Vector vortex super lens for directional selective edge detection and imaging system with same

Abstract

The invention discloses a vector vortex super lens for directional selective edge detection and an imaging system with the vector vortex super lens, and the vector vortex super lens comprises a substrate and a nano-structure unit on the substrate. The nano-structure units are arranged on the substrate according to specific phase distribution to form a nano-structure unit array; x-line polarized light carrying sample information passes through the vector vortex super lens to generate left-handed and right-handed emergent light, the two paths of emergent light are superposed to obtain an edge image carrying polarization information, and a vector edge detection function is realized. The vector vortex super lens provided by the invention has the edge extraction capability of dynamic adjustment as required, and can realize real-time directional edge detection only by rotating the polarization analyzer without other hardware modification or digital post-processing.

Description

Technical Field

[0001] This invention belongs to the field of nanophotonics and optical edge detection, and specifically relates to a vector vortex superlens for direction-selective edge detection and an imaging system having the same. Background Technology

[0002] Edge detection technology, as a method of image processing, can extract edge information from images and has significant application value in fields such as facial recognition, fingerprint extraction, and medical imaging. Signal and image processing technologies based on integrated circuits sometimes suffer from drawbacks such as slow speed and high power consumption. Optical components can replace electronic components for optical analog computation. They have advantages such as low power consumption, high speed, and multi-path parallelism, enabling real-time processing of input signals. Therefore, edge detection methods based on optical analog computation have attracted widespread attention. Previous optical edge detection methods mostly extracted image edge information by inserting spatial light modulators or liquid crystal optical elements into a 4f system. However, these traditional edge detection devices are relatively large, significantly limiting the trend towards lightweight and integrated optical devices.

[0003] Metasurfaces are periodically arranged two-dimensional structures capable of modulating the amplitude, polarization, and phase of light waves. In some related work, filtering and focusing functions are integrated onto a single metasurface to form a superlens, which is then used for optical edge detection, simplifying bulky 4f systems. However, most current superlenses used for edge detection lack flexible directional selectivity during operation, limiting their application in areas requiring directional feature extraction. Therefore, developing superlenses capable of tunable, directionally selective edge detection remains a challenge. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a vector vortex superlens for direction-selective edge detection. This superlens can extract object edge information along a specific direction as needed and can eliminate directional defects in objects, thereby better revealing the object's edge contour. This invention also provides an imaging system incorporating the aforementioned vector vortex superlens.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a vector vortex superlens for direction-selective edge detection, comprising: a substrate and nanostructure units on the substrate; the nanostructure units are arranged on the substrate according to a specific phase distribution to form a nanostructure unit array; X-ray polarized light passes through the vector vortex superlens to generate left-handed and right-handed outgoing light, and the vector point spread function distribution of the superimposed left-handed and right-handed outgoing light conforms to equation (1):

[0006] (1)

[0007] in: This indicates polar coordinates in the output plane. It is the focal length of the superlens. It is the incident wavelength. It is a constant. Denotes the first-order Bessel function of the first kind. Represents the radius of the vector vortex superlens. Represents the radial coordinates on the plane of the vector vortex superlens;

[0008] Vector edge detection can be achieved by convolving the point spread function with the input image.

[0009] Furthermore, the phase distribution of the left and right spiral exit paths of the vector vortex superlens conforms to equations (2) and (3):

[0010] (2)

[0011] (3)

[0012] in, The phase distribution of the left-hand exit path is as follows: The phase distribution of the right-handed exit path is shown. For free space wavenumber, It is the azimuth angle on the plane of the superlens.

[0013] Furthermore, the nanostructure unit is a nanopillar, which is periodically arranged on the substrate. The phase and rotation angle of the nanopillar satisfy the following equations (4) to (6):

[0014] (4)

[0015] (5)

[0016] (6)

[0017] in, and These represent the propagation phases of x-polarized light and y-polarized light as they pass through the nanostructure unit, respectively. This indicates the rotation angle of the nanostructure unit.

[0018] Furthermore, the substrate is made of silicon dioxide or sapphire.

[0019] Furthermore, the nanostructure units are made of hafnium oxide, titanium oxide, silicon carbide, silicon nitride, monocrystalline silicon, or amorphous silicon.

[0020] Furthermore, the nanopillars are on the subwavelength scale and have half-wave plate characteristics, while also covering a 2π phase range.

