Method, device and equipment for measuring refractive index of cholesteric liquid crystal and medium

Abstract

The invention relates to the technical field of optical measurement, and provides a cholesteric liquid crystal refractive index measurement method, device and equipment and a medium. According to the method, when a target polarization grating is in an abnormal diffraction state, incident parameters of an incident beam and emergent parameters of an emergent beam are collected; and the actual optical characteristics of the cholesteric liquid crystal are directly reflected in the measurement process. A Mueller matrix is constructed on the basis of incident parameters and emergent parameters, polarization state changes of light beams are described, the influence of cholesteric liquid crystal molecule arrangement on the light polarization state is more accurately captured, and measurement errors caused by optical property differences are reduced. Ellipsometry parameters are calculated through a Mueller matrix, and key features of light beam polarization state changes are further extracted. According to the method, the ellipsometry parameters are analyzed through the parameter fitting model, the refractive index of the target polarization grating is directly generated, measurement errors caused by structural differences in related technologies are avoided, and therefore the accuracy and reliability of measurement results are remarkably improved.

Description

Technical Field

[0001] This application relates to the field of optical measurement technology, and in particular to a method, apparatus, device and medium for measuring the refractive index of cholesteric liquid crystal. Background Technology

[0002] Liquid crystal polarization holographic gratings (PVGs) have been increasingly studied and applied in near-eye display devices in recent years due to their superior optical properties. The birefringence of the liquid crystal molecules has a significant impact on the optical performance of PVGs. Therefore, to ensure that the parameters of the fabricated PVG are as consistent as possible with those of the theoretically designed PVG, it is necessary to accurately measure the birefringence of the liquid crystal molecules.

[0003] In the PVG structure, the liquid crystal molecules are arranged in a cholesteric phase, meaning the optical axis of the liquid crystal molecules is rotated. However, existing methods for measuring the birefringence of liquid crystals are based on nematic phase arrangements. Nematic liquid crystal molecules have a more regular arrangement, which differs structurally from cholesteric liquid crystal molecules. Therefore, related techniques typically require the preparation of nematic liquid crystals for measurement, which not only increases experimental steps but may also lead to measurement results that do not directly reflect the actual optical properties of cholesteric liquid crystals, resulting in significant errors in the measurement results.

[0004] Therefore, how to achieve direct measurement of cholesteric liquid crystal birefringence while ensuring measurement accuracy has become an urgent technical problem to be solved. Summary of the Invention

[0005] This application provides a method, apparatus, device, and storage medium for measuring the refractive index of cholesteric liquid crystals, aiming to solve the technical problem that the existing liquid crystal birefringence measurement method, which involves preparing nematic liquid crystals, cannot directly reflect the actual optical characteristics of cholesteric liquid crystals, resulting in large errors in the measurement results. The aim is to achieve direct measurement of the birefringence of cholesteric liquid crystals while meeting the measurement accuracy requirements.

[0006] In a first aspect, this application provides a method for measuring the refractive index of cholesteric liquid crystals, comprising: When the target polarization grating is in an abnormal diffraction state, the incident parameters of the incident beam and the output parameters of the output beam are collected. Based on the incident parameters and the exit parameters, construct the Mueller matrix; Based on the Mueller matrix, calculate the elliptic parameters; Based on the parameter fitting model, the ellipticity parameters are analyzed to generate the refractive index of the target polarization grating.

[0007] Secondly, this application also provides a refractive index measuring device for cholesteric liquid crystals, comprising: The parameter acquisition module is used to acquire the incident parameters of the incident beam and the exit parameters of the exit beam when the target polarization grating is in an abnormal diffraction state. A matrix construction module is used to construct a Mueller matrix based on the incident parameters and the exit parameters; The elliptic deflection parameter calculation module is used to calculate the elliptic deflection parameters based on the Mueller matrix. The model fitting module is used to analyze the ellipticity parameters based on the parameter fitting model and generate the refractive index of the target polarization grating.

[0008] Thirdly, this application also provides a computer device, the computer device including a processor, a memory, and a computer program stored in the memory and executable by the processor, wherein when the computer program is executed by the processor, it implements the steps of the cholesteric liquid crystal refractive index measurement method as described above.

[0009] Fourthly, this application also provides a computer-readable storage medium storing a computer program, wherein when the computer program is executed by a processor, it implements the steps of the cholesteric liquid crystal refractive index measurement method as described above.

[0010] Fifthly, this application also provides a refractive index measurement system for cholesteric liquid crystals, the system comprising: A light source, used to output the incident light beam; At the incident end, a polarization controller is provided to receive the incident beam output by the light source, modulate and measure the polarization state of the incident beam through the polarization controller, and output the incident beam after polarization state modulation. A cholesteric liquid crystal polarization grating, wherein the optical axis of the cholesteric liquid crystal polarization grating is arranged in a spiral shape, for receiving the incident beam output from the incident end after polarization state modulation, and selectively reflecting or transmitting the polarization state of the incident beam. At the output end, a polarization analyzer is provided to receive the output beam of the cholesteric liquid crystal polarization grating and to modulate and measure the polarization state of the output beam.

[0011] This application provides a method, apparatus, device, and storage medium for measuring the refractive index of cholesteric liquid crystals. The method of this application acquires the incident parameters and exit parameters of the incident beam when the target polarization grating is in an anomalous diffraction state, avoiding the complex steps required to prepare nematic liquid crystals in existing technologies. This ensures that the measurement process directly reflects the actual optical properties of the cholesteric liquid crystal. A Mueller matrix is ​​constructed based on the incident and exit parameters. The Mueller matrix comprehensively and accurately describes the change in polarization state of the beam as it passes through the cholesteric liquid crystal polarization grating, thereby more precisely capturing the influence of the cholesteric liquid crystal molecule arrangement on the light polarization state. This reduces measurement errors caused by differences in optical properties between cholesteric liquid crystals and other liquid crystal types such as nematic liquid crystals, making the measurement results closer to the true optical properties of cholesteric liquid crystals. Ellipsometry parameters are calculated using the Mueller matrix to further extract key features of the beam polarization state change. By analyzing the ellipsoid parameters through a parameter fitting model, the refractive index of the target polarization grating is directly generated. This avoids measurement errors caused by the complex structure of cholesteric liquid crystals and their significant differences from other liquid crystal structures in related technologies, thereby significantly improving the accuracy and reliability of the measurement results. This achieves the technical effect of directly measuring the birefringence of cholesteric liquid crystals while meeting the requirements for measurement accuracy. Attached Figure Description

[0012] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 A schematic flowchart of a first embodiment of a method for measuring the refractive index of cholesteric liquid crystal provided in this application; Figure 2 A schematic diagram of the liquid crystal molecular structure of a cholesteric liquid crystal polarization grating provided in an embodiment of this application; Figure 3 A schematic diagram of the normal diffraction results of a cholesteric liquid crystal polarization grating provided in an embodiment of this application; Figure 4 A schematic diagram of the abnormal diffraction results of a cholesteric liquid crystal polarization grating provided in an embodiment of this application; Figure 5 A schematic diagram illustrating the diffraction efficiency of an anomalous diffraction of a cholesteric liquid crystal polarization grating provided in an embodiment of this application; Figure 6 A refractive index measurement system for cholesteric liquid crystals is provided in the embodiments of this application; Figure 7A schematic flowchart of a second embodiment of a method for measuring the refractive index of cholesteric liquid crystal provided in this application; Figure 8 This is a schematic diagram of the structure of a first embodiment of a cholesteric liquid crystal refractive index measuring device provided in this application; Figure 9 This is a schematic block diagram of the structure of a computer device provided in an embodiment of this application.

