A non-contact micro-displacement measurement device based on vortex light self-conjugate interference

Abstract

This invention belongs to the field of micro-displacement measurement technology and discloses a non-contact micro-displacement measurement device based on vortex beam self-conjugate interference. The device includes: a 532nm laser, an adjustable attenuator, a laser beam expander, a first beam splitter (BS1), a spatial light modulator, a second beam splitter (BS2), a plane mirror 1, a plane mirror 2, a third beam splitter (BS3), a target object, and a CCD. This system utilizes the principle of vortex beam self-conjugate interference, combined with an improved dual-path ring conjugate interference system, to achieve high-precision micro-displacement measurement through the linear relationship between the angle change of the interference pattern and the displacement. The phase singularity of the vortex beam is highly sensitive to minute displacements, and conjugate vortex beam technology further enhances this characteristic. Through the enhancement effect of the phase singularity, this technology can effectively detect even smaller displacement changes, thereby improving the sensitivity and accuracy of the measurement. The system's structural design is simpler and more efficient, avoiding complex optical path setup and debugging processes, making operation more convenient.

Description

Technical Field

[0001] This utility model belongs to the field of micro-displacement measurement technology, and in particular relates to a non-contact micro-displacement measurement device based on vortex light self-conjugate interference. Background Technology

[0002] High-precision displacement measurement technology is crucial in precision machining and chip manufacturing, especially in fields such as semiconductor precision template manufacturing and high-precision displacement sensor calibration, where the demand for micro- and nano-scale measurement accuracy is particularly urgent. Optical interferometry, especially vortex interferometry, has become the mainstream method for displacement measurement due to its non-contact nature, high sensitivity, and high accuracy, and is widely used for high-precision measurement of geometric quantities such as displacement and rotational speed.

[0003] In recent years, researchers have employed innovative methods, such as utilizing the interference effect of vortex light and spherical waves, to achieve highly sensitive and precise micro-displacement measurements by measuring the slope of the tangent at the center of the interference pattern. Furthermore, by fitting phase change curves to accurately obtain the rotation angle of the image, they have acquired minute displacements, further improving measurement efficiency and accuracy.

[0004] However, current research still faces several challenges. The conventional optical imaging approach based on optical path interferometry is the root cause of the trade-off between measurement range and accuracy. While traditional laser interferometric displacement measurement techniques, based on spherical wave, plane wave, and vortex interferometry, offer advantages such as simple structure and measurement resolution down to the picometer level, the spiral interferometric pattern fails to fully utilize its rich spiral phase information, resulting in insufficient accuracy in rotation angle extraction. Furthermore, as the measurement range increases, the interferometric pattern becomes susceptible to environmental factors such as temperature fluctuations and mechanical vibrations, rendering it undetectable. These factors limit further improvements in measurement performance, necessitating the exploration of new methods to overcome these limitations and enhance measurement accuracy and precision.

[0005] Based on the above analysis, the problems and shortcomings of the existing technology are as follows:

[0006] (1) Although traditional laser interferometric displacement measurement technology has the advantages of simple structure and measurement resolution down to the picometer level based on spherical wave, plane wave and vortex light interference, the spiral interference pattern fails to make full use of its rich spiral phase information, resulting in insufficient accuracy of rotation angle extraction.

[0007] (2) When the measurement range increases to a certain extent, the interference pattern is easily affected by environmental factors such as temperature fluctuations and mechanical vibrations and cannot be effectively detected. Utility Model Content

[0008] To address the problems existing in the prior art, this utility model provides a non-contact micro-displacement measurement device based on vortex light self-conjugate interference.

[0009] This invention is implemented as follows: a non-contact micro-displacement measurement device based on vortex optical self-conjugate interference, comprising:

[0010] 532nm laser, adjustable attenuator, laser beam expander, first beam splitter (BS1), spatial light modulator, second beam splitter (BS2), plane mirror one, plane mirror two, third beam splitter (BS3), target object, CCD;

[0011] An adjustable attenuator is located to the right of the 532nm laser, a laser beam expander is located to the right of the adjustable attenuator, a first beam splitter (BS1) is located to the right of the laser beam expander, a spatial light modulator is located to the right of the first beam splitter (BS1), a second beam splitter (BS2) is located above the first beam splitter (BS1), and a plane mirror is located to the left of the second beam splitter (BS2).

