Surface topography measuring device and method based on polarization phase shift

Abstract

The invention discloses a surface topography measurement device and method based on polarization phase shift. The device comprises a laser module, a polarization beam splitting and interference module, a polarization beam combining and imaging module, a polarization image acquisition module and a control and reconstruction module. The laser module comprises a monochromatic tunable laser, an optical fiber collimating amplifier and a polarizer; the polarization beam splitting and interference module comprises a polarization beam splitting prism, a first quarter-wave plate, a plane mirror and a second quarter-wave plate; the polarization beam combining and imaging module comprises a polarization splitting prism, a third quarter-wave plate and a telecentric lens; the polarization image acquisition module comprises a micro-polarization array camera and an image processing unit, and the micro-polarization array camera synchronously acquires four polarization interference images through single exposure; and the control and reconstruction module obtains measurement data of the surface topography of the to-be-measured object through a phase unwrapping algorithm and three-dimensional topography reconstruction. According to the invention, high-precision, large-field-of-view, portable and high-efficiency field detection can be realized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of optical interferometry, and particularly relates to a surface topography measurement device and method based on polarization phase shifting. BACKGROUND

[0002] With the rapid development of industry, surface defects of aircraft shells and engines pose a serious threat to flight safety. These defects not only affect the appearance, but also can cause structural integrity to be damaged, so timely and accurate detection and repair are crucial. However, traditional surface defect measurement methods such as ultrasonic detection and magnetic powder detection have poor intuitiveness, qualitative and quantitative difficulties, and cannot meet the needs of high-precision detection. Visual inspection, although the standard method in the aviation industry, is easily affected by subjective definition and lighting conditions, leading to inconsistency of detection results. At the same time, although machine vision recognition technology has improved detection efficiency to some extent, it still faces problems such as difficulty in detecting curved surfaces and equipment limitations, especially for detecting small defects and complex-shaped products.

[0003] In recent years, three-dimensional surface topography measurement technology has developed rapidly in the field of industrial detection. Existing technologies mainly evolve in two directions: one is a macroscopic detection system based on optical triangulation principle, which can achieve meter-level range measurement through laser scanning or structured light projection, but is limited by optical diffraction limit and detector resolution, and its measurement precision can only reach 20-50 microns; the second is an ultra-precision instrument based on physical probe or interference microscopy principle, such as atomic force microscope (AFM) and white light interferometer, which has nanometer-level detection precision, but has inherent defects such as small measurement field of view (usually <1mm 2

[0004] However, existing three-dimensional surface topography measurement technology has significant technical gaps in surface defect detection:

[0005] 1) There is a significant mismatch between measurement accuracy and application scenarios. Macroscopic detection equipment (such as three-dimensional laser scanners) can achieve rapid measurement of meter-level workpieces, but its precision limit (>20μm) cannot meet the identification needs of aviation skin micro-cracks (5-100μm); while nanometer-level precision instruments (such as AFM and electron microscope) are limited by millimeter-level measurement field of view and harsh environmental requirements, and require constant temperature vibration isolation, which cannot adapt to field detection scenarios.

[0006] 2) Dynamic detection capability is insufficient. Traditional phase shift interferometry requires multiple image acquisition to achieve phase calculation, while existing devices (such as confocal microscopes) are limited by the response speed of mechanical phase shift mechanisms, making it difficult to achieve hundreds of hertz-level topography capture, and cannot monitor the change process of material corrosion and coating shedding.

[0007] ​3) Partially related equipment field utility is insufficient, and the high-precision equipment generally has problems such as high system complexity (such as light path calibration of a white light interferometer) and high maintenance cost (such as a vacuum system of an electron microscope), and is difficult to be deployed on a large scale in an industrial field. SUMMARY

[0008] The purpose of the present application is to provide a surface topography measurement device and method based on polarization phase shift, which can realize high precision, large field of view, portability and high efficiency of field detection.

[0009] In order to achieve the above-mentioned purpose, one aspect of the present application provides a surface topography measurement device based on polarization phase shift, comprising a laser module, a polarization light splitting and interference module, a polarization beam combining and imaging module, a polarization image acquisition module and a control and reconstruction module.

