layer 13 can also change the propagation path of light on the surface of the grating ridge 11, making it easier for light to be guided to a predetermined diffraction direction, reducing scattering and loss of light during propagation, thereby improving the overall diffraction efficiency of the coupled grating 1.

[0071] The deposition layer 13 can be prepared by mature processes such as physical vapor deposition (PVD) and chemical vapor deposition (CVD). These processes are compatible with existing grating manufacturing processes and are easy to integrate into existing production processes.

[0072] The diffraction optical structure provided in this application embodiment also includes a coupling grating 2, see [link to application]. Figure 10 The output grating 2 is also disposed on the substrate 3, and is used to receive light from the input grating 1 and output it.

[0073] The design of the output grating 2 needs to be coordinated with the design of the input grating 1 to achieve efficient coupling of light into and out. In other words, the output grating 2 and the input grating 1 are complementary to ensure the efficient operation of the entire diffractive optical structure.

[0074] Optionally, the output grating 2 and the input grating 1 can be located on the same surface of the substrate 3. Of course, the output grating 2 and the input grating 1 can also be disposed on two opposite surfaces of the substrate 3.

[0075] The diffraction optical structure provided in this application embodiment features a novel design for the coupling grating. The two sides of each grating ridge are tilted along the height direction. The key is that the extended lines of these two sides intersect at a single point, forming a predetermined angle θ, ranging from 6° to 20°. This asymmetric tilted grating design, while breaking the Bragg effect relied upon by traditional tilted gratings, brings significant advantages:

[0076] First, it can broaden the coupling bandwidth of the coupling grating to a certain extent, so that in a single-layer diffractive optical structure, only a single coupling grating can efficiently cover the three wavelengths of light: R, G, and B. This characteristic is crucial for realizing lightweight and miniaturized optical display devices.

[0077] Secondly, although it sacrifices a certain degree of peak diffraction efficiency at specific wavelengths, this design maintains a high overall coupling efficiency by reasonably controlling the difference in tilt angles on both sides of the grating ridge. In particular, for the red light band, this design improves the coupling efficiency and makes up for the deficiency of insufficient coupling efficiency of traditional tilted gratings in the red light band.

[0078] Furthermore, by adjusting the value of θ, the diffraction performance of the coupling grating can be optimized to meet the needs of different application scenarios. For example, in applications where red light band performance needs to be emphasized, the included angle θ can be appropriately increased to broaden the coupling bandwidth of red light.

[0079] In embodiments of this application, the tilt angles of the two sides of any grating ridge 11 of the coupling grating 1 are designed to be different, and this difference is described as a set angle θ formed by the extension lines of the first side 111 and the second side 112 being 6°≤θ≤20°. This design aims to further optimize the diffraction performance of the coupling grating 1.

[0080] contrast Figure 2 and Figure 9 It is understood that the coupling grating 1 provided in this application significantly improves the coupling efficiency in the red light band, and has virtually no impact on the coupling efficiency in the blue and green light bands, resulting in a relatively high overall coupling efficiency for the coupling grating 1. This design of the present application breaks the strict wavelength and incident angle selectivity inherent in the Bragg effect of traditional tilted gratings, enabling the coupling grating 1 to maintain a high overall diffraction efficiency over a wider wavelength range, thereby improving the overall coupling efficiency.

[0081] In the application of single-layer diffractive optical structures (such as single-layer diffractive waveguides), when it is necessary to process light of three wavelengths (RGB) simultaneously, by setting the set angle θ within the reasonable range mentioned above, it can be ensured that the coupling grating 1 can achieve a relatively balanced coupling efficiency in the three wavelength bands of red, green and blue light, reducing the fluctuation of coupling efficiency caused by wavelength differences, and especially improving the coupling efficiency of the red light band.

[0082] In the embodiments of this application, the set angle θ, ranging from 6° to 20° (inclusive), provides design flexibility. Depending on specific application requirements, the set angle θ can be adjusted to optimize the coupling efficiency of a particular wavelength band. For example, in applications requiring a particular emphasis on red light band performance, a larger set angle θ can be selected to obtain a wider red light bandwidth. Conversely, in applications with higher overall efficiency requirements, a smaller set angle θ can be selected to balance diffraction efficiency and bandwidth.

[0083] In summary, by designing the first side portion 111 and the second side portion 112 of the grating ridge 11 to intersect at an angle of 6° to 20°, the diffractive optical structure in this embodiment of the application exhibits significant technical advantages in terms of broadening the coupling bandwidth, maintaining high overall diffraction efficiency, improving design flexibility and applicability, reducing manufacturing costs, and supporting the development of single-layer light guide devices.