[0014] The purpose, features, and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0015] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments of this application are only some embodiments, not all. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0016] The flowcharts shown in the accompanying drawings are merely illustrative examples. The technical solutions of this application embodiment do not necessarily include all content and operations / steps, nor do they necessarily have to be performed in the described order. For example, some operations / steps can be decomposed, combined, or partially merged, so the actual execution order may change according to the actual situation.

[0017] Where there is no conflict, the various embodiments of this application and the features in the embodiments can be combined with each other.

[0018] Please refer to Figure 1 , Figure 1 This is a flowchart illustrating the first embodiment of a method for measuring the refractive index of a cholesteric liquid crystal, as provided in this application.

[0019] like Figure 1 As shown, the method for measuring the refractive index of the cholesteric liquid crystal includes steps S101 to S104.

[0020] S101. When the target polarization grating is in an abnormal diffraction state, collect the incident parameters of the incident beam and the exit parameters of the exit beam.

[0021] In one embodiment, the target polarization grating can be a grating in which the liquid crystal molecules are arranged in a cholesteric phase, such as a liquid crystal polarization holographic grating (PVG). Figure 2 As shown, in PVG, the azimuth angle of the optical axis of the liquid crystal molecules The change from 0° to 180° produced along... Rotation period of direction .in, This indicates the tilt angle of the liquid crystal molecules, specifically the angle between the optical axis of the liquid crystal molecules and the normal to the grating plane. The x-axis represents the period length of the grating, which is the repeating interval of the grating structure along the x-axis; z represents the thickness direction of the grating, which is the extension of the grating along the z-axis; x represents a spatial coordinate axis of the grating, which is usually consistent with the period direction of the grating.

[0022] like Figure 3 The diffraction characteristics of a reflective PVG are shown. The incident beam is right-handed circularly polarized. Assuming the helical direction of the liquid crystal molecules in the PVG is the same as the helical direction of the incident beam, the beam is diffracted by the PVG, and the polarization state of the diffracted beam remains unchanged. Beams with a helical direction different from that of the liquid crystal molecules pass directly through the PVG. In the figure, RCP (Right-Circular Polarization) represents right-handed circular polarization, meaning the polarization direction of the beam rotates clockwise; LCP (Left-Circular Polarization) represents left-handed circular polarization, meaning the polarization direction of the beam rotates counterclockwise.

[0023] like Figure 4 The anomalous diffraction characteristics of the reflective PVG shown are illustrated. A rigorous coupled-wave algorithm is used to model and simulate the PVG, allowing for the calculation of the beam energy and polarization state diffracted by the incident beam at different incident angles. The calculation results are as follows: Figure 5 As shown, when the incident angle is large, the beam only has a zeroth transmission order, and the polarization state of the zeroth transmission order changes periodically with the thickness. In this case, the characteristics of the PVG are similar to those of a waveplate. Here, θ represents the incident angle.

[0024] In other words, for cholesteric liquid crystals, when an incident beam is incident on a PVG at a specific angle, the PVG only exhibits transmission orders, and the polarization state of the transmitted beam is related to the thickness of the PVG, meaning the PVG exhibits waveplate characteristics. Therefore, the birefringence of PVG can be directly measured based on interferometry or ellipsometrics without the need to prepare a nematic liquid crystal. The birefringence can be directly measured on a prepared PVG grating, making the measurement method faster and simpler.

[0025] Generally, liquid crystals are uniaxial birefringent materials, with refractive indices ne and no along the optical axis and perpendicular to the optical axis, respectively. ne is defined as the refractive index of the extraordinary ray when the vibration direction of the electric vector of the light wave is parallel to the optical axis of the crystal, and no is defined as the refractive index of the ordinary ray when the vibration direction of the electric vector of the light wave is perpendicular to the optical axis of the crystal.

[0026] In one embodiment, since the PVG only exhibits anomalous diffraction characteristics within a specific incident angle range, allowing for the measurement of birefringence based on the polarization state change of its transmitted beam, it is first necessary to determine the incident angle range of the incident beam when the target polarization grating exhibits anomalous diffraction. This ensures that when measuring the refractive index of the target polarization grating, the incident beam is directly incident into the target polarization grating at an incident angle within this range, thus placing the target polarization grating in an anomalous diffraction state.

[0027] Before measuring the refractive index of the target polarization grating, the range of incident angles of the incident beam that causes anomalous diffraction of the target polarization grating can be measured first.

[0028] Further, based on a preset angle interval, at least one second incident angle of the incident beam is determined; the polarization state of the outgoing beam after diffraction is measured after the incident beam incident on the target polarization grating at each of the second incident angles; when the outgoing beam has only the zeroth order of transmission and the polarization state of the transmission component changes periodically with the thickness of the target polarization grating, it is determined that the target polarization grating is currently in an abnormal diffraction state; each of the second incident angles of the incident beam when the target polarization grating is in an abnormal diffraction state is determined as the first incident angle.

[0029] For example, the incident angle of the incident beam can be changed successively from 0° according to a preset angle interval. For instance, the second incident angle of the incident beam is 0° in the first measurement, 5° in the second measurement, 10° in the third measurement, and so on, until the measurement of the second incident angle in the range of -180° to 180° is completed.

[0030] For each selected second incident angle, calculate the polarization state of the outgoing beam after diffraction by the target polarization grating at that second incident angle. This can be achieved by establishing a physical model and an electromagnetic field distribution model of the grating, and using Rigorous Coupled-Wave Analysis (RCWA) or other numerical simulation methods. Specifically, input the physical parameters of the grating (such as period, thickness, birefringence, etc.), input the polarization state of the incident beam (such as right-handed circularly polarized light), run the numerical simulation, and calculate the polarization state information of the outgoing beam. Through simulation calculation, the polarization state information of the outgoing beam at different incident angles can be obtained, including parameters such as polarization direction and degree of polarization.

[0031] Based on the calculation results, it is determined whether the grating is in an abnormal diffraction state. The specific judgment conditions include two points: first, the outgoing beam contains only the zeroth transmission order; second, the polarization state changes periodically with the thickness. Specifically, "the outgoing beam contains only the zeroth transmission order" means that the diffracted beam has no other orders (such as ±1st order, ±2nd order, etc.), only the zeroth transmission order; "the polarization state changes periodically with the thickness" means that the polarization state of the zeroth transmission order changes periodically with the grating thickness.

[0032] If the above two conditions for determining abnormal diffraction states are met, it can be determined that the target polarization grating is in an abnormal diffraction state at that incident angle. This is based on the characteristics exhibited by PVG in abnormal diffraction states, namely, when the incident angle is large, the beam only has the zeroth order of transmission, and the polarization state of the zeroth order of transmission changes periodically with the thickness.

