Design method of bifocus self-correction focus scanning super lens

Abstract

The invention provides a design method of a bifocus self-correction focus scanning super lens, and belongs to the technical field of optical element manufacturing, and the method comprises the following steps: determining design parameters of the super lens; using a checkerboard strategy to reduce design parameters of the superlens, and designing an independent focus in the superlens through a method of rotating a single-layer metasurface; establishing a phase distribution library of the super-lens by utilizing isotropy in an artificial atom library; optimizing the phase distribution of the superlens according to the phase distribution library by using a Jones matrix, and determining the spatial position of a focus in the target unit structure; and according to the obtained spatial position of the focus in the target unit structure, through full-wave simulation and theoretical analysis verification, designing to obtain the double-focus self-correction focus scanning super lens. The super lens designed by the method can realize multi-focus multi-section independent scanning, and provides theoretical and practical application basis for the fields of industrial design, three-dimensional modeling and scanning, surface detection and the like.

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 super lens. 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] In actual applications, the functions of single-focus scanning devices are relatively limited and inefficient. They can only achieve endoscopy at a single location or capture within a single focus. In the traditional optical component manufacturing technology, to achieve the function of multiple focuses working simultaneously, more complex design and processing technology are required. If they cannot be effectively combined, the focusing effect will be affected and the spatial position of the focus cannot be determined.

[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 fields such as industrial design, three-dimensional modeling and scanning, and surface inspection. 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 design method for 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 the checkerboard strategy, and independent focal points are designed in the metalens by rotating the single-layer metasurface.

[0010] The phase distribution library of the superlens 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 verification.

[0013] Preferably, the design parameters of the metalens are determined including the working 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] Determine two different focal positions, and the two different focal points correspond to two different groups of cascaded metalens devices respectively;

[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, so as to obtain 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 also 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 using the isotropy in the artificial atom library, comprising:

[0021] Determine the phase distribution of the metasurface through the reduced parameter combination;

[0022] Using the isotropy principle of the artificial atom library, the structural unit of the superlens is obtained;

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

[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 comprises:

[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 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 target unit structure obtained, 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 selected 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 the 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) The present invention further expands the above self-correcting focus scanning metalens theory, expands the single-focus single-section scanning to multi-focus multi-section independent scanning, and designs a dual-focus self-correcting focus scanning metalens based on a cascaded metasurface based on this theory, which can independently control the movement of two focuses on different sections by rotating the metasurface. In order to verify the design, theoretical analytical calculation verification and full-wave simulation verification are carried out. The theoretical verification results are very consistent with the full-wave simulation results, proving that the designed metalens can achieve multi-focus multi-section independent scanning.

[0038] (2) The present invention has broad application prospects in the fields of industrial design, three-dimensional modeling and scanning, surface inspection and quality control, medical imaging and diagnosis, virtual reality and augmented reality, semiconductor industry and material science. And with the emergence and application of multi-focus multi-section independent scanning devices, it will continue to promote the development and progress of various fields and bring 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 drawings required for use in the embodiments will be briefly introduced below. 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 creative work.

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

[0041] Figure 2 A visual measurement result diagram 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 An electric field distribution diagram of a focus in an xz plane provided by an embodiment of the present invention;

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

[0044] Figure 5 A full-wave simulation result diagram of the electric field intensity of the metalens in the xz plane under 0.6THz 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 0.6THz 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 be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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 creative work are within the scope of protection of the present invention.

[0048] In order to make the purpose, 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 of 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 according to the phase distribution library using the Jones matrix, 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 working wavelength, radius, numerical aperture, focal position and focusing focal length of the metalens.

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

[0057] Determine two different focal positions, and the two different focal points correspond to two different groups of cascaded metalens devices respectively;

[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, so as to obtain 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 elaborated in detail here: two independent focal points are designed in the double-layer metasurface device. First, the two different focal points correspond to two different groups of cascaded metalens devices. In order to distinguish the two focal points, the focus a is controlled to scan along the direction of increasing lateral position while the focus b is scanned along the direction of decreasing lateral position by rotating the metasurface. Here, in order to keep the lower metasurface structure of the two different groups of cascaded metalens consistent, the structure of their upper metasurface is alternately sampled with a period of 2P (here P = 140um is the period of artificial atoms), and finally the alternately sampled parts are combined into a complete upper metasurface. After the upper metasurface combined in the form of a "chessboard" is cascaded with the lower metasurface, the electromagnetic waves passing through the two different parts of the upper metasurface will form the original a and b two focal points respectively. Then, by rotating the metasurface, the two focal points can be controlled to scan along their own different paths, that is, scan 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, it also includes:

[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 moiré phase coefficient, 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, we establish Φ in the working area (area I) tot (α, r) and Φ target (rc,r) respectively obtain the positions of the focus a and b and the metasurface rotation 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, It 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, It 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 only means that as the rotation angle difference Δα increases, the focus b will scan in the direction of decreasing lateral distance.

