Diffraction waveguide device, near-eye display equipment and method for eliminating coherence

Abstract

The embodiment of the invention provides a diffraction waveguide device, near-eye display equipment and a method for eliminating coherence. The diffraction waveguide device comprises a waveguide substrate, and a coupling-in grating, a turning grating and a coupling-out grating which are arranged on the surface of the waveguide substrate, the duty ratio of the turning grating is in periodic oscillation distribution along the surface of the grating, the periodic oscillation distribution has an oscillation direction k in a grating plane, and the oscillation direction k is any direction except a direction perpendicular to a connecting line of two beam splitting points in an interference light path formed by the turning grating; the periodic oscillation distribution is configured in such a way that by generating a duty cycle difference at the two beam splitting points, an additional phase difference is introduced between light rays propagating to interference points via different paths, thereby destroying a coherence condition to weaken or eliminate an interference effect.

Description

Technical Field

[0001] This application relates to the field of optical device technology, and more specifically, to a diffractive waveguide device, a near-eye display device, and a method for eliminating coherence in a diffractive waveguide device. Background Technology

[0002] Optical waveguides are the core optical components in augmented reality (AR) devices. Their basic principle is to use total internal reflection to conduct light, and to couple, bend, and finally couple the imaging light from the image source (optical engine) to the human eye through diffractive optical elements (such as gratings) set on the waveguide.

[0003] To accommodate differences in interpupillary distance and facial contours among users, diffractive waveguides need to expand a finite incident beam in two dimensions to create a sufficiently large viewing area—the "eyebox"—allowing the user's pupil to move freely. To achieve this, a deflection grating is typically introduced between the input and output gratings to expand and deflect the light in one dimension. However, the introduction of the deflection grating inevitably introduces interference problems. For details, please refer to... Figure 1 When light rays OA from the coupled grating reach point A on the deflection grating, they split into multiple orders due to diffraction. For example, some rays (such as the 1R order, path AB) will be deflected as designed, while others (such as the 0R order, path AC) will continue to propagate forward. As these rays of different orders continue to propagate within the waveguide, they will undergo multiple total internal reflections and pass through the deflection grating again, resulting in further splitting.

[0004] The key issue is that these rays, originating from the same light source but propagating along different paths (such as path OABDF and path OACDF), will eventually converge at a certain point within the waveguide (e.g., Figure 1 The beams converge at point D. Since they originate from the same coherent light source and have a fixed optical path difference, interference occurs at the convergence point. This multi-beam interference effect, similar to that of a Mach-Zehnder interferometer, results in periodic bright and dark (constructive and destructive) fringes in the intensity distribution at the final exit pupil. This unevenness in intensity caused by interference is directly projected onto the image observed by the user, significantly reducing the visual quality of the image and the overall performance of the display system. This is a key technical deficiency that urgently needs to be addressed in this field. Summary of the Invention

[0005] The purpose of this application is to provide a new technical solution for eliminating coherence in diffractive waveguide devices, near-eye display devices, and diffractive waveguide devices, so as to solve the imaging quality problem caused by the interference effect introduced by the folding grating.

[0006] In a first aspect, embodiments of this application provide a diffractive waveguide device, the diffractive waveguide device comprising a waveguide substrate, and a coupling grating, a turning grating, and a coupling grating disposed on the surface of the waveguide substrate; The duty cycle of the folding grating is periodically oscillating along the grating surface. The periodic oscillation distribution has an oscillation direction k in the grating plane, and the oscillation direction k is any direction other than the direction perpendicular to the line connecting the two beam splitting points in the interference optical path formed by the folding grating. The periodic oscillation distribution is constructed such that by generating a duty cycle difference at the two beam splitting points, an additional phase difference is introduced between the light rays that propagate to the interference point via different paths, thereby disrupting the coherence condition and weakening or eliminating the interference effect.

[0007] Optionally, the oscillation amplitude of the periodic oscillation distribution is greater than 0.3, and the oscillation amplitude is defined as the difference between the maximum duty cycle and the minimum duty cycle within one oscillation period.

