A method and apparatus for rapid measurement of the pitch of a twisted liquid crystal polymer film

Abstract

The present application relates to a kind of twist liquid crystal polymer film pitch fast measurement method and device, belong to optical material parameter measurement technical field, solve the problem that existing method cannot be under the condition of unknown thickness to the solidified twist liquid crystal polymer film is carried out fast, non-destructive pitch measurement.This method first obtains the transmittance spectral response data after linearly polarized light transmits twist liquid crystal polymer film and wide band analyzer, obtains experimental relative transmittance curve after pre-processing;Calculate the theoretical relative transmittance curve corresponding to each pitch and thickness parameter combination in preset inversion range;Trend evaluation function is used to filter curve, form candidate parameter range;Using the oscillation degree evaluation function calculates the matching degree corresponding to each parameter combination in candidate parameter range, the pitch corresponding to the maximum value of matching degree is measured pitch.The present application can be carried out fast, non-destructive pitch measurement to the solidified twist liquid crystal polymer film, and device structure is simple, low in cost.

Description

Technical Field

[0001] This invention belongs to the field of optical material parameter measurement technology, and specifically relates to a rapid measurement method and device for the pitch of a twisted liquid crystal polymer film. Background Technology

[0002] Liquid crystal polymers (LCPs) combine the anisotropy of liquid crystals with the mechanical stability and chemical resistance of polymers, demonstrating broad application prospects in optical thin films and micro / nano photonic devices in recent years. Research shows that multilayer patterned birefringent films based on LCPs can achieve spatial modulation of the direction of light propagation and polarization state. Currently, LCP polarization gratings are widely used in non-mechanical beam manipulation scenarios such as lidar and space communication; while in augmented reality and virtual reality, LCP-based polarizing body gratings are also emerging. When these LCP devices achieve or improve performance through chiral doping, pitch becomes one of the most critical structural parameters, and deviations significantly weaken the diffraction performance of the grating. Therefore, accurate pitch measurement is crucial for calculating the diffraction efficiency of LCP polarization gratings, selectively controlling the reflection wavelength of polarizing body gratings, and optimizing display performance.

[0003] Various pitch measurement methods have been developed for traditional cholesteric liquid crystal systems. Polarizing microscopy measures pitch by observing fingerprint patterns in the liquid crystal texture; however, this method relies on manual interpretation, resulting in highly subjective results, and requires a clear fingerprint texture, making it unsuitable for cured films with small twist angles or strong anchoring. Polarimetry measures the optical rotation angle of the liquid crystal and calculates the pitch using optical rotation theory; however, this method requires precise knowledge of the liquid crystal cell thickness and is unsuitable for cured films. X-ray diffraction analyzes the arrangement of liquid crystal molecules to determine the pitch, but the equipment is expensive, sample preparation is complex, and measurements are time-consuming, making it unsuitable for rapid detection. Atomic force microscopy (AFM) can directly measure the spacing of fingerprint textures in the surface morphology, but it has a limited scanning range, is slow, damages the sample surface, and cannot obtain the average pitch within the film. Ultraviolet-visible spectrophotometry measures the optical properties of the liquid crystal to indirectly estimate the pitch, but this usually requires prior knowledge of the thickness parameter. The Grandjean-Cano prism method requires injecting liquid crystal into a liquid crystal cell with a specific wedge angle, observing Cano fringes under a polarizing microscope, and using geometric relationships to infer the pitch. This requires the liquid crystal to be in a fluid state and the thickness of the liquid crystal cell to be precisely known. The ellipsometer method calculates the pitch by measuring the optical constants of the liquid crystal film, but requires complex optical model fitting and high film surface quality. Image analysis-based methods for calculating the pitch of cholesteric liquid crystals use polarizing microscope images combined with image processing algorithms to extract pitch information, but still rely on microscope imaging and are not applicable to cured films. In the field of liquid crystal polymer films, researchers typically control the pitch of helical structures by adjusting the grafting density of liquid crystal polymers deposited on silicon wafers, but the related pitch characterization still relies on imaging measurements using electron microscopy or atomic force microscopy, thus failing to achieve rapid, non-destructive spectral inversion. Therefore, although the above methods can measure the pitch of cholesteric or twisted nematic liquid crystals in certain specific scenarios, they generally suffer from the following insurmountable limitations:

[0004] First, there is the coupling problem between thickness and pitch: Traditional pitch measurement methods usually treat pitch and thickness as independent parameters and measure or pre-calibrate them separately. When the thickness is unknown, the pitch cannot be uniquely determined solely by the transmittance spectrum, resulting in ambiguous solutions due to parameter coupling.

