Method for rapidly measuring structural parameters of liquid crystal polarization grating

Abstract

The invention relates to a method for rapidly measuring structural parameters of a liquid crystal polarization grating, and belongs to the technical field of photoelectric measurement. The method comprises the following steps: firstly, acquiring a transverse period parameter of a liquid crystal polarization grating to be measured, and then measuring a diffraction efficiency matrix of the grating by using different laser normal incidence gratings with known wavelengths; randomly initializing grating thickness and longitudinal period parameters, and inputting the parameters into the RCWA model to calculate a diffraction efficiency matrix of the grating; taking the deviation between the diffraction efficiency matrix obtained by the RCWA model and the diffraction efficiency matrix obtained by measurement as a fitness function, and judging whether the result of the fitness function meets a threshold condition or not; and if the conditions are met, outputting the current thickness and longitudinal period parameters, otherwise, iterating a group of new thickness and longitudinal period parameters through the genetic algorithm, and judging whether the threshold conditions are met or not again. Through combination of the RCWA method and the genetic algorithm, grating thickness and longitudinal period parameters can be obtained at the same time, experimental measurement steps are effectively reduced, and measurement efficiency and precision are high.

Description

Technical Field

[0001] The present invention belongs to the technical field of optoelectronic measurement, and relates to a method for rapidly determining the structural parameters of a liquid crystal polarization grating. Background Art

[0002] A liquid crystal polarization grating is a diffractive optical device based on the birefringence effect of liquid crystal molecules, which realizes precise control of the polarization state of incident light through a periodically arranged liquid crystal molecular structure. Due to its characteristics of compact volume, fast response speed, low energy consumption, and dynamic modulation, liquid crystal polarization gratings exhibit extensive application potential in the fields of optical communication, lidar (LiDAR), augmented reality (AR) / virtual reality (VR) display, optical sensing, etc. For example, in AR devices, liquid crystal polarization gratings can be used to achieve high-resolution waveguide displays; in laser communication systems, they can optimize the diffraction efficiency and polarization purity of light beams, improving signal transmission quality.

[0003] Different structural parameters of liquid crystal polarization gratings (mainly including thickness, transverse period, and longitudinal period) have different diffraction output performances. Among them, the transverse period determines the diffraction angle and bandwidth, the longitudinal period affects the cumulative effect of the birefringence effect, and the thickness is directly related to the optical path difference and the wavelength dependence of the diffraction efficiency. Therefore, precise measurement and control of the parameters of liquid crystal polarization gratings are crucial. Currently, there are significant limitations in the measurement methods for the structural parameters of liquid crystal polarization gratings.

[0004] For example, for the measurement of the thickness of a liquid crystal polarization grating, existing methods are mainly divided into two categories: contact type and non-contact type. Contact methods such as the mechanical probe method obtain thickness information by scanning the grating surface with a probe. During the measurement process, the grating film layer needs to be damaged, which is likely to cause scratches or indentations on the soft liquid crystal material and damage the sample structure. Non-contact methods such as white light interferometry or ellipsometer measurement can avoid physical damage, but they require complex optical path calibration and have measurement errors for multi-layer structures or high refractive index materials. In addition, the optical interference method has extremely high requirements for the flatness of the grating surface, which is difficult to meet in practical applications.

[0005] For the measurement of the longitudinal period of a liquid crystal polarization grating, it is usually necessary to perform inversion by combining the grating efficiency curve with a theoretical model. For example, by rotating the grating to change the incident angle, measuring the diffraction efficiency at the same thickness and different angles, and then comparing with the theoretical simulation results to fit the longitudinal period parameters. However, this method requires multiple adjustments of the optical path and data acquisition, which is extremely time-consuming, and is sensitive to the experimental environment (such as temperature, humidity, and vibration), with poor stability. In addition, existing inversion algorithms (such as the least squares method) are prone to falling into local optimal solutions, resulting in parameter estimation deviations.

[0006] In summary, the existing technologies rely on multiple independent instruments to measure different parameters separately, and cannot measure all the parameters of the liquid crystal polarization grating at one time, resulting in redundant processes and high equipment costs. For example, the lateral period needs to be observed under a microscope, the thickness needs to be measured by an interferometer, and the longitudinal period needs rotational grating experiments and numerical fitting. This segmented measurement is not only inefficient but also may lead to inaccurate parameter matching due to calibration errors between devices. In addition, the destructive nature of some methods (such as the mechanical probe method) limits their application in mass production quality inspection.