[0021] Furthermore, the nanopillar unit cell has a period of P, a length of L, a width of W, and a height of H. By scanning parameters, nanopillar structures with high polarization conversion efficiency that satisfy half-wave plate characteristics are selected.

[0022] An imaging system comprising the aforementioned vector vortex superlens for orientation-selective edge detection.

[0023] The optical system includes: a supercontinuum laser, an acousto-optic tunable filter (AOTF), a focusing lens, a linear polarizer, a sample to be tested, a vector vortex superlens, an objective lens, a linear polarizer (as an analyzer), and a charge-coupled device (CCD) camera; the above components are arranged sequentially along the optical path.

[0024] The metasurface nanopillar material is made of silicon carbide, and the substrate material is quartz. The preparation method is as follows:

[0025] (1) A silicon carbide thin film with a thickness of H was deposited on a quartz substrate by plasma-enhanced chemical vapor deposition (PECVD);

[0026] (2) Spin-coat a layer of positron beam photoresist on the silicon carbide film. In order to reduce charge accumulation during electron beam exposure, a thin layer of conductive adhesive is also spin-coated on the electron beam photoresist.

[0027] (3) The sample is exposed to electron beam and developed with developer, and the desired nanopattern is transferred onto the sample.

[0028] (4) A 30 nm thick aluminum layer is deposited on the sample surface as a hard mask using an electron beam evaporation device, and then the sample is immersed in an N-methylpyrrolidone solution heated to 80° to complete the stripping process.

[0029] (5) The sample is etched using an inductively coupled plasma etching device. Then, the sample is immersed in aluminum etching solution to completely remove the aluminum mask used in the etching process. Finally, the sample is washed with ultrapure water to remove the residual aluminum etching solution on the surface.

[0030] This invention proposes a vector vortex superlens for orientation-selective edge detection. This superlens possesses the ability to dynamically adjust edge extraction on demand, achieving real-time directional edge detection simply by rotating the analyzer, without requiring any other hardware modifications or digital post-processing. Most traditional superlenses only offer fixed operating modes; in contrast, the proposed vector vortex lens is far more flexible. Based on this orientation-selective characteristic, the vector vortex superlens can effectively eliminate directional defects in objects, thereby better revealing the object's edge contours. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the image taken by the vector vortex superlens used for direction-selective edge detection in the embodiment.

[0032] Figure 2 This refers to the phase distribution required for the left-hand and right-hand spiral exit paths of the vector vortex superlens in the embodiment. The left-hand spiral path is a superposition of the anti-spiral phase and the focusing phase, while the right-hand spiral path is a superposition of the positive spiral phase and the focusing phase.

[0033] Figure 3 This is a schematic diagram of the nanopillar unit structure of the vector vortex superlens in the embodiment, where 1-silicon dioxide, 2-silicon carbide, period P=300 nm, height H=850 nm, L is the length of the nanopillar, W is the width of the nanopillar, and θ is the rotation angle of the nanopillar.

[0034] Figure 4 The following are the parameter scanning results of the nanopillar structure in the embodiment: a) is the orthogonal transmission coefficient distribution of the nanopillar structure, and b) is the orthogonal transmission phase distribution of the nanopillar structure. Eight structural units that can cover the 2π phase range and maintain high transmittance were selected. The dimensions of the selected structural units are marked with dots in the figure.

[0035] Figure 5 These are scanning electron microscope images of the silicon carbide metasurface prepared in the examples: a. top view, b. side view, scale bar: 500 nm.

[0036] Figure 6 This is a point spread function distribution diagram of the vector vortex superlens in the embodiment. The incident wavelength is 633 nm. The arrow direction indicates the polarization detection direction. The polarization detection angles are 0°, +45°, 90°, and -45°. Scale bar: 3 μm.

[0037] Figure 7 This is a schematic diagram of the optical path during edge detection using a vector vortex superlens for direction-selective edge detection in this embodiment. From left to right: supercontinuum laser, acousto-optic tunable filter (AOTF), focusing lens, linear polarizer, sample under test, vector vortex superlens, objective lens, linear polarizer (as analyzer), and charge-coupled device (CCD) camera.

