A small angular displacement measurement system based on conjugate vortex optical interferometry

Abstract

The present application provides a micro-angular displacement measurement system based on conjugate vortex light interference, comprising: a few-mode pump source, a few-mode fiber laser, a collimator, an angular displacement measurement unit, a CCD camera and a calculation unit; the few-mode fiber laser is used to generate a vortex beam with tunable wavelength and topological charge number using the few-mode pump source; the angular displacement measurement unit is used to detect the angular displacement change of the sample to be detected using the vortex beam after beam expansion by the collimator, and generate a petal-shaped interference pattern; the calculation unit is used to calculate the rotation angle and rotation direction of the interference pattern collected by the CCD camera, and determine the angular displacement of the sample to be detected according to the rotation angle and rotation direction of the interference pattern. The measurement system can achieve more accurate and effective micro-angular displacement measurement.

Description

Technical Field

[0001] The present application relates to the field of optical sensing measurement, and in particular to a small angular displacement measurement system based on conjugate vortex optical interference. Background Art

[0002] Laser interferometry based on vortex beams (LIVB) technology integrates rich spiral phase information while retaining the inherent advantages of coherent measurement, such as non-contact measurement, high resolution and wide dynamic range. At the same time, it obtains measurement information by detecting interference intensity, phase, frequency and other methods, which improves the accuracy and robustness of traditional coherent measurement, making LIVB technology widely used in life sciences, engineering machinery, materials science, microelectronics and other scenarios. Furthermore, the coherent control measurement technology based on fiber vortex light uses few-mode fiber lasers to generate vortex light and perform interferometric sensing. Thanks to the special properties of vortex light and the high efficiency and flexibility of optical fiber as a transmission medium, it has a series of unique advantages.

[0003] At present, most of the sensing measurement methods based on vortex light coherence control measure the rotation angle of the petals by determining the center position of the light spot and the characteristic points of the petals. However, the center position of the light spot is difficult to determine, and the shape of the light spot is easily deformed by external influences. At the same time, non-contact displacement detection using vortex light beam coherence control mostly uses spatial light. This is because compared with optical fiber, spatial light is relatively easy to monitor and control, and the commonly used transmission wavelength of optical fiber is the communication wavelength, which will cause higher absorption loss when performing non-contact surface detection. However, as a transmission medium, optical fiber has flexibility, high efficiency and good compatibility. At the same time, non-contact measurement can overcome some inherent defects of optical fiber contact measurement. Therefore, the application potential of non-contact displacement detection based on all-fiber vortex light beam coherence control is huge. Summary of the invention

[0004] In view of this, the purpose of the present application is to provide a small angular displacement measurement system based on conjugate vortex light interference, which can achieve the measurement of angular displacement in a wider range by utilizing a few-mode fiber laser to generate a vortex light beam with tunable wavelength and topological charge; further, a petal-shaped interference pattern is generated, and the angular displacement change of the sample to be detected is obtained by calculating the rotation angle and rotation direction of the interference pattern. There is no need to determine the position of the center of the light spot to avoid the error caused by the center of the light spot, thereby achieving more accurate and effective small angular displacement measurement.

[0005] The present application provides a micro-angular displacement measurement system based on conjugate vortex optical interference, characterized in that the measurement system comprises: a few-mode pump source 110, a few-mode fiber laser 120, a collimator 130, an angular displacement measurement unit 140, a CCD camera 150 and a calculation unit 160;

[0006] The few-mode fiber laser 120 is used to generate a vortex beam with tunable wavelength and topological charge number using the few-mode pump source 110;

[0007] The angular displacement measuring unit 140 is used to detect the angular displacement of the sample to be detected 143 by using the vortex light beam expanded by the collimator 130 to generate a petal-shaped interference pattern;

[0008] The calculation unit 160 is used to calculate the rotation angle and rotation direction of the interference pattern collected by the CCD camera 150, and determine the angular displacement of the sample to be detected according to the rotation angle and rotation direction of the interference pattern.

