Single-point multi-axis micro-angle precision measurement based on frequency-selective metasurface

Abstract

This invention discloses a single-point multi-axis micro-angle precision measurement method based on a frequency-selective metasurface, comprising three parts: light source alignment, metasurface reflection, and reflected light reception. The light source alignment process utilizes the metasurface structure's absorption characteristics in both the visible and near-infrared bands. An optical frequency comb, as a broadband light source, contains, to some extent, the characteristic absorption bands of the metasurface. By mixing the optical frequency comb with visible light via a beam splitter, it serves as the output light source, achieving a visualized laser light source alignment process. After collimation by a collimating lens, the light source illuminates the metasurface structure. Due to differences between structures, the absorption of the optical frequency comb varies, manifesting as brightness variations in the near-infrared camera image. The metasurface is mounted on the surface of the device under test. An electrically operated turntable is used to precisely control the micro-angle changes of the device under test, and the values ​​of the turntable are used as reference values ​​for calibration. A telecentric lens receives the light reflected from the metasurface, which is then imaged by a near-infrared camera. Finally, image processing is performed to achieve precise micro-angle measurement of the device under test. This invention utilizes the absorption characteristics of frequency-selective metasurfaces for specific wavelengths to convert changes in the micro-angle of the device under test into changes in grayscale values ​​in visual imaging, thus achieving single-point multi-axis micro-angle detection of the device under test. This invention can effectively solve problems in various scientific research and industrial fields such as spatial positioning, machine tool calibration, precision instruments, and MEMS (Micro-Electro-Mechanical Systems) device testing, and has broad application prospects.

Description

Technical Field

[0001] This invention belongs to the field of geometric measurement, specifically relating to a single-point micro-angle precision measurement based on a frequency-selective metasurface. Technical Background

[0002] Precise measurement of small displacements and angles using optical methods is an essential step in many research fields, such as MEMS device inspection, the semiconductor industry, super-resolution microscopy, and gravitational wave detection. Generations of researchers have made tireless efforts to achieve higher precision geometric measurements. In the semiconductor industry and super-resolution microscopy, the space for placing displacement sensors is quite limited, making it difficult for existing measurement methods to meet the requirements for measurement range and accuracy. Frequency-selective metasurfaces use subwavelength structural units to control and guide the wavefront of a beam. Their manufacturing is closely related to semiconductor photolithography, making it easy to fabricate smaller devices. Moreover, metasurface-based measurement methods can effectively solve many drawbacks of traditional measurements, such as enabling non-contact optical measurements and effectively reducing the impact of air disturbances or instrument vibrations on measurement results compared to traditional methods. Summary of the Invention

[0003] To overcome the problems in the aforementioned technologies, this invention provides a single-point, multi-axis micro-angle precision measurement based on a frequency-selective metasurface. By using an optical frequency comb and a visible light source for mixing, the lack of visualization associated with laser light source alignment is overcome, accurately locating the anomalous optical path after reflection from the metasurface. Utilizing the absorption characteristics of the frequency-selective metasurface for characteristic wavelengths, a relationship is established between the angle change of the device under test (DUT) and the image. Visual algorithms are used to process and extract the image, and a high-precision motorized turntable is used to achieve the measurement and calibration of the DUT's angle.

[0004] The technical solution adopted in this invention is: single-point multi-axis micro-angle precision measurement based on frequency-selective metasurfaces, including:

[0005] A light source alignment module, which is used to realize the alignment of a visible laser light source, includes a visible light source, an optical frequency comb, a beam splitter, and a collimating lens;

[0006] A metasurface reflection module is used to receive a collimated hybrid light source and to perform structural reflection and angle adjustment of the device under test. The module includes a metasurface, the device under test, a high-precision motorized turntable, and software control.

[0007] A reflected light receiving module is used to receive light reflected by the metasurface structure and to perform imaging, including a telecentric lens, a near-infrared camera, and an image processing algorithm.

