Design method of bifocal self-corrected focal scanning superlens

Abstract

The application provides a design method of a bifocal self-correcting focal point scanning superlens, and belongs to the technical field of optical element manufacturing, and comprises the following steps: determining design parameters of the superlens; using a checkerboard strategy to reduce the design parameters of the superlens, and designing independent focal points in the superlens by means of rotating a single-layer super surface; using isotropy in an artificial atom library to establish a phase distribution library of the superlens; using a Jones matrix to optimize the phase distribution of the superlens according to the phase distribution library, and determining the spatial position of a focal point in a target unit structure; and according to the spatial position of the focal point in the target unit structure, a bifocal self-correcting focal point scanning superlens is designed through full-wave simulation and theoretical analysis verification. The superlens designed by the method can realize independent scanning of multiple focal points and multiple profiles, and provides a theoretical and practical application basis for the fields of industrial design, three-dimensional modeling, scanning and surface detection.

Description

Technical Field

[0001] The present invention relates to the technical field of optical element manufacturing, and in particular to a design method for a dual-focus self-correcting focus scanning metalens. Background Art

[0002] Multi-focus and multi-profile independent scanning devices have many potential applications and can play an important role in various fields, such as industrial design, 3D modeling and scanning, surface inspection and quality control, optical microscopy imaging, virtual reality and augmented reality, semiconductor industry, and medical imaging and diagnosis.

[0003] However, in practical applications, single-focus scanning devices are limited in functionality and inefficient, enabling only single-position endoscopic imaging or capturing images within a single focal point. Traditional optical component manufacturing techniques require more complex design and processing to achieve simultaneous operation of multiple focal points. Failure to effectively integrate these features can compromise focusing performance and make it impossible to determine the focal point's spatial location.

[0004] Therefore, there is an urgent need to provide a dual-focus self-correcting focus scanning metalens design method that can provide a theoretical and practical application basis for industrial design, three-dimensional modeling and scanning, and surface detection. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the purpose of the present invention is to provide a design method for a dual-focus self-correcting focus scanning metalens, which provides a theoretical and practical application basis for the fields of industrial design, three-dimensional modeling and scanning, and surface detection.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] A method for designing a dual-focus self-correcting focus scanning metalens comprises the following steps:

[0008] Determining design parameters of the metalens;

[0009] The design parameters of the metalens are reduced using a checkerboard strategy, and independent focal points are designed in the metalens by rotating a single-layer metasurface.

[0010] The phase distribution library of the metalens is established by using the isotropy in the artificial atom library;

[0011] The Jones matrix is ​​used to optimize the phase distribution of the metalens according to the phase distribution library and determine the spatial position of the focus in the target unit structure;

[0012] According to the spatial position of the focus in the target unit structure, a dual-focus self-correcting focus scanning metalens was designed through full-wave simulation and theoretical analysis.

[0013] Preferably, the design parameters of the metalens are determined to include the operating wavelength, radius, numerical aperture, focal position and focusing focal length of the metalens.

[0014] Preferably, the method of reducing the design parameters of the metalens by using a checkerboard strategy and designing independent focal points in the metalens by rotating a single-layer metasurface includes:

[0015] Determining two different focal positions, wherein the two different focal points correspond to two different sets of cascaded metalens devices;

[0016] By rotating the single-layer metasurface, the first focus is controlled to scan in a direction of increasing lateral position and the second focus is controlled to scan in a direction of decreasing lateral position, thereby obtaining alternating sampling of the metasurface;

[0017] The obtained alternating sampling of the metasurface is combined into an upper metasurface and a lower metasurface, and the upper metasurface and the lower metasurface are cascaded to control the two focal points to move in two different profiles.

[0018] Preferably, the method of reducing the design parameters of the metalens by using a checkerboard strategy and designing independent focal points in the metalens by rotating a single-layer metasurface further includes:

[0019] Based on the obtained metalens design parameters, the relationship between the parameters is determined, and the parameters are combined into a reduced parameter combination to determine the position of the focus in the metalens.