[0009] Further, the few-mode fiber laser 120 is formed by sequentially connecting the following optical components: a first few-mode tilted grating 121, a first polarization controller 122, a few-mode erbium-doped fiber 123, a few-mode wavelength division multiplexer 124, a second polarization controller 125 and a second few-mode tilted grating 126;

[0010] The second few-mode tilted grating 126 , as the output end of the few-mode fiber laser 120 , is connected to the input end of the collimator 130 .

[0011] Further, the few-mode pump source 110 is disposed between the few-mode wavelength division multiplexer 124 and the second polarization controller 125;

[0012] The few-mode erbium-doped optical fiber 123 is used to receive the pump light beam emitted by the few-mode pump source 110 to generate stimulated radiation and output a radiation light beam with a specific wavelength;

[0013] The first few-mode tilted grating 121 and the second few-mode tilted grating 126 form a resonant cavity of the few-mode fiber laser 120, and are used to provide optical positive feedback to the radiation beam to generate a vortex beam with tunable wavelength and topological charge;

[0014] The few-mode wavelength division multiplexer 124 is used to add and divide the pump light beam and the radiation light beam to achieve bidirectional signal transmission of the few-mode erbium-doped optical fiber 123;

[0015] The first polarization controller 122 and the second polarization controller 125 are used to adjust the loss in the resonant cavity to control the wavelength, topological charge and polarity of the vortex light beam.

[0016] Furthermore, the first few-mode tilted grating 121 and the second few-mode tilted grating 126 have the same grating period, tilt angle and writing length; the modulation depth of the first few-mode tilted grating 121 is greater than the modulation depth of the second few-mode tilted grating 126, so that the second few-mode tilted grating 126 becomes the output end of the vortex light beam.

[0017] Further, the angular displacement measuring unit 140 includes: a first beam splitter 141, a first reflector 142, the sample to be detected 143, a Dove lens 144, a second reflector 145 and a second beam splitter 146;

[0018] The first beam splitter 141 is connected to the output end of the collimator 130 as the input end of the angular displacement measuring unit 140;

[0019] The first reflector 142 is disposed between the first output end of the first beam splitter 141 and the sample to be detected 143;

[0020] The Dove lens 144 is disposed between the second output end of the first beam splitter 141 and the second reflector 145;

[0021] An input end of the second beam splitter 146 is connected to the sample to be detected 143 and the second reflector 145 , and an output end of the second beam splitter 146 is connected to the CCD camera 150 .

[0022] Furthermore, the first beam splitter 141 is used to split the expanded vortex beam into a first vortex beam and a second vortex beam having the same topological charge and polarity;

[0023] The first reflector 142 is used to change the transmission direction of the first vortex light beam so that the first vortex light beam penetrates the sample to be detected 143 to generate a measuring vortex light beam;

[0024] The Dove lens 144 is used to reverse the polarity of the topological charge of the second vortex beam to generate a reference vortex beam;

[0025] The second reflecting mirror 145 is used to change the transmission direction of the reference vortex beam so that the reference vortex beam is reflected to the second beam splitter 146;

[0026] The second beam splitter 146 is used to converge the measuring vortex beam and the reference vortex beam into one path, so that the measuring vortex beam and the reference vortex beam interfere with each other coaxially to form a petal-shaped interference pattern.

[0027] Furthermore, when calculating the rotation angle and rotation direction of the interference pattern collected by the CCD camera 150, the calculation unit 160 is specifically used to:

[0028] After binarizing the interference pattern, the centroid algorithm is used to determine the characteristic points of each petal in the interference pattern, and the polar coordinate positions of the characteristic points are obtained by establishing polar coordinates;

[0029] Connecting the characteristic points at the same order in a diagonal manner to obtain a characteristic point connection line of the interference pattern;

[0030] Acquire an initial interference pattern when the sample to be detected 143 does not generate an angular displacement, and determine a connecting line of characteristic points of the initial interference pattern;

[0031] The rotation angle and the rotation direction of the interference pattern are determined according to the characteristic point connection line of the interference pattern and the characteristic point connection line of the initial interference pattern.