[0010] The laser module comprises a monochromatic tunable laser, a fiber collimating amplifier and a polarizer, the fiber collimating amplifier is used to convert the light beam output by the laser into collimated parallel light, and the polarizer is used to convert the collimated parallel light into linearly polarized light.

[0011] The polarization light splitting and interference module comprises a polarization light splitting prism, a first quarter-wave plate, a plane mirror and a second quarter-wave plate, the polarization light splitting prism is used to split the incident linearly polarized light into transmitted p-polarized light and reflected s-polarized light, which enter the reference light path and the measurement light path respectively, in the reference light path, the first quarter-wave plate converts the p-polarized light into left-handed circularly polarized light, which is reflected by the plane mirror into right-handed circularly polarized light and returns to the first quarter-wave plate in the original path, and is converted into s-polarized light; in the measurement light path, the second quarter-wave plate converts the s-polarized light into right-handed circularly polarized light, which is reflected by the object to be measured into left-handed circularly polarized light and returns to the second quarter-wave plate in the original path, and is converted into p-polarized light.

[0012] The polarization beam combining and imaging module comprises a polarization light splitting prism, a third quarter-wave plate and a telecentric lens, the polarization light splitting prism is used to combine the returned s-polarized light and p-polarized light into coaxial orthogonal linearly polarized light, the third quarter-wave plate is used to convert the orthogonal linearly polarized light into superposition state of left-handed and right-handed circularly polarized light, and the telecentric lens is used to collimate and image the superposition state light field.

[0013] The polarization image acquisition module comprises a micro-polarization array camera and an image processing unit, the micro-polarization array camera comprises a pixel-level 0°, 45°, 90°, 135° polarizing plate array, and can synchronously acquire four polarization state interference images through single exposure, and the image processing unit is used to complete the pixel intensity values of each polarization direction into a complete image through an interpolation algorithm.

[0014] The control and reconstruction module is used to obtain the wrapped phase of the surface of the object to be measured through a four-step phase shift method for the four interpolated polarization interference images, and to obtain the point cloud data of the surface morphology of the object to be measured using a phase unwrapping algorithm. The measurement data of the surface morphology of the object to be measured is obtained by reconstructing the point cloud data.

[0015] Another aspect of the present invention provides a surface topography measurement method based on polarization phase shifting, which uses the above-mentioned device to perform surface topography measurement. The method includes:

[0016] The fiber collimation amplifier converts the laser output beam into collimated parallel light, the polarizer converts the collimated parallel light into linearly polarized light, and the polarization beam splitter splits the incident linearly polarized light into transmitted p-polarized light and reflected s-polarized light, which enter the reference optical path and the measurement optical path respectively.

[0017] On the reference optical path, the first quarter-wave plate converts p-polarized light into left-handed circularly polarized light, which is then reflected by the plane mirror as right-handed circularly polarized light and returns to the first quarter-wave plate along the same path, where it is converted into s-polarized light. On the measurement optical path, the second quarter-wave plate converts s-polarized light into right-handed circularly polarized light, which is then reflected by the object to be measured as left-handed circularly polarized light and returns to the second quarter-wave plate along the same path, where it is converted into p-polarized light.

[0018] The polarization beam splitter combines the returning s-polarized light and p-polarized light into coaxial orthogonal linear polarized light. The third quarter-wave plate converts the orthogonal linear polarized light into a superposition state of left-handed and right-handed circular polarized light. The telecentric lens collimates and images the superposition state light field.

[0019] The micro-polarization array camera synchronously collects polarization state interference images at four polarization directions: 0°, 45°, 90°, and 135°, and interpolates the pixel intensity values ​​of the polarization state interference images.

[0020] For the four interpolated polarization interference images, the wrapped phase of the surface of the object to be measured is obtained by the four-step phase shift method. The phase unwrapping algorithm is used to obtain the point cloud data of the surface morphology of the object to be measured. The measurement data of the surface morphology of the object to be measured is obtained by reconstructing the point cloud data.

[0021] The surface topography measurement device and method based on polarization phase shifting according to the above aspects of the present invention can achieve high-precision, large field of view, portability, and high-efficiency on-site detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the present invention, the following briefly introduces the drawings used in the description of the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive efforts.