[0008] Optionally, the oscillation period Λ of the periodic oscillation distribution and the length L of the first total reflection of light in the waveguide substrate satisfy the following relationship: Λ=b×L, where b is a proportionality coefficient and 1.5≤b≤2.5, L=2×tanα×d, α is the total reflection angle of light in the waveguide substrate 1, and d is the thickness of the waveguide substrate 1.

[0009] Optionally, the oscillation period Λ is determined based on the total reflection angle α0 corresponding to the field of view where the interference effect is strongest, and satisfies Λ=4×tan(α0)×d, where d is the thickness of the waveguide substrate.

[0010] Optionally, the total reflection angle α0 is 35°≤α0≤55°.

[0011] Optionally, the oscillation period Λ can range from 1 mm to 6 mm.

[0012] Optionally, the duty cycle of the transition grating is formed by superimposing a basic duty cycle distribution and a periodic oscillation factor, wherein the basic duty cycle distribution is a uniform distribution or a gradually changing distribution.

[0013] Optionally, the lattice is made by etching or imprinting.

[0014] Secondly, embodiments of this application provide a near-eye display device, the near-eye display device comprising: An image source, used to generate an imaging beam carrying image information; and, The diffraction waveguide device as described in the first aspect is configured to receive and conduct the imaging beam.

[0015] Thirdly, embodiments of this application provide a method for eliminating coherence in a diffractive optical waveguide device, wherein the diffractive optical waveguide device includes a transition grating, and the method includes: The duty cycle distribution of the transition grating is configured such that it oscillates periodically along the grating surface; wherein the periodic oscillation distribution has an oscillation direction in the grating plane, and the oscillation direction is any direction other than the direction perpendicular to the line connecting the two beam splitting points in the interference optical path formed by the transition grating; The periodic oscillation distribution generates a duty cycle difference at the two beam splitting points, introducing an additional phase difference between the light rays that propagate to the interference point via different paths, thereby disrupting the coherence condition and weakening or eliminating the interference effect.

[0016] The beneficial effects of this application are as follows: To address the technical problem in existing diffractive waveguides where multipath light interference caused by folding gratings leads to uneven outgoing light intensity distribution and bright / dark fringes in the image, this application designs a periodic oscillating distribution of the duty cycle of the folding grating. This design creates a duty cycle difference between the grating structures at the two beam-splitting points in the interference path. This duty cycle difference introduces an additional phase difference between the light rays propagating through different paths to the interference point, thereby disrupting the original coherence condition and weakening or even eliminating the interference effect. This design achieves uniform outgoing light intensity distribution, fundamentally improving the uniformity and clarity of the image, ultimately enhancing the visual experience of near-eye display devices.

[0017] Other features and advantages of this specification will become clear from the following detailed description of exemplary embodiments with reference to the accompanying drawings. Attached Figure Description

[0018] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments of this specification and, together with their description, serve to explain the principles of this specification.

[0019] Figure 1 This is a schematic diagram of interference caused by a folding grating in the background art; Figure 2 This is a schematic diagram of the structure of a diffraction waveguide device provided in an embodiment of this application; Figure 3 This is a schematic diagram of the formation process of the duty cycle distribution of the transition grating in one embodiment of this application; Figure 4 This is a schematic diagram of the interference optical path and key diffraction points at the turning grating in one embodiment of this application; Figure 5 This is a comparison of simulation images obtained using a uniform duty cycle and a periodic oscillating duty cycle in one embodiment of this application. Figure 6 This is a schematic diagram of different periodic oscillation functions that can be used in this application.

[0020] Explanation of reference numerals in the attached figures: 1. Waveguide substrate; 2. Coupled-in grating; 3. Turning grating; 4. Coupled-out grating; A. The incident position of light rays as they propagate from the coupling grating to the transition grating; B. The first diffraction position on the transition grating; C. The second diffraction position on the transition grating; D. The interference point. Detailed Implementation

[0021] 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.

[0022] 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.

