Light guide device and near-to-eye display equipment

Abstract

The embodiment of the invention provides a light guide device and near-to-eye display equipment. The light guide device includes: a substrate; the coupling-in device is arranged on the substrate and used for coupling incident light rays from the outside into the substrate in a reflection or transmission mode so as to form guide light rays which are transmitted in the substrate through total reflection; and the second metasurface structure is positioned on a transmission path of the guide light in the substrate and is used for carrying out polarization modulation on the guide light according to the polarization state of the guide light.

Description

Technical Field

[0001] This application relates to the field of optical display technology, and more specifically, to a light guide device and a near-eye display device. Background Technology

[0002] With the rapid development of augmented reality technology, diffractive waveguides have become a core optical solution for smart head-mounted devices due to their advantages of being thin, light, having a large viewing window, and being mass-producible. The performance of diffractive waveguides is highly sensitive to the polarization characteristics of the light source: in scenarios where polarization is not required, the light source often retains significant polarization after passing through microdisplays (LCoS, DMD, Micro-OLED). This polarization characteristic, coupled with the vector diffraction efficiency of the waveguide-coupled grating, easily leads to problems within the eye box such as uneven brightness (bright and dark stripes) and color shift with viewing angle.

[0003] Existing solutions largely rely on optical components such as integrating bars, but these all lead to increased system thickness, decreased energy efficiency, and an inability to completely eliminate polarization dependence. On the other hand, to improve diffraction efficiency, the industry commonly uses s-polarization or p-polarization as the "dominant polarization state" input. However, the polarization state output by the display light source often drifts due to panel type, folded optical path, or temperature changes, resulting in reduced coupling efficiency and consequently affecting the overall brightness stability and power consumption budget.

[0004] Therefore, there is an urgent need for a light guide device that can directly modulate the polarization characteristics of light during the coupling stage, enabling the output of unpolarized or specifically polarized light within a single waveguide module, and simultaneously improving display uniformity and energy efficiency without increasing the overall thickness of the single light guide device, thus breaking through the existing technological bottlenecks. Summary of the Invention The purpose of this application is to provide a light guide device and a near-eye display device to solve any of the above-mentioned technical defects in the prior art.

[0005] According to a first aspect of this application, a light guide device is provided. The light guide device includes: a substrate; A coupling device, disposed on the substrate, is used to couple incident light from the outside into the substrate by reflection or transmission, so as to form a guiding light transmitted within the substrate by total internal reflection; The second metasurface structure is located on the path of the guiding light propagating within the substrate, and is used to polarize the guiding light according to its polarization state.

[0006] Optionally, the second metasurface structure is configured to perform at least one of the following polarization modulations: The guide ray having a defined polarization state is converted into unpolarized light; The guide ray having a first polarization state is converted into a second polarization state that is different from the first polarization state.

[0007] Optionally, the second metasurface structure satisfies at least one of the following configurations: The second metasurface structure is embedded within the substrate in a manner that is inclined relative to the normal of the substrate surface; The second metasurface structure is disposed on the surface of the substrate and is located in the region where the guiding light undergoes total internal reflection.

[0008] Optionally, the guiding light propagates within the substrate by total internal reflection, and the degree of polarization DoP in the Stokes vector of the guiding light satisfies 0.15≤DoP≤0.85; The second metasurface structure is configured such that, according to the local polarization state of the guiding light at different spatial positions within the substrate, microstructure units with different polarization modulation functions are correspondingly provided, so that the guiding light has a specific polarization state.

[0009] Optionally, the second metasurface structure is divided into at least two independent modulation regions along its own surface extension direction. Each modulation region is matched with a corresponding polarization modulation function based on the polarization degree of the light it receives, thereby realizing regional control of the polarization state of the outgoing light.

[0010] Optionally, the polarization modulation function of at least one modulation region in the second metasurface structure satisfies the following relationship with the incident angle of the guide light received by the modulation region: the difference in polarization state conversion efficiency of the modulation region for guide light with different incident angles is within a preset range.

[0011] Optionally, the incident angle of the guiding light is in the range of 15° to 90°.

[0012] Optionally, the second metasurface structure is configured to modulate the light it processes into unpolarized light; wherein the metasurface structure for realizing the unpolarized modulation includes a plurality of microstructure units, each of which has its own optical axis direction in its plane and the optical axis direction is randomly arranged.

[0013] Optionally, the light guiding device further includes: a first metasurface structure, which is located on the transmission path of the incident light before it reaches the coupling device, and is used to polarize the incident light according to the polarization state of the incident light.

[0014] Optionally, the first metasurface structure is located in the transmission path of the incident light before it reaches the coupling device, and is arranged as follows: When the coupling device is a transmissive coupling device, the first metasurface structure is disposed on the incident side surface of the coupling device and is optically bonded to the incident side surface; When the coupling device is a reflective coupling device, the first metasurface structure is disposed on a surface opposite to and away from the reflective surface of the coupling device; and / or When the coupling device is a reflective coupling device, the first metasurface structure is embedded inside the substrate.

[0015] Optionally, the orthographic projection of the first metasurface structure at least covers the optically effective region of the transmissive coupling device; and / or The orthographic projection of the first metasurface structure onto the substrate surface at least covers the optically effective region of the reflective coupling device.

[0016] Optionally, the second metasurface structure includes a plurality of microstructure units, each microstructure unit having a first lateral dimension and a second lateral dimension in a cross-section perpendicular to the direction of light propagation. The first lateral dimension and the second lateral dimension are not equal to form in-plane anisotropy.

[0017] Optionally, the outer contour of the cross section is selected from a rectangle, ellipse, parallelogram, trapezoid, or other closed geometry having a major axis and a minor axis.

[0018] Optionally, the arrangement period P of the microstructure units along the substrate surface direction of the metasurface, the first lateral dimension L and the second lateral dimension W of their cross-sections satisfy: P > L > W.

[0019] This application also provides a near-eye display device. The near-eye display device includes the light guide device as described above.

[0020] One technical advantage of this application is: In the technical solution provided by the embodiments of this application, this application introduces a metasurface polarization modulation structure in the light transmission path. With the characteristics of submicron thickness, high efficiency and spatial variability, it solves the problems of low coupling efficiency, poor uniformity, large thickness and high cost caused by polarization selectivity of traditional diffraction waveguides. It provides a feasible optical element for thin, light, high brightness and high uniformity AR near-eye display devices.

[0021] 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

[0022] 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.

[0023] Figure 1 The diagram shows the structure of the light guide device provided in an embodiment of this application. Figure 1 .

[0024] Figure 2 The diagram shows the structure of the light guide device provided in an embodiment of this application. Figure 2 .

[0025] Figure 3 The diagram shown is a schematic diagram of a metasurface structure provided in an embodiment of this application.

[0026] Figure 4 The diagram shown is a schematic diagram of another metasurface structure provided in an embodiment of this application.

[0027] Figure 5 The diagram shows the polarization state of the guiding light at various spatial positions according to an embodiment of this application.

[0028] Figure 6 The diagram shown is a schematic diagram of another metasurface structure provided in an embodiment of this application.