[0023] Figure 1 is a structural schematic diagram of a polarization-based phase-shifting surface topography measurement device according to an embodiment of the present application;

[0024] Figure 2 is a structural schematic diagram of a fiber collimator amplifier according to an embodiment of the present application;

[0025] Figure 3 is a design pattern of a calibration plate according to an embodiment of the present application;

[0026] Figure 4 is a 0° polarization image processing unit schematic diagram according to an embodiment of the present application;

[0027] Figure 5 is a measurement principle optical path diagram of a polarization-based phase-shifting surface topography measurement method according to an embodiment of the present application;

[0028] Figure 6 is a polarization camera pixel array schematic diagram according to an embodiment of the present application. DETAILED DESCRIPTION

[0029] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described clearly and completely below with reference to the drawings. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0030] An embodiment of the present application provides a polarization-based phase-shifting surface topography measurement device, which realizes surface topography measurement of a measured object by using a micro-polarization array-based phase-shifting technology. The technology realizes synchronous acquisition of multiple phase-shifted interference images in a single exposure by integrating multiple-direction polarization units (such as 0°, 45°, 90° and 135°) on the surface of an image sensor, and then reconstructs the surface topography of the measured object by using a spatial phase synchronous demodulation algorithm.

[0031] As shown in Figure 1 , the polarization-based phase-shifting surface topography measurement device according to the embodiment of the present application includes a laser module, a polarization light splitting and interference module, a polarization beam combining and imaging module, a polarization image acquisition module and a control and reconstruction module.

[0032] The laser module includes a laser, a fiber collimator amplifier 1 and a polarizer 2. The laser is a monochromatic tunable laser, which can change the output power and use a fiber output. In the embodiment, the laser outputs a single-mode laser with a wavelength of 632 nm. The fiber collimator amplifier 1 converts the light beam output by the laser into collimated parallel light, as shown in Figure 2As shown, it includes single-mode fiber 1-1, collimating lens 1-2 and beam expander 1-3, and the output spot diameter is greater than 1.2 times the maximum transverse dimension of the surface of the object 7 to be measured. The beam expander 1-3 can be a Galilean beam expander or a Keplerian beam expander. Since the laser has a power adjustable characteristic, the fiber collimating amplifier 1 optimizes the spot uniformity by the fiber output mode, forming a collimated spot with a diameter of 1-2 cm. The polarizer 2 converts the collimated parallel light into linearly polarized light, and the polarizer 2 can be a dichroic film polarizer.

[0033] The polarization splitting and interference module includes a polarization splitting prism 3, a first quarter-wave plate 4, a plane mirror 5, and a second quarter-wave plate 6. The polarization splitting prism 3 splits the incident linearly polarized light into transmitted p-polarized light reference light path and reflected s-polarized light measurement light path. The reference light path includes: the first quarter-wave plate 4, whose fast axis direction is 45° to the p-polarization direction of the reference light path, which converts the p-polarized light into left-handed circularly polarized light; the plane mirror 5, which reverses the handedness of the left-handed circularly polarized light to right-handed circularly polarized light by reflection and returns to the first quarter-wave plate 4, which converts it into s-polarized light. The measurement light path includes: the second quarter-wave plate 6, whose fast axis direction is 45° to the s-polarization direction of the measurement light path, which converts the s-polarized light into right-handed circularly polarized light; the object 7 to be measured, which reverses the handedness of the right-handed circularly polarized light to left-handed circularly polarized light by reflection and returns to the second quarter-wave plate 6, which converts it into p-polarized light.

[0034] The first quarter-wave plate 4 and the second quarter-wave plate 6 are symmetrically installed, and the fast axis directions are both 45° to the incident polarization direction, and the installation angle error is adjusted within ±1° by a matching wave plate rotating holder.

[0035] The polarization beam combining and imaging module includes a polarization splitting prism 3, a third quarter-wave plate 8, and a telecentric lens 9. The polarization splitting prism 3 combines the returned s-polarized light reference light path and p-polarized light measurement light path into coaxial orthogonal polarized light. The third quarter-wave plate 8, whose fast axis direction is 45° to the horizontal direction, converts the orthogonal linearly polarized light into a superposition state of left-handed and right-handed circularly polarized light. The telecentric lens 9 collimates and images the superposition state light field.