[0023] Technologies and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such technologies and equipment should be considered part of the specification.

[0024] 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.

[0025] 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.

[0026] The following description, in conjunction with the accompanying drawings, details the diffractive waveguide device, near-eye display device, and method for eliminating coherence in the diffractive waveguide device provided in the embodiments of this application.

[0027] In existing diffractive waveguide designs, the deflection gratings introduced to expand the eyebox, while achieving optical path deflection and expansion, also introduce interference problems. Specifically, see... Figure 1When incident light rays from the coupling grating 2 propagate to the deflection grating 3, they are split into rays of different orders due to diffraction (e.g., the 1R order that undergoes a deflection and the 0R order that continues propagating). These rays propagate along different total internal reflection paths within the waveguide substrate 1 and undergo diffraction again when passing through the deflection grating. Some of these rays eventually converge at the interference point D (the interference point where two coherent light paths re-converge), forming a multipath interference structure similar to a Mach-Zehnder interferometer. Since these rays originate from the same light source and have fixed propagation path differences, they will produce stable constructive or destructive interference at the interference point D, resulting in periodic bright and dark fringes of the emitted light intensity within the eyepiece. This uneven intensity phenomenon caused by interference is directly mapped onto the image observed by the user, severely degrading the display effect and becoming a key technical bottleneck restricting the performance of diffractive waveguide displays.

[0028] To overcome the above-mentioned deficiencies of the prior art, this application provides a diffraction waveguide device. The technical solution of the diffraction waveguide device of this application will be described in detail below with reference to the accompanying drawings.

[0029] According to one embodiment of this application, a diffractive waveguide device is provided, see [link to relevant documentation]. Figure 2 and Figure 3 The diffraction waveguide device includes a waveguide substrate 1, and a coupling grating 2, a deflection grating 3, and a coupling output grating 4 disposed on the surface of the waveguide substrate 1. The duty cycle of the deflection grating 3 is periodically oscillating along the grating surface. The periodic oscillation distribution has an oscillation direction k in the grating plane, and the oscillation direction k is any direction other than the direction perpendicular to the line connecting the two beam splitting points in the interference optical path formed by the deflection grating 3. The periodic oscillation distribution is constructed such that by generating a duty cycle difference at the two beam splitting points, an additional phase difference is introduced between the light rays propagating to the interference point D via different paths, thereby disrupting the coherence condition and weakening or eliminating the interference effect.

[0030] This application provides a diffractive waveguide device, see [link to relevant documentation]. Figure 2 The basic structure includes a waveguide substrate 1 and optical functional structures integrated on the surface of the waveguide substrate 1. The optical functional structures, arranged sequentially along the optical path propagation direction, include a coupling grating 2, a deflection grating 3, and an output grating 4, forming a complete optical transmission path. The waveguide substrate 1, as the optical carrier, achieves low-loss light transmission through the principle of total internal reflection. The coupling grating 2 couples the imaging beam into the waveguide substrate 1. The deflection grating 3 performs two-dimensional beam expansion and guides the expanded beam to the output region. The output grating 4 couples the transmitted beam out of the waveguide substrate 1, ultimately projecting it into the user's eye so that the user can see the image.

[0031] This application presents a novel optical design for the transition grating 3. Specifically, the duty cycle (defined as the ratio of the grating groove width to the period) of the transition grating 3 is distributed using a non-uniform periodic modulation method. Unlike traditional optical designs that maintain a constant or simply gradual distribution, the duty cycle in this application exhibits a periodic oscillating distribution along the grating surface. This periodic oscillating distribution manifests as the duty cycle values ​​spatially following a predetermined mathematical law, such as... Figure 6 a to Figure 6 Figure c illustrates the periodic variations in magnitude of trigonometric functions and square wave functions, forming a grating structure that is specifically modulated in the spatial frequency domain. This actively introduced, non-uniform periodic design is the core technology for eliminating interference effects.