[0032] Further, the angular displacement includes: a rotation angle and a rotation direction; when the calculation unit 160 determines the angular displacement of the sample to be detected 143 according to the rotation angle and the rotation direction of the interference pattern, it is specifically used to:

[0033] Determine the rotation angle of the sample 143 to be detected according to the relationship curve between the rotation angle of the interference pattern and the angular displacement change of the sample to be detected;

[0034] The rotation direction of the sample to be detected 143 is determined according to the rotation direction of the interference pattern.

[0035] Furthermore, the sample 143 to be tested is fixed on a rotating translation stage with a continuously adjustable angle, so that the sample 143 to be tested produces a continuous or discontinuous angular displacement change;

[0036] When the sample to be detected 143 produces a continuous angular displacement change, the acquisition frequency of the CCD camera 150 is set according to the change rate of the angular displacement.

[0037] Furthermore, the calculation unit (160) constructs a relationship curve between the rotation angle of the interference pattern and the angular displacement change of the sample to be detected in the following manner:

[0038] Acquire the target interference pattern of the sample to be detected 143 under each preset angular displacement, and obtain the characteristic point connection line of the target interference pattern;

[0039] Determining a rotation angle and a rotation direction of the target interference pattern according to a connecting line of characteristic points of the target interference pattern and a connecting line of characteristic points of the initial interference pattern;

[0040] Based on the preset rotation angles of each angular displacement and the rotation angle of the target interference pattern, a relationship curve between the rotation angle of the interference pattern and the angular displacement change of the sample to be detected is constructed.

[0041] The micro-angular displacement measurement system based on conjugate vortex light interference provided by the present application can realize the measurement of angular displacement in a wider range by utilizing a few-mode fiber laser to generate a vortex beam with tunable wavelength and topological charge; further, a petal-shaped interference pattern is generated, and the angular displacement change of the sample to be detected is obtained by calculating the rotation angle and rotation direction of the interference pattern, without determining the position of the center of the light spot, so as to avoid the error caused by the center of the light spot, and realize more accurate and effective micro-angular displacement measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 A schematic diagram of the structure of a small angular displacement measurement system based on conjugate vortex optical interferometry provided in an embodiment of the present application is shown;

[0043] Figure 2 An example of a petal-shaped interference pattern generated under different topological charges provided by an embodiment of the present application is shown;

[0044] Figure 3 An example of generating a petal-shaped interference pattern under different angular displacements provided by an embodiment of the present application is shown. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical solution and advantages of the technical solution more clear, the technical solution is further described in detail below in conjunction with specific implementation methods. It should be understood that these descriptions are only exemplary and are not intended to limit the scope of the technical solution.

[0046] First, the design concept of the few-mode fiber laser 120 provided in this application is introduced.

[0047] The spiral phase, phase singularity, topological charge and other characteristics of vortex light give it unique physical properties, and also make it uniquely advantageous to measure the angular displacement of samples based on the interference pattern of the vortex beam. When two conjugated vortex beams interfere, assuming that the two vortex beams have the same topological charge l and opposite polarities, the electric field expressions of the two vortex beams are:

[0048]

[0049] In the formula, E lis the amplitude of the two conjugate vortex beams; θ is the azimuth in the polar coordinate system, which is determined by arctan(y / x) and is used to describe the direction of the point (x, y) relative to the x-axis; l is the topological charge; exp(ilθ) is the phase factor of the vortex beam; is the initial phase of the vortex beam with topological charge number l and positive polarity; is the initial phase of the vortex beam with topological charge number l and negative topological charge polarity.

[0050] One of the vortex beams is made to pass through the sample to be tested to become a measuring vortex beam, and the other vortex beam is made to reverse its polarity to become a reference vortex beam. Then, the light field distribution after the interference of the measuring vortex beam and the reference vortex beam can be expressed as:

[0051]

[0052] In the formula, The initial phase difference between the measured vortex beam and the reference vortex beam when the sample to be tested does not produce angular displacement is It is the phase difference between the measured vortex beam and the reference vortex beam when the sample to be detected produces angular displacement at time t.