[0038] Figure 8 This is the imaging result of the edge detection experiment using a vector vortex superlens in this embodiment. The object under test is a cross-section of the stem cells of a woody dicotyledonous plant. a) Incident wavelength is 555 nm, b) Incident wavelength is 580 nm, c) Incident wavelength is 633 nm. The arrows indicate the polarization direction, with polarization angles of +50° and -50° respectively. Scale bar: 5 μm.

[0039] Figure 9 This is the imaging result of the defect elimination experiment of the vector vortex superlens in the embodiment. The object under test is a letter with directional defects. The incident wavelength is 633 nm, the analysis angles are +45° and -45°, and the scale bar is 5 μm. Detailed Implementation

[0040] To enable those skilled in the art to better understand the present invention, embodiments of this application will be described in detail below with reference to the accompanying drawings. It should be understood that the embodiments described herein are merely one implementation of this application, and not all. For those skilled in the art, any other technical solutions that can be obtained based on the embodiments disclosed in this application without inventive effort should fall within the protection scope of the claims of this application.

[0041] like Figure 1 The image shown is an imaging schematic diagram of a vector vortex superlens used for direction-selective edge detection.

[0042] like Figure 2 As shown, the phase distribution of the left and right spiral exit paths of the vector vortex superlens must satisfy the following formula:

[0043]

[0044]

[0045] In the formula, The phase distribution of the left-hand exit path is as follows: The phase distribution of the right-handed exit path is shown. For free space wavenumber, The designed wavelength is given by polar coordinates on the superlens plane. Superlens focal length The radius of the superlens is Both left and right spiral output channels can generate point spread functions carrying spiral phase. The two channels are superimposed to obtain a vector point spread function with the polarization state distributed radially.

[0046] To achieve independent phase modulation of left and right-handed pathways, it is necessary to combine the propagation phase and geometric phase of the nanostructure. The phase and rotation angle required by the designed nanostructure unit must satisfy the following formula:

[0047]

[0048]

[0049]

[0050] In the formula, and These represent the propagation phases of x-polarized light and y-polarized light as they pass through the nanopillar, respectively. This indicates the rotation angle of the nanopillar.

[0051] like Figure 3 As shown, the metasurface nanopillar material is silicon carbide, the substrate material is quartz, the unit period is P=300nm, the length of the nanopillar is L, the width is W, and the height is H=850 nm.

[0052] like Figure 4 The image shows the orthogonal transmission coefficient and phase map obtained by scanning parameters L and W. Eight structural units that cover the 2π phase range and maintain high transmittance were selected from the scanning results. These eight structural units were then filled into the corresponding positions on the metasurface, and corresponding rotation angles were added. Thus, the designed metasurface drawings were obtained.

[0053] The micro / nano fabrication process for metasurfaces is as follows:

[0054] (1) A silicon carbide thin film with a thickness of 850 nm was deposited on a quartz substrate by plasma-enhanced chemical vapor deposition (PECVD);

[0055] (2) A 200 nm thick positron beam photoresist is spin-coated on the silicon carbide film. In order to reduce charge accumulation during electron beam exposure, a thin conductive adhesive layer is also spin-coated on the electron beam photoresist.

[0056] (3) The sample is exposed to electron beam and developed with developer, and the desired nanopattern is transferred onto the sample.

[0057] (4) A 30 nm thick aluminum layer is deposited on the sample surface as a hard mask using an electron beam evaporation device, and then the sample is immersed in an N-methylpyrrolidone solution heated to 80° to complete the stripping process.

[0058] (5) The sample is etched using an inductively coupled plasma etching device. Then, the sample is immersed in aluminum etching solution to completely remove the aluminum mask used in the etching process. Finally, the sample is washed with ultrapure water to remove the residual aluminum etching solution on the surface.

[0059] like Figure 5 The images shown are scanning electron microscope (SEM) images of the prepared silicon carbide metasurface. a) Top view, b) Side view.

[0060] like Figure 6As shown, the point spread function distribution of the fabricated vector vortex superlens at an incident wavelength of 633 nm is presented. a represents the result without polarization analysis, and b represents the intensity distribution along the dashed line in a. c, d, e, and f represent the results at polarization analysis angles of 0°, +45°, 90°, and -45°, respectively, with the arrows indicating the polarization analysis direction.

