Three-degree-of-freedom angle measurement device and method based on radial polarized light

Abstract

The present application relates to the technical field of laser quantum interference measurement, in particular to a three-degree-of-freedom angle measurement device and method based on radial polarized light, which can realize high-precision simultaneous measurement of three-degree-of-freedom small angles by using the characteristics of radial polarized light, combining advanced optical systems and signal processing technology. By using the self-collimation technology principle, the tight focusing characteristics of radial polarized light and the light splitting characteristics of Wollaston prism are combined, which can effectively improve the angle measurement resolution, angle measurement accuracy and other technical indicators; by using the focusing characteristics of the full-medium super-lens array and the CCD camera, the roll angle measurement system formed can greatly improve the measurement accuracy of the existing method.

Description

Technical Field

[0001] This invention relates to the field of laser quantum interference measurement technology, specifically to a three-degree-of-freedom angle measurement device and method based on radially polarized light. Background Technology

[0002] In optical engineering, the measurement of minute angles is crucial for the calibration of optical systems, precise beam control, and accurate positioning of optical components. In precision mechanics and aerospace, even minute angular changes can lead to performance degradation of mechanical components or deviations from the flight trajectory of aerospace vehicles. Currently, the requirements for the accuracy and stability of minute angle measurements are becoming increasingly stringent. Traditional angle measurement methods, such as photoelectric encoders and optical interferometry, suffer from limited accuracy and insufficient stability when measuring minute angles. Therefore, exploring new methods for measuring minute angles has become an important research direction.

[0003] In summary, current three-degree-of-freedom angle measurement technology has drawbacks such as low measurement accuracy and system complexity. Summary of the Invention

[0004] In view of this, the present invention provides a three-degree-of-freedom angle measurement device and method based on radially polarized light, which can utilize the characteristics of radially polarized light and combine advanced optical systems and signal processing technology to achieve high-precision simultaneous measurement of three small free angles.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A three-degree-of-freedom angle measurement device based on radially polarized light includes a radially polarized light system, a polarizing prism, and a first... Wave plate, total reflection mirror, second Waveplate, SLM, measuring target mirror, first prism, wavefront detector, wavefront controller, second prism, pitch and yaw angle measurement system and roll angle measurement system;

[0007] A radially polarized light system generates radially polarized light, which is incident on a polarizing prism.

[0008] Horizontal light transmitted through a polarizing prism is incident on the SLM (Short-Range Mirror), reflected by the SLM, and then reaches the measuring target mirror fixed on the target. The measuring target mirror reflects the incident light, which then passes through the SLM and the second... A waveplate, incident on a polarizing prism, is reflected by the polarizing prism and then passes through the first... After reaching the total reflection mirror, the waveplate reflects the light and then passes through the first... The wave plate then passes through a polarizing prism and is incident on the first prism;

[0009] The perpendicular light reflected by the polarizing prism is incident on the first prism;

[0010] The reflected light from the first prism is incident on the wavefront detector. The wavefront information detected by the wavefront detector is fed back to the wavefront controller, and the wavefront controller generates a control signal and applies it to the SLM.

[0011] The transmitted light through the first prism is incident on the second prism for beam splitting; the transmitted light through the second prism is incident on the pitch and yaw angle measurement system to measure the pitch and yaw angles; the reflected light through the second prism is incident on the roll angle measurement system to measure the roll angle.

[0012] The system also includes a computer. The pitch and yaw angle measurement system includes a Wollaston prism, a third lens, a fourth lens, a first position sensitivity detector, and a second position sensitivity detector. The transmitted light after passing through the first beam splitter is split by the second beam splitter. The transmitted light after passing through the second beam splitter reaches the Wollaston prism. After being split by the Wollaston prism, one beam of light is focused by the third lens onto the first position sensitivity detector, and the other beam of light is focused by the fourth lens onto the second position sensitivity detector. Thus, the focal position of the target when it is stationary and the focal position after the angle change are obtained on the two position sensitivity detectors. After being calculated and processed by the computer according to the formula, the pitch and yaw angle values ​​are output.