[0036] The polarization image acquisition module includes a micro-polarization array camera 10 and an image processing unit 11. The micro-polarization array camera 10 is a high frame rate camera using an integrated micro-polarization array, which includes a pixel-level 0°, 45°, 90°, 135° polarizer array, and four phase-shifted interference images are captured synchronously in a single exposure. The imaging surface of the micro-polarization array camera 10 is conjugate to the image surface of the telecentric lens 9, and the polarization image acquisition module is connected to the polarization splitting and interference module through the telecentric lens 9. Figure 3The calibration plate 13 shown achieves pixel-level alignment, ensuring exact correspondence between pixel positions in images with different polarization states. It is decorated with cross marks and a periodic fringe pattern. Placed on the imaging surface of the telecentric lens 9, the calibration plate 13 compensates for distortion and aberrations caused by the micro-polarization array camera and the telecentric lens. It also centers the circular light spot at the light output. The reference mirror is adjusted for alignment using the polarization camera.

[0037] In this embodiment, the telecentric lens 9 adopts a magnification of 0.5 times, and the light spot formed by the collimated amplification of the fiber optic collimator amplifier 1 is 1-2 cm, which basically meets the camera acquisition range. Since the telecentric lens has a large acquisition range and the depth of field can reach 1-2 mm, the large depth of field characteristic ensures the measurement adaptability of complex surfaces.

[0038] The image processing unit 11 complements the pixel intensity values ​​in each polarization direction through an interpolation algorithm, and uses a calibration plate to compensate for lens distortion and polarization array alignment errors to extract phase information. Figure 4 FIG. 1 is a schematic diagram of a 0° polarization image processing unit according to an embodiment of the present invention. Figure 4 As shown, the image processing unit 11 completes the pixel intensity values ​​of 0° polarization into a complete image through an interpolation algorithm.

[0039] The control and reconstruction module 12 executes the phase unwrapping algorithm and three-dimensional morphology reconstruction, extracts the wrapped phase based on the four-step phase shift method, uses the branch cutting method or weighted least squares method to perform phase unwrapping, and synchronously controls the laser, polarization camera 10 and telecentric lens 9. By adjusting the polarizer parameters to adapt to different surface reflection characteristics, three-dimensional morphology reconstruction is achieved.

[0040] The device of the embodiment of the present invention is a Michelson interference design as a whole, and the reference light path and the measurement light path are realized by the Michelson interference light path, wherein the reference mirror (plane reflector 5) and the object to be measured 7 are respectively located at the ends of the two interference arms, and the light beam from the front end is divided into two beams by a polarization beam splitter prism, one beam is reflected by the reference surface, and the other beam is reflected by the surface to be measured. The two beams of light are merged again through the polarization beam splitter prism to interfere. The device of the embodiment of the present invention is optimized by the Michelson interference architecture and is suitable for industrial detection scenarios with a numerical aperture of 0.4-0.6 and a working distance of 10-50 mm.

[0041] The embodiment of the present invention further provides a surface topography measurement method based on polarization phase shifting, which uses the surface topography measurement device based on polarization phase shifting according to the embodiment of the present invention to realize surface topography measurement, including steps S1 to S5. Figure 5 The schematic diagram of the embodiment of the present invention describes in detail the various steps of the method.

[0042] Step S1: laser collimation, beam expansion and polarization splitting.

[0043] The fiber collimating amplifier (collimating lens and beam expander BE) converts the 632 nm single-mode laser emitted by the laser into collimated parallel light, which is converted into linearly polarized light by the polarizer 2; the polarizing beam splitter prism (PBS) 3 divides the light beam into transmitted p-polarized light and reflected s-polarized light, which enter the reference light path and the measurement light path, respectively.

[0044] Step S2, circular polarization generation and reflection modulation.

