Full-color polarization-insensitive waveguide coupling grating and design method thereof

Abstract

The invention discloses a full-color polarization-insensitive waveguide coupling-in grating and a design method thereof. The full-color polarization-insensitive waveguide coupling-in grating comprises a coupling-in grating area arranged on a waveguide substrate; the coupled grating area is divided into at least three functional areas, and the functional areas have different structural heights and share a two-dimensional topological pattern in the same free form; the area division of the coupled grating is based on the total reflection transmission track and accumulated coupling frequency distribution of light in the waveguide medium. According to the invention, the coupled grating area is divided into a plurality of functional areas, and a brand-new design dimension is introduced: independent diffraction performance optimization can be carried out on different functional areas based on the area division of light accumulation coupling times, so that the problem of recoupling energy leakage which is generally neglected in the prior art can be radically solved; therefore, the overall lighting effect and the display brightness of the waveguide system are obviously improved.

Description

Technical Field

[0001] This invention relates to the field of augmented reality (AR) display technology, and in particular to a full-color polarization-insensitive waveguide coupling grating and its design method. Background Technology

[0002] In the field of augmented reality displays, diffractive waveguides have become the mainstream solution for near-eye displays due to their thin and light structure. As the core input element of the waveguide system, the coupling grating's function is to efficiently couple the light emitted from the image source into the waveguide medium, ensuring that it meets the conditions for total internal reflection transmission. Existing technologies, such as patent application CN117170014B, disclose a coupling grating that divides the grating into multiple symmetrically arranged sections along a first direction and sets the grating sides as inclined slopes or curved surfaces to achieve symmetrical propagation of the incident light beam to the left and right sides, thereby enabling binocular imaging using a single microdisplay and claiming a diffraction efficiency of over 80%. For example, patent application CN202311190661.0 discloses a coupling grating structure for a diffractive waveguide. This scheme attempts to improve the beam bending and transmission efficiency in terms of physical structure by introducing tilted grating sidewalls or specific curved surface designs. Patent application CN202410121871.2 proposes a design method for phase modulation using a binary surface (diffractive optical element) in the waveguide incidence window, aiming to enhance the ability to shape the incident light wavefront through the cascading of diffractive elements.

[0003] However, the aforementioned existing technologies still have significant drawbacks in practical applications: First, the aforementioned technical solution only focuses on the diffraction efficiency when light initially passes through the coupled grating, neglecting the fact that when light propagates through the waveguide via total internal reflection, it will repeatedly overlap and scan the same coupled grating region. This repeated overlap causes the light already coupled into the waveguide to interact with the grating again, resulting in a "recoupling" effect and causing severe energy leakage. This means that the actual energy entering the waveguide and reaching the human eye is far lower than the design value, limiting further improvements in the overall system brightness. Second, the grating structure in this solution is typically optimized for a single wavelength or a specific polarization state. When facing unpolarized, broadband RGB full-color light sources such as Micro-LEDs, it is difficult to ensure efficient and consistent diffraction responses for red, green, and blue light, as well as the TE and TM polarization modes, easily leading to color separation and brightness unevenness. Furthermore, its complex tilted sidewall structure requires extremely high nanometer-level processing precision; even minor process deviations can cause drastic fluctuations in diffraction efficiency, resulting in poor robustness for mass production.

[0004] Therefore, it is necessary to provide a full-color polarization-insensitive waveguide coupling grating and its design method to overcome the above-mentioned defects. Summary of the Invention

[0005] The purpose of this invention is to provide a full-color polarization-insensitive waveguide coupling grating and its design method, aiming to solve the problem of how to fundamentally suppress the recoupling energy loss inside the waveguide and achieve polarization insensitivity under full-color broadband, while improving the manufacturing robustness of the coupling grating structure.

[0006] To achieve the above objectives, the present invention provides a full-color polarization-insensitive waveguide-coupled grating, characterized in that it comprises: The coupling grating region is disposed on the waveguide substrate; The coupled grating region is divided into at least three functional regions, each with a different structural height, and each functional region shares the same free-form two-dimensional topological pattern. The region division of the coupled grating is based on the total internal reflection propagation trajectory of light in the waveguide medium and the distribution of cumulative coupling times.