[0008] The visible light source and optical frequency comb in the light source alignment module are first mixed by a beam splitter to obtain the light source for the visualization laser alignment process. After being collimated by a collimating lens, the light is output to the metasurface structure in the metasurface reflection module. The metasurface structure is installed on the device under test. The light reflected by the metasurface structure is transmitted to the telecentric lens in the reflected light receiving module and finally imaged in the near-infrared camera. By using a high-precision electric turntable to adjust the angle of the device under test, two images with slight differences before and after adjustment can be obtained. The grayscale information of the two images is found by using image processing algorithms, and then the actual value of the high-precision turntable is used for calibration, realizing the micro-angle detection of the device under test.

[0009] Furthermore, after the laser light source and optical frequency comb are mixed, the laser light source alignment module needs to first roughly hit the structure with the light source, then adjust the near-infrared camera to low gain and low exposure time, align the light spot with the structure, then increase the gain and exposure time, then adjust the pitch angle of the light source to make it deflect to a certain extent, and finally move the field of view down to find the reflected light path of the structure. The optical frequency comb used is a broadband light source, and its frequency range should overlap with the characteristic absorption frequency of the metasurface. Within the frequency domain, the initial bias frequency of the optical frequency comb is set to f. ceo Therefore, the frequency of the comb teeth in an optical frequency comb can be expressed as:

[0010] f n =nf rep +f ceo (1) Among them, f n f represents the frequency of the nth comb tooth. rep This represents the repetition frequency. The present invention requires the selection of an optical frequency comb that matches the characteristic absorption wavelength of the metasurface. This allows for maximum observation of the metasurface's absorption, resulting in more significant changes in grayscale values ​​during near-infrared imaging.

[0011] Furthermore, the metasurfaces have different absorption characteristics for different wavelengths within the characteristic band. Due to the different internal structures of the metasurface arrays used, the absorption performance of the optical frequency comb also varies, which leads to changes in brightness in the images after imaging by the near-infrared camera. When the pose of the device under test is changed by controlling the high-precision turntable with software, the pattern reflected by the structure hardly moves, but the pixel grayscale values ​​at this time can still be analyzed and calculated to realize the pose change, enabling high-precision measurement. According to the experimental results, the angle measurement resolution can reach more than 0.0005°.

[0012] Furthermore, the process of precise measurement of the pose of the device under test (DUT) utilizes the change in the position of the metasurface structure to obtain two images: the original position and the changed position. In order to achieve multi-degree-of-freedom parameter measurement of the DUT, multiple metasurfaces can be combined to overcome the limitations of single-surface measurement. The pixel values ​​of the two images before and after the pose change are converted into the change in parameters of each degree of freedom through image processing algorithms. Then, the high-precision turntable is used for calibration, thereby realizing high-precision multi-degree-of-freedom measurement of the DUT.

[0013] The beneficial effects of this invention are:

[0014] This invention proposes a single-point, multi-axis micro-angle precision measurement based on a frequency-selective metasurface. Utilizing the absorption characteristics of the frequency-selective metasurface for characteristic wavelength bands, a visualized laser alignment process is achieved. The frequency-selective metasurface employs subwavelength structural units, fabricated using etching technology, which satisfies the spatial limitations of the measurement. The proposed measurement method can be further explored by using multiple metasurfaces, employing image processing technology to precisely locate the changes in parameters at each degree of freedom, thus improving upon the shortcomings of optical interferometers, such as insensitivity to lateral displacement and measurement accuracy being affected by air disturbances and instrument vibrations. In the embodiments of this invention, even a very small angular change can be distinguished through image processing; according to experimental results, the angle measurement resolution can reach above 0.0005°. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the single-point multi-axis micro-angle precision measurement based on frequency-selective metasurfaces according to the present invention;

[0016] Figure 2 This is a simulation diagram of the metasurface subwavelength unit according to an embodiment of the present invention;

[0017] Figure 3 This is a schematic diagram of electromagnetic field simulation of a metasurface unit according to an embodiment of the present invention, showing the electric field distribution (left) and the unit's Z-axis cross-section (right).

