Structural light five-dimensional imaging method based on polarization multiplexing superstructure surface

Abstract

This invention discloses a structured light five-dimensional imaging method based on a polarization-multiplexed metasurface. The method includes: designing a target holographic image of a centrally symmetric and non-overlapping array of left-handed and right-handed circularly polarized light points; using an optimization algorithm to calculate the phase distribution of the metasurface to generate a vector holographic image of the target under linearly polarized incident light; and using the generated five-dimensional structured light for five-dimensional imaging: capturing an image of the target illuminated by the five-dimensional structured light with a camera, and using image processing methods to obtain the position and intensity of points in the captured image; combining a three-dimensional reconstruction method to reconstruct three-dimensional spatial information based on the position of the points; and combining the wavelength and polarization state of the points to reconstruct one-dimensional polarization and one-dimensional wavelength information based on the intensity of the points. This invention can realize lightweight and convenient five-dimensional structured light illumination and imaging functions on an ultra-thin and easily integrated metasurface platform, and can be widely used in multi-dimensional imaging, object recognition, advanced sensing, and other fields.

Description

Technical Field

[0001] This invention relates to the field of micro-nano optics and structured light imaging, and in particular to a structured light five-dimensional imaging method based on polarization multiplexing metasurfaces. Background Technology

[0002] Optical imaging, as an extension of human vision, is widely used in daily life, enabling us to perceive, record, and analyze the physical world. While traditional two-dimensional planar imaging has played a significant role, various complex tasks often require more imaging dimensions, such as depth imaging, spectral imaging, and polarization imaging. These additional dimensions provide indispensable data for further perceiving and analyzing the world and are widely used in different fields. However, simultaneously acquiring multi-dimensional optical information is difficult for imaging systems and leads to a significant increase in parameters such as system complexity, size, weight, and power consumption. Integrating more optical dimensions inevitably results in system complexity far exceeding that of traditional two-dimensional imaging systems, hindering the widespread application of multi-dimensional imaging systems. Therefore, developing an efficient and compact imaging system to simultaneously capture multi-dimensional optical information is both urgent and challenging.

[0003] Metasurfaces are a novel type of subwavelength diffractive optical element. Their powerful optical manipulation capabilities and ultra-thin, easily integrated nature provide an excellent platform for applications such as holographic displays, spectral modulation, beam shaping, and optical computing. In the field of multidimensional imaging, metasurfaces can replace bulky traditional optical elements to achieve compact and efficient imaging devices. Furthermore, the polarization and spectral manipulation capabilities of metasurfaces can also be used to design compact polarization and spectral imaging devices. Moreover, the most advanced metasurface imaging methods currently available utilize carefully designed metalenses to achieve both three-dimensional polarization imaging and three-dimensional spectral imaging—two types of four-dimensional imaging. However, simultaneously acquiring five-dimensional optical information (wavelength information, polarization information, and three-dimensional spatial information) with an ultra-compact integrated system and simple processing methods has not yet been achieved. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a structured light five-dimensional imaging method based on a polarization-multiplexed metasurface. This method enables the generation of five-dimensional structured light with different wavelengths and polarizations based on a designed vector lattice holography and its inherent dispersion when multi-wavelength polarized light is irradiated onto a carefully designed polarization-multiplexed metasurface. After photographing an object illuminated by this structured light, the object's three-dimensional information can be reconstructed from the positions of the structured light points in the captured image using triangulation principles. Because each point in the structured light has its specific wavelength and polarization, the intensity of the structured light point in the captured image reflects the wavelength and polarization information of the object.

[0005] The technical solution provided by this invention is as follows:

[0006] A structured light five-dimensional imaging method based on polarization-multiplexed metasurfaces includes the following steps:

[0007] Vector dot matrix holographic image of the design target;

[0008] Based on vector dot matrix holographic images, the metasurface array layout design is completed using metasurface design principles and metasurface array optimization methods.

[0009] The designed metasurface is illuminated with linearly polarized monochromatic light of multiple wavelengths to generate five-dimensional structured light with different wavelengths and polarizations.

[0010] Five-dimensional structured light is projected onto the target object, and a binocular camera is used to capture the target object illuminated by the five-dimensional structured light to obtain a binocular image. The position and intensity of the midpoint in the captured image are obtained by using image processing methods, so as to simultaneously obtain the one-dimensional polarization information, one-dimensional wavelength information and three-dimensional spatial information of the object under five-dimensional structured light illumination.

[0011] By combining three-dimensional reconstruction methods to restore three-dimensional spatial information based on location, and by combining the extracted intensity and wavelength and polarization state of each point to restore one-dimensional polarization and one-dimensional wavelength information.