[0012] Furthermore, a second plane mirror is disposed above the first plane mirror.

[0013] Furthermore, a third beam splitter (BS3) is provided on the right side of the second planar reflector.

[0014] Furthermore, a third beam splitter (BS3) is disposed above the second beam splitter (BS2).

[0015] Furthermore, a target object is positioned above the third beam splitter (BS3).

[0016] Furthermore, a CCD is provided on the right side of the third beam splitter (BS3).

[0017] In combination with the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solution to be protected by this utility model are as follows:

[0018] Vortex beam technology has shown great application potential in the field of laser interferometry, especially in the measurement of geometric quantities such as high-precision displacement and rotational speed. By combining the degrees of freedom and helical phase information of the vortex beam with a spatial light modulator (SLM) and an advanced optical interferometry system, the micro-displacement measurement device based on vortex beam self-conjugate interference not only simplifies the measurement process but also brings significant advantages.

[0019] 1. Excellent precision and robustness

[0020] This system utilizes the principle of vortex beam self-conjugate interference, combined with an improved dual-path ring conjugate interferometry system, to achieve high-precision micro-displacement measurement through the linear relationship between the angle change of the interference pattern and the displacement. The phase singularity of the vortex beam is highly sensitive to minute displacements, and conjugate vortex beam technology further enhances this characteristic. Through the enhancement effect of the phase singularity, this technical solution can effectively detect even smaller displacement changes, thereby improving the sensitivity and accuracy of the measurement. The system's structural design is simpler and more efficient, avoiding complex optical path setup and debugging processes, making operation more convenient.

[0021] 2. Key advantages of non-contact measurement

[0022] Non-contact measurement is a major advantage of this system, as it avoids the influence of the object's surface condition on the measurement results. In applications such as precision engineering and biomedicine, non-contact measurement not only eliminates physical interference with the object being measured but also reduces the risk of wear and damage caused by contact. This measurement method performs excellently under high temperature, high pressure, or other extreme environments, ensuring safe and reliable monitoring.

[0023] 3. Advantages of the improved dual-optical-path conjugate interferometry system

[0024] The improved dual-path ring conjugate interferometry system offers significant advantages in expanding the measurement range and enhancing sensitivity. By extending the optical path and adjusting the test arm length, this system can expand the measurement range without sacrificing sensitivity. This flexibility allows it to adapt to different measurement needs, from minute displacements to large distance variations.

[0025] Furthermore, the dual-path ring conjugate interferometry system enhances its anti-interference capability through a compact design that decomposes the beam into clockwise and counterclockwise propagation directions. It eliminates noise caused by optical path asymmetry during operation, effectively mitigating the effects of environmental factors such as temperature fluctuations and mechanical vibrations, ensuring high stability in complex environments. This design provides stronger physical anti-interference capabilities and reduces wavelength dependence. The improved dual-path ring conjugate interferometry system gives this technology unique advantages in high sensitivity and stability, and allows it to adapt to various complex geometries and miniaturized devices. Attached Figure Description

[0026] Figure 1 This is a structural diagram of a non-contact micro-displacement measurement device based on vortex light self-conjugate interference, provided in an embodiment of this utility model.

[0027] Figure 2 The conjugate vortex optical interference pattern l=3 provided in this embodiment of the utility model is shown in Figure 1.

[0028] Figure 3 This is a diagram of a micro-displacement measurement device based on vortex light self-conjugate interference provided in an embodiment of this utility model.

[0029] Figure 1 In the middle: 1. 532nm laser; 2. Adjustable attenuator; 3. Laser beam expander; 4. First beam splitter (BS1); 5. Spatial light modulator; 6. Second beam splitter (BS2); 7. Plane mirror one; 8. Plane mirror two; 9. Third beam splitter (BS3); 10. Target object; 11. CCD. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this utility model clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this utility model.