[0029] Figure 7 The figure shown is a cross-sectional schematic diagram of the metasurface structure provided in an embodiment of this application.

[0030] Explanation of reference numerals in the attached figures: 1. Substrate; 10. Coupled device; 11. Incident ray; 12. Guide ray; 2. First metasurface structure; 3. Second metasurface structure; 21. The first metasurface structure; 22. The second metasurface structure; 31. The first second metasurface structure; 32. The second second metasurface structure; 33. The third second metasurface structure; Detailed Implementation 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] The technical solution of this application will be further described below with reference to the embodiments and accompanying drawings.

[0036] Existing diffraction waveguide structures typically include: a substrate; a coupling grating (or coupling device) formed on the substrate surface; and an exit grating (or exit device) located on the exit pupil path. The coupling grating is often a high birefringence structure, and its diffraction efficiency exhibits significant selectivity to the polarization state of the incident light, leading to: a) Only specific polarization components are effectively coupled into the waveguide, while non-preferred polarization components are reflected or lost through transmission, resulting in a decrease in the overall optical energy utilization of the system. b) The uneven distribution of polarization states at different field angles and positions within the coupled field of view causes a deterioration in the brightness and chromaticity uniformity of the exit pupil; c) When the light source is randomly polarized or partially polarized (such as LCOS, OLED, Micro-LED), the above defects are further amplified, affecting the image quality and user experience of augmented reality (AR) near-eye display devices.

[0037] To alleviate the uniformity problem caused by polarization selectivity, the industry has tried the following solutions, but all of them have obvious shortcomings: 1) Depolarizer (depolarizer) solution: Although the polarization degree can be reduced to near zero, conventional crystal wedge, Lyot type or quartz glass type depolarizers are usually on the order of millimeters in thickness, and the lateral dimension also needs to cover the entire pupil, which cannot be embedded in AR waveguide optical paths with a thickness of only tens of micrometers and an effective area of ​​only a few millimeters.

[0038] 2) Polarizer (linear polarizer) solution: Although it can unify the polarization state, the light components in non-preferred directions are directly absorbed or reflected, resulting in energy loss of up to 50% or more, which is difficult to meet the low power consumption and high brightness requirements of AR devices.

[0039] 3) Monolithic waveplate (λ / 4, λ / 2) scheme: Although the linear deflection direction can be rotated, the monolithic structure can only provide a spatially uniform phase delay and cannot spatially modulate the polarization difference in the local area of ​​the waveguide.

[0040] In summary, existing technologies cannot achieve a balance between miniaturization, high efficiency, and spatially variable polarization control. Therefore, embodiments of this application relate to optical waveguide technology in augmented reality (AR) display devices to achieve ultra-thin, low-loss, and spatially modulated polarization conversion functions within or on the surface of the waveguide, thereby improving coupling efficiency and emission uniformity.

[0041] In the embodiments of this application, reference is made to Figures 1-2 The light guiding device includes: a substrate 1; a coupling device 10 disposed on the substrate 1, used to couple incident light 11 from the outside into the substrate 1 by reflection or transmission to form a guiding light 12 transmitted within the substrate 1 by total internal reflection; and a second metasurface structure 3 located on the path of the guiding light 12 transmitted within the substrate 1, used to perform polarization modulation on the guiding light 12 according to the polarization state of the guiding light 12.

[0042] In this embodiment, the light guide device mainly consists of a substrate 1, a coupling device 10, and a second metasurface structure 3.

[0043] Among them, the substrate 1 serves as the basic supporting structure of the entire light guide device, providing physical space for the transmission of light and guiding the light 12 to propagate in a specific manner.

[0044] The coupling device 10 is disposed on the substrate 1. The coupling device 10 couples the incident light 11 from the outside into the interior of the substrate 1 by means of reflection or transmission. Once the light enters the substrate 1, it will be transmitted in the form of total internal reflection within the substrate 1 to form a guide light 12.

[0045] In this embodiment, the second metasurface structure 3 is located on the path of the guide light 12 as it propagates within the substrate 1. The second metasurface structure 3 can further modulate the polarization of the guide light 12 based on its polarization state during propagation. This polarization modulation capability along the propagation path ensures that the light continues to propagate with an ideal polarization state. Specifically, the second metasurface structure 3 is located in the total internal reflection transmission section within the substrate 1, and is used to perform spatial polarization modulation on the guide light 12 after diffraction by the coupling device 10 and before it reaches the decoupling device. This compensates for or converts the polarization imbalance accumulated due to the inherent polarization selectivity of the coupling device 10, ensuring that the light enters subsequent optical units with the target polarization state.

[0046] Typically, the subwavelength diffraction characteristics of the coupled device 10 result in a partially polarized spatial distribution of its emitted light (typically 0.3-0.8), and this distribution varies with the field of view. The second metasurface structure 3, through a localized Jones matrix, applies a predetermined phase delay δ(x,y) and orientation angle θ(x,y) to the s and p components of each micro-region (≤10μm×10μm), respectively, to achieve: Depolarization requirements: A disordered fast-axis orientation array is adopted, with an equivalent delay of 0-λ / 4 randomly distributed, to quickly depolarize part of the polarized light to a polarization degree ≤0.2, thereby suppressing coherent speckle and color shift; Polarization conversion requirements: Based on the polarization efficiency spectrum of the coupling device, the cumulative polarization state of the entire field of view is calculated in reverse, and the parameters of each micro-region are designed point by point to convert part of the polarized light into the target linearly polarized or elliptical polarized state.

[0047] It should be noted that traditional polarization operations inevitably involve a significant energy loss—theoretically a minimum loss of 50% for unpolarized light, and a loss range of 0-100% for partially polarized or linearly polarized light. The embodiments in this application explicitly exclude any absorption or reflection polarization steps to ensure maximum system luminous efficiency.

[0048] This application incorporates a second metasurface structure 3 along the transmission path of the guiding light 12. This configuration modulates only the polarization characteristics of the guiding light 12, dynamically adjusting its polarization state through the second metasurface structure 3 to meet the imaging quality requirements of the light guide device in specific application scenarios. In other words, this configuration performs polarization compensation or conversion on the already formed guiding light 12. This setup is suitable for scenarios where the external light source already has a defined polarization state or where the coupled device 10 has low polarization sensitivity, achieving acceptable uniformity improvement while minimizing the number of components.

[0049] This application adds a second metasurface structure 3 to the total internal reflection transmission path inside the waveguide, which can perform secondary polarization modulation (e.g., depolarization or polarization state conversion) on the guide light 12 that has already propagated in the substrate 1, thereby balancing the diffraction efficiency of the coupling device for different polarization components, further homogenizing the brightness distribution of the exit pupil, reducing polarization-dependent dispersion, and improving the color difference of the color AR system.

