Design and fabrication method of grating structure

Abstract

The application provides a design and preparation method of a grating structure, comprising: constructing a first mapping relationship, the first mapping relationship taking a designed diffraction efficiency combination of multiple diffraction orders of the grating structure as an input parameter, and taking a performance parameter of a diffractive optical waveguide including the grating structure as an intermediate output; iteratively modulating the input parameter of the first mapping relationship to obtain a designed diffraction efficiency combination that makes the output parameter of the first mapping relationship overall minimum / maximum, and determining the designed diffraction efficiency combination as a target diffraction efficiency combination; constructing a second mapping relationship, the second mapping relationship taking a designed topographic parameter of the grating structure as an input parameter, and taking a predicted diffraction efficiency combination of multiple diffraction orders of the grating structure as an output parameter; iteratively modulating the input parameter of the second mapping relationship to obtain a designed topographic parameter that makes the output parameter of the second mapping relationship match the target diffraction efficiency combination as a target topographic parameter; and preparing the grating structure according to the target topographic parameter.

Description

Technical Field

[0001] This application relates to the field of augmented reality display technology, and in particular to a design and fabrication method for a grating structure. Background Technology

[0002] Augmented reality is a technology that blends the real world with virtual information. Augmented reality display systems typically include micro-projectors and optical displays. The micro-projectors provide virtual display content for the augmented reality display system, which is then projected onto the viewer's eyes through the optical displays. The optical displays are usually transparent optical components, so that users can also see the real world through the optical displays at the same time.

[0003] Diffractive waveguides are one of the mainstream implementation methods for near-eye optical displays. They rely on built-in grating structures to complete the coupling and incident of imaging light rays, light path transmission, pupil beam expansion, and coupling and outward. Current industry standard grating design and fabrication schemes generally involve designers pre-setting grating morphology parameters, simulating the corresponding diffraction efficiency, and performing single-point optimization. This traditional design method has significant limitations, making it difficult to simultaneously consider core parameters such as the efficiency, brightness uniformity, and color uniformity of the color waveguide. Consequently, conventional designs often result in grating structures meeting single-point diffraction standards, but the final displayed image exhibits imaging defects, affecting the display experience and imaging accuracy of the terminal device. Summary of the Invention

[0004] This application provides a design and fabrication method for grating structures. It adopts a two-level mapping iterative optimization system to achieve accurate solutions for the forward constraints of grating performance and the reverse inverse of structure, effectively overcoming the defects of traditional grating design.

[0005] A method for designing and fabricating a grating structure, comprising:

[0006] A first mapping relationship is constructed, wherein the first mapping relationship takes the design diffraction efficiency combination of multiple diffraction orders of the grating structure as the input parameter, and the output parameter takes the performance parameters of the diffraction waveguide including the grating structure as the intermediate output, wherein the performance parameters of the diffraction waveguide include at least one of efficiency, brightness uniformity and color uniformity.

[0007] The input parameters of the first mapping relationship are iteratively modulated to obtain a design diffraction efficiency combination that minimizes or maximizes the overall output parameters of the first mapping relationship, and the design diffraction efficiency combination is determined as the target diffraction efficiency combination.

[0008] A second mapping relationship is constructed, which takes the design morphology parameters of the grating structure as input parameters and the predicted diffraction efficiency combination of the multi-order diffraction orders of the grating structure as output parameters.

[0009] The input parameters of the second mapping relationship are iteratively modulated to obtain the design morphology parameters that make the output parameters of the second mapping relationship match the target diffraction efficiency combination as the target morphology parameters;

[0010] The grating structure is prepared according to the target morphology parameters.

[0011] Implementably, the grating structure serves as a coupling grating for the diffractive waveguide, the operating order of the coupling grating being the +1st transmission order, and the designed diffraction efficiency of the +1st transmission order ranging from 0.5 to 0.7; and / or,

[0012] The grating structure is used as the coupling grating of the diffractive waveguide. The operating order of the coupling grating is the -1st transmission order, and the design diffraction efficiency of the -1st transmission order ranges from 0.1 to 0.2.

[0013] In practice, the design diffraction efficiency of the -1st reflection order of the coupled grating is in the range of 0.02-0.05.

[0014] Alternatively, the method may further include:

[0015] The performance parameters or their deformations of the diffractive waveguide, including the grating structure, are weighted and fused to construct a comprehensive performance evaluation function, with the minimum or maximum value of the comprehensive performance evaluation function as the optimization objective.

[0016] In practice, the iterative modulation of the input parameters of the second mapping relationship to obtain design morphology parameters as target morphology parameters that match the combination of the output parameters of the second mapping relationship and the target diffraction efficiency includes:

[0017] The initial design topography parameters of the grating structure are obtained as the current design topography parameters;

[0018] Based on the second mapping relationship, the current predicted diffraction efficiency combination corresponding to the current design morphology parameters is obtained;

[0019] Compare the current predicted diffraction efficiency combination with the target diffraction efficiency combination;

[0020] When the overall deviation between the two sets of data is less than the preset accuracy threshold, it is determined that the current predicted diffraction efficiency combination matches the target diffraction efficiency combination, and the current design morphology parameter is determined as the target morphology parameter.