[0018] Figure 4 This is a schematic diagram of the unit structure of the metasurface processed in the embodiment of the present invention under electron microscopy.

[0019] Figure 5 This is a schematic diagram of the etching process of the metasurface in an embodiment of the present invention, showing a trapezoidal cross-section of the groove (left) and a unit cross-section (right);

[0020] Figure 6 This is a schematic diagram of the simulation results of the processing deviation of the metasurface unit in an embodiment of the present invention;

[0021] Figure 7The image shows a metasurface pattern after feature absorption captured by a near-infrared camera in an embodiment of the present invention.

[0022] Attached image captions:

[0023] 1--Light source alignment module 11--Visible light source

[0024] 12--Optical frequency comb 13--Beam splitter

[0025] 14--Collimating Lens 2--Metasurface Reflection Module

[0026] 21--Metasurface 22--Device under Test

[0027] 23--High-precision electric rotary table 24--Software control

[0028] 3--Reflected light receiving module 31--Telecentric lens

[0029] 32--Near-infrared camera 33--Image processing algorithm Detailed Implementation

[0030] To further understand the invention's content, features, and effects, the following embodiments are provided, along with detailed descriptions in conjunction with the accompanying drawings:

[0031] like Figure 1 As shown, a single-point multi-axis micro-angle precision measurement structure based on a frequency-selective metasurface is characterized by comprising:

[0032] The light source alignment module 1 is used to realize the visual alignment of the laser light source, including a visible light source 11, an optical frequency comb 12, a beam splitter 13, and a collimating lens 14.

[0033] Metasurface reflection module 2, which is used to receive the collimated mixed light source and can reflect and adjust the angle of the structure, includes metasurface 21, device under test 22, high-precision electric turntable 23, and software control 24;

[0034] The reflected light receiving module 3 is used to receive light reflected by the metasurface structure and perform imaging, including a telecentric lens 31, a near-infrared camera 32, and an image processing algorithm 33.

[0035] The visible light source 11 and optical frequency comb 12 in the light source alignment module 1 are first mixed by the beam splitter 13 to obtain the light source for the visualization laser alignment process. After being collimated by the collimating lens 14, the light is output to the metasurface structure 21 in the metasurface reflection module. The metasurface structure is installed on the device under test 22. The light reflected by the metasurface structure is transmitted to the telecentric lens 31 in the reflected light receiving module and finally imaged in the near-infrared camera 32. The device under test is micro-angled by using a high-precision electric turntable 23, which can obtain two images with slight differences before and after adjustment. The image processing algorithm 33 is used to find the gray value information of the two images, and then the actual value of the high-precision turntable is used for calibration, thus realizing the micro-angle detection of the device under test.

[0036] After the laser light source alignment module 1 is mixed by the visible light source 11 and the optical frequency comb 12, it needs to first roughly hit the structure with the light source, then adjust the near-infrared camera 32 to low gain and low exposure time, align the light spot with the structure, then increase the gain and exposure time, then adjust the pitch angle of the light source to make it deflect to a certain extent, and finally move the field of view down to find the reflected light path of the structure. The optical frequency comb 12 used is a broadband light source, and its frequency range should overlap with the characteristic absorption frequency of the metasurface. Within the frequency domain, the initial bias frequency of the optical frequency comb is set to f. ceo Therefore, the frequency of the comb teeth in an optical frequency comb can be expressed as:

[0037] f n =nf rep +f ceo (1) Among them, f n f represents the frequency of the nth comb tooth. rep This represents the repetition frequency. The present invention requires the selection of an optical frequency comb that matches the characteristic absorption wavelength of the metasurface. This allows for maximum observation of the metasurface's absorption, resulting in more significant changes in grayscale values ​​during near-infrared imaging.