[0013] The roll angle measurement system includes an all-dielectric superlens array, a fifth lens, and a CCD camera. Reflected light from the second beam splitter is incident on the all-dielectric superlens array. The all-dielectric superlens array contains multiple pixels, each containing two different superlenses, capable of separating two different polarization components from the incident beam. After passing through the fifth lens, the light spot is focused onto the CCD camera, obtaining the focal spot position in both static and angle-changing states. The CCD camera, in conjunction with the all-dielectric superlens array, indirectly measures and calculates the change in focal position, thereby obtaining the roll angle through the measurement and calculation of the focal position. The CCD camera receives the signal and transmits it to a computer, which processes it to obtain the roll angle numerical output.

[0014] The front surface of the CCD camera is perpendicular to the front surface of the measuring target mirror, and its position is calibrated during placement.

[0015] Among them, the all-dielectric superlens array modulates the propagation and focusing behavior of incident light by designing subwavelength structures on the surface of the dielectric.

[0016] The radially polarized light system includes a laser, an S-wave plate, a first lens, and a second lens. The laser generates linearly polarized light, which is converted into radially polarized light after passing through the S-wave plate. The radially polarized light is then expanded by a beam-expanding system composed of the first and second lenses before being incident on a polarizing prism for beam splitting.

[0017] This invention also provides a three-degree-of-freedom angle measurement method based on radially polarized light, which uses the device described in this invention to perform the measurement and includes the following steps:

[0018] The signals received by the first position sensitivity detector, the second position sensitivity detector, and the CCD camera are transmitted to the computer, and the computer processes them to obtain the numerical output of pitch angle, yaw angle, and roll angle.

[0019] The formula for calculating the pitch angle is:

[0020]

[0021] The formula for calculating the yaw angle is:

[0022]

[0023] In the formula, X PSD1 and Y PSD1 These represent the focal spot positions in the horizontal and vertical directions of the first and second position sensitive detectors, respectively, when the detectors are stationary; X PSD2 and Y PSD2 These are the focal spot positions in the horizontal and vertical directions of the first position sensitive detector and the second position sensitive detector, respectively, after the angle change is generated; f1 and f2 are the focal lengths of the third lens and the fourth lens, respectively.

[0024] The formula for calculating the roll angle is:

[0025]

[0026] In the formula, Z PSD1 The position of the focal spot in the vertical direction of the CCD camera when stationary; Z PSD2 f3 represents the position of the focal spot in the vertical direction of the CCD camera after the angle change; f3 is the focal length of the fifth lens.

[0027] Beneficial effects:

[0028] 1. Existing technologies typically employ techniques such as laser interferometry, self-collimation measurement, and visual measurement to obtain pitch and yaw angles. The device of this invention utilizes the principle of self-collimation, combining the tight focusing characteristics of radially polarized light with the beam-splitting characteristics of a Wollaston prism, which can effectively improve technical indicators such as angle measurement resolution and accuracy. Existing technologies typically measure roll angle using methods such as electronic levels. The device of this invention utilizes the focusing characteristics of an all-dielectric superlens array and a CCD camera to form a roll angle measurement system, which can greatly improve the measurement accuracy of roll angle using existing methods.

[0029] 2. In existing technologies, when measuring angles, it is rare to compensate for angle errors caused by environmental interference when the target is stationary. The device of this invention uses a wavefront detector, a wavefront controller, and a spatial light modulator (SLM) to compensate for distortions caused by environmental interference (such as vibration and temperature changes) by adjusting the minute deformation of the SLM mirror in real time. This adjustment can compensate for the three-degree-of-freedom angle error signal in a stationary state.