[0021] When the overall deviation between the two sets of data is greater than or equal to the preset accuracy threshold, the current design morphology parameters are iteratively corrected, the adjusted design morphology parameters are updated to the current design morphology parameters, and the step of obtaining the current predicted diffraction efficiency combination corresponding to the current design morphology parameters based on the second mapping relationship is returned.

[0022] In practice, the grating structure is a tilted grating, and the sidewalls of the grating structure have varying tilt angles.

[0023] Implementably, the fabrication of the grating structure according to the target morphology parameters includes:

[0024] Determine the etching angle variation parameters based on the target morphology parameters;

[0025] An AC bias voltage is applied in the vertical direction of the substrate to be etched. By controlling the phase difference of the AC bias voltage in real time, the etching direction of the etching ion beam is dynamically changed to match the etching angle change parameters.

[0026] The substrate to be etched is etched using an angle-adjustable etching ion beam to form a grating structure with varying tilt angles on the sidewalls, in order to match the target morphology parameters.

[0027] In practice, when the tilt angle of the sidewall of the grating structure is greater than a preset threshold, the method further includes:

[0028] A DC bias voltage is applied to the side of the substrate to be etched, and the phase difference of the AC bias voltage and / or the bias value of the DC bias voltage are controlled in real time to dynamically change the etching direction of the etching ion beam to match the etching angle change parameters.

[0029] The preset threshold is the maximum etching angle that can be achieved by controlling the phase difference of the AC bias voltage.

[0030] Implementably, the fabrication of the grating structure according to the target morphology parameters includes:

[0031] Determine the etching angle variation parameters based on the target morphology parameters;

[0032] A DC bias voltage is applied to the side of the substrate to be etched. By controlling the bias voltage value of the DC bias voltage in real time, the etching direction of the etching ion beam is dynamically changed to match the etching angle change parameters.

[0033] The substrate to be etched is etched using an angle-adjustable etching ion beam to form a grating structure with varying tilt angles on the sidewalls, in order to match the target morphology parameters.

[0034] Alternatively, the method may further include:

[0035] Based on the etching depth and / or grating duty cycle of each region corresponding to the target grating morphology parameters, the substrate to be etched is divided into regions, and the etching temperature corresponding to each region is determined.

[0036] During the ion beam etching process, the temperature of different regions of the substrate to be etched is independently controlled so that each region of the substrate to be etched maintains its corresponding etching temperature. Through the differentiated temperature control of each region, the different regions of the substrate to be etched form differentiated etching depths and / or grating duty cycles, matching the target morphology parameters.

[0037] The design and fabrication method of the grating structure provided in this application creatively establishes a dual mapping relationship between "diffraction efficiency and waveguide performance" and "diffraction efficiency and grating morphology." It conducts multi-objective iterative optimization around core indicators such as the efficiency and uniformity of the diffraction waveguide, outputting the optimal diffraction efficiency ratio and matching micro-morphological parameters for multiple diffraction orders of the grating structure. Compared to traditional forward design approaches, this application enables precise reverse engineering from macroscopic optical requirements to microscopic grating dimensions and contour parameters, overcoming the limitations of traditional design methods and the difficulty in simultaneously considering core parameters such as the efficiency and uniformity of the diffraction waveguide, significantly improving the display quality and optical stability of the waveguide. Furthermore, this application effectively expands the design freedom of the grating structure, reduces the difficulty of fabrication processes, and improves the speed of automated simulation design, providing a complete technical solution for the research and mass production of high-imaging-quality diffraction waveguides. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 A schematic diagram illustrating the design and fabrication steps of a grating structure provided in this application;

[0040] Figure 2 A schematic diagram of the diffraction order of a grating structure in a diffractive optical waveguide provided in this application;

[0041] Figure 3 An exploded schematic diagram of one step in the design and fabrication method of a grating structure provided in this application. Detailed Implementation

[0042] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0043] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0044] refer to Figure 1 This application provides a method for designing and fabricating a grating structure, comprising:

[0045] S1, Construct a first mapping relationship. The first mapping relationship takes the design diffraction efficiency combination of the multi-order diffraction order of the grating structure as the input parameter and the output parameter as the performance parameters of the diffraction waveguide including the grating structure as the intermediate output. The performance parameters of the diffraction waveguide include at least one of efficiency, brightness uniformity and color uniformity.

[0046] S2, iteratively modulate the input parameters of the first mapping relationship to obtain the design diffraction efficiency combination that minimizes or maximizes the overall output parameters of the first mapping relationship, and determine the design diffraction efficiency combination as the target diffraction efficiency combination.

[0047] S3, construct the second mapping relationship, which takes the design morphology parameters of the grating structure as input parameters and the predicted diffraction efficiency combination of the multi-order diffraction orders of the grating structure as output parameters;

[0048] S4, iteratively modulate the input parameters of the second mapping relationship to obtain the design morphology parameters that match the output parameters of the second mapping relationship with the target diffraction efficiency as the target morphology parameters;

[0049] S5, Prepare the grating structure according to the target morphology parameters.

[0050] The design diffraction efficiency of the diffraction order of the grating structure refers to the diffraction efficiency designed in advance during the simulation optimization process. The range of the design diffraction efficiency is the numerical range that can theoretically achieve better performance of the diffraction waveguide.