[0005] Second, there is an over-reliance on liquid crystal cells with known thickness: most existing pitch measurement methods require the liquid crystal material to be encapsulated within a liquid crystal cell of precisely known thickness. For example, the Grandjean-Cano method, the polarimeter method, and most interferometric measurement methods all presuppose that the thickness of the liquid crystal cell is known. However, for cured twisted liquid crystal polymer films, it is no longer possible to inject them into a liquid crystal cell for measurement.

[0006] Third, the unique characteristics of cured twisted liquid crystal polymer films cannot be characterized by traditional methods: Liquid crystal polymer films are typically prepared through solution coating, solvent evaporation, and UV curing. After curing, the arrangement of liquid crystal molecules is permanently locked within a solid polymer network. However, the helical twisting power (HTP) of chiral agents in twisted liquid crystal polymers is highly correlated with the intermolecular interactions and compatibility of chiral molecules within the host liquid crystal material. When the liquid crystal formulation contains organic solvents, the HTP value is significantly affected by factors such as solvent polarity and volatility; only after the solvent has completely evaporated and the film has cured to form a polymer network can the true HTP value of the chiral agent in the liquid crystal polymer be obtained. Traditional liquid crystal cell-based measurement methods, because the measurement object is liquid or uncured liquid crystal containing solvent, cannot accurately reflect the true influence of anchoring effect, residual stress, and interface anchoring on pitch in the cured polymer network. Therefore, there is a systematic deviation between the pitch measured by traditional methods and the actual pitch of the cured film.

[0007] Fourth, the measurement efficiency is low: polarizing microscopy and atomic force microscopy rely on manual interpretation or point-by-point scanning, which is time-consuming and makes it difficult to achieve rapid and batch detection; X-ray diffraction and ellipsometer methods are expensive and complicated to operate, and are not suitable for conventional thin film detection scenarios.

[0008] In summary, existing pitch measurement methods cannot simultaneously meet the following constraints: ① the test material is a cured twisted liquid crystal polymer film; ② the film thickness is an unknown parameter; ③ the measurement process is rapid (within a few minutes) and non-destructive; ④ it can reflect the true influence of the anchoring effect of the molecular network and residual stress in the cured polymer on the pitch. Therefore, there is an urgent need to develop a rapid pitch measurement method that can directly target twisted liquid crystal polymer films, quickly inverting pitch parameters from spectral data under unknown thickness conditions, to solve the technical problem that traditional measurement methods are not applicable to cured twisted liquid crystal polymer films. Summary of the Invention

[0009] The purpose of this invention is to provide a method and apparatus for rapid pitch measurement of twisted liquid crystal polymers, so as to solve the problem that existing pitch measurement methods cannot perform rapid and non-destructive pitch measurement on cured twisted liquid crystal polymer films under unknown thickness conditions.

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] A rapid method for measuring the pitch of a twisted liquid crystal polymer film includes the following steps:

[0012] Step 1: Obtain the transmittance spectral response data of linearly polarized light after it is perpendicularly incident on the twisted liquid crystal polymer film and then emitted through a broadband analyzer. The linearly polarized light is generated by light emitted from a broadband light source being perpendicularly incident on the broadband analyzer.

[0013] Step 2: Preprocess the transmittance spectral response data to obtain the experimental relative transmittance curve;

[0014] Step 3: Construct a theoretical transmittance model of the twisted liquid crystal polymer film under vertical incident conditions, obtain the theoretical transmittance curve, and calculate the theoretical relative transmittance curve corresponding to each set of pitch and thickness parameter combinations of the twisted liquid crystal polymer film within the preset inversion range.