[0030] 3. The device of this invention adopts the principle of laser self-collimation. It compensates for the angle error signal of the target under stationary state by using a spatial light modulator (SLM), a wavefront detector, and a wavefront controller. By combining the tight focusing characteristics of radially polarized light with the beam splitting characteristics of a Wollaston prism, it analyzes the position of the focal spot on the position-sensitive detector to measure the pitch and yaw angles. Utilizing the principle that the pitch angle in one direction is the roll angle in the perpendicular direction, it analyzes the position of the focal spot on the CCD camera by using the focusing characteristics of an all-dielectric superlens array and a CCD camera to measure the roll angle. The three-degree-of-freedom angle measurement results are processed and analyzed by a computer before being output, which can effectively improve the technical indicators such as the resolution and accuracy of three-degree-of-freedom micro-angle measurement.

[0031] 4. The method of the present invention is based on the device of the present invention. It adopts the self-collimation technology principle and combines the tight focusing characteristics of radially polarized light with the beam splitting characteristics of the Wollaston prism, which can effectively improve the technical indicators such as angle measurement resolution and angle measurement accuracy. The roll angle measurement system formed by using the focusing characteristics of the all-dielectric superlens array and the CCD camera can greatly improve the roll angle measurement accuracy of the existing methods.

[0032] 5. The method of the present invention is based on the device of the present invention. It utilizes a wavefront detector, a wavefront controller and a spatial light modulator (SLM) to compensate for distortions caused by environmental interference (such as vibration and temperature changes) by adjusting the minute deformation of the SLM mirror in real time. This adjustment can compensate for the three-degree-of-freedom angle error signal in a static state.

[0033] 6. The method of this invention adopts the principle of laser self-collimation. It compensates for the angle error signal of the target under stationary state by using a spatial light modulator (SLM), a wavefront detector, and a wavefront controller. By combining the tight focusing characteristics of radially polarized light with the beam splitting characteristics of a Wollaston prism, the position of the focal spot on the position-sensitive detector is analyzed to measure the pitch and yaw angles. Utilizing the principle that the pitch angle in one direction is the roll angle in the perpendicular direction, the focusing characteristics of an all-dielectric superlens array and a CCD camera are used to analyze the position of the focal spot on the CCD camera to measure the roll angle. The three-degree-of-freedom angle measurement results are processed and analyzed by a computer before being output, which can effectively improve the technical indicators such as the resolution and accuracy of three-degree-of-freedom micro-angle measurement. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the three-degree-of-freedom angle measuring device based on radially polarized light according to the present invention. Detailed Implementation

[0035] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0036] Radial polarized light, as a special form of light field distribution, exhibits a characteristic of strong intensity at the center and weak intensity at the edges, with the light field direction distributed radially. This unique property gives radially polarized light a potential advantage in small angle measurements. This invention provides a three-degree-of-freedom angle measurement device based on radially polarized light, the structure of which is as follows: Figure 1 As shown, it includes: a laser (1), an S-wave plate (2), a first lens (3), a second lens (4), a polarizing prism (5), and a first quarter-wave plate. Wave plate (6), total reflection mirror (7), second quarter mirror The system comprises a waveplate (8), a spatial light modulator (SLM) (9), a measuring target mirror (10), a first beam splitter (11), a wavefront detector (12), a wavefront controller (13), a second beam splitter (14), a Wollaston prism (15), a third lens (16), a fourth lens (17), a first position sensitivity detector (18), a second position sensitivity detector (19), an all-dielectric superlens array (20), a fifth lens (21), a CCD camera (22), and a computer (23). The Wollaston prism (15), the third lens (16), the fourth lens (17), the first position sensitivity detector (18), and the second position sensitivity detector (19) together form a pitch and yaw angle measurement system to measure pitch and yaw angles. The all-dielectric superlens array (20), the fifth lens (21), and the CCD camera (22) together form a roll angle measurement system to measure roll angles.

[0037] The laser (1) generates linearly polarized light, which is converted into radially polarized light after passing through the S-wave plate (2). The radially polarized light is expanded by a beam-expanding system composed of a first lens (3) and a second lens (4) and then incident on a polarizing prism (5) for beam splitting.