[0084] This application designs a structure with different angles on both sides of the tilted grating. See [link / reference] Figure 1This disrupts the Bragg effect inherent in traditional tilted gratings, thereby significantly broadening the coupling bandwidth while reasonably sacrificing some peak diffraction efficiency. This allows for more effective coverage of the three wavelengths of light (RGB) in a single-layer substrate diffractive optical structure through a single coupling region, ensuring overall coupling efficiency.

[0085] Today, as AR optical technology moves towards lightweight design, reducing the number of stacked layers in light guide devices has become an important trend. The diffractive optical structure proposed in this application is of great significance for realizing single-layer light guide devices. It solves the problem that the coupling region in single-layer light guide devices is difficult to cover a wide wavelength range, and provides strong technical support for the application of single-layer light guide devices in the field of augmented reality.

[0086] In some examples of this application, the top 113 of the grating ridge 11 is parallel to the first surface 31, and the vertical distance from any point on the top 113 of the grating ridge 11 to the first surface 31 is the height h of the grating ridge 11, and 150nm≤h≤400nm; the width of the grating ridge 11 at its height h / 2 is DC, and DC<0.7mm.

[0087] The height of the grating ridge 11, also known as the depth of the grating ridge 11, has a direct impact on the diffraction efficiency of the entire coupled grating 1.

[0088] Diffraction efficiency refers to the proportion of light intensity emitted at a specific diffraction order after passing through a grating structure to the total incident light intensity.

[0089] The height range design of the grating ridge 11 in this example allows the coupled grating 1 to achieve high diffraction efficiency at specific wavelengths and incident angles. By adjusting the height of the grating ridge 11, the intensity and direction of the diffracted light can be precisely controlled to meet different application requirements.

[0090] In the coupling grating provided in this application, all grating ridges 11 have the same height.

[0091] In the diffractive optical structure provided in this application embodiment, the height h of the grating ridge 11 of the coupling grating 1 and its midpoint width DC (i.e., the width of the grating ridge at a height of h / 2) are important parameters when designing the coupling grating. Specifically, the height of the grating ridge 11 is h, and its width DC at a height of h / 2 is limited to less than 0.7 mm (DC < 0.7 mm). This design feature brings the following technical effects:

[0092] First, optimize the balance between coupling efficiency and coupling bandwidth:

[0093] The width of the grating ridge 11, especially the midpoint width DC, has a significant impact on the coupling efficiency. If the width of the grating ridge is too large, it will lead to a reduction in the coupling bandwidth, because not all wavelengths of light can effectively pass through the grating ridge 11 into the substrate 3.

[0094] In this example of the application, limiting DC to less than 0.7 mm optimizes coupling efficiency while maintaining a certain coupling bandwidth. This design allows light to be coupled more effectively into the substrate 3 when passing through the coupling grating 1, which is particularly important when processing light of three wavelengths (R, G, and B) simultaneously.

[0095] Second, improve diffraction efficiency:

[0096] The height h of the grating ridge 11 also affects the diffraction efficiency. An appropriate height allows light to be refracted and reflected more effectively when passing through the grating ridge, thereby improving the diffraction efficiency. At the same time, combined with a design where DC < 0.7 mm, the propagation path of light in the coupling grating 1 can be further precisely controlled, reducing light scattering and loss, thereby improving the overall diffraction efficiency.

[0097] Third, to better achieve lightweight design of diffractive optical structures:

[0098] In AR optical display technology, lightweighting is an important design goal. By optimizing the height and width of the grating ridge, the size and weight of the diffractive optical structure can be reduced while maintaining performance. For example, a narrower grating ridge width (DC < 0.7 mm) means that thinner substrate material can be used, thereby reducing the overall weight and volume and contributing to the realization of lighter AR optical display devices.

[0099] In summary, the design features of the height h of the grating ridge 11 and its midpoint width DC (DC < 0.7 mm) of the coupling grating 1 demonstrate significant technical advantages in optimizing the balance between coupling efficiency and bandwidth, improving diffraction efficiency, and promoting lightweight design. This design not only enhances the overall performance of the diffractive optical structure but also provides strong support for its widespread application in fields such as AR optical display technology.

[0100] See some examples in this application. Figure 1 The extensions of the first side portion 111 and the second side portion 112 intersect and form a set angle θ, wherein the set angle θ is 10°≤θ≤20°.