[0050] The working process of the light guide device in this embodiment is as follows: The incident light 11 emitted by the external light source (emitted through the microdisplay, possibly with residual polarization) is directed towards the coupling device 10; the coupling device 10 couples the incident light 11 into the interior of the substrate 1 through diffraction (or reflection, transmission), and the incident light 11 undergoes total internal reflection between the upper and lower surfaces of the substrate 1, forming a guide light 12 that propagates along the length of the substrate 1; the guide light 12 passes through the second metasurface structure 3 during its transmission, and the second metasurface structure 3 modulates the polarization state of the guide light 12 according to the preset modulation requirements (modulated into unpolarized light or specific polarized light); the polarization-modulated guide light 12 continues to propagate through total internal reflection within the substrate 1, and finally exits to the human eye through the coupling device located at the other end of the substrate 1, thus completing the clear display of the image.

[0051] In summary, this application addresses the problems of low coupling efficiency, poor uniformity, large thickness, and high cost caused by polarization selectivity in traditional diffraction waveguides by introducing a metasurface polarization modulation structure inside the light guide device and in the light transmission path. With its submicron thickness, high efficiency, and spatially variable characteristics, it provides a feasible optical element for thin, light, high-brightness, and highly uniform AR near-eye display devices.

[0052] In a further embodiment, the light guiding device further includes: a first metasurface structure 2, which is located on the transmission path of the incident light 11 before it reaches the coupling device 10, and is used to perform polarization modulation on the incident light 11 according to the polarization state of the incident light 11.

[0053] Typically, to improve the uniformity of the transmission direction of the light guide device and achieve uniform brightness, the polarization characteristics of the guide light 12 transmitted within the substrate 1 have a significant impact on the imaging quality. That is, the polarization characteristics of the guide light 12 transmitted inside the light guide device have a decisive influence on the imaging quality and the uniformity of the exit pupil.

[0054] Based on this, to further improve the display effect of the light guide device, a more preferred configuration in this application is to not only provide a first metasurface structure 2 on the transmission path of the incident light 11 before it reaches the coupling device 10 to preliminarily modulate the polarization state of the incident light 11, but also to provide a second metasurface structure 3 on the transmission path of the guiding light 12 within the substrate 1. The second metasurface structure 3 can further precisely modulate the polarization state of the guiding light 12 during its transmission within the substrate 1, thereby more comprehensively ensuring the imaging quality of the light guide device and effectively improving the uniformity and brightness of its transmission direction. That is, in this configuration, the first metasurface structure 2 and the second metasurface structure 3 work together to perform spatially variable modulation of the polarization state "before coupling" and "during transmission," respectively, thereby achieving higher brightness uniformity and color difference suppression effects across the entire field of view.

[0055] This application sets a first metasurface structure 2 at the optical path front end of the coupling device 10 (i.e., before the incident light 11 reaches the coupling device 10), and uses its subwavelength microstructure units to apply spatially variable polarization modulation to the incident light 11. This allows incident light of any polarization state (linear, elliptical, random, or partially polarized) to be converted in real time into the target polarization state preferred by the coupling device 10 (polarization conversion or depolarization). As a result, the diffraction / reflection efficiency of the coupling device 10 is maximized, almost all non-preferred polarization components are utilized, the overall light energy utilization rate of the system is improved, and no additional absorptive polarizer is required, avoiding more than 50% of inherent energy loss.

[0056] The first metasurface structure 2 of this application adopts a planar, single-layer design with an overall thickness of ≤1μm. It can be directly fabricated on the incident light 11 incident side surface of the substrate 1 or share the same photolithography mask with the coupled device 10, achieving "zero thickness" integration. This completely solves the problem of traditional depolarizers / waveplates being too thick and unable to be embedded in AR waveguides, meeting the requirements for thinness and lightness of near-eye display devices.

[0057] In this embodiment, the first metasurface structure 2 is arranged on the transmission path of the incident light 11 before it reaches the coupling device 10. The first metasurface structure 2 has the ability to perform polarization modulation according to different polarization states of the incident light 11. That is, before the light enters the coupling device 10, it can precisely adjust the polarization characteristics of the light according to the specific needs of the actual application scenario, thereby creating a more suitable polarization state for the subsequent coupling operation of the light and the transmission process within the substrate 1.

[0058] In practical applications, based on different light-emitting principles and optomechanical structure designs, common optomechanical solutions encompass various types, including LBS, DLP, LCoS, micro LED, and micro OLED. Among them, DLP (using LED panels as light sources) and micro LED optomechanical systems mostly exhibit unpolarized light characteristics. This is because they are based on the self-emissive principle of LEDs and typically do not include polarizing devices in their optomechanical structures. In contrast, LBS, DLP (using laser panels as light sources), LCoS, and micro OLED solutions exhibit varying degrees of significant polarization characteristics.

[0059] Given the aforementioned differences in polarization characteristics among different optomechanical structures, the first metasurface structure 2 provided in this application can flexibly adapt to various optomechanical schemes. Through targeted polarization modulation, it ensures that the incident light 11 enters the coupling device 10 with the optimal polarization state, thereby improving the performance of the entire light guide device.

[0060] When the external optical engine uses a non-polarized light source (such as a DLP (LED panel) or Micro-LED solution based on LED self-emission), the first metasurface structure 2 can be configured in the following two different ways according to the end-user requirements: Depolarization requirement scenario: If the coupled device 10 has no significant requirements for polarization degree, and it indicates that the unpolarized state can meet the brightness uniformity and color difference index, then all micro-nano units of the first metasurface structure 2 can be omitted in the incident region (i.e., no metasurface microstructure units are set), so that ideal unpolarized light can be directly incident, simplifying the process and further reducing insertion loss.

[0061] Polarization conversion requirement scenario: If the coupling device 10 has a significant preference for a specific polarization state, and it indicates that unpolarized incident light will lead to a decrease in coupling efficiency or fluctuation in exit pupil brightness, then the random polarization component can be modulated by the first metasurface structure 2 through "partial orientation" or "full orientation". The technical implementation is as follows: The subwavelength artificial micro / nano unit of the first metasurface structure 2 decomposes the incident unpolarized light into two orthogonal polarization components (s component and p component) by locally adjusting the long axis orientation θ(x,y) and equivalent phase delay δ(x,y) of the micro / nano unit. According to the polarization efficiency curve of the coupling device 10, the weighting coefficients a1 and a2 are preset in the range of 0%-100%, so that the energy of the two components is merged into the target polarization state (target linear polarization state, target elliptic polarization state) in the ratio of a1:a2.

[0062] When the external optical engine uses a polarized light source (including but not limited to laser beam scanning LBS, DLP with a laser panel as the light source, silicon-based liquid crystal LCoS, or Micro-OLED solutions), the first metasurface structure 2 can be configured in the following two different ways according to the terminal requirements: Depolarization requirement scenario: If it is required to reduce the degree of polarization to suppress coherent speckle, chromatic aberration or human eye polarization sensitivity differences, the first metasurface structure 2 is written with a spatially varying fast axis distribution to convert incident ray-polarized or elliptically polarized light into a randomly distributed local polarization state within an equivalent delay range of λ / 4 to λ / 2, so that the degree of polarization of the outgoing light is ≤0.3, and there is no need to introduce a conventional millimeter-thick crystal depolarizer.

[0063] Polarization conversion requirement scenario: If the coupling device 10 has an efficiency preference for a specific polarization state, the first metasurface structure 2 will rotate or convert the incident polarized light as a whole into a linearly polarized or elliptical polarization state with the same high diffraction efficiency direction, thereby improving the coupling efficiency while maintaining a relatively thin overall thickness, avoiding the defects of traditional waveplates such as large size, difficulty in alignment, and inability to be arrayed.

