Measuring system for infinitesimal displacement

Abstract

The invention provides a measurement system for infinitesimal displacement, and the system comprises a laser transmitting module which is used for transmitting an original laser beam; the light beam shaping module is used for shaping the original laser beam and outputting a vortex light beam and a plane wave reference light beam; the focusing module is used for superposing the vortex light beam and the plane wave reference light beam to construct a measurement focal field, and the measurement focal field comprises a longitudinal optical singular point; the imaging acquisition module is used for acquiring a real image of a longitudinal optical singular point in a measurement focal field; and the data processing module is electrically connected with the imaging acquisition module and is used for determining the displacement of the focusing module according to the real image. The unique advantages that the spatial scale of a longitudinal optical singular point is infinitely small and the phase gradient is steep are fully utilized, optical diffraction limit restriction caused by the fact that a traditional optical metering method depends on a structured light field or an interference effect is avoided, and the precision of a displacement reference datum is improved.

Description

Technical Field

[0001] This application relates to the field of micro-displacement measurement technology, and in particular to a micro-displacement measurement system. Background Technology

[0002] High-precision measurement of minute displacements is a core requirement in modern scientific research and precision manufacturing, especially in semiconductor processing, micro / nano structure characterization, and advanced metrology, where measurement accuracy needs to reach sub-nanometer or even picometer levels. Most optical metrology methods used for measuring minute displacements rely on structured light fields or interference effects, and their measurement accuracy is limited by the optical diffraction limit, requiring further improvement in precision. Summary of the Invention

[0003] This application provides a system for measuring minute displacements to improve the accuracy of minute displacement measurements.

[0004] This application provides a system for measuring minute displacements, comprising: a laser emitting module for emitting a raw laser beam; a beam shaping module for shaping the raw laser beam to output a vortex beam and a plane wave reference beam; a focusing module for superimposing the vortex beam and the plane wave reference beam to construct a measurement focal field, the measurement focal field including a longitudinal optical singularity; an imaging acquisition module for acquiring a real image of the longitudinal optical singularity in the measurement focal field; and a data processing module electrically connected to the imaging acquisition module for determining the displacement of the focusing module based on the real image.

[0005] Optionally, the beam shaping module is loaded with a mask containing a vortex phase and a plane wave reference beam reference phase.

[0006] Optionally, the beam shaping module includes: a first shaping module for modulating the original laser beam into circularly polarized light; a second shaping module loaded with a mask containing a vortex phase and a plane wave reference beam reference phase to control the phase and amplitude of the circularly polarized light; and a third shaping module for modulating the circularly polarized light after phase and amplitude control into linearly polarized light; the linearly polarized light is the composite light field of the superposition of the vortex beam and the plane wave reference beam; wherein the first shaping module is disposed between the second shaping module and the laser emission module, and the third shaping module is disposed between the second shaping module and the focusing module.

[0007] Optionally, the second shaping module is a liquid crystal device.

[0008] Optionally, the first shaping module includes: a first polarizer for modulating the original laser beam into linearly polarized light; and a first phase delayer for modulating the linearly polarized light into circularly polarized light; wherein the first polarizer is disposed between the laser emitting module and the phase delayer.

[0009] Optionally, the first shaping module further includes: a beam expander module, disposed between the laser emitting unit and the polarizer, for adjusting the size of the original laser beam; the first polarizer is used to modulate the original laser beam after size adjustment into linearly polarized light.

[0010] Optionally, the third shaping module includes: a second polarizer for modulating the circularly polarized light after phase and amplitude modulation into linearly polarized light; and an optical filtering and imaging module for spatial frequency filtering and imaging of the linearly polarized light, retaining only the +1st order diffraction beam; wherein the second polarizer is disposed between the second shaping module and the optical filtering and imaging module.

[0011] Optionally, the third shaping module further includes a second phase delayer, disposed between the optical filtering imaging module and the focusing module, for adjusting the polarization direction of the linearly polarized light so that the polarization direction is perpendicular to the line connecting the vortex beam and the plane wave reference beam.

[0012] Optionally, the focusing module includes a first microscope objective; a vortex beam is projected onto the center of the optical axis of the first microscope objective, and a plane wave reference beam is projected onto the off-axis region. After being focused by the first microscope objective, the plane wave reference beam enters the measurement focal field in an inclined manner, so that the vortex beam and the plane wave reference beam converge at the focal plane in the measurement focal field, thereby constructing a longitudinal optical singularity.

[0013] Optionally, the imaging acquisition module includes: an imaging module for collecting the interference pattern of the measured focal field, magnifying it, and focusing it to form a real image; and an acquisition module for acquiring the real image; wherein the imaging module is located between the focusing module and the acquisition module.

[0014] Optionally, the imaging module includes: a second microscope objective for collecting wave vector components in the measurement focal field to obtain an interference pattern; and a magnification module for magnifying the interference pattern and focusing it into a real image.

[0015] Optionally, the measurement system further includes: a displacement stage module, which is fixedly connected to the focusing module and used to measure the standard displacement of the focusing module; and the displacement stage module is electrically connected to the data processing module.