[0031] Example 1: The system was used to calibrate a piezoelectric nanostage. A piezoelectric stage with a travel of ±10 μm and a closed-loop resolution of 1 nm was installed at the target object location, and the geometrical optical path from the second beam splitter to the target object was set to 85 mm. The laser output power was adjusted to 10 mW, and a helical phase with a topological charge of l = 1 was applied to the spatial light modulator. As the control voltage was gradually increased, the vortex interference fringes drifted horizontally; the phase difference was extracted using two-dimensional Fourier demodulation, yielding a displacement-phase conversion coefficient of 5.13 rad / μm. Compared with the readings of the built-in capacitance ruler of the piezoelectric stage, the average linear error between the two was less than 0.4%, and the minimum resolvable displacement was 7.6 nm.

[0032] The phase noise power spectrum measured in Example 1 is -88 dBcHz at 1 Hz, with an interference signal-to-noise ratio of 38 dB. While maintaining phase-locked operation, the system exhibits zero drift of less than 0.9 nm over 8 hours, verifying the thermal stability of the dual-plane reference arm. These results demonstrate that the proposed solution can replace the traditional Michelson interferometer for nanometer-level static calibration without requiring a target to be attached to it, making it particularly suitable for non-contact closed-loop control of sensitive MEMS devices.

[0033] Example 2: The system is used for real-time monitoring of the resonant amplitude of a micromechanical silicon beam. A cantilever beam with a length of 300 μm and a thickness of 2 μm is encapsulated in a vacuum cavity. The cavity's light-transmitting window is coated with an antireflection film and placed at the end of the probe arm. An excitation coil drives the beam to resonate at its fundamental frequency around 23 kHz. A spatial light modulator is set with a topological charge of l = 2, and a ring-shaped light spot covers the free end of the beam. An imaging lens with f = 200 mm is introduced at the output of the third beam splitter to directly collect the interferogram on a high-speed sCMOS (10 kfps) target.

[0034] The displacement-time curve was reconstructed using a time-series phase expansion algorithm, revealing a peak-to-peak amplitude of 220 nm and a frequency jitter (Allan deviation, 1-second average) of no more than 9 ppm. Connecting the system output to an FPGA threshold trigger port enabled a response to amplitude abrupt changes within 15 μs, providing early warning of beam crack initiation. This demonstrates that the vortex self-conjugate interferometry technique of this invention is also applicable to high-frequency dynamic displacement measurement and possesses fast electronic interface compatibility.

[0035] like Figure 1 As shown, this utility model provides a non-contact micro-displacement measurement device based on vortex light self-conjugate interference, comprising:

[0036] 1. 532nm laser, 2. Adjustable attenuator, 3. Laser beam expander, 4. First beam splitter (BS1), 5. Spatial light modulator, 6. Second beam splitter (BS2), 7. Plane mirror one, 8. Plane mirror two, 9. Third beam splitter (BS3), 10. Target object, 11. CCD.

[0037] An adjustable attenuator 2 is located to the right of the 532nm laser 1. A laser beam expander 3 is located to the right of the adjustable attenuator 2. A first beam splitter (BS1) 4 is located to the right of the laser beam expander 3. A spatial light modulator 5 is located to the right of the first beam splitter (BS1) 4. A second beam splitter (BS2) 6 is located above the first beam splitter (BS1) 4. A plane mirror 7 is located to the left of the second beam splitter (BS2) 6. A plane mirror 8 is located above the plane mirror 7. A third beam splitter (BS3) 9 is located to the right of the plane mirror 8. A third beam splitter (BS3) 9 is located above the second beam splitter (BS2) 6. A target object 10 is located above the third beam splitter (BS3) 9. A CCD 11 is located to the right of the third beam splitter (BS3) 9.