[0101] In this example of the application, a more preferred parameter design is proposed, namely, for the coupled grating 1, the set angle θ formed by the extension lines of the first side 111 and the second side 112 of its grating ridge 11 is optimized to 10° to 20° (including the two endpoint values ​​of 10° and 20°).

[0102] Compared to a wide range of 6° to 20°, optimizing the set angle θ to 10° to 20° allows for more precise control over the expansion of the coupling bandwidth of the coupling grating 1. This ensures that the coupling grating 1 can provide a wider and relatively balanced diffraction bandwidth at different wavelengths, thereby reducing fluctuations in coupling performance caused by wavelength differences.

[0103] When the set angle θ is within the range of 10° to 20°, although the peak diffraction efficiency may still decrease to some extent, this decrease is better controlled within an acceptable level. At the same time, the significant expansion of the coupling bandwidth allows the overall coupling efficiency to remain at a high level over a wider wavelength range, achieving a better balance between the peak diffraction efficiency and the coupling bandwidth.

[0104] In applications where performance in a specific wavelength band is particularly important, the coupling efficiency of that band can be further optimized by more precisely adjusting the set angle θ. For example, in situations where the red wavelength band is especially critical, a set angle θ close to 20° can be selected to obtain a wider red wavelength bandwidth, thereby improving the coupling efficiency and imaging quality in the red wavelength band. In applications where higher overall efficiency is required, a set angle θ closer to 10° can be selected to balance diffraction efficiency and bandwidth.

[0105] In one example, see Figure 1 The set angle θ formed by the extension lines of the first side portion 111 and the second side portion 112 is, for example, 14°. Based on this, see... Figure 2 From the three figures shown, it can be determined that the bandwidth of the red band in the rightmost figure is greater than before (see...). Figure 9 The peak efficiency has broadened, and the peak efficiency has only decreased slightly, which will not have a significant impact on image quality.

[0106] See some examples in this application. Figure 1 The plurality of grating ridges 11 are arranged at intervals along the same direction on the first surface 31, wherein any one of the grating ridges 11 is inclined relative to the first surface 31 of the substrate 3 and forms an asymmetrical inclined structure.

[0107] In this example of the application, the first side portion 111 and the second side portion 112 of each grating ridge 11 are inclined and not parallel in the height direction, and the extension lines of the two side portions intersect to form a set included angle θ (6°≤θ≤20°, more preferably 10°≤θ≤20°).

[0108] According to the arrangement of the grating ridges 11 provided in this example of the application, the coupled grating 1 is, for example, a one-dimensional grating.

[0109] Because the grating ridge 11 employs an asymmetrical tilted structure, this design disrupts the Bragg effect of traditional tilted gratings, thereby allowing the coupling grating 1 to achieve efficient coupling over a wider wavelength range. This is particularly important in single-layer waveguide technology, as it allows a single coupling region to efficiently couple light of R, G, and B wavelengths simultaneously, solving the problem that traditional tilted gratings struggle to cover a wide wavelength range.

[0110] Although the asymmetric tilted structure sacrifices some peak diffraction efficiency at specific wavelengths, overall, this design improves the overall coupling efficiency by broadening the coupling bandwidth. Especially in wavelengths with lower diffraction efficiency, such as the red band, this design significantly improves coupling efficiency and ensures the stability of overall performance.

[0111] By adjusting the tilt angle and arrangement period of the grating ridge 11, selective diffraction of light of specific wavelengths can be achieved. This selective diffraction helps optimize the spectral performance of the optical system and improve image display quality.

[0112] This asymmetric tilted grating structure allows diffractive optical structures to be adapted to a wider range of applications. For example, in augmented reality (AR) optical display devices, by adjusting the tilt angle and arrangement period of the grating ridges, display performance can be optimized to meet different user needs.

[0113] Of course, the design of the coupling grating 1 is flexible and can be constructed as a two-dimensional grating according to specific coupling requirements. This application does not set strict limitations in this regard.

[0114] However, in practical applications, the coupling grating 1 often prefers to adopt a one-dimensional grating design, mainly due to the high diffraction efficiency, excellent light transmission performance and relatively low manufacturing cost exhibited by the one-dimensional grating.

[0115] See some examples in this application. Figure 6 A grating groove 12 is formed between any two adjacent grating ridges 11, and the grating groove 12 is filled with a filling material; wherein the refractive index of the grating ridge 11 is n1, the refractive index of the filling material is n2, and there is a set refractive index difference between n1 and n2.