[0020] Preferably, the phase distribution library of the metalens is established by utilizing the isotropy in the artificial atom library, comprising:

[0021] The phase distribution of the metasurface is determined by combining the reduced parameters;

[0022] By using the isotropy principle of the artificial atom library, the structural unit of the super lens is obtained;

[0023] The structural units of the metalens are simulated, and the transmission phase of each structural unit is extracted to establish a phase distribution library of the metalens.

[0024] Preferably, the method of optimizing the phase distribution of the metalens using the Jones matrix according to the phase distribution library and determining the spatial position of the focus in the target unit structure includes:

[0025] Based on the phase distribution library of the superlens, the phase distribution of the superlens in two directions is obtained;

[0026] Determine the Jones matrix of the metalens in polarization basis and local coordinate system;

[0027] The phase distribution is optimized and calculated by Jones matrix to determine the validity of the parameter combination;

[0028] Based on the calculation results, the spatial position of the focus in the target unit structure is determined.

[0029] Preferably, the Jones matrix is:

[0030]

[0031] Among them, Φ tot (r)=Φ1(r)+Φ2(r), Φ tot (r) is the total phase distribution after the two layers of metasurface are superimposed, Φ1(r) is the phase of the first layer of metasurface, and Φ2(r) is the phase of the second layer of metasurface.

[0032] Preferably, according to the spatial position of the focus in the obtained target unit structure, a dual-focus self-correcting focus scanning metalens is designed through full-wave simulation and theoretical analysis verification, including:

[0033] Based on the artificial atom library, the required artificial atoms are screened and arranged according to the phase distribution to form the upper and lower layers of the metasurface structure;

[0034] The obtained upper and lower metasurface structures are cascaded, and a Gaussian light source is set as the incident light to obtain a simulation model of the metalens;

[0035] Based on theoretical analysis and simulation models, the dual-focus self-correcting focus scanning metalens is designed, and its performance is evaluated according to full-wave simulation.

[0036] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0037] (1) This invention further expands the theory of the self-correcting focus scanning metalens described above, extending single-focus, single-profile scanning to multi-focus, multi-profile independent scanning. Based on this theory, a dual-focus self-correcting focus scanning metalens based on a cascaded metasurface is designed. This metalens can independently control the movement of two focal points on different profiles by rotating the metasurface. To validate this design, theoretical analytical calculations and full-wave simulations were performed. The theoretical verification results are highly consistent with the full-wave simulation results, demonstrating that the designed metalens can achieve multi-focus, multi-profile independent scanning.

[0038] (2) The present invention has broad application prospects in industrial design, three-dimensional modeling and scanning, surface inspection and quality control, medical imaging and diagnosis, virtual reality and augmented reality, the semiconductor industry, and materials science. Furthermore, the emergence and application of multi-focus, multi-section independent scanning devices will continue to promote development and progress in various fields, bringing more convenience and innovation to people's lives and work. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0040] Figure 1 This is a flow chart of a design method for a dual-focus self-correcting focus scanning metalens of the present invention;

[0041] Figure 2 A diagram showing the visual measurement results of the optimal parameter combination measurement standard for the self-correcting oblique scanning metalens based on the cascaded metasurface provided in an embodiment of the present invention;

[0042] Figure 3 The electric field distribution diagram of the focus in the xz plane provided by the embodiment of the present invention;

[0043] Figure 4 The electric field distribution diagram of the focus in the xy plane provided by the embodiment of the present invention;

[0044] Figure 5 A full-wave simulation result diagram of the electric field intensity in the xz plane of a metalens under 0.6 THz wave irradiation provided by an embodiment of the present invention;

[0045] Figure 6 A full-wave simulation result diagram of the electric field intensity of the metalens in the focal plane under 0.6 THz wave irradiation provided by an embodiment of the present invention;

[0046] Figure 7 Schematic diagram of the metalens structure obtained by using the design method of the present invention. DETAILED DESCRIPTION

[0047] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments 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 are within the scope of protection of the present invention.