[0015] Step 4: Use a trend evaluation function to calculate the similarity between the theoretical relative transmittance curve and the experimental relative transmittance curve as wavelength changes, select theoretical relative transmittance curves with a similarity greater than or equal to a preset similarity threshold, and use the pitch and thickness parameter combination corresponding to the selected curves as the candidate parameter range.

[0016] Step 5: Within the range of the candidate parameters, the matching degree between the theoretical relative transmittance curve and the experimental relative transmittance curve with wavelength fluctuation is calculated using the oscillation degree evaluation function, and the pitch corresponding to the maximum matching degree is taken as the measured pitch of the twisted liquid crystal polymer film.

[0017] Meanwhile, the present invention also provides a rapid pitch measurement device for twisted liquid crystal polymers, comprising a broadband light source, a broadband polarizer, a twisted liquid crystal polymer film, a broadband analyzer, a spectrometer, and a data processing module arranged sequentially along the optical path. The output end of the broadband analyzer is connected to the spectrometer via an optical fiber. The light emitted from the broadband light source is polarized by the broadband polarizer to form linearly polarized light. The linearly polarized light is incident perpendicularly on the twisted liquid crystal polymer film. The light emitted from the twisted liquid crystal polymer film passes through the broadband analyzer and is coupled to the spectrometer via the optical fiber. The spectrometer outputs the collected transmittance spectral response data to the data processing module, which is configured to perform the following operations:

[0018] The transmittance spectral response data are preprocessed to obtain the experimental relative transmittance curve;

[0019] A theoretical transmittance model of the twisted liquid crystal polymer film under vertical incident conditions is constructed to obtain the theoretical transmittance curve. For each set of pitch and thickness parameter combinations of the twisted liquid crystal polymer film within a preset inversion range, the theoretical relative transmittance curve corresponding to each set of parameter combinations is calculated.

[0020] The similarity between the theoretical relative transmittance curve and the experimental relative transmittance curve with wavelength is calculated using a trend evaluation function. The theoretical relative transmittance curves with a similarity greater than or equal to a preset similarity threshold are selected, and the pitch and thickness parameter combination corresponding to the selected curves is used as the candidate parameter range.

[0021] Within the range of candidate parameters, the degree of matching between the theoretical relative transmittance curve and the experimental relative transmittance curve with wavelength fluctuations corresponding to each parameter combination is calculated using the oscillation degree evaluation function, and the pitch corresponding to the maximum matching degree is taken as the measured pitch of the twisted liquid crystal polymer film.

[0022] The present invention provides a rapid method and apparatus for measuring the pitch of twisted liquid crystal polymers, which is particularly suitable for non-destructive rapid detection of the pitch of cured liquid crystal polymer films with unknown thickness. Compared with the prior art, the present invention has the following advantages:

[0023] This invention achieves accurate pitch inversion by jointly optimizing the trend evaluation function and the oscillation degree evaluation function without prior knowledge of the thickness of the twisted liquid crystal polymer film, thus solving the core technical problem of measurement difficulties caused by the coupling of thickness and pitch in traditional measurement methods.

[0024] This invention employs a dual verification strategy combining a trend evaluation function with quantification of oscillation degree differences, which has good tolerance to noise and baseline drift, good measurement repeatability, and strong robustness.

[0025] This invention can directly perform non-destructive measurements on cured twisted liquid crystal polymer films without encapsulating the liquid crystal material in a liquid crystal cell. It can accurately reflect the combined effects of anchoring effect, residual stress, and interface anchoring on pitch in the cured polymer network. The measured pitch can be directly used to calculate the true HTP value of chiral agents in liquid crystal polymers, which is something that traditional measurement methods cannot achieve.

[0026] This invention offers fast measurement speed and high efficiency. From spectral data acquisition and processing to outputting pitch results, it typically takes no more than 10 minutes. Compared with polarizing microscopy and atomic force microscopy, which take tens of minutes, this invention has a significant efficiency advantage and is particularly suitable for batch testing and online quality control.