[0116] The slight disruption of the Bragg effect leads to a minor decrease in peak diffraction efficiency. However, this can be effectively mitigated by increasing the refractive index difference (i.e., the difference between n1 and n2) between the grating ridge 11 and the grating groove 12 (the refractive index of the grating groove is directly related to the filling material inside it), thereby optimizing the overall diffraction efficiency. This design not only balances the broadening of the coupling bandwidth with the maintenance of diffraction efficiency but also ensures that the coupling grating achieves more ideal optical performance in practical applications.

[0117] Specifically, the tilted arrangement of the grating ridge 11 and the design of the angle difference between its two sides have broadened the coupling bandwidth of light to a certain extent, covering a wider coupling wavelength range. To compensate for the potential decrease in diffraction efficiency peak caused by the broadening of the coupling bandwidth, this application also significantly enhances the interaction of incident light in the coupling grating 1 by optimizing the refractive index difference between the filling material of the grating ridge 11 and the grating groove 12. When the refractive index difference between the grating ridge 11 and the grating groove 12 is large, the incident light undergoes stronger refraction and reflection at the interface between the grating ridge 11 and the grating groove 12, thereby improving the diffraction efficiency. This is beneficial for improving the diffraction efficiency peak in certain bands, such as the red light band.

[0118] By controlling the refractive index difference between the grating ridge 11 and the grating groove 12, the coupling grating 1 can selectively enhance or suppress the diffraction behavior of light of a specific wavelength. This optimization of spectral performance helps to achieve finer spectral control while maintaining the coupling bandwidth.

[0119] This example of the application compensates for the potential decrease in diffraction efficiency caused by the widening of the coupling bandwidth by optimizing the refractive index difference between the grating ridge 11 and the grating groove 12 of the coupling grating 1. This design achieves an increase in peak diffraction efficiency in certain bands while maintaining a wide coupling bandwidth, providing a high-performance grating structure solution for optical applications such as augmented reality (AR).

[0120] See some examples in this application. Figure 6 The difference between the refractive index n1 of the grating ridge 11 and the refractive index n2 of the filling material is set to: |n1-n2|≥0.6.

[0121] In this example of the application, it is specified that the difference between the refractive index n1 of the grating ridge 11 and the refractive index n2 of the filling material in the grating groove 12 should satisfy: |n1-n2|≥0.6. It should be noted that a larger refractive index difference between the grating ridge 11 and the grating groove 12 is better, as this is beneficial for improving the overall coupling efficiency of the coupling grating 1 and the peak diffraction efficiency of certain wavelengths. However, considering current material limitations, the refractive index difference between the grating ridge 11 and the grating groove 12 cannot be controlled to be extremely high.

[0122] See Figure 7 , Figure 7 The three figures shown from left to right are the diffraction efficiency distribution diagrams of the blue, green, and red light bands when the difference in refractive index between the filling material in the grating ridge 11 and the grating groove 12 increases from 0.7 to 1.3.

[0123] Will Figure 7 The three pictures shown in the middle are Figure 9 After comparing the three images, it can be determined that... Figure 7 The coupling bandwidth of the red light band shown is significantly widened, and the diffraction efficiency is also high. In other words, by adjusting the refractive index difference between the grating ridge 11 and the grating groove 12, not only is the coupling bandwidth of the red light band widened, but its peak diffraction efficiency is also improved.

[0124] The technical solution provided in this example has little impact on the coupling efficiency and peak efficiency in the blue and green light bands. (See [link to relevant documentation]). Figure 7 , and Figure 9 The blue light band (left image) and green light band (right image) shown in the figure show little change.

[0125] When the refractive index difference between the grating ridge 11 and the grating groove 12 reaches or exceeds 0.6, light rays encounter a significant abrupt change in refractive index when projected onto the coupling grating 1, resulting in stronger refraction and reflection effects. This enhanced light-matter interaction significantly improves the diffraction efficiency of the grating, allowing more light rays to be coupled into the substrate 3 in a predetermined direction.

[0126] Although widening the coupling bandwidth of the coupling grating 1 may lead to a decrease in the peak diffraction efficiency (due to the disruption of the Bragg effect), this deficiency can be mitigated to some extent by increasing the refractive index difference between the grating ridge 11 and the grating groove 12. In other words, a larger refractive index difference between the grating ridge 11 and the grating groove 12 helps the coupling grating 1 maintain a wider coupling bandwidth while reducing the decrease in the peak diffraction efficiency, thereby improving the overall performance of the coupling grating 1.