[0016] The micro-displacement measurement system provided in this application utilizes a beam shaping module to generate a vortex beam and a plane wave reference beam. These are then superimposed by a focusing module to construct a measurement focal field containing a longitudinal optical singularity. An imaging acquisition module precisely captures the real image of the singularity, and a data processing module performs fine analysis on the image to determine the displacement. This system fully leverages the unique advantages of the infinitesimally small spatial scale and steep phase gradient of the longitudinal optical singularity, avoiding the optical diffraction limit limitations imposed by traditional optical metrology methods that rely on structured light fields or interference effects. This improves the accuracy of the displacement reference standard. Furthermore, the precise capture of the real image of the longitudinal optical singularity by the imaging acquisition module ensures that the changes in the light field corresponding to the micro-displacement are fully perceived. Thus, the accuracy of micro-displacement measurement is significantly improved.

[0017] The longitudinal optical singularities are distributed along the optical axis, and their projected positions on the transverse plane perpendicular to the optical axis change synchronously with the transverse displacement of the object under test. The focusing module is rigidly connected or in close contact with the object under test, and the movement of the sample causes the focusing module to move. When the focusing module moves laterally, the longitudinally distributed optical singularities in the focal field of the focusing module will produce an offset in the transverse plane corresponding to the actual displacement. Thus, the longitudinal singularities can serve as a high-precision displacement reference, and by detecting the offset of the longitudinal singularities in the transverse plane, the magnitude of the transverse displacement of the object under test can be deduced. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the architecture of a micro-displacement measurement system provided in one embodiment of this application; Figure 2 This is a schematic diagram of the architecture of a micro-displacement measurement system provided in another embodiment of this application; Figure 3 This is a focusing schematic diagram of a minute displacement measurement system provided in one embodiment of this application; Figure 4 This is a measurement experiment diagram of a measurement system based on micro-displacement provided in one embodiment of this application; Figure 5 This is a phase analysis diagram of a measurement system based on minute displacement provided in one embodiment of this application; Figure 6 This is a cloud computing diagram of the intersection points of a measurement system based on minute displacement provided in one embodiment of this application; Figure 7 The intersection cloud distribution is calculated by a measurement system based on minute displacement provided in one embodiment of this application. Figure 8 This is a schematic diagram of the displacement signal generated by the displacement stage module in a micro-displacement measurement system provided in one embodiment of this application; Figure 9This is a schematic diagram of the verification experiment results of the displacement measurement of the measurement system based on micro-displacement provided in one embodiment of this application; Figure 10 This is a schematic diagram of a method for measuring minute displacement provided in one embodiment of this application.

[0019] Figure Labels 10: Laser emission module; 20: Beam shaping module; 21: First shaping module; 211: First polarizer; 212: First phase delayer; 213: Beam expander module; 22: Second shaping module; 23: Third shaping module; 231: Second polarizer; 232: Optical filtering imaging module; 233: Second phase delayer; 30: Focusing module; 40: Imaging acquisition module; 41: Imaging module; 411: Second microscope objective; 412: Magnification module; 42: Acquisition module. Detailed Implementation

[0020] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings.

[0021] Combination Figures 1 to 3 As shown in the figure, this application provides a measurement system for minute displacement, including: a laser emission module 10, a beam shaping module 20, a focusing module 30, an imaging acquisition module 40, and a data processing module.

[0022] The laser emitting module 10 emits a raw laser beam. The beam shaping module 20 shapes the raw laser beam, outputting a vortex beam and a plane-wave reference beam. The focusing module 30 superimposes the vortex beam and the plane-wave reference beam to construct a measurement focal field, which includes a longitudinal optical singularity. The imaging acquisition module 40 acquires a real image of the longitudinal optical singularity in the measurement focal field. The data processing module, electrically connected to the imaging acquisition module 40, determines the displacement of the focusing module 30 based on the real image.

[0023] The micro-displacement measurement system provided in this application utilizes a beam shaping module 20 to generate a vortex beam and a plane wave reference beam. These are then superimposed by a focusing module 30 to construct a measurement focal field containing a longitudinal optical singularity. An imaging acquisition module 40 precisely captures the real image of the singularity, and a data processing module performs refined analysis on the image to determine the displacement. This system fully leverages the unique advantages of the infinitesimally small spatial scale and steep phase gradient of the longitudinal optical singularity, avoiding the optical diffraction limit limitations imposed by traditional optical metrology methods that rely on structured light fields or interference effects. This improves the accuracy of the displacement reference standard. Furthermore, the precise capture of the real image of the longitudinal optical singularity by the imaging acquisition module 40 ensures that the changes in the light field corresponding to the micro-displacement are fully perceived. Thus, the accuracy of micro-displacement measurement is improved.

[0024] The longitudinal optical singularities are distributed along the optical axis, and their projected positions on the transverse plane perpendicular to the optical axis change synchronously with the transverse displacement of the object under test. The focusing module 30 is rigidly connected or in close contact with the object under test, and the movement of the sample causes the focusing module 30 to move. When the focusing module 30 moves laterally, the longitudinally distributed optical singularities in the focal field of the focusing module 30 will produce an offset in the transverse plane corresponding to the actual displacement. Thus, the longitudinal singularities can serve as a high-precision displacement reference, and the magnitude of the transverse displacement of the object under test can be deduced by detecting the offset of the longitudinal singularities in the transverse plane.