[0053] Here, when the sample to be detected produces an angular displacement, the effective path of the vortex light function in the sample to be detected changes, thereby introducing a phase delay. This phase change is independent of the characteristics of the beam itself, so we assume that it is the same for all beams. The relative sensitivity S(l) of the vortex beam to the phase change caused by the outside world can be defined as the ratio of the phase change to the phase change of the vortex beam itself, that is,

[0054]

[0055] In the formula, It represents the phase change of the vortex beam during a complete phase change (i.e., when θ changes from 0 to 2π).

[0056] From the above formula, it can be seen that the relative sensitivity S(l) is inversely proportional to the topological charge l. This means that as the topological charge increases, the vortex beam shows relatively low sensitivity to the same externally induced phase change. Therefore, by tuning the topological charge of the vortex beam, the measurement range of the angular displacement can be increased, which can effectively improve the measurement capability of the measurement system.

[0057] Next, the structure of the small angular displacement measurement system based on conjugate vortex optical interference provided in an embodiment of the present application is described.

[0058] See also Figure 1 , Figure 1The structure diagram of a small angular displacement measurement system based on conjugate vortex light interference provided in the embodiment of the present application is shown in FIG. Figure 1 As shown, the micro-angular displacement measurement system based on conjugate vortex optical interference includes: a few-mode pump source 110, a few-mode fiber laser 120, a collimator 130, an angular displacement measurement unit 140, a CCD camera 150 and a calculation unit 160.

[0059] Among them, the few-mode fiber laser 120 is used to generate a vortex beam with tunable wavelength and topological charge using the few-mode pump source 110; the angular displacement measurement unit 140 is used to detect the angular displacement change of the sample to be detected 143 using the vortex beam after expansion by the collimator 130, and generate a petal-shaped interference pattern; the calculation unit 160 is used to calculate the rotation angle and rotation direction of the interference pattern collected by the CCD camera 150, and determine the angular displacement of the sample to be detected based on the rotation angle and rotation direction of the interference pattern.

[0060] It should be noted that the number of petals of the interference pattern is related to the topological charge of the vortex beam. For example, when the topological charge is n, the number of petals is 2n, where n ≥ 1. It can be seen that the petal-shaped interference pattern generated by the interference of two conjugated vortex beams has rotational symmetry. Furthermore, the rotation angle and rotation direction of the interference pattern can be used to determine the angular displacement change of the sample to be detected.

[0061] As an example, see Figure 2 , Figure 2 FIG. 2 shows an example of a petal-shaped interference pattern generated under different topological charges provided by an embodiment of the present application. Figure 2 As shown, the topological charges are 1, 2, and 3, respectively, and the corresponding numbers of petals are 2, 4, and 6.

[0062] As an example, see Figure 3 , Figure 3 This is an example of generating a petal-shaped interference pattern under different angular displacements provided in an embodiment of the present application. Wherein, α is the rotation angle of the interference pattern, such as Figure 3 As shown, when the topological charge of the vortex beam is 1, as the phase difference increases, the petal-shaped interference pattern rotates clockwise, and conversely, as the phase difference decreases, the petal-shaped interference pattern rotates counterclockwise. Based on this, the angular displacement change of the sample to be detected can be determined by using the rotation angle and direction of the interference pattern.

[0063] Next, the structure of the few-mode fiber laser 120 provided in the embodiment of the present application is described.

[0064] Specifically, the few-mode fiber laser 120 is composed of the following optical components connected in sequence: a first few-mode tilted grating 121, a first polarization controller 122, a few-mode erbium-doped fiber 123, a few-mode wavelength division multiplexer 124, a second polarization controller 125 and a second few-mode tilted grating 126; the second few-mode tilted grating 126 is connected to the input end of the collimator 130 as the output end of the few-mode fiber laser 120; the few-mode pump source 110 is arranged between the few-mode wavelength division multiplexer 124 and the second polarization controller 125.