[0032] The periodic oscillation distribution described in this application has a clear spatial orientation characteristic, that is, there exists a specific oscillation direction k within the two-dimensional grating plane. For details on the oscillation direction k, please refer to [link to relevant documentation]. Figure 2 As shown. The setting of the oscillation direction k must satisfy a constraint condition: its selectable direction range covers the two key beam-splitting points in the interference optical path formed by the deflection grating 3 (these two beam-splitting points are shown in the figure). Figure 3 All directions other than the line connecting points B and C (as shown). This directional design aims to ensure that a significant difference in duty cycle can be formed at the corresponding beam-splitting points B and C on the two optical paths that form the interference.

[0033] It should be noted that the two beam splitting points in this application have specific meanings, corresponding to respectively Figure 3 The first diffraction position B and the second diffraction position C shown are key locations where different propagation paths separate in the interference optical path. For reference, Figure 3 Point A in the diagram represents the initial position of the light ray when it first arrives at the deflection grating 3 from the coupling grating 2.

[0034] The core principle and desired technical effect of this application lie in the fact that, through the aforementioned specific duty cycle distribution, a certain difference in duty cycle is actively and regularly created at the two beam-splitting points of the interference optical path. This deliberately introduced, non-uniform structural design difference will directly lead to diffraction through these two beam-splitting points and ultimately propagate to the same interference point (see...). Figure 1 An unwanted and destructive additional phase difference is generated between the rays at point D in the diagram.

[0035] Ultimately, this additional phase difference disrupts the original stable phase relationship between the light rays, destroying the coherence conditions necessary for them to undergo constructive or destructive interference. Its direct technical effect is to significantly weaken or even eliminate the interference effect caused by multi-order diffraction of the deflection grating, thereby making the energy distribution of the light rays emitted from the coupling grating more uniform. This fundamentally improves image quality and eliminates the bright and dark fringe problem mentioned in the background section.

[0036] The optical principle of this application lies in the introduction of a duty cycle difference at key nodes of the interference optical path formed by the aforementioned periodic oscillation duty cycle distribution—namely, the two beam splitting points B and C. This difference causes an additional phase difference between the two beams that, after diffracting through points B and C respectively, ultimately converge at the same interference point D (point D is the interference point where the two coherent optical paths re-merge). The key function of this additional phase difference is that it breaks the original stable phase relationship between the two coherent beams, disrupting the coherence conditions necessary for constructive or destructive interference. The resulting technical effect is the significant suppression or even complete elimination of interference phenomena caused by multi-order diffraction of the grating. Ultimately, this achieves uniformity in the intensity distribution of the emitted light, fundamentally solving the image brightness and darkness stripe problem described in the background art, and significantly improving the imaging quality and visual experience of near-eye display devices.

[0037] In summary, addressing the technical problem in existing diffractive waveguides where multipath light interference caused by the transition grating leads to uneven outgoing light intensity distribution and bright / dark fringes in the image, this application designs a periodic oscillating distribution of the duty cycle of the transition grating 3. This design creates a certain duty cycle difference between the grating structures at the two beam splitting points in the interference path. This difference introduces an additional phase difference between the light rays propagating through different paths to the interference point D, thereby disrupting the original coherence conditions and weakening or even eliminating the interference effect. The effect of this design is to achieve uniform outgoing light intensity distribution, fundamentally improving the uniformity and clarity of image display and enhancing the visual experience of near-eye display devices.

[0038] In some examples of this application, the oscillation amplitude of the periodic oscillation distribution is greater than 0.3, and the oscillation amplitude is defined as the difference between the maximum duty cycle and the minimum duty cycle within one oscillation period.

[0039] In this example of the application, the key parameters of the periodic oscillation distribution have been optimized: the oscillation amplitude must be greater than 0.3. Here, the oscillation amplitude is defined as the numerical difference between the maximum duty cycle and the minimum duty cycle within a single oscillation period.