[0025] Specifically, in some embodiments, the beam shaping module 20 is loaded with a mask containing a vortex phase and a plane wave reference beam reference phase. Loading this mask into the beam shaping module 20 allows for precise phase and amplitude control of the incident laser field, generating a stable vortex beam and a plane wave reference beam. For example... Figure 1 and Figure 2 As shown, region A represents a vortex beam, and region B represents a planar beam.

[0026] More specifically, the mask template can be represented as: Where rect(.) is the rectangle function, and (x,y) is the Cartesian coordinate system. It is a constant used to define the size of the vortex light field and the plane wave field; , l The topological load number; d For the grating period, The translation distance of the plane wave needs to be precisely designed based on the incident surface of the subsequent microscope objective to ensure that the plane wave is at a specific position close to the edge of the incident surface of the objective.

[0027] Here, the specific location is determined based on the measured optical field. The closer to the edge of the objective lens, the denser the interference fringes between the vortex beam and the plane wave, and the higher the accuracy of resolving the vortex phase. At the same time, the closer to the edge of the incident surface, the higher the requirements for the imaging aperture of the subsequent optical path, and the more difficult it is to form a good image. In particular, a larger imaging aperture is required in displacement measurement. Being too close to the edge of the objective lens will limit the size of the measurement range.

[0028] This photomask defines the light field size using a rectangular function and is precisely designed in conjunction with the topological charge, grating period, and plane wave translation distance. This ensures the plane wave is positioned optimally near the edge of the objective lens's incident surface, allowing the two beams to focus and superimpose to form a densely packed crosshair interference pattern, providing a foundation for the stable construction of the longitudinal optical singularity. Furthermore, by appropriately setting the grating period, it facilitates effective filtering of interfering light, thereby improving the purity of the light field. Thus, the generation of vortex beams and plane wave reference beams can be achieved without complex optical paths, simplifying the beam shaping process.

[0029] In some embodiments, the original laser beam emitted by the laser emitting module 10 is linearly polarized light. The laser emitting module 10 selects to emit linearly polarized light to meet the control requirements of the subsequent beam shaping module 20, laying the foundation for high-precision displacement detection of the entire measurement system. Linearly polarized light has a definite and singular vibration direction, providing a standardized incident reference for the optical field control of the measurement system. This avoids the adjustment uncertainty caused by the chaotic vibration direction of unpolarized or randomly polarized light, thereby improving the signal-to-noise ratio of the interferogram acquired by the subsequent imaging acquisition module 40, reducing analytical errors during data processing, and ultimately ensuring the measurement accuracy of the measurement system.

[0030] Specifically, in some embodiments, the laser emitting module 10 is a continuous-wave helium-neon laser that outputs linearly polarized light. This linearly polarized light output by the laser emitting module 10 serves as the incident light field for the entire system. The wavelength λ of the laser emitting module 10 is, for example, 632.8 nm. The continuous-wave helium-neon laser provides a stable and continuous laser output, avoiding problems such as intensity fluctuations and phase instability that may occur with pulsed laser output. This provides a constant incident light field basis for subsequent light field control and measurement processes, ensuring the reliability of the entire measurement system and laying the foundation for high-precision displacement measurement.

[0031] In some embodiments, the beam shaping module 20 includes a first shaping module 21, a second shaping module 22, and a third shaping module 23. The first shaping module 21 modulates the original laser beam into circularly polarized light. The second shaping module 22 is loaded with a mask containing a vortex phase and a plane wave reference beam reference phase to control the phase and amplitude of the circularly polarized light. The third shaping module 23 modulates the phase- and amplitude-controlled circularly polarized light into linearly polarized light; the linearly polarized light is the composite light field resulting from the superposition of the vortex beam and the plane wave reference beam. The first shaping module 21 is disposed between the second shaping module 22 and the laser emitting module 10, and the third shaping module 23 is disposed between the second shaping module 22 and the focusing module 30. The internal structure of the beam shaping module 20 is further described here. The first shaping module 21 modulates the original laser beam into circularly polarized light, providing a suitable polarization state basis for the phase and amplitude control of the second shaping module 22. Compared to direct incident linearly polarized light, circularly polarized light, when passing through a mask loaded with a vortex phase and a plane wave reference phase, can reduce the interference of polarization direction on phase modulation accuracy. This ensures that the mask can accurately control the phase partitioning of the light field, which is beneficial to improving the stability of the subsequently generated hybrid light field that combines vortex and reference characteristics. The second shaping module 22 generates a vortex beam and a plane wave reference beam through the control of the mask. Its simple structure helps to simplify the overall structure of the measurement system. The third shaping module 23 then remodulates the controlled circularly polarized light into linearly polarized light. This linearly polarized light is a composite light field resulting from the superposition of the two beams, which is compatible with the subsequent focusing module 30, thus improving the measurement accuracy of minute displacements.

[0032] In some embodiments, the second shaping module 22 is a liquid crystal device. The arrangement direction of the liquid crystal molecules inside the liquid crystal device can be controlled to change, and the change in the arrangement direction of the liquid crystal molecules will directly affect the phase and amplitude modulation results of the incident circularly polarized light. Here, when the liquid crystal device is loaded with a mask containing a vortex phase and a plane wave reference phase, the liquid crystal device can, according to the phase distribution law of the mask, locally adjust the arrangement of the liquid crystal molecules to achieve partitioned phase and amplitude modulation of the incident light field, thereby generating a mixed light field of vortex beam and plane wave reference beam that meets the requirements, and the process is accurate and controllable. At the same time, the liquid crystal device itself has a compact structure. Using a liquid crystal device as the second shaping module 22 in the measurement system is beneficial to saving space, thereby improving the structural compactness of the final measurement system.