[0038] The metasurface 21 has different absorption characteristics for different wavelengths within the characteristic band. Due to the different internal structures of the metasurface arrays used, the absorption performance of the optical frequency comb also varies. This results in changes in brightness in the image after imaging by the near-infrared camera 32. When the high-precision turntable 24 is controlled by software to make a micro-angle change in the structure under test 22, the pattern reflected by the structure hardly moves. However, the pixel gray value at this time can still be analyzed to realize the position change analysis and calculation, and high-precision measurement can be achieved. According to the experiment, the angle measurement resolution can reach more than 0.0005°.

[0039] The process of micro-angle precision measurement of the device under test 22 is to change the position of the structure of the metasurface 21 to obtain two images: the original position and the changed position. In order to achieve multi-degree-of-freedom parameter measurement, multiple metasurfaces can be combined to overcome the limitations of single-surface measurement. The pixel values ​​of the two images before and after the pose change are converted into the change of parameters in each degree of freedom by the image processing algorithm 33. Then, the high-precision multi-degree-of-freedom measurement of the device under test can be achieved by calibrating the values ​​of the high-precision turntable.

[0040] Figure 2 , 3 This is a schematic diagram and an electromagnetic field simulation diagram of the metasurface subwavelength unit according to an embodiment of the present invention.

[0041] like Figure 2 , 3 As shown, the metasurface unit constructed in this embodiment of the invention is Y-shaped. According to the results of electromagnetic field simulation, the position with the largest resonance intensity occurs at the connection of the three arms in the cavity. The greater the resonance intensity, the more obvious the final imaging result will be. It is worth noting that once the units are interconnected, the resonance position will change. It can be considered that the metasurface with this situation is unqualified.

[0042] Figure 4 This is a schematic diagram of the unit structure of the metasurface processed in an embodiment of the present invention under electron microscopy.

[0043] like Figure 4 As shown, whether the metasurface is qualified is the key to the effectiveness of this detection method. It can be seen that the subwavelength unit under electron microscopy is consistent with the shape we simulated. Therefore, it can be considered that the resonant wavelength of the unit is around 1550nm.

[0044] Figure 5 This is a schematic diagram of the etching process of the metasurface in an embodiment of the present invention, showing a trapezoidal cross-section of the groove (left) and a unit cross-section (right); Figure 6 This is a simulation diagram of machining errors.

[0045] like Figure 5 As shown, since ion beam lithography (IBE) is used to process the metasurface in this embodiment, the IBE etching exhibits anisotropic characteristics, which can lead to deviations in the etching results. The groove walls of the processed metasurface are trapezoidal. To further investigate whether this affects the absorption wavelength, we conducted further simulation analysis to simulate the actual processing conditions. Figure 6 The simulation results shown demonstrate that the anisotropy of IBE etching has negligible impact. This measurement method utilizes an optical frequency comb, a broadband light source, which can accommodate minute deviations in the characteristic wavelengths of the metasurface.

[0046] Figure 7 The image shows a metasurface pattern after feature absorption, captured by a near-infrared camera in an embodiment of the present invention.

[0047] like Figure 7 As shown in the embodiment, we successfully observed the absorption of the metasurface in a near-infrared camera, and controlled the metasurface development angle deflection by a high-precision turntable. We also successfully estimated the measured angle resolution using image processing algorithms, which can reach more than 0.0005°.

[0048] In summary, this invention proposes a single-point multi-axis micro-angle precision measurement based on a frequency-selective metasurface. Utilizing the absorption characteristics of the frequency-selective metasurface 21 for characteristic wavelength bands, a visualized laser alignment process is achieved. The frequency-selective metasurface 21 employs subwavelength structural units, processed using etching technology, and its size meets the limitations of the microstructure 22 to be measured. Furthermore, combining the proposed measurement method, multiple metasurfaces can be used, and image processing technology 33 can be used to precisely locate the change in each degree of freedom, improving upon the shortcomings of optical interferometers such as insensitivity to lateral displacement and measurement accuracy affected by air disturbances and instrument vibration. In this embodiment, even a very small angular change can be distinguished through image processing; according to experimental results, the angle measurement resolution can reach above 0.0005°.

