Design method of self-correcting focal scanning superlens with scan angle chromatic dispersion eliminated

Abstract

The application provides a design method of a scanning-angle-dispersion self-correcting focal point scanning superlens, and belongs to the technical field of super surface optical element design, and comprises the following steps: constructing an artificial atom library through a scanning parameter mode; designing a cascade superlens based on the phase distribution of a super surface according to the artificial atom library; testing the function of the cascade superlens through full-wave simulation and experimental verification, and obtaining full-wave simulation results and experimental verification results respectively; judging the consistency of the full-wave simulation results and the experimental verification results, and obtaining a scanning-angle-dispersion self-correcting focal point scanning superlens structure based on a cascade super surface. The superlens designed by the method can automatically correct the axial off-axis error in the scanning process, improves the accuracy and stability of the three-dimensional scanning system, and provides higher efficiency for the equipment and process in the fields of laser cutting, marking, laser rapid prototyping and three-dimensional application.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of super surface optical element design, in particular to a design method of a self-correcting focal point scanning super lens with scanning angle dispersion eliminated. BACKGROUND

[0002] Super surface material is a kind of artificially manufactured material with special structure and properties, which has excellent electromagnetic response characteristics on a microscopic scale. Its unique feature is that by precisely designing and arranging micro unit structures, it can achieve precise control and manipulation of electromagnetic waves, including light propagation, reflection, absorption, transmission, etc. The lens obtained by adjusting the phase and amplitude of the light field by this new type of material is a super lens.

[0003] The super surface structure can not only change the phase, amplitude and polarization of light, but also can integrate multiple devices on a super surface substrate, which makes large-scale integrated optical applications possible. The super lens based on geometric phase design has realized achromatism and sub-resolution focusing functions. However, these designs do not solve the problem of light source. The addition of a quarter-wave plate leads to a reduction in incident light energy, and the axial off-axis error cannot be automatically corrected during scanning.

[0004] In addition, the three-dimensional scanning system of the super lens currently often needs large and complex optical elements and mechanical structures, which has the disadvantages of large system size, high energy consumption, etc. SUMMARY

[0005] The purpose of the present application is to provide a design method of a self-correcting focal point scanning super lens with scanning angle dispersion eliminated, to solve the problems existing in the prior art.

[0006] To achieve the above purpose, the present application provides the following scheme:

[0007] A design method of a self-correcting focal point scanning super lens with scanning angle dispersion eliminated, comprising the following steps:

[0008] Constructing an artificial atom library through scanning parameters;

[0009] Designing a cascaded super lens based on the phase distribution of the super surface according to the artificial atom library;

[0010] Testing the function of the cascaded super lens through full-wave simulation and experimental verification, and obtaining full-wave simulation results and experimental verification results, respectively;

[0011] Judging the consistency of the full-wave simulation results and the experimental verification results, and obtaining a self-correcting focal point scanning super lens structure with scanning angle dispersion eliminated based on the cascaded super surface.

[0012] Preferably, the artificial atom library is constructed by scanning parameters, comprising:

[0013] two silicon columns with square cross sections are deposited on different surfaces of the continuous silicon partition to obtain an artificial atom geometric structure; wherein a silicon wafer with a thickness of 500 μm is selected as a base material;

[0014] the top silicon column and the bottom silicon column of the artificial atom geometric structure are optimized respectively to obtain an optimized artificial atom;

[0015] geometric parameters of the optimized artificial atom are determined by scanning parameters, and corresponding transmission phases are obtained by changing the geometric parameter values, so as to establish an artificial atom library.

[0016] Preferably, the function of the cascade superlens is tested by full-wave simulation and experimental verification, and full-wave simulation results and experimental verification results are obtained respectively, including:

[0017] The parameter combination is substituted into the phase distribution of the metasurface to obtain the phase distribution of the metasurface at the corresponding point;

[0018] The required artificial atom is screened out based on the artificial atom library, and is arranged according to the obtained phase distribution to obtain the upper and lower metasurfaces;

[0019] The upper and lower metasurfaces are cascaded, and a Gaussian light source is set as an incident light simulation condition to obtain a simulation model of the cascade superlens;

[0020] The simulation model of the cascade superlens is subjected to full-wave simulation to obtain the focal points formed at different rotation angle differences under a fixed frequency;

[0021] Based on different rotation angle differences, the positions of the focal points and the scanning angles are determined to obtain full-wave simulation results.