[0007] In recent years, researchers have tried to optimize parameter measurement by combining numerical simulation and experiments. For example, the rigorous coupled wave analysis (RCWA) is used to simulate the diffraction characteristics of the grating, and then compared with experimental data to invert the structural parameters. However, traditional RCWA inversion methods usually only optimize a single parameter and rely on artificially setting initial values, which is prone to convergence difficulties due to parameter coupling problems.

[0008] Therefore, there is an urgent need to develop a fast, non-destructive, and high-precision comprehensive measurement method to simplify the determination of parameters in the design and development process of liquid crystal polarization gratings and meet the R & D requirements of high-integration optoelectronic devices. Summary of the Invention

[0009] In view of this, the purpose of the present invention is to provide a method for quickly determining the structural parameters of a liquid crystal polarization grating. By combining the rigorous coupled wave analysis (RCWA) and the genetic algorithm, the structural parameters of the liquid crystal polarization grating are iteratively optimized, so as to quickly, simply, and non-destructively measure the thickness and period parameters of the liquid crystal polarization grating at the same time.

[0010] To achieve the above purpose, the present invention provides the following technical solutions:

[0011] A method for quickly determining the structural parameters of a liquid crystal polarization grating, comprising:

[0012] S1. Obtain the lateral period parameter of the liquid crystal polarization grating to be measured;

[0013] S2. Use lasers with different known wavelengths to perpendicularly irradiate the liquid crystal polarization grating to be measured, and measure the diffraction efficiency matrix of the liquid crystal polarization grating to be measured;

[0014] S3. Establish an RCWA model and a genetic algorithm model; randomly initialize the thickness and longitudinal period of the liquid crystal polarization grating to be measured;

[0015] S4. Input the parameters of the horizontal period, thickness, vertical period, and the laser wavelength normally incident on the liquid crystal polarization grating to be measured into the established RCWA model, and calculate the diffraction efficiency matrix of the liquid crystal polarization grating to be measured through the RCWA model;

[0016] S5. Calculate the deviation between the diffraction efficiency matrix obtained from the RCWA model and the measured diffraction efficiency matrix. Take this deviation as the fitness function, and determine whether the result of the fitness function meets the threshold condition;

[0017] S6. If it meets the conditions, output the thickness and vertical period parameters in the current RCWA model as the optimal structure parameters of the liquid crystal polarization grating to be measured;

[0018] If it does not meet the conditions, return the thickness and vertical period parameters in the current RCWA model to the established genetic algorithm model. Obtain new thickness and vertical period parameters through genetic algorithm iteration and input them into the RCWA model. Calculate the diffraction efficiency matrix of the liquid crystal polarization grating to be measured again, and calculate the fitness function between the diffraction efficiency matrix obtained from the RCWA model and the measured diffraction efficiency matrix, and determine whether the result of the fitness function meets the threshold condition;

[0019] S7. Repeat the above process of genetic algorithm iteration, RCWA model calculating the diffraction efficiency matrix, calculating the fitness function, and determining whether the result of the fitness function meets the threshold condition, that is, repeat the operations in steps S4 - S6 until the fitness function calculated from the diffraction efficiency matrix output based on the thickness and vertical period parameters obtained through genetic algorithm iteration by the RCWA model can meet the threshold condition, that is, obtain the optimal structure parameters of the liquid crystal polarization grating to be measured.

[0020] Furthermore, in step S1, the horizontal period of the liquid crystal polarization grating to be measured can be obtained through an exposure system or a polarization microscope.

[0021] Furthermore, in step S2, red, green, and blue lasers can be used to normally incident on the liquid crystal polarization grating to be measured respectively, and measure the diffraction efficiency matrix of the liquid crystal polarization grating to be measured.

[0022] Specifically, measure the diffraction efficiency matrices of the 0, +1, and -1 orders of the liquid crystal polarization grating to be measured, expressed as:

[0023]

[0024] where η B,-1 、η B,0 、η B,+1 respectively represent the diffraction efficiencies of the -1, 0, and +1 orders measured when the blue laser is normally incident on the liquid crystal polarization grating to be measured; η G,-1 、η G,0 、ηG,+1 respectively represent the diffraction efficiencies of the -1st, 0th, and +1st orders measured when green light is normally incident on the liquid crystal polarization grating to be measured; η R,-1 , η R,0 , η R,+1 respectively represent the diffraction efficiencies of the -1st, 0th, and +1st orders measured when red light is normally incident on the liquid crystal polarization grating to be measured.

