Calibration method of liquid crystal variable retarder based on interference method

Abstract

The invention discloses a liquid crystal variable retarder calibration method based on an interference method. The method is used for accurate calibration of LCVR electric control retardation. According to the method, an interference image is collected through a CCD camera, and after the image is preprocessed, FFT transformation unwrapping is carried out on an image column average intensity vector to obtain an LCVR electric control phase retardation curve. A polarization camera collects a light intensity image containing multi-polarization information at a time, polarization sub-images corresponding to 0 degree, 90 degrees, 45 degrees and 135 degrees are decomposed through sub-pixel sampling, a polarization judgment curve is formed through difference calculation of Stokes parameters S0 and S2, and the LCVR half-wave delay voltage is determined through the position of the minimum value of the curve. According to the method, the vibration resistance of the interference method and the noise reduction characteristic of the Stokes vector method are combined, the LCVR electric control delay curve can be calculated through the interference method, meanwhile, the half-wave delay voltage is synchronously indicated through Stokes vector calculation, the problems of unstable laser light source intensity, environmental disturbance, noise influence and the like are effectively solved, and the method has important significance on accurate calibration of the LCVR.

Description

Technical Field

[0001] The present invention belongs to the technical field of precision instrument measurement, and specifically relates to a calibration method for a liquid crystal variable retarder based on the interference method. Background Art

[0002] Liquid crystal is a unique material state between isotropic liquid and anisotropic crystal. Most of them are organic substances and their mixtures. Their molecules are rod-shaped, and their arrangement mechanism shows a certain degree of order. Their physical properties show anisotropy in certain directions. The intermolecular interaction force of liquid crystal molecules is relatively weak, which enables liquid crystal to quickly adjust its molecular arrangement when the external physical environment changes, thereby changing its optical properties.

[0003] CN200910076360.9 discloses a "Calibration System for Characteristic Parameters of Liquid Crystal Phase Variable Retarder". This method modulates the angles of the polarizer and analyzer, and uses the light intensity values detected under different adjustment states to establish a Stokes vector expression, and measures the phase retardation of the LCVR at a specific voltage. This method requires adjusting the analyzer angle during the measurement process, and system errors are easily introduced during the adjustment process. Currently, common calibration methods cannot obtain the calculated data at one time in a set of systems. Summary of the Invention

[0004] In order to solve the problem that in the existing calibration methods for liquid crystal variable retarders, a single interference method cannot obtain the overall constant term difference of the electro-optic phase retardation curve in a single test and additional tests are required, the present invention proposes a calibration method for a liquid crystal variable retarder based on the interference method. In the same test system, the interference method is simultaneously used to measure the phase retardation distribution, and the Stokes vector is used to accurately calculate the constant term difference of the phase retardation curve, thereby avoiding the error accumulation caused by step-by-step measurement in the traditional method, improving the calibration accuracy and consistency of the liquid crystal variable retarder, and providing a reliable technical means for high-precision polarization device measurement.

[0005] The technical solution for achieving the purpose of the present invention is as follows: A calibration method for a liquid crystal variable retarder based on the interference method, the steps are as follows:

[0006] Step 1: Build an interference calibration device;

[0007] The interference calibration device includes a light source module, an interference module, and a Stokes vector measurement module. The light source module includes a laser light source, a first lens, and a first polarization beam splitter. The interference module includes a first half-wave plate, a second polarization beam splitter, a first reflector, the LCVR to be calibrated, a first beam splitter, a linear polarizer, and a CCD camera. The Stokes vector measurement module includes a second reflector, a second half-wave plate, a second beam splitter, a second lens, a diaphragm, a third lens, and a polarization camera.

[0008] Step 2: Turn on the laser light source and the power supply for the LCVR to be calibrated. The laser light source outputs a point light source through the fiber optic flange. Adjust the position of the point light source so that it is located at the focal point of the first lens. The light beam emitted by the point light source is collimated by the first lens and then incident on the first polarization beam splitter. The first polarization beam splitter divides the collimated light into the first P-light and the first S-light.