[0048] In order to make the objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0049] like Figure 1 As shown, the present invention provides Figure 1 As shown, the present invention provides a design method for a dual-focus self-correcting focus scanning metalens, comprising the following steps:

[0050] Step 100: Determine the design parameters of the metalens;

[0051] Step 200: Using a checkerboard strategy to reduce the design parameters of the metalens, and designing independent focal points in the metalens by rotating a single-layer metasurface;

[0052] Step 300: using the isotropy in the artificial atom library to establish a phase distribution library of the metalens;

[0053] Step 400: Optimizing the phase distribution of the metalens using the Jones matrix according to the phase distribution library, and determining the spatial position of the focus in the target unit structure;

[0054] Step 500: Based on the obtained spatial position of the focus in the target unit structure, a dual-focus self-correcting focus scanning metalens is designed through full-wave simulation and theoretical analysis verification.

[0055] Specifically, in step 100, the design parameters of the metalens are determined, including but not limited to the operating wavelength, radius, numerical aperture, focal position, and focusing focal length of the metalens.

[0056] Specifically, in step 200, it specifically includes:

[0057] Determining two different focal positions, wherein the two different focal points correspond to two different sets of cascaded metalens devices;

[0058] By rotating the single-layer metasurface, the first focus is controlled to scan in a direction of increasing lateral position and the second focus is controlled to scan in a direction of decreasing lateral position, thereby obtaining alternating sampling of the metasurface;

[0059] The obtained alternating sampling of the metasurface is combined into an upper metasurface and a lower metasurface, and the upper metasurface and the lower metasurface are cascaded to control the two focal points to move in two different profiles.

[0060] The above process is explained in detail here: two independent focal points are designed in the double-layer metasurface device. First, these two different focal points correspond to two different sets of cascaded metalens devices. To distinguish the two focal points, the metasurface is rotated to control focus a to scan in the direction of increasing lateral position while focus b is scanned in the direction of decreasing lateral position. Here, to maintain the consistency of the lower metasurface structure of the two different sets of cascaded metalens, the structure of their upper metasurface is alternately sampled with a period of 2P (where P = 140um is the period of the artificial atom). Finally, the alternately sampled parts are combined to form a complete upper metasurface. After the upper metasurface combined in a "checkerboard" form is cascaded with the lower metasurface, the electromagnetic waves passing through the two different parts of the upper metasurface will form the original two focal points a and b respectively. Then, by rotating the metasurface, the two focal points can be controlled to scan along different paths, that is, according to the originally preset trajectory as the metasurface angle changes. Therefore, by integrating these two different phase distributions in the same layer, the entire device can achieve functional multiplexing and independently control the movement of the two focal points in two different profiles.

[0061] More specifically, in step 200, the following steps are also included:

[0062] Based on the obtained metalens design parameters, the relationship between the parameters is determined, and the parameters are combined into a reduced parameter combination to determine the position of the focus in the metalens.

[0063] Among them, the two parameter spaces M a and M b The parameters in the space are merged into the reduced parameter space M = {m, F0, X0, Q0, Q2, a, Q2, b}, where F0 = F 0,a =F 0,b is the focal length, X0=X 1,a =X 2,a =X 1,b =X 2,b is the coefficient of the moiré phase, Q0=Q 1,a =Q 1,b is the initial rotation angle of the moiré phase.

[0064] First, based on the reduced parameter space M, Φ is established in the working area (area I). tot (α, r) and Φ target (rc,r) respectively get the position of focus a and b and the metasurface angle C i And the relationship between the parameter space M: For focus a:

[0065]

[0066] in, Represents the distance between the focus a and the origin O, α av =(α1+α2) / 2 is the azimuth angle of focus a in three-dimensional space, Δα=(α2-α1) / 2 is the elevation angle of focus a in three-dimensional space, is half of the initial rotation angle difference of the moiré phase.