[0025] Furthermore, in step S5, the fitness function is expressed as:

[0026] F η = max|η iB ′ - η B | + max|η iG ′ - η G | + max|η iR ′ - η R |

[0027] In the formula, η iB ′ is the diffraction efficiency matrix of the liquid crystal polarization grating calculated based on the parameters obtained by the RCWA model through the i-th iteration of the genetic algorithm when blue light is normally incident, and η B is the diffraction efficiency matrix of the liquid crystal polarization grating measured when blue light is normally incident; η iG ′ is the diffraction efficiency matrix of the liquid crystal polarization grating calculated based on the parameters obtained by the RCWA model through the i-th iteration of the genetic algorithm when green light is normally incident, and η G is the diffraction efficiency matrix of the liquid crystal polarization grating measured when green light is normally incident; η iR ′ is the diffraction efficiency matrix of the liquid crystal polarization grating calculated based on the parameters obtained by the RCWA model through the i-th iteration of the genetic algorithm when red light is normally incident, and η R is the diffraction efficiency matrix of the liquid crystal polarization grating measured when red light is normally incident.

[0028] The beneficial effects of the present invention are as follows:

[0029] (1) The present invention proposes to combine the RCWA and the genetic algorithm to determine the structural parameters of the liquid crystal polarization grating. The genetic algorithm is used to generate the thickness and longitudinal period, and the RCWA model calculates the diffraction efficiency matrix of the liquid crystal polarization grating based on the transverse period and the generated thickness and longitudinal period, and calculates the fitness function. By judging whether the fitness function meets the threshold condition, it is determined whether the obtained thickness and longitudinal period parameters meet the design requirements. The present invention utilizes the global search ability of the genetic algorithm, can simultaneously optimize the grating thickness and longitudinal period parameters, avoids the cumbersome processes of multi-device switching and multiple experiments, and significantly improves the R & D efficiency; in addition, through the fitness function threshold judgment and the genetic algorithm iterative traversal optimization, the present invention can obtain the optimal grating structure parameters that meet the design requirements.

[0030] (2) The method proposed by the present invention only needs to calculate the diffraction efficiency of the liquid crystal polarization grating, without physical contact or complex optical path adjustment, avoiding the damage risk to the grating to be measured by the mechanical probe method or the rotating grating method, and is non-destructive.

[0031] (3) The method proposed by the present invention is also applicable to the layer-by-layer determination of the multi-layer structure parameters of the liquid crystal polarization grating, which can greatly simplify the determination of parameters in the design and development process of the liquid crystal polarization grating.

[0032] In summary, the present invention not only overcomes the defects of low measurement efficiency, strong destructiveness, insufficient accuracy, etc. of the prior art, but also provides reliable technical support for the intelligent design and mass production quality inspection of liquid crystal gratings, and has significant engineering application value and market prospects.

[0033] Other advantages, objectives and features of the present invention will be described to some extent in the subsequent specification, and to some extent, will be obvious to those skilled in the art based on the study of the following text, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following specification. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in detail preferably with reference to the accompanying drawings, where:

[0035] Figure 1 is a schematic flow chart of a method for quickly determining the structure parameters of a liquid crystal polarization grating provided by an embodiment of the present invention;

[0036] Figure 2 is a schematic diagram of the measurement principle of the diffraction efficiency matrix of the liquid crystal polarization grating. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] The following specific examples illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the drawings provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and the features in the embodiments can be combined with each other without conflict.

[0038] Among them, the accompanying drawings are only for illustrative purposes, showing only schematic diagrams rather than physical diagrams, and should not be construed as a limitation on the present invention; for better illustration of the embodiments of the present invention, some components in the accompanying drawings will be omitted, enlarged or reduced, which do not represent the dimensions of the actual product; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the accompanying drawings may be omitted.