[0064] It should be noted that, given that traditional polarization operations inevitably involve a significant energy loss—theoretically a minimum loss of 50% for unpolarized light and a loss range of 0-100% for partially polarized or linearly polarized light—the embodiments of this application explicitly exclude any absorption or reflection polarization steps to ensure maximum system luminous efficiency.

[0065] Therefore, in this embodiment, this application introduces a metasurface polarization modulation structure both before light coupling and during light transmission on the substrate. With its submicron-level thickness, high efficiency, and spatially variable characteristics, it solves the problems of low coupling efficiency, poor uniformity, large thickness, and high cost caused by polarization selectivity in traditional diffraction waveguides. This provides a feasible optical element for thin, light, high-brightness, and highly uniform AR near-eye display devices.

[0066] According to embodiments of this application, the first metasurface structure 2 and / or the second metasurface structure 3 are configured to perform at least one of the following polarization modulations: The incident light 11 and / or the guide light 12, which have a defined polarization state, are converted into unpolarized light. The incident ray 11 and / or the guide ray 12, which have a first polarization state, are converted into a second polarization state that is different from the first polarization state.

[0067] That is, when only the second metasurface structure 3 is provided on the light guide device, the second metasurface structure 3 is configured to perform at least one of the following polarization modulations: The guide ray 12, which has a defined polarization state, is converted into unpolarized light; The guide ray 12, which has a first polarization state, is converted into a second polarization state that is different from the first polarization state.

[0068] In this embodiment, the first metasurface structure 2 and / or the second metasurface structure 3 possess powerful polarization modulation capabilities. These two metasurface structures can perform various polarization modulation operations on the incident light 11 and / or the guiding light 12 in the light guide device. Specifically, there are two main polarization modulation methods: Depolarization modulation: This can convert incident light 11 or guide light 12, which originally has a defined polarization state, into unpolarized light. This operation is very useful in scenarios where it is necessary to eliminate the interference of light polarization characteristics on subsequent optical processes. For example, in some imaging or display systems that are not sensitive to polarization, ensuring that light propagates in an unpolarized state can avoid problems such as uneven brightness and color deviation caused by polarization.

[0069] Polarization state conversion modulation: The incident light 11 or guide light 12 with a first polarization state can be converted into a second polarization state different from the first polarization state. This flexible polarization state conversion capability allows the system to adjust the polarization state of the light according to actual needs. For example, in the process of light transmission, different signal transmissions can be achieved by changing the polarization state of the light; in optical sensing, polarization state conversion is used to improve the sensitivity and accuracy of sensing.

[0070] In this embodiment, the polarization characteristics of light have a significant impact on the final imaging effect. By modulating the polarization of the first metasurface structure 2 and / or the second metasurface structure 3, problems such as uneven brightness and color deviation caused by polarization can be effectively eliminated, resulting in clearer imaging and more accurate colors.

[0071] It should be noted that polarization modulation converts unpolarized incident light 11 or guide light 12 into polarized light with a defined polarization state. In some optical systems with specific polarization requirements, such as liquid crystal displays (LCDs) and polarized imaging, light with a specific polarization state is needed to achieve normal display or imaging functions. This modulation method can meet such requirements and provide the system with a polarized light source that meets the requirements. However, given that traditional polarization operations inevitably involve a non-negligible energy loss—theoretically a minimum loss of 50% for unpolarized light and a loss range of 0-100% for partially polarized or linearly polarized light—the embodiments of this application explicitly exclude any absorption or reflection polarization steps to ensure maximum system luminous efficiency.

[0072] According to the embodiments of this application, refer to Figure 1 and Figure 2 The second metasurface structure 3 is arranged on the path of the guiding light 12 within the substrate 1 for total internal reflection transmission, and satisfies at least one of the following configurations: The second metasurface structure 3 is embedded inside the substrate 1 in a manner that is inclined relative to the surface normal of the substrate 1; The second metasurface structure 3 is disposed on the surface of the substrate 1 and is located in the corresponding region where the guiding light 12 undergoes total internal reflection.

[0073] In this embodiment, the second metasurface structure 3 is embedded inside the substrate 1 at an angle γ to the surface normal of the substrate 1. The design principle of this inclined arrangement is to ensure that the second metasurface structure 3 can accurately receive and intercept the guiding light 12 transmitted by total internal reflection within the substrate 1.

[0074] Based on this arrangement, the second metasurface structure 3 can directly intercept light rays that are transmitted through total internal reflection within the substrate 1 and effectively modulate their optical properties. Specifically, the phase delay generated by the second metasurface structure 3 can be adjusted according to the tilt angle γ, thereby achieving continuous tunability of the phase delay within the range of λ / 4 to λ / 2, where λ represents a specific wavelength in the relevant optical application scenario.

[0075] Furthermore, the embedding depth of the second metasurface structure 3 within the substrate 1 can be controlled within the range of ≤1μm. This shallow embedding design ensures that the second metasurface structure 3 effectively modulates light while causing a minimal lateral offset to the total internal reflection propagation path, specifically less than 0.3μm. Such a small lateral offset ensures that the propagation direction of light within the substrate 1 remains essentially unchanged. Consequently, the optical system does not need to redesign the coupling grating period for this minute change, simplifying the overall design process of the optical system and reducing design complexity and cost.

[0076] For example, in the case where the metasurface structure is embedded inside the substrate 1, the specific implementation method can be as follows: First, the substrate 1 is precisely cut using a suitable cutting tool or process, so that the cut substrate 1 forms a groove or hole structure that matches the shape and size of the metasurface structure; then, the metasurface structure is accurately embedded into the structure formed by the above cutting, thereby completing the embedding operation of the metasurface structure inside the substrate 1.

[0077] In addition, the second metasurface structure 3 can also be surface-attached, that is, the second metasurface structure 3 is disposed on the surface of the substrate 1 and covers a certain total reflection area of ​​the guiding light 12, and the light is modulated by the subwavelength structure to complete polarization modulation while keeping the critical angle of total reflection unchanged.

[0078] For example, the surface-attached setup requires only one nanoimprinting process, which is formed simultaneously with the coupled grating, without the need for additional etching inside the substrate 1.

[0079] Combination Figure 1 As shown, when the coupling device 10 is a transmissive coupling device 10, a first second metasurface structure 313 is provided between the transmissive coupling device 10 and the substrate 1; at the same time, a second second metasurface structure 323 is provided in an inclined position inside the substrate 1; in addition, a third second metasurface structure 333 is provided on the surface of the substrate 1 in the corresponding region where the guiding light 12 undergoes total internal reflection for the first time.

[0080] Combination Figure 2 As shown, if the coupling device 10 is a reflective coupling device 10, a first second metasurface structure 313 is provided in an inclined manner inside the substrate 1; and a second second metasurface structure 323 is provided on the surface of the substrate 1 in the corresponding area where the guiding light 12 undergoes its first total internal reflection.