[0009] Step 3: After the first P-light passes through the first half-wave plate and the second polarization beam splitter in sequence, it is divided into the second P-light and the second S-light. The second P-light is reflected by the first mirror, passes through the LCVR to be calibrated, and then is reflected by the first beam splitter and turns back to the second polarization beam splitter; the second S-light is reflected by the first beam splitter, passes through the LCVR to be calibrated, and then is reflected by the first mirror back to the second polarization beam splitter; adjust the pitch angle of the first mirror so that the light spots of the second P-light and the second S-light reflected back onto the second polarization beam splitter coincide; the light after the second P-light and the second S-light are combined is incident on the target surface of the CCD camera through the linear polarizer. Rotate the linear polarizer to make the interference image on the target surface of the CCD camera the clearest.

[0010] Step 4: After the first S-light is reflected by the second mirror, it passes through the second half-wave plate and the first beam splitter in sequence. Adjust the pitch angle of the second mirror so that the first S-light is reflected by the second beam splitter after passing through the LCVR to be calibrated; the first S-light, the second P-light, and the second S-light are focused after passing through the second lens. Adjust the aperture size of the aperture so that only the first S-light exists in the light beam passing through the third lens. Adjust the position of the third lens so that the first S-light is collimated and incident on the target surface of the polarization camera after passing through the third lens.

[0011] Step 5: Set the power supply for the LCVR to be calibrated to start from 0V, and the voltage increases by a predetermined step amount every second. At the same time, the CCD camera collects interference images every second, and the polarization camera collects intensity images every second.

[0012] Step 6: Preprocess the interference images collected by the CCD camera to obtain the preprocessed interference images. Take the column average of the interference fringes in the preprocessed interference images, apply FFT to the column average intensity vector for unwrapping, take the first peak outside the zero frequency, calculate the phase delay amount through the above first peak, and obtain the unwrapped delay amount curve.

[0013] Step 7: Perform sub-pixel reconstruction on the intensity images collected by the polarization camera, divide them into several 2×2 pixel blocks, decompose each 2×2 pixel block into polarization sub-images corresponding to 0°, 90°, 45°, and 135°, calculate the Stokes parameters S0 and S2, construct a difference matrix using S0 and S2, sum all the elements in the above difference matrix, construct a polarization discrimination curve, and determine the half-wave delay voltage V of the LCVR to be calibrated through the minimum value of the curve. λ / 2 , where λ represents the maximum delay amount of the LCVR to be calibrated.

[0014] Step 8: Using the half-wave delay voltage V of the LCVR to be calibrated λ / 2 as a reference, translate the unwrapped delay curve, and after correcting the constant term error, obtain the final LCVR electro-optic delay curve to achieve the calibration of the LCVR.

[0015] Compared with the prior art, the remarkable advantages of the present invention are as follows:

[0016] (1) The calibration device of the present invention has strong resistance to low signal-to-noise ratio and background noise.

[0017] (2) The calibration device of the present invention relies on the common-path interference effect, can directly extract phase information from the interference fringes, and has a low dependence on the polarization angle of the incident light.

[0018] (3) Applying the calibration device of the present invention to calibrate by combining the interference method and the Stokes vector method can effectively solve the problem of insufficient universality of the calibration results under different devices. Description of the Drawings

[0019] Figure 1 is the optical path diagram of the calibration device applying the present invention.

[0020] Figure 2 is the final LCVR electro-optic delay curve of the calibration device of the present invention. Detailed Embodiment

[0021] The present invention will be further described in detail below with reference to the drawings.

[0022] Combined with Figure 1 , a calibration method for a liquid crystal variable retarder based on the interference method is as follows:

[0023] Step 1: Build an interference calibration device;

[0024] The interference calibration device includes a light source module, an interference module, and a Stokes vector measurement module. The light source module includes a laser light source 1, a first lens 2, and a first polarization beam splitter 3. The interference module includes a first half-wave plate 4, a second polarization beam splitter 5, a first mirror 6, the LCVR to be calibrated 7, a first beam splitter 8, a linear polarizer 9, and a CCD camera 10. The Stokes vector measurement module includes a second mirror 11, a second half-wave plate 12, a second beam splitter 13, a second lens 14, a diaphragm 15, a third lens 16, and a polarization camera 17.