[0033] The first incident angles are defined as the second incident angles of the incident beam when the target polarization grating is in an anomalous diffraction state. These first incident angles are the incident angles required for subsequent refractive index measurements, ensuring that the PVG is in an anomalous diffraction state during the measurement process. This allows for the direct measurement of the PVG's birefringence by measuring the polarization state change of the transmitted beam.

[0034] Further, at least one first incident angle corresponding to the incident beam is obtained, wherein the first incident angle is the incident angle of the incident beam when the target polarization grating is in an abnormal diffraction state; based on the maximum and minimum incident angles among the first incident angles, the target incident angle range is obtained.

[0035] In one embodiment, relevant measurement data for each measurement process is recorded, including but not limited to parameters of the incident beam (including polarization state, incident angle, wavelength, etc.), grating diffraction state (normal, abnormal, etc.), parameters of the outgoing beam (polarization state, outgoing angle, etc.), and grating parameters (such as thickness, grating period, tilt angle, refraction range, etc.). The relevant measurement data for each measurement can be recorded and saved in a table or other data recording format. Then, measurement data with abnormal grating diffraction states are filtered out. The maximum and minimum incident angles are identified from this data, and the interval between the maximum and minimum incident angles is determined as the target incident angle range.

[0036] All incident angles within the target incident angle range can cause the target polarization grating to exhibit anomalous diffraction characteristics during the measurement process, thus allowing direct measurement of the birefringence of the target polarization grating based on the polarization state change of the transmitted beam.

[0037] In one embodiment, if higher accuracy is required, the preset angle interval can be further reduced (e.g., from 5° to 1° or less) to obtain a more accurate range of incident angles.

[0038] At this point, it is only necessary to filter the first incident angle of the maximum value and the incident angle between it and the adjacent second incident angle, as well as the first incident angle of the minimum value and the incident angle between it and the adjacent second incident angle. For example, if the maximum incident angle in the initially determined range of first incident angles is 150° and the minimum incident angle is 80°, then it is only necessary to further filter the incident angles in the two angle ranges of [75°, 80°] and [150°, 155°].

[0039] When performing more precise incident angle range filtering, the preset angle interval used is smaller than the preset angle interval used in the previous filtering. For example, if the preset angle interval used in the previous filtering was 5°, the preset angle used in the current filtering can be 1°, that is, the second incident angle of the incident beam is adjusted by 1° each time. For example: in the range of [75°, 80°], the second incident angle is changed successively at 1° intervals (75°, 76°, 77°, 78°, 79°, 80°); in the range of [150°, 155°], the second incident angle is changed successively at 1° intervals (150°, 151°, 152°, 153°, 154°, 155°).

[0040] In the process of selecting a more precise range of incident angles, apart from adjusting the second incident angle of the incident beam, the other measurement steps are the same. That is, for each selected second incident angle, simulation methods such as the rigorous coupled-wave algorithm are used to calculate the polarization state of the outgoing beam after diffraction by the target polarization grating at that second incident angle. Through simulation calculation, the polarization state information of the outgoing beam at different incident angles is obtained, including parameters such as polarization direction and degree of polarization. Based on the calculation results, it is determined whether the grating is in an abnormal diffraction state. The second incident angles that meet the abnormal diffraction conditions are recorded and determined as the first incident angles, forming a new list of first incident angles. From the new list of first incident angles, the largest incident angle (maximum value) and the smallest incident angle (minimum value) are found to determine a more precise target incident angle range.

[0041] This embodiment, by gradually reducing the preset angle interval and focusing on screening key intervals, can efficiently obtain a more accurate incident angle range when the target polarization grating is in an abnormal diffraction state. This not only improves the measurement accuracy but also avoids unnecessary angle scanning, thereby significantly improving experimental efficiency.

[0042] Furthermore, based on the target incident angle range of the predicted quantity, the target incident angle of the incident beam is determined; the incident beam is incident into the target polarization grating at the target incident angle so that the target polarization grating is in an abnormal diffraction state.

[0043] In one embodiment, the range of incident angles previously determined through preliminary and further screening is used as the target range of incident angles for the predicted quantity. For example, if the range of incident angles determined by preliminary screening is [80°, 150°], the more precise range after further screening may be [82°, 148°].

[0044] Within the target incident angle range of the predicted quantity, select one or more incident angles as the target incident angle. Adjust the incident angle of the incident beam to the target incident angle to ensure that the target polarization grating is in an anomalous diffraction state.

[0045] Please refer to Figure 6 The method for measuring the refractive index of cholesteric liquid crystals provided in this application embodiment is applied in... Figure 6 In the cholesteric liquid crystal refractive index measurement system shown, a laser outputs an incident beam. Before the incident beam reaches the target polarization grating, its polarization state is modulated and measured using a polarizer and a rotation compensator. Similarly, the outgoing beam, after being reflected or transmitted through the target polarization grating, is also modulated by the rotation compensator and polarizer before being measured by a detector. This process obtains the Stokes parameters of the outgoing beam after reflection or transmission through the target polarization grating under different polarization states. and .

[0046] Specifically, a polarization controller (such as a polarizer or a rotation compensator) can be used to modulate the polarization state of the incident beam. The incident beam can be set to different polarization states, such as linear, circular, or elliptical polarization, and the specific parameters for each polarization state, such as polarization direction and degree of polarization, can be recorded, along with the incident angle, wavelength, and polarization state of the incident beam.

[0047] Similarly, at the output end, a polarization analyzer (such as a combination of a polarizer, a rotary compensator, and a photodetector) can be used to measure the polarization state of the output beam. Specifically, the polarization analyzer can measure the intensity of the output beam in different polarization directions by changing the azimuth angle of the polarizer and the rotary compensator.

[0048] In one embodiment, continue to refer to Figure 6 The refractive index measurement system of the cholesteric liquid crystal includes a light source, an incident end, a cholesteric liquid crystal polarization grating, and an exit end.

[0049] The system includes: a light source for outputting an incident light beam; an incident end equipped with a polarization controller for receiving the incident light beam output from the light source, modulating and measuring the polarization state of the incident light beam, and outputting the polarization-modulated incident light beam; a cholesteric liquid crystal polarization grating with its optical axis arranged in a spiral shape for receiving the polarization-modulated incident light beam output from the incident end and selectively reflecting or transmitting the polarization state of the incident light beam; and an exit end equipped with a polarization analyzer for receiving the exit light beam output from the cholesteric liquid crystal polarization grating and modulating and measuring the polarization state of the exit light beam.

[0050] Specifically, the light source is the starting point of the entire measurement system. Its main function is to output a stable and suitable incident beam. A laser light source with good coherence and monochromaticity, such as a helium-neon laser, can be selected to output an incident beam with a relatively single wavelength and a clear beam direction.