[0051] Specifically, the design diffraction efficiency combination, which serves as the input parameter for the first mapping relationship, includes not only the diffraction efficiency of the working order of the grating structure (such as ±1st order transmission order, ±1st order transmission order), but also the diffraction efficiency of the zeroth order and some higher order diffraction orders (such as ±2nd order transmission order, ±2nd order reflection order, etc.). This breaks the limitation of focusing only on the working order. By incorporating the zeroth order and some higher order, it can better balance the conservation of grating energy distribution calculation and the accuracy of simulation prediction.

[0052] The diffractive waveguide includes the grating structure designed by the method provided in this application. The performance parameters of the diffractive waveguide are related to the diffraction efficiency of multiple diffraction orders of the grating structure. The first mapping relationship does not directly use the performance parameters of the diffractive waveguide as output parameters, but uses them as intermediate outputs. The intermediate outputs are then processed and used as the final output parameters. By setting intermediate and final outputs in different orders, the mapping process between the grating diffraction efficiency and each performance parameter, as well as the process of processing multiple performance parameters, are decoupled. This allows for independent control and traceability of the performance parameters of each diffractive waveguide, and also enables adjustments during the processing stage to adapt to the performance preferences of different application scenarios, thereby improving the interpretability and iterative flexibility of the solution.

[0053] It is understandable that the core purpose of constructing the first mapping relationship is to achieve reverse design "starting with the end in mind". After determining the target waveguide performance (such as requiring an efficiency greater than 1000 nits / lm, brightness uniformity greater than 70%, and color uniformity less than 0.06), designers do not need to blindly traverse the grating structure. Instead, they can use this first mapping relationship to quickly deduce the target combination of the required grating multi-order diffraction order efficiencies, thereby significantly reducing the search space for micro-nano structure optimization and shortening the R&D cycle.

[0054] On the other hand, the design topography parameters of the grating structure refer to the topography parameters pre-designed during the simulation optimization process, which are the initial data in the iterative optimization process. A direct mapping from the grating topography parameters to multi-order diffraction efficiency combinations is achieved through the second mapping relationship. Then, combined with the target diffraction efficiency combination output from the first mapping relationship, the target diffraction efficiency combination is used to inversely match the processable grating topography parameters, thereby realizing the conversion from optical parameters to the fabricated structure.

[0055] This application creatively constructs a dual mapping relationship. On the one hand, it establishes a first mapping relationship between the diffraction efficiency combination of multiple diffraction orders of the grating structure and multiple performance parameters of the diffractive waveguide. It iterative optimization is performed with the overall optical performance of the diffractive waveguide as the goal, obtaining the globally optimal target diffraction efficiency combination. On the other hand, based on this, a second mapping relationship is constructed between the grating morphology parameters and the diffraction efficiency combination. Iterative modulation achieves precise matching between the microstructure and the target diffraction efficiency, overcoming the design drawbacks of traditional empirical trial-and-error methods and realizing coordinated control of optical energy across multiple diffraction orders. Furthermore, this application decouples the complex optimization problem of strongly coupled multiple parameters into a two-step iterative process of overall performance optimization and structural parameter matching. This reduces the difficulty of simulation calculations, accelerates algorithm convergence, and avoids local extrema problems, effectively shortening the R&D iteration cycle and reducing computing power and time costs. Furthermore, this application has strong logic versatility and can be adapted to various grating structures. It is suitable for the design of various functional gratings such as diffractive waveguide coupling-in, pupil expansion, and coupling-out, and can meet the needs of diffractive waveguide products with different fields of view, resolutions, and color specifications. It lowers the R&D threshold of high-performance gratings and has broad prospects for engineering promotion and industrial application.

[0056] It should be noted that the type and morphology of the grating structure designed in this application are not limited, and can be realized as one or more of the various diffractive optical elements (such as coupling gratings, pupil gratings and coupling gratings) included in diffractive waveguides.

[0057] In practice, an embodiment of this application designs a grating structure as a coupling grating for a diffractive waveguide. The working order of the coupling grating is the +1st transmission order, and the design diffraction efficiency of the +1st transmission order ranges from 0.5 to 0.7.

[0058] In practice, an embodiment of this application designs a grating structure as a coupling grating for a diffracting waveguide. The operating order of the coupling grating is the -1st transmission order, and the design diffraction efficiency of the -1st transmission order ranges from 0.1 to 0.2.

[0059] In practice, this application embodiment designs two grating structures. One grating structure is used as the coupling grating of the diffractive waveguide. The working order of the coupling grating is +1st transmission order, and the design diffraction efficiency of the +1st transmission order ranges from 0.5 to 0.7. The other grating structure is used as the coupling grating of the diffractive waveguide. The working order of the coupling grating is -1st transmission order, and the design diffraction efficiency of the -1st transmission order ranges from 0.1 to 0.2.

[0060] Specifically, a grating structure diffracts light to produce multiple transmission and reflection orders. When used as a coupling element in a diffracting waveguide, the grating structure can operate in either the transmission or reflection order. Due to the conservation of energy in grating diffraction, the sum of the diffraction efficiencies of each diffraction order produced in each diffraction cycle is 1.