[0127] Furthermore, a large difference in refractive index typically implies a significant difference in material properties between the grating ridge 11 and the grating groove 12. This difference helps enhance the stability of the entire grating structure and reduces performance fluctuations caused by factors such as temperature changes and mechanical stress.

[0128] In some examples of this application, the filling material in the grating groove 12 is air. When the grating groove 12 is an air groove, the refractive index n1 of the grating ridge satisfies: |n1-1|≥0.6.

[0129] The material filling the grating groove 12 can be air, a design that facilitates a large refractive index difference between the grating groove 12 and the grating ridge 11. This is because the refractive index of air is close to 1, which is much lower than that of most solid materials. Therefore, when the grating groove 12 is an air groove, a large refractive index difference can easily be formed with the grating ridge 11 (typically made of a high-refractive-index material). This large refractive index difference is a key factor in achieving high diffraction efficiency and widening the coupling bandwidth. Ensuring high diffraction efficiency can lead to improved coupling efficiency.

[0130] Furthermore, the presence of the air slots allows for greater flexibility in the material selection for the grating ridge 11. The most suitable high-refractive-index material can be chosen to fabricate the grating ridge based on specific application requirements and manufacturing process limitations. This flexibility helps optimize grating performance while reducing manufacturing costs.

[0131] As previously mentioned, a larger difference in refractive index can also help enhance the interaction of light within the grating structure, thereby increasing the peak diffraction efficiency. In this example of the present application, with the air groove design, due to the significant difference in refractive index, light undergoes stronger refraction and reflection effects when passing through the coupling grating 1, which can further help improve the peak diffraction efficiency.

[0132] Furthermore, compared to other grating groove designs that require complex material processing and filling techniques, the manufacturing process of air grooves is relatively simple. It does not require additional material filling or complex processing steps; it only requires leaving space between the grating ridges. This simplified manufacturing process helps reduce manufacturing costs and improve production efficiency.

[0133] In summary, designing the grating groove 12 as an air groove easily creates a large refractive index difference with the grating ridge 11, thereby improving the diffraction efficiency peak, optimizing spectral characteristics, and simplifying the manufacturing process. This design choice provides a high-performance, low-cost, and easy-to-manufacture grating structure solution for optical applications such as augmented reality (AR).

[0134] In some examples of this application, the coupled grating 1 is a transmission grating.

[0135] Transmissive gratings have a relatively simple structure and are easy to integrate with other optical components. Their manufacturing process is relatively mature and cost-effective. Choosing a transmissive grating as the coupling grating can reduce the overall manufacturing cost of the diffractive optical structure, thereby improving the product's market competitiveness.

[0136] In some examples of this application, the sum of the grating vectors of the input grating 1 and the output grating 2 is zero.

[0137] When the sum of the grating vectors of two gratings, such as input grating 1 and output grating 2, is zero, it means that the two gratings have a certain optical symmetry or complementarity.

[0138] When the sum of the grating vectors of the input grating 1 and the output grating 2 is zero, the propagation direction of light passing through these two gratings remains consistent. This helps reduce light scattering and loss in the diffractive optical structure, improving light utilization efficiency. For AR near-eye display devices, this helps improve image clarity and brightness.

[0139] When the sum of the grating vectors of the input grating 1 and the output grating 2 is zero, aberrations caused by the gratings can be reduced to a certain extent. This is because the symmetry or complementarity of the two gratings helps to cancel each other's influence on light propagation, thereby reducing aberrations.

[0140] Furthermore, the coupling grating 1 and the coupling grating 2 are key components in the diffractive optical structure, and their coupling efficiency directly affects the performance of the entire optical system. When the sum of the grating vectors of these two gratings is zero, more efficient light coupling can be achieved. This is because after light enters the substrate 3 through the coupling grating 1, it can be coupled out more smoothly through the coupling grating 2, reducing light reflection and loss.

[0141] In some examples of this application, the diffractive optical structure further includes a folding grating disposed on the substrate 3 and located in the optical path between the coupling grating 1 and the coupling grating 2. The folding grating is used to receive light from the coupling grating 1 and propagate the light to the coupling grating 2 after pupil dilation along a first predetermined direction. At this time, the coupling grating 2 is used to dilate the propagated light along a second predetermined direction, wherein the second predetermined direction is a direction different from the first predetermined direction.

[0142] The sum of the grating vectors of the coupled-in grating 1, the coupled-out grating 2, and the turning grating is zero.

[0143] In some examples of this application, the diffractive optical structure is, for example, a light guide device.