[0038] Horizontal light (P-light) transmitted through the polarizing prism (5) is incident on the spatial light modulator (SLM) (9) and reaches the measuring target mirror (10) after reflection by the SLM (9). The surface of the measuring target mirror (10) is coated with a total reflection film to achieve total internal reflection of the incident light. The measuring target mirror (10) is fixed on the target to be measured. When the target to be measured moves, the measuring target mirror (10) will move along with it. Thus, by measuring the measuring target mirror, the change angle of the target to be measured can be measured. The light reflected by the measuring target mirror (10) passes through the spatial light modulator (SLM) (9) and the second quarter-wave plate (8) again. The reflected light carries information about the change in angle position. Due to passing through the second quarter-wave plate (8) twice, the horizontal light (P light) is converted into vertical light (S light). The vertical light (S light) is incident on the polarizing prism (5). After being reflected by the polarizing prism (5), it passes through the first quarter-wave plate (6) and reaches the total reflection mirror (7). After being reflected by the total reflection mirror (7), it passes through the first quarter-wave plate (6) again. Due to passing through the first quarter-wave plate (6) twice, the vertical light (S light) becomes horizontal light (P light). The horizontal light (P light) passes through the polarizing prism (5) and is incident on the first beam splitter (11).

[0039] The vertical light (S-ray) reflected by the polarizing prism (5) is incident on the first beam splitter (11) for beam splitting.

[0040] The reflected light (carrying angle change information) from the first beam splitter (11) is incident on the wavefront detector (12) for detection. The detected wavefront information (such as the slope or curvature distribution of the phase disturbance caused by the angle change) is fed back to the wavefront controller (13). This information is processed by the algorithm inside the wavefront controller (13) and converted into phase information, thereby realizing wavefront reconstruction. The main purpose of this step is to obtain the complete phase distribution of the distorted wavefront. The wavefront controller (13) generates control signals through the control algorithm according to the phase distribution of the distorted wavefront. These control signals are converted from digital to analog and then amplified by a high voltage amplifier, and finally applied to the spatial light modulator (SLM) (9). The spatial light modulator (SLM) (9) changes the direction of the reflected beam through the feedback state control of the spatial light modulator (SLM) (9) according to these control signals, thereby achieving the purpose of correcting the wavefront. Since the spatial light modulator (SLM) (9) can be used to adjust the small deformation of the mirror in real time to compensate for the distortion caused by environmental interference (such as vibration and temperature changes). This adjustment compensates for three-degree-of-freedom angle error signals in a static state. The purpose of compensation is that when the target is stationary, environmental interference can cause minute angle changes, introducing errors into the angle measurement. Therefore, it's necessary to compensate for these minute angle changes in a relatively static state. It's important to note that angle error compensation requires a pre-set angle threshold. When the angle change caused by environmental interference is less than the set threshold, compensation is applied; when the angle change is greater, no compensation is performed. The purpose of setting the angle threshold is to prevent the system from compensating for the minute angles that need to be measured from the target itself during minute angle measurements. The angle threshold is set according to the required angle measurement accuracy.

[0041] The transmitted light through the first beam splitter (11) is incident on the second beam splitter (14) for beam splitting; the transmitted light through the second beam splitter (14) is incident on the pitch and yaw angle measurement system to measure the pitch and yaw angles; the reflected light through the second beam splitter (14) is incident on the roll angle measurement system to measure the roll angle. The first beam splitter (11) and the second beam splitter (14) each have different beam splitting ratios.

[0042] In the pitch and yaw angle measurement system, which includes a Wollaston prism (15), a third lens (16), a fourth lens (17), a first position sensitivity detector (18), and a second position sensitivity detector (19), the transmitted light after passing through the first beam splitter (11) is split by the second beam splitter (14). The transmitted light after passing through the second beam splitter (14) reaches the Wollaston prism (15). After being split by the Wollaston prism (15), one beam of light is focused by the third lens (16) onto the first position sensitivity detector (18), and the other beam of light is focused by the fourth lens (17) onto the second position sensitivity detector (19). Thus, the focal position X of the target when it is stationary is obtained on the two position sensitivity detectors. PSD1 and Y PSD1 And the focal position X after the angle change PSD2 and Y PSD2 After being processed by the computer (23) according to the formula, the pitch angle and yaw angle values ​​are output.