[0061] For example, when a grating structure is used as a coupling grating, the first-order diffraction order is typically the operating order. Since the coupling grating is used to couple imaging rays into the diffractive waveguide, in order to effectively improve the coupled light energy of the diffractive waveguide while avoiding degradation of other optical properties due to excessively high diffraction efficiency, the diffraction efficiency of the operating order needs to be controlled within a reasonably high range, typically 0.5-0.7. Typically, refer to... Figure 2 The diffractive waveguide 100 includes a coupling grating 110, the operating order of which is +1 transmission order (T). +1 The design diffraction efficiency is set to a range of 0.5-0.7.

[0062] For example, when a grating structure is used as a coupling grating, its operating order is typically the first-order diffraction order. Since the coupling grating is used to extend the coupling of light out of the diffractive waveguide, its design must be comprehensively matched to the gradient of the propagating optical field within the diffractive waveguide and the requirement for uniform light output across the entire field of view. Therefore, the diffraction efficiency of the operating order needs to be controlled within a reasonably low range, typically 0.1-0.2. Typically, refer to... Figure 2 The diffractive waveguide 100 also includes a coupling grating 120, the operating order of which is -1st order transmission order (T). -1 The design diffraction efficiency is set to a range of 0.1-0.2.

[0063] In practice, the design diffraction efficiency of the 0th reflection order of the coupling grating is typically between 0.8 and 0.9. Specifically, the diffracted light of the 0th reflection order generated by the coupling grating continues to propagate along the total internal reflection path within the waveguide, forming the basis for pupil replication and expansion. By continuously replicating and extending the pupil to the complete exit pupil region, a large-size uniform eyebox is achieved. Therefore, the diffraction efficiency of the 0th reflection order of the coupling grating needs to be controlled within a reasonably high range, typically between 0.8 and 0.9.

[0064] In practice, the design diffraction efficiency of the -1st reflection order of the coupled grating can be in the range of 0.02-0.05.

[0065] Specifically, the diffraction of light by a grating structure simultaneously generates transmission and reflection orders. When one type of diffraction order is selected as the working order for achieving diffraction waveguide coupling imaging, the diffracted light corresponding to the diffraction order in the other propagation direction will exit the diffraction waveguide away from the human eye, escaping outward and forming light leakage, causing the displayed image information to leak outward. When the coupling grating operates at the transmission order, the leakage order is usually the first-order reflection order. To avoid information leakage, the diffraction efficiency of the leakage order usually needs to be strictly suppressed to an extremely low level, typically 0.02-0.05. Typically, refer to... Figure 2 The main leakage order of the coupling grating 120 is the -1st order reflection order (R -1 The design diffraction efficiency is set to a range of 0.02-0.05.

[0066] In practice, this application can also design a grating structure to be used as a pupil-expanding grating for a diffractive waveguide. When the grating structure is used as a pupil-expanding grating, the design diffraction efficiency for the +1st reflection order ranges from 0.05 to 0.15, and the design diffraction efficiency for the 0th reflection order ranges from 0.85 to 0.95.

[0067] Specifically, the pupil-expanding grating, on the one hand, deflects light towards the coupling region through the +1st order reflection. This requires a comprehensive design that considers both the gradient of the propagating light field within the diffractive waveguide and the uniformity of light output across the entire field of view. Therefore, the diffraction efficiency of the +1st order reflection of the pupil-expanding grating is controlled within a reasonable low range, typically 0.05-0.15. On the other hand, it uses the 0th order reflection in conjunction with the coupling grating to replicate and expand the pupil in one direction, achieving pupil replication and expansion in the other direction. By continuously replicating and extending the pupil to the complete exit pupil region, a large-size uniform eyebox is achieved. Therefore, the diffraction efficiency of the 0th order reflection of the pupil-expanding grating needs to be controlled within a reasonable high range, typically 0.85-0.95.

[0068] As clearly demonstrated in the foregoing embodiments, to achieve excellent imaging performance in a diffractive waveguide, the diffraction efficiency of each specific diffraction order of the coupling element must be controlled within its corresponding value range. Therefore, when iteratively adjusting the input parameters of the first mapping relationship, the diffraction efficiency of these diffraction orders must be limited to their respective suitable ranges as optimization constraints.

[0069] It should be noted that the criteria for judging the quality of various performance parameters of diffractive waveguides are not uniform, and the numerical values ​​of different performance parameters show different correlations with performance quality: for example, for efficiency and brightness uniformity, higher values ​​indicate better performance of the diffractive waveguide; while for color uniformity, lower values ​​indicate better performance. Therefore, when comprehensively processing multiple performance parameters of diffractive waveguides as intermediate outputs, it is necessary to perform normalization and reverse adaptation processing on different types of evaluation indicators, unifying positive and negative indicators to the same evaluation dimension, eliminating calculation biases caused by opposite parameter value trends, and then constructing a unified comprehensive evaluation function to conduct overall performance evaluation.

[0070] Specifically, when unifying to the reverse index evaluation dimension, the design diffraction efficiency combination that minimizes the overall output parameters of the first mapping relationship is obtained. When unifying to the positive index evaluation dimension, the design diffraction efficiency combination that maximizes the overall output parameters of the first mapping relationship is obtained.