[0027] The measuring device of the present invention is simple and low in cost, requiring only a broadband light source, polarizer, analyzer, optical fiber, spectrometer and data processing module, without the need for a precision displacement stage, X-ray source or atomic force microscope, and is easy to integrate and promote. Attached Figure Description

[0028] Figure 1 This is a flowchart of a rapid pitch measurement method for twisted liquid crystal polymers according to an embodiment of the present invention;

[0029] Figure 2 This is a schematic diagram of the structure of a rapid pitch measurement device for twisted liquid crystal polymer according to an embodiment of the present invention;

[0030] Figure 3 This is a comparison chart of the experimental relative transmittance curve and the theoretical optimal inversion curve for relative transmittance.

[0031] Explanation of reference numerals in the attached figures: 1. Broadband light source; 2. Broadband polarizer; 3. Twisted liquid crystal polymer film; 4. Broadband analyzer; 5. Optical fiber; 6. Spectrometer. Detailed Implementation

[0032] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and preferred embodiments.

[0033] like Figure 1 As shown, this embodiment provides a method for rapid measurement of the pitch of a twisted liquid crystal polymer, which specifically includes the following steps:

[0034] Step 1: Light emitted from a broadband light source is incident perpendicularly onto a broadband polarizer. After passing through the broadband polarizer, it is converted into linearly polarized light. The linearly polarized light is incident perpendicularly onto the front surface of the twisted liquid crystal polymer film. Light exiting perpendicularly from the rear surface of the twisted liquid crystal polymer film is incident onto a broadband analyzer. The transmittance spectral response data of the outgoing light after passing through the broadband analyzer is obtained. For example, the outgoing light from the broadband analyzer is coupled into a spectrometer through an optical fiber, and the transmittance spectral response data is acquired by the fiber optic spectrometer.

[0035] Optionally, the broadband light source is a continuous spectrum light source with an output wavelength range of 360nm to 2400nm.

[0036] Both the wideband polarizer and the wideband analyzer are wire grid polarizers with operating wavelengths from 400 nm to 1100 nm.

[0037] The wavelength range of the fiber optic spectrometer is 190nm to 1100nm.

[0038] The thickness direction of the twisted liquid crystal polymer film, the transmission axis of the broadband analyzer, and the transmission axis of the broadband polarizer are respectively... axis, axis, Establish a rectangular coordinate system based on the axes. ,like Figure 2 As shown.

[0039] In this embodiment, the twisted liquid crystal polymer film is a film doped with a chiral agent and cured. Its thickness is unknown. The optical axis of its liquid crystal molecules changes in a spiral manner and satisfies the following relationship:

[0040] (1)

[0041] In equation (1), The unit vector representing the direction of the optical axis of the liquid crystal molecules; The coordinate variable representing spatial position information along the thickness direction of the twisted liquid crystal polymer film; The pitch of the twisted liquid crystal polymer film.

[0042] Step 2: Preprocess the transmittance spectral response data obtained in Step 1 to obtain the experimental relative transmittance curve.

[0043] Specifically, the preprocessing in this step includes the following steps:

[0044] The transmittance spectral response data were denoised and smoothed to obtain the experimental transmittance curve. ;

[0045] The experimental transmittance curve Divide by its maximum value The experimental relative transmittance curve was obtained. Its formula can be expressed as: .

[0046] Step 3: Construct a theoretical transmittance model for the twisted liquid crystal polymer film under vertical incident conditions, and obtain the theoretical transmittance curve, the expression of which is:

[0047] (2)

[0048] In equation (2), This is the theoretical transmittance value; For the Singer function; The angle between the transmission axes of the broadband polarizer and the broadband analyzer; The twist angle of the twisted liquid crystal polymer film; The thickness of the twisted liquid crystal polymer film; The pitch of the twisted liquid crystal polymer film; , The wavelength of light (in nm) ranges from visible light (>400 nm) to near-infrared (<1 µm). The birefringence dispersion curve of the liquid crystal in the liquid crystal polymer film is shown, which was pre-determined using the Cauchy model.