[0065] The functions of the optical components of the few-mode fiber laser 120 based on the above structure are as follows: the few-mode erbium-doped fiber 123 is used to receive the pump beam emitted by the few-mode pump source 110 to generate stimulated radiation, and output a radiation beam of a specific wavelength; the first few-mode tilted grating 121 and the second few-mode tilted grating 126 form the resonant cavity of the few-mode fiber laser 120, which is used to provide optical positive feedback to the radiation beam to generate a vortex beam with tunable wavelength and topological charge; the few-mode wavelength division multiplexer 124 is used to sum and split the pump beam and the radiation beam to achieve bidirectional signal transmission of the few-mode erbium-doped fiber 123; the first polarization controller 122 and the second polarization controller 125 are used to adjust the loss in the resonant cavity to control the wavelength, topological charge and polarity of the vortex beam.

[0066] In addition, the first few-mode tilted grating 121 and the second few-mode tilted grating 126 have the same grating period, tilt angle and writing length; the modulation depth of the first few-mode tilted grating 121 is greater than the modulation depth of the second few-mode tilted grating 126, so that the second few-mode tilted grating 126 becomes the output end of the vortex light beam.

[0067] Next, the structure of the angular displacement measurement unit 140 provided in the embodiment of the present application is described.

[0068] Specifically, the angular displacement measuring unit 140 includes: a first beam splitter 141, a first reflector 142, the sample to be detected 143, a Dove lens 144, a second reflector 145 and a second beam splitter 146; the first beam splitter 141 is connected to the output end of the collimator 130 as the input end of the angular displacement measuring unit 140; the first reflector 142 is arranged between the first output end of the first beam splitter 141 and the sample to be detected 143; the Dove lens 144 is arranged between the second output end of the first beam splitter 141 and the second reflector 145; the input end of the second beam splitter 146 is connected to the sample to be detected 143 and the second reflector 145, and the output end of the second beam splitter 146 is connected to the CCD camera 150.

[0069] The functions of the optical components of the angular displacement measurement unit 140 based on the above structure are as follows: the first beam splitter 141 is used to split the expanded vortex beam into a first vortex beam and a second vortex beam with the same topological charge and polarity; the first reflector 142 is used to change the transmission direction of the first vortex beam so that the first vortex beam penetrates the sample to be detected 143 to generate a measuring vortex beam; the Dove lens 144 is used to reverse the topological charge polarity of the second vortex beam to generate a reference vortex beam; the second reflector 145 is used to change the transmission direction of the reference vortex beam so that the reference vortex beam is reflected to the second beam splitter 146; the second beam splitter 146) is used to converge the measuring vortex beam and the reference vortex beam into one path so that the measuring vortex beam and the reference vortex beam interfere coaxially to form a petal-shaped interference pattern.

[0070] The following describes a specific implementation of the calculation unit 160 provided in an embodiment of the present application.

[0071] Specifically, when calculating the rotation angle and rotation direction of the interference pattern collected by the CCD camera 150, the calculation unit 160 is specifically used to: after binarizing the interference pattern, use the centroid algorithm to determine the feature points of each petal in the interference pattern, and obtain the polar coordinate position of the feature points by establishing polar coordinates; connect the feature points at the same order in a diagonal manner to obtain the feature point connection lines of the interference pattern; obtain the initial interference pattern when the sample 143 to be tested does not produce angular displacement, and determine the feature point connection lines of the initial interference pattern; determine the rotation angle and rotation direction of the interference pattern according to the feature point connection lines of the interference pattern and the feature point connection lines of the initial interference pattern.

[0072] Among them, the angular displacement includes a rotation angle and a rotation direction; when the calculation unit 160 determines the angular displacement of the sample to be detected 143 according to the rotation angle and rotation direction of the interference pattern, it is specifically used to: determine the rotation angle of the sample to be detected 143 according to a relationship curve between the rotation angle of the interference pattern and the change in the angular displacement of the sample to be detected; determine the rotation direction of the sample to be detected 143 according to the rotation direction of the interference pattern.