[0071] In practice, the design and fabrication method of the grating structure provided in this application, when obtaining the design diffraction efficiency combination that minimizes or maximizes the overall output parameters of the first mapping relationship, further includes: weighted fusion of the performance parameters or their deformations of the diffraction waveguide including the grating structure to construct a comprehensive performance evaluation function, and using the minimum or maximum value of the comprehensive performance evaluation function as the optimization target.

[0072] Specifically, in this embodiment, based on the influence weights of each performance parameter on the imaging quality, mass production practicality, and display effect of the diffractive waveguide, the preprocessed performance parameters are weighted and fused to balance the optimization priorities of each performance, thus constructing a comprehensive performance evaluation function that can fully characterize the overall optical quality of the diffractive waveguide. Finally, the extreme value of this comprehensive performance evaluation function is used as the core optimization objective. For evaluation functions where higher values ​​after unified transformation indicate better overall performance, the maximum value is used as the iterative optimization objective; for evaluation functions where lower values ​​indicate better overall performance, the minimum value is used as the iterative optimization objective. Relying on a quantitative evaluation system, the global optimal iterative solution for the grating diffraction efficiency combination is achieved, avoiding the overall performance imbalance caused by optimizing a single performance parameter, and realizing the synergistic optimization of multiple performance aspects of the diffractive waveguide.

[0073] Furthermore, when directly mapping grating topography parameters to multi-order diffraction efficiency combinations via the second mapping relationship, it can be implemented by referring to... Figure 3 Step S4 specifically includes:

[0074] S41, obtain the initial design topography parameters of the grating structure as the current design topography parameters;

[0075] S42, based on the second mapping relationship, obtain the current predicted diffraction efficiency combination corresponding to the current design morphology parameters;

[0076] S43, compare the current predicted diffraction efficiency combination with the target diffraction efficiency combination;

[0077] S44, when the overall deviation between the two sets of data is less than the preset accuracy threshold, it is determined that the current predicted diffraction efficiency combination matches the target diffraction efficiency combination, and the current design morphology parameters are determined as the target morphology parameters.

[0078] S45, when the overall deviation between the two sets of data is greater than or equal to the preset accuracy threshold, the current design morphology parameters are iteratively corrected, the adjusted design morphology parameters are updated to the current design morphology parameters, and the process returns to S42.

[0079] Specifically, the initial design topography parameters of the grating structure are obtained and used as the current design topography parameters. Based on a preset second mapping relationship, the current predicted diffraction efficiency combination corresponding to the current design topography parameters is obtained. The deviation between the current predicted diffraction efficiency combination and the pre-solved target diffraction efficiency combination is compared, and the overall deviation value of the two sets of data is calculated. If the overall deviation value is less than a preset accuracy threshold, it is determined that the current predicted diffraction efficiency combination and the target diffraction efficiency combination meet the matching requirements, and the corresponding current design topography parameter is determined as the final target topography parameter of the grating structure. If the overall deviation value is greater than or equal to the preset accuracy threshold, the current design topography parameters are iteratively corrected and optimized, and the predicted diffraction efficiency combination corresponding to the updated topography parameters is obtained again based on the second mapping relationship. The above comparison and iterative correction process is repeated until the accuracy convergence condition is met. This accuracy convergence condition is that there exists a set of design topography parameters for which the overall deviation value between the current predicted diffraction efficiency combination and the target diffraction efficiency combination is less than the preset accuracy threshold.

[0080] The grating structure can be a straight-tooth structure, an inclined structure, a blazed structure, or an irregular structure, etc. The morphological parameters of the grating structure include the profile shape, grating depth, and grating duty cycle.

[0081] In one embodiment, the diffraction efficiency combination of multiple diffraction orders of the grating structure, including the diffraction efficiencies of the 0th, 1st, and 2nd order diffraction orders, is used as an example for illustration. The initial design topography parameters (the first set of design topography parameters) are obtained as the current design topography parameters. Based on the second mapping relationship, the current predicted diffraction efficiency combination (the first set of predicted diffraction efficiency combinations) corresponding to the first set of design topography parameters is obtained. Obtain the target diffraction efficiency combination obtained in the previous step. ,in, Combine the first group of predicted diffraction efficiencies. Combined with target diffraction efficiency The overall deviation value is obtained by comparison: Then, the overall deviation value of the two sets of data is... Compared with the preset accuracy threshold If a comparison is made, If the predicted diffraction efficiency combination of the first group matches the target diffraction efficiency combination, then the designed topography parameters of the first group are determined as the target topography parameters. Then, the first set of design morphology parameters is iteratively corrected to obtain the second set of design morphology parameters. The second set of design morphology parameters is used as the current design morphology parameters. Based on the second mapping relationship, the current predicted diffraction efficiency combination (the second set of predicted diffraction efficiency combination) corresponding to the second set of design morphology parameters is obtained. Combine the second group of predicted diffraction efficiencies Combined with target diffraction efficiency The overall deviation value is obtained by comparison: Then, the overall deviation value of the two sets of data is... Compared with the preset accuracy threshold If a comparison is made, If the predicted diffraction efficiency combination of the second group matches the target diffraction efficiency combination, then the designed topography parameters of the second group are determined as the target topography parameters. Then, the second set of design morphology parameters is iteratively corrected to obtain the third set of design morphology parameters. The third set of design morphology parameters is used as the current design morphology parameters. The above comparison and iterative correction process is repeated until the accuracy convergence condition is met.