[0061] like Figure 7 The diagram illustrates the optical path of a vector vortex superlens for direction-selective edge detection. Its optical system includes: a supercontinuum laser, an acousto-optic tunable filter (AOTF), a focusing lens, a linear polarizer, a sample to be tested, a vector vortex superlens, an objective lens, a linear polarizer (as an analyzer), and a charge-coupled device (CCD) camera; these components are arranged sequentially along the optical path. The coherent monochromatic light output by the system passes through the focusing lens, is polarized by the linear polarizer to generate an x-polarized beam, and illuminates the sample. The outgoing light carrying sample information passes through the superlens, is converted into an edge image carrying polarization information, is collected by a 50x objective lens, and then captured by the CCD camera. A linear analyzer is inserted between the objective lens and the camera; by rotating its angle, direction-selective edge detection is achieved.

[0062] First, the edge detection capability of the vector vortex superlens was experimentally verified over a wide bandwidth. For example... Figure 8 As shown, the object under test is a cross-section of the stem cells of a woody dicotyledonous plant. a) Incident wavelength is 555 nm, b) Incident wavelength is 580 nm, and c) Incident wavelength is 633 nm. The first column is the bright-field image of the cells, the second column is the cell edge image without an analyzer, and the third and fourth columns are the cell edge images after +50° and -50° polarization, respectively. Experimental results show that the designed superlens can extract the edge features of the object along a specific direction as needed.

[0063] like Figure 9 The image shows the experimental imaging results of defect elimination of the fabricated vector vortex superlens. Letters with directional defects are used as the objects being tested. The incident wavelength is 633 nm. The first row shows the brightfield image of the object, the second row shows the edge image without an analyzer, and the third row shows the edge images after +45° and -45° polarization, respectively. The experimental results show that the designed superlens has the ability to eliminate directional defects.

[0064] The embodiments described above are merely one approach to the present invention and do not limit the scope of the invention. Within the scope of the claims of the present invention, any equivalent substitutions, technical modifications, or detailed improvements based on the present invention, as long as they do not depart from the core design concept of the present invention, shall fall within the protection scope of the present invention.

Claims

1. A vector vortex superlens for direction-selective edge detection, characterized in that... include: Substrate and nanostructure units on the substrate; The nanostructure units are arranged on the substrate according to a specific phase distribution to form a nanostructure unit array; X-ray polarized light passes through the vector vortex superlens to generate left-handed and right-handed outgoing light, and the vector point spread function distribution of the superimposed left-handed and right-handed outgoing light conforms to equation (1): （1） in: This indicates polar coordinates in the output plane. It is the focal length of the superlens. It is the incident wavelength. It is a constant. Denotes the first-order Bessel function of the first kind. Represents the radius of the vector vortex superlens. Represents the radial coordinates on the plane of the vector vortex superlens; Vector edge detection can be achieved by convolving the point spread function with the input image.

2. The vector vortex superlens for direction-selective edge detection according to claim 1, characterized in that: The phase distribution of the left and right spiral exit paths of the vector vortex superlens conforms to equations (2) and (3): （2） （3） in, The phase distribution of the left-hand exit path is as follows: The phase distribution of the right-handed exit path is shown. For free space wavenumber, It is the azimuth angle on the plane of the superlens.

3. The vector vortex superlens for direction-selective edge detection according to claim 1, characterized in that: The nanostructure unit is a nanopillar, which is periodically arranged on the substrate. The phase and rotation angle of the nanopillar satisfy the following equations (4) to (6): （4） （5） （6） in, and These represent the propagation phases of x-polarized light and y-polarized light as they pass through the nanostructure unit, respectively. This indicates the rotation angle of the nanostructure unit.

4. The vector vortex superlens for direction-selective edge detection according to claim 1, characterized in that: The substrate is made of silicon dioxide or sapphire.

5. The vector vortex superlens for direction-selective edge detection according to claim 1, characterized in that: The nanostructure units are made of hafnium oxide, titanium oxide, silicon carbide, silicon nitride, monocrystalline silicon, or amorphous silicon.

6. The vector vortex superlens for direction-selective edge detection according to claim 1, characterized in that: The nanopillars are on the subwavelength scale and have half-wave plate characteristics, while also covering a 2π phase range.

7. An imaging system, characterized in that: Includes the vector vortex superlens for orientation-selective edge detection as described in any one of claims 1 to 6.

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