[0012] Furthermore, the vector dot matrix holographic image is characterized by the fact that, based on the traditional dot matrix image, each point in the image is encoded with a specific optical polarization state, and the different polarization states are interleaved.

[0013] Furthermore, the method for designing the vector dot matrix holographic image of the target is as follows: design a traditional dot matrix structured light target image, and assign a linear or circular polarization state to each point in the structured light, and when assigning the polarization state, try to make the polarization states of adjacent points non-repeating.

[0014] Furthermore, the metasurface design principle includes the metasurface unit structure design principle of transmission phase, geometric phase, detour phase, and multi-atom interference. Its goal is to design a metasurface unit structure that can independently control the phase, amplitude, or complex amplitude of a set of orthogonally polarized outgoing light under specific polarized light incident conditions.

[0015] Furthermore, the metasurface array optimization method includes holographic optimization algorithms such as the Gerchberg-Saxton algorithm, annealing algorithm, and gradient descent algorithm. Its goal is to optimize the phase distribution of orthogonal outgoing polarization during the iteration process so that the vector structured light obtained by the corresponding far-field optical holography after complex amplitude superposition is consistent with the target vector dot matrix holographic image.

[0016] Furthermore, a method for designing the arrangement of metasurface arrays using metasurface design principles and metasurface array optimization methods includes the following steps:

[0017] (1) Design a metasurface formed by a periodic array of multiple unit structures; the unit structure includes nanobricks and a substrate below them;

[0018] (2) Using the principle of metasurface design combined with electromagnetic simulation, the wide-band Jones matrix optical response parameters of nanobrick unit structures under different periods, lengths, widths, heights, rotation angles, and center displacements were obtained.

[0019] (3) Decompose the holographic image of the dot matrix target into multiple sets of images corresponding to different Jones matrix parameters, and use simulated annealing, gradient descent and Gerchberg-Saxton algorithm to optimize each image to obtain the optical response arrangement of the metasurface Jones matrix.

[0020] (4) Select the unit structure that is closest to the optical response of the Jones matrix and the optimized target optical response to form the final metasurface nanobrick array arrangement.

[0021] Furthermore, in step (1) of the metasurface array arrangement design method, the electromagnetic simulation method includes the finite-difference time-domain method, the finite element method, or the pattern matching method.

[0022] Furthermore, the image processing method includes: performing Gaussian filtering, binarization, and Hough transform on the binocular image to extract the position of the structured light spot within the image; using a correlation point drift algorithm to match the same structured light spot in two viewpoints of the binocular image; using the triangulation principle, calculating the relative position of the light spot with respect to the camera based on the intrinsic and extrinsic parameters calibrated by the binocular camera and the position of the same structured light spot in the two viewpoints; taking the average gray value of the light spot within a fixed range in the two viewpoints to obtain the intensity of the point, determining the wavelength of the point based on its color information, and obtaining its polarization based on its relative position in the structured light.

[0023] Furthermore, the three-dimensional reconstruction method is a method that uses the position of a light point on the camera image plane to calculate and restore its relative position in real three-dimensional space, including the principles of triangulation and camera calibration.

[0024] This invention provides a method for five-dimensional structured light imaging based on polarization-multiplexed metasurfaces. It utilizes the polarization multiplexing capability of metasurfaces and the inherent dispersion of holography to generate five-dimensional structured light with different polarizations and wavelengths. After a target object illuminated by the five-dimensional structured light is captured by a camera, the three-dimensional spatial information of the object can be reconstructed based on the position of the structured light points on the image plane. The wavelength and polarization information of the object can be reconstructed based on the intensity, polarization, and wavelength of the structured light points.

[0025] Compared with existing methods and elements for realizing actively controlled holography, this application has the following advantages:

[0026] (1) The structured light five-dimensional imaging method described above uses five-dimensional active illumination to achieve multi-dimensional imaging, which is more adaptable to low-brightness environments than the multi-dimensional imaging method that decouples different light parameters at the receiving end.

[0027] (2) The structured light five-dimensional imaging method described above uses an ultra-thin and easily integrated metasurface to realize five-dimensional structured light. Compared with traditional multi-dimensional imaging schemes, the device is smaller and has a higher degree of integration.

[0028] (3) The structured light five-dimensional imaging method described above has more imaging dimensions than other metasurface multidimensional imaging methods, and can acquire richer optical information at the same time.