[0025] The laser light source 1, the first lens 2, and the first polarization beam splitter 3 are arranged in sequence along the first optical path, followed by the first half-wave plate 4, the second polarization beam splitter 5, and the first mirror 6; the common-path linear polarizer 9 and the CCD camera 10 are arranged in sequence along the second optical path, and the second mirror 11, the second half-wave plate 12, the first beam splitter 8, the LCVR 7 to be calibrated, and the second beam splitter 13 are arranged in sequence along the third optical path, and the second lens 14, the aperture 15, the third lens 16, and the polarization camera 17 are arranged in sequence along the fourth optical path. The first optical path and the second optical path are perpendicular to each other, and the third optical path and the fourth optical path are perpendicular to each other.

[0026] Among them, the second mirror 11 is located on the reflection optical path of the first polarization beam splitter 3, the second beam splitter 13 is located on the reflection optical path of the second mirror 11, the aperture 15 is located on the reflection optical path of the second beam splitter 13, the first beam splitter 8 is located on one side of the second polarization beam splitter 5, and the linear polarizer 9 is located on one side of the second polarization beam splitter 5.

[0027] Go to step 2.

[0028] Step 2: Turn on the laser light source 1 and the driving power supply of the LCVR 7 to be calibrated. The laser light source 1 outputs a point light source through the fiber optic flange. Adjust the position of the point light source so that it is located at the focal point of the first lens 2. The light beam emitted by the point light source is collimated by the first lens 2 and then incident on the first polarization beam splitter 3. The first polarization beam splitter 3 divides the collimated light into the first P light and the first S light.

[0029] Go to step 3.

[0030] Step 3: After the first P light passes through the first half-wave plate 4 and the second polarization beam splitter 5 in sequence, it is divided into the second P light and the second S light; rotate the first half-wave plate 4 to adjust the intensity ratio of the second P light and the second S light so that the intensities of the second P light and the second S light are equal; the second P light is reflected by the first mirror 6, passes through the LCVR 7 to be calibrated, and then is reflected by the first beam splitter 8 and turns back to the second polarization beam splitter 5. The second S light is reflected by the first beam splitter 8, passes through the LCVR 7 to be calibrated, and then is reflected by the first mirror 6 back to the second polarization beam splitter 5; the first mirror 6 is equipped with a pitch adjustment bracket, and the pitch inclination angle of the first mirror 6 is adjusted by rotating the knob so that the spots of the second P light and the second S light reflected back to the second polarization beam splitter 5 coincide, and the optical paths of the second P light and the second S light are the same, forming a common-path interference structure. The common-path design has anti-vibration performance and does not introduce additional optical path difference; the light after the second P light and the second S light are combined is incident on the target surface of the CCD camera 10 through the linear polarizer 9, and the linear polarizer 9 is rotated to make the interference image on the target surface of the CCD camera 10 the clearest.

[0031] Go to step 4.

[0032] Step 4: After the first S light is reflected by the second mirror 11, it passes through the second half-wave plate 12 and the first beam splitter 8 in sequence, and then the first S light passes through the LCVR 7 to be calibrated and is reflected by the second beam splitter 13; the second mirror 11 is equipped with a pitch adjustment bracket, and the pitch inclination angle of the second mirror 11 is adjusted by rotating the knob, so that the first S light passes through the LCVR 7 to be calibrated and is reflected by the second beam splitter 13 and separated from the interference cavity formed by the second P light and the second S light; the first S light, the second P light and the second S light are reflected by the second beam splitter 13 and then turn and pass through the second lens 14. The position of the second lens 14 is adjusted to make the first S light, the second P light and the second S light focused after passing through the second lens 14. The aperture size of the aperture stop 15 is adjusted so that only the first S light passes through the third lens 16; the position of the third lens 16 is adjusted so that the first S light is collimated and incident on the target surface of the polarization camera 17 after passing through the third lens 16.

[0033] Proceed to Step 5.

[0034] Step 5: It is set that the driving power supply of the LCVR 7 to be calibrated starts from 0V, and the voltage increases by a predetermined step amount every second. At the same time, the CCD camera 10 collects interference images every second, and the polarization camera 17 collects intensity images every second until the voltage of the driving power supply of the LCVR 7 to be calibrated reaches the preset maximum value; the driving program controls the whole process to proceed synchronously, ensuring the measurement accuracy, solving the problem that the single interference method cannot obtain the overall constant term difference of the electro-optic phase delay curve in a single test and requires additional tests, and avoiding the error accumulation caused by step-by-step measurement.

[0035] Proceed to Step 6.