[0051] A polarization controller is installed at the incident end. This polarization controller can be implemented using a combination of various components, such as a structure combining a polarizer and a rotary compensator. The polarizer can convert the natural light or partially polarized light output from the light source into linearly polarized light with a specific polarization direction, such as transverse electric (TE) mode or transverse magnetic (TM) mode. The rotary compensator can continuously change the polarization state of the beam within a certain range. By rotating the angle of the compensator, the polarized light can be converted between multiple polarization states, such as elliptically polarized light or even circularly polarized light, thereby achieving comprehensive modulation of the polarization state of the incident beam.

[0052] Meanwhile, polarization beam splitters, waveplates, and other analytical elements can be installed at appropriate locations on the polarization controller to split the incident beam into beam branches with different polarization directions or different polarization states. Then, photodetectors are used to detect parameters such as the light intensity of these branch beams, and the polarization state parameters of the incident beam, such as the degree of polarization and the polarization angle, can be accurately deduced through corresponding calculation formulas and algorithms.

[0053] The incident beam, modulated by the polarization controller, will propagate along a predetermined optical path to enter the cholesteric liquid crystal polarization grating section for interaction.

[0054] The optical axes of the cholesteric liquid crystal polarization grating are arranged in a spiral shape, which enables the cholesteric liquid crystal to selectively reflect and transmit light of different polarization states.

[0055] Specifically, when an incident light beam enters a cholesteric liquid crystal polarization grating, the left-handed circularly polarized (LCP) and right-handed circularly polarized (RCP) components of the beam interact with the helical structure of the cholesteric liquid crystal. According to the optical principles of cholesteric liquid crystals, if the wavelength of the incident light and parameters such as the pitch of the helical structure satisfy relevant matching conditions such as the Brewster condition, one type of circularly polarized light (e.g., left-handed circularly polarized light) will be selectively reflected, while the other type (right-handed circularly polarized light) will be transmitted through the liquid crystal grating. Conversely, if the polarization state or other parameters of the incident light are changed, the polarization components of the transmitted and reflected light will also change accordingly. By analyzing the relevant characteristics of the reflected and transmitted light, optical parameters such as the refractive index of the cholesteric liquid crystal can be obtained, thereby achieving the purpose of measuring its refractive index.

[0056] A polarization analyzer is installed at the output end to receive the output beam after it has been processed by a cholesteric liquid crystal polarization grating, and to modulate and measure the polarization state of the output beam. The polarization analyzer can also adopt a similar structure to the polarization controller at the input end, including components such as polarizers, rotation compensators, and photodetectors.

[0057] Once the emitted light beam enters the polarization analyzer, the polarizer performs initial polarization direction selection, decomposing the beam into components with different polarization directions. The rotation compensator further adjusts the polarization state of the beam for a more comprehensive analysis of the emitted light's polarization characteristics. The photodetector detects parameters such as the light intensity of different polarization components and converts these optical signals into electrical signals, facilitating analysis by the data processing system.

[0058] By taking detailed measurements of the polarization state of the outgoing beam, including obtaining parameters such as its degree of polarization, polarization angle, and ellipticity, and combining this with known measurement data of the polarization state of the incident beam at the incident end, a set of equations can be established using the corresponding optical theoretical models and formulas to calculate the refractive index and other related parameters of the cholesteric liquid crystal, thereby completing the accurate measurement of its refractive index.

[0059] This cholesteric liquid crystal refractive index measurement system provides a stable incident beam through a light source, uses a polarization controller at the incident end to precisely modulate and measure the beam polarization state, then uses the selective reflection and transmission of the cholesteric liquid crystal polarization grating, and finally uses a polarization analyzer at the exit end to analyze the polarization state of the outgoing beam, thus realizing the effective measurement of the refractive index of cholesteric liquid crystal.

[0060] For example, the Stokes parameter of the emitted beam under each incident polarization state can be calculated by measuring the light intensity values ​​of the emitted beam in four different polarization directions (e.g., 0°, 45°, 90°, 135°). , , , ).

[0061] The formula for calculating the Stokes parameter is as follows:

[0062] in, , , , These are the light intensity values ​​measured when the polarizer azimuth angle is 0°, 45°, 90°, and 135°, respectively. and These are the light intensity values ​​measured under right-handed and left-handed circular polarization, respectively.

[0063] By modulating and measuring the polarization states of the incident and emitted beams at the incident and emitted ends, respectively, the Stokes parameters of the emitted beams after reflection or transmission through the target polarization grating under different polarization states can be obtained. This method can comprehensively characterize the polarization characteristics of the target polarization grating.

[0064] S102. Construct the Mueller matrix based on the incident parameters and the exit parameters.

[0065] Generally, the Mueller matrix is ​​a 4×4 matrix used to describe the effect of an optical system on polarized light. The Mueller matrix of a target polarization grating can be constructed based on the Stokes parameters of the incident and outgoing beams.

[0066] First, the Stokes parameters of the incident and emitted beams are measured. The Stokes parameters consist of four components: , , , , representing the total intensity, linear polarization degree, polarization direction, and circular polarization degree of the beam, respectively.

[0067] Specifically, a polarization controller is used to set the incident beam to different polarization states (such as linear polarization, circular polarization, elliptic polarization, etc.). For each incident polarization state, its Stokes parameters are recorded:

[0068] The incident beam is incident on the target polarization grating at the target incident angle, and the Stokes parameters of the outgoing beam are measured using a polarization analyzer:

[0069] Muller matrix It is a 4×4 matrix that describes the linear transformation of the optical system with respect to the Stokes parameters of the incident beam:

[0070] in, Each element The incident beam is represented by the first... The Stokes parameter affects the first... The influence of the Stokes parameter.

[0071] Generally, to construct a complete Mueller matrix, at least 16 different incident polarization states are required (because the Mueller matrix has 16 elements). Four or more different incident polarization states can be selected, and the corresponding outgoing Stokes parameters are measured for each state.

[0072] For example, for each set of incident and exit Stokes parameters, the equation is established as follows:

[0073] in, and These represent the components of the Stokes parameters for the outgoing and incoming signals (from 0 to 3).

[0074] Substituting all the measurement data into the above system of equations forms a linear system of equations. The elements of the Mueller matrix are then solved using the least squares method or other numerical methods. The Mueller matrix is ​​obtained. For specific solution methods, please refer to relevant techniques in this field; these will not be described in detail here.

[0075] By measuring the Stokes parameters of the incident and outgoing beams and solving the Mueller matrix using a system of linear equations, the polarization characteristics of the target polarization grating can be fully characterized, thereby evaluating the birefringence, polarization rotation, and other properties of the grating.

[0076] S103. Calculate the elliptic parameters based on the Mueller matrix.

[0077] Generally, ellipticity parameters typically include two parameters: and .

[0078] in, (psi) is used to describe the angle between the major axis of elliptically polarized light and the reference direction; (delta) is used to describe the ellipticity of elliptically polarized light, that is, the ratio of the major axis to the minor axis.

[0079] Elliptic parameters and It can be calculated using the following formula:

[0080] in, and The first two rows of parameters in the Mueller matrix are typically used to calculate ellipticity parameters, as they describe the variations in incident beam intensity and linear polarization components.

[0081] S104. Based on the parameter fitting model, the ellipticity parameters are analyzed to generate the refractive index of the target polarization grating.