[0039] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "rear", etc. indicating the orientation or positional relationship, they are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the accompanying drawings are only for illustrative purposes and should not be construed as a limitation on the present invention. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0040] Embodiment 1

[0041] Aiming at the problems existing in the prior art, such as the need for multiple measuring instruments or devices, redundant and time-consuming measuring steps, some measuring methods being destructive to the liquid crystal polarization grating, difficult to measure certain specific parameters, and unable to measure all the parameters of a one-dimensional liquid crystal grating at one time, this embodiment provides a rapid determination method for the structural parameters of a liquid crystal polarization grating. This method uses the structural RCWA and genetic algorithm to obtain the thickness and period parameter values of the liquid crystal polarization grating, thereby reducing the experimental measurement steps and greatly simplifying the parameter determination in the design and development process of the liquid crystal polarization grating.

[0042] As Figure 1 shown, the rapid determination method for the structural parameters of the liquid crystal polarization grating provided in this embodiment includes:

[0043] The first step: First, determine the transverse period A of the liquid crystal polarization grating to be measured through an exposure system or a polarization microscope x .

[0044] The second step: Use a laser with a known wavelength to be incident perpendicularly on the liquid crystal polarization grating to be measured, and obtain the measured value of the diffraction efficiency of the grating to be measured. The measurement principle is as Figure 2 shown.

[0045] Among them, the diffraction efficiency of the liquid crystal polarization grating can be expressed as:

[0046]

[0047] Where, Δn is the birefringence difference of the liquid crystal polarization grating, S3 is the Stokes parameter of the incident light, d is the thickness of the liquid crystal polarization grating, λ is the wavelength of the incident light, η0 is the diffraction efficiency of the 0th order of the liquid crystal polarization grating, and η ±1 is the diffraction efficiency of the ±1st order of the liquid crystal polarization grating.

[0048] The diffraction efficiency of the liquid crystal polarization grating is directly related to the wavelength and thickness of the incident light. At a determined thickness d of the liquid crystal polarization grating, by measuring the diffraction efficiency of the liquid crystal polarization grating at different incident light wavelengths, it can provide a basis for measuring the thickness of the liquid crystal polarization grating.

[0049] Based on this, light with three wavelengths of red, green, and blue can be respectively incident perpendicularly on the liquid crystal polarization grating to be measured, and the measured diffraction efficiency matrices of its 0, ±1st orders are:

[0050]

[0051] Where, η B,-1 , η B,0 , η B,+1 respectively represent the diffraction efficiencies of the -1, 0, +1st orders measured when blue light is incident perpendicularly on the liquid crystal polarization grating to be measured; η G,-1 , η G,0 , η G,+1 respectively represent the diffraction efficiencies of the -1, 0, +1st orders measured when green light is incident perpendicularly on the liquid crystal polarization grating to be measured; η R,-1 , η R,0 , η R,+1 respectively represent the diffraction efficiencies of the -1, 0, +1st orders measured when red light is incident perpendicularly on the liquid crystal polarization grating to be measured.

[0052] Step 3: Establish an RCWA model and establish a genetic algorithm optimization method.

[0053] Randomly initialize the thickness and longitudinal period of the liquid crystal polarization grating to be measured, and set the parameter ranges: A ≤ d i ≤ B, C ≤ A yi ≤ D. Where, d i represents the thickness of the liquid crystal polarization grating to be measured in the i-th iteration of the genetic algorithm, and A and B are respectively the lower and upper limit values of the thickness; A yi represents the longitudinal period of the liquid crystal polarization grating to be measured in the i-th iteration of the genetic algorithm, and C and D are respectively the lower and upper limit values of the longitudinal period.

[0054] Among them, the RCWA model is a numerical algorithm widely used to simulate the interaction between electromagnetic waves and periodic optical structures. By inputting the transverse period A x , thickness d, and longitudinal period A y, such as the incident angle of the incident light and the wavelength of the incident light, to calculate the diffraction output efficiency of the liquid crystal polarization grating.