[0036] Step 6: Preprocess the interference images collected by the CCD camera 10, including but not limited to vertical correction, edge detection and cropping, so that the interference image fringes are vertical and clear, meeting the requirements for taking column averages of the interference fringes. Take the column average of the interference fringes in the preprocessed interference images, apply FFT to the column average intensity vector for unwrapping, take the first peak outside the zero frequency, and calculate the phase delay amount through the above first peak to obtain the unwrapped delay amount curve, specifically as follows:

[0037] Step 6-1: Rotate the interference images collected by the CCD camera 10 frame by frame at a step of 0.1° according to the preset angle sequence, and compare the amplitude ranges A(θ) calculated for the images I θ (x,y) at all rotation angles, and select the rotation angle θ* with the largest amplitude range A(θ) as the best rotation angle. At this time, the interference fringes in the image are closest to the vertical state:

[0038]

[0039] Among them, represents the average gray value of the interference fringe column, (x, y) represents the image index, M represents the height of the region of interest, and θ represents the rotation angle.

[0040] Step 6-2: For each frame of the interference image collected by the CCD camera 10, perform rotational correction of the optimal rotation angle θ* using the bicubic interpolation method, adjust the interference fringe direction to obtain a rotationally corrected image, and crop out the effective interference fringe region from the rotationally corrected image according to the preset region parameters to obtain a preprocessed interference image.

[0041] Step 6-3: Read the preprocessed interference image frame by frame, calculate the average gray value of the image along the column direction to form a column average intensity vector; perform FFT transformation on the column average intensity vector to obtain its spectrum, take the first peak outside the zero frequency, calculate the phase delay amount through the above first peak to obtain an unwrapped delay amount curve; perform unwrapping processing on all preprocessed interference images to construct an unwrapped delay amount curve.

[0042] Proceed to Step 7.

[0043] Step 7: Perform sub-pixel reconstruction on the intensity image collected by the polarization camera 17, divide it into several 2×2 pixel blocks, decompose each 2×2 pixel block into corresponding polarization sub-images of 0°, 90°, 45°, and 135°, calculate the Stokes parameters S0 and S2, construct a difference matrix using S0 and S2, sum all elements in the above difference matrix to construct a polarization discrimination curve, and determine the half-wave delay voltage V of the LCVR7 to be calibrated through the minimum value of the curve λ / 2 ; specifically as follows:

[0044] Step 7-1: Read the intensity image collected by the polarization camera 17 frame by frame. Each intensity image I(i, j) contains intensity information in different polarization directions. Take out four sub-pixels with different polarization angles. The sub-pixel intensity expressions are as follows:

[0045] I0(i, j) = I(2i - 1, 2j - 1), I1(i, j) = I(2i - 1, 2j)

[0046] I2(i, j) = I(2i, 2j - 1), I3(i, j) = I(2i, 2j)

[0047] Among them,

[0048] (i, j) is the sub-pixel horizontal and vertical coordinate index;

[0049] I0(i, j) and I3(i, j) correspond to the intensities in the 0° and 90° polarization directions;

[0050] I1(i, j) and I2(i, j) correspond to the intensities in the 45° and 135° polarization directions.

[0051] Step 7-2: Calculate the Stokes vector components based on the sub-pixel intensity data of four different polarization angles selected:

[0052] S0 = I0(i,j) + I3(i,j)

[0053] S2 = I1(i,j) - I2(i,j)

[0054] Where,

[0055] S0 represents the total intensity component;

[0056] S2 reflects the intensity difference between the polarization directions of 45° and 135°;

[0057] Step 7-3: Use S0 and S2 to construct a difference matrix, define the calculation result S = S0 - S2, sum over all pixels, construct a polarization discrimination curve, and obtain the global statistic ∑S:

[0058]

[0059] To determine the optimal polarization modulation state, plot the polarization discrimination curve of ∑S versus the frame number:

[0060] To determine the optimal polarization modulation state, plot the polarization discrimination curve of ∑S versus the frame number:

[0061]

[0062] Where,

[0063] idx represents the image frame number;

[0064] x represents the abscissa corresponding to the voltage value;

[0065] In the polarization discrimination curve, find the minimum value:

[0066] minS = min(∑S)

[0067] The corresponding voltage value is the half-wave delay voltage V λ / 2 :

[0068]

[0069] Where,

[0070] min Index represents the frame number when the curve ∑S reaches the minimum point.