[0082] In one embodiment, after the ellipticity parameters are calculated using the Mueller matrix, the thickness and refractive index of the target polarization grating can be fitted from the ellipticity parameters using a model fitting method.

[0083] Before proceeding, a parameter fitting model describing the PVG needs to be constructed: obtain the first ellipticity parameter of the test polarization grating; based on the initial fitting model, fit the ellipticity parameter of the test polarization grating to obtain the second ellipticity parameter; calculate the fitting error between the first ellipticity parameter and the second ellipticity parameter; when the fitting error is less than a preset error threshold, determine the initial fitting model as the parameter fitting model.

[0084] In one embodiment, a test polarization grating is used to verify the reliability of the model parameters. Therefore, the relevant parameters of the test polarization grating are known and accurate, and the test polarization grating is also a cholesteric liquid crystal polarization grating. The initial parameters of the test polarization grating, including birefringence, can be obtained through experimental measurement. ),thickness( ),wavelength( ) and incident angle ( Based on the physical properties of PVG, a mathematical model describing its optical behavior is established. This model should include key parameters such as birefringence and thickness, and be able to predict ellipsometric parameters. and ).

[0085] In one embodiment, the parameter fitting model may include the following parameters: thickness ( ), birefringence ( ),wavelength( and the angle of incidence ( ) etc. Among them, thickness ( The ) represents the physical thickness of the PVG; the birefringence ( ) represents the birefringence of liquid crystal molecules; wavelength ( ( ) represents the wavelength of the incident light beam; the incident angle ( ) () represents the incident angle of the incident beam relative to the normal of the target polarization grating.

[0086] Thickness can be selected ( ) and birefringence ( ) is used as the fitting parameter, and other parameters (such as wavelength) ) and incident angle ( The elliptic parameters can be used as known quantities. Based on the definition of elliptic parameters, the fitting equation is established:

[0087] in, and These are elliptic parameters. It is birefringence. It's about thickness. It is the wavelength.

[0088] Experiments were conducted using a test polarization grating with known thickness and refractive index to verify the results, comparing the fitted thickness and refractive index with the actual values. If the fitted results differed significantly from the actual values, the model needed to be adjusted until the errors between the fitted thickness and refractive index and the actual values ​​met the requirements.

[0089] Specifically, this can be done for unknown parameters in the model (such as...) and Set initial values. These initial values ​​can be based on experience, literature data, or preliminary experimental results. Using the initial parameter values, the predicted ellipsoidal parameters are calculated through the model. and The ellipsometric parameters of the test polarization grating are measured using an ellipsometry or other polarization measurement equipment. and ).

[0090] The model parameters are fitted using a nonlinear least squares method (such as the Levenberg-Marquardt algorithm). This is achieved by adjusting the parameters in the model (e.g., ...). and This minimizes the error between the ellipticity parameters predicted by the model and the experimentally measured ellipticity parameters.

[0091] in, and These are the measured ellipticity parameters. and These are the elliptic parameters used for model fitting.

[0092] Generally, fitting algorithms are usually an iterative process that continuously adjusts parameter values ​​until convergence conditions are met (such as the error being less than a preset threshold).

[0093] In one embodiment, an error threshold can be set. If the model fitting error is greater than or equal to the error threshold, the model is considered not to meet the requirements and needs to be adjusted and optimized until the fitting error is less than the error threshold. In this case, the model fitting accuracy can be considered to meet the requirements and can be used to fit the ellipticity parameters of the target polarization grating, and to calculate the thickness and birefringence of the target polarization grating.

[0094] The thickness and refractive index of PVG can be derived from ellipticity parameters through model fitting. This method combines experimental measurements with theoretical models, providing crucial data support for PVG performance evaluation and optimization. Data validation and model tuning can further improve the accuracy of the fitting results.

[0095] After the parameter fitting model is constructed and optimized, it can be directly used to fit the ellipticity parameters of the target polarization grating calculated earlier. The ellipticity parameters are then analyzed using the parameter fitting model to obtain the thickness and birefringence of the target polarization grating.

[0096] This embodiment provides a method for measuring the refractive index of cholesteric liquid crystals. This method, when the target polarization grating is in an anomalous diffraction state, collects the incident parameters of the incident beam and the exit parameters of the exit beam, avoiding the complex steps required to prepare nematic liquid crystals in existing technologies. This ensures that the measurement process directly reflects the actual optical properties of the cholesteric liquid crystal. A Mueller matrix is ​​constructed based on the incident and exit parameters. The Mueller matrix comprehensively and accurately describes the change in polarization state of the beam as it passes through the cholesteric liquid crystal polarization grating, thereby more precisely capturing the influence of the cholesteric liquid crystal molecule arrangement on the light polarization state. This reduces measurement errors caused by differences in optical properties between cholesteric liquid crystals and other liquid crystal types such as nematic liquid crystals, making the measurement results closer to the true optical properties of cholesteric liquid crystals. Ellipsometry parameters are calculated using the Mueller matrix to further extract key features of the beam polarization state change. By analyzing the ellipsoid parameters through a parameter fitting model, the refractive index of the target polarization grating is directly generated. This avoids measurement errors caused by the complex structure of cholesteric liquid crystals and their significant differences from other liquid crystal structures in related technologies, thereby significantly improving the accuracy and reliability of the measurement results. This achieves the technical effect of directly measuring the birefringence of cholesteric liquid crystals while meeting the requirements for measurement accuracy.

[0097] Please refer to Figure 7 , Figure 7 This is a flowchart illustrating a second embodiment of a method for measuring the refractive index of a cholesteric liquid crystal, as provided in this application.

[0098] like Figure 7 As shown, based on the above Figure 1 In the illustrated embodiment, after step S104, the method further includes: S201. Fix the current azimuth angle of the target polarization grating, and based on the first angular interval, successively deflect the incident angle of the incident beam within the target incident angle range to obtain the next incident angle corresponding to at least one deflection of the incident beam. In one embodiment, the azimuth angle of the target polarization grating can be fixed, and the incident angle can be changed successively within the target incident angle range according to a preset first angular interval, and the refractive index corresponding to each incident angle can be calculated.

[0099] For example, suppose the target incident angle range is X~Y, where X is less than Y, and the preset first angle interval is k. Suppose the initial incident angle is a, which needs to satisfy X < a < Y; the second incident angle is a+k, which needs to satisfy X < a+k < Y; that is, the initial incident angle can be any angle within the target incident angle range, and the incident angle after each adjustment also needs to be within the target incident angle range.

[0100] Generally, the preset first angle interval can be set according to actual needs, or a fixed angle interval can be not set, and multiple incident angles within the target incident angle range can be randomly selected for measurement.

[0101] S202. Based on the next incident angle after each deflection, calculate the refractive index corresponding to the next incident angle to obtain the next refractive index corresponding to each next incident angle. Each time the incident angle is adjusted, the same operation is performed: the polarization states of the incident and exit beams are modulated and measured at the incident and exit ends, respectively, to obtain the Stokes parameters of the exit beam after reflection or transmission through the target polarization grating under different polarization states. and Obtain at least four sets of Stokes parameters, according to Construct the Mueller matrix. Then, the ellipticity parameter, i.e., the phase difference, can be calculated from the Mueller matrix. and ellipticity Finally, the fitted thickness and fitted refractive index of the target polarization grating under the current incident angle can be obtained from the ellipsoid parameters through model fitting.

