High-resolution superlattice microprobe for chromatic confocal measurement

Abstract

The application discloses a high-resolution super micro probe for dispersion confocal measurement, comprising a fiber port, an achromatic focusing super surface, an intermediate micro hole and a dispersion super surface. The configuration of the achromatic focusing super surface, the intermediate micro hole and the dispersion super surface is first proposed in the application, which fundamentally overcomes the restriction problem of transverse and axial resolution. The design enables the incident light to pass through the intermediate micro hole fully and uniformly through the achromatic focusing super surface in the whole working waveband, improves the light energy utilization rate, and sets the size of the intermediate micro hole near the diffraction limit spot size of the dispersion super surface, so that the dispersion imaging through the dispersion super surface can also realize the near-diffraction limit transverse resolution.

Description

Technical Field

[0001] This invention belongs to the field of optical measurement instruments and technology, specifically relating to a high-resolution meta-microprobe for dispersive confocal measurement. Background Technology

[0002] Dispersive confocal measurement technology is a high-precision, non-contact method for displacement and profile measurement. It boasts advantages such as no axial scanning required, non-contact operation, and strong anti-interference capabilities, showing broad application prospects in precision manufacturing, semiconductor inspection, and optical 3D imaging. Traditional dispersive confocal systems typically rely on multiple discrete optical components to construct complex optical systems, resulting in large size, high integration difficulty, and limitations on system miniaturization and array development. In recent years, with the rapid development of micro-nano optics technology, metasurfaces based on subwavelength structures have provided a novel solution for designing compact, high-performance optical components. By precisely controlling the phase, amplitude, and polarization of light at the subwavelength scale, metasurfaces can achieve complex functions similar to traditional refractive lenses and diffraction gratings, while possessing significant advantages such as flat structure, lightweight design, and ease of integration with microsystems. They are a crucial component driving the next generation of miniature optical measurement systems.

[0003] Previous studies have attempted to use metasurfaces to partially or completely replace traditional dispersive lens groups, simplifying the configuration of confocal measurement systems while achieving structural thinning. However, metasurfaces suffer from low focusing efficiency and sensitivity to incident and reflected wavefronts, leading to a significant decrease in the signal-to-noise ratio of the detected spectral signal, making them unsuitable for practical measurement scenarios requiring extremely high resolution, stability, and measurement accuracy. Therefore, this invention fully combines the characteristics of metasurfaces with the advantages of dispersive confocal measurement methods to design a compact metasurface measurement device that balances high signal-to-noise ratio and high resolution. This is of great significance for promoting the engineering application and miniaturization of dispersive confocal measurement technology. Summary of the Invention

[0004] This invention addresses the shortcomings of existing technologies by providing a high-resolution meta-microprobe for dispersive confocal measurements.

[0005] The technical solution of the present invention is as follows:

[0006] A high-resolution metamorphic microprobe for dispersive confocal measurements includes an optical fiber port, an achromatic focusing metamorphic surface, an intermediate micropore, and a dispersive metamorphic surface.

[0007] The fiber optic port is used to transmit a broadband light source and receive reflected light signals; the achromatic focusing metasurface is used to achromatic focus the light emitted from the fiber and receive reflected light signals; the intermediate micro-aperture is located at the common focal plane of the achromatic focusing metasurface and the dispersive metasurface, and is used for spatial filtering and establishing dispersive confocal conditions; the dispersive metasurface is used to dispersively image the intermediate micro-aperture to different axial depths and receive the reflected light from the target object.

[0008] In one possible implementation, the numerical aperture of the achromatic focusing metasurface is in the range of 0.2 to 0.8, and it is composed of subwavelength dielectric nanounits below a set loss threshold, which is used to achieve efficient achromatic near-diffraction-limited focusing of incident broadband light, thereby ensuring that light in the entire working wavelength band can pass through the central micropore uniformly.

[0009] In one possible implementation, the diameter of the intermediate micro-aperture is 1 to 2 times the size of the diffraction-limited spot of the dispersive metasurface in the working band, which is used both to select reflected light that satisfies the confocal condition wavelength and to block interference from stray light in the incident light.