[0007] In a preferred embodiment, the structural height of each functional region of the coupling grating is configured such that, along the light transmission direction, different height parameters are configured for overlapping regions of different total internal reflections, so as to balance the initial coupling efficiency of each region with the internal reflectivity in the subsequent recoupling process.

[0008] In a preferred embodiment, the coupling grating region achieves an optimal balance between the effective aperture of the coupling grating and the average coupling efficiency by removing higher-order recoupling interaction regions, thereby minimizing higher-order recoupling energy leakage.

[0009] In a preferred embodiment, the higher-order recoupling refers to the interaction of light with the coupled grating a fourth or more times within the waveguide.

[0010] In a preferred embodiment, the structural height of each functional region and the two-dimensional topological pattern together construct a polarization-insensitive diffraction response, so that the difference in diffraction efficiency between the TE polarization mode and the TM polarization mode of the coupled grating in the red, green, and blue panchromatic bands is less than a preset threshold.

[0011] In a preferred embodiment, the cumulative coupling number distribution is obtained by calculating the lateral displacement of the light rays inside the waveguide and the number of light overlaps at each spatial coordinate point using a ray tracing algorithm.

[0012] This invention also provides a design method for a full-color polarization-insensitive waveguide coupling grating, comprising: Step S10: Establish a hybrid simulation model combining electromagnetic wave theory and geometric optics, and define the target wavelength range and field of view; Step S20: Calculate the lateral displacement of the light rays inside the waveguide and the cumulative coupling number distribution at each spatial coordinate point using a ray tracing algorithm; Step S30: Based on the cumulative coupling number distribution map, the coupled grating is functionally partitioned to identify and remove high-order recoupling regions that cause serious energy leakage; Step S40: Introduce a hybrid topology optimization and simulated annealing framework, treat the structural height as an independent parameter, and the two-dimensional topology distribution as a shared optimization variable, and independently iterate and adjust the structural height of each functional area until the preset coupling efficiency evaluation index is met.

[0013] In a preferred embodiment, the method further includes: Step S50: During the optimization process, a temperature-dependent hypercurvature function is used for density binarization mapping, and a spatial Gaussian filter constraint is applied to ensure the manufacturability and robustness of the final design.

[0014] In a preferred embodiment, in step S40, the simulated annealing framework is iteratively optimized through the following sub-steps: Step S41: Perform spatial Gaussian filtering on the topological density distribution of the current iteration, and perform binarization mapping through a temperature-dependent hypercurvature function to obtain a binarized topological pattern; Step S42: For each functional region, based on the shared binarized topological pattern and the current structural height of the region, electromagnetic simulation is performed through rigorous coupled-wave analysis to solve for the coupling transmittance of each region. T in With total internal reflectivity R TIR ; Step S43: Based on the cumulative coupling frequency distribution diagram, calculate the effective coupling efficiency using a preset integral formula, which is as follows: In the formula, To be at a given incident angle i and wavelength l Under these conditions, the effective coupling efficiency of light rays successfully coupled into the waveguide and into the transition or coupling-out region is achieved. A eff The effective aperture area of ​​the coupled grating region; T in ( i , l ) is for a given incident angle i and wavelength l ; R TIR ( i , l ) is at a given angle i and wavelength l Internal reflectivity under total internal reflection; N(x,y) Let dx and dy be the cumulative number of times a ray is scanned by overlapping rays during its propagation through the waveguide at the spatial coordinates (x, y) within the grating region, where the rays undergo total internal reflection; dx and dy are the area elements. Step S44: Construct a global optimization quality factor based on a preset formula to achieve unified optimization across the entire field of view and all spectral bands. The preset formula is as follows: In the formula, FoM To optimize the quality factor globally; α These are weighting coefficients; Step S45: Update the two-dimensional topological distribution for the next iteration based on the gradient of the global optimization quality factor with respect to the topological density; Step S46: The structural height of each functional area is independently perturbed and iteratively optimized using the simulated annealing algorithm.