[0043] In a roll angle measurement system comprising an all-dielectric superlens array (20), a fifth lens (21), and a CCD camera (22), reflected light from the second beam splitter (14) is incident on the all-dielectric superlens array (20). The all-dielectric superlens array (20) contains multiple pixels, each containing two different superlenses, capable of separating two different polarization components from the incident beam. After passing through the fifth lens (21), the light spot is focused onto the CCD camera (22). Similar to the measurement of pitch and yaw angles, the focal spot position Z after stationary and angle-changing states can be obtained respectively. PSD1 and Z PSD2 Utilizing the principle that the pitch angle in one direction is the roll angle in the perpendicular direction, the CCD camera (22), in conjunction with the all-dielectric metalens array (20), can indirectly measure and calculate the change in the focal position, thereby obtaining the roll angle through the measurement and calculation of the focal position. Specifically, the CCD camera (22) receives the signal and transmits it to the computer (23), which processes it to obtain the roll angle value output. It should be noted that the front surface (receiving surface) of the CCD camera (22) needs to be perpendicular to the front surface of the measuring target mirror (10), and position calibration is required during placement. The all-dielectric metalens array (20) is a novel optical element based on metamaterial technology, which controls the propagation and focusing behavior of incident light by precisely designing the subwavelength structure (atomic atoms) on the surface of the medium.

[0044] In summary, the first position sensitivity detector (18), the second position sensitivity detector (19), and the CCD camera (22) receive signals and transmit them to the computer (23). The computer (23) processes the signals to obtain the pitch angle, yaw angle, and roll angle values. The device of this invention can achieve simultaneous high-accuracy measurement of small angles with three degrees of freedom.

[0045] This invention also provides a three-degree-of-freedom angle measurement method based on radially polarized light, implemented using the device of this invention, comprising the following steps:

[0046] The signals received by the first position sensitivity detector (18), the second position sensitivity detector (19) and the CCD camera (19) are transmitted to the computer (23), and the computer (23) processes them to obtain the pitch angle, yaw angle and roll angle values.

[0047] The formula for calculating the pitch angle is:

[0048]

[0049] The formula for calculating the yaw angle is:

[0050]

[0051] In the formula, X PSD1 and Y PSD1 These represent the focal spot positions in the horizontal and vertical directions of the first position sensitive detector (18) and the second position sensitive detector (19) respectively, under static conditions; X PSD2 and Y PSD2 These are the focal spot positions in the horizontal and vertical directions of the first position sensitive detector (18) and the second position sensitive detector (19) after the angle change is generated, respectively; f1 and f2 are the focal lengths of the third lens (16) and the fourth lens (17), respectively.

[0052] The formula for calculating the roll angle is:

[0053]

[0054] In the formula, Z PSD1 In a stationary state, the position of the focal spot in the vertical direction of the CCD camera (22); Z PSD2 f3 is the position of the focal spot in the vertical direction of the CCD camera (22) after the angle change is generated; f3 is the focal length of the fifth lens (21).

[0055] In summary, the above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A three-degree-of-freedom angle measuring device based on radially polarized light, characterized in that, Including radial polarization system, polarization prism, first Wave plate, total reflection mirror, second Waveplate, SLM, measuring target mirror, first beam splitter, wavefront detector, wavefront controller, second beam splitter, pitch and yaw angle measurement system and roll angle measurement system; A radially polarized light system generates radially polarized light, which is incident on a polarizing prism. Horizontal light transmitted through a polarizing prism is incident on the SLM (Short-Range Mirror), reflected by the SLM, and then reaches the measuring target mirror fixed on the target. The measuring target mirror reflects the incident light, which then passes through the SLM and the second... A waveplate, incident on a polarizing prism, is reflected by the polarizing prism and then passes through the first... After reaching the total reflection mirror, the waveplate reflects the light and then passes through the first... The wave plate then passes through a polarizing prism and is incident on the first beam splitter. The perpendicular light reflected by the polarizing prism is incident on the first beam splitter; The reflected light from the first beam splitter is incident on the wavefront detector. The wavefront information detected by the wavefront detector is fed back to the wavefront controller, which generates a control signal and applies it to the SLM. The transmitted light through the first beam splitter is incident on the second beam splitter for beam splitting; the transmitted light through the second beam splitter is incident on the pitch and yaw angle measurement system to measure the pitch and yaw angles; the reflected light through the second beam splitter is incident on the roll angle measurement system to measure the roll angle.