[0040] The basis for this parameter design is that when the oscillation amplitude exceeds the threshold of 0.3, it is possible to achieve this at the two key beam-splitting points of the interference optical path (see...). Figure 3 A significant duty cycle difference is generated at points B and C shown in the diagram. This significant difference is a necessary condition for generating the additional phase difference required to effectively disrupt the coherence condition. Conversely, if the oscillation amplitude is insufficient (e.g., less than or equal to 0.3), the duty cycle difference is too small to generate sufficient phase modulation depth, and the interference suppression effect will be significantly weakened.

[0041] By setting the lower limit of the oscillation amplitude to be greater than 0.3, this application ensures that the periodic oscillation distribution can produce a substantial phase modulation effect, providing a key parameter guarantee for achieving a reliable interference cancellation effect.

[0042] The specific parameter design proposed in this example ensures that the transition grating 3 can establish an effective duty cycle gradient in the interference optical path, thereby generating a sufficient phase difference to disrupt the coherence condition, significantly improving the interference cancellation effect, ensuring the uniformity of the outgoing light field, and ultimately achieving a substantial improvement in image quality.

[0043] In some examples of this application, the oscillation period Λ of the periodic oscillation distribution and the length L of the first total reflection of light in the waveguide substrate 1 satisfy the following relationship: Λ=b×L, where b is a proportionality coefficient and 1.5≤b≤2.5, L=2×tanα×d, α is the total reflection angle of light in the waveguide substrate 1, and d is the thickness of the waveguide substrate 1.

[0044] This example of the application optimizes the design of one of the parameters of the periodic oscillation distribution—the oscillation period Λ. The oscillation period Λ is related to the light propagation characteristics of the waveguide substrate 1, specifically, it maintains a quantitative relationship of Λ=b×L with the length L of the first total internal reflection of light in the waveguide substrate 1, wherein the proportionality coefficient b is optimized to be between 1.5 and 2.5.

[0045] The total internal reflection length L is determined by the structural parameters of the waveguide substrate 1, and its calculation formula is L = 2 × tanα × d, where d is the thickness of the waveguide substrate 1 and α is the angle at which the light undergoes total internal reflection within the waveguide. This parameter relationship is established based on considerations of the interference optical path: when the oscillation period Λ is controlled within the range of 1.5L to 2.5L (approximately twice the total internal reflection length L), a significant duty cycle difference can be ensured at the critical beam-splitting points B and C of the interference optical path, thereby generating effective phase modulation. Establishing this parameter range ensures sufficient modulation effect while avoiding a reduction in modulation efficiency due to unsuitable period dimensions.

[0046] In some examples of this application, the oscillation period Λ is determined based on the total reflection angle α0 corresponding to the field of view where the interference effect is strongest, and satisfies Λ=4×tan(α0)×d, where d is the thickness of the waveguide substrate 1.

[0047] In some examples of this application, the total reflection angle α0 is 35°≤α0≤55°.

[0048] In a preferred embodiment of this application, a method for determining the oscillation period Λ is proposed. This method is based on the analysis of the interferometric characteristics of the optical system, selecting the field-of-view position where the interference effect is most significant as the design benchmark, and using the total internal reflection angle α0 corresponding to this specific field-of-view position for parameter calculation. The oscillation period Λ is determined by the formula Λ=4×tan(α0)×d, where d is the thickness of the waveguide substrate 1.

[0049] Under the field-of-view conditions where the interference effect is strongest, this oscillation period Λ design ensures that the two key beam-splitting points, B and C, are located at specific phase positions of the oscillation period (such as peaks and troughs), thereby maximizing the duty cycle difference between the two points. This design method effectively guarantees that the diffraction waveguide device can achieve stable and reliable interference suppression throughout the entire field of view.

[0050] Furthermore, this application optimizes and limits the value of the total reflection angle α0, which is 35°≤α0≤55°. This angle range comprehensively considers the practical application requirements and optical design constraints of augmented reality near-eye display devices, covering the typical operating range of diffractive waveguides. This optimized design, while ensuring a sufficient field of view, effectively balances the relationship between thickness control and aberration management of the waveguide substrate 1, achieving a balance between optical performance, structural compactness, and process feasibility, thus providing sufficient assurance for the practical application of the product.