[0022] Preferably, the function of the cascade superlens is tested by full-wave simulation and experimental verification, and full-wave simulation results and experimental verification results are obtained respectively, further including:

[0023] An experimental sample is prepared based on the simulation model of the cascade superlens;

[0024] The obtained experimental sample is processed by using a photolithography overlay method;

[0025] The processed experimental sample is fixed on a specific sample stage, and the experimental sample is cascaded to obtain the cascade superlens;

[0026] The rotation of the sample stage is controlled by a servo motor, and the cascade superlens is tested based on a terahertz time-domain spectroscopy technology to obtain the focal points formed at different rotation angle differences;

[0027] Based on different rotation angle differences, the positions of the focal points and the scanning angles are determined to obtain experimental verification results.

[0028] Preferably, the consistency of the full-wave simulation results and the experimental verification results is judged to obtain a self-corrected focal point scanning superlens structure based on the cascaded super surface, which eliminates the scanning angle dispersion, and the self-corrected focal point scanning superlens structure based on the cascaded super surface comprises:

[0029] By changing the rotation angle between the upper and lower layers of the super surface, the positional relationship of the focal points in the three-dimensional space is controlled, and the axial positional relationship of the focal points when performing horizontal scanning under different rotation angle differences is determined, the consistency of the full-wave simulation results and the experimental verification results is judged, and thus the self-corrected focal point scanning superlens structure based on the cascaded super surface which eliminates the scanning angle dispersion is obtained.

[0030] According to the specific embodiments provided by the present application, the following technical effects are disclosed:

[0031] (1) The superlens designed by the above method can automatically correct the off-axis error in the scanning process, improve the accuracy and stability of the three-dimensional scanning system, and provide higher efficiency for the equipment and process in the fields of laser cutting, marking, laser rapid prototyping, three-dimensional application, etc.

[0032] (2) The superlens of the present application can also greatly reduce the size of the three-dimensional scanning system. The volume of the system is greatly reduced, and the energy consumption is also reduced.

[0033] (3) The present application constructs an artificial atom library and designs a self-corrected focal point scanning superlens based on the cascaded super surface which eliminates the scanning angle dispersion, and further proves the feasibility and superiority of the design method through full-wave simulation and experimental verification results. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0035] Figure 1 The flowchart of the design method of the self-corrected focal point scanning superlens which eliminates the scanning angle dispersion of the present application;

[0036] Figure 2 The artificial atom structure schematic diagram provided by the embodiment of the present application;

[0037] Figure 3 The full-wave simulation result schematic diagram of the electric field intensity of the superlens in the xz plane under the 0.6THz wave irradiation under full-wave simulation provided by the embodiment of the present application;

[0038] Figure 4 A full-wave simulation result schematic diagram of the electric field intensity of the superlens in the z=4mm plane under 0.6THz wave irradiation is provided for an embodiment of the present application;

[0039] Figure 5 A schematic diagram of the electric field distribution of the superlens in the xz plane under 0.6THz wave irradiation is provided for an embodiment of the present application under experimental verification;

[0040] Figure 6 A full-wave simulation result schematic diagram of the electric field intensity of the superlens in the z=4mm plane under 0.6THz wave irradiation is provided for an embodiment of the present application under experimental verification;

[0041] Figure 7 A schematic diagram of the superlens structure obtained by using the design method provided by the present application. DETAILED DESCRIPTION

[0042] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of the present application.

[0043] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0044] Embodiment one

[0045] As shown in the drawings, Figure 1 The present application provides a design method of a scanning angle dispersion elimination self-corrected focal point scanning superlens, comprising the following steps:

[0046] Step 100: constructing an artificial atom library by means of scanning parameters;

[0047] Step 200: designing a cascaded superlens based on the phase distribution of the super surface according to the artificial atom library;

[0048] Step 300: testing the function of the cascaded superlens by full-wave simulation and experimental verification, respectively obtaining full-wave simulation results and experimental verification results;

[0049] Step 400: judging the consistency of the full-wave simulation results and the experimental verification results, obtaining a scanning angle dispersion elimination self-corrected focal point scanning superlens structure based on the cascaded super surface.