[0045] The two beams of light are respectively incident on the reference mirror (plane mirror 5) and the object to be measured 7 through the first quarter wave plate (first QWP) 4 and the second quarter wave plate (second QWP) 6, whose fast axis is at an angle of 45° with the polarization direction, at this time the two beams of light on the surface of the reference mirror and the object to be measured are respectively converted into left-handed circularly polarized light and right-handed circularly polarized light. After reflection, the circularly polarized light rotates in the opposite direction, and the left-handed circularly polarized light and the right-handed circularly polarized light again pass through the quarter wave plate are converted into linearly polarized light perpendicular to the original incident light polarization direction. Specifically, the reference light path: the p-polarized light is converted into left-handed circularly polarized light through the quarter wave plate, and becomes right-handed circularly polarized light after reflection by the reference mirror; the measurement light path: the s-polarized light is converted into right-handed circularly polarized light through the quarter wave plate, and becomes left-handed circularly polarized light after reflection by the object to be measured; the two beams of reflected light pass through the original quarter wave plate again and are converted into orthogonal s-polarized light and p-polarized light, respectively.

[0046] Here, the basic process of introducing the polarization phase shift principle is introduced. According to the analysis of the Jones matrix theory, the combined light beams of the object to be measured and the reference surface can be represented by mutually orthogonal linearly polarized light, and their Jones matrices can be respectively represented as:

[0047]

[0048] E1 is the light beam on the surface of the object to be measured, a and φ1 are the amplitude and phase thereof, respectively, E2 is the light beam on the surface of the reference mirror, b and φ2 are the amplitude and phase thereof, respectively, and the two components have the same vibration frequency and stable phase difference.

[0049] Step S3, interference light beam combination and polarization modulation.

[0050] The two beams of orthogonal linearly polarized light are combined into a coaxial light beam again on the polarizing beam splitter prism 3, at this time the s-polarized light is reflected and the p-polarized light is transmitted, that is, the two beams of orthogonal linearly polarized light are combined into a light beam again, which passes through the third quarter wave plate (third QWP) 8, whose fast axis is at an angle of 45° with the polarization direction, and the Jones matrix of the wave plate is represented as:

[0051]

[0052] After passing through the third quarter wave plate 8, the linearly polarized light is converted into circularly polarized light (left-handed and right-handed circularly polarized light), and its Jones matrix can be respectively represented as:

[0053]

[0054] After the conversion into the left and right circularly polarized combined beam, imaging is realized through the telecentric lens 9. By adjusting the aperture size of the telecentric lens, the gray value range of the collected image is controlled to be between 0 and 255.

[0055] Step S4, polarization interference image collection.

[0056] The micro-polarization array polarization camera 10 realizes 0°, 90°, 180°, and 270° polarization phase shifts. Figure 6 A schematic diagram of a polarization camera pixel array is given, and each unit pixel saves one polarization state pixel in each of the four adjacent pixels, which are 0°, 45°, 90°, and 135°, respectively. One pixel can be represented as a circularly polarized surface beam and a reference mirror beam passing through a polarizer with an angle a between the polarization direction and the x direction. The Jones matrix of the polarizer can be represented as:

[0057]

[0058] The exit light after passing through the quarter-wave plate and the polarizer can be represented by the Jones matrix

[0059]

[0060] The expression of the corresponding interference light intensity is

[0061]

[0062] The micro-polarization array camera synchronously captures 0°, 45°, 90°, and 135° polarization state interference images, collects images of four polarization directions through the pixel-level polarizer array, and fills in the pixel intensity values of each polarization state image through interpolation.

[0063] Step S5, phase unwrapping and three-dimensional reconstruction.

[0064] After the collected images are reconstructed through interpolation, four phase-shifted interference images (polarization state interference images) are obtained, and the wrapped phase of the measured surface is obtained through the four-step phase shift method. Subsequently, the branch cut method or weighted least squares method is used for phase unwrapping algorithm to obtain the point cloud data of the measured surface topography. The point cloud data is reconstructed to obtain the measured surface topography measurement data. Phase extraction is realized through the four-step phase shift technique, where I is the interference light intensity, a 2 +b 2 is the background light intensity, I2=2ab is the modulation light intensity, is the phase difference, and a is the angle between the polarization direction and the x direction. Therefore, the intensity in the interference image is determined by the phase difference And the azimuth angle a of the polarizer determines that, under the condition of a certain phase difference, different phase shift amounts are introduced by changing the transmission direction of the polarizer, the phase shift amount is twice the angle between the polarizer and the x direction, and then 0°, 90°, 180° and 270° polarization phase shifts are realized.