[0051] See some examples in this application. Figure 2 The oscillation period Λ ranges from 1mm to 6mm.

[0052] In this example of the application, the physical dimensions of the oscillation period Λ are preferably designed to be within a range of 1 mm to 6 mm. In terms of optical performance, the range of the oscillation period Λ is consistent with the period value calculated by the formula Λ=4×tan(α0)×d under typical waveguide substrate thickness (e.g., 0.5 mm to 1 mm), which ensures that an effective duty cycle difference is formed at the key beam splitting points B and C of the interference optical path, thereby producing a sufficient phase modulation effect.

[0053] For example, the oscillation period Λ can be calculated using the formula Λ=4×tan(α0)×d under typical waveguide substrate thickness and total reflection angle conditions, where the waveguide substrate thickness d is 0.5mm~1mm and the total reflection angle α0 is 35°≤α0≤55°; the calculation results of the formula Λ=4×tan(α0)×d are as follows: Minimum Λ value: When d=0.5mm and α0=35°, Λ=4×0.5×tan(35°)=2×0.7002≈1.40mm; Maximum Λ value: When d=1mm and α0=55°, Λ=4×1×tan(55°)=4×1.4281≈5.712mm.

[0054] Clearly, this is consistent with the value range of 1mm to 6mm in this application. This calculation result verifies the rationality of the parameter design in this application, ensuring that an effective duty cycle difference can be formed at the key beam splitting points B and C in the interference optical path, thereby generating sufficient phase modulation effect to disrupt the coherence condition.

[0055] It should be noted that when the oscillation period Λ is less than 1 mm, the modulation becomes too dense, causing unnecessary diffraction effects and reducing the overall efficiency of the grating. When the period exceeds 6 mm, it becomes difficult to form a sufficient modulation period within the limited waveguide size, thereby weakening the interference cancellation effect.

[0056] Furthermore, in terms of manufacturing process, the period size of 1mm to 6mm is compatible with the current grating fabrication technologies (including nanoimprinting and laser direct writing), ensuring both the accurate realization of structural features and the feasibility and efficiency of manufacturing. Thus, this parameter range strikes a balance between optical performance and process implementation.

[0057] Optionally, the oscillation period Λ can be 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, 5.5mm, 6mm, etc.

[0058] In some examples of this application, the duty cycle of the transition grating is formed by superimposing a basic duty cycle distribution and a periodic oscillation factor, wherein the basic duty cycle distribution is a uniform distribution or a gradually changing distribution.

[0059] In this example of the application, a specific method for constructing the duty cycle distribution of the transition grating is described. The duty cycle distribution consists of two components: a basic duty cycle distribution and a periodic oscillation factor. The basic duty cycle distribution is a uniform or gradually changing distribution, which performs the basic diffraction function of the grating; while the periodic oscillation factor is responsible for introducing specific periodic modulation.

[0060] This superimposed design approach offers significant technical advantages: while maintaining the basic optical performance of the grating, the interference cancellation effect can be optimized by independently adjusting key parameters of the oscillation factor (including the oscillation period Λ, oscillation amplitude, and oscillation direction k). For example, a uniform basic distribution is suitable for scenarios requiring uniform diffraction efficiency, while a gradient basic distribution can achieve additional optical effects such as aberration correction or efficiency equalization while fulfilling the basic function. This flexible design architecture provides an effective technical approach for multi-objective optimization of grating performance, enabling the design scheme to better adapt to different application requirements and process constraints.

[0061] In some examples of this application, the lattice 3 is fabricated by etching or imprinting processes.

[0062] This application specifies the optional manufacturing processes for the aforementioned transition grating 3, which may include two technical paths: etching and nanoimprint lithography. Etching constructs the grating structure through selective material removal, offering advantages such as precise control of feature dimensions and high structural stability. Nanoimprint lithography, on the other hand, utilizes the principle of template replication to achieve batch transfer of micro- and nano-structures, exhibiting significant advantages in high production efficiency and low manufacturing cost.