[0102] Therefore, the fitted thickness and fitted refractive index of the target polarization grating corresponding to multiple incident angles can be obtained.

[0103] S203. Calculate the average refractive index of the target polarization grating and the next refractive index corresponding to each next incident angle to obtain the average refractive index of the target polarization grating.

[0104] The average value of multiple fitted thicknesses is calculated and used as the thickness of the target polarization grating; the average value of multiple fitted refractive indices is calculated and used as the refractive index of the target polarization grating.

[0105] This embodiment, by fixing the azimuth angle of the target polarization grating and successively changing the incident angle within the target incident angle range based on a preset first angular interval, ensures that the measurement process covers multiple incident angles and avoids measurement errors caused by improper angle selection. By calculating the average value of the fitted thickness and refractive index corresponding to multiple incident angles, the stability and representativeness of the measurement results are further improved, making the refractive index measurement results of cholesteric liquid crystals more accurate.

[0106] In another embodiment, the incident angle of the incident beam can be fixed, and the azimuth angle of the target polarization grating can be changed successively according to the preset second angle interval to obtain the azimuth angles of multiple target polarization gratings. The measurement and calculation process of the ellipsoid parameters can be performed in sequence to obtain the refractive index corresponding to each azimuth angle.

[0107] In one embodiment, the current incident angle of the incident beam is fixed, and the azimuth angle of the target polarization grating is deflected at least once based on a second angular interval to obtain the next azimuth angle corresponding to each deflection of the target polarization grating; based on the next azimuth angle after each deflection, the refractive index corresponding to the next azimuth angle is calculated to obtain the next refractive index corresponding to each next azimuth angle; the average refractive index of the target polarization grating and the next refractive index corresponding to each next azimuth angle are calculated to obtain the average refractive index of the target polarization grating.

[0108] The incident angle of the incident beam refers to the angle between the incident beam and the plane where the target polarization grating is located. The target polarization grating can be rotated on its plane to adjust its azimuth angle so that the incident beam enters the target polarization grating from different positions.

[0109] Specifically, the target polarization grating can be rotated around its center point as the origin of rotation to change its azimuth angle. The initial attitude of the target polarization grating during its first test can be used as the initial attitude, with an azimuth angle of 0°. Starting from the initial attitude, the target polarization grating is deflected according to a preset second angular interval, successively changing its azimuth angle, and the refractive index corresponding to each azimuth angle is calculated. If the target polarization grating rotates one full revolution around the origin of rotation, it means that its azimuth angle has rotated from 0° to 360°.

[0110] Generally, the second angle interval can be set according to actual needs, or a fixed angle interval can be not set, and multiple different azimuth angles can be randomly selected for measurement.

[0111] Each time the azimuth angle of the target polarization grating is adjusted, the same operation is performed: at each new azimuth angle, the polarization states of the incident and outgoing beams are repeatedly modulated and measured at the incident and outgoing ends, respectively, to obtain the Stokes parameters of the outgoing beam after reflection or transmission through the target polarization grating under different polarization states. and Obtain at least four sets of Stokes parameters, according to Construct the Mueller matrix. Then, the ellipticity parameter, i.e., the phase difference, can be calculated from the Mueller matrix. and ellipticity Finally, the fitted thickness and fitted refractive index of the target polarization grating under the current azimuth angle can be obtained from the ellipticity parameters through model fitting. Therefore, the fitted thickness and fitted refractive index of the target polarization grating under multiple azimuth angle conditions can be obtained.

[0112] Then, the average value of multiple fitted thicknesses is calculated, and the average thickness is used as the thickness of the target polarization grating; the average value of multiple fitted refractive indices is calculated, and the calculated mean refractive index is used as the refractive index of the target polarization grating.

[0113] It is understood that the embodiments of this application can measure multiple thicknesses and refractive indices corresponding to multiple azimuth angles for a single incident angle, and can also measure multiple thicknesses and refractive indices corresponding to multiple incident angles for a single azimuth angle. Therefore, the two measurement methods can be combined to further calculate the average of multiple thicknesses corresponding to multiple azimuth angles for a single incident angle and the average thickness, and use the average thickness as the final thickness value of the target polarization grating. The average of multiple refractive indices corresponding to multiple azimuth angles for a single incident angle and the average refractive index is calculated, and the average refractive index is used as the final refractive index of the target polarization grating.

[0114] This embodiment, by fixing the incident angle of the incident beam and changing the azimuth angle of the target polarization grating, allows for measurements of the grating from different positions, thereby obtaining more comprehensive data. Constructing the Mueller matrix and calculating the ellipsometric parameters accurately describes the grating's influence on polarized light, providing a detailed data foundation for model fitting. By averaging the fitted thickness and refractive index at multiple azimuth angles, errors caused by single-angle measurements can be effectively reduced, improving the accuracy of cholesteric liquid crystal refractive index measurements.

[0115] Please see Figure 8 , Figure 8This is a schematic diagram of the structure of a first embodiment of a cholesteric liquid crystal refractive index measuring device provided in this application. The cholesteric liquid crystal refractive index measuring device is used to perform the aforementioned cholesteric liquid crystal refractive index measuring method.

[0116] like Figure 8 As shown, the cholesteric liquid crystal refractive index measuring device 300 includes: a parameter acquisition module 301, a matrix construction module 302, an ellipticity parameter calculation module 303, and a model fitting module 304. Specifically, the parameter acquisition module 301 is used to acquire the incident parameters of the incident beam and the exit parameters of the exit beam when the target polarization grating is in an anomalous diffraction state; the matrix construction module 302 is used to construct a Mueller matrix based on the incident and exit parameters; the ellipticity parameter calculation module 303 is used to calculate the ellipticity parameters based on the Mueller matrix; and the model fitting module 304 is used to analyze the ellipticity parameters based on the parameter fitting model to generate the refractive index of the target polarization grating.

[0117] In one embodiment, the parameter acquisition module 301 includes a target incident angle determination unit and an abnormal diffraction construction unit. The target incident angle determination unit is used to determine the target incident angle of the incident beam based on the target incident angle range of the predicted quantity. The abnormal diffraction construction unit is used to incident the incident beam into the target polarization grating at the target incident angle so that the target polarization grating is in an abnormal diffraction state.

[0118] In one embodiment, the parameter acquisition module 301 further includes a first incident angle acquisition unit and a target incident angle range determination unit, wherein the first incident angle acquisition unit is used to acquire at least one first incident angle corresponding to the incident beam, wherein the first incident angle is the incident angle of the incident beam when the target polarization grating is in an abnormal diffraction state; the target incident angle range determination unit is used to obtain the target incident angle range based on the maximum and minimum incident angles among the first incident angles.