[0071] In the polarization discrimination curve, find the minimum point, and the corresponding voltage value is the half-wave delay voltage V λ / 2 。

[0072] Proceed to Step 8.

[0073] Step 8: Using the half-wave delay voltage V of the LCVR to be calibrated as a reference, and combining with the phase unwrapping curve measured by the interferometry method, perform an overall translation correction on the phase delay curve to correct the constant term error and translate the unwrapped delay amount curve; specifically, calculate the translation amount C between the phase delay value corresponding to the position of the half-wave voltage V obtained by using the Stokes vector difference calculation and the interferometry unwrapping curve, and perform a global translation correction on the unwrapping curve: λ / 2 λ / 2 λ / 2 δ′(U) = δ(U) + C

[0074] δ′(U) = δ(U) + C

[0075] where,

[0076] δ(U) is the unwrapped phase delay curve;

[0077] δ′(U) is the corrected phase delay curve.

[0078] After correcting the constant term error, obtain the final LCVR electro-control delay amount curve to complete the calibration of the LCVR.

[0079] Example 1

[0080] Set the driving power supply of the LCVR7 to be calibrated to start from 0V, and increase the voltage by a predetermined step of 0.01V per second. At the same time, the CCD camera 10 collects 1001 interference images per second, and the polarization camera 17 collects 1001 light intensity images per second until the driving power supply voltage of the LCVR7 to be calibrated reaches the preset maximum value of 10V; unwrap the 1001 interference images collected by the CCD camera 10 to obtain the unwrapped phase delay curve; the polarization camera 17 collects the light intensity images, and through Stokes vector calculation, the experimental results show that the voltage corresponding to the calibrated half-wave delay amount of the present invention is 2.45V; using the half-wave voltage of 2.45V as a reference, translate the unwrapped phase delay curve, as Figure 2 , to obtain the final electro-control delay amount curve of the liquid crystal variable retarder.

[0081] In summary, the present invention can replace most of the existing electro-control phase delay amount measurement methods for liquid crystal variable retarders. This method combines the interferometry method and the Stokes vector method, proposes a calibration method for liquid crystal variable retarders based on the interferometry method, and realizes high-precision measurement of the LCVR electro-control phase delay curve. Using the Stokes vector difference calculation to determine the half-wave voltage, compensating for the global offset in the interferometry unwrapping curve, and realizing the elimination of the constant term. This method effectively reduces the systematic error introduced by two independent measurements before and after, and improves the absolute measurement accuracy of the liquid crystal variable retarder phase delay curve.

[0082] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all 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, it should be considered as within the scope described in this specification.