[0055] Step 4: Input the parameters d i and A yi into the RCWA model, and calculate the diffraction efficiency matrices η i ′ of the 0, ±1 order when red, green, and blue light are normally incident on the liquid crystal polarization grating to be measured. Among them, η′ is expressed as:

[0056]

[0057] Step 5: Use the evaluation function F η (η, η i ′) to evaluate the deviation between the diffraction efficiency matrix of the liquid crystal polarization grating to be measured calculated by the RCWA model based on the current thickness and longitudinal period parameters and the measurement results obtained in the second step. The specific calculation formula is as follows:

[0058] F η =max|η iB ′ - η B | + max|η iG ′ - η G | + max|η iR ′ - η R | (4)

[0059] In the formula, η iB ′ is the diffraction efficiency matrix calculated by the RCWA model based on the parameters obtained from the i-th iteration of the genetic algorithm under normal incidence of blue light, and η B is the diffraction efficiency matrix measured under normal incidence of blue light; η iG ′ is the diffraction efficiency matrix calculated by the RCWA model based on the parameters obtained from the i-th iteration of the genetic algorithm under normal incidence of green light, and η G is the diffraction efficiency matrix measured under normal incidence of green light; η iR ′ is the diffraction efficiency matrix calculated by the RCWA model based on the parameters obtained from the i-th iteration of the genetic algorithm under normal incidence of red light, and η R is the diffraction efficiency matrix measured under normal incidence of red light.

[0060] Step 6: Determine whether the result of the fitness function F η satisfies the threshold H condition. If the condition is satisfied, the genetic algorithm outputs the thickness d i and the longitudinal period A yi in the current RCWA model.

[0061] If the condition is not satisfied, the parameters d i and A yiReturning to the genetic algorithm, a new set of parameters is obtained through operations such as replication, crossover, and mutation; this new set of parameters is re-input into the RCWA model to calculate the diffraction efficiency matrix η of the liquid crystal polarization grating to be measured. i ′, calculate the result of the fitness function and determine whether the result of the fitness function meets the threshold condition.

[0062] Step 7: Repeat Steps 4 to 6 until the result of the fitness function meets the threshold condition, and then output the current thickness and longitudinal period parameter results in the RCWA model.

[0063] Embodiment 2

[0064] This embodiment is based on a specific example of measuring the structural parameters of a liquid crystal polarization grating to verify the excellent effects of the method described in the present invention, as follows:

[0065] Step 1: Set the structural parameters of a liquid crystal polarization grating to A x = 1μm, d = 1.42μm, A y = 2.0μm.

[0066] Step 2: Select three linearly polarized lights with different wavelengths as incident lights. The wavelengths of these three linearly polarized lights are 650nm, 532nm, and 457nm respectively. Take the theoretical diffraction results of the liquid crystal polarization grating under these three wavelengths of incident lights as the measured values of the diffraction efficiency matrix, and its theoretical values are:

[0067]

[0068] Step 3: Establish an RCWA model of the liquid crystal polarization grating and establish a genetic algorithm model. Randomly initialize the two parameters of thickness and longitudinal period. Set the range of thickness in the genetic algorithm to 1 - 3μm, and the range of longitudinal period to 1 - 3μm. During each iteration, the change amplitude of thickness and longitudinal period is 0.1μm.

[0069] Step 4: Input the parameters d i and A yi into the RCWA model, calculate the diffraction efficiency matrix η i ′ of the liquid crystal polarization grating under normal incidence of three linearly polarized lights with wavelengths of 650nm, 532nm, and 457nm, calculate the fitness function F η according to the diffraction efficiency matrix, and determine whether the fitness function F η meets the threshold H condition.

[0070] If it meets the condition, the genetic algorithm outputs the thickness d i and the longitudinal period A yi in the current RCWA model.

[0071] If not, the parameters d i and A yi in the current RCWA model are returned to the genetic algorithm. After operations such as replication, crossover, and mutation, a new set of parameters is obtained. This new set of parameters is re - input into the RCWA model to calculate the diffraction efficiency matrix η i ′ of the liquid - crystal polarization grating, calculate the result of the fitness function, and determine whether the result of the fitness function meets the threshold condition.

[0072] Among them, the threshold H is set to 0.0001.

[0073] Step 5: Repeat Step 4 until the fitness function meets the threshold condition, and output the current thickness and longitudinal period parameter results in the RCWA model.

[0074] The results output after the genetic - algorithm iteration are d = 1.40μm, A y = 2.01μm.

[0075] It can be seen that the result parameters obtained by using the method of the present invention are basically consistent with the theoretical values. The method of the present invention can simultaneously obtain the thickness and longitudinal period parameters of the grating structure, effectively reducing the experimental measurement steps, and having high efficiency and measurement accuracy.