[0119] In one embodiment, the first incident angle acquisition unit includes a second incident angle determination subunit, a polarization state measurement subunit, an abnormal diffraction state determination subunit, and a first incident angle determination subunit. The second incident angle determination subunit is used to determine at least one second incident angle of the incident beam based on a preset angular interval. The polarization state measurement subunit is used to measure the polarization state of the outgoing beam after diffraction of the incident beam incident on the target polarization grating at each of the second incident angles. The abnormal diffraction state determination subunit is used to determine that the target polarization grating is currently in an abnormal diffraction state when the outgoing beam only has a zeroth order of transmission and the polarization state of the transmission component changes periodically with the thickness of the target polarization grating. The first incident angle determination subunit is used to determine each of the second incident angles of the incident beam when the target polarization grating is in an abnormal diffraction state as the first incident angle.

[0120] In one embodiment, the cholesteric liquid crystal refractive index measuring device 300 further includes an average refractive index calculation module. The average refractive index calculation module specifically includes a next incident angle acquisition unit, a next refractive index calculation unit, and an average refractive index calculation first unit. The next incident angle acquisition unit is used to fix the current azimuth angle of the target polarization grating and, based on a second angular interval, successively deflect the incident angle of the incident beam within the target incident angle range to obtain the next incident angle corresponding to at least one deflection of the incident beam. The next refractive index calculation unit is used to calculate the refractive index corresponding to the next incident angle based on the next incident angle after each deflection, obtaining the next refractive index corresponding to each next incident angle. The average refractive index calculation first unit is used to perform an average calculation on the refractive index of the target polarization grating and the next refractive index corresponding to each next incident angle to obtain the average refractive index of the target polarization grating.

[0121] In one embodiment, the mean refractive index calculation module further includes a next azimuth angle determination unit, a next refractive index calculation unit, and a second mean refractive index calculation unit. The next azimuth angle determination unit is used to fix the current incident angle of the incident beam and, based on a first angular interval, perform at least one angular deflection on the azimuth angle of the target polarization grating to obtain the next azimuth angle corresponding to each deflection. The next refractive index calculation unit is used to calculate the refractive index corresponding to the next azimuth angle based on the next azimuth angle after each deflection, thereby obtaining the next refractive index corresponding to each next azimuth angle. The second unit for calculating the mean refractive index is used to calculate the mean of the refractive index of the target polarization grating and the next refractive index corresponding to each of the next azimuth angles, so as to obtain the mean refractive index of the target polarization grating.

[0122] In one embodiment, the cholesteric liquid crystal refractive index measuring device 300 further includes a model building module. The model building module specifically includes a first ellipticity parameter acquisition unit, a second ellipticity parameter fitting unit, a fitting error calculation unit, and a model acquisition unit. The first ellipticity parameter acquisition unit acquires the first ellipticity parameter of the test polarization grating; the second ellipticity parameter fitting unit fits the ellipticity parameter of the test polarization grating based on an initial fitting model to obtain the second ellipticity parameter; the fitting error calculation unit calculates the fitting error between the first ellipticity parameter and the second ellipticity parameter; and the model acquisition unit determines the initial fitting model as the parameter fitting model when the fitting error is less than a preset error threshold.

[0123] It should be noted that those skilled in the art will understand that, for the sake of convenience and brevity, the specific working process of the device and each module described above can be referred to the corresponding process in the aforementioned embodiment of the cholesteric liquid crystal refractive index measurement method, and will not be repeated here.

[0124] The apparatus provided in the above embodiments can be implemented as a computer program, which can be used in, for example... Figure 9 It runs on the computer device shown.

[0125] Please see Figure 9 , Figure 9 This is a schematic block diagram illustrating the structure of a computer device according to an embodiment of this application. The computer device may be a server.

[0126] See Figure 9 The computer device includes a processor, memory, and network interface connected via a system bus, wherein the memory may include non-volatile storage media and internal memory.

[0127] The non-volatile storage medium can store an operating system and a computer program. This computer program includes program instructions that, when executed, cause the processor to perform any method for measuring the refractive index of a cholesteric liquid crystal.

[0128] The processor provides computing and control capabilities, supporting the operation of the entire computer device.

[0129] The internal memory provides an environment for the execution of computer programs in non-volatile storage media. When executed by a processor, the computer program enables the processor to perform any method for measuring the refractive index of cholesteric liquid crystals.

[0130] This network interface is used for network communication, such as sending assigned tasks. Those skilled in the art will understand that... Figure 9The structure shown is merely a block diagram of a portion of the structure related to the present application and does not constitute a limitation on the computer device to which the present application is applied. Specific computer devices may include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements.

[0131] It should be understood that the processor can be a Central Processing Unit (CPU), but it can also be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. Among these, a general-purpose processor can be a microprocessor or any conventional processor.

[0132] In one embodiment, the processor is configured to run a computer program stored in memory to perform the following steps: When the target polarization grating is in an abnormal diffraction state, the incident parameters of the incident beam and the output parameters of the output beam are collected. Based on the incident and exit parameters, construct the Mueller matrix; Based on the Mueller matrix, calculate the elliptic parameters; Based on the parameter fitting model, the ellipticity parameters are analyzed to generate the refractive index of the target polarization grating.

[0133] In one embodiment, when the processor acquires the incident parameters of the incident beam and the exit parameters of the exit beam when the target polarization grating is in an abnormal diffraction state, it is configured to: The target incident angle of the incident beam is determined based on the predicted target incident angle range. The incident beam is incident on the target polarization grating at the target incident angle, so that the target polarization grating is in an abnormal diffraction state.

[0134] In one embodiment, before determining the target incident angle of the incident beam based on the predicted range, the processor is further configured to perform: Obtain at least one first incident angle corresponding to the incident beam, wherein the first incident angle is the incident angle of the incident beam when the target polarization grating is in an abnormal diffraction state; The target incident angle range is obtained based on the maximum and minimum incident angles among the first incident angles.

[0135] In one embodiment, when the processor acquires at least one first incident angle corresponding to the incident beam, it is configured to: Based on a preset angle interval, at least one second incident angle of the incident beam is determined; The polarization state of the outgoing beam after diffraction is measured when the incident beam is incident on the target polarization grating at each of the second incident angles. When the outgoing beam has only the zeroth order of transmission and the polarization state of the transmission component changes periodically with the thickness of the target polarization grating, it is determined that the target polarization grating is currently in an abnormal diffraction state. The second incident angles of the incident beam when the target polarization grating is in an abnormal diffraction state are determined as the first incident angles.

[0136] In one embodiment, after implementing the parameter fitting model to analyze the ellipticity parameters and generate the refractive index of the target polarization grating, the processor is further configured to implement: The current azimuth angle of the target polarization grating is fixed, and the incident angle of the incident beam is deflected successively within the target incident angle range based on the second angle interval to obtain the next incident angle corresponding to at least one deflection of the incident beam. Based on the next incident angle after each deflection, calculate the refractive index corresponding to the next incident angle to obtain the next refractive index corresponding to each next incident angle. The mean refractive index of the target polarization grating is obtained by averaging the refractive index of the target polarization grating and the next refractive index corresponding to each next incident angle.