[0081] According to the embodiments of this application, refer to Figure 5 and Figure 6 The guiding light 12 propagates within the substrate 1 via total internal reflection. In the Stokes vector of the guiding light 12, the polarization degree DoP satisfies 0.15≤DoP≤0.85. The second metasurface structure 3 is configured to: provide microstructure units with different polarization modulation functions according to the local polarization state of the guiding light 12 at different spatial positions within the substrate 1, so that the guiding light 12 has a specific polarization state.

[0082] In this embodiment, combined with Figure 1 and Figure 2It can be seen that the guiding light 12 propagates within the substrate 1 via total internal reflection. Total internal reflection is a phenomenon in which light rays traveling from an optically denser medium to an optically less dense medium at an angle greater than the critical angle are completely reflected back into the optically denser medium. Using total internal reflection to propagate the guiding light 12 within the substrate 1 effectively reduces energy loss, allowing the light to propagate efficiently within the substrate 1 and providing a stable and sufficiently strong optical signal for subsequent optical processing.

[0083] Due to the polarization selectivity of the coupling device 10, the degree of polarization DoP in the Stokes vector of the guide ray 12 satisfies 0.15 ≤ DoP ≤ 0.85. The Stokes vector is a commonly used method to describe the polarization state of light, and the degree of polarization DoP is an important parameter in the Stokes vector, reflecting the strength of the light's polarization. The value of DoP ranges from 0 to 1; when DoP = 0, it represents completely unpolarized light, and when DoP = 1, it represents completely polarized light. In this embodiment, the degree of polarization of the guide ray 12 is in the range of 0.15 to 0.85, indicating that the guide ray 12 is partially polarized light—neither completely unpolarized nor completely polarized, but rather intermediate, possessing certain polarization characteristics. (Refer to...) Figure 5 This is a schematic diagram of the polarization state of partially polarized rays at various spatial positions.

[0084] The second metasurface structure 3 is equipped with microstructure units having different polarization modulation functions according to the local polarization state of the guide ray 12 at different spatial positions within the substrate 1. Since the guide ray 12 propagates within the substrate 1 via total internal reflection, the interaction between the ray and the substrate 1, as well as other possible optical elements, differs at different spatial positions, resulting in variations in its local polarization state. Based on these changes in local polarization state, the second metasurface structure 3 specifically sets up microstructure units. Each microstructure unit has specific structural parameters such as shape, size, and orientation, which determine its polarization modulation function, such as changing the polarization direction and degree of polarization. Through this method of dynamically setting up microstructure units according to local polarization state, the second metasurface structure 3 can achieve more precise and effective polarization conversion of the guide ray 12, meeting the specific requirements of different optical application scenarios for the polarization state of the ray.

[0085] According to the embodiments of this application, refer to Figure 1 and Figure 2 The second metasurface structure 3 is divided into at least two independent modulation regions along its own surface extension direction. Each modulation region is matched with the corresponding polarization modulation function based on the polarization degree of the light it receives, thereby realizing the regional control of the polarization state of the outgoing light.

[0086] In this embodiment, the second metasurface structure 3 is disposed inside the substrate 1. The second metasurface structure 3 is divided into at least two independent modulation regions along its own surface extension direction. The second metasurface structure 3 extends along its main extension direction when it is continuously distributed within its plane. For example, along... Figure 1 As indicated by arrow A, the second metasurface structure 3 is divided into at least two independent modulation regions along... Figure 2 In the direction indicated by arrow B, the second metasurface structure 3 is divided into at least two independent modulation regions.

[0087] To enhance the flexibility and specificity of polarization modulation, the second metasurface structure 3 is divided into at least two independent modulation regions along its extension direction. The boundaries of each independent modulation region are precisely aligned with the spatial distribution boundaries of the polarization degree of the guiding light 12 within the substrate 1. This ensures that each independent modulation region covers only the light transmission area of ​​a single polarization degree range, achieving precise matching between "region" and "polarization degree". The boundary alignment accuracy can be achieved through laser positioning calibration, with deviations controlled within ±3μm, preventing light rays of different polarization degrees from crossing into the same modulation region.

[0088] Each modulation region is matched with a corresponding exclusive polarization modulation function based on its preset received light polarization degree range. The core design goal is to enable each modulation region to perform differentiated processing on light with different polarization degrees, so that the final output guide light 12 has a uniform preset target polarization characteristic. Specifically, depending on the application scenario requirements, the guide light 12 can form a uniform specific polarization state or form a non-polarized light state, ensuring that the polarization characteristics of the light received by the subsequent optical path are consistent, and improving the stability and efficiency of the overall optical system.

[0089] In practice, the global target polarization characteristics are first clarified: if the target is a uniform specific polarization state (such as the s-polarization state matched with the coupling grating), then targeted modulation paths are designed for modulation regions with different polarization degree ranges to achieve polarization state uniformity; if the target is a non-polarized state, then the functions of all modulation regions are designed around depolarization optimization to ensure that the polarization degree of the processed light DoP ≤ 0.1.

[0090] In one exemplary example, if the goal is to output unpolarized light, then each modulation region is matched with the "efficient depolarization" function, optimizing the microstructure parameters according to different polarization degree ranges: Specifically, for regions with high polarization, medium polarization, and low polarization, arrays of metasurface units with different shapes and parameters are configured to break polarization uniformity. For example, for regions with low polarization, randomly arranged cylindrical metasurface unit arrays can be configured to weaken residual polarization components, ensuring that the polarization degree DoP of the light after processing is ≤0.1 in all regions, thus achieving a unified output of non-polarized states.

[0091] Therefore, in this embodiment, the microstructure unit parameters of different modulation regions are designed differently to adapt to their respective polarization modulation function requirements.

[0092] To avoid crosstalk between different modulation regions, isolation grooves with a width of 2μm-3μm are set at the boundaries of adjacent modulation regions. The isolation grooves are filled with low refractive index material, and optical isolation is formed by the difference in refractive index, ensuring that each region modulates only the guide light 12 within its own coverage area. In addition, the area of ​​each independent modulation region can be flexibly adjusted according to the spatial distribution range of the corresponding polarization degree light. For example, if the distribution range of high polarization degree light within the substrate 1 is large, the area of ​​the modulation region can be increased to improve the overall modulation coverage.

[0093] According to an embodiment of this application, the polarization modulation function of at least one modulation region in the second metasurface structure satisfies the following relationship with the incident angle of the guide light 12 received by the modulation region: the difference in polarization state conversion efficiency of the modulation region for guide light 12 at different incident angles is within a preset range.

[0094] This matching relationship can also be understood as the modulation region having similar polarization state conversion efficiency for guide rays 12 at different incident angles. Through the above design, it can be ensured that the guide rays 12 can be stably polarized by the modulation region at different incident angles, guaranteeing the optical performance stability of the light guide device.