[0033] In some embodiments, the second shaping module 22 includes a spatial light modulator. The spatial light modulator can precisely control the optical characteristics of its pixel units through electrical signals, thereby achieving dynamic and zoned modulation of the phase and amplitude of incident circularly polarized light. When a mask containing a vortex phase and a plane wave reference phase is loaded, the spatial light modulator can, according to the phase distribution of the mask, independently adjust the modulation parameters of different pixel regions to finely impart phase and constrain the amplitude of the incident light field, thereby generating a mixed light field of the vortex beam and the plane wave reference beam. Simultaneously, during implementation, updating the mask data is sufficient to adjust the modulation effect of the spatial light modulator without updating physical components, which improves the flexibility of the measurement system.

[0034] In some embodiments, the first shaping module 21 includes a first polarizer 211 and a first phase delayer 212. The first polarizer 211 modulates the original laser beam into linearly polarized light. The first phase delayer 212 modulates the linearly polarized light into circularly polarized light. The first polarizer 211 is disposed between the laser emitting module 10 and the phase delayer. The first polarizer 211 filters out stray polarization components in the original laser beam, outputting linearly polarized light with a uniform vibration direction, providing standardized input for the subsequent polarization state conversion of the first phase delayer 212. The first phase delayer 212 modulates the linearly polarized light into circularly polarized light, which can adapt to the second shaping module 22's requirements for partitioned control of the optical field phase and amplitude, helping to avoid modulation deviations and ensuring the accuracy of the mask's control over the optical field phase. Meanwhile, the arrangement of the first polarizer 211 between the laser emission module 10 and the phase delayer ensures that the generation of linearly polarized light and the conversion of circularly polarized light form a coherent link, guaranteeing the polarization state conversion effect and laying the foundation for the second shaping module 22 to output a stable mixed light field.

[0035] In some embodiments, the first phase delayer 212 includes a quarter-glass slide. When linearly polarized light is incident on the quarter-glass slide at a specific angle, a 1 / 4 wavelength optical path difference can be generated between the o-ray and e-ray of the linearly polarized light, which then superimpose to form circularly polarized light. This can accurately meet the conversion requirements of linearly polarized light to circularly polarized light. In some embodiments, the first shaping module 21 also includes a beam expanding module 213. The beam expanding module 213 is disposed between the laser emitting unit and the polarizer and is used to adjust the size of the original laser beam. The first polarizer 211 is used to modulate the original laser beam after size adjustment into linearly polarized light. By disposing the beam expanding module 213 between the laser emitting unit and the polarizer, the beam expanding module 213 can accurately adjust the size of the original laser beam according to the spatial size of the mask in the second shaping module 22, so that the adjusted beam size matches the effective control area of ​​the mask, avoiding problems such as the beam size being too small and wasting mask control resources, or too large and exceeding the mask range and generating stray light, ensuring that the light field can fully and orderly enter the mask control range. Meanwhile, the beam expander module 213 is located before the polarizer, allowing the polarizer to modulate the linearly polarized light after the beam size adjustment is complete. This avoids the disruption of the polarization state stability of the generated linearly polarized light due to refraction and reflection of optical elements when the beam expander module 213 is placed after the polarizer, thus ensuring the circularly polarized light conversion effect of the subsequent phase delayer. In this way, the beam expander module 213 can simultaneously achieve optical field size matching and ensure polarization control effects.

[0036] In some embodiments, the third shaping module 23 includes a second polarizer 231 and an optical filtering imaging module 232. The second polarizer 231 modulates the circularly polarized light, after phase and amplitude modulation, into linearly polarized light. The optical filtering imaging module 232 performs spatial frequency filtering and imaging on the linearly polarized light, retaining only the +1st order diffraction beam. The second polarizer 231 is positioned between the second shaping module 22 and the optical filtering imaging module 232. The second polarizer 231 modulates the phase- and amplitude-modulated circularly polarized light output from the second shaping module 22 into linearly polarized light, avoiding problems such as decreased focusing quality due to polarization mismatch when the circularly polarized light directly enters the focusing module 30, thus helping to ensure the contrast of the interference pattern. The optical filtering and imaging module 232 can perform spatial frequency filtering and imaging on linearly polarized light, retaining only the +1st order diffraction beam. It filters out zero-order DC light and higher-order diffraction noise in the optical field, preventing stray light from interfering with the purity of the vortex beam and the plane wave reference beam. This prevents background noise in the interference pattern formed by subsequent focusing and superposition, ensuring the resolving accuracy of the longitudinal optical singularity. Simultaneously, the arrangement order of the two modules avoids disrupting the polarization state during the filtering process, ensuring the stability of the linearly polarized light and the purity of the +1st order diffraction beam, providing a high-quality optical field input for accurately constructing the longitudinal optical singularity.

[0037] During implementation, by adjusting the grating period d of the mask, the interfering light can be filtered out by the optical filtering imaging module 232.