[0049] Although preferred embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other modifications under the guidance of the present invention without departing from the spirit and scope of the claims, and all of these modifications are within the scope of protection of the present invention.

Claims

1. A single-point multi-axis micro-angle precision measuring device based on a frequency-selective metasurface, characterized in that, include: The light source alignment module (1) is used to realize the alignment of the laser light source in a visual manner, including a visible light source (11), an optical frequency comb (12), a beam splitter (13), and a collimating lens (14). Metasurface reflection module (2), the metasurface reflection module (2) is used to receive the collimated mixed light source and can reflect the structure and adjust the micro-angle of the test mechanism, including metasurface (21), test mechanism (22), high-precision electric turntable (23), software control (24); The reflected light receiving module (3) is used to receive light reflected by the metasurface structure and to perform imaging, including a telecentric lens (31), a near-infrared camera (32), and an image processing algorithm (33). The visible light source (11) and optical frequency comb (12) in the light source alignment module (1) are first mixed by the beam splitter (13) to obtain the light source in the visualization laser alignment process. After being collimated by the collimating lens (14), the light is output to the metasurface (21) structure in the metasurface reflection module (2). The metasurface (21) structure is installed on the device under test (22). The light reflected by the metasurface structure is transmitted to the telecentric lens (31) in the reflected light receiving module (3) and finally imaged in the near-infrared camera (32). The device under test is micro-angled by using a high-precision electric turntable (23) to obtain two images with slight differences before and after adjustment. The gray value information of the two images is found by using the image processing algorithm (33), and then the actual value of the high-precision turntable is used for calibration, thus realizing the micro-angle detection of the device under test (22).

2. The single-point multi-axis micro-angle precision measuring device based on a frequency-selective metasurface according to claim 1, characterized in that, After the light source alignment module (1) mixes the visible light source (11) and the optical frequency comb (12), it needs to first roughly hit the structure with the light source, then adjust the near-infrared camera (32) to low gain and low exposure time, align the light spot with the structure, then increase the gain and exposure time, then adjust the pitch angle of the light source to make it deflect to a certain extent, and finally move the field of view down to find the reflected light path of the structure. The light frequency comb used is a broadband light source, which contains a frequency range that should overlap with the characteristic absorption frequency of the metasurface. In the frequency domain, the initial bias frequency of the light frequency comb is set to f ceo Then the comb tooth frequency contained in the light frequency comb can be expressed as: f n =nf rep +f ceo (1) Among them, f n f represents the frequency of the nth comb tooth. rep Representing the repetition frequency, an optical frequency comb must be selected that matches the characteristic absorption wavelength of the metasurface. This allows for the observation of the metasurface's absorption to the greatest extent possible, resulting in a more significant change in grayscale values ​​in near-infrared imaging.

3. The single-point multi-axis micro-angle precision measuring device based on a frequency-selective metasurface according to claim 1, characterized in that, The metasurface (21) has different absorption characteristics for different wavelengths within the characteristic band. Due to the different internal structures of the metasurface arrays used, the absorption performance of the optical frequency comb also varies. This results in changes in brightness in the image after imaging by the near-infrared camera (32). When the measured mechanism is changed by micro-angle by controlling the high-precision turntable with software, the pattern reflected by the structure hardly moves. However, the pixel gray value at this time can still be analyzed and calculated to realize the angle change, thus achieving high-precision measurement.

4. The single-point multi-axis micro-angle precision measuring device based on a frequency-selective metasurface according to claim 1, characterized in that, Based on multiple metasurfaces, parameter measurement of multiple degrees of freedom of the mechanism under test can be realized. The above-mentioned method for measuring micro-angles is not limited to measuring a certain angle. By combining multiple metasurfaces, the limitation of single-surface measurement can be overcome. The pixel values ​​of the two images before and after the pose change are converted into the change of parameters in each degree of freedom through the image processing algorithm (33). Then, the high-precision turntable values ​​are used for calibration, thereby realizing high-precision multi-degree-of-freedom measurement of the mechanism under test.

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