[0076] In addition, according to the method proposed by the present invention, the layer - by - layer determination of the multi - layer structure of the liquid - crystal polarization grating can also be carried out to achieve the purpose of quickly measuring the multi - layer structure parameters.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the present technical solution, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A method for quickly measuring the structural parameters of a liquid crystal polarization grating, characterized in that, The method includes: Obtaining the transverse period parameter of the liquid crystal polarization grating to be measured; Using lasers with different known wavelengths to perpendicularly incident on the liquid crystal polarization grating to be measured, and measuring the diffraction efficiency matrix of the liquid crystal polarization grating to be measured; Establishing an RCWA model and a genetic algorithm model; randomly initializing the thickness and longitudinal period of the liquid crystal polarization grating to be measured; Inputting the transverse period, thickness, longitudinal period, and the laser wavelength parameter perpendicularly incident on the liquid crystal polarization grating to be measured into the established RCWA model, and calculating the diffraction efficiency matrix of the liquid crystal polarization grating to be measured through the RCWA model; Calculating the deviation between the diffraction efficiency matrix obtained by the RCWA model and the measured diffraction efficiency matrix, using this deviation as the fitness function, and determining whether the result of the fitness function meets the threshold condition; If it meets the condition, outputting the thickness and longitudinal period parameters in the current RCWA model as the optimal structure parameters of the liquid crystal polarization grating to be measured; If it does not meet the condition, returning the thickness and longitudinal period parameters in the current RCWA model to the established genetic algorithm model, obtaining new thickness and longitudinal period parameters through genetic algorithm iteration and inputting them into the RCWA model, calculating the diffraction efficiency matrix of the liquid crystal polarization grating to be measured again, and calculating the fitness function between the diffraction efficiency matrix obtained by the RCWA model and the measured diffraction efficiency matrix, and determining whether the result of the fitness function meets the threshold condition; Repeating the processes of the above genetic algorithm iteration, calculating the diffraction efficiency matrix by the RCWA model, calculating the fitness function, and determining whether the result of the fitness function meets the threshold condition until the fitness function calculated from the diffraction efficiency matrix output based on the thickness and longitudinal period parameters obtained by genetic algorithm iteration according to the RCWA model can meet the threshold condition, that is, obtaining the optimal structure parameters of the liquid crystal polarization grating to be measured.

2. The method according to claim 1, characterized in that, Using red, green, and blue lasers respectively to perpendicularly incident on the liquid crystal polarization grating to be measured, and measuring the diffraction efficiency matrix of the liquid crystal polarization grating to be measured.

3. The method according to claim 2, characterized in that Measuring the diffraction efficiency matrices of the 0, +1, and -1 orders of the liquid crystal polarization grating to be measured, expressed as: Where η B,-1 , η B,0 , η B,+1 They respectively represent the -1, 0, and +1 order diffraction efficiencies measured when blue light is incident normally on the liquid crystal polarization grating to be tested; η G,-1 、η G,0 、η G,+1 respectively represent the diffraction efficiencies of the -1st, 0th, and +1st orders measured when green light is normally incident on the liquid crystal polarization grating to be measured; η R,-1 、 η R,0 、 η R,+1 respectively represent the diffraction efficiencies of the -1, 0, and +1 orders measured when red light is normally incident on the liquid crystal polarization grating to be measured.

4. The method according to claim 1, wherein The fitness function is expressed as: F η = max|η iB ′ - η B | + max|η iG ′ - η G | + max|η iR ′ - η R | where η iB ′ is the diffraction efficiency matrix of the liquid crystal polarization grating calculated based on the parameters obtained from the i-th iteration of the genetic algorithm in the RCWA model under normal incidence of blue light, and η B is the diffraction efficiency matrix of the liquid crystal polarization grating measured under normal incidence of blue light; η iG ′ is the diffraction efficiency matrix of the liquid crystal polarization grating calculated based on the parameters obtained from the i-th iteration of the genetic algorithm in the RCWA model under normal incidence of green light, and η G is the diffraction efficiency matrix of the liquid crystal polarization grating measured under normal incidence of green light; η iR ′ is the diffraction efficiency matrix of the liquid crystal polarization grating calculated based on the parameters obtained from the i-th iteration of the genetic algorithm in the RCWA model under normal incidence of red light, and η R is the diffraction efficiency matrix of the liquid crystal polarization grating measured under normal incidence of red light.

5. The method according to claim 1, wherein Obtaining the transverse period of the liquid crystal polarization grating to be measured through an exposure system or a polarization microscope.

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