[0038] In some embodiments, the optical filtering imaging module 232 includes a 4-f system. A 4-f system is a lens group consisting of two convex lenses with a focal length of f, arranged in a specific manner, and the overall optical path length is approximately 4f. The use of a 4-f system in the optical filtering imaging module 232 significantly improves the accuracy and purity of light field manipulation, ensuring the stable construction of the subsequent longitudinal optical singularity and the accuracy of displacement measurement.

[0039] In some embodiments, the third shaping module 23 further includes a second phase delayer 233. The second phase delayer 233 is disposed between the optical filtering imaging module 232 and the focusing module 30, and is used to adjust the polarization direction of the linearly polarized light so that the polarization direction is perpendicular to the line connecting the vortex beam and the plane wave reference beam. Although the linearly polarized light output by the optical filtering imaging module 232 has had stray light removed, its polarization direction may not match the distribution direction of the vortex beam and the plane wave reference beam. If it is directly incident on the focusing module 30, the interference contrast may decrease when the two beams are superimposed due to polarization direction interference, affecting the stable construction of the longitudinal optical singularity. Adding the second phase delayer 233 and placing it between the optical filtering imaging module 232 and the focusing module 30 allows for targeted adjustment of the polarization direction of the linearly polarized light, ultimately making it perpendicular to the line connecting the vortex beam and the plane wave reference beam. This ensures that the polarization states of the two beams are compatible during focusing, reducing problems such as energy cancellation or interference disorder caused by mismatched polarization directions. It allows the two beams to stably form a high-contrast crosshair interference pattern at the focal plane, providing polarization-compatible light field conditions for the precise construction of the longitudinal optical singularity. Simultaneously, placing the second phase delayer 233 between the optical filtering imaging module 232 and the focusing module 30 allows for polarization direction adjustment after light field purification, preventing the introduction of new stray light during the adjustment process and ensuring the purity of the light field.

[0040] In some embodiments, the second phase delayer 233 is, for example, a half-glass slide. The half-glass slide can stably change the vibration direction of linearly polarized light. Specifically, during implementation, by adjusting the placement angle of the half-glass slide, the polarization direction of the linearly polarized light can be rotated to a target direction perpendicular to the line connecting the vortex beam and the plane wave reference beam as needed. This adjustment process is simple to operate and precisely controllable.

[0041] In some embodiments, the focusing module 30 includes a first microscope objective. For example... Figure 3As shown, a vortex beam is projected onto the center of the optical axis of the first microscope objective, while a plane-wave reference beam is projected onto the off-axis region. After being focused by the first microscope objective, the plane-wave reference beam enters the measurement focal field at an angle, causing the vortex beam and the plane-wave reference beam to converge at the focal plane in the measurement focal field, thus constructing a longitudinal optical singularity. The first microscope objective provides the optical basis for the precise convergence of these two beams. Specifically, projecting the vortex beam onto its optical axis center ensures stable transmission along the optical axis and focusing on the central region of the focal plane; projecting the plane-wave reference beam onto the off-axis region allows it to enter the measurement focal field at an angle after being focused by the first microscope objective. In this way, by using an angled incident method, the two beams form a specific optical path difference distribution at the focal plane, rather than being directly incident in the same direction, to form a stable interference pattern. Furthermore, the optical axis direction of this interference pattern naturally forms a longitudinal optical singularity with an infinitesimally small spatial scale and a steep phase gradient. In this way, by clearly defining the projection position and focusing path of the two beams on the first microscope objective, the formation shape of the interference pattern and the generation position of the longitudinal optical singularity are directly determined, avoiding the problem of the two beams not being able to interfere effectively or the singularity shape being unstable due to improper beam projection position, and ultimately ensuring the accuracy of subsequent displacement measurement.

[0042] The first microscope objective is, for example, a high numerical aperture microscope objective, and further, the numerical aperture of this high numerical aperture microscope objective is set to, for example, 0.95. This high numerical aperture characteristic can greatly enhance the light-gathering ability of the objective, collect light at a wider angle, and more efficiently focus the vortex beam output by the beam shaping module 20 and the plane wave reference beam onto the focal plane, so that the two beams form a crosshair interference pattern with clear contrast and dense fringes, which provides a guarantee for the stable construction of the longitudinal optical singularity.

[0043] In some embodiments, the imaging acquisition module 40 includes an imaging module 41 and an acquisition module 42. The imaging module 41 is used to collect the interference pattern of the measured focal field, magnify it, and focus it to form a real image. The acquisition module 42 is used to acquire the real image. The imaging module 41 is disposed between the focusing module 30 and the acquisition module 42. In the measured focal field output by the focusing module 30, the interference pattern corresponding to the longitudinal optical singularity is tiny. If it is directly acquired by the acquisition module 42, the small pattern size can easily lead to loss of detail, making it impossible to accurately reflect the position information of the longitudinal singularity. The imaging module 41 can first collect the interference pattern, magnify it to clearly present the tiny interference details, and then focus it to form a real image, solving the problem of mismatch between the size of the interference pattern and the detection capability of the acquisition module 42. The acquisition module 42 then receives the real image and completes the acquisition, ensuring that the information of the interference pattern is completely recorded. Meanwhile, the imaging module 41 is located between the focusing module 30 and the acquisition module 42, forming a continuous link from the generation and magnification of the interference pattern to its acquisition. This avoids pattern transmission loss caused by the reversal of the module order, ensuring that the acquired real image can truly reflect the distribution characteristics of the longitudinal optical singularities in the measured focal field. This provides a reliable image basis for subsequent data processing to analyze the singularity position and calculate the displacement, thereby ensuring the accuracy of the final measured displacement.