[0050] In step 100, a set of all-dielectric artificial atoms with high transmission efficiency for 0.6 THz waves are selected. The design of these artificial atoms can cover the required phase shift range (0-2π), thereby achieving precise control of the focal position. Specifically, it includes:

[0051] Referring to Figure 2 The artificial atom is composed of two silicon pillars with square cross-sections, deposited on different sides of a continuous silicon spacer. The bottom silicon pillar is mainly used to reduce the reflection of the artificial atom to terahertz waves, while the top part realizes the accumulation of transmission phase by changing the cross-sectional side length (w1). Therefore, it is also necessary to optimize the cross-sectional side length (w1) and thickness (h1) of the top silicon pillar to ensure that the artificial atom can produce the required phase shift. At the same time, by optimizing the bottom silicon pillar, the artificial atom can obtain high transparency. It should be noted that, in order to facilitate subsequent processing and handling, a silicon wafer with a total thickness of h1+h2+h3=500μm is selected as the base material.

[0052] The design of the top silicon pillar is that for normally incident terahertz waves, the transmission characteristics and phase of the artificial atom vary with the two geometric parameters w1 and h1 of the top silicon pillar, and other parameters are fixed as h2=130μm and P=140μm. Within the range of variation of the geometric parameters of the top silicon pillar, the artificial atom can obtain high transmittance, and for a given h1=310μm, a 2π phase shift coverage can be well obtained by changing the value of w1.

[0053] Secondly, the bottom silicon pillar also has an impact on the transmittance and phase of the artificial atom. Using finite-difference time-domain (FDTD) simulation, the values of the transmittance and phase of the entire artificial atom can be obtained as w1 and w3 vary, with the height of the bottom silicon pillar fixed at h3=60μm (determined by the total thickness and h1, h2). By adding the bottom silicon pillar, the transmittance of the artificial atom can be effectively improved while ensuring that the phase of the artificial atom covers 0-2π. Therefore, by taking w3=80μm and changing w1, the artificial atom can be quickly selected according to the required phase to form a metasurface device.

[0054] Finally, after determining the parameters of the artificial atom, the transmission phase corresponding to each w1 can be obtained, thereby establishing an artificial atom library to facilitate the quick selection of suitable artificial atoms to produce different phase jumps at different positions on the metasurface. After establishing the artificial atom library, the phase distribution of the metasurface is discretized (determined by the periodicity of the artificial atom), and suitable artificial atoms are selected to form two layers of metasurfaces for full-wave simulation verification.

[0055] In step 200, the full-wave simulation process is performed, which specifically includes:

[0056] Firstly, the solved parameter set M is brought into the phase distribution of the metasurface to obtain the required phase distribution of the metasurface at each point (due to the periodicity of artificial atoms, the phase distribution is discretized according to the period P = 140 μm). Then, the required artificial atoms are selected from the artificial atom library and arranged according to the phase distribution to form the upper and lower two-layer metasurfaces. Finally, the two-layer metasurfaces are cascaded, and a Gaussian light source with a frequency of 0.6 THz is set as the incident light, the wave vector direction is perpendicular to the lowermost metasurface upward, and the simulation model of the superlens is obtained. In addition, since the superlens is non-periodic at this time, the boundary conditions x and y are both open, and the z direction is open addspace, and the metasurface is simulated in a circular shape to facilitate rotation. The distance between the two layers of metasurfaces is selected as d = 300 μm to eliminate the diffraction effect (which may cause Φtot(c,r) to deviate from ΣΦi(ri)) to ensure the stability of the entire system.

[0057] After setting the above simulation conditions, the full-wave simulation of the superlens is performed, and the focal points formed at different rotation angle differences (ΔC = 0°, 10°, 20°, 30°) at a frequency of 0.6 THz are obtained (the position of the focal point is defined as the maximum normalized intensity of the electric field). Here, the rotation angle and the lock of the metasurface are Cav = 0 to control the movement of the focal point along the x direction in the xy plane.

[0058] Referring to Figure 3 , Figure 3 The electric field intensity distribution of the focal point in the xz plane at different rotation angle differences is shown. When ΔC = 0°, the lateral position of the focal point is at (0, 0), and the scanning angle of the focal point is zero at this time, which is in good agreement with the theory. As the rotation angle difference ΔC gradually increases, the intensity of the focal point gradually decreases, the shape is gradually elongated, and the lateral position of the focal point gradually deviates from the position when it is emitted. The positions of the focal points at different rotation angle differences (ΔC = 0°, 10°, 20°, 30°) are (0, 0, 3.95), (0.75, 0, 4.025), (1.55, 0, 4.025), (2.3, 0, 3.95), and the numerical aperture is 0.53. Obviously, the full-wave simulation result can prove that the obtained superlens can control the scanning of the focal point in the same focal plane by independently rotating the single-layer metasurface, and the dispersion of the axial position of the focal point with the scanning angle during the scanning process is well eliminated.