[0095] Furthermore, in this embodiment, the incident angle of the guiding light 12 is limited to 15° to 90°. It should be noted that, in practical applications, the incident angle of the guiding light 12 is preferably set above the critical angle of total internal reflection from the substrate of the light guide device to the outside world, so as to ensure that the guiding light 12 can be stably transmitted within the substrate and effectively incident on the modulation region of the second metasurface structure. When the substrate refractive index of the light guide device is 1.8 and the external environment is air (refractive index 1), the critical angle for total internal reflection can be calculated as C≈arcsin(1 / 1.8)≈33.75°. Therefore, in this example, the incident angle range of the guiding light 12 is preferably 33.75°~90°. This angle range satisfies the total internal reflection condition to ensure stable light transmission and also ensures that the polarization state conversion efficiency of the modulation region for the guiding light 12 meets the preset requirements.

[0096] When the substrate refractive index of the light guide device is 1.8, and the external surface is bonded with adhesive (refractive index 1.3, meaning the light guide device and the external surface are fully bonded), similarly, according to the formula for calculating the critical angle of total internal reflection, the critical angle of total internal reflection C≈arcsin(1.3 / 1.8)≈43.17° can be obtained. Therefore, in this example, the incident angle range of the guiding light 12 is preferably 43.17°~90°.

[0097] It should be noted that, due to the refractive index dispersion of optical materials, the critical angle for total internal reflection differs for different wavelengths of the guide light 12. Therefore, when determining the range of incident angles for the guide light 12, its minimum value should be limited to the critical angle for total internal reflection corresponding to the shortest wavelength within the operating wavelength range of the light guide device, and its maximum value should be 90°. This ensures that the guide light 12 meets the incident angle requirements throughout the entire operating wavelength range, thereby guaranteeing that the modulation region can achieve stable polarization state conversion for guide light 12 of different wavelengths and incident angles.

[0098] According to the embodiments of this application, refer to Figure 3 The first metasurface structure 2 and / or the second metasurface structure 3 are configured to modulate the light they process into unpolarized light; wherein the metasurface structure that realizes the unpolarized modulation includes a plurality of microstructure units, each of which has its own optical axis direction in its plane and the optical axis direction is randomly arranged.

[0099] In this embodiment, the first metasurface structure 2 and / or the second metasurface structure 3 possess a specific light modulation function, namely, the ability to modulate light processed by them into unpolarized light (depolarization). The metasurface structure realizing unpolarized modulation is composed of multiple microstructure units. These microstructure units have their own independent optical axis directions within their respective planes, and these optical axis directions are not neatly arranged but rather randomly distributed. This random arrangement of optical axis directions is one of the key factors in achieving unpolarized modulation of light, enabling light to produce diverse interaction effects when passing through different microstructure units.

[0100] In the optical system described in this embodiment, the light emitted from the optomechanical system for the incident ray 11 is linearly polarized. The principle of modulating linearly polarized light into unpolarized light is as follows: Taking a common LCoS optical mechanism as an example, linearly polarized light is obtained after modulation by a PBS (polarizing beam splitter). For ease of description and analysis, it is assumed that the polarization state of the light source is linearly polarized along the x-direction, and the Stokes vector is used to represent the polarization state of the linearly polarized light.

[0101] The representation of linearly polarized light is as follows: .

[0102] In practical applications, there is a need to modulate linearly polarized light into unpolarized light (i.e., depolarization), and the key to achieving this is to introduce disordered microstructure units.

[0103] When light passes through these randomly arranged microstructural units, it interacts with units at different locations, each with a different optical axis, resulting in linearly polarized light with varying vibration directions. The Stokes vector is used to represent the state of linear polarization at different locations.

[0104] Among them, the Stokes vector of the linear polarization state at different positions is , where i is the position number. Due to the randomness of the optical axis direction of the microstructure unit at different positions, the values ​​of m and n at different positions in the formula range from -1 to 1. As long as the total number of each value appearing in the whole is equal, the cumulative Stokes vector at these different positions is summed to obtain the final cumulative Stokes vector. This is the Stokes vector representation of unpolarized light, thus achieving the goal of modulating linearly polarized light into unpolarized light.

[0105] In the optical system described in this embodiment, for the guiding light 12, the coupling device 10 itself has polarization selectivity, meaning it responds and processes light with different polarization directions differently. After the light is modulated by the coupling device 10, the polarization state of its outgoing light cannot maintain its original state before entering the coupling device 10. This change in polarization state is not random but requires precise calculation and analysis. In actual light transmission, considering spatial cumulative effects, the outgoing light typically exhibits a partially polarized state. For example, when using a Stokes vector to represent this partially polarized state, its form might be... The Stokes vector, with its various parameters reflecting different characteristics of the light's polarization state, accurately describes the degree and direction of polarization in partially polarized light. In optical systems, there is a need to further modulate partially polarized light into unpolarized light (i.e., depolarization). To achieve this, this embodiment also introduces a disordered array of microstructure units. This disordered array disrupts the original polarization pattern of light, allowing it to undergo diverse interactions within different microstructure units. Through these interactions, the polarization components of the light in various directions are redistributed and adjusted, thereby reducing the degree of polarization and gradually approaching an unpolarized state.

[0106] In this embodiment, by configuring the first metasurface structure 2 and / or the second metasurface structure 3 to modulate the corresponding processed light into unpolarized light, the need for depolarization of linearly polarized light in the optical system can be effectively met. In particular, by employing a metasurface structure composed of microstructure units randomly arranged along multiple optical axes, the diverse modulation effects it produces on light at different positions can achieve a highly efficient and stable depolarization effect, making the processed light approach an ideal unpolarized light state, thus improving the optical system's control over the polarization state of light.

[0107] In the embodiments of this application, reference is made to Figure 1 and Figure 2 The first metasurface structure 2 is located in the transmission path of the incident light 11 before it reaches the coupling device 10, and is arranged as follows: When the coupling device 10 is a transmissive coupling device 10, the first metasurface structure 2 is disposed on the incident side surface of the coupling device 10 and is optically bonded to the incident side surface. When the coupling device 10 is a reflective coupling device 10, the first metasurface structure 2 is disposed on a surface opposite to and away from the reflective surface of the coupling device 10; and / or When the coupling device 10 is a reflective coupling device 10, the first metasurface structure 2 is embedded inside the substrate 1.

[0108] In this embodiment, when the coupling device 10 is a transmissive type, the first metasurface structure 2 is disposed on the incident side surface of the coupling device 10 and optically bonded to the incident side surface. This arrangement ensures that the incident light 11 can pass smoothly and efficiently through the first metasurface structure 2 before reaching the coupling device 10, allowing the first metasurface structure 2 to perform sufficient polarization modulation and other operations on the incident light 11. At the same time, the optical bonding design minimizes the reflection and scattering losses of light at the interface, ensuring the transmission efficiency of light.

[0109] When the coupling device 10 is a reflective coupling device 10, the first metasurface structure 2 has two arrangement methods.

[0110] Firstly, refer to Figure 2 The first metasurface structure 2 is disposed on the surface opposite to and away from the reflective surface of the coupling device 10, that is, the first metasurface structure 21 is disposed on the surface opposite to and away from the reflective surface. This arrangement allows the incident light 11 to be modulated by the first metasurface structure 2 first, and then reach the reflective surface of the reflective coupling device 10, and continue to propagate in the optical system after reflection.