[0144] In one specific example, the diffractive optical structure is a diffractive waveguide, which can be applied to devices such as AR optical display devices.

[0145] According to another embodiment of this application, a near-eye display device is provided. The near-eye display device includes a housing, an image source, and a diffractive optical structure as described above, wherein light emitted from the image source can be incident on a coupling grating 1 on the diffractive optical structure; both the image source and the diffractive optical structure are disposed on the housing.

[0146] The image source is, for example, an optical engine.

[0147] The near-eye display device provided in this application embodiment is, for example, an AR optical display device. Further, the AR optical display device may be, for example, AR smart glasses or an AR smart helmet.

[0148] The specific implementation of the near-eye display device in this application can refer to the above-described embodiments of the diffractive optical structure. Therefore, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, and will not be described in detail here.

[0149] The above embodiments mainly describe the differences between the various embodiments. As long as the different optimization features between the various embodiments are not contradictory, they can be combined to form a better embodiment. For the sake of brevity, they will not be elaborated here.

[0150] While specific embodiments of this application have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of this application. Those skilled in the art should understand that modifications can be made to the above embodiments without departing from the scope and spirit of this application. The scope of this application is defined by the appended claims.

Claims

1. A diffractive optical structure, characterized in that, include: The substrate (3) has two opposing surfaces for total internal reflection of light coupled into it; A coupling grating (1) is disposed on the first surface (31) of the two opposing surfaces of the substrate (3) for coupling light into the substrate (10); A coupling grating (2) is disposed on any surface of the substrate (3) for coupling light from the coupling grating (1) and propagating within the substrate (10) out of the substrate (10); The coupled grating (1) includes a plurality of spaced grating ridges (11). Each grating ridge (11) includes a first side portion (111) and a second side portion (112) that are inclined along its height direction. The extension lines of the first side portion (111) and the second side portion (112) intersect and form a set angle θ, and the set angle θ is 6°≤θ≤20°. When the light emitted from the image source is incident on the coupled grating (1), a deposition layer (13) is provided on the side surface of the grating ridge (11) that directly faces the image source. The deposition layer (13) covers the first side portion (111) and the top (113) of the grating ridge (11), and the refractive index n3 of the deposition layer (13) is greater than the refractive index n1 of the grating ridge (11).

2. The diffractive optical structure according to claim 1, characterized in that, The top (113) of the grating ridge (11) is parallel to the first surface (31), and the vertical distance from any point on the top (113) of the grating ridge (11) to the first surface (31) is the height h of the grating ridge (11), and 150nm≤h≤400nm; The width of the grating ridge (11) at its height h / 2 is DC, and DC < 0.7 mm.

3. The diffractive optical structure according to claim 1, characterized in that, The set included angle θ is 10°≤θ≤20°.

4. The diffractive optical structure according to any one of claims 1-3, characterized in that, The plurality of grating ridges (11) are arranged at intervals along the same direction on the first surface (31); wherein any of the grating ridges (11) is inclined relative to the first surface (31) of the substrate (3) and forms an asymmetrical inclined structure.

5. The diffractive optical structure according to claim 4, characterized in that, A grating groove (12) is formed between any two adjacent grating ridges (11), and the grating groove (12) is filled with a filling material; wherein the refractive index of the grating ridge (11) is n1, the refractive index of the filling material is n2, and there is a set refractive index difference between n1 and n2.

6. The diffractive optical structure according to claim 5, characterized in that, The refractive index difference between the refractive index n1 of the grating ridge (11) and the refractive index n2 of the filling material is set to: |n1-n2|≥0.

6.

7. The diffractive optical structure according to claim 6, characterized in that, The filling material in the grating groove (12) is air. When the grating groove (12) is an air groove, the refractive index n1 of the grating ridge satisfies: |n1-1|≥0.

6.

8. The diffractive optical structure according to claim 1, characterized in that, The coupling grating (1) is a transmission type grating.

9. The diffractive optical structure according to claim 1, characterized in that, The deposited layer (13) is a titanium oxide layer.

10. The diffractive optical structure according to claim 1, characterized in that, The sum of the grating vectors of the coupled-in grating (1) and the coupled-out grating (2) is zero.

11. A near-eye display device, characterized in that, include: shell; Image source; and The diffractive optical structure as described in any one of claims 1-10, wherein the light emitted from the image source can be incident on the coupling grating (1) of the diffractive optical structure; Both the image source and the diffractive optical structure are disposed in the outer shell.

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