[0065] In summary, the surface topography measuring device and method of the embodiment of the application perform high-precision surface topography measurement based on orthogonal polarization interference and a micro-polarization array, a micro-polarization plate array camera is used to collect a polarization interference image containing phase information of a surface to be measured, which is realized by a laser, a light splitting prism, a quarter phase delay wave plate and the like, four different polarization state images are extracted, and then a surface three-dimensional topography reconstruction is performed using an extracted phase and unwrapping algorithm.

[0066] Compared with the prior art, the device and method of the embodiment of the application have the following beneficial effects:

[0067] 1. The application uses precise polarization phase shift to accurately control the polarization state evolution of the reflected light of the reference arm and the test arm when returning to the PBS (polarization beam splitter prism), so that the polarization state components with fixed and accurate phase difference can be generated in advance when the light interacts with the micro-polarization array. This provides a physical basis for the subsequent single-exposure synchronous phase shift. The cumbersome mechanical phase shift device (such as a piezoelectric ceramic driver PZT) and the complex time-sharing acquisition system in the traditional phase shift interferometer are abandoned. Through precise configuration of the polarization optical element and direct use of the micro-polarization array camera, the core optical path and detection unit of the entire high-precision interferometric measurement system are integrated in an extremely compact module, realizing the lightweight and portability of the device, and enabling micron-level surface topography measurement of laboratory-level precision to be applied in field, online or mobile scenarios.

[0068] 2. The application uses micro-polarization plate array technology to realize single-exposure, full-field synchronous phase shift interferogram capture of the camera, and combines illumination and imaging design to significantly improve dynamic measurement capability and measurement range. The telecentric optical path design has the core advantages of maintaining constant magnification in the entire field of view and ensuring that the chief ray is parallel to the optical axis. This effectively eliminates perspective distortion, so that the imaging quality at the edge of the field of view is consistent with that in the central region, providing optical protection for accurate phase extraction of uniform and coherent illumination spots in a large field of view (up to 1-2 cm in diameter).

[0069] 3. The application solves the problem that the traditional scanner has insufficient precision for on-site detection of micron-level surface topography, nanometer-level precision instrument detection has a small field of view and large volume, and cannot achieve rapid on-site detection. The micro-polarization array phase shift breaks through the problem that multiple frame image acquisition is required for phase calculation in the traditional phase shift interference method, and a Michelson interference and telecentric imaging system are used to achieve low distortion and stable polarization phase shift measurement, which can meet the efficient identification demand of micron-level defects (5-100 mu m) such as surface cracks, corrosion and coating falling off.

[0070] The foregoing merely describes some exemplary embodiments of the present application by way of illustration, and it is needless to say that those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present application. Therefore, the above drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present application.

Claims

1. A surface topography measurement device based on polarization phase shifting, characterized in that: It includes laser module, polarization splitting and interference module, polarization beam combining and imaging module, polarization image acquisition module, and control and reconstruction module; The laser module includes a monochromatic tunable laser, a fiber collimating amplifier and a polarizer. The fiber collimating amplifier is used to convert the light beam output by the laser into collimated parallel light, and the polarizer is used to convert the collimated parallel light into linearly polarized light. The polarization splitting and interference module includes a polarization splitting prism, a first quarter-wave plate, a plane reflector, and a second quarter-wave plate. The polarization splitting prism is used to split the incident linearly polarized light into transmitted p-polarized light and reflected s-polarized light, which enter the reference optical path and the measurement optical path respectively. On the reference optical path, the first quarter-wave plate converts the p-polarized light into left-handed circularly polarized light, which is reflected by the plane reflector as right-handed circularly polarized light and returns to the first quarter-wave plate along the original path to be converted into s-polarized light. On the measurement optical path, the second quarter-wave plate converts the s-polarized light into right-handed circularly polarized light, which is reflected by the object to be measured as left-handed circularly polarized light and returns to the second quarter-wave plate along the original path to be converted into p-polarized light. The polarization beam combining and imaging module includes a polarization beam splitter prism, a third quarter-wave plate, and a telecentric lens. The polarization beam splitter prism is used to combine the returning s-polarized light and p-polarized light into coaxial orthogonal linear polarized light. The third quarter-wave plate is used to convert the orthogonal linear polarized light into a superposition state of left-handed and right-handed circularly polarized light. The telecentric lens is used to collimate and image the superposition state light field. The polarization image acquisition module includes a micro-polarization array camera and an image processing unit. The micro-polarization array camera contains pixel-level 0°, 45°, 90°, and 135° polarizer arrays, capable of synchronously capturing four polarization state interference images through a single exposure. The image processing unit is used to interpolate the pixel intensity values ​​in each polarization direction into a complete image through an interpolation algorithm. The control and reconstruction module is used to obtain the wrapped phase of the surface of the object to be measured through a four-step phase shift method for the four interpolated polarization interference images, and to obtain the point cloud data of the surface morphology of the object to be measured using a phase unwrapping algorithm. The measurement data of the surface morphology of the object to be measured is obtained by reconstructing the point cloud data.

