Non-contact local curvature measurement method and system based on calculation metasurface

Abstract

The invention discloses a non-contact local curvature measurement method and system based on a computational metasurface, and the method comprises the steps: S1, phase modulation: carrying out the phase modulation of an incident light field carrying the information of a to-be-measured object through an optical computational metasurface, so as to generate transverse displacement light field distribution related to the contour of the to-be-measured object; s2, signal extraction: separating and extracting a first-order differential signal carrying the edge information of the object to be measured by using a biorthogonal polarization filtering system; s3, reconstructing a three-dimensional shape: reconstructing the three-dimensional shape of the object to be measured according to the first-order differential signal; and S4, curvature calculation: calculating the curvature radius of any local part of the object to be measured according to the three-dimensional shape. The optical calculation metasurface is combined with a biorthogonal polarization filtering system, differential operation of a light field is achieved, the edge contour of an intensity object and the three-dimensional shape of a phase object can be obtained without difference, and therefore non-contact and high-precision measurement of the curvature of the object is achieved, the problem of physical damage of traditional contact type measurement is solved, and the measurement accuracy is improved. And the detection efficiency and adaptability are improved.

Description

Technical Field

[0001] The present invention relates to the field of optical precision measurement, and specifically to a non-contact local curvature measurement method and system based on computational metasurfaces. The method is suitable for measuring the local curvature of optical elements, micro-nano devices, and biomaterials, and is particularly suitable for submicron curvature detection of curved glass, flexible OLED screens, and biological corneas. Background Art

[0002] In the fields of precision manufacturing and inspection, the radius of curvature, a core parameter for characterizing an object's geometric morphology, directly impacts the performance evaluation and quality control of optical components, micro-nano devices, and biomaterials. Existing mechanical contact measurement systems (such as spherometers) acquire contour data through contact between a stylus and the measured surface. However, these physical contact methods have inherent drawbacks: stylus pressure can easily cause sample deformation during measurement, and the geometric constraints of standard spherical probes make it difficult to adapt to the dynamic monitoring requirements of complex curved surfaces.

[0003] Meanwhile, optical interferometry is limited by the mismatch between the coherence length of the light source and the detection resolution, making it prone to fringe distortion when measuring surfaces over a wide dynamic range. While non-contact methods such as scanning electron microscopy can achieve nanometer-level resolution, they suffer from high equipment costs, demanding vacuum operating environments, and the inability to perform in-situ dynamic measurements. As ultra-precision machining and flexible electronics advance toward submicron precision, the industry urgently needs a non-destructive, highly adaptable curvature radius measurement solution with micron-level resolution.

[0004] In recent years, computational imaging technology based on optical metasurfaces has provided an innovative solution to the above-mentioned problems. As a two-dimensional planar optical device, computational metasurfaces break through the diffraction limit of traditional optical elements by regulating the spatially continuous phase gradient distribution of subwavelength structural units, and achieve precise control of the amplitude, phase and polarization state of the light field without physical moving parts. Thanks to its ultra-thin structure and programmable characteristics, this technology has demonstrated disruptive potential in the fields of optical simulation computing, adaptive optical systems and intelligent imaging. It is worth noting that although metasurfaces have made significant progress in scenarios such as all-optical signal processing and three-dimensional reconstruction, there is still a significant gap in their application in the field of precision geometric parameter measurement. In particular, how to deeply integrate the light field control capabilities of metasurfaces with the needs of curvature radius measurement has not yet formed a mature technical path. Summary of the Invention

[0005] In view of the fact that the existing technology is easy to damage samples, has insufficient accuracy on complex / steep surfaces and in vibration environments, and the equipment is expensive and slow, in order to overcome the above shortcomings, the present invention provides a non-contact local curvature radius measurement method and system based on optical computing metasurface, so as to realize non-destructive, fast and high-precision curvature measurement of various materials, and have good vibration resistance and the ability to adapt to complex surface morphology.

[0006] The present invention provides a non-contact local curvature radius measurement method based on optical computing metasurface, the method comprising the following steps:

[0007] S1. Phase modulation: Phase modulating the incident light field carrying the information of the object to be measured through the optical computing metasurface to generate a lateral displacement light field distribution related to the contour of the object to be measured;

[0008] S2. Signal extraction: using a dual-orthogonal polarization filter system to separate and extract the first-order differential signal carrying the edge information of the object to be measured;

[0009] S3, 3D shape reconstruction: reconstructing the 3D shape of the object to be measured according to the first-order differential signal;

[0010] S4. Curvature calculation: Calculate the curvature radius of any part of the object to be measured based on the three-dimensional shape.