[0015] In a preferred embodiment, step S46 includes: during the iteration process, applying different height perturbations to different functional regions, and accepting or rejecting the perturbations based on the changing trend of the global optimization quality factor, in order to search for the optimal combination of structural heights for each region that maximizes the global optimization quality factor. This invention provides a full-color polarization-insensitive waveguide coupling grating and its design method, abandoning the traditional single-structure or physical partition design of coupling gratings and proposing a "quasi-three-dimensional" coupling grating architecture. The core lies in dividing the coupling grating region into multiple functional regions and introducing a new design dimension: region division based on the cumulative coupling number of light rays. Using a ray tracing algorithm, the number of times light rays overlap and scan each spatial position during multiple total internal reflections within the waveguide (i.e., the cumulative coupling number) is accurately calculated. Based on this distribution, the grating region is divided into functional regions corresponding to different coupling number intervals. Therefore, through this region division, the diffraction performance of different functional regions can be independently optimized. For example, in the high coupling number region where light rays initially pass through, the structure can be optimized to maximize coupling efficiency; while in the low coupling number region where light rays subsequently pass through, the structure can be optimized to suppress energy re-coupling (i.e., recoupling loss), thereby fundamentally solving the recoupling energy leakage problem commonly neglected in existing technologies, and significantly improving the overall luminous efficiency and display brightness of the waveguide system. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 A schematic diagram of the coupling grating structure provided by the present invention; Figure 2 for Figure 1 A schematic diagram showing the functional area division and structural height of the coupled grating structure. Figure 3 This is a two-dimensional topological structure feature diagram of the coupled grating unit provided by the present invention; Figure 4 A flowchart illustrating the design method provided by this invention; Figure 5 The coupling efficiency characteristics of the RGB three channels in TE / TM polarization and non-polarization modes are shown in the figure. Figure 6 A tolerance robustness analysis diagram for the structural height of this invention; Figure 7 This is a comparison chart of the numerical simulation results of RCWA and FDTD of the present invention.

[0018] The labels in the figure are as follows: 1. Incident beam; 2. Waveguide substrate; 3. Coupled grating region; 4. Total internal reflection transmission path; 5. Micro / nano structure features; 6. Two-dimensional topology; 31. First functional region; 32. Second functional region; 33. Third functional region. Detailed Implementation

[0019] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described in this specification are merely for explaining the invention and are not intended to limit the invention.

[0020] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0021] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0022] In an embodiment of the present invention, a full-color polarization-insensitive waveguide-coupled grating is provided. For example... Figure 1 As shown, the coupling grating is positioned at the incident position of the waveguide substrate 2 to receive the incident beam 1 from the image source and couple it into the interior of the waveguide substrate 2 through diffraction. The light propagates along the total internal reflection transmission path 4 within the waveguide substrate 2, and the lateral displacement between two adjacent total internal reflections is denoted as Δs.

[0023] Unlike existing gratings that employ a single structure or simple physical partitioning, the coupling grating in this embodiment is spatially divided into multiple functional regions. Specifically, as... Figure 2 As shown, the coupled grating region 3 is divided into at least three functional regions, such as a first functional region 31, a second functional region 32, and a third functional region 33. These functional regions are arranged sequentially along the light transmission direction. Each functional region has an independently optimized structural height. For example, the height of the first functional region can be set to 280 nanometers, the height of the second functional region can be set to 250 nanometers, and the height of the third functional region can be set to 300 nanometers.

[0024] Each functional region is composed of a series of micro / nano structural features 5, which share the same free-form two-dimensional topology 6, but are configured with different structural heights for different regions based on the cumulative coupling number of light rays. Through this quasi-3D structural arrangement, the present invention achieves local diffraction modulation optimization in different partitions of the grating, thereby suppressing recoupling loss while maximizing coupling efficiency in the panchromatic band.

[0025] It should be noted that although the heights of the various functional areas differ, they share the same free-form two-dimensional topology 6. This two-dimensional topology 6 is not a simple periodic array, but a complex micro-nano structure that is non-periodic and asymmetric, generated through a reverse design algorithm. For example, it can be a quasi-three-dimensional grating unit containing multiple protrusions and depressions. Its free-form nature is reflected in the fact that parameters such as the pattern outline, duty cycle, and distribution density can vary with spatial position.

