High-numerical-aperture visible light wave band chromatography focusing super-structure lens and design method thereof

Abstract

The invention relates to a high-numerical-aperture visible light wave band tomography focusing super-structure lens and a design method thereof. The super-structure lens comprises a substrate, the substrate is provided with a visible light wave band chromatography focusing super-structure lens composed of a plurality of super-structure lens structure units, and each super-structure lens structure unit is of a cuboid structure. Through the compact simple micro-nano structure, high-numerical-aperture visible light wave band chromatography focusing is achieved, meanwhile, the integration degree is high, and effective separation and accurate control of multi-wave-band spectrum focal lengths can be achieved. Under the condition of reaching a high numerical aperture of 0.61, the chromatography depth can reach 13 microns; meanwhile, the full width at half maximum of the super-structure lens is close to or even smaller than the diffraction limit, and the focusing imaging effect is good. The design method disclosed by the invention is simple and easy to implement, adjustable in parameter design, wide in range and particularly suitable for large-scale industrial production design, and provides a thought for the integration and miniaturization development of the tomography technology. The method can be widely applied to the fields of biomedicine, microscopic imaging and the like.

Description

(I) Technical field

[0001] The present invention belongs to the technical field of metasurface metalens focusing imaging, and specifically relates to a high numerical aperture visible light band tomographic focusing metalens and a design method thereof. (II) Background technology

[0002] Tomography is a method of information imaging. Due to the limited depth of field in traditional optical systems, mechanical scanning is often used to achieve tomography. As optical systems are moving towards a compact and stable architecture, mechanical solutions are gradually attracting the attention of researchers. Metalenses are having a revolutionary impact on traditional optical imaging due to their compact size, powerful modulation capabilities, and flexible design. Using metalenses for tomography will greatly reduce the size of traditional tomography systems and help improve the resolution and stability of tomography systems.

[0003] Taking the frog egg cell as an example, it has a cell depth of 35μm. Although the meta-lens itself has a certain dispersion, it is far from meeting the requirements of practical application. Therefore, it is critical to expand the dispersion imaging of the meta-lens in the visible light band through necessary design and optimization. In addition, the application scenarios of tomography are different from other application scenarios. The object distance is very limited, and the incident light is closer to spherical light. In order to improve the lateral resolution and longitudinal resolution, a large numerical aperture is also necessary. At present, the design wavelength of the meta-lens in the visible light band is limited, and there is still a blank for the meta-lens working in the longer wavelength band of visible light. Moreover, the bandwidth of the longer wavelength band can increase the scanning depth of the tomography. Therefore, it is necessary to study the high numerical aperture visible light band tomography focusing meta-lens. (III) Summary of the invention

[0004] The present invention provides a high numerical aperture visible light band tomographic focusing meta-lens and a design method thereof to solve the problem in the prior art that high-resolution tomographic focusing imaging cannot be performed in the longer wavelength band of visible light.

[0005] In order to achieve the purpose of the present invention, the technical solution of the present invention is: a high numerical aperture visible light band tomographic focusing meta-lens based on a simple micro-nano structure, comprising a substrate, on which is arranged a visible light band tomographic focusing meta-lens composed of a plurality of meta-lens structural units, wherein the meta-lens structural unit structure is a rectangular parallelepiped structure.

[0006] Furthermore, the above-mentioned meta-lens structural units constitute a plurality of arrays.

[0007] Furthermore, the height of the above-mentioned meta-lens structure unit is h=0.8μm, the length L ranges from 0.025μm to 0.225μm, and the width w ranges from 0.025μm to 0.225μm.

[0008] Furthermore, the above-mentioned substrate period p=0.25 μm.

[0009] Furthermore, the substrate material is Al2O3, and the meta-lens structural unit material is GaN.

[0010] Furthermore, in the above-mentioned design method of the high numerical aperture visible light band tomographic focusing meta-lens, after selecting the material structure, the finite difference time domain method is used to simulate and optimize the performance parameters of the visible light band structure unit to meet the phase delay of 2π, and the meta-lens structure unit is first constructed according to the wavefront reconstruction equation. After the meta-lens structure unit is constructed, the positions of all the meta-lens structure units and the structure size of the structure unit are obtained, and the design of the high numerical aperture visible light band tomographic focusing meta-lens is completed based on this data.

[0011] Compared with the prior art, the present invention has the following beneficial effects:

[0012] 1. The present invention adopts a structure in which a rectangular structural unit is stacked on a substrate. By placing a simple rectangular structural unit on a substrate, tomographic focusing imaging in the visible light band is realized. When light waves pass through the structure, they will be regulated by the structural units of their respective bands. At the same time, through a compact and simple micro-nano structure, high-resolution tomographic focusing imaging is realized, and the degree of integration is high.

[0013] 2. The high numerical aperture visible light band tomographic focusing meta-lens designed in the present invention can achieve a tomographic depth of 13 μm while reaching a high numerical aperture of 0.61; at the same time, the half-maximum full width of the meta-lens is close to or even less than the diffraction limit, and the focusing imaging effect is better.

[0014] 3. The design method of the present invention is simple and easy to implement, and the parameter design is adjustable and has a wide range. It is particularly suitable for large-scale industrial production design, and provides ideas for the development of tomography technology towards integration and miniaturization. It can be widely used in the fields of biomedicine, microscopic imaging, etc. (IV) Description of the drawings

[0015] Figure 1 It is a schematic diagram of the structure of the present invention.

[0016] Figure 2 Schematic diagram of the metalens structural unit.

[0017] Figure 3 This is the electric field intensity distribution diagram of the metalens in the xz plane.