[0071] Specifically, step 300 includes:

[0072] Determine the phase distribution of the metasurface through the reduced parameter combination;

[0073] Using the isotropy principle of the artificial atom library, the structural unit of the superlens is obtained;

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

[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 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 influence of the metasurface on the propagation of light is studied. Figure 5 , we fix the rotation angle of the hypersurface to C during 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 angle difference Δα between the two layers of the metasurface. 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 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 layers of the metasurface gradually increases, the scanning directions of the two foci 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, and 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, the azimuth angles of the 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 point is considered, and the focal points a and b move on the y=0 and y=sin(30°)x lines respectively, and in opposite directions. It should be emphasized that these results are calculated based on the rotation angle of the given metasurface. 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 the propagation and focusing effects of light.

[0085] Specifically, in step 500, according to 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 selected 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 the 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 in the y=0 plane and the y=sin(30°)x plane at four different rotation angle differences (Δα=0°, 10°, 20°, 30°). First, from Figure 5 It can be seen that once the rotation angle and αav between the metasurfaces are locked, the change of the rotation angle difference Δα will only affect the elevation angle of the focus a and b in the three-dimensional space. Similarly, once the rotation angle difference Δα between the metasurfaces is locked, the change of the rotation angle and αav will only affect the azimuth angle of the focus a and b in the three-dimensional space. Subsequently, as the rotation angle difference Δα between the two layers of metasurfaces gradually increases, it can be seen that the scanning directions of focus a and focus b 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 observed that the moving trajectory of focus a is basically stable in the z=4mm plane, that is, the focal plane of focus a basically does not change with the change of Δα, while the axial position of focus b will increase with the increase of Δα, that is, the focal plane of focus b will become 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 intensity distribution of the electric field and the corresponding transverse intensity distribution of the focus a and b in their respective focal planes are shown. By analyzing the provided data, as the rotation angle difference Δα gradually increases, the focus a and b move on the y=0 and y=sin(30°)x lines respectively and in opposite directions. This is because the fixed α av = 0, and the azimuths of the focal points a and b in three-dimensional space are locked accordingly. Figure 6 The electric field intensity distribution of the focus along y = 0 in the focal plane is also given in the figure. Then, the above method is used to simulate and obtain the following: Figure 7 The superlens 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 the fields of industrial design, three-dimensional modeling and scanning, and surface detection.

[0092] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood 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 the checkerboard strategy, and independent focal points are designed in the metalens by rotating the single-layer metasurface. The phase distribution library of the superlens is established by using the isotropy in the artificial atom library; 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; 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 verification.

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 including the working 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 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: Determine two different focal positions, and the two different focal points correspond to two different groups of cascaded metalens devices respectively; 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, so as to obtain 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.

4. The design method of a dual-focus self-correcting focus scanning metalens according to claim 3, characterized in that: 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 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 focus in the metalens.

5. The design method of a dual-focus self-correcting focus scanning metalens according to claim 1, characterized in that: The method of using the isotropy in the artificial atom library to establish a phase distribution library of the superlens comprises: Determine the phase distribution of the metasurface through the reduced parameter combination; Using the isotropy principle of the artificial atom library, the structural unit of the superlens is obtained; The structural units of the superlens are simulated, and the transmission phase of each structural unit is extracted to establish a phase distribution library of the superlens.

6. The design method of a dual-focus self-correcting focus scanning metalens according to claim 1, characterized in that: 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: 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 parameter combination; Based on the calculation results, the spatial position of the focus in the target unit structure is determined.

7. The design method of a dual-focus self-correcting focus scanning metalens according to claim 6, 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.

8. 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 selected 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 the performance is evaluated according to full-wave simulation.

Images