[0010] In one possible implementation, the dispersive metasurface is composed of two bilayer metasurfaces disposed on both sides of the same transparent substrate. The two layers have different subwavelength nanounit structures and arrangements, ensuring the symmetry of the forward and reverse propagation of light, guaranteeing the integrity of the confocal condition and a high signal-to-noise ratio in the reflection spectrum. The abrupt phase distribution required by the bilayer metasurface is expressed by the following equation:

[0011]

[0012] In this context, the focal lengths f1(λ), ​​f2(λ), and the abrupt phase φ(r, λ) are all related to the working wavelength λ, and the distance from the subwavelength nanounit to the center of the lens is r. The dispersive metasurface that satisfies the above-mentioned double-layer abrupt phase distribution can simultaneously achieve near-diffraction-limited axial dispersion focusing of the light emitted from the central micro-aperture and near-diffraction-limited focusing of the reflected light.

[0013] In one possible implementation, the numerical aperture of the dispersive metasurface is smaller than that of the achromatic focusing metasurface, so as to ensure that most of the light focused by the achromatic focusing metasurface can pass through the central micro-aperture, while the spatial filtering effect of the central micro-aperture can also obtain high lateral measurement resolution.

[0014] In one possible implementation, the subwavelength nanounits on the dispersive metasurface are made of a dielectric material that operates below a set loss threshold in the operating wavelength range.

[0015] In one possible implementation, the achromatic focusing metasurface and the dispersive metasurface are designed as needed to operate in a single band or a combination of bands in the visible, near-infrared, mid-infrared, and terahertz bands to achieve dispersive confocal measurements.

[0016] In one possible implementation, the intermediate micro-aperture is replaced with a micro-slit, and an achromatic focusing metasurface is used with linear focusing and the length of the focusing line spot is equal to the length of the slit. The micro-slit acts as an approximately ideal line light source, and the dispersive metasurface performs axial dispersion imaging, thereby achieving linear dispersion confocal measurement, which can significantly improve measurement efficiency.

[0017] In one possible implementation, the high-resolution meta-microprobe is used as follows:

[0018] 1) A single port of a Y-type fiber optic coupler is used as the fiber optic port of the metamicroprobe. The two ports of the Y-type fiber optic coupler are connected to a broadband light source and a spectrometer, respectively. The target analyte is set within the measurement range of the metamicroprobe.

[0019] 2) A broadband light source is introduced into the achromatic focusing metasurface through a Y-type fiber coupler from a single port, i.e., the fiber port. Then, it is achromatic focused onto the central micro-aperture, and the broadband light passing through the central micro-aperture is regarded as a point light source.

[0020] 3) The central micro-aperture is imaged to different positions along the axis by the dispersive metasurface, wherein light of a specific wavelength that meets the confocal condition is reflected by the target analyte and propagates back to the dispersive metasurface, and is then refocused on the central micro-aperture. Finally, it is received by the achromatic focusing metasurface and transmitted to the spectrometer via the fiber optic port and Y-type fiber coupler.

[0021] 4) After receiving the reflected spectral signal, the spectrometer performs point-type dispersive confocal displacement measurement by locating the position of the spectral peak of the received spectral signal.

[0022] In one possible implementation, to achieve three-dimensional morphology measurement, the target object is placed on a two-dimensional plane scanning stage, and after displacement measurement is performed using a high-resolution metamicroprobe, a two-dimensional scan is performed based on the displacement measurement results to finally obtain the three-dimensional morphology of the target object.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. Addressing the inherent trade-off between lateral and axial resolution in traditional dispersive confocal systems—namely, small aperture sizes leading to reduced light throughput and signal-to-noise ratio, thus decreasing axial resolution, while larger aperture sizes increase the dispersive focusing spot size, hindering axial resolution improvement—this invention, for the first time, proposes a configuration of an achromatic focusing metasurface, an intermediate microaperture, and a dispersive metasurface that fundamentally overcomes the constraints on lateral and axial resolution. This design allows incident light to pass through the achromatic focusing metasurface and the intermediate microaperture uniformly across the entire operating wavelength range, improving light energy utilization. Furthermore, by positioning the intermediate microaperture size near the diffraction-limited spot size of the dispersive metasurface, near-diffraction-limited lateral resolution can be achieved through dispersive imaging via the dispersive metasurface.

[0025] 2. The bilayer symmetrical structure design of the dispersive metasurface in this invention ensures that it produces the same modulation for both incident and reflected light, guaranteeing the integrity of the confocal condition. Compared to the asymmetric transmission of traditional single-layer metasurfaces, this method enables the reflection spectrum to have a high signal-to-noise ratio, improving the axial resolution and accuracy of dispersive confocal measurements.