[0083] The above-described embodiments merely represent several implementation manners of the present invention. The description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A calibration method for a liquid crystal variable retarder based on interferometry, characterized in that: Here are the steps: Step 1: Build an interferometric calibration device; The interference calibration device comprises a light source module, an interference module and a Stokes vector measurement module. The light source module comprises a laser light source (1), a first lens (2) and a first polarization beam splitter (3). The interference module comprises a first half-wave plate (4), a second polarization beam splitter (5), a first reflector (6), a LCVR to be calibrated (7), a first beam splitter (8), a linear polarizer (9) and a CCD camera (10). The Stokes vector measurement module comprises a second reflector (11), a second half-wave plate (12), a second beam splitter (13), a second lens (14), an aperture (15), a third lens (16) and a polarization camera (17). Step 2: Turn on the laser light source (1) and the driving power of the LCVR (7) to be calibrated. The laser light source (1) outputs a point light source through the optical fiber flange. The position of the point light source is adjusted so that it is located at the focus of the first lens (2). The light beam emitted by the point light source is collimated by the first lens (2) and then incident on the first polarization beam splitter (3). The first polarization beam splitter (3) splits the collimated light into a first P light and a first S light. Step 3: The first P light is sequentially passed through the first half-wave plate (4) and the second polarization beam splitter (5), and then is split into the second P light and the second S light. The second P light is reflected by the first reflector (6), passes through the LCVR to be calibrated (7), and then is reflected by the first beam splitter (8) and then is folded back to the second polarization beam splitter (5); the second S light is reflected by the first beam splitter (8), passes through the LCVR to be calibrated (7), and then is reflected by the first reflector (6) back to the second polarization beam splitter (5); the pitch angle of the first reflector (6) is adjusted so that the light spots reflected back to the second polarization beam splitter (5) overlap with the light spots reflected by the second P light and the second S light on the second polarization beam splitter (5); the light after the second P light and the second S light are combined is incident on the target surface of the CCD camera (10) through the linear polarizer (9), and the linear polarizer (9) is rotated so that the interference image on the target surface of the CCD camera (10) is clearest; Step 4: After the first S light is reflected by the second reflector (11), it passes through the second half-wave plate (12) and the first beam splitter (8) in sequence, and the pitch angle of the second reflector (11) is adjusted so that the first S light passes through the LCVR (7) to be calibrated and is reflected by the second beam splitter (13); the first S light, the second P light and the second S light are incident on the second lens (14) and then focused, and the aperture size of the diaphragm (15) is adjusted so that the light beam passing through the third lens (16) contains only the first S light, and the position of the third lens (16) is adjusted so that the first S light passes through the third lens (16) and is collimated and incident on the target surface of the polarization camera (17); Step 5: Setting the driving power of the LCVR (7) to be calibrated to start from 0V, the voltage increases by a predetermined step amount every second, while the CCD camera (10) collects interference images every second, and the polarization camera (17) collects light intensity images every second; Step 6: preprocessing the interference image collected by the CCD camera (10) to obtain a preprocessed interference image, taking a column average of the interference fringes in the preprocessed interference image, applying FFT to the column average intensity vector to unwrap, taking the first peak outside the zero frequency, calculating the phase delay amount through the first peak, and obtaining a delay amount curve after unwrapping; Step 7: Perform sub-pixel reconstruction on the light intensity image collected by the polarization camera (17) and divide it into several 2×2 pixel blocks. Decompose each 2×2 pixel block into polarization sub-images corresponding to 0°, 90°, 45° and 135°, calculate the Stokes parameters S0 and S2, use S0 and S2 to construct a difference matrix, sum all the elements in the difference matrix, construct a polarization discrimination curve, and determine the half-wave delay voltage V of the LCVR (7) to be calibrated through the minimum value of the curve. λ / 2 , λ represents the maximum delay of the LCVR to be calibrated (7); Step 8: Use the half-wave delay voltage V of the LCVR (7) to be calibrated λ / 2 As a reference, the unwrapped delay curve is translated, and after correcting the constant term error, the final LCVR electronically controlled delay curve is obtained to achieve the calibration of the LCVR.

2. The calibration method of a liquid crystal variable retarder based on interferometry according to claim 1, characterized in that: In step 1, build an interferometric calibration device as follows: A laser light source (1), a first lens (2), a first polarization beam splitter (3), a first half-wave plate (4), a second polarization beam splitter (5), and a first reflector (6) are sequentially arranged on a common first optical path; a linear polarization plate (9) and a CCD camera (10) are sequentially arranged on a common second optical path; a second reflector (11), a second half-wave plate (12), a first beam splitter (8), a LCVR to be calibrated (7), and a second beam splitter (13) are sequentially arranged on a common third optical path; a second lens (14), an aperture (15), a third lens (16), and a polarization camera (17) are sequentially arranged on a common fourth optical path; the first optical path is perpendicular to the second optical path, and the third optical path is perpendicular to the fourth optical path; The second reflector (11) is located in the reflection light path of the first polarization beam splitter (3), the second beam splitter (13) is located in the reflection light path of the second reflector (11), the diaphragm (15) is located in the reflection light path of the second beam splitter (13), the first beam splitter (8) is located on one side of the second polarization beam splitter (5), and the linear polarizer (9) is located on one side of the second polarization beam splitter (5).

3. The calibration method of a liquid crystal variable retarder based on interferometry according to claim 1, characterized in that: In step 3, the ratio of the second P light and the second S light intensity is adjusted by rotating the first half-wave plate (4) so ​​that the second P light and the second S light intensity are equal; the first reflector (6) is equipped with a pitch adjustment frame, and the pitch tilt angle is adjusted by rotating the knob so that the light spots of the second P light and the second S light reflected back to the second polarization beam splitter (5) overlap; the second reflector (11) is equipped with a pitch adjustment frame, and the pitch tilt angle is adjusted so that the first S light passes through the LCVR (7) to be calibrated and is reflected by the second beam splitter (13).