[0044] In some embodiments, the acquisition module 42 includes a CCD (Charge-Coupled Device) camera. It records the magnified interference intensity distribution and outputs an interference image. For example, in this embodiment, a CCD camera with a resolution of 2046×1086 and a pixel size of 5.5μm is used as the acquisition module 42. The CCD camera can convert light signals into electrical signals to capture and record optical images. In this application, the CCD camera converts the light intensity information of the interference light field into corresponding electrical signals, processes them, and then outputs an interference image, thereby recording the interference intensity distribution magnified by the imaging module 41, providing raw image data for the subsequent data processing module to analyze the longitudinal optical singularity position.

[0045] In some embodiments, the imaging module 41 includes a second microscope objective 411 and a magnification module 412. The second microscope objective 411 is used to collect wave vector components in the measurement focal field to obtain an interference pattern. The magnification module 412 is used to magnify the interference pattern and focus it into a real image. In the measurement focal field, the interference pattern of the longitudinal optical singularity is formed by the superposition of different wave vector components. If the wave vector components are not collected completely, the interference pattern will lack key details and cannot accurately reflect the characteristics of the singularity. The second microscope objective 411 can selectively collect all wave vector components in the measurement focal field to ensure the complete generation of the interference pattern and avoid pattern distortion caused by the loss of wave vector components. The magnification module 412 receives the interference pattern output by the second microscope objective 411, magnifies the tiny interference details through magnification processing, and then focuses it to form a real image. This avoids the problem that the interference pattern size is too small and the acquisition module 42 cannot distinguish the details, ensuring that sufficient details are acquired subsequently, thereby ensuring the accuracy of the tiny displacement measurement.

[0046] In some embodiments, the numerical aperture of the second microscope objective 411 is larger than that of the first microscope objective. This is used to collect and amplify all wave vector components in the focal field, avoiding truncation. The numerical aperture of the second microscope objective 411 is designed to be larger than that of the first microscope objective to ensure that it can completely collect all wave vector components in the focal field, avoiding interference pattern distortion due to wave vector component truncation and ensuring the accuracy of subsequent imaging and measurement. Specifically, the numerical aperture of the first microscope objective determines the distribution range of wave vector components in the focal field. The larger the numerical aperture, the richer the wave vector components contained in the focal field. Since the second microscope objective 411 needs to collect the wave vector components in this focal field to generate the interference pattern, if its numerical aperture is smaller than that of the first microscope objective, insufficient receiving capacity will result in some wave vector components not being collected, i.e., wave vector truncation, which will cause the generated interference pattern to lack some details, directly affecting the accuracy of subsequent resolution of longitudinal optical singularities. Therefore, designing the numerical aperture of the second microscope objective 411 to be larger allows its receiving range to completely cover all wave vector components in the focal field of the first microscope objective, ensuring that the wave vector components are not truncated, thereby generating a complete and realistic interference pattern, which ultimately helps to ensure the accuracy of the displacement calculation of the entire measurement system.

[0047] Thus, during implementation, the laser first passes sequentially through a beam expander, a first polarizer 211, and a quarter-glass slide. The beam expander adjusts the beam size to match the spatial dimensions of the mask. The first polarizer 211 modulates the laser's light field into linearly polarized light. The quarter-glass slide converts the linearly polarized light formed by the first polarizer 211 into left-handed circularly polarized light, which serves as the incident light for the mask. Simultaneously, the grating period d of the mask needs to be adjusted to ensure that the subsequent 4-f system can effectively filter out interference light. The custom liquid crystal sheet loaded with this mask forms a custom liquid crystal device, which can perform mixed control of the phase and amplitude of the incident left-handed circularly polarized light. The diffracted light field modulated by the custom liquid crystal device enters the 4-f system, completing spectral filtering and polarization control. In this system, the 4-f system retains only the +1st order diffraction field through the aperture, completely eliminating the zeroth order DC light and higher-order noise, resulting in a clean vortex beam and plane wave reference light. Then, a polarizer is used to convert the amplitude-phase modulated circularly polarized light field back into linearly polarized light. The polarization direction is then adjusted by a half-glass plate to match the distribution of the modulated light field, i.e., the polarization direction is perpendicular to the line connecting the vortex and the plane wave.

[0048] The light field after the above processing is incident on the first microscope objective of the focusing module 30. The vortex beam is projected to the center of the optical axis of the first microscope objective, and the plane wave reference beam is located in the off-axis region. After being focused by the first microscope objective, it enters the focal field in an inclined manner. The two beams converge and superimpose at the focal plane of the first microscope objective to form a typical crosshair interference pattern and construct a longitudinal optical singularity in the optical axis direction. This focal field is the longitudinal optical singularity interference optical scale.

[0049] An imaging module 41, consisting of a second microscope objective 411 and a magnification module 412, is set at the focal field output end. The numerical aperture of the second microscope objective 411 is larger than that of the first microscope objective, enabling it to completely collect all wave vector components in the focal field, avoiding interference pattern distortion caused by wave vector truncation. After collection by the second microscope objective 411 and magnification by the lens group, for example, the entire imaging system has a magnification of approximately 600 times, corresponding to an equivalent spatial resolution of approximately 9 nm. The interference field is then projected onto the CCD camera plane, and the CCD camera records the interference intensity distribution. This provides raw image data for subsequent data processing.