[0059] In order to further demonstrate the scanning of the focal point position with the rotation angle difference Δa in the focal plane and the performance of the focal spot in the focal plane, as Figure 4The normalized intensity distribution of the electric field in the xy plane (z=4mm) and the corresponding lateral intensity distribution are shown. As the rotation angle difference Δa gradually increases, the focal point gradually moves along the +x direction, away from the position at normal incidence. The corresponding focal point full width at half maximum (FWHM) at different rotation angle differences are 530μm, 550μm, 620μm, and 700μm, respectively.

[0060] Secondly, the experimental verification in step 300 also includes an experimental verification process, which specifically includes:

[0061] An experimental sample is made through the simulation model of the cascaded superlens;

[0062] The obtained experimental sample is processed by using a photolithography overlay method;

[0063] The processed experimental sample is fixed on a specific sample stage, and the experimental sample is cascaded up and down to obtain the cascaded superlens;

[0064] The rotation of the sample stage is controlled by a servo motor, and the cascaded superlens is tested based on a terahertz time-domain spectroscopy technology to obtain the focal points formed at different rotation angle differences;

[0065] Based on different rotation angle differences, the positions of the focal points and the scanning angles are determined to obtain the experimental verification results.

[0066] The photolithography overlay technology is a technology based on photochemical reaction. A photosensitive glue is coated on the surface of silicon, and then a pattern on a template is projected onto the photosensitive glue by using a photolithography machine to form a photolithography pattern. Then, the photolithography pattern is exposed to chemical etching or ion beam etching to form the required structure on the surface of silicon.

[0067] In addition, the manufactured superlens (refer to Figure 7 The structure shown) is used to prove its focal point scanning ability of eliminating the scanning angle chromatic aberration through experiments. In order to facilitate the experimental characterization of the experimental sample, the rotation angle of the super surface is locked at c av=0 The focus is controlled to scan in the xz plane by changing the value of the rotation angle difference Δc. The metalens is irradiated with a linearly polarized beam of light at normal incidence at 0.6THz, and the electric field distribution through the metalens at four different rotation angle differences (Δc=0°, 10°, 20°, 30°) is measured using a terahertz time-domain spectroscopy system. When experimentally characterizing the samples at different times, in order to obtain stable results, the rotation angles of different layers are fixed at the corresponding rotation angle differences. Since the speed of movement of objects in a vacuum is much slower than the speed of light, such treatment will not introduce any errors to the actual performance of the device. The distance between the two layers of the metasurface is selected to be d=300μm to eliminate the diffraction effect and ensure the stability of the entire system. Finally, the xz plane of the focal electric field distribution measured at different rotation angle differences (Δc=0°, 10°, 20°, 30°) is shown as follows Figure 5 As shown in the figure, the probe collects electric field information every 0.1mm, where the shaded area is a safety distance reserved to avoid direct contact between the probe and the sample during testing, which may damage the sample or the probe. When Δc = 0°, the focus position of the positive emission can be determined to be at (0, 0, 3.95). At this time, the scanning angle of the focus is zero, which is very consistent with the preset focus position. As the angle difference Δc gradually increases, the intensity of the focus gradually decreases and is elongated, and the lateral position of the focus gradually moves away from the position at the positive emission, while the axial position of the focus remains basically stable in the focal plane of the positive emission (z = 4mm), with a numerical aperture of 0.53. Calculations show that the value of Δc at different angle differences is basically consistent with the scanning angle of the focus.

[0068] At the same time, in order to further demonstrate the scanning of the focus position in the focal plane as the angle difference Δc changes, the electric field intensity distribution of the xy plane (z = 4mm) at different angle differences (Δc = 0°, 10°, 20°, 30°) was scanned using a terahertz near-field integrated spectrometer test system, and the scanning step size was set to 0.1mm. Figure 6 Figure 2 shows the normalized electric field intensity distribution and the corresponding transverse intensity distribution in the xy plane (z = 4 mm). As the rotation angle difference Δc increases, the focus gradually moves along the +x direction, away from the normal emission position. The corresponding focal width at half maximum at different rotation angles is 450μm, 510μm, 560μm, and 930μm, respectively.