[0073] Here, the sample to be detected 143 is fixed on a rotating translation stage with continuously adjustable angle so that the sample to be detected 143 produces continuous or discontinuous angular displacement changes; when the sample to be detected 143 produces continuous angular displacement changes, the acquisition frequency of the CCD camera 150 is set according to the change rate of the angular displacement.

[0074] In addition, the embodiment of the present application also provides a method for constructing a relationship curve between the rotation angle of the interference pattern and the angular displacement change of the sample to be detected. Specifically, the calculation unit (160) constructs the relationship curve between the rotation angle of the interference pattern and the angular displacement change of the sample to be detected in the following manner:

[0075] Step 1: Obtain the target interference pattern of the sample to be detected 143 under each preset angular displacement, and obtain the characteristic point connection line of the target interference pattern.

[0076] Step 2: Determine the rotation angle and rotation direction of the target interference pattern according to the characteristic point connection line of the target interference pattern and the characteristic point connection line of the initial interference pattern.

[0077] Step 3: constructing a relationship curve between the rotation angle of the interference pattern and the angular displacement change of the sample to be detected based on the preset rotation angles of each angular displacement and the rotation angle of the target interference pattern.

[0078] The above contents are only preferred embodiments of the present invention. For ordinary technicians in this field, many changes can be made in the specific implementation methods and application scopes based on the ideas of the technical content. As long as these changes do not deviate from the concept of the present invention, they all fall within the scope of protection of this patent.

Claims

1. A micro-angular displacement measurement system based on conjugate vortex optical interferometry, characterized in that: The measurement system comprises: a few-mode pump source (110), a few-mode fiber laser (120), a collimator (130), an angular displacement measurement unit (140), a CCD camera (150), and a calculation unit (160); The few-mode fiber laser (120) is used to generate a vortex beam with tunable wavelength and topological charge number using the few-mode pump source (110); The angular displacement measuring unit (140) is used to detect the angular displacement of the sample to be detected (143) using the vortex light beam expanded by the collimator (130) to generate a petal-shaped interference pattern; The calculation unit (160) is used to calculate the rotation angle and rotation direction of the interference pattern collected by the CCD camera (150), and determine the angular displacement of the sample to be detected according to the rotation angle and rotation direction of the interference pattern; The few-mode fiber laser (120) is formed by sequentially connecting the following optical components: a first few-mode tilted grating (121), a first polarization controller (122), a few-mode erbium-doped fiber (123), a few-mode wavelength division multiplexer (124), a second polarization controller (125), and a second few-mode tilted grating (126); The second few-mode tilted grating (126) is connected to the input end of the collimator (130) as the output end of the few-mode fiber laser (120); The few-mode pump source (110) is arranged between the few-mode wavelength division multiplexer (124) and the second polarization controller (125); The few-mode erbium-doped optical fiber (123) is used to receive the pump light beam emitted by the few-mode pump source (110) to generate stimulated radiation and output a radiation light beam with a specific wavelength; The first few-mode tilted grating (121) and the second few-mode tilted grating (126) form a resonant cavity of the few-mode fiber laser (120), and are used to provide optical positive feedback to the radiation beam, so as to generate a vortex beam with tunable wavelength and topological charge; The few-mode wavelength division multiplexer (124) is used to combine and divide the pump light beam and the radiation light beam, so as to realize bidirectional signal transmission of the few-mode erbium-doped optical fiber (123); The first polarization controller (122) and the second polarization controller (125) are used to adjust the loss in the resonant cavity to control the wavelength, topological charge and polarity of the vortex light beam; The first few-mode tilted grating (121) and the second few-mode tilted grating (126) have the same grating period, tilt angle and writing length; the modulation depth of the first few-mode tilted grating (121) is greater than the modulation depth of the second few-mode tilted grating (126), so that the second few-mode tilted grating (126) becomes the output end of the vortex light beam.