[0082] Among them, the requirements for matching accuracy are different, and the preset accuracy threshold is... The values ​​can vary. Usually... The value is 0.01. When the value is 0.01, if it is impossible to find a set of design morphology parameters whose overall deviation between the current predicted diffraction efficiency combination and the target diffraction efficiency combination is less than 0.01, then... The value is adjusted to 0.02. If it is still not possible to find a set of design morphology parameters whose overall deviation between the current predicted diffraction efficiency combination and the target diffraction efficiency combination is less than 0.02, it indicates that there is over-optimization when determining the target diffraction efficiency combination based on the first mapping relationship. In this case, the target waveguide performance of the diffraction waveguide can be relaxed, and a new target diffraction efficiency combination can be determined again based on the first mapping relationship.

[0083] The design method for the grating structure provided in this application has been described in detail above through multiple embodiments. Based on this, the grating structure obtained by this design method can be fabricated through various process schemes, which are specifically described below.

[0084] In practice, the grating structure designed in this application can be a straight-tooth structure, a tilted structure, a blazed structure, or an irregular structure, etc. When the grating structure is a tilted grating, the sidewalls of the grating structure have varying tilt angles. This variation can be continuous or a stepped, segmented variation. For example, if the sidewalls of the grating structure have continuously varying tilt angles, the sidewall profile can be represented as a continuously varying curve function, such as... The sidewalls of the grating structure have stepped, segmented tilt angles, and the sidewall profile can be represented as a piecewise linear function.

[0085] The following describes the fabrication process using a grating structure that is a tilted grating with varying tilt angles on the sidewalls.

[0086] In one embodiment, step S5 specifically includes:

[0087] S51, determine the etching angle variation parameters based on the target morphology parameters;

[0088] S52, an AC bias voltage is applied in the vertical direction of the substrate to be etched. By controlling the phase difference of the AC bias voltage in real time, the etching direction of the etching ion beam is dynamically changed to match the etching angle change parameters.

[0089] S53 uses an angle-adjustable etching ion beam to etch the substrate, forming a grating structure with varying tilt angles on the sidewalls to match the target morphology parameters.

[0090] Specifically, in this embodiment, the etching angle variation parameters are first determined based on the target morphology parameters of the grating structure. These parameters include the grating depth, grating duty cycle, and the distribution of sidewall tilt angles along the depth direction. The etching angle variation parameters characterize the relationship between the incident angle of the etching ion beam and the etching process and depth. During etching, an AC bias voltage is continuously applied in the vertical direction of the substrate to be etched. By real-time adjustment of the phase difference of the AC bias voltage, the trajectory and incident etching direction of the etching ion beam are dynamically changed through electric field control, ensuring that the ion beam matches the etching angle variation parameters in real time. Subsequently, anisotropic etching is performed on the substrate using an etching ion beam with a dynamically adjustable incident angle. As etching continues and material is continuously removed, the incident angle of the ion beam is continuously updated, allowing the etching direction to be dynamically adjusted according to the sidewall forming requirements. Finally, a tilted grating structure with varying sidewall tilt angles is etched onto the substrate. The sidewall tilt angles of the grating can be continuously varied or steppedly varied, so that the morphological features such as the sidewall contour and tilt angle distribution of the formed grating are basically consistent with the set target morphological parameters.

[0091] The substrate to be etched can be a glass substrate or a resin substrate, or other conventional materials that are transparent to visible light, such as those with a grating material layer formed on their surface. The grating material layer can be an inorganic material such as titanium oxide or niobium oxide, or an organic or organic-inorganic hybrid imprinting material. The substrate to be etched can also be a material that is transparent to visible light and has a higher refractive index than glass, such as lithium niobate, lithium tantalate, or silicon carbide.

[0092] It should be noted that in the etching process of the above embodiments, the tilted incident effect of the etching ion beam is mainly achieved by controlling the phase difference of the AC bias voltage. Specifically, by controlling the phase difference generated by the AC bias voltage applied in the vertical direction, the etching ion beam can obtain lateral kinetic energy, thereby incident at a specific tilt angle onto the surface of the substrate to be etched, achieving the etching of the tilted sidewalls. The incident tilt angle of the ion beam is linearly related to the phase difference of the AC bias voltage. However, limited by the voltage control range, the phase difference of the AC bias voltage has an upper limit to its adjustable range. Therefore, the incident tilt angle achievable by the ion beam also has a fixed adjustable range and cannot be increased or decreased indefinitely. Based on this process characteristic, when the etching tilt angle range corresponding to the target morphology parameters of the grating structure falls within the ion beam tilt angle range where the AC bias phase difference is adjustable, the target etching tilt angle change requirement can be dynamically matched by real-time control of the AC bias phase difference, accurately fabricating a variable tilt angle grating structure that meets the target morphology. Conversely, when the etching tilt angle range required for the grating target morphology parameters exceeds the maximum and minimum tilt angle range achievable by the AC bias phase difference, relying solely on a single AC bias phase control method cannot cover all target tilt angle requirements, making it difficult to accurately achieve the etching fabrication of over-range tilt angle grating structures.