[0050] The data processing procedure will be explained in detail below.

[0051] To obtain the complex amplitude distribution of the measured focal field, a double Fourier transform method can be used.

[0052] Specifically, firstly, regarding the interference intensity Perform a Fourier transform to extract the +1 order spectral component, then perform an inverse Fourier transform on this component to recover the complex amplitude of the superposition of the vortex optical field and the reference wave. In numerical processing, remove the uniform phase of the reference plane wave to obtain the phase distribution of the vortex optical field. ,like Figure 5 As shown.

[0053] By removing the plane wave reference light field from the optical path and measuring again, the intensity distribution of the longitudinal phase singularity light field can be obtained, such as... Figure 4 As shown. The intensity and phase distributions can be used to construct a complex expression for the light field: .

[0054] in, A(x,y) The amplitude distribution of the light field is equal to the square root of the measured intensity. This represents the phase distribution. The complex amplitude contains complete information about the longitudinal optical singularity.

[0055] Then, singularity localization is performed based on singularity line technology.

[0056] Calculate the energy flux of the light field based on the constructed complex amplitude E(x,y). p (Poynting vector). That is: .

[0057] At the reference point The local orbital angular momentum density is defined as follows: .

[0058] When the reference point coincides with the singularity, the entire field exhibits a uniform sign for j. z Distribution; when the reference point deviates from the singularity position, a boundary line appears in the field between positive and negative regions. This boundary is the OAM=0 zero-value line, such as... Figure 6 As shown.

[0059] Thus, by selecting multiple reference points, preferably symmetrically distributed vertically and horizontally, multiple zero-value lines are obtained. The intersection of these zero-value lines will inevitably converge to a singularity, such as... Figure 6 As shown. Further, all intersection points are counted to form an intersection cloud, as shown... Figure 7 As shown, by fitting a two-dimensional Gaussian distribution, the optimal estimated position of its center as the singularity is extracted, and the full width at half maximum (FWHM) is fitted as the positioning accuracy index. Figure 7 As shown, the final half-height and full width are 10.6pm horizontally and 12.8pm vertically.

[0060] Thus, the interference pattern output by the acquisition module 42 is processed by the data processing module. The +1 level spectrum is extracted using a double Fourier transform method to remove the phase of the reference plane wave and recover the complex amplitude distribution E(x,y) of the vortex optical field. The optical field energy flux is calculated based on the complex amplitude. The local orbital angular momentum density is calculated at different reference points r0, and the zero-value line OAM=0 is extracted. The intersection points of multiple zero-value lines are solved and statistically analyzed to form an intersection cloud. The singularity position is extracted using two-dimensional Gaussian fitting, and finally, picometer-level positioning is achieved.

[0061] In some embodiments, the measurement system further includes a displacement stage module. The displacement stage module is fixedly connected to the focusing module 30 and is used to measure the standard displacement of the focusing module 30; the displacement stage module is also electrically connected to the data processing module. This displacement stage module is positioned at the measured end of the optical path. By adding a displacement stage module to the measurement system and fixing it to the focusing module 30 and electrically connecting it to the data processing module, the system's measurement accuracy can be verified and calibrated by providing a standard displacement, ensuring the reliability of the displacement measurement results. The displacement stage module acquires a standard displacement signal, which serves as a benchmark for measuring the accuracy of the system's measurement. Without this benchmark, it is impossible to determine whether the displacement calculated by the data processing module is accurate.

[0062] Combination Figure 8 and Figure 9 As shown, during implementation, the displacement stage module is fixedly connected to the focusing module 30. Its output standard displacement directly corresponds to the actual displacement of the focusing module 30, ensuring the accuracy of the reference. Simultaneously, the displacement stage module is electrically connected to the data processing module, enabling real-time transmission of standard displacement data. This allows the data processing module to compare its calculated displacement with the standard displacement. If the deviation is small, the system's measurement accuracy meets requirements; if the deviation is large, the measurement system can be calibrated based on the comparison results to correct the measurement error. Verification results are as follows: Figure 9 As shown.

[0063] In addition, the displacement stage module can also be used to provide a stable standard displacement signal during system debugging or switching between different measurement scenarios, verify the measurement stability of the system under different conditions, avoid measurement result distortion caused by system drift or environmental interference, and ultimately ensure the accuracy and reliability of the output results of the entire measurement system in sub-nanometer and even picometer-level displacement measurements.

[0064] The measurement system provided in this application can be used for position measurement of microscopic samples such as nanostructures and microdevices, and can also be extended to the detection of lateral displacement of macroscopic objects. The response is achieved through a displacement stage or the reflected / scattered light from the object being measured, making it suitable for displacement measurement needs across multiple scales and scenarios. Simultaneously, this measurement system utilizes the characteristics of optical singularities—infinitely small spatial scale and phase gradients tending towards infinity—to use the singularity position as a displacement measurement benchmark. Theoretically, it can achieve positioning with infinite precision; under experimental conditions, by combining singularity line technology with statistical fitting methods of intersection clouds, picometer-level lateral displacement positioning capability has been achieved. Furthermore, the measurement system provided in this application can be constructed using conventional lasers, custom liquid crystal devices, high numerical aperture objectives, and CCD cameras. The overall device structure is simple, requiring no special materials or complex components. The optical path has a high degree of modularity, allowing for flexible adjustment and compatibility with existing microscopic detection platforms, facilitating widespread application and engineering implementation.