[0038] After a linearly polarized continuous beam is emitted from a 532nm laser 1, it passes sequentially through an adjustable attenuator 2 and a laser beam expander 3, thereby allowing for precise control of power and spot diameter. After being split by the first beam splitter (BS1) 4, one beam enters the spatial light modulator 5, where it is infused with vortex phase and forms a vortex light field with orbital angular momentum; the other transmitted beam retains high coherence, providing a reference for subsequent interference. The vortex light output from the spatial light modulator 5 continues its journey and re-merges with the reference beam at the second beam splitter (BS2) 6, thus establishing the starting point for equal-path interference.

[0039] The second beam splitter (BS2) 6 divides the combined optical field into a reference arm and a probe arm. The reference arm beam is reflected by (BS2) 6 and reaches the first plane mirror 7, then refracted back to the second plane mirror 8, and after a second reflection, it returns to the third beam splitter (BS3) 9. Mirrors 1 and 2 are optical planes with an absolute flatness of λ / 10 to ensure the phase stability of the reference arm; the fixing structure between the two mirrors is precisely locked by an integrated aluminum alloy bracket, so that the optical path of the reference arm can remain constant for a long time within the thermal drift range.

[0040] The probe arm beam, after being directly incident from the second beam splitter (BS2) 6 onto the third beam splitter (BS3) 9, is guided by (BS3) 9 towards the target object 10, forming a ring-shaped vortex spot on its surface. The optical path difference caused by the micro-displacement of the target object is superimposed on the vortex phase. When the reflected light returns via (BS3) 9, it undergoes self-conjugate interference with the synchronously returning reference arm within the same beam splitter cavity. (BS3) 9 uses a 50:50 unpolarized cubic beam splitter to match the reflectivity of the two arms and minimize phase insertion error.

[0041] The two interfering beams are ultimately transmitted through the third beam splitter (BS3) 9 into the CCD 11 for imaging. The fringe phase recorded by the CCD pixels includes the phase shift caused by the micro-displacement of the target object. The back-end digital signal processing module performs Fourier filtering and phase unrolling on the CCD output. By utilizing the helical characteristics of the vortex phase, the axial and lateral displacement components can be separated, achieving non-contact displacement measurement with nanometer-level resolution. The entire system requires no mechanical scanning and relies on the inherent self-conjugate interference characteristics of the vortex light to complete real-time measurements within a single frame, making it suitable for online monitoring of high-speed vibrations and micro-deformations.

[0042] Traditional micro-displacement measurement techniques mostly employ Michelson interferometers or dual-frequency laser interferometers, relying on mechanical scanning and long optical path split-arm designs. However, in high-frequency vibration environments, such as precision spindle operation or MEMS resonant testing, the instability of the mechanical structure often introduces interference fringe drift or phase jumps caused by thermal-vibration coupling, severely affecting measurement accuracy and repeatability. On the other hand, contact sensors (such as eddy current sensors and displacement gratings) are highly dependent on the topography of the measured surface, making it difficult to achieve non-destructive testing of high-speed or flexible targets. Therefore, the industry urgently needs a micro-displacement detection device with common optical path stability, a non-scanning architecture, and self-suppression capabilities against environmental interference.

[0043] To address the aforementioned problems, this invention proposes a non-contact displacement measurement device based on a vortex light self-conjugate interference structure. The system uses a 532nm laser 1 as the light source. The output linearly polarized single-longitudinal-mode laser first has its power controlled by an adjustable attenuator 2, and then the laser beam expander 3 adjusts the spot diameter to match the aperture of subsequent optical elements. After passing through a first beam splitter (BS1) 4, it is split into two paths: one path is transmitted as a reference beam, retaining its original high coherence; the other path is reflected into a spatial light modulator 5, where an m-order vortex phase is loaded, forming a ring-shaped vortex beam with orbital angular momentum (OAM).