[0049] Divide the theoretical transmittance curve by its maximum value Ultimately, the results depend on the parameters of the twisted liquid crystal polymer thin film device (pitch). and thickness The theoretical relative transmittance curve of () is given by the following formula: For the pitch of each set of twisted liquid crystal polymer films within the preset inversion range... and thickness Calculate the theoretical relative transmittance curve for each parameter combination.

[0050] Step 4: Given that the transmittance curve may exhibit non-monotonic behavior, this step uses a classic correlation parameter, such as the Pearson correlation coefficient, as a trend evaluation function to quantify the similarity between the trend of each theoretical relative transmittance curve in Step 3 and the experimental relative transmittance curve in Step 2 as wavelength changes.

[0051] Optionally, the trend assessment function is the Pearson correlation coefficient, whose expression is:

[0052] (3)

[0053] In equation (3), This represents a function that takes the larger value. This is the theoretical relative transmittance curve; The experimental relative transmittance curve; and These represent the theoretical and experimental relative transmittance curves at the operating wavelength, respectively. The average value within; Indicates pitch and thickness Below, the theoretical relative transmittance curve Relative transmittance curve compared to experiment The Pearson correlation coefficient between them.

[0054] Within a preset inversion range, the Pearson correlation coefficient between each calculated theoretical relative transmittance curve and the experimental relative transmittance curve is used as the similarity score, and a preset similarity threshold is set. Filter out all that meet the requirements The theoretical relative transmittance curve is used to obtain the pitch and thickness parameter combination corresponding to the screening curve. All parameter combinations selected A range of candidate parameters is formed for the actual device parameters of the twisted liquid crystal polymer thin film. Among these, a preset similarity threshold is defined. The threshold value can be set according to the required measurement accuracy; in this embodiment, it is set to 0.98. Generally, an effective range of candidate parameters can be obtained when this threshold is not lower than 0.9.

[0055] Step 5: Within the range of candidate parameters, calculate each parameter combination using the oscillation degree evaluation function. The degree of matching between the theoretical and experimental relative transmittance curves with wavelength fluctuations was determined, and the pitch corresponding to the maximum matching degree was used as the measured pitch of the twisted liquid crystal polymer film.

[0056] Specifically, in this step, an oscillation degree evaluation function is used to quantify each parameter combination within the candidate parameter range. The degree of matching between the theoretical and experimental relative transmittance curves and the degree of wavelength fluctuation. The expression for the oscillation degree evaluation function is as follows:

[0057] (4)

[0058] In equation (4), Indicates pitch and thickness Below, the value of the oscillation degree evaluation function; This represents a function that takes a smaller value. The closer the value is to 1, the higher the consistency of the oscillation degree between the two curves. Using the value of the oscillation degree evaluation function as the matching degree, the parameter range determined in step 4 is used to find the optimal match. Maximize the optimal combination of parameters that yields the maximum matching degree. In the optimal parameter combination, the pitch This refers to the measured pitch of the twisted liquid crystal polymer film obtained through inversion.

[0059] This embodiment presents a rapid pitch measurement method for twisted liquid crystal polymers. By jointly optimizing a trend evaluation function and an oscillation degree evaluation function, the pitch can be accurately inverted without prior knowledge of the twisted liquid crystal polymer film thickness, solving the core technical problem of measurement difficulties caused by the coupling of thickness and pitch in traditional measurement methods. This method employs a dual verification strategy combining trend evaluation functions such as the Pearson correlation coefficient with quantification of oscillation degree differences, exhibiting good tolerance to noise and baseline drift, good measurement repeatability, and strong robustness. Furthermore, this method can directly perform non-destructive measurements on cured twisted liquid crystal polymer films without encapsulating the liquid crystal material in a liquid crystal cell. It can accurately reflect the combined influence of anchoring effect, residual stress, and interface anchoring on the pitch in the cured polymer network. The measured pitch can be directly used to calculate the true HTP value of the chiral agent in the liquid crystal polymer, which is impossible with traditional measurement methods. In addition, this method is fast and efficient. From spectral data acquisition and processing to outputting pitch results, it usually takes no more than 10 minutes. Compared with polarizing microscopy and atomic force microscopy, which take tens of minutes, it has a significant efficiency advantage and is particularly suitable for batch testing and online quality control.