[0026] It is important to emphasize that the core of the above structure lies in the fact that the region division of the coupling grating is not based on simple geometric symmetry, but rather on the total internal reflection propagation trajectory of light within the waveguide medium and the distribution of cumulative coupling times. For example... Figure 1As shown, due to the lateral displacement Δs, light rays propagate through the waveguide and overlap multiple times, scanning the coupled grating region 3. Using a ray tracing algorithm, the lateral displacement between two consecutive total internal reflections within the waveguide, and the cumulative number of overlapping scans at each spatial coordinate point, can be accurately calculated under given waveguide thickness (e.g., 0.5 mm) and refractive index (e.g., 1.8) at different field of view angles (e.g., -20° to 20°), for light rays incident at different angles. For example, the cumulative coupling count is 1 in the region near the initial light incidence; 2 in the region covered again after one reflection; and so on. Based on this distribution map, the coupled grating is divided into functional regions corresponding to different cumulative coupling count intervals, allowing subsequent optimizations to be more targeted.

[0027] Understandably, this region division based on the distribution of cumulative coupling times addresses the problem of neglecting recoupling loss in existing technologies. Its implementation principle lies in: by accurately modeling the complete propagation path of light within the waveguide, the energy interaction history of each spatial location is quantified, enabling proactive identification and handling of energy leakage risk areas during the design phase. Therefore, recoupling energy leakage is suppressed at its source, preventing light already coupled into the waveguide from being ineffectively coupled out again due to interaction with the grating, significantly improving the overall luminous efficiency and display brightness of the system.

[0028] In terms of specific configuration, to further balance the initial coupling efficiency and the internal reflectivity during subsequent recoupling, the structural height of each functional region is configured along the light transmission direction, with different height parameters for overlapping areas of different total internal reflections. For example, in the region where the cumulative coupling count is 1 (i.e., the first functional region 31), the structural height is optimized to maximize the initial coupling efficiency, such as setting it to 320nm; while in the regions where the cumulative coupling count is 2 or 3 (i.e., the second functional region 32 and the third functional region 33), the structural height is adjusted to prioritize increasing the internal reflectivity to suppress the re-coupling of energy, such as setting it to 250nm and 280nm respectively. Through this spatially differentiated height configuration, the globally optimal allocation of light energy is achieved, balancing the two contradictory goals of initial coupling and recoupling suppression. Therefore, by independently configuring the structural height of each region, the contradictory pair of initial coupling efficiency and subsequent internal reflectivity can be precisely balanced. In the region where light first enters, a higher coupling efficiency is crucial; while in the region after multiple reflections, it is necessary to increase the internal reflectivity (i.e., reduce the probability of re-coupling). Through this spatially differentiated high-altitude configuration, the present invention achieves globally optimal allocation of light energy, further improving energy utilization.

[0029] Furthermore, to maximize energy utilization efficiency, the coupling grating region in this embodiment achieves an optimal balance between the effective aperture and average coupling efficiency by actively removing high-order re-coupling interaction regions. Specifically, based on the aforementioned cumulative coupling number distribution map, downstream regions corresponding to the fourth and subsequent interactions of light (i.e., high-order re-coupling regions) can be identified. In these regions, the light energy has been significantly attenuated due to multiple reflections, and the probability of it being coupled out of the waveguide again is extremely high, contributing very little to the system brightness. Removing these regions from the effective grating aperture not only reduces ineffective energy leakage but also effectively reduces the physical size of the grating, facilitating the miniaturization of the waveguide system. Therefore, by removing these ineffective or inefficient regions that contribute very little to the system brightness but may lead to additional energy loss, this invention can optimize the effective aperture of the coupling grating. This is equivalent to reducing the physical size of the grating while ensuring coupling efficiency, making miniaturization and weight reduction of the waveguide system possible, while also reducing manufacturing difficulty and cost.