[0011] Preferably, step S1 specifically includes:

[0012] S11: Femtosecond laser direct writing technology is used to etch periodic nanogrooves on a fused silica substrate, and the phase modulation of the light field is achieved by regulating its spatial phase gradient distribution.

[0013] Preferably, step S2 specifically includes:

[0014] S21: Setting the dual-orthogonal polarization filtering system, which includes a first Glan laser polarizer and a second Glan laser polarizer, and the optical axes of the two are orthogonal to each other, so as to effectively separate and extract the first-order differential signal.

[0015] Preferably, step S3 specifically includes:

[0016] S31: For an intensity object, directly obtain its edge contour according to the first-order differential signal, and use the edge contour as its three-dimensional shape;

[0017] S32: For the phase object, reconstructing a two-dimensional phase gradient field by introducing a positive and negative bias difference operation according to the first-order differential signal;

[0018] S33: reconstructing a phase field from the two-dimensional phase gradient field by inverse Fourier transform combined with least squares calibration; wherein the calibration minimizes the error between the reconstructed phase and the original phase by least squares calibration to improve the accuracy of phase field reconstruction;

[0019] S34: based on a preset phase-thickness quantitative mapping relationship, converting the phase field into a three-dimensional topography of the phase object;

[0020] The mapping relationship is:

[0021]

[0022] Where d is the thickness, λ is the operating wavelength, is the phase, n~obj~ is the refractive index of the object to be measured, and n~air~ is the refractive index of air.

[0023] Preferably, step S4 specifically includes:

[0024] S41: Extracting the base circle radius r and the sag h according to the three-dimensional topography, and calculating the local curvature radius using a geometric optics formula, which is:

[0025]

[0026] Where R is the radius of curvature, r is the base circle radius, and h is the sag height.

[0027] The present invention also provides a non-contact local curvature radius measurement system based on optical computing metasurface, characterized in that the system comprises:

[0028] Phase modulation module: includes an optical computing metasurface, which is used to phase modulate the incident light field carrying information about the object to be measured;

[0029] Signal extraction module: includes a dual orthogonal polarization filter system for separating and extracting the first-order differential signal carrying object edge information;

[0030] A shape reconstruction module includes a processing unit for reconstructing the three-dimensional shape of the object to be measured according to the first-order differential signal;

[0031] Curvature calculation module: The processing unit is further used to calculate the curvature radius of any part of the object to be measured based on the three-dimensional shape.

[0032] Preferably, the optical computing metasurface in the phase modulation module is a periodic nano-groove structure etched on a fused silica substrate using femtosecond laser direct writing technology.

[0033] Preferably, the dual orthogonal polarization filtering system in the signal extraction module includes a first Glan laser polarizer and a second Glan laser polarizer whose optical axes are orthogonal to each other.

[0034] Preferably, the morphology reconstruction module is configured as follows: for intensity objects, directly obtaining their edge contours; for phase objects, reconstructing their phase fields by introducing positive and negative bias differential operations, inverse Fourier transforms, and least squares calibration, and converting them into three-dimensional morphology based on the phase-thickness quantitative mapping relationship.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. Non-destructive testing: It uses all-optical signal processing to avoid physical contact and prevent sample damage. It is suitable for brittle materials and precision devices.

[0037] 2. High precision and resolution: The measured curvature radius error is less than 1.34%, and the spatial resolution reaches the sub-micron level, meeting the requirements of ultra-precision detection.

[0038] 3. Wide adaptability: Through the collaboration of the polarization system and the reconstruction algorithm, intensity objects and phase objects can be detected without distinction, and the application scenarios are wide.

[0039] 4. Real-time: All-optical parallel processing, no mechanical scanning required, fast measurement speed and timely response.

[0040] 5. Multi-dimensional information fusion capability: can simultaneously extract parameters such as refractive index and thickness, and provide multimodal data support.