[0060] Another embodiment of the present invention provides a device for rapid measurement of pitch of a twisted liquid crystal polymer, such as... Figure 2 As shown, the device mainly includes a broadband light source 1, a broadband polarizer 2, a sample stage, a broadband analyzer 4, a spectrometer 6, and a data processing module arranged sequentially along the optical path. The twisted liquid crystal polymer film 3 to be tested is placed on the sample stage. The output end of the broadband analyzer 4 is connected to the spectrometer 6 via an optical fiber 5. The light emitted from the broadband light source 1 passes perpendicularly through the broadband polarizer 2, and after being polarized by the broadband polarizer 2, it is converted into linearly polarized light. This linearly polarized light then strikes the front surface of the twisted liquid crystal polymer film 3 perpendicularly. The light exiting perpendicularly from the rear surface of the twisted liquid crystal polymer film 3 passes through the broadband analyzer 4 and is coupled into the spectrometer 6 by the optical fiber 5.

[0061] The parameters of the rapid pitch measurement device for twisted liquid crystal polymer in this embodiment are configured as follows:

[0062] Broadband light source 1 is a long-life halogen tungsten lamp with an output wavelength coverage range of 360nm to 2400nm;

[0063] Both the wideband polarizer 2 and the wideband analyzer 4 are linear grid polarizers with a working wavelength covering 400nm to 1100nm. The angle between the transmission axes of the wideband polarizer 2 and the wideband analyzer 4 is 90° orthogonal.

[0064] Fiber 5 is an ultra-strong UV-resistant fiber with a core diameter of 230 μm;

[0065] Spectrometer 6 is a fiber optic spectrometer with a wavelength coverage range of 190 nm to 1100 nm;

[0066] The chiral agent in the twisted liquid crystal polymer film 3 to be tested has a mass fraction of 0.053%, and the pitch is estimated to be between 10 μm and 18 μm. The thickness of the twisted liquid crystal polymer film 3 is estimated to be between 1 μm and 6 μm, but it has not been precisely calibrated and is used as an unknown parameter in pitch inversion.

[0067] Based on all the parameters and configurations in this embodiment, the broadband light source 1 is turned on, the optical path is adjusted so that the light beam is perpendicularly incident on the surface of the twisted liquid crystal polymer film 3 to be tested, the spectrometer 6 collects the transmittance spectral response data, and outputs the collected transmittance spectral response data to the data processing module, which is then configured to perform the following operations:

[0068] The raw transmittance spectral response data is smoothed and filtered, including denoising and smoothing, to obtain the experimental transmittance curve. The inversion wavelength range is 420 nm to 860 nm; the experimental transmittance curves are shown. Divide by its maximum value The experimental relative transmittance curve was calculated. .

[0069] For each parameter combination within the preset inversion range Based on formula (2), the theoretical relative transmittance curve corresponding to each parameter combination is calculated. The birefringence dispersion curve of the liquid crystal in the twisted liquid crystal polymer film 3 was pre-determined using the Cauchy model, and its expression is: The pitch of the twisted liquid crystal polymer film 3 and thickness The preset inversion ranges are 2μm~30μm and 1μm~8μm, respectively.

[0070] A classic correlation parameter, such as the Pearson correlation coefficient, is used as the trend assessment function to quantify the similarity between the theoretical and experimental relative transmittance curves as a function of wavelength. For example, according to formula (3), the similarity between the theoretical and experimental relative transmittance curves as a function of wavelength is calculated. and thickness Theoretical relative transmittance curve Relative transmittance curve compared to experiment Pearson correlation coefficient between And using the Pearson correlation coefficient As a measure of similarity, it is compared with a preset similarity threshold. Compare and filter out all that meet the requirements. Pitch and thickness parameter combination All parameter combinations selected Candidate parameter range for actual device parameters formed by twisted liquid crystal polymer thin film 3.