[0069] Therefore, the feasibility of the design method of this embodiment is demonstrated through experimental verification results. For scanning angles within the range of ΔCe[0°, 30°], a good focused light spot can be found on the focal plane. This shows that the designed focus scanning device can automatically correct the longitudinal position of the focus as the lateral position of the focus changes, eliminating the chromatic aberration of the scanning angle, thereby effectively keeping the focus on the same focal plane.

[0070] Therefore, the superlens designed by the method has a structure as shown in Figure 7 The axial off-axis error can be automatically corrected during the scanning process, the accuracy and stability of the three-dimensional scanning system are improved, and higher efficiency is provided for equipment and processes in the fields of laser cutting, marking, laser rapid prototyping, three-dimensional application, etc.

[0071] The principles and implementation manners of the present application are described by using specific examples in the present application, and the above examples are only used to help understand the method and core idea of the present application; meanwhile, for the general skilled in the art, the specific implementation manners and application ranges will be changed according to the idea of the present application. In conclusion, the content of the present application should not be understood as a limitation of the present application.

Claims

1. A design method of a self-corrected focal scanning superlens with scan angle chromatic dispersion elimination, characterized in that, The method comprises the following steps: Constructing an artificial atom library by scanning parameters; comprising: Depositing two silicon columns with square cross sections on different surfaces of a continuous silicon partition to obtain an artificial atom geometric structure; wherein a silicon wafer with a thickness of 500 μm is selected as a base material; Optimizing the top silicon column and the bottom silicon column of the artificial atom geometric structure respectively to obtain an optimized artificial atom; Determining the geometric parameters of the optimized artificial atom by scanning parameters, and obtaining the corresponding transmission phase by changing the geometric parameter values to establish an artificial atom library; Designing a cascaded superlens based on the phase distribution of the super surface according to the artificial atom library; Testing the function of the cascaded superlens through full-wave simulation and experimental verification to obtain full-wave simulation results and experimental verification results respectively; comprising: Substituting the parameter combination into the phase distribution of the super surface to obtain the phase distribution of the super surface at the corresponding point; Selecting the required artificial atom from the artificial atom library and arranging it according to the obtained phase distribution to obtain the upper and lower super surfaces; Cascading the upper and lower super surfaces and setting a Gaussian light source as the incident light simulation condition to obtain a simulation model of the cascaded superlens; Performing full-wave simulation on the simulation model of the cascaded superlens to obtain the focal points formed at different rotation angle differences under a fixed frequency; Determining the position and scanning angle of the focal points based on different rotation angle differences to obtain full-wave simulation results; Determining the consistency of the full-wave simulation results and the experimental verification results to obtain a cascaded super surface-based self-corrected focal point scanning superlens structure with scanning angle dispersion eliminated.

2. The design method of a self-corrected focal scanning superlens with no scanning angle dispersion according to claim 1, wherein, The testing of the function of the cascaded superlens through full-wave simulation and experimental verification to obtain full-wave simulation results and experimental verification results respectively further comprises: Manufacturing an experimental sample through the simulation model of the cascaded superlens; Processing the obtained experimental sample by using a photolithography overlay method; Fixing the processed experimental sample on a sample stage and cascading the experimental sample to obtain the cascaded superlens; Controlling the rotation of the sample stage by a servo motor and performing experiments on the cascaded superlens based on terahertz time-domain spectroscopy to obtain the focal points formed at different rotation angle differences; Determining the position and scanning angle of the focal points based on different rotation angle differences to obtain experimental verification results.

3. The design method of a self-corrected focal scanning superlens with no scanning angle dispersion according to claim 1, wherein, The determination of the consistency of the full-wave simulation results and the experimental verification results to obtain a cascaded super surface-based self-corrected focal point scanning superlens structure with scanning angle dispersion eliminated comprises: Controlling the position relationship of the focal points in the three-dimensional space by changing the rotation angle between the upper and lower layers of the super surface, determining the axial position relationship of the focal points when they are horizontally scanned at different rotation angle differences, judging the consistency of the full-wave simulation results and the experimental verification results, and thus obtaining a cascaded super surface-based self-corrected focal point scanning superlens structure with scanning angle dispersion eliminated.

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