[0093] To address the aforementioned technical limitations and expand the grating morphology fabrication range of this method, it is feasible to further include, when the tilt angle of the sidewall of the grating structure is greater than a preset threshold, the design and fabrication method of the grating structure also includes: applying a DC bias voltage to the side of the substrate to be etched, controlling the phase difference of the AC bias voltage and / or the bias value of the DC bias voltage in real time, and dynamically changing the etching direction of the etching ion beam to match the etching angle variation parameters; the preset threshold is the maximum etching angle that can be achieved by controlling the phase difference of the AC bias voltage.

[0094] The preset threshold is the upper limit of the adjustable range of the phase difference based on the AC bias voltage, which determines the upper limit of the adjustable range of the incident tilt angle that the ion beam can achieve. This embodiment adds lateral bias voltage control, applying an additional DC bias voltage to the side of the substrate to be etched. During the etching process, the phase difference of the AC bias voltage and / or the bias value of the lateral DC bias voltage are controlled in real time. By coordinating the control of the ion beam base tilt angle with AC bias voltage and the control of the lateral offset of the ion beam with DC bias voltage, the etching direction of the ion beam is further dynamically broadened and precisely adjusted, so that the incident angle of the ion beam can be fully matched with the etching angle change parameters under the large tilt angle requirement. This enables precise etching processing of large tilt angle and variable tilt angle grating structures beyond the threshold, effectively making up for the tilt angle range limitation of single AC bias voltage control.

[0095] Of course, in another alternative embodiment, the control can also be achieved solely by relying on the lateral DC bias. By adjusting the bias value of the DC bias in real time, the lateral kinetic energy and incident direction of the etching ion beam can be changed independently, dynamically matching different target etching tilt angle changes. Without the need for AC bias phase control, it is still possible to etch and prepare a variable tilt angle grating structure that meets the target morphology parameters, further improving the process flexibility and adaptability of this preparation method.

[0096] Specifically, in this embodiment, step S5 includes:

[0097] S'51, Determine the etching angle variation parameters based on the target morphology parameters;

[0098] S'52, apply a DC bias voltage to the side of the substrate to be etched, and dynamically change the etching direction of the etching ion beam to match the etching angle change parameters by controlling the DC bias voltage value in real time.

[0099] S'53 uses an angle-adjustable etching ion beam to etch the substrate, forming a grating structure with varying tilt angles on the sidewalls to match the target morphology parameters.

[0100] Furthermore, the grating fabrication method of this application can also be combined with a zoned temperature control process to achieve differentiated fabrication of morphological parameters in different regions of the grating, thus adapting to differentiated grating processing requirements.

[0101] In practice, the design and fabrication method of the grating structure further includes: dividing the substrate to be etched into regions based on the etching depth and / or grating duty cycle of each region corresponding to the target grating morphology parameters, and determining the etching temperature corresponding to each region; during the ion beam etching process, independently controlling the temperature of different regions of the substrate to be etched, so that each region of the substrate to be etched maintains its corresponding etching temperature; and through differentiated temperature control of each region, forming differentiated etching depths and / or grating duty cycles in different regions of the substrate to be etched, matching the target morphology parameters.

[0102] It is understandable that since the etching rate, sidewall forming accuracy, and grating duty cycle are all highly correlated with the etching temperature, differentiated isothermal control in each region can create stable differences in ion etching efficiency and material removal rate in different areas. Based on the dynamic angle control of the ion beam, differentiated auxiliary control of the temperature in each region can simultaneously and precisely control the final etching depth and grating duty cycle of each region. This effectively solves the problem that a single etching process cannot simultaneously handle the differentiated morphology processing of multiple regions, ultimately enabling the overall structural parameters of the formed grating to match the target morphology parameters, significantly improving the fabrication accuracy and structural consistency of complex variable tilt gratings.

[0103] In summary, this application creatively constructs a dual mapping relationship between "diffraction efficiency and waveguide performance" and "diffraction efficiency and grating morphology." It conducts multi-objective iterative optimization around core indicators such as the efficiency and uniformity of the diffractive waveguide, outputting the suboptimal diffraction efficiency ratio and matching micro-morphological parameters of the grating structure across multiple diffraction orders. Compared to traditional forward design approaches, this application enables precise reverse engineering from macroscopic optical requirements to microscopic grating dimensions and contour parameters, overcoming the limitations of traditional design methods and the difficulty in simultaneously considering core parameters such as the efficiency and uniformity of the diffractive waveguide. This significantly improves the display quality and optical stability of the waveguide. Furthermore, this application effectively expands the design freedom of the grating structure, reduces the difficulty of fabrication processes, and improves the speed of automated simulation design, providing a complete technical solution for the research and mass production of high-imaging-quality diffractive waveguides. On the other hand, a flexible and adaptable fabrication method is provided for grating structures with varying tilt angles on the sidewalls. Based on the dynamic angle control of the ion beam, the fabrication accuracy and structural consistency of complex variable tilt angle gratings are significantly improved by differential auxiliary control of the partition temperature.