[0071] Within the candidate parameter range, the oscillation degree evaluation function shown in formula (4) is used to quantify each parameter combination within the candidate parameter range. The degree of matching between the theoretical and experimental relative transmittance curves and the degree of wavelength fluctuation. Oscillation assessment function. The closer the value is to 1, the higher the consistency of the oscillation degree between the two curves. Using the value of the oscillation degree evaluation function as the matching degree, the optimal match is found within the candidate parameter range. The optimal combination of parameters that maximizes the matching degree is: At this point, the oscillation degree evaluation function The value is 0.9891.

[0072] The pitch measurement time of the twisted liquid crystal polymer film 3 obtained by inversion using the twisted liquid crystal polymer pitch rapid measurement device proposed in this embodiment is less than 5 minutes. Furthermore, the optimal parameter combination obtained by inversion based on the measurement device proposed in this embodiment... The calculated theoretical relative transmittance optimal inversion curve (i.e., optimal parameter combination) The comparison results between the corresponding theoretical relative transmittance curve and the experimental relative transmittance curve are as follows: Figure 3 As shown. From Figure 3 As can be seen, throughout the entire inversion band, the trend, oscillation degree, and peak wavelength of the theoretical relative transmittance optimal inversion curve with respect to light wavelength all show very good consistency with the experimental relative transmittance curve. This indicates that the pitch value of 12.415 μm obtained from the above inversion is the actual pitch of the twisted liquid crystal polymer film 3. Therefore, the measuring device of the present invention can well meet the current demand for accurate measurement of the pitch of twisted liquid crystal polymer films.

[0073] The rapid pitch measurement device for twisted liquid crystal polymers in this embodiment has a simple structure and low cost. It only requires a broadband light source, two broadband polarizers, optical fiber and spectrometer. It does not require a precision displacement stage, X-ray source or atomic force microscope. It is easy to integrate and promote. At the same time, it has the advantages of fast measurement speed and high efficiency. It has significant advantages and application prospects in the pitch measurement of twisted liquid crystal polymer films.

[0074] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0075] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A rapid method for measuring the pitch of a twisted liquid crystal polymer film, characterized in that, Includes the following steps: Step 1: Obtain the transmittance spectral response data of linearly polarized light after it is perpendicularly incident on the twisted liquid crystal polymer film and then emitted through a broadband analyzer. The linearly polarized light is generated by light emitted from a broadband light source being perpendicularly incident on the broadband analyzer. Step 2: Preprocess the transmittance spectral response data to obtain the experimental relative transmittance curve; Step 3: Construct a theoretical transmittance model of the twisted liquid crystal polymer film under vertical incident conditions, obtain the theoretical transmittance curve, and calculate the theoretical relative transmittance curve corresponding to each set of pitch and thickness parameter combinations of the twisted liquid crystal polymer film within the preset inversion range. Step 4: Use a trend evaluation function to calculate the similarity between the theoretical relative transmittance curve and the experimental relative transmittance curve as wavelength changes, select theoretical relative transmittance curves with a similarity greater than or equal to a preset similarity threshold, and use the pitch and thickness parameter combination corresponding to the selected curves as the candidate parameter range. Step 5: Within the range of the candidate parameters, the matching degree between the theoretical relative transmittance curve and the experimental relative transmittance curve with wavelength fluctuation is calculated using the oscillation degree evaluation function, and the pitch corresponding to the maximum matching degree is taken as the measured pitch of the twisted liquid crystal polymer film.

2. The rapid measurement method for the pitch of a twisted liquid crystal polymer film according to claim 1, characterized in that, The preprocessing process includes: The transmittance spectral response data is denoised and smoothed to obtain the experimental transmittance curve; Divide the experimental transmittance curve by its maximum value to obtain the experimental relative transmittance curve.