[0030] To achieve full-color polarization insensitivity, in this embodiment, the structural height of each functional region and the shared two-dimensional topological pattern are co-designed to jointly construct a polarization-insensitive diffraction response. Specifically, by optimizing the geometry of the shared two-dimensional topological pattern, it achieves consistent diffraction efficiency for both TE (Transverse Electric) and TM (Transverse Magnetic) polarization modes across the red (626nm), green (532nm), and blue (465nm) full-color bands, meaning the difference in diffraction efficiency between the two is less than a preset threshold (e.g., 5%). Simultaneously, the independent structural height of each functional region compensates for local polarization differences caused by varying cumulative coupling times. This quasi-three-dimensional structural arrangement gives the grating excellent compatibility with unpolarized light across a wide spectral range, eliminating the need for additional polarization conversion elements.

[0031] Specifically, the independent height of each region serves as another optimization variable to compensate for polarization differences caused by varying incident angles or cumulative light frequencies in different regions. This ensures that the final grating structure is perfectly compatible with unpolarized, broadband light sources such as Micro-LEDs. Without the need for additional polarization conversion components, color balance and brightness uniformity in full-color displays can be achieved, eliminating the dispersion and brightness unevenness problems caused by polarization dependence in traditional gratings. This significantly simplifies system complexity and improves image quality.

[0032] like Figure 5As shown, within a 20° field of view (FOV), the coupling efficiency curves remain highly consistent regardless of whether the incident light is in TE or TM polarization mode. Specifically, the figure shows the coupling efficiency distribution for three wavelength channels: 465nm (blue light), 532nm (green light), and 626nm (red light). Within a 20° field of view (FOV), the coupling efficiency curves remain highly consistent regardless of whether the incident light is in TE or TM polarization mode, and the average efficiency curve (Avg) in the non-polarized mode is stable. This result verifies that the present invention, through... Figure 3 The free-form geometry optimization of the two-dimensional topology 6 in the model successfully eliminated the diffraction response differences of traditional diffraction gratings under different polarization states, achieving perfect compatibility with non-polarized light sources and providing a foundation for high-quality imaging in AR systems.

[0033] To obtain the aforementioned grating with its complex structure, this invention also provides a design method for a full-color polarization-insensitive waveguide-coupled grating. This method is implemented using a hybrid topology optimization with simulated annealing (HTO-SA) framework, as detailed below. Figure 4 As shown, it includes steps S10-S50.

[0034] First, perform step S10: establish a hybrid simulation model combining electromagnetic wave theory and geometric optics, and define the target wavelength range (e.g., RGB three wavelengths) and field of view (e.g., ±20°). This hybrid model considers both the macroscopic geometric propagation path of light within the waveguide and the electromagnetic field modulation effect of micro / nano structures on light waves, laying the foundation for subsequent accurate calculations.

[0035] Subsequently, step S20 is executed: using a ray tracing algorithm, the lateral displacement of the ray within the waveguide and the cumulative coupling frequency distribution at each spatial coordinate point are calculated. Specifically, this involves traversing all target field-of-view angles. i With RGB wavelength l According to the waveguide thickness t and diffraction angle θ diff Calculate the lateral displacement Δs = 2 due to total internal reflection of the light ray. t tan(θ diff Then, the effective aperture A of the grating is solved using a ray tracing algorithm. eff Distribution of cumulative coupling times at each spatial coordinate (x, y) within the space N(x, y, θ, λ) This distribution map is the core basis for subsequent functional zoning and recoupling suppression.

[0036] Next, step S30 is executed: based on the cumulative coupling number distribution map obtained in step S20, the coupled grating is functionally partitioned, and high-order recoupling regions that cause severe energy leakage are identified and removed. For example, regions with a cumulative coupling number of 1 are divided into the first functional region, regions with a number of 2 are divided into the second functional region, regions with a number of 3 are divided into the third functional region, and regions with a number of ≥4 are marked as high-order recoupling regions and removed from the effective aperture.

[0037] Subsequently, step S40 is executed: A hybrid topology optimization and simulated annealing (HTO-SA) framework is introduced, treating structural height as an independent parameter and two-dimensional topology distribution as a shared optimization variable. The structural height of each functional region is independently iteratively adjusted until the preset coupling efficiency evaluation index is met. The specific iterative process can be further broken down into the following sub-steps S41-S46.