[0111] Secondly, refer to Figure 2The first metasurface structure 2 is embedded inside the substrate 1, that is, a second first metasurface structure 22 is set inside the substrate 1. Embedding it inside the substrate 1 can make full use of the space of the substrate 1, while providing a certain degree of protection for the first metasurface structure 2, and does not affect the normal transmission path of light in the substrate 1. Before the light reaches the reflective surface of the coupling device 10, the light can be modulated according to the design requirements.

[0112] In this embodiment, regardless of whether the coupling device 10 is transmissive or reflective, polarization management can be completed before the light first interacts with the coupling device 10, reducing the brightness non-uniformity of the exit pupil and providing a feasible optical element for thin, high-brightness, and highly uniform AR near-eye displays.

[0113] According to this specific embodiment, the orthographic projection of the first metasurface structure 2 further covers at least the optically effective area of ​​the transmissive coupling device 10; and / or The orthographic projection of the first metasurface structure 2 onto the surface of the substrate 1 at least covers the optically effective area of ​​the reflective coupling device 10.

[0114] In this embodiment, for the transmissive coupling device 10, the orthographic projection of the first metasurface structure 2 at least covers its optically effective region, ensuring that all incident light rays 11 entering this region and effective for optical performance can be modulated by the first metasurface structure 2. Similarly, for the reflective coupling device 10, the orthographic projection of the first metasurface structure 2 covers its optically effective region, so that light rays effective for imaging and other performance during reflection can first pass through the first metasurface structure 2. This comprehensive modulation ensures that light rays are always in the expected polarization state or other characteristic state throughout the optical system, thereby improving the overall performance and stability of the system and enhancing the efficiency of the optical system.

[0115] Meanwhile, for the reflective coupling device 10, the reasonable orthographic projection coverage design enables the light to reach the reflecting surface more effectively and be reflected in the expected direction after being modulated by the first metasurface structure 2, reducing the ineffective propagation and loss of light, thereby improving the energy utilization efficiency of the entire optical system and enabling the system to output a stronger effective signal under the same input optical power.

[0116] According to the embodiments of this application, refer to Figure 4 The first metasurface structure 2 is configured to modulate the incident light 11 having a first polarization state into an incident light 11 having a second polarization state. The first metasurface structure 2 includes multiple microstructure units arranged in an array. Each microstructure unit has its own optical axis direction in its plane, and the optical axis directions are arranged in parallel.

[0117] In this embodiment, the first metasurface structure 2 is composed of multiple microstructure units arranged in an array. These microstructure units are the basic units for realizing polarization modulation. They each have an independent optical axis direction in their respective planes, and these optical axis directions are arranged in parallel. This parallel arrangement of optical axis directions provides an ordered structural basis for subsequent precise polarization conversion through specific design, enabling light to interact with the microstructure units in a predetermined manner as it passes through the entire metasurface structure, thereby achieving a change in polarization state.

[0118] In the optical system described in this embodiment, the light emitted from the optomechanism is linearly polarized. Taking a common LCoS optomechanism as an example, it obtains linearly polarized light after being modulated by a PBS (polarizing beam splitter). In practical applications, there is a need to convert this linearly polarized light into other polarization states (i.e., a second polarization state), such as converting it into elliptically polarized light, circularly polarized light, or linearly polarized light in different directions, to meet the requirements of different optical components or systems for the polarization state of light.

[0119] The principles and methods for implementing polarization conversion in the embodiments of this application may include: Polarization rotation based on PB phase: A repeating array of microstructure units with specific orientations is introduced. In the simple PB phase case, when the rotation direction of the microstructure unit is θ (equivalent to an orientation angle), according to the PB phase principle, the polarization direction of the light will rotate by an angle of 2θ. This method of rotating the polarization direction of light by controlling the rotation angle of the microstructure unit is precisely controllable and can flexibly adjust the rotation angle of the polarization direction according to actual needs.

[0120] Polarization state conversion based on birefringent metasurfaces: For birefringent metasurfaces, anisotropy can be introduced by designing the aspect ratio and rotation angle of the nanopillars. This anisotropy allows light rays with different polarization directions to have different propagation characteristics when passing through the nanopillars, thus enabling the conversion of linearly polarized light into arbitrarily elliptically polarized light, circularly polarized light, or linearly polarized light in different directions. This polarization state conversion method based on the principle of birefringence further expands the modulation capability of the first metasurface structure 2 for the polarization state of light, and can meet more complex polarization conversion requirements.

[0121] According to an embodiment of this application, the first metasurface structure 2 and the second metasurface structure 3 include a plurality of microstructure units. The microstructure units have a first lateral dimension and a second lateral dimension in a cross-section perpendicular to the direction of light propagation. The first lateral dimension and the second lateral dimension are not equal to form in-plane anisotropy.

[0122] In this embodiment, the metasurface structure, as a novel optical element, exhibits performance largely dependent on the shape and size of its microstructure units. When these microstructure units are anisotropic in-plane, they produce different responses to light rays with different polarization directions. Specifically, light rays with different polarization directions undergo different phase delay processes when passing through these microstructure units, thereby enabling the manipulation of the light polarization state.

[0123] Specifically, the in-plane anisotropy formed by the unequal first and second lateral dimensions of the microstructure units in the cross-section perpendicular to the direction of light propagation in the first metasurface structure 2 and the second metasurface structure 3 brings polarization control performance to the optical system. Due to the anisotropy, the microstructure units have differentiated interactions with light rays of different polarization directions, which can precisely change the polarization state of the light.

[0124] In this specific embodiment, further referring to... Figure 7 In ah, the outer contour of the cross section is selected from a rectangle, ellipse, parallelogram, trapezoid, or other closed geometry having a first lateral dimension (major axis) and a second lateral dimension (minor axis).

[0125] According to embodiments of this application, the cross-sectional outer contour of the microstructure unit is selected from rectangles, ellipses, parallelograms, trapezoids, or other closed geometric shapes with defined major and minor axes.

[0126] Combined with appendix Figure 7 As shown in 'ah', a rectangle has right angles and a symmetrical aspect ratio, with its major and minor axes corresponding to its length and width, respectively. An ellipse has its major and minor axes as its principal and secondary axes, respectively, exhibiting continuous curvature. A parallelogram breaks symmetry through its hypotenuse design; its major and minor axes can be defined based on side lengths and inclination angles. Other closed shapes (such as the irregular contours in the attached diagram) achieve differentiation between their major and minor axes through freeform surface design to meet specific optical requirements.

[0127] In this embodiment, by differentiating the major and minor axes of the cross-sectional outer contour, the microstructure unit exhibits significant anisotropic characteristics in-plane, enabling the application of differentiated phase delays or amplitude modulations to components of incident light with different polarization directions. Furthermore, the asymmetry of the cross-section in both directions provides multidimensional design freedom for polarization state manipulation. By combining different major / minor axis ratios and asymmetric forms (such as irregular contour curvature), the metasurface response characteristics can be customized for specific applications (such as partial polarization compensation), optimizing metasurface performance to match specific light source characteristics (such as linearly polarized output of LCoS optical engines). Moreover, integrating anisotropic microstructure units into a single-layer metasurface structure can replace traditional multilayer waveplate or polarization beam splitter combinations, reducing the number of optical components and alignment complexity.