[0026] 3. The meta-micro probe system of the present invention is simple and compact, highly integrated, lightweight and easy to assemble. It can also be integrated into a single unit using two-photon 3D printing technology, and can be integrated onto the end face of an optical fiber for highly flexible scanning, measurement and control. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the high-resolution metamicroprobe structure and dispersive confocal measurement principle of the present invention.

[0028] Figure 2 This is a schematic diagram illustrating the principle of dispersive confocal measurement using a traditional metamicroprobe.

[0029] Figure 3 To achieve the ideal abrupt phase distribution between the front and back layers of the dispersive metasurface and to realize the phase.

[0030] Figure 4 The abrupt phase change of the subwavelength nanounit is the response of height and incident angle.

[0031] Figure 5 This shows the electric field distribution of subwavelength nanounits at different incident angles. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the present invention clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. However, it should be understood that the embodiments specifically described herein are merely illustrative of the invention and are not intended to limit the scope of protection of the invention in any way.

[0033] This application provides a high-resolution metamural microprobe for dispersive confocal measurements, designed to operate in the visible light band. For example... Figure 1 As shown, it includes: an optical fiber port 1 for transmitting broadband light sources and receiving reflected light signals, with an optical fiber core diameter of 20 μm; an achromatic focusing metasurface 2 with a diameter of 30 μm and a focal length f0 of 30 μm, used for achromatic focusing of the light emitted from the optical fiber and receiving reflected light signals; a central micro-aperture 3 with a diameter of 2 μm, located at the common focal plane of the achromatic focusing metasurface 2 and the dispersive metasurface 4, i.e., 50 μm from the achromatic focusing metasurface and 120 μm from the dispersive metasurface, used for spatial filtering and establishing dispersive confocal conditions; and a dispersive metasurface 4 with a diameter of 100 μm and a central spacer layer thickness of 50 μm, the focal length f1 of the first metasurface being 120 μm and the central focal length f2 of the second metasurface being 400 μm. The two layers work together to dispersively image the central micro-aperture to different axial depths and receive the reflected light from the target object.

[0034] In one possible implementation, the achromatic focusing metasurface 2 has a numerical aperture of 0.45 μm, corresponding to an Abbe diffraction limit of approximately 0.87 μm, and is composed of subwavelength dielectric nanounits with a loss of less than 5%. Optional dielectric materials include TiO2, GaN, Si, and Ge. The achromatic focusing metasurface 2 enables highly efficient achromatic near-diffraction-limited focusing of incident broadband light, thereby ensuring that light across the entire operating wavelength band can pass uniformly through the central micropore.

[0035] In one possible implementation, the diameter of the intermediate micro-hole 3 is 1 to 2 times the size of the diffraction-limited spot of the dispersive metasurface 4 in the working band, and the diameter is set to 2 μm. This is used both to select the reflected light that satisfies the confocal condition wavelength and to block the interference of stray light in the incident light.

[0036] In one possible implementation, the dispersive metasurface 4 is composed of two bilayer metasurfaces disposed on both sides of the same transparent substrate. The two layers have different subwavelength nanounit structures and arrangements, ensuring the symmetry of the forward and reverse propagation of light, guaranteeing the integrity of the confocal condition and a high signal-to-noise ratio in the reflection spectrum. The required abrupt phase distribution of the metasurface near the central micropore 3 is expressed by the following formula:

[0037]

[0038] Where f1 is the focal length of the metasurface, 120 μm, and this abrupt phase change is determined solely by the distance r of the subwavelength nanounit from the lens center, and is independent of the operating wavelength λ. The required abrupt phase distribution of the metasurface on the dispersion side is expressed by the following formula:

[0039]

[0040] In this context, both the focal length f2(λ) and the abrupt phase φ(r, λ) are related to the operating wavelength. For a linearly dispersive metasurface, the focal length f2(λ) can be expressed as f2(λ) = kλ + b, where k and b are dispersion coefficients. The value of k determines the magnitude of the dispersion range, and the value of b determines the size of the numerical aperture. A dispersive metasurface satisfying the above-described double-layer abrupt phase distribution can simultaneously achieve near-diffraction-limited axial dispersion focusing of light emitted from the central microaperture and near-diffraction-limited focusing of reflected light.

[0041] In one possible implementation, the numerical aperture of the dispersive metasurface 4 is smaller than that of the achromatic focusing metasurface 2, to ensure that most of the light focused by the achromatic focusing metasurface 2 can pass through the intermediate micro-aperture 3. Simultaneously, the spatial filtering effect of the intermediate micro-aperture 3 can also achieve high lateral measurement resolution. Specifically, the numerical aperture of the first surface of the dispersive metasurface is 0.39, and the Abbe diffraction limit is 1 μm.