[0038] Step S41: Topological density distribution for the current iteration r (it) Spatial Gaussian filtering is performed to eliminate high-frequency noise, and a binarization mapping is performed using a temperature-dependent hypercurvature function to obtain a binarized topological pattern. r bin This ensures the manufacturability of the final structure. Among these, the binarization parameters... β The value gradually increases from 1 to 10 during the iteration process. 3 This causes the intermediate density to gradually converge toward 0 or 1.

[0039] Step S42: For each functional area k ∈{1,2,3}, based on shared binary topological patterns r bin and the current structural height of the area h k (it) Electromagnetic simulations were performed using rigorous coupled-wave analysis (RCWA) to determine the coupling transmittance in each region. T in k With total internal reflectivity R TIR k It should be noted that RCWA, as an existing precise vector diffraction analysis method, can accurately calculate the diffraction efficiency of arbitrary periodic micro / nano structures; its specific implementation process will not be elaborated here.

[0040] Step S43: Combine the cumulative coupling number distribution map obtained in step S20 N(x,y) The effective coupling efficiency is calculated using an integral formula: In the formula, To be at a given incident angle i and wavelength l Under these conditions, the effective coupling efficiency of light rays successfully coupled into the waveguide and into the transition or coupling-out region is achieved. A eff The effective aperture area of ​​the coupled grating region; T in ( i , l ) is for a given incident angle i and wavelength l ; R TIR ( i , l ) is at a given angle i and wavelength l Internal reflectivity under total internal reflection; N(x,y) Let dx and dy be the cumulative number of times a light ray is scanned by overlapping light rays during its propagation through the waveguide at the spatial coordinates (x, y) within the grating region, where the light ray undergoes total internal reflection; dx and dy are the area elements.

[0041] Therefore, the microscopic diffraction properties of the grating ( T in and R TIR ) and the macroscopic trajectory of light propagation ( N(x,y) By combining these methods, the impact of recoupling loss on overall efficiency was precisely quantified. Each time light passes through a grating region, the remaining energy is multiplied by the internal reflectivity of that region. R TIR After N iterations, the remaining energy is [ ] of the initial coupling energy. R TIR ] N The average effective coupling efficiency is obtained by integrating over the entire region.

[0042] Step S44: Construct a global optimized quality factor (FoM) based on a preset formula to achieve unified optimization across the entire field of view and all spectral bands: Wherein, FoM (Figure of Merit) is the global optimization quality factor; α For weighting coefficients (e.g., can be taken as follows) α =5), used to control the degree of attention paid to "worst performance" during the optimization process; This represents the summation of the field of view angles and the target operating wavelength for all targets.

[0043] Therefore, by using logarithmic summation and exponential transformation, multiple independent optimization objectives (different angles, different wavelengths) are unified into a differentiable global objective function. When α is large, this function approximates the minimum value under each operating condition. or i The smooth version allows the optimization algorithm to automatically focus on and improve the weakest link in the system, thereby ensuring balanced performance across the entire field of view and all bands.

[0044] Step S45: Optimize the quality factor globally FoM The gradient of the topological density ρ is used to update the two-dimensional topological distribution for the next iteration: In the formula, λ is the learning rate, which is used to control the step size of the update; r This refers to the topological density. Specifically, by utilizing adjoint sensitivity analysis, the gradient of the FoM with respect to each design variable is efficiently calculated, enabling inverse optimization of the two-dimensional topological pattern.

[0045] Step S46: The structural height of each functional region is independently perturbed and iteratively optimized using a simulated annealing algorithm. Specifically, during the iteration process, different height perturbations are applied to different functional regions (for example, in the current iteration, the height of the first functional region is perturbed from 280 nm to 290 nm, the second region from 250 nm to 245 nm, and the third region from 300 nm to 305 nm), and the perturbation is accepted or rejected based on the trend of FoM (FoM). If the FoM increases after the perturbation, the perturbation is accepted; if the FoM decreases, the perturbation is accepted with a certain probability (decreasing as the iteration temperature decreases) to avoid getting trapped in local optima. Through this independent perturbation and probabilistic acceptance mechanism, the optimal combination of structural heights for each region with FoM can be searched in a broad height parameter space.