2. The device according to claim 1, characterized in that The first quarter-wave plate and the second quarter-wave plate are installed symmetrically, the fast axis direction of the first quarter-wave plate is 45° to the p-polarization direction of the reference light path, the fast axis direction of the second quarter-wave plate is 45° to the s-polarization direction of the measurement light path, and the fast axis direction of the third quarter-wave plate is 45° to the horizontal direction.

3. The device according to claim 1 or 2, characterized in that The polarization image acquisition module also includes a calibration plate, which is placed on the imaging surface of the telecentric lens. The imaging surface of the micro-polarization array camera is conjugate with the imaging surface of the telecentric lens, and pixel-level alignment is achieved through the calibration plate. The calibration plate is provided with a cross mark and a periodic stripe pattern.

4. The device according to claim 1 or 2, characterized in that The optical fiber collimating amplifier comprises a single-mode optical fiber, a collimating lens and a beam expander, and the output light spot diameter is greater than 1.2 times the maximum transverse dimension of the surface of the object to be measured.

5. The device according to claim 4, characterized in that The laser outputs a single-mode laser with a wavelength of 632 nm, the beam expander is a Galilean beam expander or a Keplerian beam expander, and the polarizer is a dichroic thin film polarizer.

6. A surface topography measurement method based on polarization phase shifting, characterized in that: Surface topography measurement is performed using the device according to any one of claims 1 to 5, the method comprising: The fiber collimation amplifier converts the laser output beam into collimated parallel light, the polarizer converts the collimated parallel light into linearly polarized light, and the polarization beam splitter splits the incident linearly polarized light into transmitted p-polarized light and reflected s-polarized light, which enter the reference optical path and the measurement optical path respectively. On the reference optical path, the first quarter-wave plate converts p-polarized light into left-handed circularly polarized light, which is then reflected by the plane mirror as right-handed circularly polarized light and returns to the first quarter-wave plate along the same path, where it is converted into s-polarized light. On the measurement optical path, the second quarter-wave plate converts s-polarized light into right-handed circularly polarized light, which is then reflected by the object to be measured as left-handed circularly polarized light and returns to the second quarter-wave plate along the same path, where it is converted into p-polarized light. The polarization beam splitter combines the returning s-polarized light and p-polarized light into coaxial orthogonal linear polarized light. The third quarter-wave plate converts the orthogonal linear polarized light into a superposition state of left-handed and right-handed circular polarized light. The telecentric lens collimates and images the superposition state light field. The micro-polarization array camera synchronously collects polarization state interference images at four polarization directions: 0°, 45°, 90°, and 135°, and interpolates the pixel intensity values ​​of the polarization state interference images. For the four interpolated polarization interference images, the wrapped phase of the surface of the object to be measured is obtained by the four-step phase shift method. The phase unwrapping algorithm is used to obtain the point cloud data of the surface morphology of the object to be measured. The measurement data of the surface morphology of the object to be measured is obtained by reconstructing the point cloud data.

7. The method according to claim 6, characterized in that By adjusting the aperture size of the telecentric lens, the grayscale value range of the captured image is controlled between 0 and 255.

8. The method according to claim 6 or 7, characterized in that The imaging plane of the micro-polarization array camera is conjugate with the imaging plane of the telecentric lens. A calibration plate is placed on the imaging plane of the telecentric lens to achieve pixel-level alignment, ensuring that the pixel positions of interference images with different polarization states strictly correspond.

Images