[0137] In one embodiment, after implementing the parameter fitting model to analyze the ellipticity parameters and generate the refractive index of the target polarization grating, the processor is further configured to implement: With the current incident angle of the incident beam fixed, the azimuth angle of the target polarization grating is deflected at least once based on the first angular interval to obtain the next azimuth angle corresponding to each deflection of the target polarization grating. Based on the next azimuth angle after each deflection, calculate the refractive index corresponding to the next azimuth angle to obtain the next refractive index corresponding to each next azimuth angle. The mean refractive index of the target polarization grating is obtained by averaging the refractive index of the target polarization grating and the next refractive index corresponding to each next azimuth angle.

[0138] In one embodiment, before implementing the parameter fitting model to analyze the ellipticity parameters and generate the refractive index of the target polarization grating, the processor is further configured to implement: Obtain the first ellipticity parameter of the test polarization grating; Based on the initial fitting model, the ellipticity parameters of the test polarization grating are fitted to obtain the second ellipticity parameters; Calculate the fitting error between the first elliptic deviation parameter and the second elliptic deviation parameter; When the fitting error is less than a preset error threshold, the initial fitting model is determined to be the parameter fitting model.

[0139] The embodiments of this application also provide a computer-readable storage medium storing a computer program, the computer program including program instructions, and the processor executing the program instructions to implement any of the cholesteric liquid crystal refractive index measurement methods provided in the embodiments of this application.

[0140] The computer-readable storage medium can be an internal storage unit of the computer device described in the foregoing embodiments, such as the hard disk or memory of the computer device. The computer-readable storage medium can also be an external storage device of the computer device, such as a plug-in hard disk, SmartMedia Card (SMC), Secure Digital (SD) card, or Flash Card equipped on the computer device.

[0141] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method of measuring the refractive index of a cholesteric liquid crystal, characterized in that, The method comprises: When the target polarization grating is in an anomalous diffraction state, collecting an incident parameter of an incident light beam and an exit parameter of an exit light beam; Based on the incident parameter and the exit parameter, a Mueller matrix is constructed; Based on the Mueller matrix, an ellipsometric parameter is calculated; Based on a parameter fitting model, the ellipsometric parameter is analyzed to generate a refractive index of the target polarization grating.

2. The method of measuring the refractive index of a cholesteric liquid crystal according to claim 1, wherein The method comprises: Based on a predicted target incident angle range, a target incident angle of the incident light beam is determined; The incident light beam is incident into the target polarization grating at the target incident angle, so that the target polarization grating is in an anomalous diffraction state.

3. The method of measuring the refractive index of a cholesteric liquid crystal according to claim 2, wherein Before the target incident angle of the incident light beam is determined based on the predicted target incident angle range, the method further comprises: At least one first incident angle corresponding to the incident light beam is obtained, wherein the first incident angle is an incident angle of the incident light beam when the target polarization grating is in an anomalous diffraction state; Based on a maximum incident angle and a minimum incident angle in each of the first incident angles, the target incident angle range is obtained.

4. The method of measuring the refractive index of a cholesteric liquid crystal according to claim 3, wherein The at least one first incident angle corresponding to the incident light beam is obtained by: Based on a preset angle interval, at least one second incident angle of the incident light beam is determined; The polarization state of the exit light beam after diffraction of the incident light beam incident into the target polarization grating at each of the second incident angles is measured; When the exit light beam only has a transmission zero order, and the polarization state of the transmission zero order changes periodically with the thickness of the target polarization grating, it is determined that the target polarization grating is currently in an anomalous diffraction state; Each of the second incident angles of the incident light beam when the target polarization grating is in an anomalous diffraction state is determined as the first incident angle.

5. The method of measuring the refractive index of a cholesteric liquid crystal according to claim 1, wherein After the refractive index of the target polarization grating is generated based on the parameter fitting model, the method further comprises: Fixing a current azimuth angle of the target polarization grating, the incident angle of the incident light beam is sequentially deflected within the target incident angle range based on a second angle interval, to obtain a next incident angle corresponding to at least one deflection of the incident light beam; Based on the next incident angle after each deflection, a refractive index corresponding to the next incident angle is calculated, to obtain a next refractive index corresponding to each of the next incident angles; The refractive index of the target polarization grating and the next refractive index corresponding to each of the next incident angles are subjected to mean value calculation, to obtain a mean refractive index of the target polarization grating.

6. The method of measuring the refractive index of a cholesteric liquid crystal according to claim 1, wherein After the refractive index of the target polarization grating is generated based on the parameter fitting model, the method further comprises: Fixing a current incident angle of the incident light beam, the azimuth angle of the target polarization grating is subjected to at least one angle deflection based on a first angle interval, to obtain a next azimuth angle corresponding to each deflection of the target polarization grating; Based on the next azimuth angle after each deflection, a refractive index corresponding to the next azimuth angle is calculated, to obtain a next refractive index corresponding to each of the next azimuth angles; The mean refractive index of the target polarization grating is obtained by averaging the refractive index of the target polarization grating and the next refractive index corresponding to each next azimuth angle.

7. The method of measuring the refractive index of a cholesteric liquid crystal according to claim 1, wherein Before the refractive index of the target polarization grating is generated by analyzing the ellipsometric parameters based on the parameter fitting model, the method further comprises: obtaining first ellipsometric parameters of a test polarization grating; fitting the ellipsometric parameters of the test polarization grating based on an initial fitting model to obtain second ellipsometric parameters; calculating a fitting error of the first ellipsometric parameters and the second ellipsometric parameters; when the fitting error is less than a preset error threshold, determining that the initial fitting model is the parameter fitting model.

8. A device for measuring the refractive index of a cholesteric liquid crystal, characterized in that The refractive index measuring device of the cholesteric liquid crystal comprises: a parameter acquisition module configured to acquire incident parameters of an incident light beam and exit parameters of an exit light beam when the target polarization grating is in an abnormal diffraction state; a matrix construction module configured to construct a Mueller matrix based on the incident parameters and the exit parameters; an ellipsometric parameter calculation module configured to calculate ellipsometric parameters based on the Mueller matrix; a model fitting module configured to analyze the ellipsometric parameters based on a parameter fitting model to generate the refractive index of the target polarization grating.

9. A computer device, comprising: The computer device comprises a processor, a memory, and a computer program stored on the memory and executable by the processor, wherein when the computer program is executed by the processor, the steps of the cholesteric liquid crystal refractive index measuring method according to any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium, characterized in that, The computer readable storage medium stores a computer program, wherein when the computer program is executed by the processor, the steps of the cholesteric liquid crystal refractive index measuring method according to any one of claims 1 to 7 are implemented.

11. A system for measuring the refractive index of a cholesteric liquid crystal, characterized in that The system comprises: a light source configured to output an incident light beam; an incident end provided with a polarization controller, configured to receive the incident light beam output by the light source, modulate and measure the polarization state of the incident light beam through the polarization controller, and output the incident light beam after polarization state modulation; a cholesteric liquid crystal polarization grating, wherein the optical axis of the cholesteric liquid crystal polarization grating is arranged in a spiral shape, configured to receive the incident light beam output by the incident end after polarization state modulation, and selectively reflect or transmit the polarization state of the incident light beam; an exit end provided with a polarization analyzer, configured to receive the exit light beam output by the cholesteric liquid crystal polarization grating, and modulate and measure the polarization state of the exit light beam.

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