[0046] To further improve the manufacturability of the design, this method also includes step S50: During the optimization process, a temperature-dependent hypercurvature function is used for density binarization mapping, and a spatial Gaussian filter constraint is applied to ensure the manufacturability and robustness of the final design. The temperature-dependent hypercurvature function forces the intermediate density values ​​to 0 or 1 in the later stages of optimization, forming clear boundaries; the spatial Gaussian filter eliminates overly fine and difficult-to-process structural features, ensuring that the final topological pattern meets the minimum feature size requirements of mainstream processes such as nanoimprint lithography or electron beam lithography.

[0047] Using the above design method, an optimal free-form two-dimensional topological pattern and a set of optimal structural heights for each functional area are finally output.

[0048] like Figure 6The figure shown is a robustness analysis diagram of the structural height manufacturing tolerance provided by the present invention. This diagram characterizes the fluctuation of coupling efficiency when manufacturing deviations occur in the grating structure. Using the nominal height as the zero-error benchmark, the structural height deviation range (Δ) within ±20nm is analyzed. h Within the region 31, the coupling efficiency remains at a high level, verifying the extremely high tolerance of this design to height fluctuations during nanofabrication. Through the independent height compensation mechanisms of each functional region 31, 32, and 33, the optical system's tolerance to height fluctuations during nanofabrication is significantly enhanced. This highly robust design ensures that, even with conventional processing errors during industrial mass production, the final fabricated coupling grating region 3 can stably maintain the expected diffraction efficiency, greatly improving the overall product yield and process consistency.

[0049] like Figure 7 The figure shows a comparison of numerical simulation results of the design scheme described in this invention using RCWA (Rigorous Coupled Wave Analysis) and FDTD (Finite-Difference Time-Domain). The coupling efficiency of the red, green, and blue wavelength channels within a 20° field of view was compared using two independent high-precision electromagnetic field numerical calculation methods. It can be seen that the efficiency curves of the two simulations show consistent trends and a high degree of agreement in absolute values. This comparison confirms the accuracy of the hybrid simulation model established in this invention, demonstrating that the coupling grating structure provided by this invention has extremely high numerical calculation reliability and physical feasibility under the complex optical environment considering the total internal reflection transmission path 4.

[0050] In summary, this invention fundamentally suppresses recoupling energy loss within the waveguide by scientifically partitioning the coupling grating based on the cumulative coupling count and combining a shared two-dimensional topology with an independent height quasi-three-dimensional structural design. Simultaneously, it achieves efficient and uniform coupling of full-color broadband unpolarized light sources. Furthermore, the reverse design method employed integrates manufacturing constraints, resulting in a final structure with extremely high tolerance for height errors in nanofabrication, significantly improving mass production yield and providing a practical solution for high-performance AR diffraction waveguide systems.

[0051] The present invention is not limited to the description in the specification and embodiments, and thus other advantages and modifications can be readily realized by those skilled in the art. Therefore, the present invention is not limited to the specific details, representative devices and illustrated examples shown and described herein without departing from the spirit and scope of the general concept as defined by the claims and their equivalents.

Claims

1. A full color polarization insensitive waveguide in-coupler grating, characterized in that, The application relates to a polarization-insensitive in-coupling grating for a waveguide display, and a design method thereof. The application comprises: An in-coupling grating region arranged on a waveguide substrate; The in-coupling grating region is divided into at least three functional regions, each functional region has a different structure height, and the functional regions share a same free-form two-dimensional topological pattern; 2. The full color polarization insensitive in-coupling grating of claim 1, wherein, The region division of the in-coupling grating is based on the total reflection transmission trajectory of light in the waveguide medium and the cumulative coupling number distribution.

3. The full color polarization insensitive in-coupling grating of claim 1, wherein, The structure height of each functional region of the in-coupling grating is configured as follows: along the light transmission direction, different height parameters are configured for different total reflection overlapping regions, so as to balance the initial in-coupling efficiency and the internal reflectivity in the subsequent recoupling process.

4. The full color polarization insensitive in-coupling grating of claim 3, wherein, The in-coupling grating region realizes the optimal balance between the effective aperture and the average coupling efficiency of the in-coupling grating by removing the high-order recoupling interaction region, so as to minimize the high-order recoupling energy leakage.