[0018] Figure 4 The xy plane electric field intensity distribution diagram of the metalens and the ratio line graph of the half-maximum full width of each wavelength to the diffraction limit.

[0019] in:

[0020] (1) - substrate, (2) - meta-lens structural unit. (V) Specific implementation methods

[0021] In order to make the purpose, technical solution and advantages of the technical solution of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of specific embodiments of the present invention. It should be noted that the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the described 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.

[0022] See also Figure 1 A high numerical aperture visible light band tomographic focusing meta-lens comprises a substrate (1), on which is arranged a visible light band tomographic focusing meta-lens composed of a plurality of meta-lens structural units (2), wherein the meta-lens structural unit (2) is a rectangular parallelepiped structure. In this embodiment, the radius of the meta-lens is 20 μm, wherein the specific number of structural units is determined according to the period of the substrate (2) in which they are located.

[0023] In this embodiment, the substrate (1) is a square with a period p=0.25 μm. A visible light band tomographic focusing meta-lens composed of a plurality of meta-lens structural units (2) is arranged on the square substrate (1). The meta-lens structural unit (2) is a rectangular parallelepiped structure with a length L ranging from 0.025 μm to 0.225 μm and a width w ranging from 0.025 μm to 0.225 μm. The meta-lens structural units (2) form a plurality of arrays.

[0024] In order to facilitate processing, GaN is selected as the unit material of the meta-lens structure unit (2), and Al2O3 is selected as the substrate material.

[0025] With respect to the structural design of the meta-lens structural unit (2) in the visible light band, according to simulation calculation of transmittance, in this embodiment, the height h of the structural unit is selected to be 0.8 μm.

[0026] The basic principle of the design of the present invention is to change the size of the metasurface structural unit to control the phase of the incident light in the sub-wavelength scale. The phase to be controlled can be obtained by using the optical path difference of the plane incident light from each point on the surface of the metalens device to the focus, satisfying the wavefront reconstruction equation:

[0027]

[0028] r 2 =x 2 +y 2

[0029] Where: λ is the wavelength of the incident light, f is the focal length, Δφ is the phase difference, and (x, y) is the position coordinate of the metalens unit. In the calculation, the metalens surface is divided into several periods. To simplify the calculation, only the position of the center point in each period is substituted into the formula to calculate the phase value.

[0030] When all structural units on the surface of the metalens satisfy the above expressions, the metalens can achieve focusing function at the focal position.

[0031] The preparation process of the present invention is as follows: after selecting the material structure, the visible light band structural unit is simulated by the finite difference time domain (FDTD) method, and the phase delay coverage of 2π is satisfied by changing the structural unit size parameters. Then, a meta-lens structural unit (2) array is constructed according to the wavefront reconstruction equation, and the positions of all meta-lens structural units (2) are obtained by the particle swarm optimization algorithm, and the high numerical aperture visible light band tomographic focusing meta-lens design is completed according to the data.

[0032] See also Figure 3 It can be seen that the focal lengths corresponding to different wavelengths in the visible light band are different, and the separation effect of each focus is good. The tomography depth is close to 13μm. The maximum numerical aperture can reach 0.61 by calculation, realizing the high numerical aperture tomography focusing effect of the meta-lens.

[0033] See also Figure 4 , it can be seen that the focus of each wavelength in the xy plane is close to a circle, which is relatively tight and well focused; the ratio of the diffraction limit (σ) to the full width at half maximum (FWHM) is close to or even greater than 1, breaking the diffraction limit. The designed meta-lens has a high resolution and a good overall focusing effect.

[0034] The above is an explanation of the specific implementation of the present invention, rather than a limitation of the present invention. Those skilled in the relevant technical field can also make various equivalent technical solutions without departing from the scope of the present invention, so all equivalent technical solutions should be included in the patent protection scope of the present invention.

Claims

1. A high numerical aperture visible light band tomographic focusing meta-lens, characterized by: It comprises a substrate (1), on which a visible light band tomographic focusing meta-lens composed of a plurality of meta-lens structural units (2) is arranged, wherein the meta-lens structural unit (2) is a rectangular parallelepiped structure.

2. The high numerical aperture visible light band tomographic focusing meta-lens according to claim 1, characterized in that: The meta-lens structural units (2) form a plural array.

3. A high numerical aperture visible light band tomographic focusing meta-lens according to any one of claims 1 to 2, characterized in that: The meta-lens structure unit (2) has a height h=0.8 μm, a length L in the range of 0.025 μm-0.225 μm, and a width w in the range of 0.025 μm-0.225 μm.

4. A high numerical aperture visible light band tomographic focusing meta-lens according to any one of claims 1 to 2, characterized in that: The substrate (1) has a period p=0.25 μm.

5. A high numerical aperture visible light band tomographic focusing meta-lens according to claims 3-4, characterized in that: The material of the substrate (1) is Al2O3, and the material of the meta-lens structure unit (2) is GaN.

6. The design method of a high numerical aperture visible light band tomographic focusing meta-lens according to claim 1, characterized in that: After selecting the material structure, the performance parameters of the visible light band structural unit are simulated and optimized through the finite difference time domain method to meet the phase delay of 2π. The meta-lens structural unit is first constructed according to the wavefront reconstruction equation. After the meta-lens structural unit is constructed, the position of all meta-lens structural units (2) and the size of the structural unit are obtained, and the design of high numerical aperture visible light band tomographic focusing meta-lens is completed based on this data.

7. The high numerical aperture visible light band tomographic focusing meta-lens according to claim 1, characterized in that: When the numerical aperture reaches a high of 0.61, the tomography depth can reach 13μm; at the same time, the full width at half maximum of the meta-lens is close to or even less than the diffraction limit, and the focusing imaging effect is better.

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