[0063] See Figure 5 The example shown is a case of fabricating a diffractive waveguide device using an etching process. In this example, the folding grating adopts a straight grating configuration. By implementing the periodic duty cycle modulation scheme of this application on this basic structure, the significant effect of the optical scheme provided by this application in solving the interference problem of etched waveguides is demonstrated.

[0064] See Figure 5 The comparison results show that when using a traditional gradient and relatively uniformly distributed lattice grating duty cycle design, the ray tracing simulation image exhibits obvious intensity oscillation fringes, which is a phenomenon caused by multi-beam interference induced by the lattice grating.

[0065] In contrast, after implementing the periodic modulation scheme provided in this application on the original duty cycle distribution of the transition grating 3, the final simulated image shows that the original intensity oscillation phenomenon has been basically eliminated, and the outgoing light field distribution tends to be uniform. This comparative result intuitively verifies the effectiveness of the periodic oscillation distribution method described in this application in eliminating interference effects and improving image uniformity.

[0066] According to another embodiment of this application, a near-eye display device is provided, the near-eye display device including an image source and a diffraction waveguide as described above; wherein, the image source is configured to generate an imaging beam carrying image information; and the diffraction waveguide is configured to receive and conduct the imaging beam.

[0067] The image source, as the optical engine of the near-eye display device, plays a crucial role in generating the original imaging beam carrying image information. The image source can be a micro-OLED display, a Micro-LED display, or a laser beam scanner, and its selection directly determines key parameters such as the system's basic brightness, contrast, and color performance.

[0068] As described above, the diffractive waveguide device serves as the core optical component of the entire near-eye display device, playing a crucial role in light transmission and image output. In this application, the diffractive optical device receives the imaging beam from the image source via the coupling grating 2; then, utilizing the total internal reflection effect within the waveguide substrate 1, it transmits the imaging beam with extremely low loss; finally, through the synergistic effect of the deflection grating 3 and the output grating 4, the image information is output to the user's eye in an expanded eye-box format.

[0069] The diffraction waveguide device provided in this application effectively eliminates the interference fringe problem commonly found in traditional diffraction waveguide devices through its innovative design of the transition grating 3. This feature enables near-eye display devices integrating this diffraction waveguide device to provide a more uniform and clearer visual experience.

[0070] According to another embodiment of this application, a method for eliminating coherence in a diffractive waveguide device is provided. The diffractive waveguide device includes a transition grating 3. The method includes: configuring the duty cycle distribution of the transition grating 3 such that it exhibits a periodic oscillating distribution along the grating surface; wherein the periodic oscillating distribution has an oscillation direction in the grating plane, and the oscillation direction is any direction other than the direction perpendicular to the line connecting two beam splitting points in the interference optical path formed by the transition grating 3; the periodic oscillating distribution introduces an additional phase difference between the light rays propagating to the interference point D via different paths by generating a duty cycle difference at the two beam splitting points, thereby disrupting the coherence condition and weakening or eliminating the interference effect.

[0071] This application provides a method for eliminating coherence in a diffractive waveguide device. This method achieves interference suppression by redesigning the duty cycle distribution of a transition grating 3 on the waveguide substrate 1. The main steps of the method provided in this application include specifically configuring the duty cycle distribution of the transition grating 3 to form a periodic oscillating distribution along the grating surface.

[0072] In the implementation of this application, the method for eliminating coherence emphasizes the spatial orientation design of the periodic oscillation distribution. The oscillation direction is limited to any direction other than the direction perpendicular to the line connecting the two beam splitting points in the interference optical path formed by the turning grating 3. This direction selection ensures that an effective modulation effect can be generated at the key position of interference formation.

[0073] The optical principle of this anticoherence method lies in: through the periodic oscillation distribution, at the two beam-splitting points of the interference optical path ( Figure 3 A certain difference in duty cycle is generated at points B and C in the diagram. This introduced structural difference causes an additional phase difference between the light rays that propagate to the interference point D via different paths, thereby effectively disrupting the original coherence conditions. This process achieves active control and effective suppression of the interference effect, ultimately achieving the technical effect of significantly weakening or completely eliminating interference.