5. The full color polarization insensitive in-coupling grating of claim 1, wherein, The high-order recoupling refers to the fourth and subsequent interactions of light in the waveguide with the in-coupling grating.

6. The full color polarization insensitive in-coupling grating of claim 1, wherein, The structure height of each functional region and the two-dimensional topological pattern jointly construct a polarization-insensitive diffraction response; and the in-coupling grating has a diffraction efficiency difference between TE polarization mode and TM polarization mode less than a preset threshold in the red, green and blue full-color waveband.

7. A method of designing a full-color polarization-insensitive waveguide in-coupler grating, characterized in that, The cumulative coupling number distribution is obtained by calculating the lateral displacement of light in the waveguide and the light overlapping number at each spatial coordinate point by using a ray tracing algorithm. The application further comprises: Step S10: a hybrid simulation model combining electromagnetic wave theory and geometric optics is established, and a target wavelength range and a field of view are defined; Step S20: the lateral displacement of light in the waveguide and the cumulative coupling number distribution map at each spatial coordinate point are calculated by using a ray tracing algorithm; Step S30: based on the cumulative coupling number distribution map, the in-coupling grating is functionally divided, and a high-order recoupling region causing serious energy leakage is identified and removed; 8. The method of designing a polarization insensitive in-coupling grating for a full color waveguide according to claim 7, wherein, Step S40: a hybrid topological optimization and simulated annealing framework is introduced, the structure height is taken as an independent parameter, the two-dimensional topological distribution is taken as a shared optimization variable, the structure height of each functional region is independently iteratively adjusted, and the adjustment is stopped until a preset coupling efficiency evaluation index is met. The application further comprises:

9. The method of designing a polarization insensitive in-coupling grating for a full color waveguide according to claim 7, wherein, Step S50: in the optimization process, a temperature-dependent hyperbolic function is used for density binary mapping, and a spatial Gaussian filtering constraint is applied, so as to ensure the manufacturability and robustness of the final design. In the step S40, the simulated annealing framework is iteratively optimized through the following substeps: Step S42: For each functional region, based on the shared binary topological pattern and the current structure height of the region, electromagnetic simulation is performed by rigorous coupled-wave analysis to solve the in-coupling transmittance of each region T in with total internal reflection R TIR ; Step S41: the topological density distribution of the current iteration is subjected to spatial Gaussian filtering, and binary mapping is performed through a temperature-dependent hyperbolic function, so as to obtain a binary topological pattern; In the formula, To be at a given incident angle Step S43: based on the cumulative coupling number distribution map, the effective coupling efficiency is calculated through a preset integral formula, the integral formula is as follows: and wavelength θ Under these conditions, the effective coupling efficiency of light rays successfully coupled into the waveguide and into the transition or coupling-out region is achieved. A eff The effective aperture area of ​​the coupled grating region; T in ( λ , θ ) is for a given incident angle λ and wavelength θ ; R TIR ( λ , θ ) is at a given angle λ and wavelength θ Internal reflectivity under total internal reflection; N λ Let dx and dy be the cumulative number of times a ray is scanned by overlapping rays during its propagation through the waveguide at the spatial coordinates (x, y) within the grating region, where the rays undergo total internal reflection; dx and dy are the area elements. (x,y) In the formula, Step S44: a global optimization quality factor is constructed based on a preset formula, so as to realize unified optimization of the full field of view and the full waveband, the preset formula is as follows: is a global optimization quality factor; α is a weighting factor; FoM Step S45: the two-dimensional topological distribution of the next round of iteration is updated based on the gradient of the topological density of the global optimization quality factor. Step S46: The structural height of each functional area is independently perturbed and iteratively optimized using the simulated annealing algorithm.

10. The method of designing a polarization insensitive in-coupling grating for a full color waveguide according to claim 9, wherein, Step S46 includes: during the iteration process, applying different height perturbations to different functional regions, and accepting or rejecting the perturbations according to the changing trend of the global optimization quality factor, in order to search for the combination of structural heights of each region that makes the global optimization quality factor optimal.

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