[0065] Here, combined Figure 10 The method for measuring minute displacements is described, which includes steps S10 to S30.

[0066] Step S10: Construct a longitudinal optical singularity optical scale.

[0067] That is, the structure of the aforementioned measurement system for minute displacements, and the measurement light field constructed by the measurement system is the longitudinal optical singularity interference optical scale.

[0068] Step S20: Obtain the imaging of the longitudinal phase singularity light field.

[0069] At the objective lens output end, a second microscope objective lens and a magnification module are set up to magnify and image the focal field interference light field onto the acquisition module. The intensity distribution recorded by the acquisition module is an interference pattern. .

[0070] Step S30: High-precision analysis and positioning of longitudinal phase singularities.

[0071] Singularity localization based on singularity line technology.

[0072] Then, the displacement can be detected by the displacement stage module as a reference for verification and calibration.

[0073] The above embodiments are merely illustrative of several implementation methods of this application, and their descriptions are quite specific and detailed. However, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the inventive concept of this application, and these modifications and improvements all fall within the protection scope of this application.

[0074] In the description of this application, it should be understood that the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first," "second," etc., may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0075] In the description of this application, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

Claims

1. A micro-displacement measurement system, characterized by, The system comprises: a laser emission module for emitting an original laser beam; a beam shaping module for shaping the original laser beam to output a vortex beam and a plane wave reference beam; a focusing module for superimposing the vortex beam and the plane wave reference beam to construct a measurement focal field, the measurement focal field comprising a longitudinal optical singularity; an imaging acquisition module for acquiring a real image of the longitudinal optical singularity in the measurement focal field; a data processing module electrically connected to the imaging acquisition module, configured to determine a displacement amount of the focusing module according to the real image.

2. The system according to claim 1, wherein: the beam shaping module is loaded with a mask plate containing a vortex phase and a plane wave reference beam reference phase.

3. The system according to claim 1 or 2, wherein: the beam shaping module comprises: a first shaping module for modulating the original laser beam into circularly polarized light; a second shaping module loaded with a mask plate containing a vortex phase and a plane wave reference beam reference phase to regulate the phase and amplitude of the circularly polarized light; a third shaping module for modulating the circularly polarized light after phase and amplitude regulation into linearly polarized light; the linearly polarized light is a combined light field after superimposition of the vortex beam and the plane wave reference beam; wherein the first shaping module is arranged between the second shaping module and the laser emission module, and the third shaping module is arranged between the second shaping module and the focusing module.

4. The system according to claim 3, wherein: the second shaping module is a liquid crystal device.

5. The system according to claim 3, wherein: the first shaping module comprises: a first polarizer for modulating the original laser beam into linearly polarized light; a first phase retarder for modulating the linearly polarized light into circularly polarized light; wherein the first polarizer is arranged between the laser emission module and the phase retarder.

6. The system according to claim 5, wherein: the first shaping module further comprises: a beam expander arranged between the laser emission unit and the polarizer for adjusting the size of the original laser beam; the first polarizer is used to modulate the original laser beam after size adjustment into linearly polarized light.

7. The system according to claim 3, wherein: the third shaping module comprises: a second polarizer for modulating the circularly polarized light after phase and amplitude regulation into linearly polarized light; an optical filtering and imaging module for spatial frequency filtering and imaging the linearly polarized light, and only retaining +1 order diffracted beams; wherein the second polarizer is arranged between the second shaping module and the optical filtering and imaging module.

8. The measurement system of claim 7, wherein, the third shaping module further comprises: a second phase retarder arranged between the optical filtering and imaging module and the focusing module, for adjusting the polarization direction of the linearly polarized light, so that the polarization direction is perpendicular to the line connecting the vortex beam and the plane wave reference beam.

9. The system according to claim 1, wherein: The focusing module comprises a first microscopic objective lens; The vortex light beam is projected to the center of the optical axis of the first microscopic objective lens, and the plane wave reference light beam is projected to an off-axis region. After being focused by the first microscopic objective lens, the plane wave reference light beam enters the measurement focal field in an inclined manner, so that the vortex light beam and the plane wave reference light beam converge in the focal plane in the measurement focal field, and a longitudinal optical singularity is constructed.

10. The measurement system according to claim 1, wherein, The imaging acquisition module comprises: An imaging module for collecting an interference pattern of the measurement focal field, amplifying and focusing to form a real image; An acquisition module for acquiring the real image; The imaging module is arranged between the focusing module and the acquisition module.

11. The measurement system according to claim 10, wherein, The imaging module comprises: A second microscopic objective lens for collecting wave vector components in the measurement focal field to obtain an interference pattern; An amplification module for amplifying the interference pattern and focusing to form a real image.

12. The measurement system of claim 1, wherein, Further comprising: A displacement table module fixedly connected with the focusing module for measuring a standard displacement amount of the focusing module; The displacement table module is electrically connected with the data processing module.

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