[0128] In this specific embodiment, the arrangement period P of the microstructure unit along the substrate surface direction of the metasurface, the first lateral dimension L and the second lateral dimension W of its cross-section satisfy: P > L > W.

[0129] In this embodiment, the following properties of the metasurface can be independently controlled by designing the three-dimensional dimensional relationship between P, L, and W: Spatial sampling rate: The P-value determines the metasurface's spatial frequency response to light waves; Anisotropy intensity: The L / W ratio directly affects the polarization modulation depth; Duty cycle optimization: By adjusting the cell density based on the difference between P and L, modulation efficiency and transmittance are balanced. This multi-parameter collaborative design enables the metasurface to adapt to the modulation requirements of complex light sources (such as partially polarized light and non-uniform wavefronts).

[0130] The arrangement period P > L avoids higher-order diffraction effects caused by excessively small spacing between microstructure units, ensuring that the incident light mainly undergoes zero-order diffraction modulation, thereby improving the purity of wavefront modulation. The size difference L > W enhances the in-plane anisotropy of the microstructure units, making the metasurface produce more significant phase delay differences for light rays with different polarization directions.

[0131] For example, the microstructure unit is composed of a high-refractive-index inorganic material, specifically selected from TiO2 (titanium dioxide), GaN (gallium nitride), and SiN. x At least one of silicon nitride and niobium pentoxide (Nb2O5).

[0132] The recommended arrangement period of the microstructure units on the substrate surface is 250 nm; the range is 150 nm to 350 nm; and more preferably 220 nm to 280 nm, in order to balance the spatial sampling rate and the diffraction suppression effect.

[0133] The height of the microstructure unit along the normal direction of the substrate 1 can be selected from 50 nanometers to 1000 nanometers; to balance modulation efficiency and manufacturing feasibility, it is further preferred to be from 100 nanometers to 800 nanometers.

[0134] When the arrangement period is set to 250 nanometers, the first lateral dimension (L) and the second lateral dimension (W) of the cross-section of the microstructure unit satisfy the following: the length L and the width W are both in the range of 50 nanometers to 230 nanometers; and the aforementioned size relationship constraint condition P > L > W (i.e., the arrangement period is greater than the first lateral dimension and the first lateral dimension is greater than the second lateral dimension) must be satisfied to maintain the in-plane anisotropic modulation characteristics.

[0135] This application also provides a near-eye display device. The near-eye display device includes the light guide device described above. Specifically, this application discloses a near-eye display device integrating metasurface optical elements, which can be applied to wearable devices such as augmented reality (AR) displays and virtual reality (VR) displays.

[0136] 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.

[0137] 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 light guide device, characterized by, include: Base (1); A coupling device (10) is disposed on the substrate (1) for coupling incident light (11) from the outside into the substrate (1) by reflection or transmission to form a guiding light (12) transmitted by total internal reflection within the substrate (1). The second metasurface structure (3) is located on the path of the guide light (12) in the substrate (1) and is used to polarize the guide light (12) according to the polarization state of the guide light (12).

2. The light guide device of claim 1, wherein, The second metasurface structure (3) is configured to perform at least one of the following polarization modulations: The guide ray (12) with a defined polarization state is converted into unpolarized light; The guide ray (12) having a first polarization state is converted into a second polarization state that is different from the first polarization state.

3. The light guide device of claim 1, wherein, The second metasurface structure (3) satisfies at least one of the following configurations: The second metasurface structure (3) is embedded inside the substrate (1) in a manner that is inclined relative to the surface normal of the substrate (1); The second metasurface structure (3) is disposed on the surface of the substrate (1) and is located in the corresponding region where the guiding light (12) undergoes total internal reflection.

4. The light guide device according to claim 1, characterized in that, The guiding ray (12) propagates within the substrate (1) by total internal reflection, and the polarization degree DoP in the Stokes vector of the guiding ray (12) satisfies 0.15≤DoP≤0.85; The second metasurface structure (3) is configured to: according to the local polarization state of the guide light (12) at different spatial positions in the substrate (1), microstructure units with different polarization modulation functions are correspondingly provided so that the guide light (12) has a specific polarization state.

5. The light guide device according to claim 1, characterized in that, The second metasurface structure (3) is divided into at least two independent modulation regions along the extension direction of its surface. Each modulation region is matched with the corresponding polarization modulation function based on the polarization degree of the light it receives, thereby realizing the regional control of the polarization state of the outgoing light.

6. The light guide device according to claim 1, characterized in that, The polarization modulation function of at least one modulation region in the second metasurface structure (3) satisfies the following relationship with the incident angle of the guide light (12) received by the modulation region: the difference in polarization state conversion efficiency of the modulation region for guide light (12) at different incident angles is within a preset range.

7. The light guide device according to claim 6, characterized in that, The incident angle range of the guiding light (12) is 15° to 90°.

8. The light guide device according to claim 1, characterized in that, The second metasurface structure (3) is configured to modulate the light it processes into unpolarized light; wherein the metasurface structure that realizes the unpolarized modulation includes a plurality of microstructure units, each of which has its own optical axis direction in the plane in which it is located, and the optical axis direction is randomly arranged.

9. The light guide device according to claim 1, characterized in that, The light guide device further includes a first metasurface structure (2), which is located on the transmission path of the incident light before it reaches the coupling device, and is used to polarize the incident light according to the polarization state of the incident light.

10. The light guide device according to claim 9, characterized in that, The first metasurface structure (2) is located in the transmission path of the incident light ray (11) before it reaches the coupling device (10), and is arranged as follows: When the coupling device (10) is a transmission type coupling device (10), the first metasurface structure (2) is disposed on the incident side surface of the coupling device (10) and is optically bonded to the incident side surface; When the coupling device (10) is a reflective coupling device (10), the first metasurface structure (2) is disposed on a surface opposite to and away from the reflective surface of the coupling device (10); and / or When the coupling device (10) is a reflective coupling device (10), the first metasurface structure (2) is embedded inside the substrate (1).

11. The light guide device according to claim 9, characterized in that, The orthographic projection of the first metasurface structure (2) at least covers the optically effective region of the transmissive coupling device (10); and / or The orthographic projection of the first metasurface structure (2) onto the surface of the substrate (1) at least covers the optically effective area of ​​the reflective coupling device (10).

12. The light guide device according to claim 1, characterized in that, The second metasurface structure (3) includes multiple microstructure units, each of which has a first lateral dimension and a second lateral dimension in a cross section perpendicular to the direction of light propagation. The first lateral dimension and the second lateral dimension are not equal to form in-plane anisotropy.

13. The light guide device according to claim 12, characterized in that, The outer contour of the cross section is selected from a rectangle, ellipse, parallelogram, trapezoid, or other closed geometry with a major axis and a minor axis.

14. The light guide device according to claim 12, characterized in that, The arrangement period P of the microstructure units along the substrate surface direction of the metasurface, and the first lateral dimension L and the second lateral dimension W of their cross-sections satisfy: P > L > W.

15. A near-eye display device, characterized in that, The near-eye display device includes a light guide device as described in any one of claims 1-14.

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