[0029] (4) This invention utilizes the inherent dispersion of holography and the polarization multiplexing capability of metasurfaces to further encode wavelength and polarization information for traditional structured light. This enables lightweight and convenient five-dimensional structured light illumination and imaging functions to be realized on an ultra-thin and easily integrated metasurface platform. It can be widely used in fields such as multidimensional imaging, object recognition, and advanced sensing. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram illustrating the design principle of a target vector dot matrix holographic image provided in an embodiment of the present invention;

[0032] Figure 2 This is a schematic diagram of the array design principle of a metasurface based on a single polarized target dot matrix holographic image provided in an embodiment of the present invention;

[0033] Figure 3 This is a schematic diagram of the metasurface unit structure and array provided in an embodiment of the present invention;

[0034] Figure 4 This is an experimental result of structured light on a metasurface sample under single-wavelength irradiation, provided in an embodiment of the present invention.

[0035] Figure 5 This is an experimental result diagram of the polarization information of an object restored under five-dimensional structured light illumination, provided in an embodiment of the present invention.

[0036] Figure 6 This is an experimental result diagram showing the wavelength information of an object reconstructed under five-dimensional structured light illumination, provided in an embodiment of the present invention.

[0037] Figure 7This is an experimental result image of the three-dimensional spatial information of an object being restored under five-dimensional structured light illumination, provided in an embodiment of the present invention.

[0038] Figure 8 A schematic diagram of structured light five-dimensional imaging of a polarization-multiplexed metasurface is shown. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Example

[0041] A structured light five-dimensional imaging method based on polarization-multiplexed metasurfaces includes the following steps:

[0042] 1. The vector dot matrix holographic image of the design target is as follows:

[0043] (1) Select the array size (1500*1500 in this embodiment) and construct a dot matrix image with 2n*2n points that satisfies central symmetry (n=19 in this embodiment);

[0044] (2) Decompose the dot matrix image into two images corresponding to different circularly polarized light, and make the two images centrally symmetrical and the points in the images staggered.

[0045] (3) Take one of the images after decomposition as the target holographic image under left circular polarization and the other image as the target holographic image under right circular polarization. The two images are combined to form the target vector dot matrix holographic image.

[0046] Figure 1 The target vector dot matrix holographic image is shown. This image can be decomposed into a left-handed circularly polarized light dot matrix holographic image and a right-handed circularly polarized light dot matrix holographic image. The two decomposed single-polarized target images are centrally symmetrical to each other, and the points representing different polarizations are staggered.

[0047] 2. Based on vector dot matrix holographic images, the metasurface array layout design is completed using metasurface design principles and metasurface array optimization methods, as detailed below:

[0048] (1) The dimensions of the nanobrick unit structure with broadband polarization conversion capability are designed based on the finite difference time-domain simulation (in this embodiment, the unit structure period is 400nm, the height of the micro-nano structure is 500nm, the length is 230nm, and the width is 80nm).

[0049] (2) Based on the target holographic image under left-hand circular polarization, the phase arrangement of the metasurface is optimized by iteratively using the Gerchberg-Saxton algorithm (the number of iterations is 100 in this embodiment);

[0050] (3) According to the principle of geometric phase, the rotation angle of each nanobrick in the metasurface array is numerically equal to half of the phase of the corresponding point in the optimized phase arrangement, thus obtaining the metasurface array.

[0051] like Figure 2 As shown, the phase array arrangement of the polarization multiplexing metasurface is obtained by optimization based on a single-polarization target image. The near-field electric field distribution can be obtained from the single-polarization phase distribution, and its Fourier transform yields the far-field holographic electric field distribution. Taking the square of the modulus gives the theoretical holographic image. Conversely, the near-field electric field distribution is obtained by performing an inverse Fourier transform on the far-field electric field distribution, thus obtaining the near-field phase distribution. Based on the conjugate symmetry of the Fourier transform, performing a Fourier transform on a centrally symmetric image yields a spectrum conjugate to the original image's spectrum, meaning they are in opposite phases. Therefore, using only a left-handed circularly polarized light dot matrix holographic image as the target image, the GS algorithm is used to optimize and obtain the left-handed circularly polarized light phase distribution Φ. L The phase distribution Φ of right-hand circularly polarized light can be obtained by simply inverting the polarization. R =-Φ L .

[0052] It should be noted that the selected GS algorithm can be replaced by algorithms such as annealing and gradient descent; the Fourier transform used to convert the electric field distribution of metasurfaces to the electric field distribution of holographic surfaces can be replaced by methods such as diffraction integral and angular spectrum diffraction.