[0042] For traditional ordinary metamorphic microprobes, in such cases... Figure 2 In the schematic diagram of the dispersive confocal measurement principle shown, since the dispersive imaging is performed directly on the fiber port, the obtained spot size is relatively large, comparable to the fiber core size, thus greatly limiting the lateral resolution. At the same time, since a single-layer dispersive metasurface is used, its dispersive focusing and reflection refocusing processes are asymmetric, which to some extent disrupts the confocal conditions, reduces the signal-to-noise ratio of the reflection spectral signal, and limits the improvement of the accuracy of dispersive confocal measurement.

[0043] In one possible implementation, the subwavelength nanounits on the dispersive metasurface 4 are made of a dielectric material with a loss threshold of less than 5% in the operating band. Optional dielectric materials include: TiO2, GaN, Si, Ge, and photoresist.

[0044] This embodiment uses photoresist with a refractive index around 1.52 in the visible light band to design a dispersive metasurface, such as... Figure 3 The diagram shows the ideal abrupt phase distribution and the achieved phase of the two layers, employing a cylindrical nanounit structure with a unit period of 1 μm and a maximum aspect ratio of 5:1. This bilayer structure design reduces the requirement for a very large aspect ratio of the nanounits, lowers the manufacturing difficulty, and also increases the degree of freedom in phase manipulation. Figure 4 The paper demonstrates the response of subwavelength nanounits to abrupt phase changes with height and incident angle. For nanounits at different distances from the lens center, the desired abrupt phase response needs to be selected at the corresponding incident angle. Combined with... Figure 5As can be seen from the electric field distribution of the subwavelength nanounit under different incident angles, the change in incident angle will change the equivalent refractive index of the nanounit to a certain extent, thereby affecting its abrupt phase response.

[0045] In one possible implementation, the achromatic focusing metasurface 2 and the dispersive metasurface 4 can also be designed to operate in a single band or a combination of bands in the visible, near-infrared, mid-infrared and terahertz bands to achieve dispersive confocal measurement, depending on the requirements.

[0046] In one possible implementation, the intermediate micro-aperture 3 is replaced with a micro-slit, and an achromatic focusing metasurface is used with linear focusing and the length of the focusing line spot is equal to the length of the slit. The micro-slit acts as an approximately ideal line light source and is imaged axially by the dispersive metasurface 4, thereby realizing linear dispersive confocal measurement, which can significantly improve measurement efficiency.

[0047] In one possible implementation, the high-resolution meta-microprobe is used as follows:

[0048] 1) A single port of a Y-type fiber optic coupler is used as the fiber optic port of the metamicroprobe. The two ports of the Y-type fiber optic coupler are connected to a broadband light source and a spectrometer, respectively. The target analyte is set within the measurement range of the metamicroprobe.

[0049] 2) A broadband light source is input to the achromatic focusing metasurface 2 through a Y-type fiber coupler via a single port, i.e., the fiber port, and then achromatic focusing is applied to the central micro-aperture 3. The broadband light passing through the central micro-aperture 3 is regarded as a point light source.

[0050] 3) The intermediate micro-aperture 3 is imaged to different positions along the axis through the dispersive metasurface 4. Light of a specific wavelength that meets the confocal condition is reflected by the target object and propagates back to the dispersive metasurface 4, and then refocused on the intermediate micro-aperture 3. Finally, it is received by the achromatic focusing metasurface 2 and transmitted to the spectrometer via the fiber optic port and Y-type fiber coupler.

[0051] 4) After receiving the reflected spectral signal, the spectrometer can perform point-type dispersive confocal displacement measurement by locating the position of the spectral peak of the received spectral signal.

[0052] In one possible implementation, to achieve three-dimensional morphology measurement, the target object is placed on a two-dimensional plane scanning stage, and after displacement measurement is performed using a high-resolution metamicroprobe, a two-dimensional scan is performed based on the displacement measurement results to finally obtain the three-dimensional morphology of the target object.