[0074] Compared to traditional uniform or gradually varying duty cycle designs, the method presented in this application provides an effective and feasible technical approach to solving the interference problem in diffractive waveguide devices by introducing controllable periodic spatial modulation. The method provided in this application exhibits good compatibility with existing grating fabrication processes, offering an important technical means for optimizing the performance of diffractive waveguides.

[0075] The specific implementation of the method for eliminating coherence in the near-eye display device and diffractive waveguide device of this application can refer to the various embodiments of the diffractive waveguide device described above. Therefore, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, and will not be described in detail here.

[0076] 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.

[0077] 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 waveguide device, characterized in that, It includes a waveguide substrate (1), and a coupling grating (2), a turning grating (3) and a coupling grating (4) disposed on the surface of the waveguide substrate (1). The duty cycle of the folding grating (3) is periodically oscillating along the grating surface. The periodic oscillation distribution has an oscillation direction k in the grating plane, and the oscillation direction k is any direction other than the direction perpendicular to the line connecting the two beam splitting points in the interference optical path formed by the folding grating (3). The periodic oscillation distribution is constructed such that by generating a duty cycle difference at the two beam splitting points, an additional phase difference is introduced between the light rays that propagate to the interference point (D) via different paths, thereby disrupting the coherence condition and weakening or eliminating the interference effect.

2. The diffraction waveguide device according to claim 1, characterized in that, The oscillation amplitude of the periodic oscillation distribution is greater than 0.3, and the oscillation amplitude is defined as the difference between the maximum duty cycle and the minimum duty cycle within one oscillation period.

3. The diffraction waveguide device according to claim 1, characterized in that, The oscillation period Λ of the periodic oscillation distribution and the total reflection length L of the light in the waveguide substrate (1) satisfy the following relationship: Λ=b×L, where b is a proportionality coefficient and 1.5≤b≤2.5, L=2×tanα×d, where α is the total reflection angle of the light in the waveguide substrate (1) and d is the thickness of the waveguide substrate (1).

4. The diffraction waveguide device according to claim 3, characterized in that, The oscillation period Λ is determined based on the total reflection angle α0 corresponding to the field of view where the interference effect is strongest, and satisfies Λ=4×tan(α0)×d, where d is the thickness of the waveguide substrate (1).

5. The diffraction waveguide device according to claim 4, characterized in that, The total reflection angle α0 is 35°≤α0≤55°.

6. The diffraction waveguide device according to any one of claims 2-4, characterized in that, The oscillation period Λ ranges from 1 mm to 6 mm.

7. The diffraction waveguide device according to claim 1, characterized in that, The duty cycle of the transition grating (3) is formed by the superposition of the basic duty cycle distribution and the periodic oscillation factor, wherein the basic duty cycle distribution is a uniform distribution or a gradually changing distribution.

8. The diffraction waveguide device according to claim 1, characterized in that, The lattice (3) is made by etching or imprinting.

9. A near-eye display device, characterized in that, include: An image source is used to generate an imaging beam that carries image information. as well as, The diffraction waveguide device as described in any one of claims 1-8 is configured to receive and conduct the imaging beam.

10. A method for eliminating coherence in a diffractive optical waveguide device, the diffractive optical waveguide device comprising a transition grating (3), characterized in that, The method includes: Configure the duty cycle distribution of the transition grating (3) so that it oscillates periodically along the surface of the grating; wherein the periodic oscillation distribution has an oscillation direction in the grating plane, and the oscillation direction is any direction other than the direction perpendicular to the line connecting the two beam splitting points in the interference optical path formed by the transition grating (3); The periodic oscillation distribution introduces an additional phase difference between the light rays that propagate to the interference point (D) via different paths by generating a duty cycle difference at the two beam splitting points, thereby disrupting the coherence condition and weakening or eliminating the interference effect.

Images