2. The apparatus as claimed in claim 1, characterized in that, It also includes a computer; the pitch and yaw angle measurement system includes a Wollaston prism, a third lens, a fourth lens, a first position sensitivity detector, and a second position sensitivity detector; wherein, the transmitted light after passing through the first beam splitter is split by the second beam splitter, and the transmitted light after passing through the second beam splitter reaches the Wollaston prism. After being split by the Wollaston prism, one beam of light is focused by the third lens onto the first position sensitivity detector, and the other beam of light is focused by the fourth lens onto the second position sensitivity detector, thereby obtaining the focal position of the target when it is stationary and the focal position after the angle changes on the two position sensitivity detectors. After being calculated and processed by the computer according to the formula, the pitch and yaw angle values ​​are output.

3. The apparatus as described in claim 2, characterized in that... The roll angle measurement system includes an all-dielectric superlens array, a fifth lens, and a CCD camera. Reflected light from the second beam splitter is incident on the all-dielectric superlens array. The all-dielectric superlens array contains multiple pixels, each containing two different superlenses, capable of separating two different polarization components from the incident beam. After passing through the fifth lens, the light spot is focused onto the CCD camera, obtaining the focal spot position in both static and angle-changing states. The CCD camera, in conjunction with the all-dielectric superlens array, indirectly measures and calculates the change in focal position, thereby obtaining the roll angle through the measurement and calculation of the focal position. The CCD camera receives the signal and transmits it to the computer, which processes it to obtain the roll angle numerical output.

4. The apparatus as described in claim 3, characterized in that... The front surface of the CCD camera is perpendicular to the front surface of the measuring target mirror, and its position is calibrated during placement.

5. The apparatus as described in claim 3, characterized in that... All-dielectric superlens arrays control the propagation and focusing behavior of incident light by designing subwavelength structures on the surface of the dielectric.

6. The apparatus according to any one of claims 1-5, characterized in that... The radially polarized light system includes a laser, an S-wave plate, a first lens, and a second lens. The laser generates linearly polarized light, which is converted into radially polarized light after passing through the S-wave plate. The radially polarized light is expanded by a beam-expanding system composed of the first lens and the second lens, and then incident on a polarizing prism for beam splitting.

7. A three-degree-of-freedom angle measurement method based on radially polarized light, characterized in that, The measurement is performed using the apparatus described in any one of claims 3-5, comprising the following steps: The signals received by the first position sensitivity detector, the second position sensitivity detector, and the CCD camera are transmitted to the computer, and the computer processes them to obtain the numerical output of pitch angle, yaw angle, and roll angle.

8. The method as described in claim 7, characterized in that The formula for calculating the pitch angle is: The formula for calculating the yaw angle is: In the formula, X PSD1 and Y PSD1 These represent the focal spot positions in the horizontal and vertical directions of the first and second position sensitive detectors, respectively, when the detectors are stationary; X PSD2 and Y PSD2 These are the focal spot positions in the horizontal and vertical directions of the first position sensitive detector and the second position sensitive detector, respectively, after the angle change is generated; f1 and f2 are the focal lengths of the third lens and the fourth lens, respectively.

9. The method as described in claim 7 or 8, wherein the formula for calculating the roll angle is: In the formula, Z PSD1 The position of the focal spot in the vertical direction of the CCD camera when stationary; Z PSD2 f3 represents the position of the focal spot in the vertical direction of the CCD camera after the angle change; f3 is the focal length of the fifth lens.

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