[0067] For focus b:

[0068]

[0069] in, Represents the distance between the focus a and the origin O, α av +m is the azimuth angle of focus b in three-dimensional space, Δα-m is the elevation angle of focus b in three-dimensional space, is half of the initial rotation angle difference of the moiré phase.

[0070] Reference Figure 2 , Figure 2 (a) are the relationship between the average working area ratio of focus a during scanning and the maximum scanning angle, and the deviation between the focus position and the target during scanning. Here, the maximum scanning angle Δα max ≥0° is defined as scanning in the direction of increasing lateral position of the focus, Δα max <0° is defined as scanning in the direction of decreasing lateral position of the focus, and the asterisk represents the final selected parameter value Δα max =30°, F0=8.4λ, X0=16.3k. Figure 2 (b) are the relationship between the average working area ratio of focus b during scanning and the maximum scanning angle, and the deviation between the focus position and the target during scanning. In order to control the focus a and b to be not in the same xz plane as much as possible during scanning, m = 30° is selected to facilitate locking α max = 0°, the focus a moves in the y = 0 plane, and the focus b moves in the y = sin (30°) x plane. The asterisk represents the final selected parameter value Δα max =-30°, Here the maximum scanning angle Δα max The negative sign of Δα simply means that the focus b will scan in the direction of decreasing lateral distance as the rotation angle difference Δα increases.

[0071] Specifically, step 300 includes:

[0072] The phase distribution of the metasurface is determined by combining the reduced parameters;

[0073] By using the isotropy principle of the artificial atom library, the structural unit of the super lens is obtained;

[0074] The structural units of the metalens are simulated, and the transmission phase of each structural unit is extracted to establish a phase distribution library of the metalens.

[0075] Specifically, in step 400, the phase distribution of the metalens is optimized according to the phase distribution library using the Jones matrix, and the spatial position of the focus in the target unit structure is determined, including:

[0076] Based on the phase distribution library of the superlens, the phase distribution of the superlens in two directions is obtained;

[0077] Determine the Jones matrix of the metalens in polarization basis and local coordinate system;

[0078] The phase distribution is optimized and calculated by Jones matrix to determine the validity of the parameter combination;

[0079] Based on the calculation results, the spatial position of the focus in the target unit structure is determined.

[0080] The Jones matrix is:

[0081]

[0082] Among them, Φtot(r)=Φ1(r)+Φ2(r), Φ tot (r) is the total phase distribution after the two layers of metasurface are superimposed, Φ1(r) is the phase of the first layer of metasurface, and Φ2(r) is the phase of the second layer of metasurface.

[0083] Specifically, a beam of normalized linearly polarized Gaussian light with a frequency of 0.6THz is used to illuminate the cascaded metasurface. Normalized linearly polarized Gaussian light is a special light source with a frequency of 0.6THz and a linear polarization characteristic. By irradiating this beam of light onto the cascaded metasurface, the effect of the metasurface on the propagation of light is studied. Figure 5 , we fix the angle of the hypersurface and C in the calculation αv = 0 to lock the two different focal points a and b in the y = 0 plane and y = sin (30 °) x plane respectively, and then control the movement of the focal points a and b by changing the value of the rotation angle difference Δα between the two metasurfaces. Here, the normalized intensity distribution of the electric field passing through the metalens in the y = 0 plane and y = sin (30 °) x plane at four different rotation angle differences (Δα = 0 °, 10 °, 20 °, 30 °) is shown. First, from Figure 5 It can be seen that the fixed C αv = 0, the plane where the focus is located is locked to the y = 0 plane and the y = sin (30 °) x plane, which is consistent with the theoretical design. Once the parameter combination in the parameter space is determined, the azimuth of the focus is only related to C αvAt this time, changing the value of the angular difference Δα will only change the position of the focus in the y=0 plane and the y=sin(30°)x plane, that is, change the elevation angle of the focus. Secondly, as the angular difference Δα between the two metasurfaces gradually increases, the scanning directions of the two focal points are opposite. Focus a scans in the direction of increasing lateral position, while focus b scans in the direction of decreasing lateral position. Finally, with the change of Δα, it can be seen that focus a is basically stable in the z=4mm plane, while the axial position of focus b increases with the increase of Δα. The final calculated focus position is also basically consistent with the pre-designed trajectory. As Δα increases, the intensity of focus a gradually decreases and is slowly stretched, while the intensity of focus b gradually increases and is slowly contracted.