[0044] After being output from the spatial light modulator 5, the vortex beam is coaxially recombinated with the reference beam at the second beam splitter (BS2) 6, constructing a two-arm equal optical path interference path. This design inherently possesses the characteristic of "common path": the probe arm and the reference arm share the support structure, air path, and thermal field. Therefore, the common-mode phase caused by external disturbances can be canceled in the interference signal, improving phase stability in industrial applications. Especially in field environments with vibration amplitudes greater than 10g and temperature drifts exceeding 5℃, the fringe clarity and signal-to-noise ratio are significantly superior to traditional interferometric systems.

[0045] The reference arm beam, after being reflected by (BS2)6, is sequentially reflected back by plane mirror 7 and plane mirror 8, forming a return path. The two mirrors have an accuracy of λ / 10 and are rigidly fixed by an integrated aluminum alloy frame, ensuring the optical path stability of the reflecting arm is better than 0.5 nm / ℃. The probe arm beam is transmitted through BS26 to the third beam splitter (BS3)9, where it is deflected and illuminates the target surface 10, forming a ring-shaped vortex spot with a diameter of approximately 50 μm. This spot possesses high radial symmetry and a spiral phase structure, significantly enhancing the sensitivity to phase shifts caused by micrometer-level displacements.

[0046] The optical path difference modulation caused by the micro-displacement of the target object 10 is superimposed on the vortex phase. The reflected return light is then returned via (BS3)9, achieving self-conjugate interference with the wavefront returning from the reference arm within the BS3 cavity. (BS3)9 employs a 50:50 unpolarized cubic beam splitter to ensure amplitude matching between the two arms, minimizing interference distortion caused by amplitude difference. Due to the helical phase distribution of the vortex light, the axial displacement of the target manifests as a shift in the polar angle of the interference fringes, while the lateral displacement causes a change in the fringe radius, achieving decoupling and extraction of axial / lateral information.

[0047] The interference fringes are ultimately received by the CCD11, and the image information directly reflects the three-dimensional displacement of the target object. Back-end signal processing uses Fourier transform bandpass filtering and Itoh phase expansion technology to quickly resolve the minute displacement information Δz (axial) and Δr (radial) contained in the fringes. The system requires no mechanical scanning components, has a single-frame measurement resolution better than 5nm at a 1kHz frame rate, and an overall size of less than 200mm. 3It is applicable to typical scenarios such as wafer bonding, scanning mirror calibration, and high-speed bearing condition detection, and provides a new paradigm for industrial-grade micro-displacement measurement that is highly sensitive, highly stable, and compact.

[0048] The above description is only a specific embodiment of this utility model, but the protection scope of this utility model is not limited thereto. Any modifications, equivalent substitutions and improvements made by those skilled in the art within the technical scope disclosed in this utility model, and within the spirit and principles of this utility model, should be included within the protection scope of this utility model.

Claims

1. A non-contact micro-displacement measurement device based on vortex light self-conjugate interference, characterized in that, The laser, adjustable attenuator, laser beam expander, first beam splitter, spatial light modulator, and second beam splitter are arranged sequentially along the same optical axis. The reflected light path of the second beam splitter sequentially reaches the first plane mirror and the second plane mirror, then returns to the second beam splitter and enters the third beam splitter to form a reference arm; The transmitted light path of the second beam splitter directly enters the third beam splitter and illuminates the target object to form a measuring arm; The reference arm and the measuring arm are combined by the third beam splitter and then enter the image acquisition unit. The reference arm and the measuring arm share optical elements within the third beam splitter to form a self-conjugate interference.

2. The system of claim 1, wherein, The vortex beam output by the spatial light modulator has a fixed integer topological charge and exhibits a ring-shaped intensity distribution.

3. The system of claim 1, wherein, Plane mirror one and plane mirror two are parallel to each other and have a fixed distance between them to ensure the stability of the optical path of the reference arm.

4. The system of claim 1, wherein, The third beam splitter has a reflectance and a transmittance equal to match the power of the reference arm and the measurement arm.

5. The system of claim 1, wherein, The image acquisition unit is a charge-coupled sensor with a pixel size of no more than four micrometers and is equipped with a synchronous trigger module.

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