[0104] The specific embodiments described above do not constitute a limitation on the scope of protection of this application. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A method for designing and fabricating a grating structure, characterized in that, include: A first mapping relationship is constructed, wherein the first mapping relationship takes the design diffraction efficiency combination of multiple diffraction orders of the grating structure as the input parameter, and the output parameter takes the performance parameters of the diffraction waveguide including the grating structure as the intermediate output, wherein the performance parameters of the diffraction waveguide include at least one of efficiency, brightness uniformity and color uniformity. The input parameters of the first mapping relationship are iteratively modulated to obtain a design diffraction efficiency combination that minimizes or maximizes the overall output parameters of the first mapping relationship, and the design diffraction efficiency combination is determined as the target diffraction efficiency combination. A second mapping relationship is constructed, which takes the design morphology parameters of the grating structure as input parameters and the predicted diffraction efficiency combination of the multi-order diffraction orders of the grating structure as output parameters. The input parameters of the second mapping relationship are iteratively modulated to obtain the design morphology parameters that make the output parameters of the second mapping relationship match the target diffraction efficiency combination as the target morphology parameters; The grating structure is prepared according to the target morphology parameters.

2. The design and fabrication method of the grating structure according to claim 1, characterized in that, The grating structure serves as the coupling grating for the diffractive waveguide, the operating order of the coupling grating is +1st transmission order, and the designed diffraction efficiency of the +1st transmission order ranges from 0.5 to 0.7; and / or, The grating structure is used as the coupling grating of the diffractive waveguide. The operating order of the coupling grating is the -1st transmission order, and the design diffraction efficiency of the -1st transmission order ranges from 0.1 to 0.

2.

3. The design and fabrication method of the grating structure according to claim 2, characterized in that, The design diffraction efficiency of the -1st order reflection of the coupled grating ranges from 0.02 to 0.

05.

4. The design and fabrication method of the grating structure according to claim 1, characterized in that, The method further includes: The performance parameters or their deformations of the diffractive waveguide, including the grating structure, are weighted and fused to construct a comprehensive performance evaluation function, with the minimum or maximum value of the comprehensive performance evaluation function as the optimization objective.

5. The design and fabrication method of the grating structure according to claim 1, characterized in that, The iterative modulation of the input parameters of the second mapping relationship to obtain the design morphology parameters as the target morphology parameters, which make the output parameters of the second mapping relationship match the target diffraction efficiency combination, includes: The initial design topography parameters of the grating structure are obtained as the current design topography parameters; Based on the second mapping relationship, the current predicted diffraction efficiency combination corresponding to the current design morphology parameters is obtained; Compare the current predicted diffraction efficiency combination with the target diffraction efficiency combination; When the overall deviation between the two sets of data is less than the preset accuracy threshold, it is determined that the current predicted diffraction efficiency combination matches the target diffraction efficiency combination, and the current design morphology parameter is determined as the target morphology parameter. When the overall deviation between the two sets of data is greater than or equal to the preset accuracy threshold, the current design morphology parameters are iteratively corrected, the adjusted design morphology parameters are updated to the current design morphology parameters, and the step of obtaining the current predicted diffraction efficiency combination corresponding to the current design morphology parameters based on the second mapping relationship is returned.

6. The design and fabrication method of the grating structure according to claim 1, characterized in that, The grating structure is a tilted grating, and the sidewalls of the grating structure have varying tilt angles.

7. The design and fabrication method of the grating structure according to claim 6, characterized in that, The step of preparing the grating structure according to the target morphology parameters includes: Determine the etching angle variation parameters based on the target morphology parameters; An AC bias voltage is applied in the vertical direction of the substrate to be etched. By controlling the phase difference of the AC bias voltage in real time, the etching direction of the etching ion beam is dynamically changed to match the etching angle change parameters. The substrate to be etched is etched using an angle-adjustable etching ion beam to form a grating structure with varying tilt angles on the sidewalls, in order to match the target morphology parameters.

8. The design and fabrication method of the grating structure according to claim 7, characterized in that, When the tilt angle of the sidewall of the grating structure is greater than a preset threshold, the method further includes: A DC bias voltage is applied to the side of the substrate to be etched, and the phase difference of the AC bias voltage and / or the bias value of the DC bias voltage are controlled in real time to dynamically change the etching direction of the etching ion beam to match the etching angle change parameters. The preset threshold is the maximum etching angle that can be achieved by controlling the phase difference of the AC bias voltage.

9. The design and fabrication method of the grating structure according to claim 6, characterized in that, The step of preparing the grating structure according to the target morphology parameters includes: Determine the etching angle variation parameters based on the target morphology parameters; A DC bias voltage is applied to the side of the substrate to be etched. By controlling the bias voltage value of the DC bias voltage in real time, the etching direction of the etching ion beam is dynamically changed to match the etching angle change parameters. The substrate to be etched is etched using an angle-adjustable etching ion beam to form a grating structure with varying tilt angles on the sidewalls, in order to match the target morphology parameters.

10. The design and fabrication method of the grating structure according to claim 1, characterized in that, The method further includes: Based on the etching depth and / or grating duty cycle of each region corresponding to the target morphology parameters, the substrate to be etched is divided into regions, and the etching temperature corresponding to each region is determined. During the ion beam etching process, the temperature of different regions of the substrate to be etched is independently controlled so that each region of the substrate to be etched maintains its corresponding etching temperature. Through the differentiated temperature control of each region, the different regions of the substrate to be etched form differentiated etching depths and / or grating duty cycles, matching the target morphology parameters.

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