[0084] Finally, refer to Figure 4 , the normalized electric field intensity distribution of the two focal points a and b in the corresponding focal plane (xy plane) calculated at different rotation angle differences (Δα=0°, 10°, 20°, 30°). By analyzing these data, we can better understand the position of the focal point and the distribution of the electric field intensity in the focal plane. Obviously, due to the fixed C αv = 0, and the azimuth angles of focal points a and b in three-dimensional space are also locked accordingly. Therefore, as the rotation angle difference Δα gradually increases, only the lateral position of the focal points is considered, and focal points a and b move on the x-line y = 0 and y = sin(30°), respectively, in opposite directions. It is important to emphasize that these results are calculated based on a given metasurface rotation angle. Therefore, in practical applications, different rotation angle differences can be selected as needed to achieve specific focal positions and light field distributions. These results are of great significance for optimizing light propagation and focusing effects.

[0085] Specifically, in step 500, based on the obtained spatial position of the focus in the target unit structure, a dual-focus self-correcting focus scanning metalens is designed through full-wave simulation and theoretical analysis verification, including:

[0086] Based on the artificial atom library, the required artificial atoms are screened and arranged according to the phase distribution to form the upper and lower layers of the metasurface structure;

[0087] The obtained upper and lower metasurface structures are cascaded, and a Gaussian light source is set as the incident light to obtain a simulation model of the metalens;

[0088] Based on theoretical analysis and simulation models, the dual-focus self-correcting focus scanning metalens is designed, and its performance is evaluated according to full-wave simulation.

[0089] Reference Figure 5, the normalized electric field intensity distribution of the electric field through the metalens at four different rotation angles (Δα=0°, 10°, 20°, 30°) in the y=0 plane and y=sin(30°)x plane. First, from Figure 5 It can be seen that once the rotation angle and αav between the metasurfaces are locked, the change in the rotation angle difference Δα will only affect the elevation angle of the focal points a and b in three-dimensional space. Similarly, once the rotation angle difference Δα between the metasurfaces is locked, the change in the rotation angle and αav will only affect the azimuth angle of the focal points a and b in three-dimensional space. Subsequently, as the rotation angle difference Δα between the two metasurfaces gradually increases, it can be seen that the scanning directions of the focal points a and b are opposite. The focal point a scans in the direction of increasing lateral position, while the focal point b scans in the direction of decreasing lateral position. Finally, as Δα changes, it can be observed that the movement trajectory of the focal point a is basically stable in the z = 4mm plane, that is, the focal plane of the focal point a basically does not change with the change of Δα, while the axial position of the focal point b increases with the increase of Δα, that is, the focal plane of the focal point b becomes higher with the increase of Δα.

[0090] In order to further demonstrate the change of the positions of the two focal points a and b in the corresponding focal plane with the rotation angle difference Δα, and to show the performance of the corresponding focal spot, Figure 6 The normalized electric field intensity distribution and the corresponding transverse intensity distribution of focus a and b in their respective focal planes are shown. By analyzing the provided data, as the rotation angle difference Δα gradually increases, focus a and b move on the x-line y=0 and y=sin(30°) respectively and in opposite directions. This is because the fixed α av = 0, and the azimuths of the focal points a and b in the three-dimensional space are also locked accordingly. Figure 6 The electric field intensity distribution of the focus along y = 0 in the focal plane is also given in the above method, and then the simulation is carried out to obtain the following Figure 7 The metalens structure shown.