4. The calibration method of a liquid crystal variable retarder based on interferometry according to claim 1, characterized in that: In step 4, the aperture size of the diaphragm (15) is adjusted, and the diaphragm (15) isolates the reflected light of the second P light and the second S light, so that the light beam incident on the third lens (16) and collimated contains only the first S light.

5. The calibration method of a liquid crystal variable retarder based on interferometry according to claim 1, characterized in that: In step 6, the interference image collected by the CCD camera (10) is preprocessed, including but not limited to vertical correction and edge detection and cropping, so that the interference image fringes are vertically clear and meet the requirement of averaging the interference fringes.

6. The calibration method of a liquid crystal variable retarder based on interferometry according to claim 5, characterized in that: In step 6, the interference image collected by the CCD camera (10) is preprocessed, the interference fringes in the preprocessed interference image are averaged, the column average intensity vector is unwrapped by applying FFT, the first peak outside the zero frequency is taken, the phase delay is calculated by the first peak, and the delay curve after unwrapping is obtained, which is specifically as follows: Step 6-1: The interference image collected by the CCD camera (10) is rotated frame by frame in a preset angle sequence with a step length of 0.1°, and the image I at all rotation angles is θ The amplitude range A(θ) calculated by (x, y) is compared, and the largest rotation angle θ* in the amplitude range A(θ) is selected as the optimal rotation angle. At this time, the interference fringes in the image are closest to the vertical state: in, represents the average gray value of the interference fringe column, (x, y) represents the image index, M represents the height of the region of interest, and θ represents the rotation angle; Step 6-2: performing rotation correction of the interference image collected by the CCD camera (10) frame by frame using a bicubic interpolation method at an optimal rotation angle θ*, adjusting the direction of the interference fringes to obtain a rotation correction image, and cropping an effective interference fringe area from the rotation correction image according to preset area parameters to obtain a preprocessed interference image; Step 6-3: Read the preprocessed interference image frame by frame, calculate the average grayscale value of the image along the column direction, and construct a column average intensity vector; perform FFT transformation on the column average intensity vector to obtain its spectrum, take its first peak outside the zero frequency, calculate the phase delay amount through the above first peak value, and obtain the unwrapped delay amount curve; perform unwrapping processing on all preprocessed interference images to construct the unwrapped delay amount curve.

7. The calibration method of a liquid crystal variable retarder based on interferometry according to claim 1, characterized in that: In step 7, the light intensity image collected by the polarization camera (17) is reconstructed by sub-pixel and divided into a plurality of 2×2 pixel blocks. Each 2×2 pixel block is decomposed into polarization sub-images corresponding to 0°, 90°, 45° and 135°. The Stokes parameters S0 and S2 are calculated. A difference matrix is ​​constructed using S0 and S2. All elements in the difference matrix are summed to construct a polarization discrimination curve. The half-wave delay voltage V of the LCVR (7) to be calibrated is determined by the minimum value of the curve. λ / 2 ; The details are as follows: Step 7-1: Read the light intensity image collected by the galvanometer camera (17) frame by frame. Each light intensity image I(i, j) contains intensity information of different polarization directions. Take out four sub-pixels with different polarization angles. The sub-pixel intensity expression is as follows: I0(i,j)=I(2i-1,2j-1), I1(i,j)=I(2i-1,2j) I2(i,j)=I(2i,2j-1), I3(i,j)=I(2i,2j) in, (i, j) is the horizontal and vertical coordinate index of the sub-pixel; I0(i,j) and I3(i,j) correspond to the intensities in the 0° and 90° polarization directions; I1(i,j) and I2(i,j) correspond to the intensities at 45° and 135° polarization directions; Step 7-2: Calculate the Stokes vector components based on the sub-pixel intensity data of the four selected different polarization angles: S0=I0(i,j)+I3(i,j) S2=I1(i,j)-I2(i,j) in, S0 represents the total intensity component; S2 reflects the intensity difference between polarization directions of 45° and 135°; Step 7-3: Define the calculation result S = S0-S2, and sum all pixels to obtain the global statistic ∑S: In order to determine the optimal polarization modulation state, a polarization discrimination curve of ∑S varying with the frame number is plotted; in the polarization discrimination curve, the minimum point is found, and the corresponding voltage value is the half-wave delay voltage V λ / 2 .

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