[0041] 6. Strong environmental adaptability: It can work in normal pressure air environment and has strong robustness to environmental interference such as vibration and temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a schematic diagram of the principles of the all-optical object recognition technology and 3D reconstruction technology used in an embodiment of the present invention.

[0043] Figure 2 This is the optical path and results of the metasurface differential optics operation experiment.

[0044] Figure 3 This is the experimental process and results of the local curvature detection experiment of the strength object of the present invention.

[0045] Figure 4 These are the experimental results of the three-dimensional reconstruction and local curvature detection of phase objects according to the present invention.

[0046] Figure 5 This is an experiment for phase object thickness reconstruction and accuracy verification of the present invention. DETAILED DESCRIPTION

[0047] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0048] Example 1: Detection of curvature radius of strong objects

[0049] This embodiment uses a standard metal ball with a radius of 2.25 mm as a detection object to verify the measurement capability of the present invention for strength objects.

[0050] S1: Design and fabricate a metasurface. The metasurface used in this embodiment is fabricated on a fused silica substrate by femtosecond laser direct writing, with a period of 4×4 mm, a groove depth of 200 μm, and a designed operating wavelength of 532 nm.

[0051] S2: Build an optical differential imaging system. A continuous laser with a wavelength of 532 nm was used as the light source. A 4f system with focal lengths f1 = 150 mm and f2 = 125 mm was constructed. Orthogonal Glan polarizers GLP1 and GLP2 were integrated into the system, and the metasurface prepared in step S1 was placed in the system's Fourier plane. A CCD camera (pixel size 3.45 μm × 3.45 μm, frame rate 100 fps) was used as the detector.

[0052] S3: Collect and process the edge contours of intensity objects. Figure 3 ,First, when the metasurface is not placed, the bright field image of the steel ball is collected ( Figure 3 (g)) as a reference. Then the metasurface is inserted, and GLP1 and GLP2 are adjusted to orthogonal polarization states to obtain differential images along the x and y directions respectively ( Figure 3 (h) and Figure 3 (i)). Finally, the two-dimensional edge profile of the steel ball is extracted by superimposing the gradient images in the x and y directions through the algorithm ( Figure 3 (j)).

[0053] S7: Calculate the local curvature radius. In the edge contour map obtained in step S3 ( Figure 3 In Figure (j), select the red-framed area at the edge and the yellow-framed area at the center. By performing curve fitting on the contour data of these two areas, the local curvature radius is calculated. The measured curvature radius of the red-framed area is 2.2828mm, with a relative error of 0.13%. The measured curvature radius of the yellow-framed area is 2.258mm, with a relative error of 0.62%. Compared with the nominal value, the overall system accuracy reaches 99.62%.

[0054] Example 2: Reconstructing the 3D curvature of a phase object

[0055] In this embodiment, a convex lens with a nominal curvature radius of 386.3 mm and a center thickness of 2.2 mm is used as a detection object to verify the measurement capability of the present invention for phase objects.

[0056] The steps of S1-S2 are the same as those in Example 1. A polarization control module is added to the system device to achieve precise rotation of the orthogonal polarization states of the dual GLPs with a step accuracy of 0.1°.

[0057] S4: Collect and reconstruct the two-dimensional phase distribution. Figure 4 By rotating GLP2 by ±4°, a bias-delayed response (e.g. Figure 4 (a)-(f)), thereby extracting the phase gradient field of the convex lens in the x and y directions ( Figure 4 (g) and Figure 4 (h)). The gradient field is processed using inverse Fourier transform to reconstruct the two-dimensional phase distribution of the lens ( Figure 4 (i)).

[0058] S5: Calibrate the phase scaling factor. Use the least squares method to calibrate the reconstructed phase gradient, and calculate the phase scaling factor τ = 0.21666 under the experimental conditions.

[0059] S6: Reconstruct 3D shape. Figure 5 Based on the phase-thickness mapping relationship, the phase distribution reconstructed in step S4 is inverted into a three-dimensional physical thickness model of the lens ( Figure 4 (k)).

[0060] S7: Calculate the local curvature radius. On the three-dimensional model obtained in step S6, select three characteristic curves along the lens surface ( Figure 4 (k) and calculate their curvature radii. Figure 4 (l)) are 383.448 mm (error 0.74%), 387.43 mm (error 0.29%) and 391.494 mm (error 1.34%) respectively.