[0053] like Figure 3 As shown, this embodiment provides a structured light five-dimensional imaging element based on a polarization-multiplexed metasurface. Its structure is a silicon micro / nanostructure array on a glass substrate, with characteristic dimensions of its unit structure: period 400 nm, micro / nanostructure height 500 nm, length 230 nm, and width 80 nm. According to the geometric phase principle, rotating nanobricks apply opposite phase delays to the outgoing cross-polarized left-handed and right-handed circularly polarized light, which is numerically twice the rotation angle of the nanobricks. Therefore, a rotating nanobrick array can simultaneously generate the desired Φ under linearly polarized light incident light. L and Φ R To generate a target vector holographic image.

[0054] like Figure 4As shown, the structured light five-dimensional imaging element based on polarization multiplexing metasurface prepared and implemented in this embodiment of the invention generates the required structured light with alternating left-handed and right-handed circularly polarized light points after passing through a pinhole, polarizer and metasurface under incident linearly polarized light with a wavelength of 520nm, which is consistent with the design scheme.

[0055] 3. The designed metasurface is illuminated with multiple linearly polarized monochromatic lights to generate five-dimensional structured light with different wavelengths and polarizations.

[0056] 4. Obtain binocular images of the target object illuminated by five-dimensional structured light using a binocular camera, and use image processing methods to obtain the position and intensity of the midpoint in the captured image, as detailed below:

[0057] (1) Place the target object in the projection area of ​​the five-dimensional structured light;

[0058] (2) Use a binocular camera to photograph the target object in the direction of the observable structured light array;

[0059] (3) The center position of the structured light dot reflected by the target object is identified by Gaussian filtering, binarization and Hough transform;

[0060] (4) Using the position of the dot as the center, select a fixed range of windows and calculate the average gray level, that is, the intensity of the projected point.

[0061] 5. Combining 3D reconstruction methods, 3D spatial information is reconstructed based on location. One-dimensional polarization and wavelength information are then reconstructed by combining the extracted intensity, wavelength, and polarization state of each point, as detailed below:

[0062] (1) The correlation point drift algorithm is used to match the projection points of the same point in the structured light under the two viewpoints of the binocular image;

[0063] (2) Take the average intensity of the two matching projection points as the intensity of that point;

[0064] (3) Based on the triangulation method, the relative position of the point in the structured light with the camera is calculated using the official parameters of the binocular camera and the relative position of the two matching points, i.e., the three-dimensional spatial information.

[0065] (3) Calculate the chromaticity based on the three color values ​​of the projection point, and then mark it as a specific wavelength;

[0066] (4) Based on the position of the projection point in the wavelength dot matrix, mark it with a specific polarization according to the polarization design of the dot matrix.

[0067] Specifically, in this embodiment, five-dimensional structured light can be generated by illuminating the designed metasurface with linearly polarized light of multiple wavelengths (488nm and 520nm). Using 3D glasses, white paper, green square clay, and blue triangular clay as target objects, five-dimensional structured light is projected onto the target objects and captured by a calibrated binocular camera to obtain binocular images. Gaussian filtering, binarization, and Hough transform are applied to the binocular images to extract the positions of the structured light points within the images. A correlation point drift algorithm is used to match the same structured light point in two viewpoints of the binocular images. Using the principle of triangulation, the relative position of the light point with respect to the camera is calculated based on the intrinsic and extrinsic parameters calibrated by the binocular camera and the position of the same structured light point in the two viewpoints. The average grayscale value of the light point within a fixed range in the two viewpoints is taken to obtain the intensity of the point, and its wavelength is determined based on its color information. Its polarization is obtained based on its relative position in the structured light. Therefore, one-dimensional polarization information, one-dimensional wavelength information, and three-dimensional spatial information of an object can be simultaneously obtained under five-dimensional structured light illumination. The experimental measurement results are as follows: Figures 5-7 As shown. Figure 8 A schematic diagram of structured light five-dimensional imaging of a polarization-multiplexed metasurface is shown.

[0068] The solution in this embodiment can generate five-dimensional structured light illumination with different polarizations and wavelengths under multi-wavelength linearly polarized light irradiation. Based on traditional structured light three-dimensional imaging, the wavelength and polarization information of the object can be restored according to the intensity, wavelength and polarization of the light spot. This solution is lighter and more compact than traditional structured light imaging systems and can simultaneously acquire the wavelength and polarization information of the object.

[0069] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the invention.