[0091] Therefore, the above-mentioned design method of a dual-focus self-correcting focus scanning metalens provides a theoretical and practical application basis for fields such as industrial design, three-dimensional modeling and scanning, and surface detection.

[0092] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. At the same time, those skilled in the art will find that the specific implementation methods and application scopes may vary based on the concept of the present invention. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims

1. A design method for a dual-focus self-correcting focus scanning metalens, characterized in that: The following steps are involved: Determining design parameters of the metalens; The design parameters of the metalens are reduced using a checkerboard strategy, and independent focal points are designed in the metalens by rotating a single-layer metasurface. This includes: Determining two different focal positions, wherein the two different focal points correspond to two different sets of cascaded metalens devices; By rotating the single-layer metasurface, the first focus is controlled to scan in a direction of increasing lateral position and the second focus is controlled to scan in a direction of decreasing lateral position, thereby obtaining alternating sampling of the metasurface; The obtained alternating sampling of the metasurface is combined into an upper metasurface and a lower metasurface, and the upper metasurface and the lower metasurface are cascaded to control the two focal points to move in two different profiles; Also includes: Based on the obtained metalens design parameters, the relationship between the parameters is determined, and the parameters are combined into a reduced parameter combination to determine the position of the focal point in the metalens; The phase distribution library of the metalens is established by using the isotropy in the artificial atom library; including: The phase distribution of the metasurface is determined by combining the reduced parameters; By using the isotropy principle of the artificial atom library, the structural unit of the super lens is obtained; Simulate the structural units of the metalens, extract the transmission phase of each structural unit, and establish a phase distribution library of the metalens; The Jones matrix is ​​used to optimize the phase distribution of the metalens according to the phase distribution library and determine the spatial position of the focus in the target unit structure; including: Based on the phase distribution library of the superlens, the phase distribution of the superlens in two directions is obtained; Determine the Jones matrix of the metalens in polarization basis and local coordinate system; The phase distribution is optimized and calculated by Jones matrix to determine the validity of the parameter combination; According to the calculation results, the spatial position of the focus in the target unit structure is determined; According to the spatial position of the focus in the target unit structure, a dual-focus self-correcting focus scanning metalens was designed through full-wave simulation and theoretical analysis.

2. The design method of a dual-focus self-correcting focus scanning metalens according to claim 1, characterized in that: The design parameters of the metalens are determined to include the operating wavelength, radius, numerical aperture, focal position and focusing focal length of the metalens.

3. The design method of a dual-focus self-correcting focus scanning metalens according to claim 1, characterized in that: The Jones matrix is: Among them, Φ tot (r)=Φ1(r)+Φ2(r), Φ tot (r) is the total phase distribution after the two layers of metasurface are superimposed, Φ1(r) is the phase of the first layer of metasurface, and Φ2(r) is the phase of the second layer of metasurface.

4. The design method of a dual-focus self-correcting focus scanning metalens according to claim 1, characterized in that: According to the spatial position of the focus in the target unit structure, a dual-focus self-correcting focus scanning metalens is designed through full-wave simulation and theoretical analysis verification, including: Based on the artificial atom library, the required artificial atoms are screened and arranged according to the phase distribution to form the upper and lower layers of the metasurface structure; The obtained upper and lower metasurface structures are cascaded, and a Gaussian light source is set as the incident light to obtain a simulation model of the metalens; Based on theoretical analysis and simulation models, the dual-focus self-correcting focus scanning metalens is designed, and its performance is evaluated according to full-wave simulation.

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