[0061] Through the above specific implementation examples, the present invention proposes a non-contact local curvature radius measurement method and system based on optical computing metasurface, which can realize efficient, high-precision, and non-destructive detection of the curvature characteristics of intensity objects and phase objects through all-optical object recognition and three-dimensional quantitative reconstruction technology, providing an innovative solution for the performance characterization and quality monitoring of metasurface optical devices.

Claims

1. A non-contact local curvature measurement method based on computational metasurface, characterized in that: The method comprises the following steps: S1. Phase modulation: Phase modulating the incident light field carrying the information of the object to be measured through the optical computing metasurface to generate a lateral displacement light field distribution related to the contour of the object to be measured; S2. Signal extraction: using a dual-orthogonal polarization filter system to separate and extract the first-order differential signal carrying the edge information of the object to be measured; S3, 3D shape reconstruction: reconstructing the 3D shape of the object to be measured according to the first-order differential signal; S4. Curvature calculation: Based on the three-dimensional morphology, use the curvature radius formula The curvature radius of any part of the object to be measured is calculated, where R is the curvature radius, r is the base circle radius, and h is the sagittal height.

2. The method according to claim 1, characterized in that The step S3 comprises: S31. For an intensity object, directly obtain its edge contour according to the first-order differential signal, and use the edge contour as its three-dimensional shape; S32. For the phase object, reconstruct a two-dimensional phase gradient field by introducing a positive and negative bias difference operation according to the first-order differential signal; S33, reconstructing the phase field from the two-dimensional phase gradient field by inverse Fourier transform combined with least squares calibration; S34. Based on a preset phase-thickness quantitative mapping relationship, convert the phase field into a three-dimensional morphology of the phase object.

3. The method according to claim 1, wherein: The optical computing metasurface in step S1 is a periodic nanogroove structure etched on a fused silica substrate using femtosecond laser direct writing technology, and the light field is controlled by regulating the spatial phase gradient distribution; in step S2, the dual orthogonal polarization filtering system includes a first Glan laser polarizer and a second Glan laser polarizer, and the optical axes of the first Glan laser polarizer and the second Glan laser polarizer are orthogonal.

4. The method according to claim 2, characterized in that In step S33, the calibration is performed by using the least square method to minimize the error between the reconstructed phase and the original phase, so as to improve the accuracy of phase field reconstruction.

5. The method according to claim 2, characterized in that In step S34, the phase-thickness quantitative mapping relationship is Where d(x,y) is the thickness, λ is the operating wavelength, is the phase, n g is the refractive index of the object to be measured, n a is the refractive index of air.

6. The method according to claim 1, wherein: The curvature calculation step is performed based on geometric parameters of one or more local areas arbitrarily selected from the reconstructed three-dimensional topography, thereby eliminating the need for prior geometric adaptation of the overall shape of the object to be measured.

7. The method according to claim 1, wherein: The method can detect intensity objects and phase objects indiscriminately, and based on the reconstructed phase field and combined with the phase-thickness quantitative mapping relationship, the thickness distribution or material refractive index of the object to be measured can be further calculated.

8. A non-contact local curvature measurement system based on computational metasurface, characterized in that: The system comprises: Phase modulation module: includes an optical computing metasurface, which is used to phase modulate the incident light field carrying information of the object to be measured to generate a lateral displacement light field distribution related to the contour of the object to be measured; Signal extraction module: including a dual orthogonal polarization filter system for separating and extracting the first-order differential signal carrying the edge information of the object to be measured; A shape reconstruction module includes a processing unit for reconstructing the three-dimensional shape of the object to be measured according to the first-order differential signal; Curvature calculation module: The processing unit is further used to calculate the curvature radius of any part of the object to be measured based on the three-dimensional shape.

9. The system according to claim 8, characterized in that The shape reconstruction module is configured as follows: For intensity objects, directly obtain their edge contours; For phase objects, their phase fields are reconstructed by introducing positive and negative bias differential operations, inverse Fourier transform and least squares calibration, and converted into three-dimensional morphology based on the phase-thickness quantitative mapping relationship.

10. The system according to claim 8, characterized in that: The system can detect intensity objects and phase objects indiscriminately, and can be configured to further calculate the thickness distribution or material refractive index of the object to be measured based on the reconstructed phase field.

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