Claims

1. A structured light five-dimensional imaging method based on polarization-multiplexed metasurfaces, characterized in that, Includes the following steps: Vector dot matrix holographic image of the design target; Based on vector dot matrix holographic images, the metasurface array layout design is completed using metasurface design principles and metasurface array optimization methods. The designed metasurface is illuminated with linearly polarized monochromatic light of multiple wavelengths to generate five-dimensional structured light with different wavelengths and polarizations. Five-dimensional structured light is projected onto the target object, and a binocular camera is used to capture the target object illuminated by the five-dimensional structured light to obtain a binocular image. The position and intensity of the midpoint in the captured image are obtained by using image processing methods, so as to simultaneously obtain the one-dimensional polarization information, one-dimensional wavelength information and three-dimensional spatial information of the object under five-dimensional structured light illumination. By combining three-dimensional reconstruction methods to restore three-dimensional spatial information based on location, and by combining the extracted intensity and wavelength and polarization state of each point to restore one-dimensional polarization and one-dimensional wavelength information.

2. The structured light five-dimensional imaging method based on polarization-multiplexed metasurfaces according to claim 1, characterized in that, The vector dot matrix holographic image is characterized by the fact that, based on the traditional dot matrix image, each point in the image is encoded with a specific optical polarization state, and the different polarization states are interleaved.

3. The structured light five-dimensional imaging method based on polarization multiplexing metasurface according to claim 2, characterized in that, The method for creating a vector dot matrix holographic image of the design target is as follows: design a traditional dot matrix structured light target image, and assign a linear or circular polarization state to each point in the structured light, while ensuring that the polarization states of adjacent points do not overlap when assigning polarization states.

4. The structured light five-dimensional imaging method based on polarization multiplexing metasurface according to claim 1, characterized in that, The metasurface design principle includes the metasurface unit structure design principle of transmission phase, geometric phase, detour phase, and multi-atom interference. Its goal is to design a metasurface unit structure that can independently control the phase, amplitude, or complex amplitude of a set of orthogonally polarized outgoing light under specific polarized light incident conditions.

5. The structured light five-dimensional imaging method based on polarization multiplexing metasurface according to claim 1, characterized in that, The metasurface array optimization method includes holographic optimization algorithms such as the Gerchberg-Saxton algorithm, annealing algorithm, and gradient descent algorithm. Its goal is to optimize the phase distribution of orthogonal outgoing polarization during the iteration process so that the vector structured light obtained by the corresponding far-field optical holography after complex amplitude superposition is consistent with the target vector dot matrix holographic image.

6. The structured light five-dimensional imaging method based on polarization-multiplexed metasurfaces according to claim 4 or 5, characterized in that, A method for designing the arrangement of metasurface arrays using metasurface design principles and metasurface array optimization methods includes the following steps: (1) Design a metasurface formed by a periodic array of multiple unit structures; the unit structure includes nanobricks and a substrate below them; (2) Using the principle of metasurface design combined with electromagnetic simulation, the wideband Jones matrix optical response parameters of the nanobrick unit structure under different periods, lengths, widths, heights, rotation angles, and center displacements were obtained. (3) Decompose the dot matrix target holographic image into multiple sets of images corresponding to different Jones matrix parameters, and use simulated annealing, gradient descent and Gerchberg-Saxton algorithm to optimize each image to obtain the optical response arrangement of the metasurface Jones matrix. (4) Select the unit structure that is closest to the optical response of the Jones matrix and the optimized target optical response to form the final metasurface nanobrick array arrangement.

7. The structured light five-dimensional imaging method based on polarization-multiplexed metasurfaces according to claim 6, characterized in that, In step (1) of the metasurface array arrangement design method, the electromagnetic simulation method includes the finite-difference time-domain method, the finite element method, or the pattern matching method.

8. The structured light five-dimensional imaging method based on polarization multiplexing metasurface according to claim 1, characterized in that, The image processing method includes: performing Gaussian filtering, binarization, and Hough transform on the binocular image to extract the position of the structured light spot within the image; using a correlation point drift algorithm to match the same structured light spot in two viewpoints of the binocular image; using the triangulation principle, calculating the relative position of the light spot with respect to the camera based on the intrinsic and extrinsic parameters calibrated by the binocular camera and the position of the same structured light spot in the two viewpoints; taking the average gray value of the light spot within a fixed range in the two viewpoints to obtain the intensity of the point, determining the wavelength of the point based on its color information, and obtaining its polarization based on its relative position in the structured light.

9. The structured light five-dimensional imaging method based on polarization-multiplexed metasurfaces according to claim 1, characterized in that, The three-dimensional reconstruction method includes the principles of triangulation and camera calibration, which utilize the position of a light point on the camera image plane to calculate and reconstruct its relative position in real three-dimensional space.

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