2. The measuring system according to claim 1, characterized in that The angular displacement measurement unit (140) comprises: a first beam splitter (141), a first reflector (142), the sample to be detected (143), a Dove lens (144), a second reflector (145) and a second beam splitter (146); The first beam splitter (141) is connected to the output end of the collimator (130) as the input end of the angular displacement measurement unit (140); The first reflecting mirror (142) is arranged between the first output end of the first beam splitter (141) and the sample to be detected (143); The Dove lens (144) is arranged between the second output end of the first beam splitter (141) and the second reflector (145); The input end of the second beam splitter (146) is connected to the sample to be detected (143) and the second reflector (145), and the output end of the second beam splitter (146) is connected to the CCD camera (150).

3. The measuring system according to claim 2, characterized in that The first beam splitter (141) is used to split the expanded vortex beam into a first vortex beam and a second vortex beam having the same topological charge and polarity; The first reflector (142) is used to change the transmission direction of the first vortex light beam so that the first vortex light beam penetrates the sample to be detected (143) to generate a measuring vortex light beam; The Dove lens (144) is used to reverse the polarity of the topological charge of the second vortex beam to generate a reference vortex beam; The second reflecting mirror (145) is used to change the transmission direction of the reference vortex light beam so that the reference vortex light beam is reflected to the second beam splitter (146); The second beam splitter (146) is used to converge the measuring vortex beam and the reference vortex beam into one path, so that the measuring vortex beam and the reference vortex beam interfere with each other on the same axis to form a petal-shaped interference pattern.

4. The measuring system according to claim 1, characterized in that When calculating the rotation angle and rotation direction of the interference pattern collected by the CCD camera (150), the calculation unit (160) is specifically used to: After binarizing the interference pattern, the centroid algorithm is used to determine the characteristic points of each petal in the interference pattern, and the polar coordinate positions of the characteristic points are obtained by establishing polar coordinates; Connecting the characteristic points at the same order in a diagonal manner to obtain a characteristic point connection line of the interference pattern; Acquiring an initial interference pattern when the sample to be detected (143) does not generate an angular displacement, and determining a connecting line of characteristic points of the initial interference pattern; The rotation angle and the rotation direction of the interference pattern are determined according to the characteristic point connection line of the interference pattern and the characteristic point connection line of the initial interference pattern.

5. The measuring system according to claim 4, characterized in that The angular displacement includes: a rotation angle and a rotation direction; when the calculation unit (160) determines the angular displacement of the sample to be detected (143) according to the rotation angle and the rotation direction of the interference pattern, it is specifically used to: Determining the rotation angle of the sample to be detected (143) according to a relationship curve between the rotation angle of the interference pattern and the angular displacement change of the sample to be detected; The rotation direction of the sample to be detected (143) is determined according to the rotation direction of the interference pattern.

6. The measuring system according to claim 1, characterized in that The sample to be tested (143) is fixed on a rotating translation stage whose angle can be continuously adjusted, so that the sample to be tested (143) produces a continuous or discontinuous angular displacement change; When the sample to be detected (143) produces a continuous angular displacement change, the acquisition frequency of the CCD camera (150) is set according to the rate of change of the angular displacement.

7. The measuring system according to claim 5, characterized in that The calculation unit (160) constructs a relationship curve between the rotation angle of the interference pattern and the angular displacement change of the sample to be detected in the following manner: Acquiring a target interference pattern of the sample to be detected (143) at each preset angular displacement, and obtaining a connecting line of characteristic points of the target interference pattern; Determining a rotation angle and a rotation direction of the target interference pattern according to a connecting line of characteristic points of the target interference pattern and a connecting line of characteristic points of the initial interference pattern; Based on the preset rotation angles of each angular displacement and the rotation angle of the target interference pattern, a relationship curve between the rotation angle of the interference pattern and the angular displacement change of the sample to be detected is constructed.

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