3. A method for rapid measurement of pitch in a twisted liquid crystal polymer according to claim 1 or 2, characterized in that, The expression for the theoretical transmittance curve is: （2） in, This is the theoretical transmittance value; For the Singer function; The angle between the transmission axes of the wideband polarizer and the wideband analyzer; The twist angle of the twisted liquid crystal polymer film; The thickness of the twisted liquid crystal polymer film; The pitch of the twisted liquid crystal polymer film; ; Wavelength; The birefringence dispersion curve of the liquid crystal in the twisted liquid crystal polymer film is shown.

4. The method for rapid measurement of pitch in a twisted liquid crystal polymer according to claim 3, characterized in that, The theoretical relative transmittance curve is obtained by dividing the theoretical transmittance curve by its maximum value.

5. A method for rapid measurement of pitch in a twisted liquid crystal polymer according to claim 1 or 2, characterized in that, The trend assessment function is the Pearson correlation coefficient, and its expression is: （3） in, Indicates pitch and thickness Below, the theoretical relative transmittance curve Relative transmittance curve compared to experiment The Pearson correlation coefficient between them; This represents a function that takes the larger value. and These represent the theoretical and experimental relative transmittance curves at the operating wavelength, respectively. The average value within the range.

6. The method for rapid measurement of pitch in a twisted liquid crystal polymer according to claim 5, characterized in that, The expression for the oscillation degree evaluation function is: （4） in, Indicates pitch and thickness Below, the value of the oscillation degree evaluation function; This represents a function that takes a smaller value.

7. A method for rapid measurement of pitch in a twisted liquid crystal polymer according to claim 1 or 2, characterized in that, The broadband light source is a continuous spectrum light source with an output wavelength range of 360nm to 2400nm; Both the wideband polarizer and the wideband analyzer are linear grid polarizers with operating wavelengths from 400 nm to 1100 nm.

8. A method for rapid measurement of pitch in a twisted liquid crystal polymer according to claim 1 or 2, characterized in that, In step 1, the transmittance spectral response data is acquired by a fiber optic spectrometer with a wavelength range of 190 nm to 1100 nm.

9. A method for rapid measurement of pitch in a twisted liquid crystal polymer according to claim 1 or 2, characterized in that, The preset similarity threshold is 0.

98.

10. A device for rapid measurement of pitch in a twisted liquid crystal polymer, characterized in that, The system includes a broadband light source (1), a broadband polarizer (2), a sample stage for placing a twisted liquid crystal polymer film (3), a broadband analyzer (4), a spectrometer (6), and a data processing module arranged sequentially along the optical path. The output end of the broadband analyzer (4) is connected to the spectrometer (6) via an optical fiber (5). The light emitted from the broadband light source (1) is polarized by the broadband polarizer (2) to form linearly polarized light. The linearly polarized light is incident perpendicularly on the twisted liquid crystal polymer film (3). The light emitted from the twisted liquid crystal polymer film (3) is then coupled to the spectrometer (6) via the optical fiber (5) after passing through the broadband analyzer (4). The spectrometer (6) outputs the collected transmittance spectral response data to the data processing module. The data processing module is configured to perform the following operations: The transmittance spectral response data are preprocessed to obtain the experimental relative transmittance curve; A theoretical transmittance model of the twisted liquid crystal polymer film (3) under vertical incident conditions is constructed to obtain the theoretical transmittance curve. For each set of pitch and thickness parameter combinations of the twisted liquid crystal polymer film (3) within the preset inversion range, the theoretical relative transmittance curve corresponding to each set of parameter combinations is calculated. The similarity between the theoretical relative transmittance curve and the experimental relative transmittance curve with wavelength is calculated using a trend evaluation function. The theoretical relative transmittance curves with a similarity greater than or equal to a preset similarity threshold are selected, and the pitch and thickness parameter combination corresponding to the selected curves is used as the candidate parameter range. Within the range of candidate parameters, the degree of matching between the theoretical relative transmittance curve and the experimental relative transmittance curve with wavelength fluctuation is calculated using the oscillation degree evaluation function, and the pitch corresponding to the maximum value of the matching degree is taken as the measured pitch of the twisted liquid crystal polymer film (3).

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