[0053] The above embodiments are preferred embodiments of the present invention, and are only used to illustrate the technical concept and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A high-resolution meta-microprobe for dispersive confocal measurements, characterized in that, This includes fiber optic ports, achromatic focusing metasurfaces, intermediate micropores, and dispersive metasurfaces; The fiber optic port is used to transmit broadband light sources and receive reflected light signals; the achromatic focusing metasurface is used to achromatic focus the light emitted from the fiber and receive reflected light signals; the intermediate micro-aperture is located at the common focal plane of the achromatic focusing metasurface and the dispersive metasurface, and is used for spatial filtering and establishing dispersive confocal conditions; the dispersive metasurface is used to dispersively image the intermediate micro-aperture to different axial depths and receive the reflected light from the target object. The diameter of the central micro-aperture is 1 to 2 times the size of the diffraction-limited spot of the dispersive metasurface in the working band. It is used both to select the reflected light that satisfies the confocal condition wavelength and to block the interference of stray light in the incident light. The dispersive metasurface is composed of two layers of metasurfaces disposed on both sides of the same transparent substrate. The two layers have different subwavelength nanounit structures and arrangements, which can ensure the symmetry of the forward and reverse propagation process of light, ensure the integrity of the confocal condition and the high signal-to-noise ratio of the reflection spectrum. The numerical aperture of the dispersive metasurface is smaller than that of the achromatic focusing metasurface.

2. The high-resolution metamicroprobe for dispersive confocal measurement according to claim 1, characterized in that, The numerical aperture of the achromatic focusing metasurface ranges from 0.2 to 0.8 and is composed of subwavelength dielectric nanounits below a set loss threshold. This enables efficient achromatic near-diffraction-limited focusing of incident broadband light, thereby ensuring that light can pass uniformly through the central micropore across the entire operating wavelength range.

3. The high-resolution meta-microprobe for dispersive confocal measurement according to claim 1, characterized in that, The abrupt phase distribution required for the bilayer metasurface is expressed by the following equation: Among them, the focal length f1(λ), ​​the focal length f2(λ), and the abrupt phase φ(r, λ) are all related to the working wavelength λ, and the distance of the subwavelength nanounit from the center of the lens is r.

4. A high-resolution meta-microprobe for dispersive confocal measurement according to claim 1 or 3, characterized in that, The subwavelength nanounits on the dispersive metasurface are made of dielectric materials that operate below a set loss threshold in the operating wavelength range.

5. A high-resolution meta-microprobe for dispersive confocal measurement according to claim 1, characterized in that, The achromatic focusing metasurface and the dispersive metasurface are designed to operate in a single band or a combination of bands in the visible, near-infrared, mid-infrared and terahertz bands, respectively, to achieve dispersive confocal measurement.

6. A high-resolution meta-microprobe for dispersive confocal measurement according to claim 1, characterized in that, The intermediate micro-aperture is replaced with a micro-slit, and an achromatic focusing metasurface with linear focusing and a focal spot length equal to the slit length is used. The micro-slit acts as an approximately ideal line light source, and the dispersive metasurface performs axial dispersion imaging, thereby achieving linear dispersion confocal measurement.

7. The method of using a high-resolution meta-microprobe for dispersive confocal measurement according to claim 1, characterized in that, Specifically as follows: 1) A single port of a Y-type fiber optic coupler is used as the fiber optic port of the metamicroprobe. The two ports of the Y-type fiber optic coupler are connected to a broadband light source and a spectrometer, respectively. The target analyte is set within the measurement range of the metamicroprobe. 2) A broadband light source is introduced into the achromatic focusing metasurface through a single port (i.e., the fiber port) via a Y-type fiber coupler, and then achromaticly focused onto the central micro-aperture. The broadband light passing through the central micro-aperture is regarded as a point light source. 3) The central micro-aperture is imaged to different positions along the axis by the dispersive metasurface. Light of a specific wavelength that meets the confocal condition is reflected by the target object and propagated back to the dispersive metasurface, then refocused on the central micro-aperture, and finally received by the achromatic focusing metasurface and transmitted to the spectrometer via the fiber optic port and Y-type fiber coupler. 4) After receiving the reflected spectral signal, the spectrometer performs point-type dispersive confocal displacement measurement by locating the position of the spectral peak of the received spectral signal.

8. The method of using a high-resolution meta-microprobe for dispersive confocal measurement according to claim 7, characterized in that, To achieve three-dimensional morphology measurement, the target object is placed on a two-dimensional plane scanning stage. After displacement measurement is performed using a high-resolution meta-micro probe, a two-dimensional scan is performed based on the displacement measurement results, and finally the three-dimensional morphology of the target object is obtained.

Images